Study On Shrinkage Characteristics Of (Super) High Strength Concrete

(Ultra)high-strength concrete(U/HCP)is a typical modern concrete product prepared by selecting materials,controlling the ratio of water to binder,and incorporating additives.Due to its high mechanical strength and durability,U/HCP has been widely used in high-rise buildings,complex structures,and long-span bridges.Compared with general concrete,U/HPC's performance such as frost resistance and impermeability can be greatly improved.In addition,U/HPC uses industrial waste residue as a mineral additive,which directly reduces the amount of cement used,and can alleviate the environmental and energy consumption problems caused by the use of cement-based materials and waste discharge to some extent.The use of U/HCP can also reduce the cross-sectional dimensions of structural engineering components,reduce the gravity of the components themselves,improve the appearance of buildings,and realize the smooth construction of complex structures.It has important economic,environmental,and engineering practical values.However,a lot of practice shows that U/HCP is more prone to cracking,which jeopardizes the safety of the structure and thus limits the use of U/HCP in construction projects.The research on the shrinkage problem and the corresponding reduction measure for U/HCP has become the research focus in the field of concrete materials at home and abroad.Therefore,this paper systematically studies the drying shrinkage,chemical shrinkage and autogenous shrinkage of U/HCP.research shows:(1)Silica fume as a mineral additive can reduce the degree of hydration in U/HCP and reduce the chemical shrinkage.The greater the amount,the greater the reduction effect.Silica powder can increase U/HCP strength to a certain extent,and the greater the content,the greater the increase in strength;the influence of the content of silica powder on U/HCP self-shrinkage and drying shrinkage is similar.with the addition of silicon powder increased,autogenous shrinkage or shrinkage increased first and then decreased.The addition of 30% silica powder caused the two kinds of shrinkage to appear maximum,and the autogenous shrinkage ratio also showed an increasing trend.This shows that for U/HCP,autogenous shrinkage is the main shrinkage deformation in various shrinkages;(2)The chemical shrinkage of cementitious materials in high-strength mortars isthe driving force for autogenous shrinkage.With the same amount of silica fume,the early chemical shrinkage of cementitious materials is positively related to the water-binder ratio.The larger the water-binder ratio,the higher the degree of hydration reaction of the cement and the greater the chemical shrinkage.U/HCP self-shrinkage deformation is generally larger and decreases with increasing water-to-rubber ratio.With the same amount of silica fume,the shrinkage of drying is positively correlated with the water-binder ratio.The higher the water-binder ratio is,the higher the internal pore water content is.After the water is lost,the drying shrinkage of the mortar becomes more obvious.