Pure, MgO doped and B2C3 doped monocalcium, dicalcium, and tricalcium silicates were prepared with different glass contents. Characterization of the anhydrous materials was carried out using optical microscopy, infrared absorption spectroscopy, and X-ray powder diffraction. The hydration of these compounds was studied as a function of the glass contents. The hydration studies were conducted at 25°C. Water/solid ratios of 0.5, 1, 10, and 16 were used for the various experiments. The hydration behavior was monitored through calorimetry, conductometry, pH measurements, morphological developments by scanning electron microscopy, phase development by X-ray powder diffraction, and percent combined water by thermogravimetry. A highly sensitive ten cell pseudo-adiabatic microcalorimeter was designed and constructed for early hydration studies. Conductometry was found to be of great utility in monitoring the hydration of monocalcium silicate and the borate doped dicalcium silicates.

The search for a new environmentally friendly construction material that will match the durability of ancient concrete has stimulated interest in geopolymerisation in recent times. Despite extensive research that has been conducted on various aspects of geopolymerisation, especially in enhancing the properties of resultant binders and understanding the chemical mechanisms involved, a number of questions remain to be answered. The role of calcium in geopolymerisation is one of them. It is known that the presence of a moderate amount of calcium in a geopolymeric binder will improve the resultant compressive strength. However, it is still unclear whether calcium will play a charge-balancing role within the aluminosilicate structure (to maintain electro-neutrality in a similar way as alkali metal cations, Na+ or K+, or perhaps an alternative role). In addition, the role of calcium in geopolymerisation is of great interest because it is proposed for the first time that calcium links geopolymer chemistry to, and distinguishes it from, ordinary Portland cement (OPC). (For complete abstract open document)

Thesis (Ph.D.)--Michigan State University. Dept. of Civil & Environmental Engineering, 2008. / Title from PDF t.p. (viewed on Apr. 2, 2009) Includes bibliographical references (p. 217-225). Also issued in print.

Thesis (Ph.D.)--Victoria University of Wellington, 2007. / Includes bibliographical references.

Thesis (M.Sc.)--Victoria University of Wellington, 2009. / Includes bibliographical references.

Homogeneous single C-S-H gels have been prepared for the investigation of alkali binding potential and crystallisation. A distribution coefficient, R_d, was introduced to express the partition of alkali between solid and aqueous phases at 25°C. R_d is independent of alkali hydroxide concentration and depends only on Ca:Si ratio over wide ranges of alkali concentration. The trend of numerical values of R_d indicates that alkali bonding into the solid improves as its Ca:Si ratio decreases. Reversibility is demonstrated, indicating a possibility of constant R_d value of the material. Al has been introduced to form C-A-S-H gels and their alkali sorption properties also determined. Al substituted into C-S-H markedly increases R_d, indicating enhancement of alkali binding. However, the dependence of R_d on alkali concentration is non-ideal with composition. A two-site model for bonding is presented. Crystallisation both under saturated steam and 1 bar vapour pressure has been investigated. It has been shown that heat treatment by saturated steam causes crystallisation of gels. The principal minerals obtained were (i) C-S-H gel and Ca(OH)₂ at ~55°C, (ii) 1.1 nm tobermorite, jennite and afwillite at 85-130°C, and (iii) xonotlite, foshagite and hillebrandite at 150-180°C. Properties of crystalline C-S-H were also reported for reversible phase transformation, pH conditioning ability, seeding effect and solubility. At 1 bar pressure, crystallisation is slower than in saturated steam due to lower water activity. Tobermorite-like nanodomains develop during reaction at low Ca/Si ratios. In some Ca-rich compositions, Ca(OH)₂ is exsolved and occurs as nano-sized crystallites.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 144-152).

