Abstract: All-light Weight Aggregate Concrete (ALWAC) and Sub-light Weight Aggregate Concrete (SLWAC) were prepared by absolute volume method, and were compared with Normal Concrete (NC) in terms of carbonation depth at different ages. The microstructure changes of NC and ALWAC before and after carbonation were compared by Mercury Intrusion Porosimetry (MIP). The results showed that ALWAC and SLWAC had better carbonation resistance than NC because of special internal curing effect of lightweight aggregate which led to more compact cement stone surrounding the ceramsite. The carbonation rate of ALWAC and SLAWAC also decreased apparently with the increasing of carbonation age. Microstructural analysis showed that after 28 days of accelerated carbonation experiment, the porosity of NC and ALWAC declined from 14.36% and 30.33% to 13.53% and 28.70%, respectively. The result quantitative explained the reduction of pore diameter and the augment of compactness by the intrusion of carbon which filled and refined a large number of pores and reacted with cement hydration products to generate CaCO₃. In addition, a model predicting the carbonation depth of lightweight aggregate concrete in consideration of ceramsite content was given.

Key words: light weight aggregate concrete, shale ceramisite, carbonation resistance performance, MIP, microscopic structure, carbonation depth prediction