Effects of nano-SiO_2 and secondary water curing on the carbonation and chloride resistance of autoclaved concrete

摘要

Nano-SiO2 (NS) was used to replace cement in autoclaved concrete at replacement levels of 0%, 1%, 2%, and 3%. The concrete specimens were cured through three different methods: (1) standard curing (SD), (2) autoclave curing (AC), and (3) AC + secondary water (SW) curing. Accelerated carbonation and Coulomb charge tests were periodically conducted on the specimens. XRD, TG-DTG, SEM, and MIP tests were also performed to investigate the hydration products and concrete microstructure. Results indicated that AC concrete had higher porosity, larger average pore diameter, and larger pores than SD concrete, which led to increased chloride penetration and carbonation depth of AC concrete. After NS introduction and SW curing, the hydration degree of AC cement was promoted and additional tobermorite and Ca (OH)(2) were produced. Consequently, the porosity, average pore diameter, and pore size of AC concrete were significantly reduced. As a result, the carbonation and chloride resistance of AC concrete were effectively improved, even reaching or exceeding that of SD concrete. The optimal NS replacement level was found to be 2%. (C) 2019 Elsevier Ltd. All rights reserved.