Effect of secondary curing on the performance of microwave cured concrete

Abstract

In this paper, microwave curing and secondary water curing were combined together to cure C30 concrete. Based on this, the influence of secondary curing on the performance of concrete was explored. Compared with air cured concrete, microwave curing increased the 1 d compressive strength of C30 concrete from 4.7 MPa to 15.9 MPa. However, microwave curing + air curing (MW + A) decreased the 28 d compressive strength from 34.7 MPa to 30.2 MPa. On the contrary, microwave curing + water curing (MW + W) increased the 28 d compressive strength rather than reducing it. Then, the chemically bonded water content was measured, and the results indicate that although microwave curing can improve the hydration degree of cement in the early age, it can reduce the later hydration extent. However, the secondary water curing can enhance the hydration degree in the later stage. The SEM results show that microwave curing can cause cracks between cement matrix and aggregate, and weaken the interfacial transition zone (ITZ). However, secondary water curing can eliminate these cracks and strengthen the ITZ. Additionally, MW + W curing can refine the pores in concrete, and make concrete more compact, decreasing the porosity from 17.55% to 14.23%. Hence, MW + W curing also improved the carbonation resistance of concrete. More interestingly, MW + W curing can reduce the mass loss ratio of steel corrosion, and improve the corrosion resistance of reinforced concrete. This shows that microwave curing is not only suitable for plain concrete, but also for reinforced concrete.