| This paper unfolds engineering disposition and theoretical research of Negative Temperature High Performance Concrete (NTHPC) with the damage of many factors motivation, the project background based on Qing-Zang railway engineering, which is one of four-emphasized engineering during the tenth Five-plan. Due to the difference of environment of construction and service between NTHPC and ordinary concrete, and therefore durability of NTHPC is required to higher level. At a first, NTHPC must avoid frozen damage at early age and possess anti-freezing property at later period, in order to meet engineering practicable application need, and this are two emphasized and difficult problems, as for NTHPC; By means of mechanism analysis about deicing-agent ingredient and anti-freezing at early period, adopting composite technique routine of mineral addition+anti-freezing element+water-reducer4- air-entraining+anti-erosion of steel component etc, based on orthogonal experimental approach, FD-1 composite functional admixture was manufactured, which has more property and orientation on Qing-Zang railway. And different strength grade NTHPC has been manufactured based on the FD-1, Influence on the durability of NTHPC such as anti-sulfate corrosion, chloride penetration, freezing-thaw, shrinkage and antifriction etc is studied. The compatibility and harmony among workability, mechanical grade and durability are optimized, with the ground of adjusting composition and dosage of FD-1;After analyzing anti-freezing damage mechanism, it is concluded that temperature is main factor, which affects structure and property of concrete. After two processes of temperature-elevation of hydration heat and temperature-descent of cold-environment, there is original damage in concrete and its existence leads to temperature fields, as results in temperature damage on transition phase > aggregate and cement mortar of concrete. Main factors impact on frozen-damage of concrete are water, temperature and pore structure. The author hypothesizes anti-freezing threshold interface structure model, its token is that water nearby plump micro-pore possesses continuity of migration and mechanical strength range fluctuating 3.3~4.0Mpa, and they are two basic premise conditions to realize anti-freezing property of concrete at early age.Adopting FD-1 admixture, C50 concrete can be obtained, which has excellent adaptability for environment temperature ?5 C; Self-shrinkage of concrete is inevitable, and its variation tendency based on w/c and hydration age, FD-1 has wonderful inhibition for self-shrinkage, and meanwhile anti-friction property can be promoted. Two-addition technique of flying ash and silica fumecan meliorate durability of concrete; Air-entraining admixture possesses anti-freezing, descending ice point, and improving workability, and thereof it should be used in concrete. But controlling its dosage is very important to avoid strength loss. There is correspondence in evaluating sulfate resistance of cement paste by three test methods such as rapid boiling, gypsum mixing and wet-dry test. High strength grade cement can meliorate property of sulfate resistance. And chloride-resistance property is promoted by increasing dosage of cementttious materials; there is obvious difference on chloride-solidified performance of different cement variety. When CsA content is low, anti-chloride penetration property can be descent. According to the experience formula of Feng Naiqian and N.S.Berke, M.C.Hicks, diffusion coefficient is calculated respectively and compared. It is concluded that the latter is 2.05 ~ 2.30 multiple than the former, and Feng's formula approaches the practical diffusion coefficient of NTHPC.By means of XREK SEM, MIP, BET modern testing apparatus and avenue, Reinforced durability of NTHPC mechanism by FD-1 is studied. It is proved that mineral admixture can prompt pore tiny, promote interface station and decrease CH phase. Ca(NO2)2 can activate hydration reaction at early age, but it harasses migration mechanism of water in mi... |
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