Slag Binders Research Articles

One-part alkali-activated slag binder for cemented fine tailings backfill: proportion optimization and properties evaluation.

In this study, a one-part alkali-activated slag (AAS) composed of ground-granulated blast furnace slag, desulfurized gypsum, and hydrated lime is proposed as alternative to cement for the production of cemented fine tailings backfill (CFTB), which is an environmentally friendly binder consisting of 93.72 wt.% industrial solid waste. Results show that AAS with 67.83 wt.% slag, 25.92 wt.% desulfurized gypsum, and 6.25 wt.% hydrated lime yields the highest strength, which is 1.7-3.2 times that of ordinary Portland cement (OPC). Aside from calcium silicate hydrate gel, appreciable quantity of ettringite characterized by interlocking needles structure and high bound water is also produced during the AAS hydration process. In addition, the hydration heat of the AAS binder is 48% less than that of OPC. Moreover, CFTB made of AAS provides better workability than that of CFTB with OPC up to 20h. The findings of this study will contribute to the production of more cost-effective, durable, and environmental-friendly cemented fine tailings backfill.

Antimicrobial performance and biodeterioration mechanisms of alkali-activated slag

Eco-friendly antimicrobial alkali-activated slag (AAS) binders show great promise in newly designed and existing wastewater infrastructure threatened by microbial induced concrete corrosion (MICC). This work investigates the antimicrobial performance and biodegradation mechanisms of a new benzoate (BZ)-modified AAS binder. The bacterial activity, corrosion morphology, and material degradation mechanisms, of the novel BZ-modified antimicrobial AAS post-simulated MICC tests are analysed. The bacterial activity assessments (pH value, sulphate concentration, and live/dead staining) results demonstrate the remarkable antimicrobial efficacy of BZ-modified AAS in killing sulphur-oxidising bacteria A. thiooxidans and inhibiting biogenic acidification. The BZ-modified AAS demonstrates excellent microbial corrosion resistance with greatly suppressed production of deleterious gypsum and corrosion depth. The mechanisms of biodeterioration of antimicrobial AAS matrix are revealed, suggesting the nanoscale rupture of calcium-aluminosilicate-hydrate (C-A-S-H) in short chains and networking of aluminosilicate unites upon the removal of interlayer CaO polyhedral. The removal of Al-tetrahedra from bridging sites of C-A-S-H is more susceptible than that of Si-tetrahedra in AAS pastes under microbial corrosion. This study has demonstrated the potentials of novel antimicrobial AAS-based concrete as the next-generation construction materials for wastewater infrastructure.

Sustainable Alkali-Activated Slag Binders Based on Alternative Activators Sourced From Mineral Wool and Glass Waste

In the present study, four different locally available waste glass materials (bottle glass-BG, glass wool-GW, stone wool-SW and cathode-ray tube glass-CRTG) were treated with hot concentrated potassium hydroxide (KOH) in order to obtain alternative alkali activators (AAAs). We evaluated the suitability of the solutions obtained for use as AAAs in the production of AAMs. AAMs were prepared using electric arc furnace slag and selected AAAs with a higher content of dissolved Si. We evaluated the performance of the AAMs in comparison to that of slags activated with KOH or potassium-silicate (K-silicate). The compressive strength of the AAMs prepared with KOH-based AAAs were high when Si and Al were simultaneously abundant in the AAA (9.47 MPa when using the activator sourced from the CRTG), and low with the addition of KOH alone (1.97 MPa). The AAM produced using commercial K-silicate yielded the highest compressive strength (27.7 MPa). The porosity of the KOH-based AAM was lowest when an alternative BG-based activator was used (24.1%), when it was similar to that of the AAM prepared with a K-silicate. The BG-based activator had the highest silicon content (33.1 g/L), and NMR revealed that Si was present in the form of Q0, Q1 and Q2. The concentrations of toxic trace elements in the AAAs used for alkali activation of the slag were also determined, and leaching experiments were performed on the AAMs to evaluate the immobilisation potential of alkali-activated slag. In the SW AAAs the results show acceptable concentrations of trace and minor elements with respect to the regulations on waste disposal sites, while in the activators prepared from BG, CRTG and GW some elements exceeded the allowable limits (Pb, Ba, Sb, and As).