Groundnuts (Arachis hypogaea L.) are an important subsistence and cash crop for smallholder farmers in Southern Africa. They require well drained light textured soils. However, most light textured soils are acidic and inherently infertile, and therefore require supplementary nutrients and amelioration with lime. In addition to application of a basal fertilizer, groundnut production also requires Ca. This increases the inputs required to produce the crop, particularly for smallholder farmers. The study examined two options for smallholder farmers, outside the classical lime application, for ameliorating soil acidity, i.e., evaluating the response of different groundnut genotypes for tolerance to soil acidity and low-cost liming alternatives. Initially ten groundnuts genotypes were screened for tolerance to soil acidity. Following this, three genotypes classified as tolerant and susceptible were used to evaluate the effect of high acid saturation on germination, emergence and seedling establishment. Thereafter, selected cultivars were used to compare calcium silicate, as an alternative to dolomitic lime, for ameliorating soil acidity and supplying calcium to developing pods. All three studies were conducted under controlled conditions: 25 ± 5°C and 20 ± 3°C day/night temperatures, 65% RH. Results measured as plant height, leaf area, yield, concentration and uptake of selected macro-and micro-nutrients showed that different groundnut genotypes differed in their response to soil acidity. Genotypes like Billy, Selmani, Rambo and JL 24 had low Al uptake and high Ca and P uptake and were classified as tolerant to acidity. In addition, these genotypes also had a higher leaf area and high number of nodules compared with Anel, Harts, Sellie, RG 784 and Robbie. With the exception of JL 24 all other tolerant genotypes (Billy, Selmani and Rambo) were large seeded. In the early establishment stage especially, root development was susceptible to soil acidity, but Rambo appeared to perform better than Jasper and Harts. Calcium silicate reduced soil acid saturation and provided enough calcium for pod development, suggesting that it may be used as an additional source of calcium. Soil acidity increased grain protein concentration and reduced its oil content, however, amelioration with either lime source reversed this trend. Thus, growing groundnuts in acid soils has implications for the commercial value of the product in terms of oil or protein supply. Overall, the study suggests that a combination of application of a cheap liming source like calcium silicate and growing tolerant cultivars, like Rambo, Billy and JL 24 might provide a window of opportunity for smallholder farmers to produce groundnuts possibly with only a fraction of the costs associated with ameliorating soil acidity. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

A la suite d’une lésion carieuse ou traumatique du complexe pulpo-dentinaire, une inflammation locale est initiée. Cette inflammation peut être délétère car la pulpe dentaire est localisée au sein de parois dentinaires rigides, elle doit donc être résolue pour initier la régénération.Lors de lésions juxta-pulpaires, le praticien réalise un coiffage pulpaire direct afin de conserver la vitalité de la dent. Un biomatériau est placé au contact des tissus pulpaires afin de maintenir l’intégrité de la pulpe, en promouvant les processus de guérison tout en la protégeant du milieu buccal hostile.Les silicates de calcium sont aujourd’hui les matériaux de choix pour ces actes thérapeutiques. Des modifications de leur formulation visant à réduire leur temps de prise ont conduit au développement de silicates tricalciques photo-polymérisables. Cependant, la présence importante de résines dont la toxicité pulpaire est connue, soulève des questions. Cette thèse a pour objectif d’évaluer l’effet de différents biomatériaux de coiffage pulpaire sur l’inflammation et la régénération, au niveau cellulaire et tissulaire et d'étudier les conséquences de l'ajout de résines. Nos résultats démontrent que les matériaux de coiffage pulpaire affectent les étapes précoces de l'inflammation et de la régénération pulpaire. Alors que les silicates tricalciques modifient l'équilibre vers le processus de régénération, les biomatériaux contenant de la résine déplacent cet équilibre vers une réaction inflammatoire. Ce travail met en évidence l'importance capitale du choix du biomatériau de coiffage et restreint l'utilisation de biomatériaux contenant de la résine pour le coiffage pulpaire indirect. / Deep carious or physical lesions may lead to dental pulp injuries. Subsequently, both infiltrating bacteria and injured tissues initiate an inflammatory reaction. This may be detrimental to the healing process within the pulp inextensible environment.Clinically, during juxta-pulpal lesions, the practitioner performs a direct pulp capping in order to preserve the tooth vitality. A biomaterial is placed directly in contact with the pulp tissues to maintain pulp integrity, promoting the healing processes and protecting it from the hostile oral environment. Tricalcium silicates are now considered as the biomaterials of choice for vital pulp therapy. Modifications of this type of biomaterials aiming at reducing their setting time led to the development of light-cured tricalcium silicates. However, the presence of a high percentage of resins in this material raises questions about its possible effects on the pulp inflammatory reaction due to its reported toxicity. This aim of this thesis was to determine the influence of tricalcium silicate-based capping biomaterials on the initial steps of pulp inflammation and healing and to investigate the consequences of adding resins.Our results demonstrate that pulp capping biomaterials affect the early steps of pulp inflammation and healing. While tricalcium silicates shift the balance towards the healing process, resin-containing biomaterials drive this balance towards an inflammatory reaction. Overall, this work highlights the fact that the choice of pulp capping biomaterial is of prime importance in direct pulp capping procedures and does not support using resin containing biomaterials for direct pulp capping.

Made available in DSpace on 2014-10-09T12:51:48Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:58Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP