Research Of Double Expansive Sources Admixture For Hydraulic Mass Concrete

Concrete is a brittle material, so its compressive strength is high, but tensile is low. When the concrete is restrained, shrinkage will result in tension stress in the concrete. And when the tension stress is beyond the tensile strength of the concrete, cracks arise in the concrete. Because of the cracks, the strength and reliability of the concrete are reduced.Compared with the other shrinkages of hydraulic mass concrete, temperature shrinkage is the most prominent. Because of the huge volume of the hydraulic mass concrete, the heat of the cement hydration emits from the surface of the concrete. So a great deal of heat cumulates in the centre of the concrete, which will lead to a high and long temperature rise, a long temperature drop period and huge amounts of temperature shrinkage. Because of the restraint of the base, the great temperature shrinkage will cause great tension stress and cracks in the concrete of the dam foundation. In hydraulic mass construction, water cooling system, adding ice and medium or low heat cement are introduceed to reduce temperature rise. After dam construction technology with MgO concrete springing up, micro-expansive concrete with MgO is applied to compensate temperature shrinkage of hydraulic mass concrete, for the sake of reducing temperature cracks. Because that the content of MgO in cement is restricted by national cement standard, When MgO concrete temperature shringkage compensating, the expansive capacity of the MgO concrete is not enough.A double expansive sources admixture is introduced to cover the shortage of existing expansive admixtures in temperature shringkage compendating of hydraulic mass concrete. Firstly, two kinds of early expansive admixtures and later expansive admixtures are used in study. Next, through the expansion ratio and strength experiments of cement mortar of early expansive admixtures and later expansive admixtures, an early expansive admixture and a later expansive admixture are picked out. Then, through the expansion ratio and strength experiments of cement mortar, which early expansive admixture and laterexpansive admixture mix each other by different compound proportion, and according the analysis of results, reasonable compound proportions are pick out as the double expansive sources admixture that are fit for temperature shrinkage compensating of hydraulic mass concrete.The double expansive sources admixture supplies not only enough early expansive change but also the steady later micro-expansion. The early expansion establishs the pressure stress that can delay the crack time in the concrete. And the steady later micro-expansion is very suit for the temperature shrinkage compensating of the hydraulic mass concrete.