Studies And Controls On Shrinkage Of Sulfoaluminate Cement Concrete

Sulfoaluminate cement concrete is known as a new type of concrete with low energy consumption, low carbon emissions and corrosion resistance, but it is easy to crack due to early-age shrinkage, which can induce many severe damages to concrete structures. So, present research is aimed to study early-age shrinkage and interior humidity reduction of sulfoaluminate cement concrete and find specific measures to reduce shrinkage and to improve the crack resistance of sulfoaluminate cement concrete.In the research, high-, moderate-, and low-strength concrete mix proportions were designed. The basic mechanical properties such as elastic modulus and compressive strength of the three series of concrete were measured. Based on isothermal calorimeter test, the degree of hydration of sulfoaluminate cement was determined.On the basis of the above study, experimental measurements on development of shrinkage and internal humidity of early-age sulfoaluminate cement concrete were carried out under both sealing and drying conditions. The development of shrinkage of sulfoaluminate cement concrete includes two stages. In the first stage when shrinkage of concrete is growing fast, shrinkage of sulfoaluminate cement concrete can reach a level in 2 hours while it takes 2 days for shrinkage of Portland cement concrete to reach the same level. In the second stage, shrinkage of concrete is growing slowly, using sulfoaluminate cement can dramatically reduce the drying shrinkage of concrete.In order to study the internal curing effect of pre-saturated lightweight aggregate on sulfoaluminate cement concrete, a large number of measurement on development of early-age shrinkage and internal humidity of sulfoaluminate cement concrete internal cured with pre-saturated lightweight aggregate were carried out under both sealing and drying conditions. Internal curing can dramatically reduce the autogenous shrinkage of sulfoaluminate cement concrete. The higher the strength of the concrete, the better the effect of the shrinkage reduction due to internal curing is. However, internal curing can’t reduce drying shrinkage. Based on the measurements on internal humidity distribution and development inside of sulfoaluminate cement concrete slabs with a larger scale, the conclusion can be obtained that internal curing can dramatically extend the period that internal relative humidity of sulfoaluminate cement concrete remains 100%.Based on the steel ring tests, the conclusion can be obtained that high-strength sulfoaluminate cement concrete has a better crack resistance than Portland cement concrete. Internal curing can improve crack resistance of sulfoaluminate cement concrete by a wide margin.In the end, the shrinkage prediction model and the humidity field prediction model which apply to sulfoaluminate cement concrete were presented. The development of shrinkage and internal relative humidity of different series of sulfoaluminate cement concrete can be well predicted using the models above.