Research On Using Construction Waste Product Recycled Concrete And Building Mortar

The recycling of construction waste is an important way to achieve sustainable development.On the one hand,it can solve the environmental pollution problem caused by waste landfill.On the other hand,it can mitigate the serious shortage of resources of building materials and mineral admixture.Several key problems about recycling of construction waste are studied in this paper,which has important practical value.Firstly,characterization,evaluation and classification of the recycled aggregate with granular sizes of 10 to 31.5mm and in form of powder are performed.The results show that the water absorption and crush value of recycled aggregate are 6 to 16.6 times and 1.3 to 1.9 times,respectively,compared to natural aggregate.The apparent density of recycled aggregate varies from 2270 to 2540 kg/m3.Compared with fly ash,the amount of recycled powder from construction waste with size larger than 45 um decreases by 52.4 to 57.1%.The water requirement ratio of the recycled powder from construction waste increases by 9.3 to 12.4%.The loss of ignition decreased by 33.8 to 84.0% and 28 d activity index by 2.8 to 20.8%.The recycled aggregates are categorized into 4 series according to water absorption rate,crushing index and apparent density of the aggregates which fluctuate apparently and have great impacts on the performance of aggregate.The recycled powders are categorized into 3 series according to fineness,water demand ratio,loss of ignition rate and 28 d activity index that have great impacts on the performance of recycled powder.Secondly,preparation of high quality concrete by using recycled aggregates based on principles of mixture design and aggregate gradation optimization is investigated.The results show that the flowability and compressive strength of concrete prepared with recycled aggregates based on self-compacting concrete mixture design method are better than based on ordinary concrete mix design method.With the increase of recycled aggregate content,the selfcompacting concrete mix design method is more obvious for the improvement of the flowability and compressive strength of concrete with recycled aggregates.The slump and compressive strength of concrete with most densely packed recycled aggregates increased by 5.7 to 12.7% and 3 to 8%,respectively,than that of concrete prepared based on two-grade aggregate pack method.When the content of waste concrete aggregate is less than 50%,concrete with strength grade of C30 and a slump of 160 mm can be prepared.Thirdly,surface modification of recycled aggregate of low quality is carried out.The result shows that sodium silicate solution and silane solution can effectively improve the apparent density.In addition,the maximum water absorption can be reduced by 42% and the crushing value can be reduced by 24%.When the concentration of sodium silicate solution is 8% and the duration of immersion treatment is 24 h,the modification effect is the best.What’s more,the worse the performance of the original recycled aggregate,the more significant the modification effect.The modification effect for the recycled aggregate with sizes ranging between10 and 31.5 mm is better than that for aggregates with sizes of 5 to 10 mm.In addition,the slump of concrete prepared by modified recycled aggregate is almost the same as the concrete prepared by natural aggregate,and the reduction of compressive strength of concrete prepared by modified recycled aggregate is less than 10% of that by natural aggregate.With the increase of recycled aggregate content,the modified treatment have a better effect on the slump and compressive strength.Fourthly,the application of recycled powder for preparing plastering mortar is investigated in this thesis.The results show that the workability,mechanical properties,drying shrinkage and capillary water absorption performance of mortar prepared with different kinds of recycled powder declines in the following order: mortar with recycled powder from waste brick > mortar with recycled powder from waste concrete > mortar with mixed recycled powder from waste brick and concrete.When the content of recycled powder from waste bricks is 100%,or the contents of recycled powders from waste concrete and waste brick are 50%,respectively,the mortar strength grade can be M15,water retention rate beyond 83%,28 d flexural strength up to 4.0 MPa,14 d tensile adhesive strength beyond 0.20 MPa,28 d shrinkage less than 0.12%,meeting the requirements in "Dry-mixed masonry and plastering mortar of building "(JC / T291-2011).Finally,cost analysis and life cycle assessment on the utilization of construction waste are performed in this study.The results show that the utilization of construction waste has obvious cost advantage when the waste was recycled as aggregate for self-use.Compared with natural aggregate concrete,energy consumption(ADP)for the use of recycled aggregate decreased by 3.65%,greenhouse effect(GWP)decreased by 9.20%,the effect of acidification(AP)decreased by 3.62%,and the effect of photochemical smog(POCP)decreased by 5.98%,the impact of human health damage(HTP)decreased by 2.94%,and the mitigation on environmental load is obvious during the process of life cycle.