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The purpose of this research was to determine the accuracy of two test methods used in measuring the water to cement ratio (w/c) of fresh and hardened concrete. The microwave oven test based on a current ASTM Draft was used in determining the w/c of fresh concrete while the modified Norwegian PF-method was used to determine the w/c of hardened concrete. The microwave oven evaporates the water of a 1500 gram sample of fresh concrete to determine a w/c and can accurately measure the w/c within 0.05 of the true value. The modified PF-method uses an absorption method similar to ASTM C97 and Powers’ hydrations models to determine the w/c of hardened concrete. 100mm diameter concrete cores were prepared from slabs and 50mm thick concrete cylinders were tested. The results from this hardened concrete test had a large degree of variability; however, it was a useful indicator of concrete segregation.

The intention of this study is not to present the technique as a new one in the realm of sculpture, but rather to investigate the various ways in which cement is being employed in the sculptural form and to point out its prominent use as well as the reasons for its popularity in Mexico.

Knowledge of energy requirements, solid solutions and phase compatibilities of high temperature cement phases is essential to the economics and performance of cement clinkers. Both chemical engineering and chemical approaches have been used to determine phase compatibilities and solid solutions of calcium sulfoaluminate, C4A3 S, C3S and C2S as well as to develop a new type of cement based on calcium monosulfoaluminate, C4A3S, tricalcium silicate, C3S, and dicalcium silicate, C2S. Investigation of solid solutions, substitution mechanisms and phase compatibilities of C4A3S, C3S and C2S form the basis of this thesis, and the subject is addressed as follows: (i) Investigation of the structures, solid solutions, phase compatibilities, polymorphism and stabilisation of C4A3S (literature review, theoretical and experimental research). This research discloses the existence of a high temperature polymorph (a) of C4A3S. It can be stabilised to ambient temperature by Fe or Na-Si coupled substitution. Limits of Na, Fe, Si and P solubilities in the C4A3S structure were investigated. When limits of Na2O or NaF in C4A3S solid solutions (~3%) is exceeded, C4A3S becomes unstable as a result of Na2SO4 or Na2Ca(SO4)2 formation. C4A3S is compatible with C2S, with CaO, with C3A, with C12A7, with CA, with CA2, with Al2O3, with C2AS and with Ca3(PO4)2 at 1300 C. (ii) Investigation of the microstructure and microchemistry of commercial calcium sulfoaluminate cement (literature review, theoretical and experimental research). Because of extensive A1 and S substitution, a large Si deficiency can occur in C2S solid solutions. The open structured texture of calcium sulfoaluminate cement explains why it is easily ground. (iii) Investigation of A1 and sulfur substitution into C2S solid solutions (literature review, theoretical and experimental research). A1 and S substitute into C2S by several mechanisms, the most important of which are 2A1+S for 3Si and Ca+S for 2Ca+Si. (iv) Investigation of the NaF-CaO-SiO2 phase equilibria and its resultant effect on C3S formation (literature review, theoretical and experimental research). This investigation revealed that NaF not only acts as flux but mainly it has a mineralising effect on C3S formation and results in extensive solid solutions, NaxCa3.xSiO5.xFx. C3Sss, can be obtained as low as ~1000 C in the presence of NaF. In the course of this study, I phase, structurally similar to that of 9 C3S but consisting of 15 and 24 layer variants, has been characterised. (v) Investigation of the NaF-CaO-Al2O3-SiO2-SO3 system and its resultant effect on both C3S and C4A3S formation. Cement based on C3Sss and C4A3S can be made at ~1300 C if F and SO3 concentrations in the raw materials are controlled. SO3 in excess relative to that required for the formation of C4A3S should be added to inhibit C11A7.CaF2 and C3A formation. In the course of this study, large amount of Si deficiency in the C2S structure, such as that of belite in commercial calcium sulfoaluminate cement (as a result of 2A1+S for 3Si substitution), has been found.

