The growth of electricity usage in Thailand leads to a greater amount of flue-gas desulfurization gypsum (FGDG) to be stockpiled within the power plants. Similar to natural mined gypsum, the disadvantages of FGDG for its utilization in structural materials are mainly due to its low compressive strength and slight water solubility. The present work aims to extend the applicability of FGDG as a structural material by calcining it into flue-gas desulfurization plaster (FGDP) and blending it with fly ash (FA) and ordinary Portland cement (OPC). The amounts of FGDP, FA and OPC were altered to search for the formulation that yielded the lower gypsum dissolution to improve the water resistance, compressive strength and minimize the risk of sulfate attack under the wet condition. This development will not only save the cost of landfill, add value to the abundant industrial byproducts, but also reduce the production cost of the construction material. The lowest gypsum dissolution and the highest compressive strength were achieved in the paste with FGDP: FA: OPC = 20 : 40: 40 at the water/binders ratio of 0.5, that also showed the Vicat initial setting time longer than 45 min. Only insignificant drop in the compressive strength was observed when it was cured by soaking in water, compared to curing by storing in a 100% relative humidity container. After adjusting either the amount of sand or superplasticizer to achieve the flow of 110 ± 5, the mortars with FGDP: FA: OPC = 20 : 40: 40 and 40 : 30: 30 from both adjustments could all attain the compressive strengths as required by ASTM C150. The insignificant compressive strength drop due to curing by soaking in water was observed and became even more insignificant after longer curing time. The most improved water resistance, based on the compressive strength at 91 days, was achieved from the mortar with FGDP: FA: OPC = 20 : 40: 40, at the water/binders ratio of 0.485 and the sand/binders ratio of 1. These results and the coverage on the gypsum particles observed in the SEM micrographs confirmed the reduction of gypsum dissolution, hence the improved water resistance and the very low risk of sulfate attack. Potential improvement could be further explored by increasing the amount of FGDP and decreasing the amount of OPC through the use of more reactive pozzolanic materials.

Water resistant blended cements containing flue-gas desulfurization gypsum, Portland cement and fly ash for structural applications

Effect of ultra-sonic activation on early hydration process in 3D concrete printing technology

Evaluation of Portland and Pozzolanic cement on the self-healing of mortars with calcium lactate and bacteria

Investigation of gypsum composites with different lightweight fillers

This paper presents the results of an experimental study about the effect of the incorporation of masonry residue (RM) from construction and demolition wastes (RCD) on the hydration of cementitious pastes. Kinetics of the exothermic reactions during early stage of hydration was monitored by calorimetry and the presence of hydration products was determined by scanning electron microscopy (SEM), thermogravimetry analysis (DTG), X-ray diffractometry (XRD) and Fourier-transform infrared (FTIR). The results indicate that the presence of RM in the pastes does to decrease the heat of hydration in the first 48 hours. On the other hand, the SEM, DTG, XRD and FTIR techniques indicate that the main hydration products in the pastes added with RM are calcium silicate hydrates (C-S-H), calcium aluminate hydrates (CAH) and calcium aluminum silicate hydrates (CASH).

Efecto del residuo de mampostería en la hidratación de pastas de cemento Portland

The strength, hydration products, microstructure and heat of early hydration were investigated on alternative hydraulic green cements based on calcium sulphate anhydrite partially blended with Portland cement and pozzolans Four pozzolans of different physical and chemical nature, namely a geothermal waste, silica fume, metakaolin and pulverized fuel ash were characterized The composite binders showed hydraulic behavior The use of Portland cement favoured the strength, which was also higher with the incorporation of siliceous nanometric pozzolans compared to the micrometric silicoaluminate pozzolans The nanoparticles enhanced the early hydration and changed the gypsum morphology promoting denser matrices of hydration products The geothermal waste pozzolan was the most effective, while one of the composites with metakaolin showed formation of ettringite and strength losses The heat of hydration of the composites was considerably lower than that of the neat Portland cement

O.A. Martínez-Aguilar

Papers

Calcium sulphate anhydrite based composite binders; effect of Portland cement and four pozzolans on the hydration and strength