Optimal Design Of Recycled Concrete Mixture Ratio And Research On Freeze-Thaw Performance

In order to alleviate the scarcity of resources and the increasingly serious environmental problems in construction projects,it is particularly important to rationally use the recycled aggregate resources produced by abandoned buildings.Taking into account the maximum use of recycled aggregates under the premise of maintaining basic mechanical properties,this paper uses pre-wet recycled aggregates based on the principles of basic concrete design,uses orthogonal experiments to optimize the mix design,and conducts freeze-thaw durability research.The specific research content is as follows:(1)Aiming at the disadvantage of the high water absorption of the internal aggregates of recycled concrete,6.8% of the total mass of recycled aggregates is used as the pre-wetting water volume to make specimens after pre-wetting.According to the orthogonal test design,through visual analysis and analysis of variance,it is found that the amount of recycled aggregate has the most significant impact on the slump,the water-binder ratio has the most significant impact on the compressive strength,and the water-binder ratio and the amount of recycled aggregate are both the flexural strength.The main influencing factors.In this study,the strong performance of recycled concrete is optimal when the content of recycled aggregate is 70%,the water-binder ratio is 0.4,and the content of the superplasticizer is 0.25%.(2)Based on the optimal mix ratio,select natural aggregate concrete,70% recycled concrete,and 100% recycled concrete for freeze-thaw cycle tests.The quality change,compressive strength change,ultrasonic wave speed change,and stress of each group of concrete specimens-The strain curve changes are analyzed,and the compressive strength and quality are used as the main indicators to evaluate the frost resistance durability.The results show that the frost resistance grade of 70% recycled concrete reaches F100.The exponential function can be used to establish a freeze-thaw cycle damage model based on the loss of compressive strength.(3)Analyzing the stress-strain curve of each group of materials after freezing and thawing,and obtain the fitting curve of relative peak stress and relative peak strain with the number of freeze-thaw cycles.The results show that the relative peak stress has a negative correlation with the number of freeze-thaw cycles.The relative peak strain is positively correlated with the number of freeze-thaw cycles.Using the Zhenhai model to fit the constitutive models of each group of concrete and analyzing the law of the change of the parameter in the polynomial with the number of freeze-thaw cycles,the results show that compared with 100% recycled concrete,70% of recycled concrete has better resistance to plasticity deformability and frost resistance.