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The hydration of calcium silicate phases (i.e. C3S and b-C2S) in Portland cement results in the formation of calcium silicate hydrate (C-S-H) ? a major contributor to the strength and durability of hardened cement paste. The stoichiometry of C-S-H (e.g. C/S and H/S ratio) can vary depending on various parameters such as the initial water/cement ratio and the use of supplementary cementitious materials. The change in the composition of C-S-H has been shown to be related to its mechanical and chemical behavior. A method for modifying the nanostructure of hydrating cement systems that employs synthetic C-S-H as a nucleation seeding agent during the hydration process was developed., 13th International Congress on the Chemistry of Cement: 03 July 2011, Madrid, Spain

Nanosized Ca(OH)2 particles having different physical characteristics e.g. surface area, degree of crystallinity, have been prepared. Endothermal doublets present in the thermoanalytical spectral information reflect differences in the degree of crystallinity of the various Ca(OH)2 preparations. A thermodynamic analysis of their thermal behavior is presented. The thermodynamic analyses validate the experimental observations based on the estimates of the decomposition temperatures of the Ca(OH)2 nanoparticles.

Quantitative Rietveld analysis of cements is now a common tool in both industry and research. Many papers analyse cements without any additional sample preparation over and above the griding carried out by the manufacturer. The particle sizes in cements are usually in the range of 25-40pm, which is much coarser than recommended in texts dealing with particle statistics in diffraction. Coarse particles will have an effect on the particle statistics, and consequently the reproducibility of the relative peak intensities. A systematic study has been undertaken to examine the effect of particle statistics on the results from Rietveld analysis of cements, and the influence of reducing the particle size by micronizing. In addition, the effects of changing divergence slit and use of sample rotation have been examined., 12th International Congress on the Chemistry of Cement: 8 July 2007, Montreal, QC.

Using supplementary cementing materials provides environmental advantages, but the decreased rate of hydration is a disadvantage. This study investigated the accelerating effect of nano-sized CaCO3 on cement paste containing high volumes of fly ash. It employed conduction calorimetry and used determinations of microhardness and modulus of elasticity to assess the effect of the nano-sized CaCO3., 12th International Congress on the Chemistry of Cement: 08 July 2007, Montreal, QC.

Pure and doped calcium silicate hydrates (C-S-H) were synthesised and characterised. Pure preparations with calcium to silica (C/S) ratios ranging from 0.6 to 2.0 were made. Doped preparations with C/S ratios of 1.0 and 1.7 were synthesised with one molar lithium and sodium hydroxide solutions. Each preparation was characterised using Nuclear Magnetic Resonance (NMR), X-ray Diffraction (XRD), Fourier Transform InfraRed (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM). As expected, results for the pure control C-S-H preparations largely agreed with published literature. The lithium and sodium doped preparations both contain residual Ca(OH)2, indicating that their final C/S ratio is not equal to that of the starting materials. The lithium-doped material at low C/S ratio (1.0) exhibits chemical and structural behaviour more consistent with a pure C-S-H having a higher C/S ratio (1.7). Sodium doped C-S-H exhibited characteristics consistent with that of the purer control preparations., 12th International Congress on the Chemistry of Cement, 8 July 2007, Montreal, QC.

Equations are developed to describe the combined effect of diffusion and adsorption of water and methanol vapor in hydrated cement paste. The dynamic equation of flow is obtained by equating the space derivative of the spreading pressure of the adsorbed film to a resistive force equal to the product of the coefficient of resistance and the velocity of the film. Qualitative agreement is found for the diffusion of water and methanol vapor through cement paste when the BET and Langmuir equations respectively are used for adsorption. The diffusion of methanol vapor is underestimated due to intercalation and chemical interaction effects. The validity of Fick's law is discussed.

The presence of at least two different forms of Ca(OH)2 is confirmed by the results of a thermoanalytical study on the decomposition and re-hydration characteristics of Ca(OH)2. The study comprised a series of differential scanning calorimetry (DSC) experiments (at temperatures up to 700°C) performed in an atmosphere of a continuous flow of nitrogen pre-conditioned to various relative humidities ranging from 12 to 100%. The emergence of two separate and distinct decomposition endotherms occurred. The endothermic peak temperatures were dependent on the relative humidity and temperature history of the Ca(OH)2 samples. Exposure of CaO to higher temperatures and different humidities would appear to promote the formation of both crystalline and microcrystalline products. Under these conditions, higher temperatures give rise to formation of very crystalline products and after some time, vapor phase exposure promotes the formation of microcrystalline products. Factors affecting the formation of the different forms of Ca(OH)2 are described.

The thermal decomposition of different polymorphs of Ca(OH)2 with varying degrees of crystallinity and surface area was investigated. The nitrogen surface area values ranged from 3.7 to 31.1 m2/g. The presence of two separate and distinct thermal decomposition events was observed depending on the degree of crystallinity. Binary mixtures of Ca(OH)2 with substantially different degrees of crystallinity exhibited well defined thermal decomposition doublets. In addition Differential Scanning Calorimetry (DSC) experiments (for cycles of heating and cooling) performed in controlled environments pre-conditioned to various relative humidities (RH) also indicated the presence of two distinct endothermal doublets. The endothermic peak temperatures were dependent on the RH and temperature history of the Ca(OH)2 samples. An assessment of factors affecting the observed thermal behavior included: investigation of particle size and degree of crystallinity; observation of combined strain and particle size broadening (Williamson-Hall X-ray plots); heat capacity-temperature characteristics. A thermodynamic analysis of the thermal decomposition process is presented., RILEM - 2nd International Symposium on Advances in Concrete Through Science and Engineering: 11 September 2006, Québec City

The use of high volumes of supplementary cementing materials in cement systems is considered strategic with respect to sustainable development issues. The decreased rate of hydration at early ages, however, continues to be a disadvantage. The accelerating effect of nano-sized CaCO3 addition to ordinary Portland cement paste (OPC) containing high volumes of ground granulated blast-furnace slag (GGBFS) in lieu of micro-sized CaCO3 addition was investigated by conduction calorimetry and determinations of microhardness and modulus of elasticity. The results indicate that the hydration of OPC containing high volumes of GGBFS is significantly accelerated by the nano-sized CaCO3 addition. The times of occurrence of the main calorimetry peaks are remarkably decreased and the rate of heat development increases depending on the amount of the nano-sized CaCO3 addition. It is apparent from the calorimetry results and the engineering properties of the systems studied that the nano-sized CaCO3 addition to cement systems containing high volumes of GGBFS fully compensates for the delayed hydration process., 2nd International RILEM Symposium on Advances in Concrete Through Science and Engineering: 11 September 2006, Québec City