Study On Early Age Chemical Shrinkage Test Method And Prediction Model Of Cement Paste

There are many test methods and theoretical prediction models for the early age shrinkage of cement-based materials,but there are few test methods and prediction models for chemical shrinkage,there are also some problems in the practical use of test methods and prediction models.This study focuses on the application of chemical shrinkage test methods and prediction models for cement paste,carried out the innovation and simplification of chemical shrinkage test method,the experimental fitting construction of prediction model and the preliminary study of chemical shrinkage compensation measures.The innovation and simplification of the chemical shrinkage test method for cement paste provides an early age chemical shrinkage test method based on three-dimensional size measurement.The early age chemical shrinkage volume ratios of ordinary Portland cement,reference cement and composite Portland cement paste were measured by this method,and the compensation ability of active magnesium oxide to the early age chemical shrinkage of ordinary Portland cement paste was measured;The research on the experimental fitting construction of the prediction model is to analyze and discuss the shortcomings of the theoretical calculation prediction model of chemical shrinkage of cement paste.According to the theoretical calculation prediction model and the experimental results,the chemical shrinkage test fitting prediction model of the above three kinds of cement paste is established,and make the experimental fitting prediction model compared with the ACI 209 autogenous shrinkage prediction model recommended by the American Concrete Association.（1）A chemical shrinkage test method based on three-dimensional size measurement was established.The test method can accurately and easily measure the early age chemical shrinkage volume rate of ordinary Portland cement,reference cement,composite Portland cement（fly ash）and ordinary Portland cement paste with active magnesium oxide.（2）The early age chemical shrinkage volume rate of different kinds of cement paste is different.Under the same curing age and water-binder ratio,the early-age chemical shrinkage volume rate of different types of cement paste from large to small is:reference cement>ordinary Portland cement>composite Portland cement（fly ash）.（3）The chemical shrinkage of cement paste is proportional to its total hydration heat.In the case of the same hydration time and water-binder ratio,the total hydration heat release of different types of cement paste at early age from large to small is:reference cement>ordinary Portland cement>composite Portland cement（fly ash）.（4）A fitting prediction model of chemical shrinkage test was established.The fitting prediction model of chemical shrinkage test can better fit the early age chemical shrinkage volume rate of different types of cement paste,the calculation coefficients k₁ and k₂ of ordinary Portland cement are 8.48 and 3.31,respectively.The calculation coefficients k₁ and k₂ of reference cement are 9.34 and 10.14,respectively.The calculation coefficients k₁ and k₂ of composite Portland cement are 2.27 and 6.01,respectively.By comparing the chemical shrinkage test fitting prediction model with the autogenous shrinkage prediction model,it is found that the test fitting prediction model can be used to predict the early age chemical shrinkage of cement paste.（5）Adding active magnesium oxide can effectively compensate the early age chemical shrinkage of ordinary Portland cement paste.When the water-binder ratio and curing age are the same:the volume expansion of active magnesium oxide content of 10%>the volume expansion of active magnesium oxide content of 5%.