Concrete is the most produced construction material in the world and has a close tie to carbon dioxide emissions. To reduce the gas pollution and resource drain of cement production and utilization, ...researchers have replaced some of the cement and natural aggregate content with industrial by-products such as steel slag, ferronickel slag, copper tailings, and copper slag. However, a comparison of these widely used by-products in the construction industry, especially in the environmental health aspect, has not been discussed. This paper examines and compares these four by-products critically, with a particular emphasis on their chemical compositions, performance in concrete, and environmental suitability as construction materials. Generally, these industrial wastes can be used to increase specific mechanical properties of the concrete when used as a partial cement and fine aggregate replacement. The environmental concerns were evaluated by looking at leaching test data, finding most studies reporting leached heavy metal contents below specific standards. This paper's comprehensive review and analysis can be considered for practical use. The paper also addresses gaps in different slags (e.g., steel and copper slag) and copper waste (e.g., copper slag and tailing), and future research opportunities for using metal production by-products.
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A deeper insight into SO3/Al2O3 ratio including the contribution of alumina in slag at early age is required to ensure a properly sulfated slag cement. In this paper, to investigate the effect of ...gypsum and alumina of slag, emphasis was laid on the hydration characteristics of C3S-gypsum-slag system during the early age, of which slag was synthesized in the laboratory with varying Al2O3 contents from 3.69 to 18.19 wt%.
The duration of dormant period during the hydration of C3S depended on Al2O3 content of slag significantly; however, the amount of silicate reaction before the onset of aluminate reaction was independent of slag chemistry and gypsum content added. The rate of aluminate reaction was controlled by the availability of reactants, SO42− and Al3+ ions in particular, which were sourced from gypsum and slag, respectively. Calcium monosulfoaluminate only occurred in mixture when slag contained a high amount of Al2O3 (18.19 wt% in this study) at early age, and its formation proceeded continuously at the expense of ettringite. Sulfur rich species incorporated in slag started to participate into aluminate reaction after the main hydration peak of C3S, and it played a similar role to gypsum.
•Mechanical and microstructure properties of FA-GGBS-HMNS based GPC are investigated.•Addition of HMNS in FA-GGBS based GPC can enhance the intermolecular bonding of GPC matrix.•Mechanical properties ...are improved when HMNS is added in FA-GGBS based GPC cured at ambient conditions.•SEM analysis showed that FA-GGBS-HMNS based GPC is highly compacted, with a dense matrix and fewer pores.
This paper presents an experimental investigation on the mechanical properties and microstructure of geopolymer concrete mixed using class F fly ash (FA), ground granulated blast-furnace slag (GGBS) and high-magnesium nickel slag (HMNS). An optimal combination of FA, GGBS and HMNS was determined using the compressive strength tests of geopolymer (GP) pastes mixed with various different replacements of FA with GGBS and/or HMNS. It was found that the replacement of FA with 20% of GGBS and 10% of HMNS in GP concrete increases the 28-day compressive strength by 100% and the 28-day splitting tensile strength by 58%. The microstructure analysis of the GP concrete using SEM, XRD, and FTIR showed the formation of aluminosilicate amorphous phase in a three-dimensional network. The SEM images revealed a fully compact and cohesive geopolymer matrix, which explains the reason why the mechanical properties of the FA based GP concrete with both GGBS and HMNS are improved.
Steel furnace slag (SFS) is an industrial by-product that is not commonly utilized in bound applications because of its potential to contain high contents of free calcium and magnesium oxides, which ...expand when hydrated. In this study, a process was developed to quickly screen SFS aggregates for free oxide contents and expansion potential using complexometric titration, thermogravimetric analysis, and an autoclave expansion test. Two of the three SFS aggregate sources (high and low expansion) were selected for testing as a coarse aggregate in concrete. It was confirmed that SFS aggregates in concrete can produce acceptable strength properties, suitable freeze/thaw durability, and exceptional fracture properties. However, these SFS aggregates produced greater free drying shrinkage than concrete with dolomite aggregates. For SFS aggregates having low expansion potential, the hardened property tests indicate that SFS may be a suitable aggregate for concrete.
Shrinkage of alkali‐activated slag (AAS) cement is a critical issue for its industrial application. This study investigated the mechanisms and effectiveness of shrinkage‐reducing agent (SRA) and ...magnesia expansive agent on reducing autogenous and drying shrinkage of AAS mortars that were activated by liquid sodium silicate (LSS) solution with modulus (SiO2/Na2O molar ratio) of 0‐1.5. The results showed that the autogenous shrinkage of AAS mortars increased with the increase of LSS modulus from 0 to 0.5, then decreased as modulus increased up to 1.5. The drying shrinkage consistently increased with the increase in the modulus of LSS. The oxyalkylene alcohol‐based SRA could significantly reduce the autogenous and drying shrinkage of AAS mortars while the magnesia expensive agent was comparatively less effective. The autogenous shrinkage of AAS mortars was inversely proportional to the internal relative humidity, while the drying shrinkage was more related to the mass loss of samples. Mathematical models were established to describe the autogenous and drying shrinkage behavior of AAS mortars.
