Dissertations / Theses on the topic 'Stabilization of recycled aggregate'

A construção civil gera impactos ambientais que merecem atenção especial, uma vez que é uma das áreas que mais produz resíduos dentre as atividades econômicas. Os agregados reciclados de resíduos de construção e demolição podem ser utilizados em diversas áreas, apresentando desempenhos mecânico e hidráulico adequados quando comparados aos agregados naturais. Esta pesquisa consiste em estudar a viabilidade o uso de agregado reciclado misto (ARM) e misturas solo-ARM como materiais geotécnicos em camadas de bases e sub-bases de pavimentos. Para isso, foram realizados ensaios de caracterização física e comportamento mecânico. Para comparação, foram estudados também um agregado natural (AN) e uma mistura de solo-AN. Os resultados mostraram que a energia de compactação teve efeito positivo sobre o comportamento do ARM e misturas de solo-ARM. Observou-se ainda que o ARM apresentou ganho de resistência e rigidez devido ao efeito de auto-cimentação. No que se refere à adição de solo, as misturas de solo-ARM apresentaram uma diminuição no valor de CBR em relação a misturas compostas exclusivamente por ARM, contudo houve um aumento nas demais propriedades mecânicas. Com base nos resultados obtidos, pode-se concluir que o ARM e as misturas solo-ARM apresentam características físicas e comportamento mecânico adequados para uso em camadas de base e sub-base de pavimentos urbanos.
Civil construction generates environmental impacts that deserve special attention, since it is one of the areas that produces the most waste among economic activities. The recycled aggregates of construction and demolition waste can be used in several areas, presenting adequate mechanical and hydraulic performances when compared to natural aggregates. This research consists of studying the feasibility of using recycled mixed aggregate (RMA) and soil-RMA mixtures as geotechnical materials in base and sub-base layers of pavements. For that, tests of physical characterization and mechanical behavior were carried out. For comparison, a natural aggregate (NA) and a soil-NA mixture were also studied. The results showed that the compaction energy had a positive effect on the behavior of RMA and soil-RMA mixtures. It was also observed that the RMA showed strength gain and stiffness due to the self-cementing properties. Concerning soil addition, the soil-RMA mixtures presented a decrease in the CBR value in relation to mixtures exclusively composed by RMA, but there was an increase in the other mechanical properties. Based on the results obtained, it can be concluded that the RMA and the soil-RMA mixtures present physical characteristics and mechanical behavior suitable for the use in base and sub-base layers of urban pavements.

Full-depth reclamation (FDR) in conjunction with cement stabilization is an established practice for rehabilitating deteriorating asphalt roads. Conventionally, FDR uses dry cement powder applied with a pneumatic spreader, creating undesirable fugitive cement dust. The cement dust poses a nuisance and, when inhaled, a health threat. Consequently, FDR in conjunction with conventional cement stabilization cannot generally be used in urban areas. To solve the problem of fugitive cement dust, the use of cement slurry, prepared by combining cement powder and water, has been proposed to allow cement stabilization to be utilized in urban areas. However, using cement slurry introduces several factors not associated with using dry cement that may affect road base strength, dry density (DD), and moisture content (MC). The objectives of this research were to 1) identify construction-related factors that influence the strength of road base treated with cement slurry in conjunction with FDR and quantify the effects of these factors and 2) compare the strength of road base treated with cement slurry with that of road base treated with dry cement. To achieve the research objectives, road base taken from an FDR project was subjected to extensive full-factorial laboratory testing. The 7-day unconfined compressive strength (UCS), DD, and MC were measured as dependent variables, while independent variables included cement content; slurry water batching temperature; cement slurry aging temperature; cement slurry aging time; presence of a set-retarding, water-reducing admixture; and aggregate-slurry mixing time. This research suggests that, when road base is stabilized with cement slurry in conjunction with FDR, the slurry water batching temperature; haul time; environmental temperature; and presence of a set-retarding, water-reducing admixture will not significantly affect the strength of CTB, provided that those factors fall within the limits explored in this research and are applied to a road base with similar properties. Cement content and cement-aggregate mixing time are positively correlated with the strength of CTB regardless of cement form. Additionally, using cement slurry will result in slightly lower strength values than using dry cement.

This document reports on a research project aimed at developing a concrete acoustic barrier made from Recycled Aggregate (RA) Concrete. The research project was undertaken in response to the needs expressed by the Victorian concrete recycling industry. The industry, the scientific community conducting research into relevant disciplines, and the community at large, represented by Victorian government agencies, are of the opinion that there is a need to devise a higher value utilisation application for selected concrete recycling products. This document outlines the rationale and objectives of the research project which involves the examination of Recycled Concrete (RC) Aggregate, the design and examination of RA Concrete, and finally the development of an acoustic barrier made from RA Concrete. The literature review presented in this report examines aspects of concrete recycling and concrete technology pertaining to traditional and alternative constituent materials for concrete production. Firstly, the importance and influence of fine and coarse aggregate on basic properties of concrete is introduced. Secondly, an account on the use of alternative materials in concrete technology, especially of coarse recycled aggregates and supplementary cementitious materials (SCM) is described. Thirdly, some of the physical and mechanical properties and how the use of RC Aggregate and SCM changes these properties are discussed. Fourthly, a number of commonly used techniques and neutron scattering techniques to investigate aggregate and concrete properties are introduced and discussed. Fifthly, the porosity of aggregate and concrete including durability are specifically discussed and testing methods are reasoned. The literature review also discusses the use of no-fines concrete; its physical, mechanical and acoustic properties. Finally it presents an account of the use of concrete in transportation traffic noise attenuation devices. This document continues with an outline of a methodology that was adopted in this research project. It outlines experimental work aimed at examining the properties of RC Aggregate which amongst other properties includes porosity, particle size distribution, water absorption, shape and density. It continues examining RA Concrete properties and includes, among other properties, compressive strength, porosity and durability as well as sound absorption of acoustic barrier. The methodology introduces standard and purposely modified test procedures used in the examination of aggregates, concrete and acoustic barrier. An account of various research techniques is presented, spanning from simple visual observations to more sophisticated neutron scattering techniques. The summary of test procedures follows a description of test specimen composition and their sizes, and a suite of tested specimens. It also introduces statistical methods used to analyse test results. After a detailed description of the aggregate, concrete and RA Concrete acoustic barrier, the document outlines a summary of data generated through the experimental program of this research project. The data on fine aggregate, on selected 14/10mm coarse RC Aggregate, on concrete made from natural and recycled aggregate and on acoustic barrier are presented and discussed. Test results of various physical, mechanical and acoustic properties of aggregate, concrete and barrier are reported, analysed and discussed. The data from observations, visual assessment and scientific experimentation of specific properties are then crossed analysed in a search for relationships between properties of fine and coarse aggregates and properties of concrete made from such aggregates. A cross analysis of data on ?less-fines? RA Concrete and on the acoustic performance of barrier is examined, and the relationship between the volume of interconnected voids in a porous part of ?less-fines? concrete, and the sound absorption of acoustic barrier is discussed and reported. The document then presents a synthesis of the literature review results, project aims adopted within the experimental program and test results in the three main areas of this research project. These areas include recycled concrete aggregate, recycled aggregate concrete and acoustic barrier made from RA Concrete. Finally, conclusions reached through the course of this investigation are summarised and recommendations are proposed in relation to the RA Concrete acoustic barrier. The main conclusion is that selected RC Aggregate can be used in the production of concrete of a compressive strength of 25MPa, if the moisture content and water absorption in the aggregate are closely monitored, and the foreign material content is kept below 1.5%. The author concludes that acoustic barrier made from selected RC Aggregate has unique sound absorption characteristics that can easily be tunable by a selection of appropriate aggregate and by specific concrete mix designs. Recommendations for further research are also proposed.

Thesis (PhD) - Swinburne University of Technology, 2006.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering, Swinburne University of Technology - 2006. Typescript. Includes bibliographical references.

Sustainable development is gaining popularity around the globe nowadays. Governments are under pressure, on many fronts, to embed sustainable development in policies, practice, and operations to secure the planet's future. Adding to this, increased populations, and the need for more infrastructures, have unfortunately led to the unacceptable depletion of raw materials, increasing amounts of construction and demolition waste (C&DW) and accelerated deterioration of the natural environment in many places worldwide. For the conservation of natural resources, reuse and recycling of C&DW is the most obvious way to achieve sustainability in the construction sector. Currently, recycled aggregate (RA) is produced from C&DW in modern recycling facilities, under good quality control provisions which could lead to improve its performance compared with the earlier days of recycling. In addition to C&DW, large amounts of industrial and mining by-products such as fly ash, slag, limestone powders, aggregate dust, etc. are dumped in landfills. Fly ash has been used successfully in concrete for a long time due to its numerous advantages across a wide range of properties, including aspects of durability. A concrete produced with the combination of PFA and RA i.e. recycled aggregate concrete (RAC) is obviously more sustainable and economical than conventional natural aggregate concrete (NAC). To date, statistics show that a considerable proportion of the world's RA is used for low-utility applications due to perceived risks and uncertainty over their performance formed as a result of previous history of use when RA was produced manually and low strength cement and higher water to cement ratios were used. Despite the advances in recycling, materials and concreting technologies, this impression prevails. However, to increase the use of RA, it is believed that the quality of RAC should be improved by chemical and mineral additives. For cost effectiveness, quality-improving additives should be abundant, safe, and inexpensive; PFA and new generation polymer-based superplasticizer (SP) are deemed to be a good option. The aims of this study are to investigate the possibility of producing good quality RAC that could be used as a substitute for NAC in normal strength concrete members, and to study its fundamental properties. An attempt has been made to create superplasticized RAC concretes, in which new generation polymer-based SP and PFA produced to the latest European standards were used. PFA was used to partially replace fine aggregate and cement in ordinary and self-compacting concretes. The thesis also includes an investigation into the potential of utilising an aggregate by-product (red granite dust (RGD) in producing environmentally beneficial RAC. The findings show that good performance RAC can be produced with the help of SP and PFA. The study also revealed that it is possible to utilise RGD to substitute up to 30% of cement without substantially influencing the performance of concrete, while also providing cost savings. Strengths and stifnesses of the ensuing RAC either with SP, PFA, or RGD were comparable, or better than, a wide range of counterpart NACs. The author's produced RAC concretes can replace NAC concrete used unnecessarily for many applications including structural concrete.

