Concrete used in pavements has to be durable to withstand the load and wear imposed by vehicles moving across it and the effects of drying shrinkage and thermal changes. Failure of the pavement by either excessive cracking or degradation of the surface results in poor riding quality and low skid resistance. The inclusion of Pulverised Fuel Ash (PFA), otherwise known as fly ash, generally improves the quality of pavement concrete and thus extends its useful life. The PFA used for the thesis was from the Lethabo power station's second electrostatic precipitator field (Lethabo Field 2 PFA). This Field 2 PFA has a very close resemblance to the expected classified commercial Lethabo PFA of the future. PFA is characterised by its fineness. The Field 2 PFA had 7.7 percent retained on the 45 micron sieve. This was considerably finer than the current commercial Matla PFA with about 12 percent retained. It was thus expected that the higher quality Lethabo Field 2 PFA could be used to produce higher quality concrete. The other mix materials were those commonly used in the Western Cape. The aggregates used were Cape Flats Dune sand and Malmesbury shale (hornfels). The dune sand typically has very little fines content, causing severe bleeding problems in normal concrete mixes. The crushed coarse aggregate was 13 mm and flaky in shape. Ordinary Portland cement (OPC) was obtained from the De Hoek cement factory. The investigation was carried out in two parts. First was the development of a wide range of mixes, varying 28 day design strength (10, 20, 30, 40, 50 MPa), percentage of PFA as part cement replacement (OPC only, 15% PFA, 30% PFA, 50% PFA and 70% PFA) and the coarse aggregate content to give under-, average- and over-sanded mixes. Over this wide range of mixes, the fresh properties and development of the compressive strength were observed. Secondly, properties affecting pavement quality concrete were observed on a similar range of mixes. These properties were flexural strength, surface wear resistance by wire brush, sand blasting and ball race abrasion and the drying shrinkage.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

It is generally very difficult to produce high-performance concrete having concurrently high strength, high durability, high workability and high dimensional stability. This is because low water content is required to achieve high strength and high durability, high water content and large paste volume are required to achieve high workability, and low cement content and small cement paste volume are required to achieve high dimensional stability. One way of overcoming such conflicts is to add fillers to increase the packing density of concrete so that the amounts of water and paste needed to fill voids could be reduced. In this study, the use of fillers to improve the packing density and performance of concrete is investigated by measuring the packing density and overall performance of cement paste and concrete mix samples with different types and amounts of fillers added. The packing density results revealed that finer fillers are more effective in improving the packing density for releasing more excess water (water in excess of that needed to fill voids) to lubricate the solid particles. Moreover, triple blending of two fillers of different fineness with cement can better increase the packing density than double blending of just one filler with cement. On the other hand, the workability, strength and dimensional stability results showed that the addition of condensed silica fume, fly ash microsphere or superfine cement could improve the overall workability-strength performance of cement paste through increasing the packing density of the cementitious materials, while the addition of condensed silica fume, fly ash or limestone fine coeuld improve the overall dimensional stability-strength performance of concrete through decreasing the cement content or cement paste volume. Hence, the incorporation of fillers to improve the packing density opens up the possibility of using ultra-low W/CM ratio and ultralow paste volume to produce an ultrahigh-performance concrete. However, despite increases in packing density and excess water, the addition of fillers does not always improve the workability. Generally, the addition of fillers would more significantly increase the workability at low W/CM ratio and less significantly increase or even decrease the workability at high W/CM ratio. In-depth analysis indicated that both the excess water and solid surface area have great effects on the rheology. In this regard, a parameter called water film thickness (WFT), which is defined as the average thickness of water films coating the solid particles and may be determined as the excess water to solid surface area ratio, is proven to be the key factor governing the rheology. Therefore, it should be the WFT rather than the packing density that should be maximized in the mix design of high-performance concrete. The addition of fillers would increase both the excess water and solid surface area. If the proportional increase in excess water is larger than the proportional increase in solid surface area, the WFT would increase, but if otherwise, the WFT would decrease. To increase the WFT, a filler that can significantly increase the packing density without excessively increasing the solid surface area is the best choice. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

