Research On Recycled Aggregate Performance And Design Method Of Recycled Concrete

As the early construction of cement concrete pavements has a large number of pavement diseases with the increase of service life and traffic load,more and more cement concrete pavements need to be maintained,repaired and even upgraded.The large amount of construction waste which generated from the cement concrete pavement has a great impact on the ecological environment.How to properly dispose of construction waste has become a hot research topic.At the same time,with the increase of China’s infrastructure construction,a large number of natural stone materials,sand and other resources have been seriously scarce,so the research on the reuse of broken concrete has very important strategic significance.However,due to the performance defects of recycled aggregates,the performance of recycled concrete will vary with different dosages.Therefore,this paper firstly studies the reinforced coarse aggregates,and then studies the optimum ratio of low-recycled coarse aggregates for highway concrete.Finally,came up with the optimal ratio of high-strength concrete under high-volume recycled coarse aggregates.These research results can be used as a reference in highways and high-strength buildings.Four reinforcement methods were selected to strengthen the recycled coarse aggregates.The thesis found that the optimal strengthening methods for the apparent density,water absorption,angularity and surface texture of the physical properties of the aggregates in the four strengthening methods are:cement slurry with fly ash(7d)、sodium hydroxide and polyvinyl alcohol、sulfuric acid and cement slurry with fly ash(7d).The best performance of the aggregate mechanical properties is the cement slurry with fly ash(3d).The strengthening method which is minimally affected in angularity by the abrasion is sodium hydroxide and polyvinyl alcohol.The strengthening method which is minimally affected in surface texture by the abrasion is also sodium hydroxide and polyvinyl alcohol.By summarizing the mechanism of several strengthening methods:the cement-mixed mineral-doped material is reacted with Ca(OH)2 to produce gelling hydration products on the basis of void filling and micro-crack repair;5%sulfuric acid concentration soaking Corrosion of low-strength,porous mortar,thereby increasing the aggregate strength,so that the water absorption rate is reduced;while NaoH and PVA treatment of the aggregate,the silicate and PVA in the surface of the regenerated aggregate react,free water and PVA The hydration reaction.Based on the common concrete mix design method,highway concrete mix design method and pre-water absorption ratio design method,the cement concrete mix ratio of 20%,40%and 60%of the three types of recycled coarse aggregates in the three-stage and four-stage highway was determined.The research shows that the 28d compressive strength of the blended aggregate without regeneration is up to 49.6MPa,which meets the compressive strength requirement of C40 concrete.At the same time,with the increase of recycled aggregate content to 20,40 and 60%,the compressive strength gradually decreases.The declines are 12.3%,18.9%and 16.9%,respectively,but still meet the C40 strength requirements;the conversion results of 7-day bending strength of cement concrete under six different empirical formulas are all greater than 4.0MPa,which indicates that the ratio design of these three dosages meets the highway design requirements of light grade traffic load level;The shrinkage rate of concrete becomes larger as the amount of recycled coarse aggregate increases.The orthogonal test method was used to study the proportion of recycled concrete with high strength and high content.The range analysis shows that the optimal ratio is 10%for fly ash,7.5%for silica ash,80%for substitution rate,2%for water reducing agent,and 0.31 for water-to-gel ratio in Queuing analysis.The optimum ratio is water-to-binder ratio 0.31,substitution rate 80%,water reducing agent 2%,fly ash 10%,and silica fume 0%in Matrix analysis.The results of variance analysis showed that the factors that had the greatest influence on the slump.7-day compressive strength and 7-day splitting tensile strength among the five factors were the amount of water reducing agent,the amount of fly ash and silica fume.Through two different comprehensive evaluation studies,it is found that although the optimal ratios obtained by different comprehensive evaluation methods are not the same,the factors have the same points.The influence of the amount of water reducing agent,fly ash and silica fume on the comprehensive performance of high-strength and high-performance recycled concrete is greater than the water-to-binder ratio and the replacement rate.