Effect Of Internal Curing On The Mechanical Properties And Shrinkage Of Engineered Cementitious Composites

Engineered cementitious composites(ECC)have excellent toughness and crack controlling ability,and has been extensively concerned by domestic and foreign scholars in recent years.But compared with traditional concrete materials,the ratio of cementitious materials and water-binder ratio for ECC increase.Besides,the hydration is insufficient and shrinkage ratio has been increased in the curing process.In order to solve those problems in practical engineering applications,internal curing technology has been used in ECC material in this paper.Water from the internal curing agent can improve the hydration degree of ECC,so as to improve the mechanical properties and shrinkage properties of materials.Super waterabsorbing polymer(SAP)and sintered fly ash ceramsite(LWA)have been used in this paper.The amount of SAP in quality content is 0%,0.05%,0.1%.And two different aggregate particle size LWA have been used in volume replacement rate 0%,10% and 20%.The compressive strength,splitting tensile strength,flexural strength and shrinkage performance of ECC material has been studied.Meanwhile,the curing effects,advantages and disadvantages of each internal curing agent have been compared and analyzed.Suggestions on how to choose the most suitable internal curing method under different circumstances have been put forward.The main contents and conclusions of this paper are as follows:(1)SAP had a significant effect on reducing the shrinkage of ECC material,and the shrinkage reduction reached 18% at 60 d.SAP can improve the compressive strength and splitting tensile strength of ECC material,but has less influence on the material's flexural strength.However,it can promote the stable development of cracks.The cracks' numbers under three-point-bending have been increased significantly in the failure process,and the distribution range of cracks has been increased too using SAP for internal curing.With the increase of SAP content,the shrinkage of ECC material decreases.And the splitting tensile strength and compressive strength has decreased.(2)Fine LWA can reduce the self-shrinkage of ECC material to a certain extent,and the selfshrinkage reduction reached 17.2% at 60 d.Using fine LWA for internal curing can improve the splitting tensile strength of the material,but can reduce the compressive strength and flexural strength.Meanwhile,fine LWA is not conducive to the stable development of cracks in the flexural failure process of ECC material.(3)Coarse LWA has the most significant reduction on the shrinkage performance of ECC material,reducing the self-shrinkage by 26.4% at 60 d.Using coarse LWA for internal curing can improve the splitting tensile strength,but reduce the compressive strength and flexural strength.Coarse LWA promotes the stable development of cracks,and the fiber toughening effect is better played.(4)It is recommended to use SAP as internal curing agent when it is required to ensure that the mechanical properties of ECC material do not decrease and the reduction effect of shrinkage under internal curing is relatively low.It is recommended to use coarse LWA as internal curing agent when the strength of mechanical performance is allowed to float within a certain range and the reduction effect of shrinkage under internal curing is required strictly.It is not recommended to use fine LWA as internal curing agent when there is a strict requirement for the ductility failure of ECC material.Meanwhile,SAP is easier to control than LWA in construction process.