Rozprawy doktorskie na temat „Lime Stabilized Soil”

Modification of black cotton soils by chemical admixtures is a common method for stabilizing the swell-shrink tendency of expansive soils. Advantages of chemical stabilization are that they reduce the swell-shrink tendency of the expansive soils and also render the soils less plastic. Among the chemical stabilization methods for expansive soils, lime stabilization is most widely adopted method for improving the swell-shrink characteristics of expansive soils. Lime stabilization of clays in field is achieved by shallow mixing of lime and soil or by deep stabilization technique. Shallow stabilization involves scarifying the soil to the required depth and lime in powder or slurry form is spread and mixed with the soil using a rotovator. The use of lime as deep stabilizer has been mainly restricted to improve the engineering behaviour of soft clays Deep stabilization using lime can be divided in three main groups: lime columns, lime piles and lime slurry injection. Lime columns refer to creation of deep vertical columns of lime stabilized material. Lime piles are usually holes in the ground filled with lime. Lime slurry pressure injection, as the name suggests, involves the introduction of a lime slurry into the ground under pressure. Literature review brings out that lime stabilization of expansive clays in field is mainly performed by mixing of lime and soil up to shallow depths. The use of lime as deep stabilizer has been mainly restricted to improve the engineering behaviour of soft clays. Use of lime in deep stabilization of expansive soils however has not been given due attention. There exists a definite need to examine methods for deep stabilization of expansive soils to prevent the deeper soil layers from causing distress to the structures in response to the seasonal climatic variations. In addition, there exists a need for in-situ soil stabilization using lime in case of distressed structures founded on expansive soil deposits. The physical mixing of lime and soil in shallow stabilization method ensures efficient contact between lime and clay particles of the soil. It however has limitation in terms of application as it is only suited for stabilization of expansive soils to relatively shallow depths. Studies available have not compared the relative efficiency of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soils. To achieve the above objectives laboratory experiments are performed that study: 1. the efficacy of lime piles in stabilizing compacted black cotton soil specimens from Chitradurga District in Karnataka. The efficiency of lime piles in chemically stabilizing the compacted black cotton soil mass was investigated as a function of: a)amount of lime contained in the lime pile b)radial migration of lime from the central lime pile c)migration of lime as a function of soil depth 2. the relative impact of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soil. The organization of this thesis is as follows After the first introductory chapter, a detailed review of literature performed towards highlighting the need to examine stabilization of expansive soils using lime pile technique is brought out in Chapter 2. Chapter 3 presents a detailed experimental programme of the study. 25 mm and 75 mm diameter lime piles were installed in the compacted soil mass to study the influence of amount of lime contained in the lime pile on the soil properties. The amount of quick lime contained in the 25 mm and 75 mm lime piles corresponded to 1 % and 3 % by dry weight of the soil mass respectively. Radial and vertical migration of lime from the central lime pile was examined by sampling soil specimens at different radial distances from the central lime pile and at different depths of soil sample. At a given depth and radial distance, migration of lime was estimated by comparing the exchangeable cation composition, pH and pore salinity of the treated soil with that of the natural (untreated) black cotton soil specimen. Alterations in the soil engineering properties at a given depth and radial distance were evaluated by comparing the index properties, swell potential and unconfined compressive strength of the lime pile treated soil specimen with those of the untreated specimen. To compare the relative efficiency of lime mixing and lime pile technique in altering the swelling behaviour of black cotton soil, batches of black