Experimental Research On The Mechanical Properties Ofprecast Members Joint Concrete

In the assembly integral building structure,the joint is the key part that affects the mechanical performance of the assembly structure,and the wet connection is the most important connection mode of the current assembly structure.Precast members joint concrete with greater fluidity demands more cementitious materials,which will increase the autogenous shrinkage of concrete and make it prone to cracking and disconnection,which will seriously affect the engineering quality of prefabricated buildings.Therefore,through reasonable selection of fine and coarse aggregate,adding high quality mineral admixture,expansive agent and water reducing agent and optimizing the mixture ratio design,conducting research on joint concrete with self-compacting work performance,no shrinkage or micro expansion,good volume stability,and matching strength with precast members,will have important practical significance.In this paper,precast members joint concrete with different water-binder ratio,sand ratio,type and dosage of mineral admixtures was designed and joint concrete working properties,mechanical properties and autogenous shrinkage performance tests were conducted to explore the mixture ratio design method of precast members joint concrete and analyze the effects and function mechanisms of water-binder ratio,sand ratio,type and dosage of mineral admixtures on the working performance,mechanical properties and shrinkage performance of precast members joint concrete.The main conclusions are as follows:(1)When water-binder ratio was larger,the fluidity of concrete was better while compressive strength,splitting tensile strength and elastic modulus became smaller.When the water-binder ratio was smaller,the concrete mixture had larger plastic viscosity;when the water-binder ratio was 0.38,the working performances of the mixture were good.(2)The addition of mineral admixtures can improve the working performance ofconcrete mixture.The addition of fly ash and ultra-fine silica powder improved the performance of the mixture better than adding fly ash alone.Under the same condition,with the increase in fly ash content,the compressive strength and splitting tensile strength of the mixture decreased;when fly ash content was constant,the concrete strength increased with the increase in ultra-fine silica powder content.(3)The autogenous shrinkage of concrete increased rapidly before the age of48 h,but tended to be gradual after the age of 48 h.It was larger when the water-binder ratio was smaller.(4)Adding expansive agent into mortar reduced the autogenous shrinkage of concrete remarkably.The shrinkage of concrete decreased with the increase in fly ash content.When the fly ash content was constant,adding ultra-fine silica powder reduced the shrinkage of concrete.The mixing addition of fly ash,ultra-fine mineral powder and expansive agent into concrete can effectively reduce the early cracking caused by the autogenous shrinkage of concrete and improve the overall stability of concrete.