The Rietveld-internal standard method for Bragg-Brentano reflection geometry (θ/2θ) X-ray diffraction (XRD) patterns is implemented to determine the amorphous phase content. The effect of some minor phases on quantitative accuracy is assessed. The numerical simulation analysis of errors and the related corrections are discussed. The results reveal that high purity of crystalline phases in the standard must be strictly ensured. The minor amorphous or non-quantified crystalline phases exert significant effect on the quantitative accuracy, even with less than 2 wt% if ignored. The error levels are evaluated by numerical simulation analysis and the corresponding error-accepted zone is suggested. To eliminate such error, a corrected equation is proposed. When the adding standard happens to be present in sample, it should be also carefully dealt with even in low amounts. Based on that ignorance, the absolute and relative error equations (Δ_AE, Δ_RE) are derived, as proposed. The conditions for high quantitative accuracy of original equation is strictly satisfied with a lower amount of standard phase present in sample, less than 2 wt%, and a higher dosage of internal standard, larger than 20 wt%. The corrected equation to eliminate such quantitative error is suggested.

Results of Bragg coherent diffraction imaging (BCDI) confirm that ion migration and consumption occur during hydration of calcium monoaluminate (CA). The chemical phase transformation promotes the hydration process and the formation of new hydrates. There is a potential for the formation of hydrates near where the active ions accumulate. BCDI has been used to study the in situ hydration process of CA over a 3 day period. The evolution of three-dimensional (3D) Bragg diffraction electron density, the “Bragg density”, and strain fields present on the nanoscale within the crystal was measured and visualized. Initial Bragg densities and strains in CA crystal derived from sintering evolve into various degrees during hydration. The variation of Bragg density within the crystal is attributed to the change of the degree of crystal ordering, which could occur through ion transfer during hydration. The observed strain, coming from the interfacial mismatch effect between high Bragg density and low Bragg density parts in the crystal, remained throughout the experiment. The first Bragg density change during the hydration process is due to a big loss of Bragg density as seen in the image amplitude but not its phase. This work provides new evidence supporting the through-solution reaction mechanism of CA.

AFt is one of the major products at the early stage of cement hydration. It is an important product that influences the performance of the fresh and hardened cement pastes such as the setting time. However, there is a lack of detailed investigation on the growth of AFt in the cement pastes with a long-time scale. In this work, we reported a detailed analysis by using in-situ powder X-ray diffraction (XRD) on the growth of AFt in the cement pastes during hydration. Samples of the hydrated ordinary Portland cement (OPC) and another locally produced Portland cement with very high tricalcium silicate (C₃S) content with different water–cement (w/c) ratios were investigated continually till they were hydrated for about 270 days by powder XRD. The work shows that during Portland cement hydration, the AFt reaches its maximum content with very high speed within about 24 h, which is influenced by the content of C₃S in the raw cement samples and the w/c ratios of the cement pastes. Once the maximum content of AFt was reached, it decreases very fast within the following couple of days, and then decreases slowly and finally reaches a stable level at the late stage of hydration. The results also present that a lower w/c ratio is beneficial to the formation of AFt and the conversion of AFt to AFm as well. While higher w/c ratios are favorable for the AFt to remain stable in the hardened cement pastes.

This paper describes the results of an investigation into the effect of the variation of curing temperatures between 0 and 60 °C on the hydration process, pore structure variation, and compressive strength development of activated coal gangue-cement blend (ACGC). Hardened ACGC pastes cured for hydration periods from 1 to 360 d were examined using the non-evaporable water method, thermal analysis, mercury intrusion porosimetry, and mechanical testing. To evaluate the specific effect of activated coal gangue (ACG) as a supplementary cementing material (SCM), a fly ash-cement blend (FAC) was used as a control. Results show that raising the curing temperature accelerates pozzolanic reactions involving the SCMs, increasing the degree of hydration of the cement blends, and hence increasing the rate of improvement in strength. The effect of curing temperature on FAC is greater than that on ACGC. The pore structure of the hardened cement paste is improved by increasing the curing temperature up to 40 °C, but when the curing temperature reaches 60 °C, the changing nature of the pore structure leads to a decrease in strength. The correlation between compressive strength and the degree of hydration and porosity is linear in nature.

This paper deals with the hydration of a blend of Portland cement and activated coal gangue in order to determine the relationship between the degree of hydration and compressive strength development. The hydration process was investigated by various means: isothermal calorimetry, thermal analysis, non-evaporable water measurement, and X-ray diffraction analysis. The results show that the activated coal gangue is a pozzolanic material that contributes to the hydration of the cement blend. The pozzolanic reaction occurs over a period of between 7 and 90 d, consuming portlandite and forming both crystal hydrates and ill-crystallized calcium silicate hydrates. These hydrates are similar to those found in pure Portland cement. The results show that if activated coal gangue is substituted for cement at up to 30% (w/w), it does not significantly affect the final compressive strength of the blend. A long-term compressive strength improvement can in fact be achieved by using activated coal gangue as a supplementary cementing material. The relationship between compressive strength and degree of hydration for both pure Portland cement and blended cement can be described with the same equation. However, the parameters are different since blended cement produces fewer calcium silicate hydrates than pure Portland cement at the same degree of hydration.