Study On The Design And Properties Evaluation Of Sustainable UHPC Including Expanded Perlite

Ultra-High Performance Concrete(UHPC)is also called Ultra-High Performance Fibre Reinforced Concrete(UHPFRC)due to the incorporation of steel fibers and polymer fibers.Because of the ultra-high mechanical properties,excellent durability,and high toughness of UHPC,it has broad application prospects in engineering such as bridge,highway,maintenance and reinforcement,external wall decoration,light and thin structure and protective structure.However,the high cement dosage in traditional UHPC could exacerbate the greenhouse effect(the cement content in UHPC is800-1100 kg/m~3,about 3-4 times that of normal concrete).In addition,the use of ground quartz sand with a maximum particle size of 600μm increases the cost and energy consumption of UHPC and aggravates air pollution.At present,the development of sustainable UHPC by replacing cement with mineral admixtures,such as fly ash,limestone powder,slag and metakaolin,as well as replacing quartz sand with other fine aggregates such as river sand is the effective approach to reduce the energy consumption of UHPC.However,according to the previous literature,the development and application of sustainable UHPC are limited by the issues of mineral admixtures and fine aggregate,including the unstable quality,short supply,and regional characteristics.Thus,it is essential to seek materials with wide sources and commonly available to substitute cement and quartz sand for the promotion of developing sustainable UHPC.Expanded perlite(EP)has gradually attracted attention due to its light weight,widely available and heat insulation.At present,EP has been widely used as a mineral admixture and aggregate in building thermal insulation materials,partition,and lightweight concrete,while the application and research in UHPC have not yet been reported.Based on the current research status of EP in cement-based composite materials,this study explores the effect of the addition of EP filler and aggregate to replace cement and quartz sand respectively and simultaneously on the fresh behavior,hardened properties,hydration process and carbon footprint of UHPC.In addition,the approach of design and preparation of sustainable UHPC with EP,the following conclusions can be drawn:(1)The results of fresh behavior tests show that the addition of EP filler increases the slump flow of fresh slurry significantly,increases the air content,increases the packing density,shortens the mini-V-funnel time and reduces the plastic viscosity and shear stress.For EP sand,the water demand of slurry increases,the slump flow,plastic viscosity and shear stress decrease with the addition of EP aggregate due to high water absorption and the porous and rough particle morphology of EP aggregate.In addition,the compounding of EP filler and EP aggregate increases water demand,leading to worse workability.(2)The results of hardened properties tests show that the addition of EP filler and aggregate,and the combination of both significantly reduce the early compressive strength of UHPC.With the extension of the curing age,the negative effect of the addition of EP on the compressive strength of UHPC in the later period(28d)gradually decreases.As a result,the prepared EP-based sustainable UHPC still exhibits excellent mechanical properties.In addition,the steel fiber sedimentation occurred in the specimens with high EP aggregate content due to the decrease of viscosity,resulting in the reinforcement effect weakened and the 28d compressive strength decrease.The results of the electric flux and RCM test shows that the addition of EP significantly reduces the early(7d)anti-chloride ion permeability of UHPC.However,the negative effect of the addition of EP on the anti-chloride ion permeability of UHPC is weakened.As a result,the prepared EP-based sustainable UHPC still exhibits excellent durability.Moreover,the dry apparent density of UHPC reduces with the addition of EP.Finally,the impact test results show that the addition of EP improves the impact resistance of UHPC.(3)The results of the hydration process show that the type of hydration products of UHPC does not alter with the addition of EP filler.TG and DTG test results show that,when the EP filler content is within 40%,the content of calcium hydroxide decreases and the content of C-S-H increases with the EP filler content increases,which is mainly related to the pozzolanic reaction of EP filler.When the content of EP filler reaches 60%,the lowest content of calcium hydroxide and C-S-H in the UHPC due to its dilution effect.The results of hydration heat show that the addition of EP filler reduces the 24h cumulative heat,while the hydration rate is accelerated.(4)The addition of EP fillers and the compounding of EP fillers and EP aggregates can significantly reduce the carbon emissions of UHPC.Compared with the previous literature,the sustainable UHPC developed in this study can further reduce the environmental impact while ensuring excellent mechanical properties,which verify the feasibility of the potential use of EP in developing sustainable UHPC.