| The metallurgical processes involved in mineral processing generate large volumes of wastes,which may result in various kinds of environmental concerns.Because of the extraction of low grade ore and maximization of economic benefit,the disposal of copper tailing?CT?may be seen to be tedious to the mining companies which may lead into incorrect CT disposal if the close monitoring and regulations are not reinforced.Increasing accumulation of CT in Zambia has been seen to be accompanied with the leachability of heavy metals into nearby water bodies and siltation along rivers and streams.On the other hand,previous researchers have documented that open burning,stockpiling/landfilling of scrap tyres is accompanied with derivation of heavy metal leachability and toxic gasses into the ambient.Despite,the negative impact of the CT and scrap tyres,previous researchers have documented the utilization of CT and tyre derived aggregates?TDA?in the construction industry because of the increasingly awareness of the detrimental effect that both materials pose to the ambient and the increasing cost of concrete aggregate raw materials.In this study,copper tailing?CT?from five different tailing storage facilities has been studied as natural fine aggregate replacer material in low strength concrete on a singular basis and multiple natural fine and coarse aggregate replacement with CT and TDA simultaneously.The five types of CT samples were acquired from China and Zambia.Two CT from Yunnan Province of China and named as Yunnan-CT I&II,the other three types of CT were from Kakosa,Muntimpa and Mindolo Tailing storage facilities?TSFs?of the Zambian Copperbelt.Concrete specimens with CT as fine aggregate replacer attained the UCS of 35.6MPa as the highest at 30%CT replacement and 24.9MPa was the lowest at 100%CT replacement using 28.77%Ordinary Portland cement?OPC42.5N?.The cementitious properties of the five types of CT were investigated through the means of UCS and it was found that CT from Mindolo tailing storage facility had cementitious properties.Investigation of multiple aggregate replacement TDA was subdivided into coarse aggregate replacement with tyre derived aggregate?C-TDA?and fine-grained tyre derived aggregate?F-TDA?and on this stage Mindolo CT was utilized because of it being cementitious.The UCS results for the simultaneous replacement show that the compressive strength of 31.5MPa was attained at 70%fine sand replacement with CT and 8.74%of coarse aggregate replacement with C-TDA.Uniaxial compressive strength UCS of 28.6MPa and 26.5MPa was attained at 30%and 50%fine sand replacement with copper tailing respectively.In the same concrete molds fine aggregate was replaced with F-TDA at 1.5%and 4%respectively.In principle,CT and TDA can be employed simultaneously as fine and coarse aggregate replacer materials in low strength concrete.After the UCS testing the fragments were subjected to the Toxicity characteristic leaching procedure?TCLP?to investigate the reduction of heavy metals in the designed mix.In addition,the results of TCLP,XRD and SEM were discussed in order to investigate the sustainable utilization of CT.The CTs were also used to investigate the mortar paste analysis and it was noticed that the CT from Muntimpa TSF exhibited the highest UCS while Kakosa TSF had the lowest UCS during the mortar paste analysis using 27.12%OPC42.5N and 72.88%of CT.To investigate the effect of grain size gradation on the mortar paste analysis,the CTs were screen washed using sieve number 200.The CT grain size greater than 0.074mm was used for mortar paste analysis and CT grain size less than 0.074mm for Yunnan CT I&II,Mindolo CT and Muntimpa CT was discarded,while for Kakosa CT it was used in the permeability study of compacted uncemented CT,compacted cemented CT and cemented CT paste.The UCS of compacted CT<0.074mm at 2%plus optimum water content can only attain 120kPa.However,with addition of OPC the UCS of compacted cemented CT can attain the UCS of 1.4MPa using 8.4%OPC42.5N,3.0MPa using 16.8%OPC42.5N for 14 days aged cured samples and cemented CTC paste can attain 3.1MPa using 32.5%OPC42.5N specimens.Based on the laboratory results,CT can be used in the construction of vertical cut off walls within the TSFs by knowing the hydraulic gradient in question.The coefficient of permeability for compacted cemented CTC utilizing the seepage pressure of?s?28?375kPaat 8.4%and 16.8%OPC52.5N were k?28?.46?10-9m/sandk?28?5.8?10-10m/srespectively.In addition,the permeability of cemented CTC paste slurry samples using the seepage pressure of?s?28?210kP awas established and the coefficient of permeability ofk?28?0.4?10-8m/swas attained.In addition,CT cement bentonite?CTCB?for 107 days aged specimens was investigated at5.4%bentonite by weight of soil for specimen CTCB1 and 7.6%bentonite by weight of soil for the specimen CTCB2,the coefficient of permeability ofk?28?.44?10-10m/sand k?28?.41?10-10m/swere obtained respectively.A comparison was made between the CTCB permeability results with the one for Nanjing Silt cement bentonite slurry NSCB1at 5.4%and NSCB2 at 7.6%bentonite by weight of soil with their coefficient of permeability beingk?28?.18?10-10m/sandk?28?79.?10-11m/srespectively. |
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