The Effects Of Steam Curing Cement Paste Performance Factors

Steam curing could improve the early strength of concrete, expedite the circulation of matrixes and increase the efficiency of production,making it a common production techniques to make concrete products.steam curing process exerts some influences on the physical and mechanical properties,volume stability and durability of the high strength concrete whose evolution in property exist differences compared to the standard cured concrete. In allusion to the technical problems of the railway beforehand stress concrete in our country, and based on the steam curing-related parameters(rest period, thermostatic period and thermostatic temperature)and the mineral additives,the thesis adopt a systematic study on their influences of the steam curing cement paste,expatiate their function and affective mechanism on the hydration characteristics,strength characteristics and microscopic construction.The main research activities and achievements were as follows:1. The influence of curing system,steam curing-related parameters and mineral additives on the chemically combined water and compression strength of steam curing concrete paste was studied. The chemically combined water and compression strength of steam curing concrete paste obviously exceeded the standard curing concrete paste, the difference of them gradually decreased after 28 days, the chemically combined water was to some tune, but the compression strength of standard curing concrete paste had passed the steam curing concrete paste.With a longer test period,a shorter thermostatic period and a lower thermostatic temperature,the hydrating and mechanical properties of steam curing concrete paste could be evidently improved, the disadvantaged influence of high temperature on the distributing of hydration production and the development of later compression strength. Therefore, the rest period should be 2 to 4 hours,thermostatic period should be 6h to 8h and thermostatic temperature should be40℃to 60℃. Following with the progressive increase of fly ash and mineral slag, the chemically combined water and compression strength of composite material showed a downtrend, the degressive range of chemically combined water of steam curing test specimen was less.When the mineral additives of fly ash and mineral slag exceeded 30 percent of all paste material, the compression strength of steam cured samples would be under the standard curing at the age of 28d and 56d. 2.The influence of curing system,steam curing-related parameters on the hydrating products's form and appearance of steam curing concrete paste. The process of steam curing did not alter the form of mostly hydrating products of concrete paste. Under the condition of steam curing system, hydrating products of concrete paste mainly engendered during the steam curing phase, however, under the condition of standard curing, the form of hydrating products is a sustained process. There was no influence of rest period on the main form of hydrating product, but it caused greater influence on micro-structure of hydrating products. The form and micro-structure of hydrating products existed obvious differences under diverse thermostatic period and thermostatic temperature.3.The influence of curing system,steam curing-related parameters on the dry shrinkage rate of steam curing pure concrete sand mortar. The dry shrinkage rate of standard curing concrete sand mortar evidently exceeded the steam curing simples at the same age. Extend rest period and thermostatic period,increase thermostatic temperature also could reduce the dry shrinkage rate of standard curing concrete sand mortar, evidently improve its volume stability. The dry shrinkage rate of standard curing concrete sand reduced following the increase of fly ash and mineral slag, When the mineral additives of fly ash exceeded 30 percent of all paste material, the degressive range of dry shrinkage rate began to reduce.