The possibility of using demolished concrete waste as aggregate in fresh concrete in the production of prestressed concrete beams is checked in this research. As opposed to the use for road foundations or as fill-in material the use of the Recycled Aggregate (RA) for concrete structures requires more tests and processing of results. In fact to be able to use a material for construction it is essential to assess more than just its compressive strength. After the physical and chemical characteristics of the RA and the properties of both the wet and hardened Recycled Aggregate Concrete (RAC) have been determined, it is important to check if the mathematical models and numerical correlation normally used for design of ordinary concrete (such as mix-design procedure, design codes, non-linear analysis) are suitable for RAC. For this reason the main task of this investigations has been to ensure that RAC has satisfactory mechanical performance for structural use and later to guarantee a consistency of the results using methods checked for RAC. A mix-design procedure suitable for RAC to attain the desired workability and the target strength was the first step. Tests on durability of RA and RAC have been performed and the results reported. Finally three 15.0 metres span prestressd beams cast with different percentages of RA (one with 100% of RA, one with 100% of Natural Aggregate NA, and one with 50% of RA and 50% of NA) have been tested. The results show that it is practicable to make prestressed concrete elements using concrete made with Recycled Aggregate and that these elements can have satisfactory and predictable mechanical performance.

Disposal and treatment of construction and demolition (C&D) wastes are often costly and hazardous to the environment. Their recycling could lead to a greener solution to the environmental conservation and pave the way towards sustainability. This study utilizes demolished concrete as coarse aggregate often termed as recycled coarse aggregate (RCA) for producing industry quality concrete. Large scale recycling can substantially reduce the consumption of natural aggregate and help preserve the environment. However, in near future, it can raise new challenges. The use of “repeated recycled coarse aggregate” in concrete production can be a viable solution to the growing problem regarding the C&D waste disposal. During the development of new generation product like recycled and repeated recycled coarse aggregate concrete, it is essential to investigate the fresh, hardened, and durability properties of concrete to promote and escalate its application in the construction industry. This research investigates the fresh, mechanical, and durability properties of 25 MPa recycled aggregate concrete (RAC) made with different RCA replacement levels. Durability performance of 25 MPa RAC was evaluated in terms of sulphate attack and cyclic wetting and drying along with chloride exposure. Chloride propagation was evaluated after 1, 4, 9, 16, 28, 90, and 120 cycles. This study reveals that the performance of RAC is decreasing with increasing RCA replacement levels but their overall performance is comparable to natural aggregate concrete (NAC). Three different generations of repeated recycled coarse aggregate concrete were produced using 100% RCA as a replacement of natural coarse aggregate. Similar mix design was used for producing 32 MPa concrete. Along with this, their durability performance was examined under three different exposure conditions namely, freeze-thaw, sulphate, and chloride exposure. It was found that the compressive strength of different generations of repeated recycled concrete was lower than the control concrete. However, all of the mixes exceeded the target strength at 120 days. The durability performance of the different generations of repeated recycled coarse aggregate concrete was negatively affected by using different generations of such aggregates but still these findings will add a new achievement towards sustainable world.

The aim of the work presented in this thesis is to examine the thermal, dimensional and strength behaviour of glass concrete. The type of concrete used for this study differed significantly from those of other researchers. Firstly, the particle size distribution of glass identically matched the grading of natural aggregate. Secondly the glass used was free of sharp edges, uncontaminated, and produced by a unique implosion technique. The results showed that the process of cement hydration produces a much higher temperature in concrete made with glass cullet. Furthermore, when such concretes were allowed to hydrate under freezing conditions (-10°C or -20°), glass concrete was able to withstand freezing much longer than control concrete. The exposure of glass concrete to both high (60 °C) and low (-20°C) temperatures maintained greater temperature stability. This behaviour is attributed to the thermal properties of glass and the pore structure of glass concrete. These findings suggest that concrete made with recycled glass could have two important applications, namely, cold temperature concreting and in buildings where it is important to maintain greater temperature stability. The benefits of glass aggregate exceeded the enhanced performance of the best available accelerator with natural aggregate. Glass concrete probably has a lower drying shrinkage than any natural aggregate. Because of its low shrinkage, glass concrete is more affected by a change in water to cement ratio. The reduction in shrinkage was related to the glass content of the concrete. A mathematical model is suggested for the prediction of drying shrinkage of concrete made with a mix of glass and natural aggregates. This model produced a very good correlation with the experimentally obtained results. The 28 day compressive strength of standard cured glass concrete was lower than that of control concrete. However, significantly higher rates of strength development are achieved during the first 7 days due to the early acceleration of hydration resulting from the thermal properties of glass. There is also a much greater gain in the strength of glass concrete between the ages of 28 days and 1 year. As a result of these trends, the early age and long term strength of glass concrete is higher than that of control concrete. The post 28 day gain in strength is mainly attributed to better bonding of glass aggregates and the pozzolanic activity of the finest glass particles. When glass concrete is cured at either a high (40°C) or low (-10°C and -20°C) curing temperature, the 28 day compressive strength is higher than control concrete. Glass concrete that had been cured at low temperatures and then subsequently allowed normal curing recovered 100% of its strength, while the recovery for control concrete was just 50%. Thus it can be concluded that glass is better suited for both hot and cold weather concreting.

Safe disposal of construction and demolition (C&D) waste is a major challenge globally. This study explores strengthening of recycled coarse aggregate (RCA) by conventional cement slurry and novel biocement treatment. Overall, the research contributes to the understanding insights of C&D waste issues, weakness of RCA and mitigation strategies, efficacy of treatment methods and benchmarking, and finally, possible disposal solutions by complete replacement of natural aggregate with treated RCA to achieve sustainability in the concrete industry.

The Wisconsin Department of Transportation (WisDOT) uses approximately 11,000,000 tons of aggregate per year for transportation projects. Being able to select durable aggregates for use in transportation projects is of considerable importance, if the aggregate deteriorates then the constructed facility requires premature repair, rehabilitation or replacement. Realizing the importance and also that deficiencies in the current WisDOT testing protocol may exist, it has been concluded that the durability-testing program for Wisconsin aggregates needs to be updated. For example, WisDOT is currently using the Sodium Sulfate Soundness Test (ASTM C 88) to measure durability, a test that was put in place in 1960. The ability of this test to predict durability performance and simulate field conditions is questionable and it has also been criticized for its lack of precision. It should also be noted that the use of recycled and reclaimed aggregates has increased in recent years and not all typical durability tests can be used for testing these aggregates. The Sulfate Test in particular cannot be used for testing Recycled Concrete Aggregates (RCA) because the chemical reaction produces erroneous and misleading results. This project has identified recent advances in the understanding and testing of aggregate durability. An in depth literature review has been conducted and from the compiled information a laboratory testing program was developed. Selection of the tests was based upon the tests' precision, efficiency, and predictive capabilities. In the laboratory-testing phase of this project the proposed durability tests along with current WisDOT durability tests were used to evaluate the full range of Wisconsin aggregates. From the test results it was found that the WisDOT aggregate testing protocol could be reduced substantially by eliminating many of the testing requirements for aggregates that have a vacuum saturated absorption of less than 2%. Also, the addition of several tests was ruled out due to their lack of correlation with field performance records. The Micro-Deval abrasion test is recommended for inclusion in WisDOT testing protocol as a test to measure the abrasion resistance of aggregate while the L.A. Abrasion test is better suited as a measure of aggregate strength. Additional conclusions were made based on the durability testing conducted and an overall testing protocol has been developed and is recommended for implementation by WisDOT.
Master of Science

Abstract,
The interest in using recycled construction materials is derived from the growth in construction and demolition waste due to rehabilitation and natural and technological disasters. The driving force for recycling concrete is three-fold: preserving natural resources, utilizing the growing waste and saving energy and money. While some waste concrete is currently being crushed and used for grading and base material for highways, it has not been used as the aggregate in new concrete in Canada, largely because of the plentiful supply of good quality virgin material. However, crushed concrete is being used in new concrete in other parts of the world where the local aggregate is inferior, and there is now a push within the Canadian cement and concrete sector to improve the industry sustainability, one aspect of which is recycling of materials.

The research done to date has emphasized the influence of recycled concrete aggregate (RCA) on the workability and strength of the new concrete with little attention being paid to the behaviour in service. In contrast, the present study is focused on the durability of concrete containing RCA in reinforced structures. Since the most common cause of failure of reinforced concrete structures in this part of the world is corrosion of the reinforcement by de-icing salts, the focus of the project is on this aspect of durability. The project involves a comparative study of the durability of three concrete mixtures containing, as coarse aggregate:

1. new clean recycled concrete aggregate (NC-RCA) obtained by crushing the excess concrete returned to the ready mix yard;
2. old de-icing salt contaminated, recycled concrete aggregate ( OC-RCA) from a demolished bridge over Highway 401 in Ontario;
3. natural aggregate as a control material.

