Dissertations / Theses on the topic 'Concrete durability'

Master of Science
Department of Civil Engineering
Asadollah Esmaeily
Reinforced concrete exceptional durability is a major reason why it is the most popular structural material in many infrastructures around the world. Most concrete structures serve for several decades; therefore problems of concrete durability gradually arise. To insure that concrete structures perform functionally, it is necessary to maintain and inspect them regularly. The durability of the reinforced concrete structures generally depends on four major factors: structure design and construction, maintenance, concrete aggregates, and environmental conditions. The most common causes of concrete deterioration are carbonation, design and construction errors, alkali-aggregate reactions, freeze-thaw cycles, and corrosion. Each type of concrete deterioration has its own signs and characteristics. Choosing the best repair technique to address concrete deterioration requires specific analysis and tests to find the cause of the deterioration and the extent of the damage. This study analyzes concrete structures inspection techniques to recognize the source of the problem and the part of the structure which has been affected. Choosing the most proper repair and strengthening techniques to prevent the structure from getting exposed to any further environmental and chemical are the next steps.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.
Includes bibliographical references (leaves 80-81).
Recent trends in concrete durability design have favored the use of protective coatings. Although these coatings, if applied correctly, can totally inhibit degradation of the concrete member, these coatings are expensive. In the most severe conditions, the coatings are the only way to avoid extensive corrosion. In many cases, however, the coatings are used when less expensive means of avoiding concrete corrosion are available. If the type of degradation agents to which the concrete is to be exposed during its service life can be accurately predicted, the durability design requires only minor, inexpensive changes to the concrete mix proportions, the mix ingredients, or the structural detailing. This document provides a comprehensive guide to various types of concrete degradation and the mechanics involved with each type of degradation. For each of the degradation mechanisms discussed, several methods of designing concrete structural members, using only minor alterations in the concrete member, to resist degradation are provided in this document.
by Jahangir M. Abdoveis.
M.Eng.

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.

Bibliography: leaves 69-72.
Modern fast track construction methods increasingly favour the use of precast concrete elements. Precast box culverts are structurally significant units, subject to an important combination of bridge loadings. Culverts occasionally in contact with water pose a high durability risk. Despite this, the current specifications allow a reduction in cover to reinforcing steel for precast culverts to only 20 mm from at least 40 mm for cast-in-place culverts.

The main theme of this research was to investigate the durability of concrete made using waste materials as a cement replacement. This is a method to produce green sustainable concrete. The objective was to use locally available wastes to produce a concrete that could be used by the local authority. The mechanical, physical and chemical properties of concrete made predominantly with IFA as a partial cement replacement have been tested. The IFA was won locally from the domestic waste incinerator at Coventry, UK. The other materials used in the mixes included Ground Granulated Blast Furnace Slag (GGBS), silica fume and by-pass dust, which was used as an activator and was also won locally from the Rugby cement plant. Compressive strength and tensile strength, workability, corrosion of embedded steel, shrinkage and expansion, freeze and thaw, corrosion and chloride ingress were studied. Water permeability was studied by the author on mortar samples during one year and on concrete samples during the following. Carbonation was studied on concrete samples and finally mechanical experiments were carried out on concrete beams and slabs. Two further experiments were carried out to complete the study of durability of concrete made with waste materials being, the ASR (Alkaline Silica Reaction) and sulphate attack experiments. One main physical experiment, in the form of a trial mix, was carried out in one of the waste recycling sites of Warwickshire in September 2013. Subsequent to observations during the site trial, the author compared results of setting time, heat of hydration and strength of the trial mix and control mixes. The outcome of this research was a novel mix that had more than 30 percent waste material and a further 40 percent of secondary materials, making it as sustainable as possible. Both laboratory and site trial results have achieved compressive strength which are higher than 30 MPa, indicating that the novel mix concrete could be used for structural purposes. Most of the durability results of the novel mix were comparable with the control OPC mix and the novel mix concrete, in terms of transport properties, induced less electrical current seepage. Furthermore the tensile strength of the novel mix concrete was higher than the control OPC concrete and this is due to the higher ductility index of the novel mix.

Actuellement, il est largement reconnu que la durabilité des structures en béton armé, due à la corrosion des armatures engendrée par la carbonatation ou la pénétration des chlorures, peut être affectée largement par les conditions de cure et de serrage du béton coulé en place. Toutefois, les effets de ces conditions sur la qualité du béton ne sont pas encore entièrement comprises, puisqu'elles sont habituellement négligées (ou traitées superficiellement) dans les méthodologies actuelles de performance utilisées pour la spécification et contrôle de sa durabilité. Dans ce travail sont étudiés les effets des conditions habituelles de mise en place (y compris le serrage) et cure sur les propriétés de durabilité du béton, à savoir, la résistance à la carbonatation accélérée, le coefficient de migration des chlorures (dans des conditions non stationnaires), l'absorption d'eau et la perméabilité aux gaz (méthode CEMBUREAU). À cette fin, plusieurs bétons de différent composition, sans et avec cendres volantes, ont été soumis à deux principaux programmes expérimentaux. Dans le premier programme, trois bétons ont été soumis à une cure humide dans le laboratoire à différentes températures, entre 5 °C et 60 °C, et testés à différents âges, entre 28 et 182 jours, pour quantifier l'effet isolé de la température de cure sur les propriétés de durabilité du béton. Dans le deuxième programme, plusieurs éléments (dalles, poutres et poteaux) ont été coulés sur chantier, pendant l'hiver et l'été, après avoir été soumis à deux conditions différentes de serrage, vibré et non vibré, et démoulés à différentes à 24 h et 72 h. Les propriétés de durabilité du béton près de la surface et de cœur des éléments (propriétés réelles) ont ensuite été mesurées à différents âges, entre 28 et 364 jours, et comparées avec les propriétés des échantillons vibrés et curés en conditions normalisées (propriétés potentielles)
It is widely recognized that the long-term durability of reinforced concrete structures related to carbonation- and chloride-induced corrosion can be detrimentally affected by on-site placing and curing conditions of concrete. However, the effects of these conditions on concrete durability are still not fully understood, being usually overlooked in current performance-based specifications and control of concrete durability. In this work, the effects of realistic placing (including compaction) and curing conditions on the concrete durability-related properties most used in performance-based specifications are studied, such as the accelerated carbonation resistance, chloride migration coefficient (non-steady state conditions), water absorption and gas permeability (CEMBUREAU method). For that purpose, several concretes of different composition, with and without fly ash addition, were subjected to two main experimental programs. In the first program, the concretes were cured in the laboratory under several temperature regimes, ranging from 5 ºC to 60 ºC, and then tested at different ages, from 28 to 182 days, in order to evaluate the isolated effect of curing temperature on their durability-related properties. In the second program, several concrete elements (slabs, beams and columns) were cast outdoors, during the winter and summer, and subjected to different compaction (vibrated and not vibrated) and curing (demoulded after 24 h and 72 h) conditions. The durability-related properties of the inner and outermost concrete of the elements (actual properties) were then measured at different ages, from 28 to 364 days, and compared with those of standard specimens made of the same concrete (potential properties)

