Research On Shrinkage And Cracking Properties Of Iron Tailing Sand Concrete

In recent years,the cumulative stockpiles and annual emissions of iron tailings resources have gradually increased,which has caused great harm to human society and the natural environment.In order to alleviate the shortage of natural sand resources and realize the sustainable development of the building materials industry,it is of great significance to apply some or completely replace natural sand as a fine aggregate to high-performance concrete and realize the resource utilization of bulk tailings.Shrinkage cracking is a common and prominent problem in high-performance concrete,and there are few studies on early plastic shrinkage,early crack resistance,long-term volume stability and durability of iron tailings sand concrete.Therefore,research on controlling the shrinkage and cracking behavior of iron tailings sand concrete is necessary to form the complete preparation and application technical specifications of tailings sand high crack-resistant ready-mixed concrete.In this paper,the feasibility of iron tailings sand as construction sand was analyzed firstly,including:studying the compatibility of harmful components?heavy metal ions,sulfides,etc.?in iron tailings with functional chemical materials and the effect on cement hydration;studying the effect of iron tailings sand on rheological properties,mechanical properties and drying shrinkage properties of mortar;Studying the influence of basic properties of iron tailings on concrete performance,mechanical properties and shrinkage cracking performance.Then the effects of different shrinkage mitigation measures?addition of shrinkage reducing agent SRA,superabsorbent resin SAP and permeable stencil maintenance?on the workability,mechanical properties and durability of iron tailings sand concrete were studied;on this basis,different shrinkage mitigation measures on early age shrinkage cracking behavior and long-term volume stability of iron tailings sand concrete were investigated.The main conclusions of the study are as follows:?1?The leaching solution of iron tailings sand in distilled water and saturated calcium hydroxide solution had little effect on cement hydration.The iron tailings sand mortar had the same saturation point of water reducing agent as natural sand mortar,both of which are 0.8%,but the fluidity loss over time was greater;With the increase of the replacement amount of iron tailings,the compressive strength and flexural strength of mortar had increased to some extent.When the substitution amount is 100%,it increased by 12.4%and 21.5%respectively;the shrinkage of iron tailings mortar was greater than that of natural sand mortar.The shrinkage increased with the increase of the amount of substitution of iron tailings,when the substitution amount is 100%,the shrinkage at 90d reached a maximum value of 1170×10^-6.Iron tailings sand replaces different amounts of natural sand to prepare concrete,work performance and mechanical properties can meet the requirements,but 90d dry shrinkage,autogenous shrinkage value and early cracking are greater than natural sand concrete.?2?When the shrinkage mitigation measures were not taken,the workability of iron tailings sand concrete was slightly inferior to that of natural sand concrete.The compressive strength,flexural strength and dynamic elastic modulus of iron tailings sand concrete increased slightly with the increase of iron tailings sand substitution.The electric flux of iron tailings sand concrete increased with the replacement of iron tailings sand,and the electric flux of F100 concrete increased by 46.6%.After shrinkage mitigation measures being taken,the workability of iron tailings sand concrete remained unchanged,the addition of SAP and SRA was not favorable to the early compressive strength and flexural strength of iron tailings sand concrete,and the adverse effect decreased with the growth of age.The compressive strength of iron tailings increased under the permeable template cloth curing.The compressive strength of 28d increased by 5.4MPa compared with the control group.The electric flux of iron tailings concrete was the smallest after adding SRA,which was 35.9%lower than the control group,After adding SAP,the sulfate resistance of different substitute iron tailings sand concrete increased,and the corrosion resistance coefficient of iron tailings sand concrete increased by 4.7%compared with natural sand concrete.?3?The early autogenous shrinkage of iron tailings sand concrete is equivalent to that of natural sand concrete,and the early shrinkage value is greater than that of natural sand concrete.The shrinkage mitigation measures could reduce both the early autogeneous shrinkage and early shrinkage of concrete,and the addition of SAP performed the best.The early autogeneous shrinkage of concrete at 72h was reduced by up to 46.5%,and the early shrinkage of iron tailings sand concrete was reduced up to30.4%.The autogeneous shrinkage of iron tailings sand concrete decreased by 29.9%after adding SAP,and the 90d drying shrinkage of iron tailings concrete under permeable template cloth curing reduced the most,which was 41.2%.Under the permeable template cloth curing,it can effectively hinder the loss of water dispersion.Meanwhile,the iron tailings sand concrete had the least water loss per unit area and the highest internal relative humidity.After the mitigation measures,the early cracking performance of the iron tailings sand concrete could be significantly improved,and the maximum crack width was obviously reduced.Under the permeable template cloth curing,the iron tailings sand concrete was not cracked,and the total cracking area per unit area is reduced by 34.3%after the addition of SAP.