Suppressing Measure And Suppressing Mechanism Study On Sulfate Attack Of Concrete

There are two forms of sulfate attack for concrete corrosion,they are physical crystal attack and chemical crystal attack.Physical crystal attack means that when the tensile stress as a result of crystal of salt in the interspace of concrete exceeds the ultimate tensile stress of concrete,the concrete will crack,which often occurs at the concrete between the water and air.Chemical crystal attack consists gypsum attack and wollastonite attack,the volumes of these substance are large than the original substance,they bring tensile stress which exceeds the ultimate tensile stress of concrete,so the concrete cracks.The resistance to sulfate attack of gel material and its compactness are the most two importance factors for the resistance to sulfate attack of concrete,so when we want to restrain sulfate attack of concrete,these two factors must be taken into account first of all.This research relies on scientific research project of China Railway Eighth Civil Engineering Group.In this research,we use two sulfate attack restraining measures which are fly ash and preservatives,and we use many test methods to evaluate restraining effect to sulfate attack of these two sulfate attack restraining measures.These methods evaluate the restraining effect to sulfate attack of concrete respectively from improvement of the performance of the resistance to sulfate attack of the gel material,improvement of compactness of concrete and improvement of the performance of the resistance to sulfate attack of the concrete. Outcome of test indicate:fly ash and preservatives improve the performance of the resistance to sulfate attack of the gel material,the compactness of concrete and the performance of the resistance to sulfate attack of concrete,and even more the logical mixing ratio(mass)of fly ash is about 20%,and the logical mixing ratio(mass)of preservatives is about 2%.Now there are no national standard about test and evaluate of the resistance to sulfate attack of concrete.But drying-wetting cycles method is put forward when GBJ 82-^**＜Standard Test Method of Longterm Performance and Durability of Ordinary Concrete＞are recensed.Drying-wetting cycles method is a very effective method for the evaluation of the resistance to sulfate attack of concrete,but it is a heavy and longterm job.So we want to put forward a simple method according to pivotal factors(performance of resistance to sulfate attack of gel material and its compactness)of the resistance to sulfate attack of concrete.It as follows,when the 56 day-resistance modulus can not bellow 0.8(amending quick method is used),and filter modulus of chlorine ion of concrete can not exceed 1.0E-8cm²/s,we can say that the concrete has the performance of resistance to sulfate attack.Corrosion Trend Theory is put forward according to the test result in this research, it well explain the abnormal phenomena of each method,and it is the theory basis of new method.