Research On The Mechanical Properties Of Ecological Engineering Cementitious Composites(ECO-ECC)

Ultra high toughness cementitious composites(UHTCC),also known as ECC,is a new fiber-reinforced cementitious material with excellent tensile deformation properties and bending toughness.Due to the high materials cost of PVA fiber and ground quartz sand imported from Japan used in the preparation of ECC,its wide application in domestic engineering is limited.In recent years,with the continuous acceleration of the urbanization process in our country,the continuous deepening of new rural construction and the renovation of the old city,a large amount of solid construction waste such as waste concrete and waste sintered bricks have been produced.At present,most of these waste concrete and waste sintered bricks are untreated and directly transported to the suburbs or villages.They are directly treated by stacking or landfilling,which not only occupies a large amount of land,but also causes scattering and dust during the process of clearing,transportation and stacking,causing serious environmental problems.In this paper,with the goal of resource reuse and cost reduction to promote the application of ECC in a large area in China.The use of recycled bricks and recycled concrete micro-powder with a particle size of less than 300 ?m and optimized gradation to replace ground quartz sand.to prepare Ecological PVA-ECC(ECO-ECC for short)with green and low costs features,which not only makes rational use of solid waste,low energy consumption,but also has excellent performance.The properties of ECOECC were studied by changing the ratio of substitution and the proportion of micropowder,W/B,FA/B,PVA fiber volume fraction and the curing time,taking the properties of compression strength,bending strength,four-point bending and uniaxial tensile as the main inspection indexes,and optimizing the mix ratio of ECO-ECC.The main research contents and conclusions are as follows:(1)When the recycled micro-powder is used to replace quartz sand,the flexural mid-span deflection and ultimate tensile strain of the ECO-ECC gradually increase with the increase of the amount of replaced quartz sand.Under the same substitution rate,with the increase of recycled concrete micro-powder proportion,the ultimate tensile strength and ultimate flexural strength gradually increase,but the ultimate tensile strain and ultimate deflection gradually decrease.The ECO-ECC with good toughness and remarkable strain hardening characteristics is obtained through the test.Combined with the theme of "green" and "brick and concrete mixing" in this paper,a better substitution amount and the proportion of micro-powder(100%: 50%,50%)are selected for the influencing factors test.(2)The ultimate tensile strain of ECO-ECC can reach more than 1.3% under uniaxial tensile load,which shows good ductility during the tensile test,accompanied by multi-cracking and strain hardening.The tensile properties of ECO-ECC vary with W/B,FA/B,PVA fiber volume fraction and curing time.With W/B is 0.33 ? 0.39,FA/B is 35% ? 60% and PVA fiber volume fraction is 1.5% ? 2%,the tensile strain hardening effect of ECO-ECC(28d)is excellent.(3)The ultimate mid-span deflection of ECO-ECC under four point bending load is 21.63 mm ? 57.81 mm.The flexural performance index of ECO-ECC fluctuates with W/B,FA/B,PVA fiber volume fraction and curing time.With W/B is above 0.33,FA/B is above 30% and PVA fiber volume fraction is above 1.5%,the mid-span deflection of ECO-ECC(28d)can reach over 35 mm,with good toughness.(4)The 28 d compressive strength and bending strength of ECO-ECC decreased with the increase of W/B,decreased with the increase of FA/B,and increased with the increase of PVA fiber volume fraction;the compressive strength and bending strength of ECO-ECC increased with the increase of curing time.