Synthesis of nanoparticles from slag and their enhancement effect on hydration properties of CaO/CaSO4-activated slag binder

Developing a low-cost and eco-friendly alternative to cement is of great significance for reducing the CO2 emissions. CaO/CaSO4-activated slag binder may only be served as a promising cementitious material when the severe defect in the early strength is overcame. In this study, gel-like nanoparticles with an average size of ∼ 328 nm were prepared from the slag through dissolution at room temperature and reprecipitation at 50 °C. Subsequently, synthetic nanoparticles (SNPs) were added as a supplementary additive to enhance the strength of CaO/CaSO4-activated slag binder. The effects of SNPs on the strength development, hydration kinetics, hydration products, and microstructure of the slag binders were investigated. The results indicated that the addition of moderate SNPs shortened the duration of induction period and improved the reaction rate in the acceleration period of the slag binders. As a result, large amounts of calcium aluminosilicate hydrate (C-A-S-H) gel was generated at early hydration ages. Meanwhile, SNPs increased the polymerization degree of this gel through the nucleation effect. Gel products’ well-filled the pore spaces between slag particles and yielded a compact microstructure, consequently enhancing the binder strength. The sample with adding 1.5 wt% SNPs exhibited the optimum strengths of 7.78 and 39.86 MPa after 1 and 28 days.

Adoption of alkali-activated cement-based binders (geopolymers) from industrial by-products for sustainable construction of utility buildings-A field demonstration

There is an increasing interest towards using sustainable construction materials for reducing the consumption of natural resources and maximising the utilisation of industrial waste. Alkali activated alumina silicates sourced from industrial by products are environmentally friendly as they leave a low carbon footprint. In this research, performance-based mixes were designed in which a competitive cementitious binder (0% Ordinary Portland Cement) comprising a blend of fly ash–GGBSGround granulated blast furnace slag as a solid precursor and mixture of sodium hydroxide and sodium silicate was produced and utilised in the construction of a utility building after a comprehensive study. As a result of using the Alkali activated fly ash and slag (AAFS) binder, the formation of reaction product sodium-/calcium-containing alumino silicate hydrate gel of type N-A-S-H and C-A-S-Hnetworkyielded high compressive strength, good bond strength with steel and lower deterioration of the matrix on sulphuric acid exposure, which were confirmed from various test results. In-situ precast products of both structural and non-structural elements, viz. blocks, bricks, window/door frame and slabs of various sizes, were fabricated using local materials andproper training was provided to skill the workers to produce them. Different grades of concrete were produced (M20–M40) and utilised in different stages of the construction of the utility building rural children care centre. The field trials, testing methods, monitoring of various stages of the constructions and challenges are presented in this paper. The findings of this research would help in designing suitable user-defined geopolymer mixes in construction and if this technology becomes ubiquitous in the construction industry, it can contribute to reducing the adverse effects of climate change due to environmental degradation.

Simultaneous addition of slag binder, recycled concrete aggregate and sustainable powders to self-compacting concrete: a synergistic mechanical-property approach

The behavior of Self-Compacting Concrete (SCC) is very sensitive to the use of by-products in replacement of conventional cement or finer aggregate fractions. The high proportions of these raw materials in SCC can in great part explain this performance. 18 SCC mixes of slump-flow class SF3 were prepared for a thorough evaluation of different sustainable materials and for the prediction of their effects as binder or fine/powder aggregate on the mechanical properties of SCC. The mixes incorporated 100% coarse Recycled Concrete Aggregate (RCA); different amounts (0%, 50% or 100%) of fine RCA; CEM I ordinary Portland cement and CEM III/A (with 45% ground granulated blast furnace slag); and more sustainable powders compared to conventional limestone filler <0.063 mm (such as limestone powder 0/0.5 mm and RCA powder 0/0.5 mm). Flowability, hardened density, strength under compression, tensile and bending stresses and modulus of elasticity were all studied. The addition of 50% fine RCA yielded an SCC of adequate strength, stiffness and flowability. SCC manufactured with limestone powder 0/0.5 mm showed the best overall performance, while SCC behavior was improved when adding CEM III/A by adjusting the mix composition. The experimental results of all the mechanical properties were compared with the values predicted by the compressive-strength-based formulas from the European and USA standards. Overall, the values resulting from those expressions overestimated all the mechanical properties. Therefore, since all these properties followed the same simple-regression trend, a statistical analysis was performed to develop a global model capable of accurately predicting them all.

Effect of Extracted Titanium Tailing Slag on the Properties of Alkali-Activated Fly Ash-Ground Blast Furnace Slag Binder

The extracted titanium tailings slag (TS) is a by-product of titanium extraction from the blast furnace slag. Its chemical composition is similar to that of ground granulated blast furnace slag (GGBS), but the relatively lower reactivity limited its utilization as a supplementary cementitious material. In this study, the reactivity of TS was improved by mechanical grinding, and the optimum property of finely ground TS was selected to replace fly ash (FA) in the alkali-activated FA-GGBS binder. The influence of TS content on the fluidity, setting time, and compressive strength of the ternary binder was investigated. X-Ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy were used to analyze the effect of TS on the reaction process. Results showed that the optimum reactivity index of TS was 81.18% at 28 days when it was ground for 15 min in a ball mill. The highest compressive strength of the alkali-activated ternary binder was achieved when the replacement of FA by ground TS was 40%, and its 28-day compressive strength was 49.3 MPa, approximately 22% higher than the binder without TS. The addition of the TS would accelerate the reaction process of binder to form more products, including C-(A)-S-H and gismondine.

