Strength and Durability Properties of Self Compacting Concrete Incorporating Copper Slag

Abstract

Copper manufacturing industry produces abundant quantity of copper slag as an industrial by-product. Its management and disposal poses a major challenge for the environment, thus an urgent need for its potential alternative is recommended. Also, the high excavation cost of natural sand, its scarcity in the environment along with its ever increasing demand has urged the concrete industry to look for some low-cost and abundantly available alternatives. A sustainable approach is required to conserve the environment as well preserve the natural resources at the same time. The consumption of copper slag as sand replacement in concrete serves to be a viable option for progressing towards a sustainable development. The intent of the current research work is to design self-compacting concrete (SCC) mixes incorporating copper slag as fine aggregate replacement. SCC mixes were designed to have 28 days compressive strength in the range of 20-40 MPa. SCC mixes incorporated 20% fly ash as cement substitution and copper slag varying from 0% to 60% as sand replacement. A total of seven SCC mixes were developed- 0CS-SCC, 10CS-SCC, 20CS-SCC, 30CS-SCC, 40CS-SCC, 50CS-SCC and 60CS-SCC. 0CS-SCC mix was developed with 0% copper slag, 10CS-SCC for SCC mix with 10% copper slag, 20CS-SCC for SCC mix with 20% copper slag, 30CS-SCC for SCC mix with 30% copper slag, 40CS-SCC for SCC mix with 40% copper slag, 50CS-SCC for SCC mix with 50% copper slag, and 60CS-SCC for SCC mix with 60% copper slag. The fresh properties included the slump flow, V-funnel, L-box, U-box and sieve segregation resistance of SCC. The strength properties included the compressive strength and splitting tensile strength of SCC. The durability properties included the water absorption, sorptivity, chloride ion permeability, drying shrinkage and sulfate resistance of SCC made with copper slag. The strength and durability properties of SCC were performed and analysed for up to one year. The microstructural analysis included Scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) of SCC mixes at all ages of curing. Statistical analysis was conducted to study the correlations amongst various properties of SCC. The statistical significance of the strength and durability properties was evaluated using Analysis of Variance (ANOVA). Multiple comparison analysis was conducted to compare different SCC mixes using the Post Hoc Tukey test. Test results indicated that all the mixes were in good accordance with the classifications prescribed in the European code. Copper slag was effective in enhancing the filling ability, viscosity, passing ability and sieve segregation resistance of SCC mixes. The compressive strength of SCC mixes incorporating up to 60% copper slag showed almost similar/higher results in comparison with a concrete mix containing 100% sand. The strength of SCC mixes increased with the increase in curing age. The 28 days compressive strength of SCC mix incorporating 10, 20, 30, 40 and 50% copper slag achieved 6.97, 8.19, 4.20, 0.97 and 0.04% higher compressive strength as compared to control SCC mix (35.63 MPa). An insignificant decrease of 0.09% was observed in SCC mix with 60% copper slag in comparison to control SCC mix at 28 days. The splitting tensile strength of SCC mixes increased with the increase of copper slag content from 0 to 60% and also with the increase in curing age. At 28, 90 and 365 days, splitting tensile strength of SCC mixes with copper slag (0 to 60%) increased from 2.56 to 3.43, 3.65 to 4.23, 3.86 to 4.47 MPa as compared to 2.13, 3.11 and 3.42 MPa, respectively, of control mix without slag. A reduction in water absorption and volume of permeable voids was obtained in SCC mixes incorporating up to 60% copper slag. With age, reduction in water absorption and volume of permeable voids was significantly achieved. Incorporation of copper slag up to 60% exhibited reduced sorptivity values of SCC mixes up to 365 days. SCC mixes incorporating copper slag showed improved resistance to chloride ion permeability. The drying shrinkage of SCC mixes decreased on the addition of copper slag up to 60% at all curing ages. Even after one year of sulfate exposure to SCC mixes, no major catastrophic damage was visible. Copper slag was successful in improving the overall sulfate resistance of SCC mixes. The microstructure of SCC incorporating up to 60% copper slag showed the formation of calcium silicate hydrate layers under SEM analysis giving the concrete matrix a denser and homogenous structure. SCC mixes showed a crystalline behaviour up to 365 days. No major phase change was indicated while increasing the percentages of copper slag in SCC.