Ordinary Portland Cement (OPC) is a material of complex chemical and phase composition. Therefore its sorption characteristics were determined by examining the properties of its individual phases, as well as bulk OPC. The principal constituents of OPC along with its hydration products were tested for their potential to sorb Cs using radiocaesium tracer studies. Results showed that OPC had no significant sorption potential for Cs. It was therefore suggested that the cement composition required to be tailored by including materials which were likely to sorb Cs and moreover, improve the physical properties of the cement matrix. Two categories of materials were chosen for study:- (i) those which are normally permitted in civil engineering practice, including amorphous silica, pulverised fuel ashes (PFA) , natural pozzolari and blast furnace slag (BFS); (ii) those which were known or suspected to be good Cs sorbers but whose stability in cement were as yet unknown. These included hydrous titanium dioxide, calcined kaolin, acid zirconium phosphate, tobermorite and xonotlite. Amorphous silica, several PFA's, natural pozzolan and BFS were all examined for their sorption potential. All the materials showed, to a greater or lesser degree, a potential for immobilising Cs. The amorphous silica showed the greatest uptake of Cs and was chosen for further study. The sorption of Cs by amorphous silica was determined over a- wide range of Cs concentrations. daData were treated by the Freundlich isotherm and indicated that different sorptive mechanisms may be operating at different concentration aranges. The effect of water: solid ratio and initial pH were examined. Results showed that pH had 2 opposite effects on the silica:- (a) the high pH (-12.5) increases its sorption efficiency for Cs, compared to neutral conditions, presumably due to an enhanced negative charge on the silica surface; (b) the presence of Ca(0H)2, which was used to adjust the pH arid would be present in hydrated OPC, decreases the available silica content due to pozzolanic reactions consuming silica to form Calcium Silicate Hydrate gels (C-S-H). Hence if a silica containing material was added to cement and was the only sorbing material present, it might have to be proportioned carefully to maintain a permanent excess of silica. Leach tests were carried out on mixes of cement with amorphous silica, PFA and BFS. All gave significant improvements in leach characteristics compared to OPC alone. The effects-of curing, conditions were studied. Results showed that increasing the curing time from 28 days to 84- days or 168 days or increasing the curing temperature from 20 G to 4-0 C or both improved the leach resistance. Mercury intrusion porosimetry gave little indication that this was totally due to physical encapsulation and studies of the pore fluids on the samples showed beyond doubt that a strong chemical mechanism was involved. It was hypothesised that C-S-H with a high silica content was responsible for the chemical retention of Cs. In OPC the C-S-H has a C/S ratio of -1.7 but when amorphous silica or PFA is added this ratio is reduced and can be as low as 0.8. BFS hydrates independently from OPC but it also produces a C-S-H with a low C/S value. This hypothesis was confirmed by studies on synthetic C-S-H with a range of C/S ratios and by analysing OPC/PFA and OPC/silica pastes in the analytical electron microscope. Sorption experiments were also carried out on the second category of materials. All showed good sorption potential for Cs in neutral solutions. Sorption remained significant in the presence of Na and K as competitive species. However, the effect of Ca (OH)2, differed. Tobermorite and Xonotlite appeared to show the most significant sorption of Cs in the presence of Ca(OH,)2 while the others either reacted with Ca(OH)z or discharged Cs - presumably by exchange for Ca. Tobermorite and Xonotlite were further studied. Desorption experiments and the effect of varying the Cs concentration as well as pH effects were investigated. Both materials gave straight line plots on a Freundlich isotherm indicating that one sorptive mechanism operated over a wide concentration range. Sorption increased with pH but unfortunately desorption studies showed that the Cs was easily removed. Leach studies were carried out on composites with OPC containing 5-10% tobermorite. Such additions decreased the leach rate of Cs compared to OPC.

Video summarizing Ph.D. dissertation for a non-specialist audience. / National Science Foundatio (Grant No. 0846861) / Civil and Environmental Engineering / College of Engineering

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