Study On FT-I Cementitious Capillary Crystalline Waterproofing Coating

Cementitious capillary crystalline waterproofing coating (CCWC) is a new type of rigid waterproofing materials consisting of ordinary Portland cement, quartz sand and active ingredients. The active ingredients in the coating can penetrate into the capillary pores of cement paste and concrete, forming crystalline or gelatinous substances which fill the capillary pores and thus reduce the permeability of concrete.The research and application status of waterproofing materials in domestic and oversea, especially that of CCWC was comprehensively reviewed, and efforts have been taken in systematic research and development for a new type of CCWC. Ordinary Portland cement, Ca-Al compound salt, superfine quartz sand, complexation agent, active silica agent, superplasticizer and cellulose were used as the raw materials for preparing CCWC.Air-permeability index of concrete coated with the waterproofing coating being studied was taken as the main index for evaluating the quality of the coating in the first stage of research for developing the CCWC. The effect of each ingredient mentioned above on air-permeability was studied systematically with cross experiments and single-factor optimizing experiments. A new type of coating named as FT-I with low air permeability was successfully developed.The physical performances both of FT-I coating and of the concrete coated with FT-I were tested accordance with GB18445-2001. The performances of resisting water permeation, chloride penetration, chemical corrosion, carbonation, frost and thaw were also examined. The results show that the setting time, soundness, mechanical performance and binding performance of the coating satisfy all the requirements accordance with GB 18445-2001; and the coating also has low dry-shrinkage, high anti-crack performance and excellent anti-corrosion properties. The impermeable water pressure of concrete coated with FT-I is 0.9MPa, 2.25 times as high as that of the reference concrete, and the secondary impermeable pressure is0.6MPa. These all performances satisfy the index required by Type I CCWC accordance with GB18445-2001. It is thus proved that FT-I can be used as a permanent waterproofing material. The results also show that FT-I can improve the resistance of concrete to chloride penetration, carbonation and frost and thaw. The concrete coated with the coating has excellent resistance performance to dilute acid, alkali, and sulfate aqueous solution. It can be used in environment with pH higher than 3.0 and lower than 12.The phase composition, microstructure and pore structure of hardened cement paste coated with FT-I were analyzed by means of SEM, XRD and MIP. The result show that the active components in FT-I have permeated into the pores and cracks of cement paste to react with cement compound, and C-S-H gel and crystalline ettrigite formed in the pores. These products fill and block the pores, reduce the porosity and pore radius, which makes the concrete denser and higher impermeability.