Effect of Supplementary Curing after Steam-Curing on Performance of Concrete

Abstract

When the low strength grade of steam-curing concrete is produced, the temperature which the concrete leaves steam-curing kiln is about 20°C commonly. The temperature difference is too large between the environmental temperature and the temperature which the concrete leaves steam-curing kiln when the daily average temperature drops to 10°C. Because the steam-curing concrete is cooled rapidly, a large of crack will be produced in concrete and the internal structure of concrete will be damaged normally. Then the performance of concrete will be influenced badly. In order to improve the negative effect on concrete by steam curing, the different supplementary curing is used after steam curing. The C30 concrete is made in this research. The daily average temperature is 5°C~10°C and the minimum temperature is-6°C during the test. After the concrete is formed, it is placed in 20°C environment for 2h first. Then the concrete is heated to 55°C in 2h and maintained for 8h in the steam-curing kiln. In the end, the concrete is cooled to 20°C in 3h. After steam curing, the standard curing and covering by wet fabric or film outside are used separately for concrete. The supplementary curing time is 1d, 2d, 3d and 4d. Then the concrete is placed in natural environment to 28d. The microstructure of hydration products are observed by electron microscope. The density of concrete is analyzed by the result of the 28d saturated water content, softening factor and 28d rapid carbonation depth. The mechanical properties of concrete are researched by the result of the 28d strength. When the concrete adopts standard curing or covering by film after steam-curing, the saturated water content and 28d rapid carbonation depth of the concrete will reduce, but the softening factor and 28d strength of the concrete will increase with the time. The performance of concrete which adopts covering by wet fabric after steam-curing is worse than that adopting standard curing. At the same time, the saturated water content and softening factor of concrete change little. Covering by wet fabric is worse than no covering or similar. In the test environment, the performance of the steam-curing concrete with each supplementary curing is worse than that of the concrete with standard curing. The standard curing is the best supplementary curing in this test. But covering by film is a worthy supplementary curing from economy and practicability. Covering by film for 4d, the 28d strength of steam-curing concrete is 87 percent of that of the concrete with standard curing and exceeds Design grade. Its saturated water content is 1.50% and softening factor is 0.932. Its rapid carbonation depth is close to that of the concrete with standard curing and its microstructure of hydration products is preferable.