These three materials were crushed and sieved to give the same grading for each mix. Natural sand was used as fine aggregate. The mixes were adjusted to account for the different water absorption characteristics of the aggregates but were otherwise identical. Prism specimens with a centrally placed reinforcing bar, cylindrical specimens and non-reinforced slabs were cast from each of the concretes. After curing, the reinforced prisms were exposed to a saturated de-icing salt solution for two of every four weeks. For the second two week period, they were allowed to dry in the laboratory atmosphere or, to accelerate the process, dried at 32°C in a low humidity (18%) chamber.

The electrochemical corrosion behaviour of the steel was monitored using linear polarization resistance and cyclic polarization techniques. In addition, the physical properties of the materials were assessed. For the aggregates, water absorption, chloride content and susceptibility to abrasion were determined. For the concretes, compressive strength, salt scaling resistance and chloride permeability were measured and microscopic observation of the interfacial zones between the aggregate and the new cement paste were conducted.

On the basis of the results, it is concluded that the durability and the strength of the RCA concrete is very dependent on the age of the RCA aggregate. Water and chloride permeability, and, salt scaling and reinforcing steel corrosion resistance of concrete made with a very well hardened old RCA were comparable with or better than those of in normal concrete. Concrete incorporating new RCA exhibited inferior properties and consequently, it is recommended that, the OC-RCA concrete can be used as a sustainable material in structural applications.

Thesis (M.S.) -- University of Maryland, College Park, 2009.
Thesis research directed by: Dept. of Civil and Environmental Engineering . Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The use of recycled aggregates in concrete opens a whole new range of possibilities in the reuse of materials in the building industry. This could be an important breakthrough for our society in our endeavours towards sustainable development.

The trend of the utilisation of recycled aggregates is the solution to the problem of an excess of waste material, not forgetting the parallel trend of improvement of final product quality. The utilisation of waste construction materials has to be related to the application of quality guarantee systems in order to achieve suitable product properties. Therefore the complete understanding of the characteristics of new material becomes so important in order to point out its real possibilities.

The studies on the use of recycled aggregates have been going on for 50 years. In fact, none of the results showed that recycled aggregates are unsuitable for structural use. Only having inadequate number of studies in durability aspects, made recycled aggregates to be preferred just as stuffing material for road construction.

My thesis, aimed to focus on the possibility of the structural use of recycled aggregate concrete based on a better understanding of its microstructure.

To begin with the characteristics of the aggregates were established, to study their possible application in concrete production. After analysis, the dosage procedure was carried out in order to produce four concrete mixtures using different percentages of recycled coarse aggregates (0% (HC), 25% (HR25), 50% (HR50) and 100% (HR100)) with the same compression strength. Raw coarse aggregates (granite) and sand (crushed limestone) were used in the different concrete mixes.

Macroscopic and microscopic examination were carried out in HC, HR25, HR50 and HR100 concretes in order to observe the durability effects. The macroscopic examination determined the aggregates distribution, composition, the contaminants and aureoles around adhered mortar. Microscopic examination was carried out by Optical light transmitted microscope Leica Leitz DM-RXP, using Fluorescence Thin Sections, in order to analyse the cement paste, the new and old interfacial transition zones, secondary reactions as well as damage. Original aggregates and cement paste, interfacial transition zones and alkali silica gel produced due to reactive aggregates present in adhered mortar were analysed by SEM and EDX-maps.

Beside macro and micro observations, shear failure behaviour of recycled aggregate concretes was studied. Shear failure test was found more appropriate, as concrete properties had more influence in this type of failure behaviour compared to the flexural failure where the reinforcement plays the important role. Sixteen beam specimens were cast and the structural behaviour of these beams was analysed using four different transversal reinforcements for each kind of concrete. An analytical prediction of the experimental results are carried out using a numerical model (Modified Compression Field Theory), using the codes AASHTO LRFD, CSA, Eurocode-2 and expressions proposed in the Spanish code EHE-99.


Organic and inorganic compounds were found to be released from waste materials through leaching and dispersed into the soil and surface water. The leaching of these compounds were measured employing different codes, the two Dutch codes (NEN 7341 and 7345) and the European Normative (EN 12457-2).

Some recommendations are given as to the aggregates characteristics to be used in concrete mixes, taking into account the European standards for recycled aggregates. Also suggestions are made for the production process of concrete using recycled aggregate. Mechanical properties of recycled aggregate concrete are studied and they are compared with that of conventional concrete. Based on the durability of the concrete, some suggestions are proposed with respect to possible alkali silica reaction between new cement and original fine aggregates. It is also determined that the effect of the use of recycled aggregate on the beams' shear strength depend on the percentage of coarse aggregate substituted. The applicability of concrete recycled aggregate with respect to its environmental behaviour is demonstrated. In conclusion, some suggestions for future studies are made which would help us in the evolution of our understanding in this field.

Recycled concrete aggregate (RCA) is often used as a replacement of virgin aggregate in road foundations (base course), embankments, hot-mix asphalt, and Portland cement concrete. However, the use of RCA in exfiltration drainage systems, such as French drains, is currently prohibited in many states of the U.S. The French drain system collects water runoff from the road pavement and transfers to slotted pipes underground and then filters through coarse aggregate and geotextile. The primary concerns with using RCA as a drainage media are the fines content and the precipitation of calcium carbonate to cause a reducing in filter fabric permittivity. Additional concerns include the potential for rehydration of RCA fines. The performance of RCA as drainage material has not been evaluated by many researchers and the limited information limits its use. A literature review has been conducted on the available information related to RCA as drainage material. A survey was issued to the Departments of Transportation across the nation in regards to using RCA particularly in French drains. Some state highway agencies have reported the use of RCA as base course; however, no state reports the use of RCA in exfiltration drainage systems. This thesis describes the investigations on the performance of RCA as backfill material in French drains. RCA was tested for its physical properties including, specific gravity, unit weight, percent voids, absorption, and abrasion resistance. RCA cleaning/washing methods were also applied to evaluate the fines removal processes. The potential for RCA rehydration was evaluated by means of heat of hydration, pH, compressive strength, and setting time. The permeability of RCA was tested using the No. 4 gradation. Long term permeability testing was conducted to evaluate the tendency for geotextile clogging from RCA fines. Calcium carbonate precipitation was also evaluated and a procedure to accelerate the precipitation process was developed. The results show that RCA has a high abrasion value, that is, it is very susceptible to break down from abrasion during aggregate handling such as transportation, stockpiling, or placing. The most effective cleaning method was found to be pressure washing with agitation. RCA has not demonstrated the tendency to rehydrate and harden when mixed with water. The permeability test results show that the No. 4 gradation does not restrict the flow of water; the flow rate is highly dependent on the hydraulic system itself, however excessive fines can cause large reductions in permeability over time. It has been determined that No. 4 gradation of RCA can provide a suitable drainage media providing the RCA is properly treated before its use.
M.S.
Masters
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Civil Engineering; Structures and Geotechnical Engineering