Although the use of pervious concrete is expanding, only a limited number of scholarly papers have been published on the resistance of pervious concrete to deterioration under frost action. Based on this need for additional research on the durability of pervious concrete in cold regions, the objective of this research was to evaluate the resistance of pervious concrete to degradation during freeze-thaw cycling under different soil clogging and water saturation conditions. The laboratory research associated with this project involved three primary measures of pervious concrete performance, including freeze-thaw durability, compressive strength, and permeability. Testing associated with freeze-thaw durability involved two levels of soil clogging, two water saturation conditions, and two curing durations in a full-factorial experimental design. Field testing involved measurements of stiffness, permeability, and compressive strength at a single site in Orem, Utah. The factor of water saturation and the interaction between the factors of curing condition and clogging condition played significant roles in testing throughout the entire course of freeze-thaw testing. Regarding the factor of water saturation, specimens that were completely submerged in water during freeze-thaw testing were damaged at a notably faster rate than those specimens that were tested in a moist but unsaturated condition for both curing conditions. Regarding the interaction between the factors of curing condition and clogging condition, the effect of clogging on the number of freeze-thaw cycles to failure depended upon the curing condition. A comparison of in situ modulus values, core modulus values, and core compressive strengths associated with clogged locations and unclogged locations in the field indicated no significant differences in structural properties in the clogged and unclogged locations. Although the results of this research suggest that pervious concrete similar to that evaluated in this study can be successfully used in cold regions under essentially ideal conditions, further laboratory and field research should be performed to more carefully examine the effect of moisture content on the freeze-thaw durability of moist but unsaturated specimens. Also, given that clogging can reduce the freeze-thaw durability of pervious concrete, the efficacy of maintenance procedures available for cleaning partially clogged pervious concrete slabs should be investigated. Long-term monitoring of and supplementary experimentation on the pervious concrete slab tested in this research should be considered for these purposes. More conclusive data about the performance of pervious concrete in cold regions will be derived from such field tests.

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.

Pour les structures de génie civil avec un rôle d'étanchéité lors d'un accident grave, la perméabilité structurelle est une question clé. Dans ce contexte, cette thèse porte sur la modélisation numérique du taux de fuite à travers une structure en béton fissurée. Deux approches hydromécaniques dans un cadre continu sont proposés, une entièrement continu et une autre qui nécessite une analyse semi-discrète. L'approche semi-discrète est basée sur une méthode permettant de trouver le chemin de la fissure. Une fois le chemin de la fissure est trouvé, l’ouverture de fissure peut être calculée le long de la surface de la fissure discrétisé par équivalence d’une discontinuité forte. La dernière étape consiste à prescrire la loi de Poiseuille modifié le long de la surface de la fissure pour estimer le taux de fuite tout en imposant un gradient de pression. L'approche entièrement continue peut être appliquée directement dans le sens où aucun suivi de la fissure n’est nécessaire. C’est une combinaison de la perméabilité des endommagements diffus et de la perméabilité de Poiseuille modifiée. Ici, la déformation principale positive est choisie pour conduire la perméabilité de Poiseuille modifiée. Les deux approches proposées sont validées sur une campagne expérimentale de disque béton sec chargé dans un essai de fendage où la perméabilité aux gaz est réalisée. La validation est effectuée sur le taux de fuite dans la direction longitudinale. Les résultats obtenus avec les approches proposées par rapport aux données expérimentales montrent une bonne estimation de la conductivité hydraulique. En outre, l'approche continue est appliquée pour estimer le taux de fuite à travers un élément en béton armé soumis à une charge de traction où la multi-fissuration en mode I se produit (essai tirant). La comparaison avec l'expérience est effectuée sur le taux de fuite dans la direction perpendiculaire à la charge appliquée. Celui-ci montre un bon accord entre les débits estimé et mesuré si le même nombre de fissures est obtenu par le modèle mécanique.Cette thèse porte aussi sur l'effet des chargements thermomécaniques et de fluage sur la conductivité hydraulique du béton. Un système de perméabilité est développé et construit au cours de cette thèse sur la base du programme expérimental. Une campagne expérimentale est effectuée pour étudier l'effet couplé du fluage thermique et / ou mécanique sur la perméabilité à l’air sec du béton. Les propriétés de transfert dans les directions longitudinale et radiale par rapport à l'axe de charge sont étudiées. L’anisotropie de la perméabilité induite par la charge appliquée est analysée. En outre, la détermination de la perméabilité structurelle le long de l'interface acier-béton à différentes charges de cisaillement est encore une question ouverte. Un programme expérimental est réalisé qui porte sur le comportement mécanique du béton armé soumis à un essai de type push-in, ainsi que sur l’analyse de la perméabilité le long de l'interface acier-béton à des niveaux de charge différents. Une première tentative pour simuler le test en utilisant l'approche continue proposée est effectuée.Cette thèse a été l’occasion de réaliser une nouvelle campagne expérimentale, de produire de résultats originaux, d’effectuer de la modélisation numérique et de confronter les 2 approches proposées pour valider les modèles afin de les appliquer à l’échelle structurelle
For civil engineering structures with a tightness role during a severe accident, structural permeability is a key issue. In this context, this PhD deals with the numerical modelling of leakage rate through a cracked concrete structure. Two hydro-mechanical models in a continuous framework are proposed, a fully continuous one and another one that requires a semi-discrete analysis. The semi-discrete approach is based on a crack tracking method allowing to find the crack path. Once the crack path is found, the Crack Opening Displacement (COD) can be computed along the discretized crack surface by equivalence with strong discontinuity approach. The final step is to prescribe a modified Poiseuille’s law along the crack surface to estimate the leakage rate while imposing a pressure gradient. The fully continuous approach can be directly applied in a sense that no crack tracking is needed. It is a combination of permeability of diffuse damage and modified Poiseuille’s permeability. Herein, the positive principal strain is chosen to drive the modified Poiseuille’s permeability. The two proposed approaches are validated on an experimental campaign of dry concrete disk loaded in a splitting setup where gas permeability is performed. The validation is performed on the flow rate in the longitudinal direction. The results obtained with the proposed approaches compared to experimental data show a good estimation of the hydraulic conductivity. Furthermore, the fully continuous approach is applied to estimate the flow rate through a reinforced concrete element subjected to tensile loading where multi-cracking in Mode I occurs (tie-beam test). The comparison with the experiment is performed on the flow rate in the perpendicular direction to the applied loading. The latter shows a good agreement between the estimated flow rate and the measured one if the same number of cracks is obtained.This PhD deals as well with the effect of the delayed thermo-mechanical loadings on the hydraulic conductivity of concrete. A permeability system is developed and constructed during this PhD based on the experimental program. An experimental campaign is carried out to study the effect of thermal and/or mechanical creep on dry gas permeability of concrete. Permeabilities in longitudinal and radial directions with respect to load axis are addressed. The loading induced anisotropic permeability is analyzed. Furthermore, the determination of the structural permeability along the steel-concrete interface at different shear loadings is still an open issue. An experimental program is carried out which deals with the mechanical behavior of reinforced concrete subjected to a push-in test, as well as with a permeability analysis along the steel-concrete interface at different load levels. A first attempt to simulate the test using the proposed continuous approach is performed.This thesis was the occasion to conduct a new experimental campaign, to produce original results, to perform numerical modeling and to compare two proposed approaches to validate the models in order to apply them at the structural scale