cotton soil specimens were treated with 1 % and 3 % quick lime on dry soil weight basis. The compacted soil-lime mixes were cured at moisture contents of 31-34 % for a period of 10 days. The physico-chemical, index and engineering properties of the 1 % lime mixed specimens are compared with those of the 25 mm lime pile treated specimens. The properties of the 3 % lime mixed soil specimens are compared with those of the 75 mm lime pile treated specimens. Chapter 4 examines the efficacy of lime piles in stabilizing compacted black cotton soil specimens from Chitradurga District in Karnataka. Experimental results showed that controlling the swell potential of deep expansive soil deposits is possible by the lime pile technique. Treatment with lime pile caused migration of dissociated calcium and hydroxyl ions into the surrounding soil mass. In case of 25 mm lime pile, the experimental setup allowed measurement of migration of lime up to three times the lime pile diameter. In case of 75 mm lime pile, the experimental setup allowed measurement of migration of lime up to 1.6 times pile diameter. In both experiments, migration of lime was also uniform through out the soil depth of 280 mm. Migration of calcium and hydroxyl ions increased the pore salinity and pH of the treated soil mass. The increase in pH caused clustering of additional exchangeable calcium ions at the negative clay particle edges. The increased pore salinity and exchangeable calcium ions reduced the diffuse ion layer thickness that in turn suppressed the plasticity index and the swell potential of the compacted expansive soil. The laboratory results hence bring out that lime pile treatment in the field can substantially reduce the swell potential of the soil at least to a radial extent of 2 to 3 times the lime pile diameter. The 75 mm lime pile contained lime content in excess of the initial consumption of lime (ICL) value of the black cotton soil - namely 2.6 %. Laboratory results showed that migration of hydroxyl ions even from the 75 mm pile could not elevate the soil pH to levels required for soil-lime pozzoIonic reactions (pH ≥12). The very low solubility of lime in water (< 1 g/litre) and the impervious nature of the black cotton soil are considered to have impeded efficient interactions between lime and soil in course of treatment of the expansive soil with lime piles. Absence of soil-lime pozzolonic reactions precluded the formation of cementation compounds in the lime pile treated soil specimens. Cementation compounds formed by the soil-lime pozzolonic reactions are responsible for the much higher strengths of lime stabilized soils. Consequently, treatment with 25 mm pile had no impact on the unconfined compressive strength of the black cotton soil. Comparatively, treatment with 75 mm lime pile slightly increased the strength of the treated soil due to increased inter-particle attraction and particle flocculation. Chapter 5 compares the relative efficiency of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soil. Experimental results showed that mixing of soil and lime promote stronger chemical interactions between lime released hydroxyl ions and clay particles than that achieved by diffusion of lime from a central lime pile. The more alkaline pH of the lime mixed soil specimens rendered the clay particle edges more negative. Consequently, more calcium ions were adsorbed at the clay particle edges of the lime mixed soil specimens imparting them higher exchangeable calcium contents than the lime pile treated soil specimens. Also, at 3 % lime addition, the pH of the lime-mixed soil was sufficiently high (in excess of 12) to cause dissolution of silica and alumina from the clay lattice necessary for the formation of cementation compounds. The stronger lime modification reactions plus the lime-soil pozzolonic reactions (applicable for soil treated with lime content greater than ICL value) achieved by the lime mixing technique rendered the expansive soil much less plastic, much less expansive and much stronger than the lime pile treated specimens. The results of the laboratory study hence suggest that if a choice exists in the field between conventional method of spreading-mixing-compacting of soil-lime mixes and treating the ground with lime piles, the former technique should be adopted because of its greater efficacy in stabilizing the expansive soil. Chapter 6 summarizes the findings of the study.

