Effect of delayed microwaving on the strength progress of Green alkali activated cement composites

Abstract Increasing urbanization around the world has led to the emergence of many problems that must be solved, such as the tendency to use alternative materials for cement to reduce costs and environmental risks. Simultaneously, reducing time and increasing productivity have directed most of the research towards developing the precast concrete industry. In this work, these problems were combined to find an optimal way to solve them by studying the effect of a wide range of microwave radiation on alkali-activated slag (AAS) to increase building quality assurance. The impact of delayed microwave treatment time (1 and 7-days), as well as different wattage scales (0, 90, 450 and 900 W) and treatment period (2, 4 and 8 min) on the mechanical properties of AAS pastes, were examined. The X-ray diffraction (XRD), Thermogravimetric analysis/its derivative (TGA/DTG) and environmental scanning electron microscope (ESEM) were carried out to investigate the composition and morphology of the produced zeolitic phases. The results confirmed that microwave curing is an effective method of increasing the strength for AAS. The low wattage level and the short treatment period are adequate to improve the mechanical properties of AAS at late ages. However, at early ages, curing AAS for 8 min at 900 W increases the strength by 327.2% compared with the control specimen. Delaying the microwave treatment up to 7-days led to an increase in AAS strength up to 34.6% after subjection to 4 min and 900 W.