Effect Of Calcium Sulfoaluminate-calcium Oxide Expansion Agent On Self-healing Properties Of Concrete

The durability of concrete decreases due to cracks.It is more and more important to suppress the occurrence and development of cracks and repair cracks.The unhydrated cement particles in the concrete itself can be hydrated again in a suitable environment to self-heal to block the cracks.Studies have shown that the addition of expansion agents can not only suppress cracks caused by self-shrinking,but also improve the self-healing effect of concrete.Existing studies have paid more attention to the effect of swelling agents on self-healing,and less research has been done on the effect of core components of swelling agents on self-healing,which has affected the disclosure of its healing mechanism.In view of the above background,this article focuses on the effects of calcium sulfoaluminate-calcium oxide expansion agents,calcium sulfoaluminate and calcium oxide on self-healing.The main research contents and results of this article are as follows:(1)The experimental study found that when the water-to-binder ratio is 0.3 and the amount of water-reducing agent is set to 0.6% of the gelling material,the specimen has good fluidity and mechanical properties,and the mechanical properties and shrinkage are the main factors.The optimal dosage range of the expanding agent is determined.The experiment found that when the mass blending amount of the expanding agent increases from 2% to 6%,the swelling effect increases by about twofold,and the swelling efficiency decreases when the blending amount is 8%;when the blending amount is 8% and 9%,the mechanical strength drops sharply,and the swelling The optimal dosage of the agent should be 6% of the mass of the cement material.(2)The experiment studied the self-shrinkage performance of cement stone specimens containing expansion agent and calcium sulfoaluminate under different curing conditions.The study showed that the shrinkage inhibition effect was the best under water curing and the worst under air curing;Adding 6% of the expansion agent of the quality of the cement material will not cause cracking and damage in the logistic process of the cement stone,and the cement stone has good stability.The addition of calcium sulfoaluminate will reduce the mechanical strength of mortar,while the addition of calcium oxide will increase the mechanical strength of mortar.The effect of the expansion agent on the strength of mortar is between calcium sulfoaluminate and calcium oxide.(3)The experiment and numerical simulation study the crack prefabrication method of cube and cylinder specimens.The experimental research shows that the method for prefabricating cracks of cube and cylinder specimens adopts displacement control,and the crack widths of the specimens from the front and back have a goodlinear relationship;For cylindrical specimens,the cracks are mainly concentrated near the central axis,and the crack width has a good linear relationship with the vertical displacement.(4)The effects of calcium sulfoaluminate-calcium oxide expansion agents and calcium sulfoaluminate and calcium oxide agents on the self-healing effect of cement mortar were studied through crack closure observation,ultrasonic lifting and gas penetration test,and analyzed by SEM and XRD Characteristics of the healing product at the crack.The results show that the cracks on the surface and inside of the mortar will heal,and the healing effect increases with the increase of the dosage of the expansion agent and its core components and the maintenance age.The expansion agent contains calcium sulfoaluminate with mutual assistance The two components of calcium oxide and calcium oxide have the best effect on the overall healing of cracks.