Modification of black cotton soils by chemical admixtures is a common method for stabilizing the swell-shrink tendency of expansive soils. Advantages of chemical stabilization are that they reduce the swell-shrink tendency of the expansive soils and also render the soils less plastic. Among the chemical stabilization methods for expansive soils, lime stabilization is most widely adopted method for improving the swell-shrink characteristics of expansive soils. Lime stabilization of clays in field is achieved by shallow mixing of lime and soil or by deep stabilization technique. Shallow stabilization involves scarifying the soil to the required depth and lime in powder or slurry form is spread and mixed with the soil using a rotovator. The use of lime as deep stabilizer has been mainly restricted to improve the engineering behaviour of soft clays Deep stabilization using lime can be divided in three main groups: lime columns, lime piles and lime slurry injection. Lime columns refer to creation of deep vertical columns of lime stabilized material. Lime piles are usually holes in the ground filled with lime. Lime slurry pressure injection, as the name suggests, involves the introduction of a lime slurry into the ground under pressure. Literature review brings out that lime stabilization of expansive clays in field is mainly performed by mixing of lime and soil up to shallow depths. The use of lime as deep stabilizer has been mainly restricted to improve the engineering behaviour of soft clays. Use of lime in deep stabilization of expansive soils however has not been given due attention. There exists a definite need to examine methods for deep stabilization of expansive soils to prevent the deeper soil layers from causing distress to the structures in response to the seasonal climatic variations. In addition, there exists a need for in-situ soil stabilization using lime in case of distressed structures founded on expansive soil deposits. The physical mixing of lime and soil in shallow stabilization method ensures efficient contact between lime and clay particles of the soil. It however has limitation in terms of application as it is only suited for stabilization of expansive soils to relatively shallow depths. Studies available have not compared the relative efficiency of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soils. To achieve the above objectives laboratory experiments are performed that study: 1. the efficacy of lime piles in stabilizing compacted black cotton soil specimens from Chitradurga District in Karnataka. The efficiency of lime piles in chemically stabilizing the compacted black cotton soil mass was investigated as a function of: a)amount of lime contained in the lime pile b)radial migration of lime from the central lime pile c)migration of lime as a function of soil depth 2. the relative impact of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soil. The organization of this thesis is as follows After the first introductory chapter, a detailed review of literature performed towards highlighting the need to examine stabilization of expansive soils using lime pile technique is brought out in Chapter 2. Chapter 3 presents a detailed experimental programme of the study. 25 mm and 75 mm diameter lime piles were installed in the compacted soil mass to study the influence of amount of lime contained in the lime pile on the soil properties. The amount of quick lime contained in the 25 mm and 75 mm lime piles corresponded to 1 % and 3 % by dry weight of the soil mass respectively. Radial and vertical migration of lime from the central lime pile was examined by sampling soil specimens at different radial distances from the central lime pile and at different depths of soil sample. At a given depth and radial distance, migration of lime was estimated by comparing the exchangeable cation composition, pH and pore salinity of the treated soil with that of the natural (untreated) black cotton soil specimen. Alterations in the soil engineering properties at a given depth and radial distance were evaluated by comparing the index properties, swell potential and unconfined compressive strength of the lime pile treated soil specimen with those of the untreated specimen. To compare the relative efficiency of lime mixing and lime pile technique in altering the swelling behaviour of black cotton soil, batches of black cotton soil specimens were treated with 1 % and 3 % quick lime on dry soil weight basis. The compacted soil-lime mixes were cured at moisture contents of 31-34 % for a period of 10 days. The physico-chemical, index and engineering properties of the 1 % lime mixed specimens are compared with those of the 25 mm lime pile treated specimens. The properties of the 3 % lime mixed soil specimens are compared with those of the 75 mm lime pile treated specimens. Chapter 4 examines the efficacy of lime piles in stabilizing compacted black cotton soil specimens from Chitradurga District in Karnataka. Experimental results showed that controlling the swell potential of deep expansive soil deposits is possible by the lime pile technique. Treatment with lime pile caused migration of dissociated calcium and hydroxyl ions into the surrounding soil mass. In case of 25 mm lime pile, the experimental setup allowed measurement of migration of lime up to three times the lime pile diameter. In case of 75 mm lime pile, the experimental setup allowed measurement of migration of lime up to 1.6 times pile diameter. In both experiments, migration of lime was also uniform through out the soil depth of 280 mm. Migration of calcium and hydroxyl ions increased the pore salinity and pH of the treated soil mass. The increase in pH caused clustering of additional exchangeable calcium ions at the negative clay particle edges. The increased pore salinity and exchangeable calcium ions reduced the diffuse ion layer thickness that in turn suppressed the plasticity index and the swell potential of the compacted expansive soil. The laboratory results hence bring