American test methods for evaluating the durability of cement based materials agianst external sulfate attack
CAO Zheng-liang,YUAN Xiong-zhou,XING Feng,and DING ZhuCollege of Architecture and Civil EngineeringShenzhen UniversityShenzhen 518060P.R.China
Sulfate attack is one of the most important factors affecting concrete durability and has been extensively investigated,but not completely understood.This paper attempts to clarify some related problems.Firstly,what mechanism needs to be involved for the action to be described as sulfate attack? The discussion of the two forms of sulfate attack leads to a recommendation for distinct nomenclature.Secondly,recent tests,both long term and accelerated ones, need reworking.Most of the knowledge of sulfate attack has been developed from laboratory studies involving relatively simple chemical systems of pure materials,yet in actual practice the situation is more complicated Thirdly,the standards and guides for the classification of the severity of exposure of structures to sulfates lack calibration of the various classes of exposure.This paper describes the progress and consequences of sulfate attack and some preventive measures.It discusses the nature of the manifestation or the mechanisms of sulfate degradation.Factors affecting concrete durability are discussed including the exposure conditions from continuous immersion to cycles of wetting and drying.In light of the overall situation and near-future improvements,all the factors are examined accelerating the rate of deterioration caused by sulfate.The factors analyzed include different concentration of SO~(2-)_4,different temperatures,different experimental solution,different pH controlled procedure and dry-wet circulation.The differences between laboratory conditions and field exposure are pointed out.Reviewed in this paper are the current American standards for specifying cement-based materials to prevent deleterious reactions with external sulfates,and for predicting the performance of concrete exposed to external sulfate.The applicability and reliability of these standards are criticized and the deficiencies in them are pointed out.Finally,recommendations are presented for the development of improved standard test methods.
【CateGory Index】： TU528
【CateGory Index】： TU528