Acceleration mechanism of nonisothermal microwave heating on strength development of mortar

Based on the finding of little understanding of acceleration mechanism of microwave curing, this work studies the mechanism in terms of thermal and nonthermal effects of microwaves on mortars. Mortar is cured by regimes designated with varied curing intensity in order to distinguish thermal and nonthermal effects, which are normally difficult to be told apart. They are distinguished by the inconsistency of temperature and compressive strength evolution kinetics. Microstructural characteristics are studied to explore an insight to the effects. It is found that thermal effects constantly exist and nonthermal effects are initiated by threshold energy. Although they are both responsible for accelerating mortar hardening, thermal effects are more effective. Nonthermal effects increase the branching and cross-linking of aluminosilicate chains. The resultant three-dimensional C-S-H morphology is detrimental for packing densely at nanoscale, which may explain the less acceleration effectiveness of nonthermal effects on strength development.