Properties and Microstructure of Na2CO3-Activated Binders Modified with Ca(OH)2 and Mg(OH)2.

Delayed strength development and long setting times are the main disadvantageous properties of Na2CO3-activated slag cements. In this work, combined auxiliary activators of Ca(OH)2 and Mg(OH)2 were incorporated in one-part Na2CO3-activated slag binders to accelerate the kinetics of alkali activation. The properties and microstructure evolution were investigated to clarify the reaction mechanism. The results showed that the additions of auxiliary activators promoted the hardening of the pastes within 2 h. The 28 days compressive strengths were in the range of 39.5–45.5 MPa, rendering the binders practical cementitious materials in general construction applications. Ca(OH)2 was more effective than Mg(OH)2 in accelerating the kinetics of alkali activation. The dissolution of Ca(OH)2 released more OH− and Ca2+ ions in the aqueous phase to increase alkalinity in the aqueous phase and promote the formation of the main binding gel phase of calcium-aluminosilicate hydrate (C-A-S-H). An increase in the Ca(OH)2/Mg(OH)2 ratios increased autogenous shrinkage and decreased drying shrinkage of the binders. The formation of a compact pore structure restricted the water evaporation from the binders during the drying procedure.

Residual properties of alkali-activated slag concrete exposed to elevated temperatures

PurposeThis paper attempted to study the alkali-activated (AA) binder consisting of 94% of ground granulated blast furnace slag (GGBFS) and 6% of blended powder of alkali metal hydroxide and metal sulfate, which acted as an activator.Design/methodology/approachSeveral concrete specimens (cubes, cylinders and prisms), which were casted using AA binders, were further tested for mechanical properties after exposure to elevated temperatures of 200 °C, 400 °C, 600 °C and 800 °C. Additionally, to understand the structural behavior in uniaxial compressive load, reinforced concrete short columns were cast, cured and tested at ambient temperature as well as after exposure to 300 °C, 600 °C and 900 °C, to know the residual strength after exposure to elevated temperature.FindingsThe findings for the residual strength of alkali-activated slag binder concrete (AASBC) indicated a substantial agreement with the results obtained for the residual strength of Portland slag cement (PSC) concrete, thereby showing the effectiveness of binder when used as a replacement of cement.Originality/valueThe study clearly indicates that the binder developed is an effective approach for the 100% replacement of cement in the concrete.

Characterization of an aged alkali-activated slag roof tile after 30 years of exposure to Northern Scandinavian weather

Alkali-activated materials (AAMs) have been known as an alternative cementitious binder in construction for more than 120 years. Several buildings utilizing AAMs were realized in Europe in the 1950s–1980s. During the last 30 years, the interest towards AAMs has been reinvigorated due to the potentially lower CO2 footprint in comparison to Portland cement. However, one often-raised issue with AAMs is the lack of long-term studies concerning durability in realistic conditions. In the present study, we examined a roof tile, which was prepared from alkali-activated blast furnace slag mortar and exposed to harsh Northern Scandinavian weather conditions in Turku, Finland, for approximately 30 years. Characterization of this roof tile provides unique and crucial information about the changes occurring during AAM lifetime. The results obtained with a suite of analytical techniques indicate that the roof tile had maintained excellent durability properties with little sign of structural disintegration in real-life living lab conditions, and thus provide in part assurance that AAM-based binders can be safely adopted in harsh climates. The phase assemblage and nanostructural characterization results reported here further elucidate the long-term changes occurring in AAMs and provide reference points for accelerated durability tests and thermodynamic modelling.

Understanding the Shrinkage Behaviour of Alkali-Activated Slag Binders Modified by the Superabsorbent Polymer

Understanding the Shrinkage Behaviour of Alkali-Activated Slag Binders Modified by the Superabsorbent Polymer

Effect of sulphate, chloride and elevated temperature on the properties of Egyptian slag binder

Effect of sulphate, chloride and elevated temperature on the properties of Egyptian slag binder

An investigation on the performance of lightweight mortar-based geopolymer containing high-volume LECA aggregate against high temperatures.