Thesis (MScEng)--Stellenbosch University, 2011.
ENGLISH ABSTRACT: A major challenge for our society is the protection of the environment. Some of the important issues are the reduction in the consumption of energy and natural raw materials, as well as the increase in consumption of waste materials. At present these topics are getting considerable attention as part of sustainable development programs. The use of recycled concrete aggregates (RCA) from construction and demolition waste (C&DW) in construction, as alternative to virgin (natural) aggregates, has strong potential. The use of RCA preserves natural resources and reduces the space required for the disposal of RCA in landfill. It is estimated that 16 thousand million (billion) tons of concrete (and 25 billion tons of aggregate) were used in 2010. Of the 2-3 billion tons of C&DW which are produced worldwide every year, South Africa contributes 5-8 million tons. This amount is increasing rapidly every year. Significant amounts of demolished concrete find their way to landfill sites. A solution for excess waste production would be the utilization of RCA together with an improvement in the final quality of RCA. It might be an important breakthrough for our society in our attempt towards sustainable development. Worldwide, infrastructure has developed a great deal since the beginning of the twentieth century. Much of the core infrastructure, including roads, bridges, water systems, and sewers, was put in place during the first half of that century. Aggregates used as construction materials, as for instance in road pavements, or as an ingredient of concrete, are important components of infrastructure. Urbanization involves reduction of natural aggregate (NA) resources, but environmental concern and the rising cost of NA is the reason that recycled materials from different sources (like roads, buildings) are being used more and more with NA in new construction work. Environmental awareness is increasing in every country for many reasons and sustainable development is demanded of all industries, including the building and construction industries. By nature, construction is not environmentally friendly, and sometimes it also changes the behavior of nature in many ways. Recycling is one of the most important ways to minimize the waste that comes from different sources, thereby avoiding repetition of, and additional environmentally hazardous practices. It may create new wealth by diminished transport and production costs and sparing of landfill site space and cost. It has the potential to extend the life of natural resources by adding a source of material, thereby reducing environmental interference and impacting on nearby construction sites, all of which improve sustainability of our natural resources. Much research on the uses of RCA has been performed during the last few decades. In fact, most of them showed that the strength class of recycled aggregate concrete (RAC) is adequate for use as structural concrete although volume changes in and durability performance of RAC in comparison with natural aggregate concrete (NAC) are still being debated and researched. Some researchers found that the durability of concrete produced with RCA is inferior, but others have found it to be sufficient for use in structural concrete. The fact that an insufficient number of studies have been carried out on the durability aspects, has limited the use of RCA as material for road construction. The aim of this study is to determine the suitability of using the RCA in structural concrete based on its strength, stiffness, dimensional stability and durability. Three types of RCA designated RCA1, RCA2 and RCA3 in this study, were taken from three different sources. These materials were tested to establish their mechanical characteristics for use as aggregates in concrete. In the experimental program RCA was used at replacement percentages of 0%, 30% and 100% to (partially) replace NA in order to study its suitability as aggregate in concrete, and to what level of NA replacement its behavior is satisfactory for structural application. A single compressive strength class was studied, due to the limited time. By performing tests of compressive strength, Young’s modulus, creep, shrinkage, and durability performance, it has been found that selected types of RCA show a real possibility for use as aggregate in concrete. When concrete with a RCA replacement of 100% was compared with NAC100% there was a small decline in strength, but when concrete with a RCA replacement of 30% was compared with NAC100% the results showed almost equal strength. A slight reduction in durability performance was found for RAC30% compared with NAC100%, but similar dimensional stability performance in terms of specific creep and drying shrinkage was measured for RAC30% and NAC100%. Based on detailed experimental results obtained from this thesis project, a number of recommendations have therefore been made for RCA characteristics that will be used in concrete mixes also taking into account the quality of RCA. Some suggestions are proposed based on the mechanical properties and durability of the concrete. In the final conclusions, future studies on RCA properties are suggested, which would help us in increasing our knowledge in the application of RCA, and which may lead to the optimal production of structural concrete in a sustainable way. In general the use of RCA in concrete is feasible and good quality RCA at 30% replacement of NA may be suitable for any kind of structural concrete.
AFRIKAANSE OPSOMMING: ‘n Groot uitdaging vir ons samelewing is die beskerming van die omgewing. Van die belangrike sake is die vermindering in die verbruik van energie en van natuurlike, onverwerkte materiale asook die groter verbruik van afvalmateriaal. Hierdie onderwerpe kry tans aanienlike aandag as deel van volhoubare ontwikkelingsprogramme. Die gebruik van betonaggregate, herwin vanaf konstruksie-en slopingsafval, en gebruik in konstruksie as alternatief vir ongebruikte natuurlike aggregate, het goeie potensiaal. Die gebruik van herwonne aggregaat beskerm natuurlike hulpbronne en verminder die oppervlakte en volume wat nodig is vir die weggooi daarvan op stortingsterreine. Dit is beraam dat 16 duisend miljoen (biljoen) ton beton (en ongeveer 25 biljoen ton aggregaat) gedurende 2010 gebruik is. Van die 2-3 biljoen ton konstruksie-en slopingsafval wat jaarliks wêreldwyd gegenereer word, dra Suid Afrika 5-8 miljoen ton by. Hierdie hoeveelheid word elke jaar vinnig meer. Beduidende hoeveelhede gesloopte beton beland elke jaar op stortingsterreine. ‘n Oplossing vir die probleem van te veel atval generering sou wees die gebruik daarvan as herwonne beton-aggregaat, sou saamval met ‘n verbetering in die uiteindelike kwaliteit van herwonne aggregaat beton. Dit kan dalk ‘n belangrike deurbraak wees vir ons samelewing in ons strewe na volhoubare ontwikkeling. Infrastruktuur het wêreldwyd baie ontwikkel sedert die begin van die twintigste eeu. Baie van die kerninfrastruktuur insluitende paaie, brue, waterstelsels en riole is gebou tydens die eerste helfte van daardie eeu. Aggregaat gebruik as konstruksiemateriaal, byvoorbeeld in padplaveisels of as’n bestanddeel van beton, is ‘n belangrike deel van infrastruktuur. Verstedeliking veroorsaak vermindering van natuurlike aggregaat hulpbronne maar besorgdheid oor die omgewing en die stygende koste van nataurlike aggregaat veroorsaak dat herwonne materiale vanaf verskillende bronne (soos paaie en geboue) meer en meer aanvullend tot natuurlike aggregaat in nuwe konstruksiewerke gebruik word. Omgewingsbewustheid is om baie redes aan die toeneem in elke land en volhoubare ontwikkeling word vereis van alle industrieë. Herwinning is een van die hoofmaniere om afval vanaf verskillende bronne tot ‘n minimum te beperk. Dit skep nuwe rykdom, verminder vervoeren vervaardigingskoste en benut afval wat anders op stortingsterreine verlore sou gegaan het. Dit het die potensiaal om die lewensduur van natuurlike hulpbronne te verleng deur ‘n materiaalbron by te voeg, deur inmenging in die omgewing te verminder, wat almal bevorderlik is om volhoubare benutting van ons hulpbronne te verbeter. Baie navorsing is gedurende die laaste paar dekades gedoen aangaande die gebruik van herwonne aggregaat. Die meeste van die navorsing het inderdaad getoon dat die sterkte van beton met herwonne aggregaat genoegsaam is vir gebruik as struktuurbeton alhoewel daar wel debatte gevoer word oor die volumeveranderings en duursaamheid prestasie van herwonne aggregaat beton vergeleke met dié van natuurlike aggregaat beton. Sommige navorsers het bevind dat die duursaamheid van beton wat met herwonne aggregaat gemaak is, minderwaardig is maar andere het bevind dat dit voldoen aan die vereistes van struktuurbeton. Slegs die feit dat daar onvoldoende toetse rakende duursaamheid gedoen is, het die gebruik van herwonne beton aggregaat beperk tot padboumateriaal. Die doel van hierdie navorsing is om te bepaal wat die geskiktheid van herwonne betonaggregaat is vir gebruik in struktuurbeton, gegrond op sterkte en duursaamheid. Drie soorte herwonne betonaggregaat wat in hierdie studie as RCA1, RCA2 and RCA3 aangedui word, is elk vanaf ‘n ander bron geneem. Hierdie materiale is getoets om hulle meganiese kenmerke vas te stel vir gebruik as aggregaat in beton. In die eksperimentele program is 0%, 30% en 100% herwonne betonaggregaat gebruik om natuurlike aggregaat gedeeltelik be vervang om sodoende die geskiktheid as betonaggregaat te bestudeer. Deur toetse uit te voer op ‘n beperkte sterkte-klas beton, soos toetse vir die bepaling van druksterkte, Young’s modulus, kruip, krimp en duursaamheid, is daar bevind dat sekere soorte herwonne betonaggregaat heel moontlik gebruik kan word in struktuurbeton. Toe beton met 100% herwonne betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, is bevind dat daar ‘n klein vermindering in sterkte was, maar waar beton met 30% herwonne betonaggregaat vergelyk is met beton met 100% natuurlike aggregaat, het die resultate byna dieselfde sterkte getoon. Dus op grond van gedetaileerde eksperimentele resultate is ‘n aantal aanbevelings gemaak vir kenmerke van herwonne betonaggregaat wat in betonmengsels gebruik sal word met inagneming van die gehalte van herwonne betonaggregaat. Die resultate vir beton met 30% en 100% herwonne betonaggregaat word vergelyk met beton wat slegs natuurlike aggregaat bevat. Sekere voorstelle gegrond op meganiese eienskappe en duursaamheid van die beton word gemaak, asook aanbevelings vir toekomstige studies van herwonne betonaggregaat wat ons sal help om ons kennis vir die toepassing van herwonne betonaggregaat uit te brei.

The principles of sustainable construction require the prudent use of natural resources and the maximum recycling and reuse of waste. In keeping with this approach, much research was undertaken to increase the use of recycled aggregates derived from construction and demolition wastes as an alternative to primary aggregates in construction. It is now increasingly recognised that the use of coarse recycled concrete aggregate (RCA) in concrete construction represents a further potential outlet for the material. Several investigations have been made to study the effects of coarse RCA on the fresh and hardened properties of Portland Cement (PC) concrete. While these studies suggest the potential use of RCA in a range of concrete applications, issues relating to its suitability in binary cement concrete mixes, relevant to practice, have not been addressed. Against this background, the present study was undertaken to examine the suitability of using coarse RCA in BS 8500 designated concrete mixes produced using binary cements. The binary cements selected were (i) PC/PFA cement, a blend of 70% PC/ and 30% Pulverised Fuel Ash by mass and (ii) PC/SF cement, a blend of 90% PC and 10% Silica Fume by mass. The binary cements were blended in the mixer during concrete production. The effects on the fresh, engineering and durability properties of concrete, of replacing coarse natural aggregates (NA) by coarse RCA by up to 100% in concrete have been established. The RCA mixes were designed to achieve equal 28 day cube strengths as their corresponding NA mixes. The aggregate characterisation results showed that concrete debris obtained from construction and demolition waste can be used to produce clean and properly graded RCA suitable for use in concrete production in accordance with the EN 12620 requirements. The results of the fresh properties of concrete showed that although the slump measurements remained within the allowable tolerances, the use of high RCA contents affected the workability and stability of the mixes. Studies of the hardened concrete properties, comprising the bulk engineering (Compressive cube and cylinder strength, flexural strength, modulus of elasticity, drying shrinkage and swelling deformations) and durability properties (near surface absorption, carbonation, chloride ingress, sulphate attack) showed that RCA concrete mixes made with binary cements had, a comparable or better performance when compared to their corresponding concrete mixes made with PC only. Practical implications derived from the findings of the study are also outlined for the use of RCA in binary cement concrete construction. Overall, the study has shown that RCA is suitable for the production of a wide range of designated mixes made with binary cements with a satisfactory engineering and durability performance, provided that the mixes are designed for equivalent 28 days cube strength.

