Evaluating the Mechanical Properties of Admixed Blended Cement Pastes and Estimating its Kinetics of Hydration by Different Techniques

Abstract

Mineral and organic admixtures are working together to give a compacting structure of cemetinous matrix to form ultra-high performance concrete (UHPC). Superplasticizers can be used to treat some problems occurring by adding mineral admixtures. Since silica fumes has high surface area, a high amount of water is required, which is reflected on the mechanical properties of concrete showing the importance of using organic admixtures. In this research, the effect of phenol formaldehyde sulfonilate, (SI) and phenol formaldehyde sulfonilate with low phenol content (SII) admixtures which prepared laboratory as well as a commercial admixture sikament-TG (TG) on the behaviour of blended cement (BC) pastes was studied. The standard water of consistency (S-WC), water reduction percentages and mechanical compressive strength (MCS) of the prepared pastes were examined. The hydration kinetics was examined by using thermal analysis techniques, chemically combined water (CC-W), degree of hydration (DH) and gel/space ratio (G/S). In addition, the X-ray diffraction (XRD) and scanning electron microscope were used to investigate the phase composition and micro-structure of the hydration products and confirm the results. The prepared admixtures are considered as a new group of admixtures that make high water reduction up to 54%. The doses of 0.25% TG, 0.50% SI and 1.00% SII are the optimum for the compressive strength as the have the highest values of gel/space ratio. UHPC can be achieved by using these types of admixtures.