out that lime pile treatment in the field can substantially reduce the swell potential of the soil at least to a radial extent of 2 to 3 times the lime pile diameter. The 75 mm lime pile contained lime content in excess of the initial consumption of lime (ICL) value of the black cotton soil - namely 2.6 %. Laboratory results showed that migration of hydroxyl ions even from the 75 mm pile could not elevate the soil pH to levels required for soil-lime pozzoIonic reactions (pH ≥12). The very low solubility of lime in water (< 1 g/litre) and the impervious nature of the black cotton soil are considered to have impeded efficient interactions between lime and soil in course of treatment of the expansive soil with lime piles. Absence of soil-lime pozzolonic reactions precluded the formation of cementation compounds in the lime pile treated soil specimens. Cementation compounds formed by the soil-lime pozzolonic reactions are responsible for the much higher strengths of lime stabilized soils. Consequently, treatment with 25 mm pile had no impact on the unconfined compressive strength of the black cotton soil. Comparatively, treatment with 75 mm lime pile slightly increased the strength of the treated soil due to increased inter-particle attraction and particle flocculation. Chapter 5 compares the relative efficiency of the lime pile technique and lime-soil mixing method in altering the physico-chemical, index and engineering properties of expansive black cotton soil. Experimental results showed that mixing of soil and lime promote stronger chemical interactions between lime released hydroxyl ions and clay particles than that achieved by diffusion of lime from a central lime pile. The more alkaline pH of the lime mixed soil specimens rendered the clay particle edges more negative. Consequently, more calcium ions were adsorbed at the clay particle edges of the lime mixed soil specimens imparting them higher exchangeable calcium contents than the lime pile treated soil specimens. Also, at 3 % lime addition, the pH of the lime-mixed soil was sufficiently high (in excess of 12) to cause dissolution of silica and alumina from the clay lattice necessary for the formation of cementation compounds. The stronger lime modification reactions plus the lime-soil pozzolonic reactions (applicable for soil treated with lime content greater than ICL value) achieved by the lime mixing technique rendered the expansive soil much less plastic, much less expansive and much stronger than the lime pile treated specimens. The results of the laboratory study hence suggest that if a choice exists in the field between conventional method of spreading-mixing-compacting of soil-lime mixes and treating the ground with lime piles, the former technique should be adopted because of its greater efficacy in stabilizing the expansive soil. Chapter 6 summarizes the findings of the study.

Soil stabilisation is a useful civil engineering technique that enables the insitu material to be used as part of an engineered structure. Stabilised layers are used in road foundation; working platforms and for slope stabilisation and sea defences. Chemical stabilisation involves the use of a hydraulic binder (and sometimes additional pozzolans). Commonly, quicklime (CaO) or slaked-lime (Ca(OH)2) is used. On mixing into the ground, this reacts with the aluminosilicates of the clay fraction, reducing its overall water content and plasticity. Further additions increase the insitu pH. Above pH 10.4, the aluminosilicates become soluble in the pore solution. They are then able to form a range of insoluble mineral hydrates which constitute a cementitious matrix. This results in both an increase in mechanical strength and a decrease in dimensional stability. If the insitu material contains sulfur bearing mineralogies, these can react with the hydraulic binder and the aluminosilicates to form expansive minerals. If this occurs after the initial setting and hardening of the stabilised layer has occurred, it can lead to severe dimensional instability and mechanical weakening. This is termed sulfate heave and the principal agent of this heave is a hydrous calcium sulfoaluminate hydrate, ettringite (AFt). The fundamental processes of ettringite formation and associated expansion are little understood in stabilised soils. This research used a range of artificial sulfate bearing, lime stabilised blended soil samples subject to two immersion tests used for material suitability assessment in the UK. The physicochemical response (in terms of dimensional heave and mechanical weakening) was assessed as a function of soil composition and the environmental conditions imposed by the two immersion tests. The fundamental microstructure and phase composition was characterised using a range of analytical techniques (XRD, SEM-EDX, dTGA). The relationship between the observed macro-physical properties and underlying chemical environment and microstructure was explored. Key findings include that the mechanism of ettringite formation and expansion was found to be governed by the fundamental structure of the bulk clay. This explained the greater swell response of the kaolin based soils compared to those of the montmorillonite. The SEM-EDX analysis identified a primitive, Ca-rich, AFt phase termed ‘ball ettringite’, in stabilised soils. This has only relatively recently been reported in studies of cement mortars. Also, small amounts of sulfate in the bulk soil actually increase soil strength. It was suggested that the preferential formation of monosulfate (AFm) plays an important role in this mechanism. The introduction of water to the pore solution is key to the formation of ettringite. This was evidenced by X-Ray CT of the damage caused to soil specimens on immersion, as well as low angle XRD studies of the principal AFt peak. Based on the limited testing undertaken one of the immersion tests (European accelerated volumetic swell test, EN13286-49), appears to be more onerous than the other (UK CBR linear swell test, BS1924-2).