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 6, 2007) Includes bibliographical references.

There is an increasing global concern that has led to efforts to lessen the carbon footprint of the cement industry and make concrete manufacturing more sustainable by using other types of materials as supplements or alternatives, primarily for Portland cement (PC). This research work is concerned with the analytical systemisation, including the analysis, evaluation and structuring of global published experimental results, of ground limestone (GLS) used in concrete as a partial replacement of PC. The work is focussed on the physical and chemical characterisation of GLS and its effects on pore structure (in terms of porosity, water absorption and sorptivity), compressive strength and the durability of the concrete in terms of the carbonation and chloride ingress and the corrosion of steel reinforcement, including a statistical modelling of the carbonation of concrete with Portland limestone cement (PLC). Overall, it is suggested that, though the use of GLS up to 25% with PC should not impair the pore structure, the limit on GLS content for its effect on strength is likely to be about 15%. This should be considered where a higher proportion of GLS content is allowed in the standards. It is also shown that the carbonation rate and chloride ingress into concrete increase with increasing GLS content.

Inclusion of ground granulated blast furnace slag (GGBFS) together with fly-ash can have significant effects on the development of mechanical and durability properties of geopolymer concrete when cured at normal temperature. The slag blended geopolymer concretes showed durability properties comparable to those of the control OPC concrete. In general, the results show that it is possible to design fly ash and slag blended geopolymer concrete suitable for ambient curing with similar or better durability properties of conventional OPC concrete.

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 use of concrete increasing annually due its favourable properties and readily availability. Demand for concrete will continue to increase and it will remain the world’s most important construction materials for many years to come. However, the use of Portland cement concrete has an environmental burned, and so in a drive to reduce the carbon footprint of construction, there is widespread attention directed towards the utilisation of wastes and industrial by-products to minimise Portland cement (PC) consumption. The cement industry increasingly uses additions, such as fly ash. The literature has established the use of fly ash as partial replacement of Portland cement to increase strength at later age and exhibit considerable enhancement in durability. However, such binders hydrate more slowly, so proper curing conditions become more important. Ideally, the durability of concrete should not be a concern. Some degree of weathering should be expected, but improper concreting procedures can cause the deterioration to be earlier than expected. Furthermore, since durability issues cannot be seen immediately, some assessment of the impact of improper concrete curing is needed. The study has involved casting of concretes prepared with either CEM I or a CEM I blend with 30% replacement with fly ash to investigate the impact of improper curing. Performance was evaluated in terms of compressive strength, drying shrinkage, transport properties and resistance to carbonation. Paste samples were characterised by TGA, XRD and SEM to follow hydration and microstructural development. Also since the degree of saturation is known to affect the compressive strength of concrete, and curing under ambient conditions will lead to changes in the degree of concrete saturation, the work checked the impact of the degree of saturation on compressive strength; to enable an accurate understanding of the impact of improper curing. Improper curing leads to reduced compressive strength development and increased drying shrinkage. Sorptivity and permeability values were increased. This is due to reduced levels of cement hydration, as water evaporates from the concrete surface. The effect of improper curing on resistance to carbonation revealed that samples improperly cured carbonated more than those ideally cured. This study has shown that the impact on sorptivity and permeability is far greater than the impact on compressive strength, with implications for the long-term durability of concrete. Composite cements, containing 30% fly ash, showed comparable strengths to CEM I concretes and improved transport properties when ideally cured. Additions of fly ash reduced the drying shrinkage. Improper curing however led to reduced performance. Strength was compromised by improper curing to a greater degree than for equivalent CEM I mixes. However, it was sorptivity and permeability which were most severely affected. This was due to the reduced degree of cement hydration leading preventing the pozzolanic reaction between the fly ash and portlandite. Also, higher carbonation depth was seen on fly ash samples that were not cured. Low strength concrete, which already has an inherently higher porosity, is more greatly affected by improper curing than high strength concrete. This is presumed to be due to the ease with which water can evaporate from the surface of the more porous matrix. Also, concrete workability has been found to be a factor which can help to reduce the embodied carbon of concrete, with stiffer mixes having lower carbon footprints. However, this study has shown that stiff concrete mixes may be less durable and more susceptible to improper curing. This may be explained by the lower overall water contents within the stiff mixes, and therefore the greater impact of surface water evaporation. The effect of changes in the degree of saturation showed the deleterious effects of improper curing, with the saturated, ambient cured samples all exhibiting lower strengths than the equivalent ideally cured samples. The large capillary pores developed due to improper curing was seen with lower calcium hydroxide contents. The reduced hydration products obtained support the result that lower degree of hydration was produced due to improper curing since the hydration of cement cannot continues in the dry environment. This study confirms the need for good site practice, and shows that embodied carbon should not be the only factor when considering the environmental performance of concrete. Rather, durability and whole life performance should also be considered.

