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Many pavement subgrades in Virginia consist of wet, highly plastic clay or other troublesome soils. Such soils can be treated with traditional lime and cement stabilization methods. Alternatives, including lignosulfonates and polymers, are available, but their performance record is mixed and solid engineering data is lacking, which prevents reliable design. The goal of this research was to screen a suite of traditional and non-traditional stabilizers against three Virginia soils that have caused problems during construction or resulted in poor performance in service. The selected stabilizers were: quicklime, hydrated lime, pelletized lime, cement, lignosulfonate, synthetic polymer, magnesium chloride, and a proprietary cementitious stabilizer. A laboratory procedure was developed and applied to three Virginia soils obtained from Northern Virginia, Staunton, and Lynchburg. Key findings from the research include that (1) traditional lime and cement stabilizers were far more effective than liquid stabilizers (lignosulfonate, synthetic polymer, and magnesium chloride) in increasing strength, (2) the liquid stabilizers were ineffective on soils with high moisture content, (3) the proprietary cementitious stabilizer was more effective in increasing strength than lime for all cases tested, but not was not as effective as the cement stabilizer, (4) quicklime and hydrated lime increased workability of the soils although they did not produce strengths comparable to cement, (5) the strength of soils stabilized with cement and the proprietary cementitious stabilizer can be estimated based on the water-amendment ratio of the mixture, and (6) the strength of soils stabilized with lime can be estimated based on a combination of plasticity index and water-amendment ratio of the mixture. / Master of Science

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Reinforced concrete is susceptible to cracking. This makes it less durable than it would be had it been crack-free. Ingress of harmful substances into reinforced concrete through cracks – which causes corrosion of steel – is not desirable. This can be mitigated by the use of fibre reinforced-concretes or mortars showing strain hardening properties accompanied by improved ductility and multiple cracking under tensile loading. Such materials are called Strainhardening cementitious composites (SHCC’s). At Stellenbosch University, work has been done in previous years on SHCC to determine its behaviour under various loading conditions. Some of the aspects of the material that have been studied are the behaviour under uni-axial tensile loading, uni-axial compression and shear. The behaviour of SHCC under biaxial stresses was investigated to enable the prediction of the material behaviour under complex stress conditions. Square plate specimens of nominal dimensions 100 x 100 x 20 mm were cast and subjected to biaxial compressive loading at stress path angles of 00, 150, 300 and 450; which were equivalent to vertical/horizontal stress ratios of 0/1, 0.27/1, 0.58/1 and 1/1 respectively, at ages 23 to 33 days. Comparisons were made between specimens tested using steel platens and those tested using Vesconite sheets. Those tested using Vesconite yielded lower failure stresses. Vesconite was used to reduce the retraining effect of the frictional force between the specimens and the steel platens. Poisson’s ratios were calculated for specimens tested using steel and those tested using Vesconite. The values for Vesconite were found to be higher than for steel. Additionally, the values for the uni-axial case were different from those obtained for other stress ratios. This could have been due to the assumption made that plane stress was realised and that Elastic moduli in tension and in compression was the same. The possibility of the existence of a triaxial stress state could render the calculated Poisson’s ratios incorrect. Shear slip type failure accompanied by wedging was observed. Vertical to near diagonal cracks were evident on the front faces of the specimens for the stress path angles of 00 to 450 respectively. The observed crack patterns showed closely spaced multiple micro-cracking on the narrow edges of specimens indicating Strain-hardening behaviour. The stress-strain curves also showed a slight indication of strain-hardening where tensile strains were measured. / AFRIKAANSE OPSOMMING: Gewapende beton is vatbaar vir krake. Dit maak dit minder duursaam as wanneer dit kraak-vry is. Instroming van skadelike stowwe in gewapende beton deur middel van krake - wat korrosie van staal veroorsaak - is nie wenslik nie. Dit kan verbeter word deur die gebruik van veselversterkte beton of mortel wat vervormingsverharding eienskappe toon, vergesel deur verbeterde rekbaarheid en veelvuldige krake onder trekspanning. Sulke materiaal word Strainhardening cementitious composites (SHCC's) genoem. Die Universiteit Stellenbosch, het in vorige jare werk gedoen om SHCC se gedrag te bepaal onder verskillende belastingstoestande. Sommige van die aspekte van die materiaal wat bestudeer is, is gedrag onder uni-aksiale trek, uni-aksiale druk en skuif. Die gedrag van SHCC onder biaksiale spannings is ondersoek om voorspelling van materiaalgedrag onder komplekse spanningstoestande moontlik te maak. Vierkantige plaat monsters van nominale dimensies 100 x 100 x 20 mm is gemaak en aan biaksiale drukkragte onderwerp, met spannningspad hoeke van 00, 150, 300 en 450; wat soortgelyk is aan die horisontale spanning verhoudings van 0/1, 0.27/1, 0.58/1 en 1/1 onderskeidelik, op ouderdomme 23-33 dae. Vergelykings is getref tussen monsters getoets met staal plate en diegene getoets word met Vesconite plate. Die proefstukke getoets met Vesconite het laer falingsspannings opgelewer. Vesconite is gebruik om die uitwerking van die wrywingskrag tussen die monsters en die staal plate te verminder. Poisson se verhouding is bereken vir die staal en Vesconite monsters afsonderlik. Daar is gevind dat die Vesconite waarde hoër was as die vir staal. Daarbenewens het die waardes vir die uni-aksiale geval, verskil van dié vir ander spanningsverhoudings. Dit kan wees as gevolg van die aanname van vlakspanning en dat die Elastiese moduli in druk en in trek dieselfde is. Die moontlikheid van die bestaan van 'n drie-dimensionele spanningstoestand, kan beteken dat die berekende Poisson’s verhoudings onakkuraat is. Skuif-glip tipe faling, vergesel deur vaswigting is waargeneem. Vertikale tot feitlik diagonale krake is duidelik sigbaar op die voorkant van die monsters vir spanningspadhoeke van 0-450 onderskeidelik. Die waargeneemde kraak patrone het nou gespasieerde, veelvuldige mikro-krake op die smal randte van die monsters, wat dui op vervormingsverharding. Die spanningsvervormings kurwes het ook effense aanduidings getoon van die vervormingsverharding waar trekvervorming gemeet is.

