Study On Autogenous Shrinkage Properties Of Cementitious Materials

Concrete is one of the most widely used artificial materials in the world nowadays.With the progress of science and technology,high-performance concrete is widely used,and people gradually realize the influence of self-desiccation effect on concrete with low waterbinder ratio.The autogenous shrinkage is the direct result of the self-desiccation effect.For the concrete with low water-binder ratio,the proportion of autogenous shrinkage in the total shrinkage may exceed the dry shrinkage and become the main factor of cracking.In this thesis,the cement paste was taken as the main research object,combined with resistivity experiment,relative humidity test,shrinkage test,compressive strength test,heat of hydration test and other experiments,and the corresponding exploration was conducted around autogenous shrinkage.The main research contents and methods are as follows:(1)Combined with the resistivity experiment and the existing conclusions,the influence of water-cement ratio on the self-desiccation effect and hydration process of cement paste was comprehensively explored through the relative humidity experiment,compressive strength test and vertical prism shrinkage experiment.The results showed that the lower the water-cement ratio was,the more obvious the self-desiccation effect was.A shrinkage analysis method based on stress ratio is presented.(2)Based on the cement paste with water-to-binder ratio of 0.3 and naphthalene superplasticizer dosage of 0.5%,slag with different dosage was added to explore the influence of slag content on the autogenous shrinkage and hydration process of cement paste.The results show that adding slag will increase the autogenous shrinkage of cement paste,and the slag will slow down the hydration reaction at the early stage and accelerate the hydration reaction at the later stage.(3)Based on the cement paste with water-binder ratio of 0.4,metakaolin with different dosage was added to explore the influence of metakaolin content on the process of autogenous shrinkage and hydration of cement paste.The results showed that the addition of metakaolin would lead to the advance of induction and setting period and acceleration period of hydration.The autogenous shrinkage measured from the age of 24 h was increased with the inclusion of metakaolin.(4)Based on the cement paste with water-to-cement ratio of 0.3,aggregate with different volume fraction was added to explore the limitation of aggregate on autogenous shrinkage,and the autogenous shrinkage was simulated and predicted based on Pickett model.(5)The advantages and disadvantages of corrugated tube method and vertical prism method in measuring autogenous shrinkage are compared,and the actual conversion rate of corrugated tube method and the limiting effect of shell on autogenous shrinkage are explored.The corrugated tube method can measure the autogenous shrinkage from the beginning of hydration,while the vertical prism method has better repeatability and is easier to operate.