Slurry infiltrated fiber concrete (SIFCON) was first produced in 1979 in the USA, by incorporating large amounts of steel fiber in molds to form very dense network of fibers. The network is then infiltrated by a fine liquid cement-based slurry or mortar. The steel fiber content can be as high as 30 % by volume. This percentage usually does not exceed 2 % in normal fiber reinforced concrete (FRC) for reasons related to mixing and workability. Due to its high fiber content, SIFCON demonstrates unique and superior mechanical properties in the areas of both strength and ductility. Most of previous research work on SIFCON has focused mainly on investigating the mechanical properties of this material. On the other hand, the studies carried out in the field of durability of SIFCON are quite limited. v Therefore, it seemed that it would be worth to study the various durability aspects of SIFCON. In view of the above, the objectives of this study are to investigate and provide information about durability of SIFCON, mainly permeability, resistance to chloride penetration, freezing and thawing and drying shrinkage. This information will help in providing the necessary database and knowledge about the ability of SIFCON to withstand the conditions for which it has been designed without deterioration, especially when it is intended to be used in aggressive environments The investigations included studying the effects of the following on durability of SIFCON: (i) matrix type (slurry or mortar), (ii) fiber contents (7%, 9.5%, and 12% by volume), and (iii) steel fiber geometry (hooked or crimped). The results obtained indicated that SIFCON, especially when prepared using mortar not slurry, has shown good durability characteristics in spite of its apparent high water absorption. The SIFCON made with the highest possible fiber volume fractions showed the best results. However, it was concluded that SIFCON needs to be protected with suitable low permeability overlays to ensure ideal improved performance by protecting the steel fibers exposed on the surfaces especially against chloride attack.

Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xvi, 204 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 155-158).

Sustainable and durable infrastructure facilities, including bridges, require optimum use of all resources involving reduction of energy and water consumption during all project phases, including planning, design, construction, maintenance, operations, repair and rehabilitation, and finally decommissioning and disposal of the debris at the end of its service life. Design of a sustainable and durable bridge structure requires consideration of a few feasible alternatives to develop an optimum option to fulfill all of the relevant limit states, with the best life-cycle performance and with the lowest life-cycle costs. The current national standards do not account for the observed increases in operating loads and the increasing deterioration of bridge structures over their service life. While these standards emphasize quality control in choice of materials, design and construction, they do not provide guidance and scientific tools to design and maintain a bridge structure for durability over its service life, and include only prescriptive tools for preventing some deterioration modes. This research program integrates sustainability and durability in the design of a conventional bridge structure in a cold climate country, subjected to the various mechanical natural and man-made loads and an aggressive environment, and considers the performance of the various materials and structural components over the design service life. The latest available models of the relevant deterioration modes have been incorporated in the life-cycle performance and design considerations. The basic procedure adopts a multiple protection strategy for all deterioration modes, resulting from the relevant aggressive actions, and integrates durability considerations with structural calculations for the final design and defines maintenance strategies and any needed supplementary protection techniques. The design-for-durability procedure is illustrated in a worked out bridge design example.
Les infrastructures durables, incluant les ponts, ont besoin de l'utilisation optimale de ressources naturelles, en considérant une réduction de la consommation d'énergie, des matériaux et d'eau pendant toutes les phases du projet, tels que la conception, la construction, l'entretien, l'opération, la réfection, le renouvellement et finalement le démantèlement à la fin de la vie de service. La conception de ponts sous le principe du développement durable demande la mise en considération de quelques possibles solutions qui répondent aux différents états limites à respecter, avec la meilleure performance et les coûts les plus bas pendant la vie de service de l'ouvrage. Les normes de conception de ponts au niveau national ne considèrent pas l'augmentation des charges d'opération ni l'accroissement de la détérioration des ouvrages d'art pendant leur vie de service. Bien que ces normes mettent l'accent sur le contrôle de la qualité pendant la sélection des matériaux de construction, la conception et la construction, elles ne fournissent pas de directives ni des outils scientifiques pour faire la conception et l'entretien des structures pour atteindre une durabilité spécifique selon la vie de service requise. Ces normes incluent seulement des outils prescriptifs pour prévenir quelques modes de détérioration.Ce programme de recherche fait l'intégration des principes du développement durable avec la conception classique des structures de ponts dans un pays de climat froid, soumis à différents charges mécaniques et environnementales d'origine naturelle et artificielle. Il considère aussi la performance des différents matériaux de construction et composants structuraux pendant la vie de service du pont. Les plus récents modèles disponibles concernant les modes de détérioration de matériaux de construction, ont été incorporés dans les considérations de la vie de service et la conception de la structure. La procédure de base adopte une stratégie de protection multiple contre tous les modes de détérioration qui résultent des actions environnementales agressives. Elle intègre les considérations de durabilité avec les calculs de conception structurale d'une manière itérative jusqu'à l'identification de la conception définitive. Cette procédure inclut l'utilisation des mesures de protection supplémentaire, ainsi que la définition des stratégies d'entretien. La procédure de conception pour la durabilité est illustrée à travers un exemple détaillé de conception d'un pont.

Externally bonded fiber-reinforced polymer (FRP) composites represent a simple and economical solution for many repair and strengthening applications in concrete structures. However, the potential occurrence of sudden and brittle debonding failure in such repairs becomes prominent when FRP-concrete bond undergoes environmental degradation induced by moisture. Ambient-cured low-viscosity Bisphenol A epoxy adhesives are most commonly utilized in the engineering practice to bond wet-layup FRP to the concrete substrate. This study aims to elucidate the effects of Bisphenol A-based epoxy modified with commercial surface-modified nanosilica (SMNS), core-shell rubber (CSR) nanoparticles and multi-walled carbon nanotubes (MWCNT) on the improvement of mechanical properties of the epoxy adhesives, and strength and durability of FRP-concrete adhesively bonded joints. Moisture ingress in epoxy, DSC, tensile test on epoxy and three-point bending beam bond tests were performed. To determine the effects of environmental degradation, all specimens were subjected to the following environments: control—23 °C at RH 50 ± 10% for 18 weeks; and accelerated conditioning protocol (ACP)—water immersion at 45 ± 1 °C for 18 weeks. Improvement in mechanical properties were observed in dogbone specimens modified with nanoparticles without any reduction in glass transition temperature (Tg). In control conditions, nanomodified epoxy groups exhibited enhanced mechanical properties compared to the neat epoxy. Following ACP, strength, elongation and modulus of elasticity of neat epoxy deteriorated significantly, while no significant deterioration was observed in the nanomodified group of adhesives. Among all the nanomodified adhesive groups CSR Type-1 showed most improvement in mechanical properties over neat epoxy group both in control condition and in ACP. CSR-modified adhesive joints experienced practically no degradation when subjected to ACP and showed the highest maximum bond strength retention of 100% among all the adhesive groups. The bond strength of neat epoxy adhesive joints degraded most dramatically (15%) following ACP.

