Experimental Research On Key Technologies Of Non-Steam Curing Concrete

The rapid development of prefabricated buildings places higher requirement on precast concrete components.In order to accelerate the demoulding speed of precast concrete components and improve the production efficiency,1d compressive strength of precast concrete components needs to be increased.The steam curing can significantly improve 1d compressive strength of concrete and mold turnover efficiency.But,the high energy consumption of steam curing does not meet the environmental protection concept of energy conservation and emission reduction.And steam curing has adverse effect on the later performance of concrete.So,it is extremely necessary to conduct non-steam curing production of precast concrete components.In order to achieve non-steam curing production of precast concrete components,experimental research on key technologies of non-steam curing concrete was carried out in this paper.Firstly,the compound preparation of early strength agent was studied.Early strength agents suitable for summer conditions(25-35?)and winter conditions(5-15?)were selected from commonly used early strength agents by mortar test.Then,the compound preparation of early strength agents was studied by orthogonal test at different ambient temperatures(summer conditions,winter conditions).And summer-type early strength agent suitable for summer conditions and winter-type early strength agent suitable for winter conditions were obtained.The summer-type early strength agent consists of calcium formate,triethanolamine and methanol(accounting for 1.5%,0.04% and 0.03% of the cementitious material respectively).The winter-type early strength agent consists of calcium formate,calcium nitrate and methanol(accounting for 1.5%,0.5%,and 0.04% of cementitious material respectively).Under summer conditions,the summer-type early strength agent can increase 1d compressive strength of C30 concrete from 13.6MPa to 16.1 MPa,achieving the goal that 1d compressive strength of C30 concrete reaches 50% of design strength.Under winter conditions,incorporation of winter-type early strength agent can achieve short-term low-temperature steam curing of C30 concrete.The constant temperature curing at 60? for 4 h can make the 1d compressive strength of C30 concrete reach 16.5 MPa,which exceeds 50% of its design strength.Secondly,the preparation and properties of calcium silicate hydrate were studied.The waste liquid of acetic acid-treated recycled aggregate was used as calcium source,and calcium silicatehydrate was prepared by chemical co-precipitation method.The obtained hydrated calcium silicate is porous flocculent particle that the particle size disperses between 0.5 and 1 ?m.Under the condition of 20±2°C,incorporation of 0.5% hydrated calcium silicate can increase 1d compressive strength of C30 concrete from 9.8 MPa to 12.2 MPa and the 28 d compressive strength from 35.1MPa to 40.5 MPa.Also,the resulting hydrated calcium silicate can effectively improve the durability of the concrete.Thirdly,the preparation and properties of in-situ growth of hydrated calcium silicate on the surface of fly ash was studied.The in-situ growth of hydrated calcium silicate on the surface of fly ash was achieved by chemical co-precipitation.And,the effect of in-situ growth of hydrated calcium silicate on the surface of fly ash on the performance of concrete was compared with that of fly ash.The results showed that the in-situ growth of hydrated calcium silicate on the surface of fly ash can effectively improve the early strength of concrete and improve the durability of the concrete.Finally,experimental studies of microwave curing concrete were conducted.Using microwave oven to heat the concrete by spacer heating can improve the strength of the concrete quickly and efficiently.And,the concrete cured by microwave were cured in water,which can effectively increase the concrete's late strength.And,microwave curing can refine the concrete pore structure.