K. Mohan

A multi-method study of C3S hydration

Abstract C3S pastes hydrated at 25°C have been studied using QXRD (to determine uncreacted C3S), TG (to determine CH and water), and trimethylsilylation (to determinemonomeric and dimeric silicate) and the results compared with ones obtained with analytical electron microscopy. Monomeric silicate is accounted for by unreacted C3S. The silicate in the C-S-H formed during the first few days is entirely dimeric, but at later ages dimer and polymer are both present. A new hypothesis for the reaction mechanism is tentatively proposed.

A trimethylsilylation study of tricalcium silicate pastes

Tricalcium silicate and alite pastes aged from 1 day to 30 years were studied by trimethylsilylation and examination of the resulting derivatives by gas liquid chromatography, gel permeation chromatography and other methods. At ages up to about 6 months, silicate anion polymerization probably occurs predominantly during the formation of the CSH and not by changes within CSH that has already formed. The latter process is extremely slow, and only becomes significant after substantially all the C3S has reacted.

The thermal decomposition of Ca3SiO5 at temperatures below 1250°C I. Pure C3S and the influence of excess CaO or Ca2SiO4

Abstract The thermal decomposition of pure Ca3SiO5 has been studied at temperatures between 1025° and 1210°. The results are shown as a family of time-temperature-transformation curves. Analysis of the kinetics shows that decomposition is initiated by formation of nuclei of Ca2SiO4 and CaO at the surface of Ca3SiO5 grains. The presence of CaO or Ca2SiO4 increases the apparent rate of decomposition, largely by eliminating the need for a separate nucleation period.

The thermal decomposition of Ca3SiO5 at temperatures below 125o°: Part 3. The influence of water and sulphate on the decomposition

Abstract The presence of water vapor is shown markedly to increase the rate of decomposition of Ca 3 SiO 5 . Molten K 2 SO 4 -CaSO 4 eutectic mixture also drastically increases the rate of decomposition of Ca 3 SiO 5 at temperatures as low as ca 800°.

Pastes of tricalcium silicate with rice husk ash

Abstract Pastes of tricalcium silicate with rice husk ash (RHA) were cured at 25°C for 1–245 days and examined by XRD, analytical electron microscopy, TG, acid extractions to determine unreacted rice husk ash, and trimethylsilylation. The rice husk ash was highly reactive, and contents of calcium hydroxide, referred to the ignited weight, never exceeded 3%. Initially, a product having a Ca/Si atom ratio of 0.1–0.2 was formed, but this was later replaced by one having a Ca/Si ratio of approximately 1.3. The proportion of the Si in the hydration products that was present as polymeric ions was greater than that found in pure C3S or C3S-fly ash pastes of similar age, but the anion size distributions within the polymer were all broadly similar.

Autoclaved lime — quartz materials II. Thermogravimetry and trimethylsilylation

Abstract Data are presented for the series of autoclaved lime-quartz pastes made with differing bulk CaO/SiO 2 ratios and quartz particle sizes for which compressive strengths and other data were given in Part I (CCR, 7 , 493, 1977). For CSH of C/S 0.8, the Si occurs wholly as polysilicate and the TG curve resembles that of tobermorite. With increase in C/S ratio of the CSH, the fractions of the Si present as mono- and disilicate increase, but at all C/S ratios studies, polysilicate still predominates. For any given temperature on the TG curve, H/S tends to rise with C/S. These results are explained assuming the anions in the CSH to be polymeric [Si 3 O 9 H 5− ] n ,Si 2 O 7 H 5− , and possibly SiO 4 H 3− .

The thermal decomposition of Ca3SiO5 at temperatures below 1250o: Part 2. The influence of Mg, Fe, Aλ and Na oxides on the decomposition

Abstract The decomposition kinetics of Ca 3 SiO 5 solid solutions containing Aλ, Mg, Fe, Na and (Mg + Fe) have been studied by determining the rate at which free lime forms during isothermal annealing. Aλ has little effect, Fe markedly accelerates decomposition, while Na 2 O has a slight retarding effect and Mg markedly retards decomposition. In the presence of both Mg and Fe, the accelerating effect of Fe dominates.

Mőssbauer spectra of iron in Ca3SiO5 solid solutions

Mossbauer spectra have been obtained from C3S solid solutions containing 0.50 wt % Fe2O3 enriched in Fe57. After heating in air at 1550°, quenched specimens contain about 9% of this iron as Fe2+. The distribution of iron on different sites is inferred from the spectra. Upon annealing the solid solution at 1025°, C2F exsolves rapidly.