Compressive Strength And Elastic Modulus Of Ultra-high Performance Concrete With Basalt Coarse Aggregate

Compressive strength is the most basic mechanical property of concrete.Elastic modulus is an important mechanical parameter for measuring the stiffness of concrete members and structural design in engineering.Ultra-high performance concrete is a new type composite material with high strength and excellent durability.And its compressive strength is above 120 MPa and elastic modulus is 40～60 GPa.A deep understanding on UHPC’s high compressive strength and high elastic modulus is beneficial to the application of UHPC in engineering.Currently,the elastic modulus of UHPC can be obtained in the following ways:axial compression deformation test;calculated by the multi-scale model and homogeneity theory based on the micro-elastic properties;evaluated by the relationship between the compressive strength or the dynamic elastic modulus and the static elastic modulus.However,the accuracy of these methods and their differences from each other cannot be evaluated correctly.Further,due to the diversification of UHPC’s raw materials,mix design and curing system,its hydrations and microstructure are more complex,and it would further affect the macro-elastic modulus.This article aims to study the compressive strength and elastic modulus of UHPC mixed with basalt coarse aggregate,and to achieve effective prediction of UHPC’s elastic modulus.The research mainly includes:testing the effect of different water-binder ratio,basalt coarse aggregate content,cementitious material,single and hybrid blending of long and short steel fiber,curing system and age on the compressive strength and elastic modulus of UHPC;based on the test datas,the relationships between the axial compressive strength and the cubic compressive strength,dynamic elastic modulus and static elastic modulus,and compressive strength and elastic modulus are established;in addition,based on the microscopic mechanical properties of UHPC,the homogenization theory is used to predict the elastic modulus of UHPC at different scales,and a verification analysis is performed.The results mainly include:Firstly,the effect of different factors on the compressive strength and elastic modulus of UHPC is discussed.1)The microstructure of UHPC with a low water-binder ratio is denser,and the compressive strength of UHPC with water-binder ratio of 0.16 is higher than that of 0.18.However,the compressive strength of UHPC with a water-binder ratio of 0.14 is lower than that of water-binder ratio of 0.16.In addition,the elastic modulus of the unhydrated cement particles is much higher than that of the hydrated products,and its residue is beneficial to the improvement of the UHPC’s elastic modulus,so the elastic modulus of UHPC with water-binder ratio of 0.14 is relatively larger;2)When the content of cementitious materials is 750 kg/m~3～850kg/m~3,the increase of matrix phase content enhances the adhesion between the matrix and the aggregate,and the elastic modulus of UHPC increases with the increase of cementitious materials content;3)The basalt coarse aggregates will form the rigid skeleton of UHPC.The compressive strength of UHPC will increase first and then decrease with the increase of basalt aggregate content,and reaches the maximum value when the content is 800 kg/m~3.The elastic modulus of UHPC will increase linearly with the increase of coarse aggregates content;4)The hybrid blending of long and short steel fibers is more conducive to improving the compressive strength and elastic modulus of UHPC than single blending.In general,the effect of fibers is small;5)The compressive strength and elastic modulus of UHPC increased rapidly in the early stage.The compressive strength of UHPC in standard curing for 3d can reach 65%～68%of that in steam curing at 80℃for 3d,and the elastic modulus of UHPC in standard curing for 7d can reach 90%of that of 28d.The elastic modulus of UHPC cured at 80℃for3d is higher than that in standard curing for 28d.Further analysis can be drawn from the test results,the axial compressive strength of UHPC is about 0.82 times of the cubic compressive strength,and the static elastic modulus is about 0.87 times of the dynamic elastic modulus.The applicability of the existing expressions about concrete’s elastic modulus based on compressive strength was evaluated,and a power function expression about UHPC’s elastic modulus was fitted based on the dates of this study and relevant literatures.Finally,the homogenization theory is used to predict the elastic modulus of UHPC at different scales.The difference between the predicted value and the measured value is small and the accuracy is high.