A. Zayed

Quantification of supplementary cementitious content in blended Portland cement using an iterative Rietveld–PONKCS technique

An iterative Rietveld–PONKCS (partial or no known crystal structure) technique has been developed for precise and accurate determination of the weight percentages of predominantly amorphous supplementary cementitious materials (SCMs) contained in Portland cement–SCM blends. This technique involves the iterative refinement of the SCM amorphous phase (SCMAP) content, with the separation of the refinement of the SCMAP shape parameters from background refinement. The technique also includes an internal and external standard refinement of both the calibration SCM and the cement–SCM blend. This approach enables the separation of the contributions of the SCMs and the cement to the amorphous content of the cement–SCM blend. The technique has been successfully applied to binary systems of cement–slag and cement–fly ash, and ternary blends of cement–fly ash–slag, over a wide range of cement replacement levels. In the ternary systems, the proposed technique was successfully able to separate the individual amorphous contributions of slag and fly ash to the total amorphous content of the system. The approach was also implemented on a pair of commercially available binary blended cements containing 30% slag and 30% fly ash, respectively.

Predicting One-Day, Three-Day, and Seven-Day Heat of Hydration of Portland Cement

AbstractThis paper aims to develop empirical equations predicting one-day, three-day, and seven-day heat of hydration of portland cement at 23°C and water to cement ratio of 0.5. Isothermal conduction calorimetry was implemented to measure the heat of hydration of portland cements for up to seven days. X-ray diffraction was used to study the mineralogy and also for quantification of phase composition of portland cements. Particle size distribution of cements was measured using a laser scattering particle size analyzer. Blaine fineness of cements was measured using a Blaine permeability apparatus in accordance with the standard test methods for the fineness of hydraulic cement by air-permeability apparatus procedure. The results indicate that the one-day, three-day, and seven-day heat of hydration of a specific portland cement ground to different finenesses is changing linearly with the cement mean particle size. This research shows that the mean particle size is a suitable measure of cement fineness to co...

Combined Effect of Water Reducer–Retarder and Variable Chloride-Based Accelerator Dosage on Rapid Repair Concrete Mixtures for Jointed Plain Concrete Pavement

AbstractOn-site addition of accelerator to rapid repair concrete mixtures can result in accidental overdose. Since these mixtures are designed to contain large accelerator dosages, an overdose will produce concrete with extremely high accelerator amounts, well above those recommended by the manufacturer. This study investigated the effect of calcium chloride–based accelerator dosage on the stresses and cracking behavior of realistic concrete mixtures that contain multiple chemical admixtures. The findings indicate the effect of accelerator dosage on increasing the temperature gradient in concrete leading to higher tensile stress generation with upward or downward curling. The effect is exacerbated when there is a simultaneous coincidental occurrence in the maximum of cement paste heat flow and ambient temperatures. The apparent activation energy determined through the heat of hydration or strength measurements shows a drop when chemical retarders are added, whereas for accelerators the effect appears to b...