This research studied the effects of the addition of ground granulated blast furnace slag (ggbs), activated by 2% calcium hydroxide (Ca(OHh, on the strength, permeability and porosity development of a laboratory prepared clay mix (kaolinite with and without 6% gypsum) and a natural sulphide-bearing clay soil, Lower Oxford Clay. Based on shear, compressive and indirect tensile strength testing, it was found that an increase in the stabiliser slag/lime ratio results in substantial strength increase even after short curing periods (up to 12 weeks). This increase in strength is more pronounced if curing is at elevated temperatures (30 °C). The presence of sulphates (6% gypsum=2.73% SO3) resulted in an accelerated increase in the strength development for stabilised kaolinite, which was comparable to that of stabilised Lower Oxford Clay. In the absence of sulphates, large ggbs additions were only activated effectively at higher curing temperatures (20 and 30 °C) after curing periods of 24 weeks and beyond, although it is suggested that 2% lime creates a sufficiently alkaline environment for activation. The degree of slag activation and thus the subsequent cementation process was reflected by an increase in the percentage of the pore volume occupied by pores with a radius ::s;0.0Sμm, which is usually associated with the pore fraction characteristic of cementitious gels. The increase in slag addition, for kaolinite mixes, was accompanied by a reduction in total porosity. Specimens made from Lower Oxford Clay exhibited a significant increase in pore volume at higher slag additions. This is interpreted as being due to the creation of pore space resulting from restrained shrinkage of gels by inert particles during drying in this coarser, natural clay. No significant trend in the effect of curing temperature on the pore size distribution could be identified from the data. The development of permeability, however, showed some sensitivity to curing temperature. Results from specimens cured at 20 and 30 °C showed an accelerated reduction in their k-values in comparison to samples which had been cured at 10 °C. However, little correlation between measured permeability and exhibited pore size distribution could be established which is believed to be due to the strong influence of shrinkage during drying prior to mercury intrusion porosimetry in the dimensionally semi-stable soil system. The volume stability of stabilised specimens during frost action was assessed in a series of 12 freeze-thaw cycles, which were carried out in accordance to the German proposal for a European Pre-Standard. Generally an increase in the curing period prior to frost action and higher overall sample porosity resulted in relatively better performance during frost action. The influence of the slag/lime and slag/gypsum ratio on the swelling potential upon soaking was assessed in long-term soaking tests and the underlying causes were identified by findings from microstructural investigations including SEM and TG analysis. These results contributed to a better understanding of the slag activation process. In an alkaline environment slag hydration appears to be triggered earlier by sulphate, due to the more intensive disturbance of a thin protective layer of cementitious products on the slag grains. Disruption of this layer, for example by ettringite formation, exposes more unreacted slag grain surface, which will subsequently start to hydrate. Findings were complemented by two case studies, one which investigated the cause of substantial heave on a German highway on a microscale and the other which assessed the technical performance and the economic implications of a full-scale trial utilising the stabilisation technique with lime and ggbs for a temporary diversion. The overall findings from the projects indicate that soil stabilisation with lime and ggbs is, particularly for soils with significant sulphate/sulphide content, a feasible and environmentally friendly alternative to the classic soil stabilisation methods.