In the process of crushing concrete waste, significant amounts of fine by-products, the so called fine recycled concrete aggregates (FRCA), are generated and excluded from potential use. Limited research has thoroughly investigated the performance of concrete mixes with FRCA, very likely due to the complexity in analysing non-negligible amounts of adhered residual cement paste (RCP). Although some studies have proposed promising sustainable mix-design procedures accounting for the different microstructure when using coarse recycled concrete aggregates (CRCA), no similar approach exists for FRCA concrete. In this work, two promising procedures for mix-designing eco-efficient concrete with 100% FRCA are proposed accounting for the presence of RCP to reduce cement content in new mixtures. First, built on top of the existing procedure for CRCA mix-design, modifications to the Equivalent Volume (EV) method were introduced toconsider full replacement of fine natural sand by FRCA. Second, based on the concept of continuous Particle Packing Models (PPM), an optimized procedure was proposed to allow maximum packing density of FRCA mix linked to a given level of measured RCP content. Results verified the feasibility of producing eco-efficient concrete mixes with 100% FRCA, emphasizing the PPM mixes to report superior rheological and mechanical performance along with suitable durability-related properties. Yet, results also indicated the influence of simple or multistage crushed FRCA on the overall performance of mixes.

2013 - 2014
This thesis proposes a conceptual formulation for controlling the resulting mechanical properties of Recycled Aggregate Concretes (RACs) via generalised mix-design rules intended at covering the specific features of Recycled Concrete Aggregates (RCAs). As a matter of fact, the RCAs are characterised by a higher porosity and water absorption capacity than ordinary aggregates and, hence, general mix-design rules for ordinary structural concrete cannot be applied to RACs as such. Therefore, as a further step that goes beyond the currently available experimental and empirical investigations, the research presented in the present thesis proposes a rational mix design method for predicting the compressive strength evolution of RACs by considering both the mixture composition and the key properties of RCAs (i.e.; the amount of the attached mortar and indirectly the water absorption capacity). The formulations proposed in this thesis are based upon the results of several investigations carried out for characterising both RCAs and RACs. In fact, several tests were performed on different kinds of recycled aggregates, taking into account their origin, the processing procedure adopted for crushing the concrete demolition debris and their resulting size grading. The analysis of the results obtained in these tests led to proposing a comprehensive conceptual formulation that links the main engineering properties of aggregates to the porosity, particle density and attached mortar content of RCAs. Moreover, several concrete batches were produced for investigating the influence that three key parameters (viz. aggregate replacement ratio, nominal water-to-cement ratio and initial moisture condition of aggregates) have on the relevant properties for structural concrete. The behaviour of structural concrete is then analysed at a “fundamental” level, with the aim of scrutinising the physical properties and the mechanical behaviour of RACs, by taking into account the actual mixtures composition. Particularly, it is based on observing the hydration process developing inside RACs during the setting and hardening phase, and how these are influenced by the presence of RCAs. The activities described in this work were carried out at the laboratories of the University of Salerno (IT), the Federal University of Rio de Janeiro (BR), as part of the “EnCoRe” Project (FP7- PEOPLE-2011-IRSES n. 295283; www.encorefp7.unisa.it) funded by the European Union within the Seventh Framework Programme, and Delft University of Technology (NL). [edited by Author]
XIII n.s.

The growing demand of construction aggregates has raised concern about the availability of natural aggregates. Over two billion tons of natural aggregate are produced each year in the United States and that number is expected to increase to 2.5 billion tons by 2020. This has raised concern about the availability of natural aggregate. Discarding demolished concrete into landfills is a costly solution from an economical and environmental point of view. Many U.S. highway agencies are re-using Recycled Concrete Aggregates (RCA) as construction material. The use of fiber reinforcement in Portland Cement Concrete (PCC) has recently become a popular option in concrete construction because of its influence on preventing segregation, reducing early shrinkage cracks and increasing residual load capacity. Alkali-Silica Reaction (ASR) is a major problem in concrete, especially when using RCA, causing concrete expansion and cracks. Recently lithium has been found to reduce expansion due to ASR. This thesis will investigate the effect, of fibers soaked in lithium nitrate on the mechanical properties of RCA.
M.S.C.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering

Thesis (MScEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The aim of this research is to investigate the potential use of coarse recycled concrete aggregate (RCA) as a material in structural concrete. The lack of knowledge and specifications in South Africa are the main reasons for this research of RCA. By increasing the database of research of RCA in South Africa the possibility of specifications for this alternative building material can be initiated. The implications of such specifications would lead to RCA acceptance in concrete design and therefore reducing the amount of construction and demolition (C&D) waste accumulating at landfill sites and decreasing the extraction of depleting natural aggregates. The objectives that are achieved through this research project are firstly, what is the percentage replacement of RCA to a concrete blend that will produce a material that achieves similar or better results than a concrete blend containing natural aggregates. Secondly, what aggregate properties and limits should be defined in the specification of RCA for it to be accepted as a material in concrete mixtures. The objectives were assessed through examining the geometrical, physical and chemical properties of the aggregate as a material and the fresh and hardened concrete properties of concrete which contains RCA as a constituent. RCA which was processed by a commercial recycling facility which produces concrete masonry units was collected at three different instances. This material was reprocessed in the laboratory to control the grading and amount of fine material not guaranteed by the recycling process. The RCA is then combined with natural aggregate (NA) at the replacement percentages: 0, 15, 30, 50 and 100% which is then used to examine the aggregate properties. It was determined that the physical properties of RCA were dependent on the geometrical properties, while taking into consideration that the geometrical properties are dependent on the source and method of recycling of the original C&D waste. The chemical properties were established as dependent on the physical properties of the RCA. The RCA is then mixed with NA at the same replacement percentages together with other concrete constituents to produce the concrete used to examine fresh and hardened concrete properties. The fresh concrete properties investigated were: slump, slump loss, air content and fresh compacted density. The hardened concrete properties studied were: compressive strength, tensile splitting strength, oxygen permeability, water sorptivity, chloride conductivity, modulus of elasticity, shrinkage and creep. The concrete properties were not significantly influenced by the inclusion of RCA. According to the aggregate and concrete properties examined in this investigation, the full replacement of NA in structural concrete is possible and will improve the sustainable development of the construction industry.
AFRIKAANSE OPSOMMING: Die doel van hierdie navorsing is om ondersoek in te stel na die potensiele gebruik van growwe herwonne betonaggregaat (RCA) as ‘n materiaal in betonstruktuurontwerp. Die gebrek aan kennis en spesifikasies in Suid Afrika is die vernaamste rede vir hierdie navorsing van RCA. Deur die vermeerdering van die databasis van hierdie navorsing van RCA in Suid-Afrika kan die moontlikheid van spesifikasies vir hierdie alternatiewe boumateriaal geïnisieer word. Die implikasie van sodanige spesifikasies sou lei tot RCA aanvaarding in betonontwerp en dus die vermindering van die hoeveelhede konstruksie en sloping (C&D) van afvalversameling by stortterreine en om die ontginning van natuurlike aggregate te verminder. Die doelwitte wat deur hierdie navorsingsprojek bereik word is eerstens, wat is die vervangings persentasie van RCA in 'n betonmengsel wat produseer word wat dieselfde of beter resultate sal lewer as 'n betonmengsel wat uit natuurlike aggregate bestaan. Tweedens, watter aggregaat eienskappe en beperkings moet gedefinieer word in die spesifikasie van RCA sodat dit aanvaarbaar is as ‘n materiaal in betonstruktuur ontwerp. Die doelwitte word geassesseer deur die ondersoek van die geometriese, fisiese en chemiese eienskappe van die aggregaat as ‘n wesenlike materiaal en die vars en verharde betoneienskappe van RCA as ‘n bestanddeel in struktuurbetonontwerp. RCA monsters was geneem by ‘n kommersiele herwinningsfasiliteit wat RCA gebruik om betonsteen eenhede te vervaardig, is op drie verskillende tydperke ingesamel. Hierdie materiaal is herverwerk in die laboratorium om die gradering en die hoeveelheid van fyn materiaal wat nie deur die herwinningsproses beheer is nie. Die RCA was dan gekombineer met NA teen vervangingspersentasies van: 0, 15, 30, 50 en 100 % wat dan gebruik was om die eienskappe van die aggregaat te ondersoek. Daar is vasgestel dat die fisiese eienskappe van die RCA afhanklik van die geometriese eienskappe, met inagneming dat die geometriese eienskappe afhanklik is van die bron en metode van die herwinning van die oorspronklike C&D afval. Dit is gestig dat die chemise eienskappe is afhanklik van die fisiese eienskappe van die RCA. Die RCA is toe gemeng met NA teen dieselfde vervangingspersentasies saam met ander beton bestanddele om beton te produseer wat dan vergelyk kan word met vars en verharde beton eienskappe. Die volgende vars betoneienskappe is ondersoek: insinking, insinking verlies, luginhoud en vars gekompakteerde digtheid. Die volgende verharde betoneienskappe is bestudeer: druksterkte, trek die splintsing van krag, suurstofpermeabiliteit, water sorptiwiteit, chloride geleidingsvermoё, modulus van elastisiteit, krimp en kruip. Die beton eienskappe was nie beduidend beïnvloed deur die insluiting van RCA nie. Volgens die aggregate en beton eienskappe wat in hierdie navorsing ondersoek is, blyk dit dat die volle vervangingswaarde van NA in strukturele beton moontlik is en die volhoubare ontwikkeling van die konstruksiebedryf sal verbeter.

