Effect Of Fly Ash Content And Curing Condition On Ca（OH）₂ Content And Carbonation Of Cement-based Material

Because of the increasingly serious environmental pressures, the concrete research has developed into tendencies that were many kinds of mineral admixture and high volume mineral admixtures. The Portland cement in today’s engineering has been illegally mixed hybrid materials, and in the concrete mixing station again added a lot of admixture, and the moist-curing time at early ages was usually not sufficient in the construction site. Under the above conditions, the cement concrete already lack of Ca(OH)2 seriously. Because of the improvement of admixture and mineral admixture in concrete, reduction of the moist-curing time at early ages, so the concrete carbonation resistance has further decline.For the above phenomenon, this paper mainly studied about the effect of fly ash content and curing condition on Ca(OH)2 content and carbonation of cement-based material. In the condition of using Portland cement, based on XRD diffraction test, the variation of Ca(OH)2 content in cement paste with fly ash content was tested; based on accelerated carbonation test, the carbonation depth of cement paste and concrete were measured, and the influence of concrete carbonation resistance with the fly ash content and moist-curing time at early ages was researched and analyzed. At last, this paper predict the fly ash concrete carbonation life in different CO2 concentration conditions.Results of the experiments indicate.(1) Based on using I Portland cement, the Ca(OH)2 content and anti-carbonation of the cement paste obviously decreased with fly ash increasing.(2) The Ca(OH)2 content in cement paste was changed greatly with different curing conditions. The Ca(OH)2 content in cement paste of steam-curing was more than that of moist-curing.(3) The carbonation depth of the binder hardened paste which composed by Portland cement and fly ash was increased with the moist-curing time at early ages reducing and the fly ash content increasing.(4) Under conditions of different moist-curing time at early ages, the accelerated carbonation depth D and the accelerated carbonation time of the fly ash concrete were shown to satisfy the general formula: D=kt0.5.(5) Under the same condition of water binder ratio and moist-curing time at early ages, the carbonation coefficient of concrete increased obviously with fly ash content increasing. When the fly ash content was more than 50%, carbonation coefficient was significantly increased with the increase of fly-ash content, and then the carbonation resistance of concrete had been a serious shortage.(6) Under the same condition of water binder ratio and fly ash content, the carbonation coefficient of concrete decreased obviously with moist-curing time at early ages decreasing, the variation was multiplied by a power function:-bk=ax.(7) The concrete carbonation life was obviously decreased with CO2 gas concentration in the environment increasing.(8) Nowadays in the atmosphere with approximately 0.04% CO2 gas by volume of air, in order to ensure the carbonation durability of 0.45 water to binder ratio concrete to reach more than 50 a design life, it is necessary that the moist-curing time at early ages shouldn’t less 3 days and the fly ash content should be less than 40%.