Preparation Of High-strength Lightweight Aggregates And Its Effect On The Mechanical Properties And Durability Of Concrete

In this dissertation,lightweight aggregates were fiber-reinforced,and influence of fiber-reinforced lightweight aggregates on the mechanical properties,early-age shrinkage strain and chloride penetration resistance of concrete was researched.First,lightweight aggregates were reinforced by fibers and prepared in hydrothermal method.Lime,fly ash,sand,aerated concrete powder and fibers were used to prepare fiber-reinforced lightweight aggregates.Three kinds of fiber-reinforced lightweight aggregates were hydrothermal synthesized at 180℃and 1MPa pressure.The bulk density,apparent density,1h water absorption and cylinder compressive strength of fiber-reinforced lightweight aggregates were characterized.Results showed that all aggregates satisfied GB/T17431.2-2010 density requirements.Fiber could improve the cylinder compressive strength of lightweight aggregates.When fiber usage increased from 0vol.%to 3.0vol.%,cylinder compressive strength of fiber-reinforced recycled silicate aggregates（FRSAs）increased from12.5MPa to 24.4MPa;cylinder compressive strength of fiber-reinforced silicate aggregates（FSAs）increased from 21.8MPa to 31.0MPa;cylinder compressive strength of basalt fiber-reinforced aggregates（BFAs）increased from 12.4MPa to 24.2MPa.Second,FRSAs and FSAs were employed to cast concrete and enhancement mechanism of fiber-reinforced lightweight aggregates in concrete was studied.The 7 days’and 28 days’compressive strength,28 days’drying density of concrete was characterized.Results indicated that fiber-reinforced lightweight aggregates could be used in semi-lightweight aggregate concrete with high-grade.FRSAs could be suitable for concrete with 60-70MPa,while FSAs could be suitable for concrete with 70-80MPa.Besides,fiber-reinforced lightweight aggregates could improve the stress distribute between coarse aggregates and mortar,save cement usage,thus high-grade concrete with low-cement-content was cast.Finally,the early-age shrinkage strain,mechanical properties and chloride penetration resistance of concrete as a function of fiber-reinforced lightweight aggregates’level was reported.Results indicated that crushed granite and fiber-reinforced lightweight aggregates with a proportion of 2:3 could minimize shrinkage strain of concrete.The saturated fiber-reinforced lightweight aggregates had significant internal curing on concrete cured in air,the mechanical properties of concrete were improved from 46.7MPa to 61.2MPa as the crushed granite was gradually replaced by FRSAs.Chloride diffusion coefficient in concrete increased at a exponential function with volume fraction of fiber-reinforced lightweight aggregates.When crushed granite was completely replaced by FRSAs,Chloride diffusion coefficient in concrete increased from 6.97×10^-12m²/s to 12.27×10^-12m²/s.According to NTbuilding 492,concrete prepared with fiber-reinforced lightweight aggregates has a relatively high resistance to chloride penetration.