The purpose of this research is to investigate the influence of recycled coarse aggregate (RCA) on the long-term behaviour of composite steel-concrete slabs. Several types of tests were conducted to fulfil the research, including material tests on recycled aggregate concrete (RAC), non-uniform shrinkage tests on small-scale slabs, and long-term tests on full-scale slabs. In the materials tests, the influence of service time of RCA and mixing methods on the mechanical properties of RAC were first investigated. The model to predict the RAC elastic modulus was developed accounting for the influence of residual mortar content. The shrinkage tests were then conducted on RAC using RCA obtained from parent concrete having different service time and compressive strengths. The models to predict the autogenous and drying shrinkage behaviour of RAC were developed accounting for the combined effects of parent concrete quality and residual mortar content. In the shrinkage tests on the small-scale slabs, the relative humidity (RH) and strain distributions through the thickness of seventeen slabs were monitored over time. Test parameters consisted of RCA replacement ratios, slab depths and sealing conditions of the slab surfaces. The mechanism of non-uniform shrinkage in composite slabs was revealed by the measured RH distributions through the thickness of slabs. In the long-term tests on the full-scale slabs, seven slabs were prepared and measured, including three steel-bars truss slabs and four composite slabs. A nonlinear finite element model was developed to account for the time-dependent behaviour of composite slabs to include the effects of non-uniform shrinkage, creep and concrete cracking. Based on the experimental investigations and numerical simulations, a design approach to be used for routine design of RAC composite slabs was proposed and validated.

Application of recycled concrete aggregates (RCA) has increased recently as a sustainable alternative in concrete construction. Although application of RCA has substantially grown over the past decades, issues related to its structural performance and long-term behaviour still prevent its widespread application, especially in structural purposes. In this study, a new mixture proportioning method called the “Equivalent Volume (EV)” method is proposed for RCA concrete, which is developed on the assumption that the RCA mix is based on a companion conventional concrete mix having the same volume of “cement paste and aggregates” as the companion mixture. RCA mixes containing different aggregate types and mechanical properties were designed using the EV method. Chemical, mechanical and non-destructive tests were performed and their performance was investigated. Finally, a quality control protocol for evaluating the suitability of RCA sources for structural applications is proposed. Results show that the EV method seems a promising approach to mix-proportion eco-friendly recycled concrete mixes. Moreover, the RCA type and properties seem to influence in the behaviour of RCA concrete and thus should be accounted in the mix- design.

The continuous global demand for infrastructure due to persistent increase in population growth implies that more aggregate and cement would be required in concrete production. This would eventually lead to more extraction and depletion of natural resources and increased carbon emission. The aim of this research work was to develop high performance concrete using recycled coarse aggregate, microsilica, and synthetic macro fibre with the object to boost higher use of recycled coarse aggregate in the construction industry. Concrete was designed for 28-day compressive cube strength of 50MPa, high workability (60-180mm) and a constant water-cement ratio of 0.39. Microsilica was incorporated up to 20% of cement content at 5% intervals, while the natural coarse aggregate substitution by recycled coarse aggregate ranges between 0 - 100% at 25% interval. Workability, compressive cube strength, tensile splitting strength, flexural strength, static elastic modulus, and water permeability tests including fatigue assessment were conducted respectively. Results confirmed that, the incorporation of 15% microsilica with 50% recycled coarse aggregate fraction produced 28-day compressive cube strength which exceeds the characteristics and target mean compressive cube strength of the control mix which are 50MPa and 63.1MPa respectively. The result suggests that there is a potential to increase the optimum fraction of recycled aggregate from 30-50% in concrete.

With the current emphasis on sustainable development, recycling in the construction industry including highway planning, design, construction and maintenance has become a default option. Traditionally, recycled aggregate has been employed as filling or capping materials. However, the need to replace virgin materials in higher grade applications and reduce landfill has stimulated the need to enhance their performance. The requirements of using low energy and low environmental impact binders such as bituminous emulsion and industrial by-products as hydraulic binders whilst maintaining a long shelf life presented a further challenge. The primary aim of this research was to investigate methods by which a mixture of recycled aggregate composed of road planings, concrete demolitions and bricks with proprietary bitumen emulsion as binder could be enhanced to comply with the prevailing specifications and performance requirements for pavement materials, by using novel combinations of bituminous emulsions and latent hydraulic binders. The preliminary investigation focussed upon the establishment of an appropriate method of compaction of bitumen emulsion recycled aggregate mixtures to ensure results were consistent and representative of field performance. The main investigation evaluated the environmental conditions including freeze-thaw, low and high humidities and varying temperatures upon the behaviour and performance of loose pre-compacted and compacted recycled product using a range of novel latent hydraulic binders and bituminous emulsion combinations. Test methods included Indirect Tensile Stiffness Modulus test, Repeated Load Axial test, Indirect Tensile Fatigue test, Compressive Strength test and a novel modification of the Indirect Tensile Strength test was proposed and developed for enhance assessment of performance. The key findings were that whilst bitumen emulsion mixtures could perform adequately, the addition of a latent hydraulic binder enhanced the mixture's performance in terms of mechanical properties and withstanding extreme conditions exemplified by freeze-thaw and high humidity, whilst maintaining shelf life. However, it was deduced that the performance could be heavily influenced by the condition, consistency and composition of the recycled aggregate. It is recommended that further work should focus on rigorously investigating the influence of recycled components on mixture properties to optimise their performance for given applications, and extended to include tar bound material.

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study.
Higher Education Institute in the Libyan Government MONE BROS Company in Leeds (UK) for providing recycled aggregates BASF and Akzonobel Companies for providing nano silica NS, Hanson Ltd, UK, for suppling cement

This research demonstrates that rubber particle size affects concrete workability and water permeability to a greater extent than fresh density and strength. Concrete with rubber particles of larger size tends to have a higher workability and fresh density than that with smaller particle sizes. However, rubber aggregates with smaller or continuously graded particle sizes are shown to have higher strengths and water permeability resistance. Influence of recycled aggregate and rubber aggregate as part substitutions for natural aggregates on concrete compressive strength was investigated and four equations were proposed to predict compressive strength of the designed concrete. Besides, it is experimentally shown that silane coupling agent (SCA) has a positive effect on reducing the loss of strength of rubber concrete, especially when concrete is weak. This effect becomes more significant with the increase of mass fraction of SCA solution. Experiment results also show a better performance of concrete with SCA-treated rubber than with as-received or sodium hydroxide solution (NaOH)-treated rubber. A brief cost analysis suggests that this approach of surface modification is economically viable. Referring to a provided fatigue load spectrum and fatigue failure mechanism, this method is potentially to be used for rubber concrete in high-cycle fatigue condition.

The effects of biological and physical processes on the aggregate stability of some weakly structured arable and pasture soils were investigated. Preliminary investigations showed significant correlations between soil organic matter and both wet sieving and turbidimetric methods of aggregate stability; the latter method was chosen on grounds of convenience. Scanning electron microscope pictures showed the presence of both fungi and bacteria when soils were incubated. Growth of fungi, estimated by ergosterol measurement, correspond to temporary stability increases, which could be explained by retention of soil particles within the reticulum of fungal hyphae. The effect disappeared as the fungi were destroyed and replaced by bacteria and actinomycetes. Effects caused by fungi were examined separately, using vancomycin to inhibit bacterial growth, and bacterial effects by using cycloheximide to eliminate fungi. Bacterial growth had little direct effect in stabilising soil aggregates; periodate oxidation showed that polysaccharides produced by bacteria are mainly responsible. To examine the contribution of physical processes to increased stability in remoulded soils biological processes were eliminated by sterilisation. Thixotropic changes made a contribution to age hardening in remoulded aggregates similar in magnitude to biological processes. Thixotropic changes were reversible and accompanied by soil strength and metric water potential changes. Polysaccharides did not contribute to thixotropic aging processes. Remoulded soils were subjected to wetting/drying and freezing/thawing cycles. After 3 to 6 cycles the stability of both sterilised and unsteriliserd soils recovered to that of natural aggregates, suggesting a contribution by thixotropy. Repeated weathering cycles decreased the stability of unsterilised, and more so sterilised, field aggregates suggesting that in the former, bond reformation due to biological activity counteracted the destruction caused by wetting/drying and freezing/thawing.

One of the major challenges faced by civil engineering industry is to execute projects in harmony with nature. This is achieved to some extent by judicious use of natural resources in construction practices. In recent years, the demand for construction materials has grown tremendously, so has the amount of construction and demolition waste, putting huge pressure on the environment. This has encouraged the use of recycled aggregate in concrete, which not only allows for a more efficient life cycle of natural resources but also contributes to environmental protection leading to sustainable development. In this study recycled concrete aggregate (RCA) are used in the production of self-compacting concrete (SCC) in varying percentage replacements of natural coarse aggregate (NCA) The use of sustainable technologies such as supplementary cementitious materials (SCMs), and/or recycled material is expected to positively affect the performance of concrete mixtures. However, it is important to study and qualify such mixtures and check if the required specifications of their intended application are met before they can be implemented in practice. This study presents the results of a laboratory investigation of Self Consolidating concrete (SCC) containing sustainable technologies. A total of 20 concrete mixtures were prepared and tested. Mixtures were divided into five different groups, with constant water to cementitious material ratio of 0.38, based on the Recycled concrete aggregate (RCA) content: 0, 25, 50, 75, and 100% of coarse aggregate (CA) replaced by RCA. All mixtures were designed to achieve a target slump flow higher than 500 mm (19.7 in). The control mixture for each group was prepared with 100% Portland cement while all other mixtures were designed with 50% of Portland cement substituted by a combination of Supplementary Cementitious Materials (SCMs) such as class C fly ash, and granulated blast furnace slag. Several properties of fresh concrete were investigated in this study such as: flow ability, deformability; filling capacity, and resistance to segregation. Moreover, the compressive strength at 3, 14, and 28 days, the tensile strength, the unrestrained shrinkage up to 90 days and permeability were investigated. Partial replacement of the cement using Supplementary Cementitious Materials resulted in smaller 28-days-compressive strength compared to those of the control mixes. Based on the results of this study, it is not recommended to replace the natural coarse aggregate in self-consolidating concrete by more than 75% of RCA.Although, the partial replacement of cement by Supplementary Cementitious Materials had an adverse effect on the 28-days-compressive strength, most of the mixes have exceeded the SCC minimum requirements, including those with up to 100% RCA. Finally, several mix designs from the study have met the minimum Illinois Department of Transportation (IDOT) compressive strength requirements for several engineering applications such as pavements and bridges. This suggests that a practical application of results from the research is feasible in the near future.

