Studies On Cementitious Capillary Crystalline Waterproofing Agent And Its Self-healing Function For Cracks

The cementitious capillary crystalline waterproofing agent (CCCW) as a unique rigid waterproof material,characterized by it's permanent waterproofing effect,self-rehabilitating ability and so on,has a broad market prospect. However, the mechanism of its crystallization and seal-healing for cracks presents different opinions, and does not have a complete and accurate theory. In the domestic market, the performance of such materials varies greatly, seriously affecting its promotion and application. Therefore, through the mechanism of in-depth research and developed the CCCW with independent intellectual property rights, can stsndardize and promote the kind of material production and application in China, for the improvement of waterproofing engineering is of great practical significance.In this paper, based on analyzing the mechanism of self-healing function cracks, the mechanism of circulating complexing crystallization– self-healing reaction for cracks is proposed for the first time. It is considered that selection and characterization of complexing agent is the key technique for production of such waterproofing agent, hopefully providing the theoretical foundation and technical support for the preparation and application of CCCW. Research work is mainly focused on the several aspects as follows: 1) a novel kind of self-healing materials for the cracks of concrete was prepared, and researched its self-healing ability and working mechanism; 2) a crystalline waterproofing agents was prepared with the composite technologies, and its formula was optimized; 3) through self-designed experiments the self-healing properties of the water- proofing agents was investigated; 4) the properties of the waterproofing agents were investigated and evaluated in accordance with the relevant standards.The core of the mechanism of circulating complexing crystallization– self-healing reaction for cracks is complexing agent can be cyclical reaction of complex crystallization, eventually resulting crystalline precipitate can fill pores and cracks. The complexing agent JS was prepared, and the analysis results of its working mechanism showed that: the complexing agent JS could cause a complexation reaction with Ca(OH)2, and generated instability precipitated calcium complexes; such calcium complexes could be converted to calcium silicate hydrate crystalline by further reaction with the silicate ion, meanwhile, JS was recovered so that it can work forever. The calcium silicate hydrate crystalline generated continuously filled pores and cracks, and could improve significantly the impermeability of the mortar, and endow the mortar with a self-healing function.The development of crystalline waterproofing agents should follow a complex technical routine. Throughing multiple orthogonal tests and single factor optimized tests, using complexing agent JS,active silica agent,organic waterproof agent,inorganic waterproof agent,water reducing agent and silica fume as raw material, a new type of cementitious capillary crystalline waterproofing agent with good water resistance and self-healing properties was successfully developed in the laboratory. The properties of self-made waterproofing agents were investigated in accordance with the National Standard GB 18445-2001.The test results indicated that: all performance indexes of them could conform to the specified standard; 275% impermeability pressure ratio(28 d) was obtained in self-made waterproofing agents; the second impermeability pressure(56 d) was 1.3 MPa, which was higher than the first.The water permeating and leaching processes of cracked cementitious specimens were investigated. The phase composition and microstructure of the precipitate on crack surface of cementitious specimens were studied by means of XRD and SEM. All the results showed that: owing to the dissolution and sedimentation of calcium hydroxide and the crystallization of calcium carbonate precipitation, exposed to water environment the autogenous healing of the cracks in the cementitious materials occurred, but the self-healing capabilities was quite limited. The self-healing capabilities of cement paste and mortar specimens mixed with self-made waterproofing agents were superior to the blank samples, and the former had a good secondary self-healing. Chemical reaction of self-made waterproofing agents occur to produce crystalline precipitates to fill the void, but also can accelerates the hydration process of cement, which generates C-S-H gel to block up the pores and cracks.