Experimental Study On Shrinkage And Crack Resistance Of Self-compacting Lightweight Aggregate Concrete

Self-compacting lightweight aggregate concrete is a new type of high performance concrete,which has broad application prospects in engineering.The lightweight aggregate selected in this paper is 900 grade shale ceramsite with a cylindrical compressive strength of 6.5 MPa.The self-compacting lightweight aggregate concrete with good basic working performance and basic mechanical properties is obtained by adjusting the mix design several times.The development law of free shrinkage and restrained shrinkage under the combined action of autogenous shrinkage and drying shrinkage and the crack resistance performance are studied.The following research results are obtained:The main contents and conclusions are as follows:(1)Through the adjustment of mix design,it is found that spherical fly ash ceramsite can not make SCLC50 with strength up to 50MPa,and the effect of superplasticizer on fluidity is very sensitive,so the dosage of superplasticizer must be very accurate.In the basic working performance and basic mechanical properties test,fly ash can effectively improve the working performance,but too much fly ash will lead to a decline in mechanical properties;silica fume can effectively improve mechanical properties;pre-wetting light aggregate can reduce the brittleness of SCLC.The mixing ratio of the following groups has good performance:the content of fly ash alone should be controlled at 20%～25%;the content of silica fume with 25%fly ash-silica fume should be controlled at 2%～4%;the pre-wetting time of lightweight aggregate should be about 1 hour.(2)The shrinkage of self-compacting lightweight aggregate concrete is studied by free shrinkage and restrained shrinkage tests.The results show that:①autogenous shrinkage is the main restrained shrinkage of SCLC at early age,and drying shrinkage is the main restrained shrinkage with the development of age;②fly ash can restrain the shrinkage of SCLC,but too much fly ash can reduce the performance of concrete,and the optimum content should be controlled between 20%and 25%;③silica fume can improve the compressive strength and splitting of SCLC.Strength,but will increase constrained shrinkage.④Pre-wetting treatment of aggregate can delay the cracking age and reduce the brittleness of SCLC.(3)The stress analysis of concrete ring in ring restraint is carried out,the restraint tension stress caused by shrinkage is calculated,and the crack resistance is analyzed.The results show that:①when the water-binder ratio is below 0.3,the cracking risk coefficient decreases significantly,which improves the cracking resistance of SCLC;②when the fly ash content is 20%,the cracking resistance is the best;③ when silica fume is added,the cracking risk coefficient increases and the cracking risk coefficient increases;④when the pre-wetting time of aggregate is controlled for 1 h,the cracking risk coefficient can be reduced and raised.High SCLC cracking resistance,while saving construction time.Although the above conclusions can not fully understand the self-compacting lightweight aggregate concrete,the future durability test,micro-mechanism analysis and prediction equation will be the research direction of researchers.