There are many studies about how the addition of lime and rice husk ash (RHA) gives the soil a better mechanical behavior, particularly on clayey soils, where usually fine particles reach more than 75%. However, the soils with a small presence of fine particles (59-60%) do not have much research. This analysis evaluates the influence that RHA has on this kind of soil stabilized with 3% of lime. After the initial mix of soil-lime, CBR increased 11.2 times its initial value; within the addition of the ash, the CBR averaged between 45-50% up until 28% of RHA was added, where the results decreased considerably. Soil workability improved and the specimens with more ash resulted in a more granular material, with a group index value 0 following the AASHTO standards. The greatest CBR record was obtained with the specimen of 16% RHA, 3% lime and soil, reaching a 51.3% CBR, 1.58g/cm3 of MDD and 16.5% of OMC. Yet, it only showed a 1.55% more resistance than the lime-soil specimen. The CBR with more presence of RHA tends to decrease its value, therefore for silica-rich clayey soils, the addition of lime by itself should be enough for an adequate performance.

Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understanding the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies. There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is Stabilization of expansive soils with various calcium–based stabilizers (lime and cement) directly or in combinations with other solid waste materials such as fly ash and ground granulated blast furnace slag (GGBS) etc. is common approach by many foundation engineers to improve the properties, and conquer the distress caused by undesirable swell–shrink in the soil. Several researches have also been dedicated to understand the complex ionic reactions and their products, and the mechanisms by which they affect the behaviour of expansive soils. Also, protocol for the lime stabilization of soil is established for the determination of optimum lime content (OLC) based essentially on the compressive strength test. The mechanism of lime treatment works mainly through cementation of flocculated matrix caused by the reduction in repulsion between soil particles with pozzolanic reaction compounds. However, no detailed studies have been carried out to establish the relation between change in fabric and its influence on the properties of expansive soil. It is also not clear whether the optimum lime content will be the same to improve different properties viz., strength and volume change. Hence, the research is directed to address these issues by performing elaborate experimental investigations on geotechnical properties and understanding the mechanism in improvement through fundamental physico–chemical and micro–analytical studies. There are several cases documented in literatures where recent heaving and premature failures of structures constructed on lime and cement–treated soils containing sulfates exhibits, leading to question the validity of calcium-based stabilization. The failures in sulfate bearing soils are attributed to the formation and growth of ettringite/thaumasite minerals in certain environmental regime. It is reported that this swell is either by crystal growth or, expansion by hydration of the new minerals formed. Research findings contradict the swell mechanism caused by ettringite and it is still a matter of active current research. Further, the mechanism related to strength behaviour of lime treated sulfate containing soil is not well understood. Among several factors influencing ettringite formation, sources and form of sulfate and availability of water play a key role to induce the expansion in lime treated soil which is often termed as “Sulfate Induced Heave” and soil as “Manmade Expansive Soil”. Gypsum is the main source of sulfate in the soil and soil containing gypsum is termed as gypseous soil. Gypsum is an unpredictable material due to its property of changing the chemical structure under certain temperature–pressure and situations where water exists, and hence gypseous soils are not preferred as construction material. Therefore, prior to investigation of sulfate induced heave in lime treated soil, the role of gypsum in the geotechnical behaviour of soil needs to be investigated to make clear the inconsistencies and contradictions in the research findings of different investigations. Hence, the study has been taken up to investigate the impact of varying gypsum content on behaviour of lime treated expansive soil after curing for different period. The mechanism of changes in strength and volume change behaviour of lime treated soil in the presence of gypsum has been elucidated through detailed micro–mechanistic analytical study. Several remedial measures are adopted to control the sulfate induced heave in lime treated soil. Fly ash is often used to suppress this undesirable heave. Utilization of fly ash supplies additional pozzolans (silica and aluminium) with collection of adequate divalent and trivalent cations (Ca2+, Al3+, Fe3+, etc.). However, the