Study On Basic Mechanical Properties Of Geopolymer Recycled Concrete Under Compression Loading

The development of the traditional construction industry is largely realized at the expense of excessive consumption of energy and resources.With the progress of China's urbanization,we have to face two important issues,namely the transition consumption of non-renewable resources and the massive accumulation of construction waste.A large amount of raw natural resources such as sand and gravel are consumed,which leads to the lack of resources.At the same time,due to the city's own “metabolism”,a large number of demolition and rebuilding behaviors cause a lot of construction waste,which has a relatively bad impact on the environment.Large-scale use of recycled concrete technology can reuse construction waste and greatly increase the resource conversion rate of construction waste,which has attracted more and more attention.Portland cement is a kind of cementitious material with high pollution,high energy consumption and high consumption of resources.In the process of cement production,a large amount of carbon dioxide is discharged,causing serious climate anomalies.In order to reduce the application amount of cement,a large number of industrial by-products are widely used in commercial concrete to partially or completely replace cement.The geopolymer concrete,which uses industrial by-products such as mineral powder and fly ash,as cement concrete,has the advantages of low emission and high strength.Therefore,cement-free concrete based on geopolymer has emerged.In this paper,in order to provide a theoretical theory for the promotion of geopolymer recycled concrete technology,the mechanical properties of geopolymer recycled concrete and the stress-strain constitutive relationship under monotonic and repeated loading were studied through the combination of geopolymer concrete technology and recycled concrete technology.The specific research work of this paper is as follows.In this experiment,216 standard cube body specimens and 162 prismatic specimens were fabricated with recycled coarse aggregate,fine aggregate replacement rate and alkali activator content as design parameters.The compressive strength and splitting tensile strength of geopolymer recycled concrete under different alkali excitation dosages were measured,and the effects of alkali excitation doping amount on slump and setting time were studied.The effect of recycled coarse aggregate replacement rate on the basic mechanical properties of geopolymer recycled concrete was also studied.In this experiment,the monotonic compressive load test of 27 geopolymer recycled concrete prism specimens was completed,and the stress-strain full curve of each specimen was analyzed.The peak stress,peak strain and ultimate strain and the relationship between the modulus of elasticity and the replacement rate of recycled coarse aggregate were analyzed.The polynomial fitting method is used to give the variation of the parameters of the ascending and descending sections of the stress-strain full curve with the amount of recycled coarse and fine aggregate.A uniaxial compression constitutive model of geopolymer recycled concrete under monotonic loading was established.The uniaxial repeated loading test of 27 geopolymer recycled concrete prism specimens was completed.The failure modes of the specimens were observed and compared with the monotonic loading.Based on the obtained stress-strain curves of each group of specimens,the difference between the repeated loading and unloading stress-strain curve envelope and the monotonic load stress-strain curve of geopolymer recycled concrete was analyzed.The unloading curve and the reloading curve equation of each group were established.And the relationship between the unloading curve parameters and the reloading curve parameters with the amount of recycled aggregates is given.Thus the uniaxial compression constitutive model of geopolymer recycled concrete under repeated loading was established.