Includes bibliographical references.
Premature deterioration of reinforced concrete (RC) structures has become an issue of global concern. As a result, many upgrades and improvements have recently been made in design standards and specifications, to include requirements that account for durable RC structures. This dissertation examines and compares such durability requirements in design standards and specifications developed in the United States of America, Australia, Canada, Europe, India, and South Africa. It discusses issues relating to exposure conditions, limiting values of material compositions and proportions, and cover depth to the reinforcing steel. Both prescriptive and performance requirements for concrete durability are described. In general terms, this dissertation concludes that most design standards are based on prescriptive requirements with a few having some elements of performance requirements for durability design. The prescriptive approach that outlines requirements for material compositions and proportions, procedures, and test methods, is commonly used in most design standards and specifications for durability purposes. Though such approaches may encompass requirements for, inter alia, minimum compressive strength, maximum water-to-cementitious material (w/cm) ratio and cover depth, the desired concrete performance is not generally described. Material and construction variability are not taken into account, and even if intensive construction supervision is carried out, it is difficult to ensure all specified parameters are achieved. Moreover, requirements such as maximum w/cm and minimum water content are impractical or costly to measure or verify in practice. Generally, it should be acknowledged that this approach has limited applications and often stifles innovations.In an attempt to move away from the prescriptive approach, research has focused on performance approaches, which measure relevant properties of the concrete, in particular transport-related properties that account for durability. Performance approaches impose few or no restrictions on the concrete composition, proportioning, or construction methods, but rather promote innovations. Worldwide there is a consensus that in order to extend the service life of RC structure, performance approaches are imperative. This dissertation gives an overview of the international efforts in the implementation of performance approaches, either in design standards or in project specifications.

La fabrication additive ou impression 3D est la technique la plus récente introduite dans le secteur de la construction. De nombreuses questions restent posées, notamment la maîtrise des propriétés à l'état frais et durci du matériau utilisé, et la stratégie de renforcement pour fournir la ductilité et les capacités structurelles des éléments.Cette thèse traite de l’effet des propriétés à l’état frais du matériau sur l’état durci et sur la réponse mécanique des éléments imprimés. Le travail a commencé par la formulation et la caractérisation rhéologique de nouveaux mélanges imprimables. La thixotropie des mortiers, c’est à dire de la variation du seuil de cisaillement au cours du temps, a été particulièrement étudiée et permet une meilleure compréhension de l'effet de certains adjuvants chimiques et minéraux sur la vitesse de structuration du mélange. Ensuite, la relation entre la rhéologie du matériau et la liaison développée avec les armatures a été explorée, en tenant compte de la direction des couches par rapport à la barre sur la qualité de la liaison. Enfin, cette recherche comprend une caractérisation microstructurale des matériaux imprimés, ainsi qu'une évaluation de la durabilité des éléments imprimés lorsqu'ils sont soumis à des attaques d'acide sulfurique.Plus précisément, l'évolution du seuil de cisaillement a été mesurée pour différents mélanges imprimables sur une certaine période de temps à l'aide du pénétromètre à chute libre, et l'effet de certains additifs chimiques et minéraux a été examiné. Ici, il a été constaté que les paramètres de formulation influencent le taux de structuration du mélange, mais dans des amplitudes différentes. En particulier, l'ajout de superplastifiant, de filler calcaire et l’augmentation du dosage en eau diminuent le taux de structuration du matériau, alors que l’agent de viscosité l'augmente. Ensuite, l'effet de la rhéologie du matériau, de la méthode d'impression et de la direction des couches par rapport à la barre, sur la qualité de la liaison acier/béton imprimé a été étudié à travers des tests d'arrachement sur des éléments imprimés réalisés manuellement ou à l'aide d'une imprimante automatisée. Ici, différents mélanges avec des ouvrabilités et des comportements thixotropes différents ont été utilisés. Des couches parallèles et perpendiculaires à la barre ont été imprimées. Les résultats ont montré que les échantillons imprimés étaient capables de développer une contrainte d’adhérence acceptable par rapport aux échantillons moulés. Ces résultats indiquent également que l'impression manuelle peut être considérée comme une méthode d'essai préliminaire pour simuler le travail d'une imprimante, et que la rhéologie du matériau n’a pas eu d’effet majeur sur la liaison avec les barres. De plus des couches imprimées parallèlement à la barre présentent une meilleure liaison par rapport à celle obtenue pour les échantillons ayant des couches imprimées perpendiculairement. Concernant l'évaluation de la microstructure et de la durabilité des échantillons imprimés, différents mélanges ont été utilisés pour couvrir une large gamme de propriétés des matériaux. Ici, des échantillons imprimés ont été exposés à différentes concentrations d'acide sulfurique et la microstructure des échantillons dégradés et non dégradés a été évaluée. Les résultats ont montré que les échantillons qu'ils soient imprimés ou non, ont les mêmes performances contre une attaque acide. En particulier, les échantillons imprimés n'ont montré aucun signe de faiblesse entre les couches, ni à une échelle micro ni à une échelle macro. La différence majeure entre un échantillon imprimé et un échantillon coulé est que les échantillons imprimés ont une distribution et une morphologie de la taille des pores plus étalées, ce qui est causé par les paramètres d'impression utilisés
Currently, the latest technique being introduced to the construction field is known as Additive Manufacturing or 3D printing. Many challenges encounter this technique, notably the fresh and hardened state properties of the cementitious material used for 3D printing; and the reinforcement strategy to provide ductility and tensile capacity for structural elements.This thesis deals with the effect of the material’s fresh state properties on the hardened state and mechanical response of 3D printed elements. Initially, the work has started by formulating new printable mixes and testing their rheological properties; in particular their thixotropic behavior, depending on the material’s yield stress variation over a certain period of time. After then, the results were linked to the mechanical and hardened state performance of 3D printed elements. Thus, a better understanding of the effect of certain chemical and mineral admixtures on the thixotropic behavior of the mix was carried out. Then, the relation between the material’s rheology and thixotropic behavior with the bond developed between printed layers and reinforcing bars has been exposed, and the effect of the layers direction with respect to the steel bar on the quality of the bond was further assessed. At last, this research includes a microstructural characterization of 3D printed materials, as well as a durability assessment of the printed elements performance when subjected to sulfuric acid attacks.More precisely, the yield stress evolution so-called thixitropic behavior was measured for different printable mixes over a certain period of time using the fall-cone penetrometer; and the effect of some chemical and mineral additives was considered. Herein, it was found that the material variables influence the structuration rate of the mix, but in different magnitudes. In particular, the addition of HRWR, Limestone filler and water content decrease the structuration rate of the material, whereas VMA increases it. Afterwards, the effect of the material’s rheology, printing method and layers direction with respect to steel bar, on the developed link have been studied through a series of pull-out tests done over printed elements made either manually using a laboratory device or using an automated printer. Herein, different mixes with different workabilities and thixotropic behaviors were used. Alongside, concrete layers were printed either parallel or perpendicular to the steel bar. The overall results showed that printed samples were able to develop an acceptable bond strength in comparison with the mold casted specimens. Implicitly, these results indicated first that the manual printing can be considered as a preliminary testing method to simulate the work of an actual printer; second, the material’s rheology did not majorly affect the bond with steel bars; third, parallel printed layers to the steel bar can still provide better bonding with it in comparison to that attained by the samples having perpendicular printed layers. As for the microstructural and durability assessment of 3D printed samples, different mixes were used to cover a wider range of material properties. Here, 3D printed samples were exposed to different concentrations of sulfuric acid, and the microstructure of the degraded and non-degraded samples was assessed. The results showed that concrete samples whether printed or not have the same performance when subjected to acid attack. In particular, printed samples did not show any sign of inter-layer weaknesses, neither at a micro nor macro scales. However, the only difference between a printed specimen and a non-printed one is that printed samples have a more spread pore size distribution and morphology, which is caused by printing parameters used

