| While China’s urban construction is in full swing,construction waste also comes into being,which has become an important practical problem in China’s urbanization process.China’s annual output of construction waste accounts for 30%-40% of the total urban waste,but the utilization rate of resources is less than 10%.In addition,waste rubber is also a common solid waste in China.Its traditional treatment method not only costs a lot of freight,but also occupies a lot of valuable land resources,causing secondary pollution to the environment.How to recycle the solid waste effectively is a hot issue in China.The existing studies at home and abroad show that the use of construction waste and waste rubber to prepare recycled concrete is a promising green recycling technology,which can not only reduce environmental pollution,but also save the consumption of building materials,economic benefits,and has strategic significance for sustainable development.However,because of construction waste recycled aggregates high porosity,low water absorption and strength defects,and waste rubber particle strength and low elastic modulus of faults,construction waste recycled aggregates and recycled rubber particles mixed with different degree of degradation of mechanical properties and durability of the concrete,the insufficient seriously hindered the development of recycled concrete.Therefore,the research and development of high-performance recycled concrete,and the exploration of its basic mechanical properties and ecological characteristics,so as to promote the application of green building development in China has important scientific significance and engineering application value.Therefore,based on the modification technology of recycled aggregate,rubber recycled concrete(RRAC),a high-performance environmental protection building material suitable for civil engineering,was developed by using construction waste and waste rubber.Then,the axial compressive behavior of this new type of concrete was discussed,the failure mechanism was revealed,and the carbon emission characteristics of the whole life cycle ofRRAC were analyzed.The main research contents and conclusions of this paper are as follows:(1)RRACs with strength grades C30 and C40 was developed by replacing natural coarse aggregate with reclaimed aggregate generated from construction waste and natural fine aggregate with waste rubber particles.The influence rules of rubber particle size and water-binder ratio on the working performance and compressive strength of RRAC were discussed by taking rubber particle size and water-binder ratio as variables.The results show that RRAC works well,and rubber can improve the slump of regenerated concrete to some extent.The addition of rubber particles has obvious negative effect on the compressive strength of concrete.With the increase of water-cement ratio and the decrease of rubber particle size,the compressive strength of rubber recycled concrete decreases.(2)Rubber particles were treated by the combined modification method of nano-Si O2 solution and silane coupling agent,and the recycled aggregate of construction waste was modified by nano-Si O2 solution.The influence of different modification methods on the basic mechanical properties of RRAC was discussed.The results showed that the nano-Si O2 could fill the holes in the recycled coarse aggregate,improve the performance of the recycled aggregate and rubber interface,and improve the compressive strength of RRAC by5%-10%.Silane coupling agent can react with nano-Si O2 to form a network structure and improve the modification effect of nano-Si O2.At the same time,the silane coupling agent itself also has modification effect on rubber.The combined properties of the two can improve the compressive strength of RRAC by 15%-20%.The effect of simultaneously treating the regenerated coarse aggregate and rubber particles with nano-Si O2 solution is not as good as that of treating a single aggregate,mainly because the nano-Si O2 molecules on the surface of regenerated coarse aggregate tend to aggregate with the nano-Si O2 molecules on the surface of rubber particles.(3)Based on the orthogonal experiment method,a series of test was conducted to the compressive performance of the modified RRAC.Rubber particle size and dosage of water/cement ratio and modification methods were considered as the test variables.The stress strain relationship,RRAC compressive toughness,elastic modulus and failure mode were analyzed,and the RRAC microstructure was investigated by using scanning electronmicroscope(SEM),subsequently the RRAC failure mechanism were revealed.The results show that the content of rubber has little influence on the elastic modulus of rubber recycled concrete when the content of rubber is less than 15%.The larger the particle size of the rubber particles,the more likely the rubber internal damage will occur in the rubber concrete.If the rubber particles with smaller particle size are added,the cracks are more likely to appear at the rubber interface.Cracks appeared in the rubber particle and rubber interface first,and these cracks gradually extended through,leading to the destruction of the whole specimen.Rubber regenerated concrete with single particle size has better compression resistance than rubber regenerated concrete with continuous particle size.(4)In order to evaluate the CO2 emissions of RRAC,the carbon emission quantification model of the whole life cycle of RRAC was constructed,considering the four stages of RRAC preparation,transportation,construction and demolition.The carbon emission quantification model of the entire life cycle of RRAC and the calculation method of CO2 emission were established.The carbon emission coefficient of each stage was determined by collecting basic data of each stage.In the preparation stage of RRAC,the carbon emission of raw material production is determined by the carbon emission coefficient and the production volume.The carbon emission during transportation,construction and demolition mainly comes from the product of the energy consumption of transportation vehicles and construction equipment and the direct or indirect carbon emission coefficient of energy.The RRAC carbon emission of 1 m3 can be obtained by adding the above results.In addition to calculating RRAC lifetime carbon emissions,RRAC cost analysis was also carried out.The results show that RRAC has good ecological characteristics and its full lifecycle carbon emission is more than 15% lower than ordinary concrete.In the whole life cycle,the carbon emission of RRAC mainly occurred in the production and preparation stage,accounting for about 90% of the total carbon emission.In the preparation stage of RRAC,the carbon emission from raw materials plays a dominant role,accounting for more than95%.During the concrete preparation stage,RRAC reduced its carbon emission by nearly20% compared with normal concrete.In terms of preparation cost,the cost of RRAC is slightly higher than that of ordinary concrete,with an increase of about 4-8%.Consideringits positive economic effect on environmental impact,it can be concluded that RRAC is economically feasible. |
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