The aim of this research work is to gain a deep insight and understanding into the impact response of the recycled aggregate and normal aggregate concrete filled steel tube (RACFST and NACFST) columns strengthened with carbon fibre reinforced plastic (CFRP). It also includes an investigation on the compressive behaviour of RACFST and NACFST columns under concentric or eccentric loadings. The environmental protection is an important factor which requires engineers to recycle as many materials as possible to conserve natural resources. Therefore, using the recycled aggregates fits with this trend. In this project, material tests were initially carried out to obtain the mechanical properties of the concrete, steel and the CFRP. Structural tests on RACFST and NACFST columns were then undertaken to gain the corresponding lateral impact and axial compressive behaviour. The main parameters studied for the dynamic tests were the L/D ratio, impactor configuration (i.e. flat and spherical and size), concrete type (i.e. normal and recycled aggregate), the D/t ratio and the strengthening with CFRP. The CFST specimens were also tested under concentric or eccentric loadings to investigate the influence of the D/t ratio, the type of the concrete and the CFRP wrapping on the structural behaviour of those specimens. The results indicate that under impact loading both the RACFST and NACFST specimens show a similar deformation mode, which also applies to compressive loading case. However, the load carrying capacity of the RACFST specimens is slightly lower than that of the NACFST columns. The results also show that the additional confinement of the CFRP reduces the global displacement for both the RACFST and NACFST specimens. It is found that the concrete filling increases the maximum force by 217, 182 and 157 % respectively for the short, medium and long tubes. The impactor configurations have great effects on the impact force and the displacement for the tubes filled with normal and recycled aggregate concrete. The D/t ratio also has a considerable influence on the compression behaviour of the CFST column irrespective the type of the concrete. 3-D finite element models were developed using the commercial code ABAQUS/Standard and ABAQUS/Explicit to simulate the compressive behaviour and impact response of the NACFST and RACFST columns, respectively. All the numerical models were validated against the corresponding experimental data, with a very good agreement. The finite element models for both the dynamic and quasi-static tests produced accurate predictions of the force-displacement traces and deformation modes. Using the validated models, parametric studies were carried out to investigate the influence of several parameters such as the impact energy, material properties, the CFRP coverage and D/t ratio. Based on the research output, it is recommended that the RACFST column can be used as a structural composite member for construction due to the comparable load carrying capacity to the NACFST tube. This will further contribute to the conservation of the natural resources as using the recycled aggregates with appropriate mechanical properties.

A maioria dos processos de fabricação de um produto geram resíduos. Quando não se dispõem de uma tecnologia para o seu reaproveitamento, certamente este material será depositado na natureza e poderá ocasionar inúmeros problemas ambientais. Este trabalho trata da reutilização dos resíduos de concreto como agregado, para dosagens de concreto estrutural. Na maioria das vezes, os agregados provenientes de resíduos são considerados materiais de baixa qualidade, isso ocorre pelo desconhecimento de suas propriedades e da tecnologia para seu emprego. Fazendo uma pesquisa bibliográfica, teórica e experimental, o objetivo deste estudo foi de uma maneira informativa, contribuir para o entendimento do material, caracterizando algumas propriedades do agregado e do concreto reciclado.
Most of making process of a product produces residue. When there isn\'t a technology to use it again, certainly this material will be deposited in nature and it can bring about countless environmental problems. This work presents the reuse of concrete residues as aggregate, for dosage of structural concrete. Most of times, the aggregates provenient from the residues are considered low quality materials, it occurs due to the lack of knowledge of its properties and technology for its use. Doing a bibliographical, theorical and experimental research, the objective of this study was, on an informative way, to contribute for understanding of the material, characterizing some properties of aggregate and the recycled concrete.

Expansive soils are a worldwide problem that poses several challenges for civil engineers. Such soils swell when given an access to water and shrink when they dry out. The most common and economical method for stabilizing these soils is using admixtures that prevent volume changes. In this study the effect of using rock powder and aggregate waste with lime in reducing the swelling potential is examined. The expansive soil used in this study is prepared in the laboratory by mixturing kaolinite and bentonite. Lime was added to the soil at 0 to 9 percent by weight. Aggregate waste and rock powder were added to the soil at 0 to 25 percent by weight. Grain size distribution, Atterberg limits and swell percent and rate of swell of the mixtures were determined. Specimens were cured for 7 and 28 days. This method of treatment caused a reduction in the swelling potential and the reduction was increased with increasing percent stabilizers.

One area for sustainable engineering is the efficient use of recycled aggregates obtained from construction and demolition and also as by-products derived from industrial waste that optimises economic and environmental benefits. For the past five decades, studies on the effect of coarse recycled aggregates (RCA) on properties of concrete have been going on, and in fact, none of them reported that good quality coarse RCA, from the mechanical point of view, is unsustainable for structural use. However, according to the limits stated in BS EN 8500 part 2 (2006), at least 87% of the coarse RCA shall be obtained by crushing old hardened concrete debris. As it was impossible to obtain such good quality aggregates from existing plants, coarse recycled aggregate (RA*) containing 60% of coarse RCA, 10% asphalt, 10% brick, 15% unbound aggregate, and 5% fines and other materials was used in this study. The main aim of this study was to determine and compare the structural properties of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) of equal compressive strength by using different percentage of course RA* and to investigate the suitability of coarse RA* for use in steel-reinforced concrete elements. The study was carried out in three phases. Phase 1 involved the characterisation of the aggregates through a testing regime which include physical and mechanical assessments to study their possible application in concrete production. It was found that the aggregates were suitable to produce normal concrete. For the Phase 2, the effect of the coarse RA* content (up to 100%) on the main properties of concrete was investigated. The results showed that there was a gradual decrease in slump (up to 24%), compressive strength (up to 21%), flexural strength (up to 10%) and modulus of elasticity (up to 30%) as the percentage of coarse RA* increased up to 100%. Thereafter, NA concrete and RA concrete with the same slump and compressive strength made with 100% Portland cement (PC) only and also with a combination of 70% PC and 30% pulverised fuel ash (PFA), were produced. Flexural strength, modulus of elasticity, drying shrinkage, and creep were determined and compared. The compressive strength of RA concretes was increased by lowering the w/c ratio through reducing the free water content. For the Phase 3, pull-out test was carried out using 16mm and 20mm reformed bars embedded in concrete cylinders made with equal strength NA and RA concretes to investigate the bonding strength. It was discovered that the coarse RA* content had no significant effect on the values of pull-out force. Then, for studying flexural properties (cracking load, ultimate load, deflection, strain in rebar, strain in concrete, and pattern of cracks) of steel-reinforced recycled concrete (RRC) beams, two types of beam sections (under-reinforced and over-reinforced) were made with equal strength NA and RA concretes and tested. It was discovered that the difference in ultimate load values was negligible. Although higher deflections were observed for RA beams, the deflections were still within acceptable limits. Overall, it was concluded that, the flexural behaviour of steel-RRC beams made with equal strength concrete is not considerably affected by the presence of coarse RA*, as well as PFA, and the differences were minor with no practical significance. However, due to effect of coarse RA* on the shrinkage and creep strains, their use in structural elements prone to such deformations may require some special considerations.

This research developed new models to replicate metal leaching characteristics from recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP). Model development was supported by a comprehensive experimental and analytical program with multiple influential factors. New models were developed so that they are readily applicable in commercial models to replicate pollutant leaching and solute transport in soil environments. Outcomes of this study will enhance the sustainable use of waste products such as RCA and RAP in the construction industry and relieve the stresses on natural quarry products.

