Abstract
Mechanical activation of granulated copper slag (GCS) is carried out in the present study for the purposes of enhancing pozzolanic activity for the GCS. A vibration mill mills the GCS for 1, 2, and 3 h to produce samples with specific surface area of 0.67, 1.03 and 1.37 m2/g, respectively. The samples are used to replace 30% cement (PC) to get 3 PC-GCS binders. The hydration heat and compressive strength are measured for the binders and derivative thermogravimetric /thermogravimetric analysis (DTG/TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) are used to characterize the paste samples. It is shown that cumulative heat and compressive strength at different ages of hydration and curing, respectively, are higher for the binders blending the GCS milled for a longer time. The compressive strength after 90 d of curing for the binder with the longest milling time reaches 35.7 MPa, which is higher than the strength of other binders and close to the strength value of 39.3 MPa obtained by the PC pastes. The percentage of fixed lime by the binder pastes at 28 days is correlated with the degree of pozzolanic reaction and strength development. The percentage is higher for the binder blending the GCS with longer milling time and higher specific surface area. The pastes with binders blending the GCS of specific surface area of 0.67 and 1.37 m2/g fix lime of 15.20 and 21.15%, respectively. These results together with results from X-ray diffraction (XRD), FTIR, and SEM investigations demonstrate that the mechanical activation via vibratory milling is an effective method to enhance the pozzolanic activity and the extent for cement substitution by the GCS as a suitable supplementary cementitious material (SCM).
Highlights
Copper slag (CS) is a by-product generated in the process of copper smelting and converting [1].It has been estimated that for every ton of copper produced, there are about 2.2–3 tons of CS generated [2], resulting in an annual generation rate for the slag of approximately 40 million tons worldwide [3]
Microstructural characterization of the paste samples was carried out using scanning electron microscopy (SEM, Zeiss Merlin, Oberkochen, Germany), with the analysis performed on gold plated polished sample surfaces using an accelerating voltage of 5 kV
Is milled in a vibration mill with different durations (1, 2, 3 h) to obtain 3 samples, which are used to replace 30% cement (PC) forming 3 PC-granulated copper slag (GCS) binders coded as CS1, CS2 and CS3
Summary
Copper slag (CS) is a by-product generated in the process of copper smelting and converting [1]. The C–S–H formed from the reactions, with its C/S ratio lower than the one for the C–S–H produced by cement hydration, may be referred to as pozzolanic C–S–H Both types of the C–S–H contribute to the strength development in cement products. The GCS exhibited a low reaction rate, when being used to partially replace cement, and could only contribute to the development of compressive strength for mortar at late ages This has become a major obstacle to the use of GCS as a pozzolanic material and made it necessary to conduct new research work for enhancing the reaction rate, to increase the extent of cement substitution by GCS. Literatures show that mechanical activation via high-energy milling is an efficient way to enhance the reactivity for industry by-products and pozzolanic materials, such as granulated blast furnace slag (GBFS), steelmaking slag and FA [12,13,14,15]. The enhanced use can reduce the GCS deposition and, decrease consumptions of energy and natural raw materials, and emissions of greenhouse gases related to the manufacturing of cement clinker, enhancing sustainability for both copper and cement industry
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