Durability is a major concern for reinforced concrete (RC) structures. RC structures both in service and new, are subject to cracking. Irrespective of the cause of the cracking, cracks can increase the rate of penetration of aggressive species into concrete and modify the transport properties. Consequently, the service life of corrosionaffected RC structures may be drastically reduced in the presence of cracks. However, no modifications are made for the influence of cracking on the penetration of aggressive species into concrete when analysing durability test results or making service life predictions, even through concrete is very often in a cracked state. This study focused on the influence of cracks on the ingress of aggressive species (carbon dioxide and chlorides) into cracked concrete in comparison to uncracked concrete. The aim was to establish any correlations between the transport properties in uncracked and cracked concrete. Furthermore, in a broader context, the aim was to assess to what extent the modified cracked concrete parameters used in service life predictions affect the service life outputs, when compared with service life outputs obtained using the uncracked concrete parameters. Six concretes mixes were investigated comprising two water/binder (w/b) ratios (0.40 and 0.55) and three binder types (100% CEM I 52.5N (PC), 70/30 PC/FA and 50/50 PC/GGBS). 100 x 100 x 500 mm beams were cast and cracks were induced after seven days in the mid-span of each beam using three-point loading. Two crack width ranges were investigated; 0.1-0.4 mm (wcr1) and 0.5-0.8 mm (wcr2). The central section of the beam that contained the crack was sawn from the rest of the beam and used for either accelerated carbonation or bulk chloride diffusion testing. Cores were drilled from the outer sections of the beam and used as specimens for the Durability Index tests. The cracked specimens were monitored for carbonation (accelerated carbonation) and chloride ingress (bulk diffusion), while the uncracked ones were monitored for durability parameters (OPI, WSI & CCI) after 8 and 16 weeks of exposure. Firstly, it can be concluded that the presence of cracks modifies the transport properties of concrete by promoting rapid increase of ingress of aggressive species (CO₂ & Cl-) into the concrete matrix. It was found that the degree to which the transport properties were modified increased as the crack width increased. This was primarily attributed to the increase in surface area created by the crack, which allowed increased amounts of species (CO₂ & Cl-) to penetrate into the concrete matrix. In the case of carbon dioxide ingress, the presence of cracks significantly increased the rate of carbonation (up to 50 %) in the concrete specimens that contained blended cements PC/FA and PC/GGBS when compared to the PC concrete specimens. However, in the case of chloride ingress the effects of cracks in the PC mix resulted in the highest presence of chlorides (up to 78 %) in the concrete specimens in comparison to the chlorides present in the PC/FA and PC/GGBS concrete specimens. Secondly, when the sound (DI) and cracked durability parameters (carbonation and diffusion coefficient) where used in carbonation and chloride ingress service predictions, it was found that the DI service life prediction outputs were more conservative in relation to service life outputs from the durability parameters obtained from cracked concrete specimens. These results highlighted the degree of influence which the presence of cracks had on modifying transport properties in concrete. Furthermore, it also highlights the impact of the presence of cracks on the service life of RC structures and the prediction of long-term carbonation- and chloride- induced corrosion. Due to the significant influence that cracks have on modifying the transport properties of concrete, the results show that some reduction factors need to be applied to the results from the DI approach to reflect a more realistic durability potential of the concrete. Further research into understanding how other crack parameters (crack depth, frequency etc.) modify transport properties in concrete will lead to a more accurate insight into dealing with and accounting for the presence of cracks in RC structures.

Conventional concrete is a poor insulating material but has good thermal mass, while lightweight concrete provides good insulation at the price of thermal mass. Precast concrete wall systems have not been widely used in residential homes due to poor thermal and acoustic performance, despite being high quality products that are easy to construct. The variable density concrete panel was designed to combine good thermal storage, insulation and high quality precast concrete. It is produced from a single concrete mix which is vibrated to get a lightweight top layer and a normal/heavyweight bottom layer. The lightweight layer is the wall exterior, having low thermal conductivity providing good thermal insulation while the normal/heavyweight layer is the dense wall interior, having high specific heat to provide good thermal mass and sufficient strength for construction handling and to withstand service loads. The intention of this research was to estimate the hardened performance; that is the structural, serviceability and durability performance of the variable density concrete panel. Further developments to the mix design were made where the fresh properties were measured and thermal performance estimated on hardened specimens. Most of the major technical concerns were proved not being as severe as first thought, making the production of variable density concrete panels promising. To ensure that the variable density concrete would stratify, the concrete mix had to have defined fresh properties. Defined rheological ranges gave a good indication of the stratification potential, but the degree of stratification was also found to be dependent on the intensity and time of vibration. Slump flow had to be within a certain range to achieve good stratification but this alone did not guarantee stratification. Variable density concrete was found to have adequate strength capacity both in axial compression and in tension for likely service loads but the strength required to withstand handling loads at early ages was not assessed. The strength of the variable density concrete was found to be affected by several factors such as; degree of stratification, relative strength and thickness of the layers, curing environment and amount of defects. As the stratification of the concrete increased the thermal insulation improved whereas the strength decreased. Warping was found not to significantly affect the serviceability of panels despite differential shrinkage within the element. The amount of warping was mainly related to the degree of stratification. Warping decreased with better stratification as more stress and strain was relieved in the lightweight layer. The lightweight concrete was significantly weaker as well as being less stiff than the structural concrete and therefore creeps to follow the structural concrete. The thermal properties aimed for were generally not reached, but these mixes were not designed to optimise the thermal performance and were tested before the concrete was fully dried. This increased thermal conductivity and therefore reduced the measured R-values. Stratified concrete had good absorption resistance, poor permeability properties and was highly porous. If the concrete was over-vibrated it tended to have a rough surface finish that would require a coating. Delamination of the panels was not assessed in this research but is a likely mode of failure.

