Papers by Author: Ou Geng

Abstract: Studies about the resistance of carbonation capability of fly-ash (FA) concrete at different initial curing regimes and exposure time through accelerated carbonation experiments were made. Firstly, 30% replacement ratio fly-ash concrete specimens were fabricated and cured in 20°C, 30°C and 40°C water for 3d, 7d, 14d and 28d respectively, and cured in a standard air environment (20±2°C, relative humidity ≥95% ) for 28d. As a comparison, ordinary Portland concrete (OPC) specimens were also made and cured in 30°C water for 7d, and standard curing for 28d. After the initial curing, all the specimens were taken out and placed indoor natural environment. When specimen age reach 30d, 60d and 120d, 2 weeks accelerated carbonation experiments were made and concrete carbonation depth were measured. In addition to this, hydration degrees of fly ash at different initial curing conditions were measured using the selective dissolve method. Results show that the initial curing conditions play an important role in the carbonation resistance of FA concrete. Initial water curing is beneficial to the development of carbonation resistance of FA and OPC concrete. Prolonging initial curing time and increasing curing temperature is beneficial for the carbonation resistance of FA concrete. For the same curing conditions, carbonation rate of FA concrete is usually higher than OPC concrete, but with the increase of initial curing temperature, the difference can be reduced.

Abstract: In order to study the influences of initial curing conditions on fly ash (FA) cement concrete durability, fly ash cement samples with 30% replacement ratio were fabricated and cured in water at 10°C, 20°C, 30°Cand 40°C for 3d, 7d, 14d and 28d respectively. Hydration degrees of fly ash at early age were measured using the selective dissolve method. Correspondingly the pore structure and morphology of FA-cement mortar and compared cement mortar were studied by using MIP and SEM methods. Then early age compressive strengths of FA-cement concrete and compared normal cement concrete were tested. Experimental results show that initial curing temperatures and ages are important factors to fly ash early age hydration degree, FA-cement system microstructure, morphology and early age compressive strength etc. High curing temperatures and longer curing time can lead higher fly ash hydration degree, and then higher compressive strength of FA-cement concrete, and make the micro-structures of fly ash-cement system denser.