Study On Characterization And Dynamic Mechanical Properties Of Recycled Fine Aggregate Modified By Tannic Acid

Recycling waste concrete after crushing screening can not only reduce the dependence on natural sand and stone,but also reduce the landfill area of construction waste and environmental pollution,it is conductive to saving natural resources and protecting the environment,and conforms to the strategic thought of sustainable development.Recycled concrete aggregates have the disadvantages of high porosity,many microcracks,poor quality,et al.,because of the adhered cement paste.Researchers have proposed methods such as removing and strengthening the adhered cement paste in order to improve the quality of recycled concrete aggregates,however,both have certain limitations.In this study,we proposed a novel method to treat the Recycled fine aggregate(RFA)with a naturally occurring compound,tannic acid(TA),nano-particles are generated on the surface of recycled aggregate to improve the bonding property of the interface transition zone between recycled aggregate and cement,so as to improve the mechanical strength and durability of the cement mortar made with the RFA.The microstructure and products of RFA surface treated by TA solution were analysis though XRD,FTIR,and SEM.Hydration heat analysis,TGA,MIP to study the effect of treated RFA on hydration rate,hydration degree and micro-pore distribution of new mortar.The durability of mortar was studied by capillary absorption and electrical flux measurement.The results show that loose cement mortar on the RFA surface is removed,in addition,TA can react with calcium hydroxide and calcite in the RFA to produce nanoparticles to fill the capillary to reduce the porosity,effectively improve the quality of RFA,promote cement hydration and increase the mechanical strength and durability.At 28d compressive strength increased by 25.92%,respectively,while the capillary water absorption and electric flux decreased by 54.16%and 17.77%,respectively.The impact loading test was performed using the SHPB system,dynamic uniaxial compressive stress-strain curves of RFA mortar under different pressure were obtained.While,the energy dissipation and the stain rate effects of dynamic compressive strength,ultimate toughness and failure mode were studied.The results show that with the increase of the impact pressure,the diameter of fragment decreased gradually,and the dynamic compressive strength and ultimate toughness increase first and then stabilize,showing an exponential growth.The dynamic compressive strength is increased by 131.83%,150.07%,109.77%,the ultimate toughness is increased by 106.30%,164.37%,210.32%,and the absorbed energy is increased by 45.66%、32.71%、57.80%,respectively.Compared with the natural sand group,the dynamic compressive strength is increased by 20.40%,23.37%,33.57%,the ultimate toughness is increased by 26.19%,10.52%,20.33%,and the absorbed energy is increased by 17.82%、-1.57%、39.31%,respectively under different loading.The dynamic and static compressive strength and durability test results of RFA mortar treated by TA show that TA can significantly improve the quality of RFA mortar,and has a positive effect on improving the mechanical strength and durability of RFA mortar,which is beneficial to saving natural aggregate and recycling of building resources.Figure[39]table[9]reference[116]...