Optimization of strength and microstructural properties of building gypsum by ternary Ca(OH)2 - citric acid and PCEs additives

Multiple additives are usually required to achieve better constructability for building gypsumbased materials. In this work, ternary contour was designed to determine the optimal proportions of Ca(OH)2 (CH), PCEs and citric acid (CA) by comprehensive considerations of water requirement, setting time, fluidity, strength, temperature, hydration products and microstructural characteristics. The effects of different additives on water requirement, setting time, fluidity, compressive strength, hydration products and microstructure were comprehensively investigated, and the associated mechanisms were revealed by X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. The results demonstrate the synergistic impact of PCEs and CH on decrease of the water demand and enhancement of fluidity and compressive strength. The incorporation of CH led to rapid setting, but compensated the strength reduction brought by CA. The optimum additives for building gypsum were obtained with a ternary mixture containing 0.1-0.9 % CH, 0.6-1.4 % PCEs and 0-0.08 % CA, since it guaranteed a longer setting time, lower water requirement and higher strength. The present work paves the way to optimize or predict the early hydration and mechanical properties of building gypsum in both technical and economic aspects by adjusting the proportions of the three additives.