| Mining will produce a large number of tailings waste rock,most of these waste rocks are piled up in the open,which not only occupies a lot of valuable land resources,but also causes harm to the surrounding environment,and even causes geological disasters and safety hazards.Using them as construction materials can not only relieve the pressure of the scarcity of natural sand and gravel resources,but also save resources,turn waste into treasure and protect the environment.In recent years,tailings have become a hot spot for research as green building materials.The feasibility of antimony tailings waste rock as a high performance concrete coarse aggregate was investigated in view of the large stockpile of antimony tailings in the mining area of Hunan tin mine and the difficulty of disposal.Based on the previous studies on the chemical composition,rock mechanical properties and aggregate properties of antimony tailings waste rock crushed into coarse aggregate,C50 concrete was further prepared at five different coarse aggregate replacement rates of 0%,25%,50%,75%and 100%(noted as T0,T25,T50,T75 and T100),and the construction,mechanical properties,long-term performance and durability of antimony tailings waste rock coarse aggregate high performance concrete(ATWRCAHPC)were systematically investigated.The secondary pollution of ATWRCAHPC was evaluated.The main research results are as follows:(1)The ATWRCAHPC has good workability.The apparent density was slightly higher than that of the control group(T0),while other indexes decreased slightly with the increase of replacement level.The measured slump of concrete with different replacement rates was185mm～198mm;the initial setting time was 365min～398min and the final setting time was540min～570min,all of which met the specification requirements of initial setting greater than45min and final setting less than 600min;the apparent density test values were between2445kg/m~3～2475kg/m~3.(2)The ATWRCAHPC has good physical and mechanical properties.The cubic compressive strength,splitting tensile strength,prismatic compressive strength and elastic modulus were all better than the control group.In addition,the mechanical properties of antimony tailings waste rock coarse aggregate concrete improved with the increase of replacement level when the curing age was certain.For example,the compressive strength results of T25,T50,T75 and T100 specimens at 180 d age were 102%,107%,110%and 116%of those of the control group,respectively.(3)The ATWRCAHPC has good durability.The anti-carbonation,freeze-thaw and chloride ion penetration were better than the control group,and improved with the increase of replacement level;the alkali activity and early crack resistance were slightly lower than the control group,and showed a decreasing trend with the increase of replacement level,but met the specification requirements.(4)The ATWRCAHPC has good shrinkage and creep properties.The shrinkage and creep were lower than those of the control group,and the shrinkage and creep coefficients showed a decreasing trend with the increase of substitution level.The shrinkage of T25,T50,T75 and T100 specimens decreased by 3.3%,4.3%,6.1%and 8.5%,respectively,compared with the control group up to 180d of the test.For creep,the creep coefficients of T25,T50,T75 and T100 specimens decreased by 2.9%,5.9%,6.8%and 9.8%,respectively,compared with those of the control group after holding the load for 180 d.The creep coefficients of 28-d loaded specimens decreased by 1.9%,3.8%,5.7%and 8.2%,respectively,compared with those of the control group.(5)The progress of the research on heavy metal ion dissolution test method was reviewed,and the heavy metal dissolution release pattern of T100 specimens under different p H conditions was tested.The concentrations of Sb,AS and Hg reached the steady state on day 8 under the conditions of p H 4～10.The maximum concentrations of Sb,AS and Hg on day 14 were 0.266 mg/L,0.067 mg/L and 0.029 mg/L,respectively,which were all lower than the corresponding normative limits.The Nemero index method was modified to establish an evaluation model applicable to the secondary pollution of tailings concrete,and the secondary pollution of antimony tailings waste rock coarse aggregate concrete was evaluated.The results showed that the coarse aggregate concrete of antimony tailings waste rock effectively realized the solidification of heavy metals in waste rock,and its secondary pollution met the specification requirements.Based on the systematic experimental study,the results show that the construction performance,physical and mechanical properties,durability and long-term performance of antimony tailing waste rock coarse aggregate concrete perform well,and its secondary pollution meets the specification requirements.Therefore,antimony tailings waste rock has the feasibility of replacing high performance concrete coarse aggregate. |
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