effect of additional aluminium supplied by the fly ash on ionic reactions, particularly with ettringite formation in lime treated gypseous soil is not well understood. It is interesting to know that gypsum is frequently used as an accelerating agent to improve properties of fly ash with lime. Hence, an attempt has been made to understand the role of fly ash on the properties of expansive soil treated with varying lime content and the same combination by using diminutive amount of gypsum with a view to find a solution to overcome the adverse effect of sulfate, particularly in the form of gypsum. Mechanism of the strength and volume change behaviour of soil treated with varying lime content in the presence of diminutive gypsum content are investigated and explained. Though, fly ash has been recommended to control the sulfate induced heave in lime treated soil, no particular attention is given to quantify the amount of fly ash to suppress the heave. Also, the effect of intrusion of additional ions (silica and alumina), which are known to affect mineralogy and microstructure, altering the particle size by fly ash to soil is not understood. Hence, work is extended to compare and explore the effect of varying fly ash content on the behaviour of soil, lime treated soil and lime treated gypseous soil and deduce the mechanism through physico–chemical and micro–analyses studies.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg 1998.<br>Various studies have been done to show that labour-based construction can meet the high standards normally required in the construction of roads. The organisational requirements that were needed to ensure the efficient use of labour have also been dealt with in various studies. Tile need for alleviation of poverty, unemployment and the negative social impact thereof by increasing the labour input in construction is understood by all concerned. A further step is however necessary before the idea of increasing the . labour component in any kind of roadwork can be taken seriously. Engineers need to move forward from the policy and organisational issues associated with labour intensive construction and start to provide designers with sound and innovative engineering solutions to overcome the hurdles experienced on the ground. The study looks at the process of foam bitumen stabilisation of soils and gravels with a view of utilising this innovative method for labour intensive construction. The material after having been stabilised can be placed in a stockpile. Actual durations that the material can safely remain in stockpile have been determined in this study to be in excess of six months for recycled asphalt and in excess of four months for the foam stabilised sand. Foam stabilised gravel was also studied and showed that after a year in stockpile the material failed probably due to a weakening of the bitumen and aggregate bond. Covering the stockpiled material did not show any significant difference to that of a similar uncovered stockpile. The position within the stockpile also did not have much effect on the engineering properties of the stoc piled material. The fact that the foam stabilised material can be worked on when cold and that it can be stockpiled for several months implies that the material is labour friendly and can be used in labour intensive construction of road base course layers or wearing course layers.<br>AC2017

A Mechanically Stabilized Earth (MSE) wall is a vertical grade separation that uses earth reinforcement extending laterally from the wall to take advantage of earth pressure to reduce the required design strength of the wall. MSE wall systems are often prefabricated to reduce construction time, thus improving constructability when compared with conventionally cast-in-place reinforced wall systems. However, there is a lack of knowledge for predicting the service-life of MSE retaining wall systems when recycled backfill materials such as Recycled Asphalt Pavement (RAP) and Crushed Concrete (CC) are used instead of Conventional Fill Material (CFM). The specific knowledge missing is how these recycled materials, when used as backfill in MSE wall systems, affects the corrosion rate of the reinforcing strips. This work addresses this knowledge gap by providing recommendations for MSE wall systems backfilled with CC or RAP, and provides a guide to predict the service-life based on corrosion rate test data obtained from embedding steel and galvanized-steel earth reinforcing strips embedded in MSE wall systems backfilled with CC, RAP, and CFM. Experimental data from samples emulating MSE wall systems with steel and galvanized-steel reinforcing strips embedded in CC and RAP were compared to samples with strips embedded in CFM. The results of the testing provide data and methodologies that may, depending on the environmental exposure conditions, justify the use of RAP and CC for the construction of MSE walls. If these backfill materials are obtained from the construction site, this could provide a significant cost savings during construction.