Experimental Study On Montmorillonite Reinforced Recycled Concrete

Recycled aggregate is an artificial aggregate produced from waste concrete through crushing,screening and cleaning steps.The application of recycled aggregate can reduce the demand for natural sand and gravel and bring good environmental and social benefits.Recycled concrete is prepared by partially or completely replacing natural aggregates with recycled aggregates,and the high water absorption and low firmness of recycled aggregates make the mechanics and durability of recycled concrete far inferior to ordinary concrete.Montmorillonite has a good pozzolanic effect,and an appropriate amount of addition can improve the compactness of mortar and concrete and improve its mechanical properties.In this thesis,montmorillonite dosage and replacement rate of recycled aggregate were used as variables to study the influence of montmorillonite on mechanical and durability of recycled concrete.The results show that:(1)By testing the mechanical properties of recycled concrete such as split tensile strength,flexural strength and compressive strength,the effects of the replacement rate of recycled aggregate and the content of montmorillonite were analyzed.The results show that the mechanical properties gradually decrease with the increase of recycled aggregates,and an appropriate amount of montmorillonite can improve the mechanical properties of recycled concrete.When the replacement rate of recycled aggregate is 30%,2% montmorillonite can significantly improve the mechanical properties of recycled concrete,of which the compressive strength is increased by 8.68%,the splitting tensile strength is increased by 10.45%,and the flexural strength is increased by 11.55%.At this time,the mechanical properties of recycled concrete are all higher than those of ordinary concrete.(2)Through the durability test of ordinary concrete and recycled concrete,it is found that with the addition of recycled aggregate,the frost resistance and chloride ion penetration resistance of recycled concrete are different.2% montmorillonite significantly improved the chloride ion penetration resistance of ordinary concrete and recycled concrete,and the electric flux decreased by 14.99% and 15.92% respectively;2% montmorillonite had the frost resistance of ordinary concrete The improvement is obvious,and the optimum amount of montmorillonite for recycled concrete is 1%;(3)SEM was used to observe the sample,and it was found that with the addition of montmorillonite,the micro-cracks and pores of the recycled concrete were significantly reduced,and the microstructure was significantly improved.By participating in the hydration process of cement,montmorillonite generates a large amount of C-S-H gel,fills the micropores and microcracks in the recycled concrete,increases the cohesion of each component,and significantly improves the microstructure of the recycled concrete.(4)Using nuclear magnetic resonance analyzer to test the sample,it is found that there are a small number of harmful pores and harmful pores in ordinary concrete.With the addition of recycled aggregate,the number of harmful pores and harmful pores gradually increases.With the addition of montmorillonite,the number of harmful pores and harmful pores gradually decreased,and the harmful pores were the most obvious.