Study On The Shrinkage Reducing And Its Mechanism For RCC

With the construction of RCC tall dam and tall and thin arch dam, the demands of material performance become higher and higher. Therefore, the researches on the RCC shrinkage and crack resistance become much more requisite. Combined with the science and technology program of State Power Company, "key technology researching of Long Tan Project", this article lay emphasis on the experimental investigation on the new technique of shrinkage reducing and crack resistance of RCC. On the basis of the analysis and studies on the shrinkage of RCC and affecting factors, this paper applies the technique of shrinkage reducing on RCC for the first time and completes the related indoor test.The experimental research results of mortar indicate that admixing and permeating shrinkage reducing agent can all reduce its dry shrinkage and self dry shrinkage effectively. Admixing shrinkage reducing agent can improve decentrality of cement particles and working performance of mortar but decrease its compression resistant at 3d and 7d slightly, but has little effect on its compression resistant at 28d. This paper chooses two kinds of shrinkage reducing agent, "JM-SRA 和 AS20" , to have the test on the performances of RCC. Admixing these two shrinkage reducing agents can all obviously improve the physical mechanics performances of RCC such as compressive strength, cleavage crack tensile strength, axial tension performance, axes compressive strength and static pressure modulus of elasticity. Admixing JM-SRA and permeating AS20 can all effectively reduce the dry shrinkage of RCC, and admixing JM-SRA have better results: it can reduce 60% dry shrinkage at 1d~3d, and reduce more than 35% dry shrinkage at 90d. The test on crack resistance and analysis on crack resistance factors indicate that admixing the shrinkage reducing agent can reduce the plastic constraint crack of RCC at early stage, improve its crack resistance performance,By the analysis methods of recent and modern period such as the XRD and microporous structure test, this paper also researches on the function mechanism of shrinkage reducing agent on cement based materials and RCC. The test results indicate: the shrinkage reducing agent can increase the ζ —electric potential value of cement particle in early stage of hydration, reduce the water-binder ratio, reduce thesurface tension of pore liquid in hardened cement, reduce the additional pressure under curved liquid surface in the capillary bore in hardened cement and decrease the macroscopic stress who arises the shrinkage of hardened cement, improve the pore structure of hardened cement and decrease the relative ratio of minipore; moreover, the reducing of water-binder ratio can also increase the compatibility of RCC in the late stage, slow the velocity of moisture migration, and accordingly restrain shrinkage effectively.