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.

In this research, two phases of work were conducted. First, an investigation into the durability concerns for precast prestressed concrete piles exposed to marine environments was conducted. The investigation characterized the durability concerns of chemical, biological, and physical deterioration mechanisms. The results of this study were used to develop potential high performance marine concretes (HPMC) that would be capable of 100+ year service lives in marine environments. Extensive durability testing and service life modeling of the HPMC was performed. Chloride ingress resistance was investigated using accelerated and long-term test procedures and the results used to perform service life modeling to predict the time before corrosion initiation. Sulfate resistance characterization was performed using multiple techniques to characterize the physical and chemical behavior of binder compositions containing binary or ternary mixes containing cement and supplementary cementitious materials (SCM's) subjected to a sulfate-laden environment. Accelerated carbonation testing and material characterization led to the finding of relationships in the chemical composition of mix designs and the observed durability and the results used to perform corrosion initiation service life modeling. An investigation into the influence of self-healing of cracked concrete led to fundamental findings on the behavior of chloride ingress for cracked concrete structures in marine environments. The results of this research led to the development of concrete mix designs capable of providing service lives over 100 years in Georgia's marine environments, as well as the advancement of the current state of knowledge on the durability characteristics of ternary mix designs.

The main objective of this research is to establish durability design models for flexural concrete elements subjected to a given aggressive environment. Because corrosion of reinforcement due to chloride ingress is the most significant threat to an existing reinforced concrete structure such as a road bridge or a harbor facility which is exposed to chloride-rich environments, corrosion due to chloride ingress is emphasized in this research. The concrete beams can get corroded to different corrosion levels. Mass loss of the reinforcement is an important parameter, and it can help define the corrosion level, and this information can be used to develop a correlation between corrosion, cracking, bond strength at the steel-concrete interface, and the ultimate strength of the reinforced concrete elements. Therefore, the prediction model of reinforcement mass loss under different levels of chloride concentration needs to be established first using the principles of corrosion electrochemistry. Secondly, design development length is determined based on the mass loss prediction and bond strength equation. Thirdly, the model for the prediction of flexural capacity of reinforced concrete beam for a given design service life is established. Some examples of practical durability design are presented. Finally, a step-by-step durability design procedure is recommended for use by practicing engineers. (Abstract shortened by UMI.)

Epoxy-based flexible polymer concrete overlays have been used in the past 15 years in North America to protect the bridge deck from deterioration, to extend the service life, and to improve skid resistant of the riding surface. While 15 years of field applications have demonstrated the effectiveness of the protection offered by the technique, cracking and delamination failures have also been observed.
The purpose of the research reported herein is to understand the mechanism of durability failure of the epoxy polymer concrete overlay system. The tests conducted were water permeability, chloride ion penetration, water absorption, strength loss, temperature cycling, and water vapour pressure. Methods of application of polymer concrete overlay play a key role in the success of the overlay. In addition to the two commonly used methods, the multiple layer and the slurry methods, five new application methods were proposed and evaluated.
It was found that the addition of a primer in the overlay system helps reduce water permeability, and that the thin polymer concrete overlay was much less permeable than the thick asphalt overlay. The temperature cycling tests revealed that no significant delamination occurred after 103 cycles from -50°C to 40°C at an accelerated rate. The rapid chloride ion penetration test confirmed that polymer concrete overlays did provide sufficient protection to stop the chloride ion intrusion. Nevertheless, the epoxy polymer concrete overlays were found to absorb 2--3% of water, which caused a significant strength loss. This strength loss could lead to cracking inside the overlay and accelerate delamination thereafter. The water vapour pressure generated from the saturated concrete substrates was not large enough to promote delamination. Overall, the newly proposed overlay applications methods have proven effective in constructing a thin, durable, less expensive and fast overlay for aged bridge deck protection.

Steel fibre reinforced sprayed concrete is common practice for permanent linings in underground construction. Today there is a demand on "expected technical service life" of 120 years. Thin steel fibres could be expected to discontinue carrying load fast with a decrease of fibre diameter caused by corrosion, especially in cracks. The thesis contains results from inspections on existing sprayed concrete structures and a literature review on corrosion of steel fibres in cracked concrete. To study the mechanisms ruling inititation and propagation of corrosion both field exposure tests and accelerated laboratory exposure tests with cracked steel fibre reinforced sprayed concrete have been performed. Parameters tested are type of spraying method, exposure environment, fibre length, usage of accelerators, crack width and time of exposure. A discussion on how the influence of corrosion on load bearing capacity should be considered in a service-life model is also presented.
Godkänd; 2000; 20070317 (ysko)

This thesis presents an investigation where an empirical method is proposed for predicting the durability of reinforced concrete structures in the marine environment. The objective was to identify reliable means of characterizing early-age properties of concrete which affect durability and relate these to the durability performance of the material under marine conditions. Establishing a relationship between early-age testing and long-term performance of concrete is a necessary precursor to implementing a system of performance-based durability specifications.

Includes abastract.
Includes bibliographical references.
The purpose of this study was to create a framework for the development of a probabilistic model for durability design of reinforced concrete (RC) structures in South African marine conditions. Durability design of RC structures is mainly concerned with ensuring the ability of the concrete to resist the penetration of aggressive agents during the concrete‘s intended service life. RC structures in the marine environment may be attacked by aggressive chloride ions which penetrate concrete mainly through the diffusion mechanism. The chloride ions accumulate at the steel level and, upon reaching a critical concentration, cause corrosion to initiate which if not intercepted leads to the eventual deterioration of the entire structure.

Specimens from 27 batches of concrete with water to cementitious (cement plus silica fume) ratio of 0.25 to 0.32, with and without entrained air, were tested for freeze-thaw durability in accordance with ASTM C666, procedure A (freezing and thawing in water). In addition, another set of similar specimens were moist cured for 28 days instead of 14 days and tested in accordance with ASTM C666 , Procedure A to determine the effect of curing time on the freeze-thaw durability of high strength concrete. Results show that non air-entrained high strength concrete with water cementitious ratio of less than 0.30, regardless of the length of curing time, is frost resistant. Non-air-entrained concrete with water-cement ratio of 0.32 is also durable if silica fume is not used.
Ph. D.

