Coagulation time regulation for sulphoaluminate cement via microcapsule coagulant

ObjectiveRapid-hardening sulphoaluminate cement concrete has excessively short coagulation time, which is difficult to ensure construction quality. The study aims to achieve precise regulation of coagulation time via microcapsule technology, balancing construction feasibility and mechanical performance stability.MethodpH-triggered microcapsules were used to encapsulate coagulants. Microcapsules with different wall thicknesses (Type Ⅰ ruptures in 10 min, Type Ⅱ ruptures in 20 min) and dosage gradients were designed. The influences of microcapsules on hydration process, setting characteristics and mechanical properties of rapid-hardening sulphoaluminate cement were systematically studied through coagulation time test, compressive strength test and pH monitoring.ResultMicrocapsules significantly regulated coagulation time of rapid-hardening sulphoaluminate cement paste; and prolonged coagulation time by 10-20 minutes compared with the control group that added coagulant directly. The coagulant-retarder composite system significantly reduced the compressive strength of cement. Microencapsulation of coagulants obviously improved this adverse effect. The compressive strength of mortar specimens reached the optimal level in 3 hours, 24 hours and 72 hours, when the microcapsule dosage was 0.17%.ConclusionpH-triggered microcapsules can realize delayed release of coagulants by regulating the wall dissolution time. They effectively resolve the contradiction between early strength and workability of rapid-hardening sulphoaluminate cement. The optimal microcapsule dosage is 0.17%, prolonging the coagulation time by 15-20 minutes and ensuring high compressive strength of cement mortar specimens. Microencapsulation technology will alleviate the antagonism between coagulants and retarders, improving the mechanical properties of composite system.