Crushed or recycled concrete aggregates (CCA/RCA) is an increasingly popular material as a replacement for natural aggregates in concrete due to industry demands for more recycled, lower carbon and responsibly sourced materials. In the UK, the majority of CCA is utilised in non-structural applications such as: a general fill material, road base/subbase or in low-grade concrete. Recycled aggregate producers however, are seeking new ways to incorporate CCA into higher value applications such as structural concrete to increase profits. Opportunities to incorporate CCA into structural concrete may also arise because of project demands for sustainability or in situations where natural aggregates are in short supply. Limited research has been published regarding the effect of coarse CCA on the durability of structural concrete, particularly in respect to water and chloride ion ingress and possibility of corrosion initiation. The aim of this EngD research programme was to investigate the effect of coarse CCA and supplementary cementitious materials (SCMs) on the durability performance of structural concrete, with particular emphasis on the key liquid transport mechanisms within concrete, namely absorption by capillary action, diffusion and migration. This addressed an industry concern regarding the detrimental effect of coarse CCA which has resulted in a limit on replacement levels of coarse natural aggregates in structural concrete, as defined in Eurocodes and local national standards for concrete. In this study, structural concrete was produced with varying levels of coarse CCA replacement (up to 100%), from five different sources and/or structural elements across the UK, with various combinations of SCMs to replace in part the Portland cement. Petrographic analysis was used as an innovative technique to characterise the coarse CCA sources to determine suitability which yielded positive results. The durability performance of the resultant concrete was analysed by exposing the concrete to aggressive chloride environments. The results indicate that the inclusion of coarse CCA, even as low as 20%, had a detrimental effect on the durability performance of structural concrete, in relation to absorption by capillary action, diffusion and migration. This effect however, can be offset through the use of SCMs, which have been shown to outperform control Portland cement concrete with 100% natural aggregates in durability performance tests. The results also suggest that cementitious materials had a greater influence on durability performance than the type and source of coarse aggregates used. It is recommended that the replacement of natural aggregate with coarse CCA be limited to 30% in cases where compliance with the 28 day characteristic strength is of particular importance. If the criterion for compliance at 28 days can be relaxed and the compressive cube strength of concretes with SCMs tested at later ages for conformity (56 or 90 days), then higher quantities of coarse CCA may be incorporated up to 60% to produce a more sustainable structural concrete. It is recommended that Portland cement is partially replaced with 50% ground granulated blast-furnace slag (GGBS) to produce a CEM III/A concrete. This is a significant step towards the potential wider implementation of coarse CCA in structural concrete, provided a suitable quantity of SCM is adopted along with a reliable and consistent source of coarse CCA.

The reuse of CDW as a coarse aggregate in the production of new concrete could potentially conserve natural resources, reduce the amount of landfill waste and reduce energy consumption; this would contribute to improved sustainability within the construction sector. The extensive scientific research conducted on this subject to date has concluded that in comparison to natural aggregate (NA), the quality of recycled aggregate (RA) is generally poorer and replacement with recycled aggregate has a negative impact on all concrete properties. The most noticeable effect is on time-dependent deformation (i.e. creep and shrinkage). This has meant that the use of recycled aggregate concrete in various construction applications has been restricted. In this study, an experimental programme has been carried out to examine the effect of incorporating recycled aggregate and steel fibres on the mechanical properties, creep, shrinkage, long-term loss of tension stiffening and long-term flexural behaviour of beams under sustained loads. The results obtained from the tests indicated that replacement with recycled aggregate reduced all concrete properties but the addition of steel fibres proved to be highly beneficial and, in fact, countered the detrimental effect of the recycled aggregate. For instance, it was found that the addition of 0.5% and 1.0% steel fibres to concrete containing 50% and 100% recycled aggregate, respectively, resulted in concrete with almost the same performance as normal concrete. An analytical investigation was also conducted to evaluate the suitability of existing code procedures for predicting the long-term deflection of concrete beams incorporating recycled aggregate and steel fibres. It was found that there were shortcomings within the existing codes when analysing these materials and modifications to the Eurocode 2 method were thus proposed. A numerical analysis program was developed using MATLAB language for predicting the long-term deflection of beams based on the proposed modifications. The program was used for validating the modifications by using the experimental results from this research and previous studies in the literature. In addition, a 3D finite element analysis was carried out using the commercial software Midas FEA which included the development of a novel approach for predicting the long-term deflection of cracked reinforced concrete beams containing recycled aggregate and steel fibres. The approach was verified by comparing the finite element analysis predictions with the experimental results from this study and data selected from previous investigations. Sensitivity and parametric studies were carried out to investigate the effect of some model and structural parameters.

The dumping cost of wasted concrete including the rejected units in precast concrete plants is expected to keep rising as the production increases. The waste material from precast concrete hollow core floors (hcu) is high grade and uncontaminated material. This research work was carried out to investigate mainly the strength and other engineering properties of high strength concrete made with recycled concrete aggregate derived from rejected hcu. Three major categories (based on a questionnaire) were investigated: (i) Type of crushers and the crushing method, (ii) The properties of RCA output from these crushers, (iii) The performance of fresh and hardened concrete, including prestressed concrete, with these RCA. The input material for the crushers was from the same origin of disposed hcu's. The waste concrete was crushed to -14 mm using three different types of crushers - the cone, impact and jaw crushers. The recycled material was separated into fractions of 14 mm, 10 mm and - 5 mm, and tested for physical and mechanical properties relevant to use in concrete. Concrete was then made using zero (control mix), 20% and 50% replacement of recycled coarse (RCCA), recycled fine (RCFA) and mixed (RCCA+RCFA) aggregates. All three crushers produced acceptable shape and strength of RCCA. Some properties are competitive to that of natural limestone aggregate. RCFA was much coarser than river gravel and just complied with the British Standard coarse grading limits. The impact crusher performed best with regard to most aggregate properties, e. g. flakiness, strength and water absorption, but has a disadvantage in producing a large amount of fine-to-coarse RCA. Concerning shape and strength, RCA showed similar properties, and in some cases better, than the conventional limestone aggregate. The water absorption for RCA is 3 to 4 times greater than the natural aggregates. For that reason an extra amount of water (called free water) will be added to the mix to compensate the water absorptions for aggregates. Some proportions of this extra added water may not be absorbed by the aggregates and will float to interrupt the design W/C ratio and caused it to increase. The slump value of fresh concrete made with RCA varied widely depending on the percentage and type of replacement, and the type of crusher. The compaction factor of fresh concrete made with RCA was more consistent and logical. Compressive strength of concrete made with RCA were generally within ±5 N/mm2 of the control. For tensile strength, RCA showed similar performance to that of natural limestone. The SS density of concrete with RCA is lower than that of the control concrete and is lower if the replacement percentages increase. Using RCFA causes higher bleeding rate and considerably reduces density and strength, and the severity increases as the replacements of RCFA increases. Using natural limestone aggregates with RCFA will minimize this poor behaviour and maintain the strength to certain extent. However joining RCCA with RCFA will not limit the poor behaviour and is not recommended. For bonding reinforcing bars most methods indicated that high replacement (100%) of CA cause some reduction in bond strength. In pretensioning wires the RCA concrete had a better performance in bond but some reduction was still reported. Prestressed X-shape beams were used to assess the effects of using of RCA on the performance of hollow core slabs. For 20% RCCA replacements, the prestressing loss, deflection and X-beam flexure crack failure were similar to the standard X-beam, at least and within the design limit. However at higher replacements (50%) some deterioration starts to reveal and the effects are even greater when using a combination of RCCA and RCFA.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.
This study aimed to investigate the mechanical and durability properties of recycled aggre-gate concrete with a ternary binder system and optimized mix proportion. Two concretebatches were developed using a densified mix design approach (DMDA) to evaluate therequired mix proportions. Batch I have GGBS content varied at 0%, 10%, 20%, 30%, 40% and50% at constant w/b ratio of 0.45, while batch II concrete mix have varied water/binder ratios:0.3, 0.35, 0.4, 0.45 and 0.5 at constant GGBS replacement level of 30%. The fine aggregate(river sand) of the two batches was blended with fly ash at optimum loose packing density(FA + Sand) and superplasticizer (SP) was incorporated in the mix at a constant level of 1.4%.A control mix comprising of natural aggregate was also developed. The results obtainedshowcased the feasibility of producing structural concrete with recycled aggregates usingGGBS and fly ash. The mechanical and durability properties were best at 30% GGBS contentand 0.35 water/binder ratio. The DMDA for mix proportion adopted for RAC contributed sig-nificantly to improving its properties when compared to NAC, especially at the optimumobserved RAC mix with compressive strength of 52 MPa. Also, the mix demonstrated goodpermeability resistance in terms of chloride-ion ingress and capillary water absorption.

The bricks are one of the primary materials required for construction of homes that no used completely when executes all the walls due, the excess purchase, the cutting to be settle, the breaking for their transfer and its fixed dimensions; this situation requires monitoring on work site the order, cleanliness and accidents. A common practice is these bricks and/or waste are included in the clearing construction before being deposited or eliminated in dumps or sanitary landfills, with their early clogging and shortening them to ther design lifespan. An important alternative to reduce this waste, is to recycle them and reuse them as a concrete component material, due to their high absorption percentage that allows them to keep the water inside of them and then use it in the cement hydration process as internal curing of the concrete. In the present investigation, the effect of crushed clay brick as a replacement for coarse aggregate in concrete processing is studied. The results indicate that with 21 % replacement brick, the plastic contraction decreases, and the compressive strength and flexural strength increase.

The use of recycled concrete aggregates (RCA) has gained increased attention in the past few decades as an alternative to decrease the carbon footprint of concrete construction. Yet, most of the research performed so far demonstrates that RCA concrete displays inferior performance in the fresh and hardened states when compared to conventional concrete (CC). The latter is believed due to the fact that very often the different microstructure of RCA is not accounted for while the mix-proportioning of RCA concrete. Recently, a number of mix-design procedures accounting for RCA microstructure have been proposed. Amongst them, the Equivalent Volume (EV) method seems to be quite promising. The EV method may proportion RCA concrete made of coarse (CRCA) or fine (FRCA) RCA and is based on a companion CC. Previous research has demonstrated that the fresh and hardened properties of EV mix-designed CRCA are suitable for structural applications. Yet, very few research, analysis and quantification have been conducted on the fresh behaviour of EV mix- proportioned FRCA concrete. This work presents a comprehensive study on the rheological behaviour of EV mix-designed CRCA and FRCA concrete presenting distinct features (i.e. inner qualities, mineralogy, fabrication process, etc.) through the use of a planetary rheometer (IBB). Results show that the EV is capable of proportioning low embodied energy CRCA and FRCA concrete with shear thinning profiles. The latter suggests that these mixtures are suitable for applications under high torque regimes such as vibrated or pumped concrete.