The arsenic (As) vitrification in copper smelting slag derived from the FeO−SiO2−Fe2O3−B2O3−CaO− Al2O3−(MgO) system was studied. The vitrification mechanism of As was systematically investigated by ...XRD, SEM, FTIR and XPS analysis. It is determined that As exhibits favorable compatibility with the iron-silicate slag. FTIR and XPS analysis indicates that As can partially substitute for silicon to form the Si—O—As structure, thereby enhancing the degree of polymerization of the melt. The BO33− unit tends to decrease with the increase of the As content, while the opposite behavior is observed with the addition of MgO. Additionally, MgO increases the non-bridging oxygen (NBO) number of the melt. TCLP, SPLP and pH dependence tests show that the leaching toxicity of As increases with the increase of the As content but decreases with the addition of MgO. DSC analysis demonstrates that the incorporation of both As and MgO can improve the thermal stability of the As-containing glass.
In this study, Na2CO3-activated slag cements were produced from four different blast furnace slags, each blended with a calcined layered double hydroxide (CLDH) derived from thermally treated ...hydrotalcite. The aim was to expedite the reaction kinetics of these cements, which would otherwise react and harden very slowly. The inclusion of CLDH in these Na2CO3-activated cements accelerates the reaction, and promotes hardening within 24h. The MgO content of the slag also defines the reaction kinetics, associated with the formation of hydrotalcite-type LDH as a reaction product. The effectiveness of the CLDH is associated with removal of dissolved CO32− from the fresh cement, yielding a significant rise in the pH, and also potential seeding effects. The key factor controlling the reaction kinetics of Na2CO3-activated slag cements is the activator functional group, and therefore these cements can be designed to react more rapidly by controlling the slag chemistry and/or including reactive additives.
This work explored the effect of mineralogical changes of a modified basic-oxygen furnace slag (BOFS) on the properties of alkali-activated binders. The study quantified the amorphous-crystalline ...proportions of particles from three different size ranges. These size fractions were finely milled and activated with NaOH solutions. The effects on the reaction kinetics and the mechanical strength of the produced binders were established. The early-stage reaction kinetics were tracked, and the significance of the precursor fraction, the addition of admixtures (gypsum and plasticizer), and the liquid-to-solid ratio (L/S) on the reaction kinetics were identified. The relative variation in the amorphous content between fine and coarse fractions was 45%. These mineralogical differences interacted with the presence of admixtures and the L/S, which impacted the kinetics of the cementitious reactions and the rate of strength development of the binder. Nevertheless, the 30-day strength was similar for all specimens (58 MPa).
•The granulation of BOFS altered the mineralogical proportions found in slag particles of different sizes.•The mineralogical variations impacted the kinetics and the strength development rate of alkali-activated binders.•The strength of the binders after 30 days was similar and independent of the size fraction of slag used as precursor.•The kinetics of the alkali activation can be customized by using specific size fractions of the modified BOFS as precursors.
The amendment of cementitious binders with waste materials aids as a path to reduce the volume of waste and carbon emission. This review summarizes the current state of practice for cementitious ...binder fabrication in favor to the utilization of waste materials such as waste concrete powder (WCP), coal bottom ash (CBA) and steel slags. These materials have the potential to be employed as cementitious material, however much of the application is still up to the laboratory scale. This manuscript will serve as the support to understand the utilization of mentioned waste as nontraditional cementitious products. The highlighted areas likely need more refinement and research with indication on possible negative impact on application of wastes. The use of the aforementioned wastes for blending with OPC (ordinary Portland cement) can reduce carbon emissions from cement manufacturing. Additionally, it can also reduce the use of natural resources during clinker production.
This paper studies chemical composition of partially and fully hydrated slag grains in a (nearly) 40-year-old field concrete from the Netherlands. The concrete samples were assumed to be sufficiently ...aged to contain fully hydrated slag grains as well as partially hydrated large slag particles with thick rims. Our analysis showed that three different elemental zoning could be identified depending on the original slag grain size. Upon full hydration of a small slag grain (i.e., <8 μm), two distinct regions were identified corresponding to a hydrotalcite-like phase in the outer rim and a C–S–H gel phase in the core, respectively. As for medium (8–17 μm) and large (>15 μm) slag grains, three distinct regions were clearly visible. Hydrotalcite-like phase was mainly observed in the outer rim and the core. C–S–H gel phase was found to be precipitated in the region between the outer rim and the core.
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