Reinforcement spacers (i.e. bar supports, chairs) are crucial elements of reinforced concrete, but their influence on the microstructure and long-term durability is not clear. This study investigates the effect caused by plastic and cementitious spacers, and steel wire chairs combined with different aggregate sizes, curing and conditioning regimes on the transport properties, microstructure and chloride-induced corrosion of concrete structures. Concrete cylindrical samples were prepared with 25 and 50 mm high plastic, steel and cementitious spacers. Samples were then cured, conditioned and tested for oxygen diffusivity, oxygen permeability, water sorptivity and chloride diffusivity. Selected samples were pressure impregnated with fluorescent epoxy to study the extent and spatial distribution of epoxy intrusion. The interfacial zone between the spacer and concrete was examined using field-emission scanning electron microscope in the backscattered electron (BSE) mode. The ingress of chloride, particularly near the interface between spacers and concrete matrix was studied using micro X-ray fluorescence (μXRF). The effect of plastic and cementitious spacers on chloride- induced corrosion via capillary rise and cyclic wetting/drying was investigated using small reinforced concrete beams. The feasibility of improving the bond between spacer and concrete by increasing surface roughness of plastic spacers was also investigated. Results show that concrete samples containing plastic spacers consistently gave the least resistance to transport and the highest epoxy penetration followed by samples with cementitious spacers, and then steel spacers. The control samples (samples without spacers) had the highest resistance to transport in all cases. The epoxy penetration occurred mainly through the spacer-concrete interface. The microstructure of the spacer-concrete interface showed significantly lower cement content and higher porosity compared to 'bulk paste' farther away form the interface. Higher penetration of chloride ions was detected along spacer-concrete interface compared to the control sample or the bulk paste farther away. It is evident that spacers initiate early corrosion and this may reduce the service-life of reinforced concrete structures. The implications of these findings on durability of concrete structures are discussed. Several recommendations to improve the bond at the interface between spacer and concrete are presented.

Concrete is attacked by aggressive agents in the marine and softwater environments which reduce the durability of concrete. To help lessen the effect of this aggressive attack, fly ash concrete has been recommended for use in these environments. The lower permeability, increased chemical resistance and higher long-term strength of fly ash concrete are expected to improve the concrete durability. In this research the effect of fly ash was investigated with regard, initially to general concrete properties such as bleeding, early set, workability, mortar excess and compressive strength. Lethabo field 2 fly ash and Western Cape materials were used for this work. Having developed a wide range of concrete mixes, further investigation was done into specific concrete properties such as the effect of different curing regimes, water absorption, permeability and freeze-thaw resistance. These properties are considered to have an influence on concrete durability. Comparisons were made between the concrete properties of Lethabo field 2, Lethabo classified and Matla classified fly ash concrete. The three types of concrete were tested for compressive strength, sorptivity (rate of water absorption) and density. At the same time, fly ash and OPC concrete samples were exposed to the marine and softwater environment for up to 10 months. Marine exposure was done in the submerged, tidal and spray zones in Table Bay. Softwater exposure was done at Constantia Nek and Steenbras Water Treatment Plants. The performance of concrete in the various exposure conditions was measured by compressive strength, sorptivity and density tests. Fly ash improved many of the properties of concrete, with fly ash concrete having better workability, higher long-term strength, reduced bleeding, lower sorptivity and reduced permeability than similar OPC concrete. Some of the properties of concrete were however worsened by using fly ash. Fly ash concrete had longer setting times, reduced resistance to freezing and thawing and was more adversely affected by dry curing than similar OPC concrete. Lethabo field 2 fly ash concrete had higher compressive strength and lower sorptivity than either Lethabo classified or Matla classified fly ash concrete. The long-term performance of Lethabo classified and Matla classified fly ash concrete was better than that of Lethabo field 2 fly ash concrete, with regard to compressive strength development and sorptivity reduction. Fly ash concrete performed well in both the marine and softwater environments. After 10 months of exposure in either marine or softwater conditions, fly ash concrete had higher compressive strength and lower sorptivity than similar OPC concrete. The good performance of fly ash concrete in the marine and softwater environment confirmed the ability of fly ash to improve many of the important durability properties of concrete. From this medium-term durability investigation it was found that Lethabo field 2 fly ash improved the performance of concrete in marine and softwater environments while fly ash, in general, improved many of the durability properties of concrete.

Summary in English.
Includes bibliographical references.
This dissertation outlines a model developed to allow for the comparison of various design options on a life-cycle cost basis for reinforced concrete structures. The model consists of two interlinked components: the first part of the model is technical, and can be used to estimate the service life of a structure within a specified environment based on a set of prediction models; the second part of the model is used to determine the economic implications of the various design options over a specified evaluation period. The use of a particular predictive model is subject to the environment in which it was calibrated. In many cases the models which are presented were developed overseas and as such their values may not be directly applicable to South African environments. The approaches and development of the models are however useful and if calibrated to particular South African environments could be of considerable benefit. A survey of consulting engineers was also conducted to determine common perceptions of various durability related issues. The results of the survey are presented in this project. The size of the sample was relatively small and as such it would be inappropriate to apply the results categorically to all engineers or organisations. The survey is of value however in that it identifies some areas of potential opposition to the concept of designing for durability and highlights other areas where its acceptance and implementation may be more favourable.

Concrete has the largest production of all man-made materials. Compared with other construction materials, it possesses many advantages including low cost, general availability of raw materials, low energy requirement and utilization under different environmental conditions. Therefore, concrete will continue to be the dominant construction material in the foreseeable future. However, durability of concrete and reinfored concrete structures are still of worldwide concern, so producing a good quality concrete which impedes the ingress of harmful substances into it is of paramount importance. Cement replacement materials have been introduced into concrete mixtures for the purpose of improving the durability performance. Hence, the aim of the present investigation is to study the durability of concrete with and without cement replacement materials under various initial curing conditions. In this thesis various concrete mixes with and without cement replacement materials were considered. The cement replacement materials were, pulverised fuel ash, condensed silica fume, and ground granulated blast furnace slag. Superplasticiser was added to the majority of the mixes considered and air entraining agent to some of the mixes. Various curing regimes were employed which comprised hot dry curing to simulate concrete in the hot arid areas in the world and curing at normal temperature. Curing involved air curing, membrane curing and moist curing for fourteen days followed by air curing. A number of tests were conducted at either one particular age or at various ages. These included tests on porosity and pore structure of pastes obtained by mercury intrusion porosimetry technique, water absorption which covers the water absorption of concrete obtained by shallow immersion and the water absorbed by capillary action when the concrete surface is in contact with water, sulphate resistance of concrete which is performed by immersing the concrete specimens in sulphate solution, and monitoring the change in length at various periods of immersion, chloride penetration profiles of concrete at various ages of exposure. In addition to these tests on durability related properties, tests on compressive strength were also performed. Throughout the study a correlation between pore structure and durability related properties is investigated. A comprehensive compilation of chloride penetration data is made and an empirical expression is derived for the prediction of long term diffusion coefficients. At the end of the investigation, limitations of the present study, conclusions and suggestions for future research are made.