Effect Of Capillary Crystalline Reaction On Water Absorption And Strength Of Cement Based Materials And Research Of Its Mechanism

The experiment on the basis of capillary crystalline reaction, the current domestic Cementitious Capillary Crystalline Waterproof Materials referred to as CCCW mechanism was not clear, and the key raw material were mainly rely on imports, traditional capillary crystalline materials will generate sodium hydroxide and easily lead to alkali silica reaction, therefore the research were started. The mechanism generally identified with domestic scholars was that the active materials permeated cracks and pores of the concrete and reacted with Ca(OH)2 and Ca2+, C-S-H gel or something indissolvable were produced to block the cracks and pores. Then the concrete become more waterproof and compact.Therefore materials had high solubility, strong permeability and no detrimental by-product like ammonium salt and TEOS were regarded as active materials applied in CCCW.(1) Water absorption and strength test were used to screen ammonium salts, TEOS, etc. The results showed that water absorption decreased more significant after treated with TEOS, and strength increased observably after treated with ammonium phosphate. After treated with TEOS the water absorption of mortar at 28 d reduced by about 70% and the mortar treated with ammonium phosphate strength increased by 20% compare with blank. It can also be reflected in the micro morphology, the cracks and pores in surface layer of the mortar were filled with much more flocculent and fibrous material, so the porosity was reduced..(2) On the basis of the optimization, the way of introduction, concentration, dosage of TEOS,additives, and properties of the cement based material itself were studied about their effect on waterproof.Furthermore, thermal gravimetric analysis and mercury injection test were used to characterized the mortar.The results showed that brushing was the most simple and effective way, the concentration of 50%, the solution in an amount of 400 m L/m2 had good waterproofness. Cetyl trimethyl ammonium bromide accelerate the capillary crystalline reaction and water absorption was reduced by 40% compare with control,calcium formate improve the calcium content of mortar in surface layer, thus improve the reaction efficiency. In addition, the water content of the mortar before brush treatment also have an impact on waterproofness, the mortar saturated with water then dried for 2h at 55℃ were suitable for brush treatment.(3) The mortar after freeze-thaw test, flooding tolerance and the mortar at different ages were characterized by water absorption, strength test and mercury injection test. The results showed the mortar after flooding tolerance had better waterproofness water absorption was approximately 50% of the reference group, mortar strength was still increasing at 180 d, and increased by 25% compare with the mortar at 14 d.(4) Ca(OH)2 the hydration products of cement were reacted with TEOS to stimulate the repair reaction,further clarify the process of capillary crystalline active materials repair pore and crack.TEOS was hydrolyzed and the active silica were produced, then it was reacted with Ca(OH)2 or Ca2+ to generate C-S-H gel in pores and cracks.The study will provide key technology for repair pores and cracks of concrete, improve the anti-permeability at the same time, theory and evaluation methods, meanwhile provide theoretical basis and evaluation methods for CCCW.