Experimental Study On Temperature And Humidity Development And Early-age Shrinkage Of Self-compacted Lightweight Aggregate Concrete

Compared with normal concrete,self-compacting lightweight aggregate concrete(SCLC)has such characteristics as high slump(generally 240-270mm),large dosage of cementitious materials,high sand ratio and low elastic modulus,which will lead to a great difference between its basic properties and that of normal concrete.In general,most of the shrinkage and cracking of concrete occur in early age(28 days ago).Various properties of early-age concrete change rapidly with time,and when tensile stress and crack resistance of concrete are limited by shrinkage,they change and interact with each other,which determines the process and performance of early cracking of concrete.Therefore,the mechanical property,shrinkage deformation and internal temperature and humidity development of concrete at early age are the core problems of concrete early cracking.In view of the characteristics of SCLC,this paper focuses on the experimental study of its early age mechanical properties and the law of shrinkage deformation and internal temperature and humidity development,providing a basis for structural design and early crack control.Firstly,of proportion of comprehensive consideration of the existing calculation methods and relevant test,fixed sand volume method and absolute volume method is adopted to improve the calculation of concrete mixture ratio,and configuration of different water cement ratio of SCLC,changing the dosage of fly ash,silica fuine,different aggregate type and saturated degree of aggregate to study materials on the workability and mechanical properties of SCLC,provide a reference for the configuration of SCLC.Secondly,the temperature and humidity measurement test of concrete was designed to measure the development history of SCLC temperature and humidity at different ratios.Based on this,the development and distribution characteristics of concrete with different strength,different curing conditions,different aggregate characteristics and different proportions were investigated under the effect of cement hydration and heat and humidity conduction.Finally,the early free deformation of SCLC was measured accurately and completely by means of the contact linear measurement method,the full deformation curve of its early age was obtained,and the correlation between shrinkage deformation and the development law of internal temperature and humidity was analyzed.The effects of different water-gel ratios,different curing conditions(sealing or drying),aggregate characteristics(aggregate type,water absorption rate,pre-saturation degree)and material proportion on early shrinkage deformation were tested and the regularity was discussed.The results showed that the early shrinkage of SCLC was mainly caused by drying and water loss caused by external drying.The autogenous shrinkage caused by self-drying was relatively small,and the proportion of external drying and shrinkage increased with the reduction of water-binder ratio.However,due to the water-absorbing and water-storing effect of light aggregate,the effect of water-binder ratio on SCLC's long-term autogenous shrinkage was not significant.The incorporation of fly ash has an inhibitory effect on the early age contraction of SCLC,but the inhibitory efFect is not obvious when the fly ash content is low.The microstructure of SCLC can be improved by adding fly ash and silica fume.After adding 2%silica fume,the strength of concrete decreases and the early contraction increases after adding silica fume.Therefore,from the perspective of increasing SCLC strength and controlling early contraction,the optimal amount of silica fume compound mixing is about 2%.Light aggregate after prewetting has an internal curing effect on SCLC.After prewetting,the autologous contraction and total contraction of the specimen are significantly reduced,and the contraction curve changes relatively gradually with age.