Research On Flexural Behavior Of RC Slabs Strengthened With Magnesium Phosphate Cement Based Materials

As China construction market entered an era of new construction and reinforcement,the reinforcement and reconstruction of existing buildings has been rapid developed,and more and more new materials are widely used in this field.Magnesium phosphate cement(MPC)has the characteristics of fast setting,high early strength and good adhesion with core concrete,which has been extensively used as rapid repair materials in civil engineering.In this paper,the modification of MPC was studied,and the modified MPC was used to prepare three kinds of MPC concrete with different densities.MPC concrete was used to reinforce the concrete slab,and the bending tests were carried out to investigate the flexural behavior of top reinforced concrete slabs.The main results of this paper are as follows:1)K-1300 W metakaolin was added to prolong the setting time of MPC.The test results showed that the best ratio of Mg O/P was between 1:1.5 and 1:1,and the best content of K-1300 W was between 50% and 80%.The setting time of modified MPC could reach more than 20 min,with rapid development of early strength.High performance hollow glass microsphere HN60 was added to further regulate the fluidity and setting time.The best content of HN60 was between 8% and 12%,the fluidity could reach more than 100 mm and the setting time could reach more than 30 min.2)Different aggregates were added to prepare three kinds of MPC concrete with different densities: ordinary MPC concrete,sand-lightweight MPC concrete and alllightweight MPC concrete.The test results of mechanical properties show that MPC concrete is more brittle than ordinary concrete,with sudden failure characteristics and loose state after failure.Its elastic modulus is significantly lower than ordinary concrete,which is only between 12 GPa and 14 GPa.The peak strain is significantly higher than that of ordinary concrete,reaching more than 3000με.3)The concrete slabs were reinforced with two kinds of thickness and four kinds of concrete,the bending test was carried out,and the bending test results show that the flexural capacity of two kinds of thickness types were increased by more than 1.3 times and 1.7 times respectively.All reinforced concrete slabs were balanced-reinforced concrete slabs,and the reinforced layer did not come off;In addition,because the elastic modulus of MPC concrete was too low,the MPC concrete reinforced slab had low stiffness,which made the cracking load value less than the calculated value.In conclusion,modified MPC can be used to prepare MPC concrete,which can be used to significantly increase bearing capacity and stiffness of concrete slab.Because MPC concrete has the characteristics of low density,high early strength and rapid development of strength,it can obviously shorten the construction period,reduce the reinforcement material weight.This study not only broadens the application of MPC,but also makes more materials available in the design of structural reinforcement.