碳化混凝土硫酸镁盐结晶破坏微观分析

Micro-analysis of MgSO4 Crystallization of Carbonation Portland Cement Concrete

在恒温恒湿环境[温度（20±1）℃，相对湿度（60±5）％]条件下，对掺30％粉煤灰的混凝土试件（FA30，水灰比为0．45）和水灰比为0．55的混凝土试件（PC0．55）快速碳化20d与未快速碳化的混凝土试件半浸泡在10％硫酸镁溶液中，浸泡150d后混凝土试件水分蒸发区的破坏形貌、强度损失率及其微观进行分析。结果表明：碳化是混凝土蒸发区发生硫酸镁结晶的前提，碳化深度越大，混凝土破坏越严重。掺加粉煤灰的FA30比PC0．55更易碳化，强度损失率越大；快速碳化20d后，FA30碳化深度为15．4mm，强度损失率为42．2％，PC0．55碳化深度为9．3mm，强度损失率为20．5％。经过150d浸泡后，未快速碳化的FA30的水分蒸发区表层10mm也被碳化，试件出现了硫酸镁盐结晶破坏，强度损失率为22％，PC0．55水分蒸发区碳化不明显，强度没有损失。

The accelerated carbonation for 20-d concrete and non-carbonated concrete specimens were partially immersed in 10% MgSO4 solution under constant conditions （i.e., T （20±1）℃, relative humidity （60±5）% and 150 d）. The results show that concrete carbonation is the precondition of occurrence of MgSO4 crystallization in the evaporation zone of concrete and larger carbonation depth causes severer concrete scaling. The carbonation depth of concrete with fly ash （FA） of 30% and a water to binder ratio of 0.55 （FA30） is 15.4 ram, and that of the concrete with a water to Portland cement （PC） ratio of 0.55 （PC0.55） is 9.3 mm after 20-d accelerated carbonation, and the compressive strength loss rates of FA30 and PC0.55 are 42.2% and 20.5% after 150-d partial immersion in MgSO4 solution. For the non-carbonated FA30, the carbonation depth of evaporation zone of concrete specimen is approximately 10 mm after 150-d exposure, resulting in the compressive strength loss of 22%. However, the non-carbonated PC0.55 concrete does not show clear carbonation depth in the evaporation zone after 150-d exposure, and there is little compressive strength loss.