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The most prevalent method for the prevention of freeze-thaw and salt scaling damage in cement based materials is through the entrainment of air voids using air entraining chemical admixtures (AEA's). However, the common field methods for measuring air content in fresh concrete cannot distinguish between entrained and entrapped air voids, and the actual air content in the hardened concrete can vary from that determined by these tests due to a variety of factors such as workability, placing operations, consolidation efforts, and environmental conditions. Previous research has shown the ability of ultrasonic attenuation to distinguish between entrained and entrapped air voids in hardened cement paste, providing a foundation for an inversion procedure to calculate the size and volume content of the two scatterer sizes. While additional challenges are present with measurements in fresh paste, the use of an immersion setup can overcome the limitations of cement paste containment vessels and provide a means to measure air content from batching to placement. An immersion apparatus to monitor ultrasonic wave attributes including attenuation in fresh cement paste is designed and built. Results comparing air entrained and non-air entrained cement pastes are presented. Ultrasonic wave attributes are studied as a function of time and level of chemical air entrainer. Finally, recommendations are made to improve the accuracy of the immersion apparatus in order to develop an in situ, quality control procedure to quantify the air content of fresh cement paste from batching to placement.

The objective of this research is the pursuit of a better characterization method for the air voids - particularly air-entrained voids - in fresh cement-based materials through the use of ultrasonics. The use of air-entraining agents (AEA's) to incorporate a stable network of air voids into fresh cement paste is common practice in the concrete industry. These particular air voids significantly improve durability of hardened cement paste through mitigation of stresses associated with freezing and thawing cycles. It is understood that the performance of entrained air voids in cement paste is dependent on their size and distribution, or spacing factor. However, conventional methods for qualifying air content, such as the Pressure, Volume, and Gravimetric Methods, only measure total air volume and cannot assess size or spacing. In this investigation, using matched pairs of transducers, ultrasonic pulses were transmitted through fresh cement paste specimens (0.0\% up to 0.6\% AEA by weight of cement). The received signals were recorded every five minutes during the first six hours and then every fifteen minutes thereafter. Analysis shows strong distinctions between specimens with and those without the AEA. Further research is needed into the distinctions among specimens with the AEA. However, the data suggest correlations between Vicat setting times, heat of hydration, and autogenous strain and ultrasonic metrics such as pulse velocity and peak frequency of the signal. The findings of this research should be most appropriate as a foundation for an inversion process and improved air-entrainment detection methods.

Dissertation submitted in partial fulfilment of the requirements for the degree MTech Degree in Civil Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology / Self-compacting concrete is very sensitive to variation in cement properties and to the interaction between cement paste and additives such as superplasticisers. The assessment of these interactions can be done rheologically but there is as yet no consensus on how to evaluate the rheological properties (yield stress and viscosity) of cementitious materials. In addition, there is no clear understanding of the dependency of these rheological properties on early hydration, evaluations which are recommended to be done at paste scale. The evolution of rheological parameters in the early stage of hydration, of four CEM I 52.5N cements manufactured at different factories in South Africa, and their interaction with two different commercial superplasticisers (SPs) were investigated using three different rheometric techniques: conventional flow curve from hysteresis loops, amplitude sweep in oscillation mode and construction of flow curve. Amplitude sweep, time sweep, viscosity-time sweep as well as thixotropy tests were conducted to investigate the effect of hydration and the rate of rebuilding of each cement in the presence and absence of SP. The experiments were done on a MCR51 rheometer with roughened parallel plates under controlled temperatures and relative humidity. / PPC Cement

The present study deals with the physical characterization of macrodefect free cements produced by ICI. These materials are made through a specialized mixing technique which incorporates an organic polymer into the cement/water system. The high mechanical strength and low porosity of this class of hardened cement paste had been well documented, however, a detailed characterization of the physical nature of the microstructure had not previously been attempted. Two classes of macrodefect free material were studied, based on Ordinary Portland cement and High Alumina cement, respectively. The porosities of these two materials were determined in their original state and after various forms of heat treatment and conditioning. Samples based on Ordinary Portland cement had a well defined narrow pore size distribution, even after heat treatment, while the High Alumina cement samples displayed a very low total pore volume in their original state, but subsequent heat treatment led to the developement of porosity over a wide range of pore sizes. These fundamental differences in the pore size distributions had significant effects on the homogeneity and reproducibility of the microstructures of the samples. The porosity generated by heat treatment was found to be unstable in the presence of water. In general, reductions in the porosities and permeabilities were observed. This was due to the formation of fresh cement hydrate gel within the pore structure, which caused a shift in the pore size distributions towards smaller pores.

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