Experimental Study And Analysis Of Creep Behaviors Of Recycled Lump/Aggregate Concrete

The use of demolished concrete and excavated soils in structural members can significantly improve the utilization ratio of construction and demolished waste,but its impact on the long-term performance of structural members should be clarified.In this dissertation,recycled lump/aggregate concrete(RLAC)was prepared by simultaneously adopting demolished concrete lumps(DCLs),recycled coarse aggregates(RCAs)and wet-sieving sand from alluvial-diluvial soil.The compressive creep behaviors of RLAC and reinforced RLAC were investigated.The main work and achievements are summarized as follows:1.Experimental study on compressive creep behavior of 1 group of new concrete(recycled aggregate concrete)specimens,1 group of demolished concrete specimens,and 4groups of RLAC specimens was conducted.Influences of the DCLs,RCAs,the stress level,and the wet-sieving sand from alluvial-diluvial soil on the specimens’ creep behavior have been investigated.It can be found that:(1)The specific creep of RLAC is obviously larger than that of demolished concrete,and is also larger than that of new concrete;when the stress level is less than 0.4,the assumption of linear creep is acceptable for the RLAC.(2)As the replacement ratio of RCAs in new concrete increases from 30% to 50%,the specific creep of RLAC increases somewhat.However,the full replacement of alluvial-diluvial soil to river sand has ignorable influences on the creep behavior.(3)On the whole,the specific creep of RLAC is greater than that of recycled lump concrete(RLC),but close to that of recycled aggregate concrete(RAC).2.Based on the two-phase material model,methods for predicting the elastic modulus and creep of RLAC were proposed.Besides,a simplified prediction model for creep of RLAC was suggested in the view of actual application.The findings show that:(1)Predicted values of elastic modulus of RLAC,which are calculated by the Reuss model or the Voigt model,are both lower than the test results,and the Counto model has a better prediction on the elastic modulus of such kind of concrete.(2)The modified Counto model based on the AAEM method can precisely predict the specific creep of RLAC.(3)If the creep response of new concrete and demolished concrete cannot be obtained respectively in actual application,the creep behavior of RLAC can be well predicted by using the two-stage improved multi-coefficient creep model proposed in this paper.3.Creep tests of 2 groups of reinforced new concrete specimens,5 groups of reinforced RLAC specimens were investigated,and the effects of replacement ratio of DCLs and RCAs,stress level,reinforcement ratio and replacement ratio of wet-sieving sand were examined.Test results show that:(1)Longitudinal reinforcement has a restrained effect on the load-independent deformation(mainly govened by shrinkage deformation)of RLAC,and the restrained effect increases with the increase of reinforcement ratio.Compared with unreinforced concrete,the creep of reinforced RLAC tends to be stable earlier.(2)In general,the specific creep of reinforced specimens increases with the utilization of DCLs,but the increasing amplitude is within 15%.When the subjected load is comparable,the creep of reinforced RLAC decreases with the increase of reinforcement ratio.(3)After longitudinal reinforcing,the negative effect due to the increase of the RCAs replacement ratio on the creep behaviors of RLAC is diminished to some extent.(4)The impact on creep behaviors of reinforced RLAC could be neglected when the river sand in RLAC is fully replaced by wet-sieving sand from alluvial-diluvial soil.