This thesis investigates the use of nanotechnology in an extensive literature search in the field of cement and concrete. A summary is presented. The research was divided into two categories: (1) nanoparticles and (2) nanofibers and nanotubes. The successes and challenges of each category is documented in this thesis. The data from the literature search is taken and analyzed using statistical prediction by the use of the Monte Carlo and Bayesian methods. It shows how statistical prediction can be used to analyze patterns and trends and also discover optimal additive dosages for concrete mixes. / by Jonathan Glenn. / Thesis (M.S.C.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

M. Tech. Chemical Engineering / Cement based materials are of enormous technological importance and their satisfaction depends on being able to transport and mould them in the freshly mixed state. The problem of the degradation or concrete is of interests to modern society, not only in terms of money, but in terms of discomfort and safety. Global research show concrete consumption around the world to be second only to water. The situation clearly indicates the significance and the huge role concrete has in the construction industry and in the global economy. This work was to investigate the various methods of increasing the life span of concrete without compromising its properties. The techniques for improving the physical properties of concrete and the effect of bacterial biofilm were studied especially for sanitary floors of food processing industries. The aim of this study is to improve the physical, mechanical and microbial properties of concrete floors in food processing industries by extending the life span of concrete materials.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 113-114). / xi, 132 leaves, bound ill. 29 cm

This thesis is the study of the effects of several commercial admixtures on the properties of concrete in the plastic and the hardened state. The project is divided into two parts. Part I deals with the laboratory investigation and Part II takes into account the theoretical study of Part I. Three standard concrete mixtures at different water-cement ratios and approximately at constant slump were designed without the addition of admixtures to serve as a parameter for the test mixtures. Eighteen different test mixtures were made with local aggregates. Three test mixtures for each individual admixture and combination admixtures were used for comparison purposes. From the results obtained in the laboratory study, it was found that all the admixture used, separately and in combination, the test mixtures with an air entraining agent produced the greatest improvement in the plastic state as compared with their standard. In the hardened state, the cement dispersing agent (normal set) and the accelerator produced the greatest increase in the compressive strengths at all ages of testing as compared with their standard. It is further revealed that the accelerator imparted the greatest influence when used in rich mixture. In the theoretical study, by making alterations in the water-cement ratio so as to obtain a desired slump of four inches, the theoretical test mixtures so designed predicted a further increase in the compressive strengths, except in the case of the accelerator. It is noteworthy that the accelerator produced the same magnitude of compressive strength as was produced by the cement dispersing agent (normal set) at 28 days in the rich mixture, but in the case of the poor mixture, the latter was more effective. / Master of Science

Environmental factors and physical properties of latex modified concrete (LMC) are hypothesized to contribute to early age cracking in bridge deck overlays. Cracking permits the ingress of moisture and aggressive solutions into the substrate and may contribute to other subsequent distresses. Understanding the material properties and mechanisms involved is necessary to minimize these distresses. This research consisted of a two part study: first, the development of LMC strength and fracture properties at ages ranging from 5 hours to 28 days was studied, and secondly, the effects of the environment on LMC distresses were modelled. Environmental conditions: temperature, solar energy, and wind speed were determined from weather records. A fracture mechanics based model, the Fictitious Crack Model (FCM), incorporating finite element analyses and superposition techniques was employed with material properties from the first part of study on LMC performance. Different bilinear strain softening diagrams were used to predict fracture performance at different ages. The predictions agreed well with the test data. The impacts of temperature differentials on crack development were studied. The shrinkage effect was also indirectly incorporated through the temperature analysis. The material properties study indicated significant changes in strength, deformability and fracture properties, particularly during the early age. The developments differ slightly from conventional concrete. Test results indicated a significant improvement in reducing and bridging microcracks, especially in the prepeak-load region. Fracture toughness and deformability increased significantly with time. Fracture energy varied from 2.3 to 133.1 N/m, depending on age, and to some degree, on notch depth ratio. In the second stage, the FCM provided a reasonable prediction for crack initiation and propagation when only temperature effects are of concern. Age, surface conditions and structural restraint strongly affect crack resistance of the overlays. Only slight effects were observed from the overlay thickness in the study range (51-76 mm). Shallow preexisting cracks possibly reduce the crack resistance of the overlay about 30 percent. A prolonged moist cure for 48 hours after placing is suggested to reduce the risk of cracking. With available environmental information, it is possible to develop guidelines for appropriate environmental conditions for LMC bridge deck construction to minimize the risk of early age cracking. / Graduation date: 1997

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