Impact Resistance Of Geopolymer Concrete Beams

Geopolymer concrete(GC)has become a green and sustainable material with the high prospect of application because it can greatly reduce carbon dioxide emission and effectively utilize industrial waste.In order to make the material be applied and popularized in practical engineering,it is necessary to conduct in-depth research on the performance of geopolymer concrete structures,where more and more research results are obtained.Since geopolymer concrete structures might be subjected to accidental loads such as impact in the process of use,and there are relatively few research achievements on the impact resistance of geopolymer concrete structures,indepth studies on the impact resistance of geopolymer concrete structural members are of great significance to ensure the safety of such structures.In this thesis,a series of studies are carried out on the impact resistance of geopolymer concrete beams.A design method of high performance geopolymer concrete was used to design and prepare 12 geopolymer concrete beams(GC)as experimental group and 3 ordinary Portland cement concrete beams(OPC)as control group.Taking the concrete type,strength grade,longitudinal reinforcement ratio,stirrup ratio and impact height of drop hammer as the research variables,the single mid-span drop hammer impact tests was carried out on the above specimens using ultra-high heavy drop hammer testing machine,and the impact resistances of geopolymer concrete beams were studied by the mid-span deflection and the absorption of impact energy.The main achievements are as follows:(1)The time history variation of mid-span deflection,impact force,reaction force,reinforcement strain and failure mode of GC and OPC beams were compared.The results show that the crack distribution of GC beams is similar to that of OPC beams in failure mode,but the mid-span deflection and the dissipation of impact energy of GC beams are larger than those of corresponding OPC beams,and the failure degree of GC beams is larger than that of OPC beams under the same impact.(2)The influence of concrete strength on the mid-span deflection and impact energy absorption of GC beams under the same impact was studied.The results show that the mid-span deflection of medium-strength(C50)GC beams is smaller than that of low-strength(C30)GC beams,but the mid-span deflection of high-strength(C70)GC beams is larger than that of both low-strength and medium-strength GC beams because of the greater brittleness of concrete.Moreover,as concrete strength increased,the dissipation of impact energy by GC beams decreases gradually.(3)The influence of reinforcing steel on impact resistance of GC beams was studied.The mid-span deflection and dissipation of impact energy of GC beams are reduced by increasing the reinforcement ratio or stirrup ratio,indicating that the impact resistance of GC beams could be improved by increasing the number of tensile longitudinal reinforcement or stirrup reinforcement at a lower reinforcement ratio,which is similar to the one obtained in previous studies to improve the impact resistance of OPC beams.(4)The calculation methods of maximum deflection of beam in mid-span under impact in existing literatures were compared.Three empirical calculation formulas of different maximum deflection proposed by Kishi,De-bo Zhao and Yongjae were used to fit the experimental data of GC beams in this study,and the statistical theory was used to analyze the fitting results to explore an empirical method for calculating the maximum mid-span deflection of geopolymer concrete beams under impact.