The influence of lightweight expanded clay aggregate (LECA) on the physico-mechanical properties and microstructure of geopolymer mortar containing slag binder alkali-activated with sodium silicate solution before and after exposure to thermal loads was investigated. In the current procedure, siliceous sand was partially substituted with LECA fine aggregate at levels of 0%, 25%, 50%, 75%, and 100%, by volume. The effect of LECA on the performance before exposure was evaluated by measuring flowability, water absorption, bulk density, thermal conductivity, and compressive strength. To monitor the behavior after exposure, a batch of specimens having the same composition was subjected to high temperatures in the range of 400-1000°C for 2h with a heating rate of 5°C/min. In a similar fashion, mass loss and residual compressive strength were determined. New phase-based geopolymers were examined using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The findings indicated that the incorporation of LECA up to 100% as an alternative to siliceous sand aggregate in geopolymer mortar has an adverse effect on compressive strength and water absorption, but has a positive effect on workability, thermal conductivity, and relative strength after exposure to elevated temperatures.

Variation in Polymerization Degree of C-A-S-H Gels and Its Role in Strength Development of Alkali-activated Slag Binders

Variation in Polymerization Degree of C-A-S-H Gels and Its Role in Strength Development of Alkali-activated Slag Binders

Effect of Different CO2 Treatments on the Metal Leaching in Steel Slag Binders

Carbonation is an effective method to promote the quality of the steel slag binder. In this article, two carbonation approaches, namely hot-stage carbonation and accelerated carbonation, were employed to leach the metals, and the influence mechanism on the metal sequential leachability of the binders composed of 80 wt% of EAF slag incorporating 20 wt% of Portland cement (PC) was revealed. The carbonate products, microstructures, and chemical states were investigated, and the results indicated that chromium, vanadium, and titanium gradually transformed into inactive phases after two carbonation approaches, while zinc appeared the opposite trend. The sequential leachability of chromium declined with the increase of the carbonation efficiency, in which the exchangeable chromium decreased from 1.99 mg/kg in the A2A binder to below the detection limit in the A2C binder and C2C binder. Hot-stage carbonation treatment facilitated particle agglomeration, minerals remodeling, and calcite formation. The carbonation curing of the steel slag paste resulted in the formation of amorphous CaCO3, calcite crystalline and Si-bearing hydrates that covered the pores of the matrix, and silicate structure with a higher disorder. The hot-stage carbonation and accelerated carbonation curing methods were adopted to jointly prevent the leaching of harmful metals and facilitate promising high-volume steel slag-based binders with structural densification and CO2 storage.

Synthesis, application and unique effects of RGOEP on properties of alkali-activated slag binders

A highly-dispersed reduced graphene oxide/epoxy resin (RGOEP) composite was synthesized and used to improve related properties of alkali-activated slag (AAS) binders. This study scrutinizes the effects of epoxy resin and RGOEP composite on the hydration products, microstructure and mechanical properties (especially fracture toughness) of the AAS binders activated by water glass or NaOH solutions. The experimental results showed that RGOEP (3 wt%) is able to significantly improve the fracture toughness of the AAS mortars activated by water glass and NaOH, with more than 42.3 and 13.3 times greater, respectively, compared to the pure AAS counterpart. A peony flower-like hydration product was detected when RGOEP was used which is believed to result from the modification of AAS binding matrix by RGOEP at a nanoscale level. Besides, bonding tensile strength was also improved remarkably when 7 wt% GROEP was added into the BFS binders activated by water glass, almost up to 4.8 and 2.9 times as that of the control mortar and the one enhanced by 5 wt% EP, respectively. Thus, a unique advantage of reduced graphene oxide over epoxy resin in enhancing AAS binders was discovered. Considering a very low content of reduced graphene in epoxy resin (only 0.3 wt%), this research indicates great potential for wider industrial applications of this type of RGOEP in the AAS binders.

Compressive strength and hydration process of sodium carbonate-activated superfine slag/marble powder binders

Alkali-activated slag (AAS) attracted wide attention in low carbon cementitious materials. In this study, superfine slag was activated by sodium carbonate (SC), and marble powder (MP) was also used. The effect of MP on SC-activated slag binders were investigated in terms of fluidity, compressive strength , hydration heat and microstructure analysis. Additionally, carbon emissions of the binders were evaluated. Results showed that the compressive strength of SC-activated slag mortars was decreased with the addition of MP, but the strength was still at an acceptable level. The 7-day and 28-day strength of 5 % Na 2 O-E activated slag mortars was 52.0 MPa and 64.7 MPa, while that of the mortars containing 30 % MP was 21.9 MPa and 51.0 MPa, with an obvious decrease. The main hydration products of SC-activated slag/MP pastes were C-A-S-H, calcite, hydrotalcite and gaylussite, and MP seemed no hydration activity in this system. Moreover, carbon emissions of SC-activated superfine slag/MP binders were 104–126 kg CO 2 -e/t, and it seemed much lower than that of strong bases-activated slag system. Such results indicated that this kind of binders had great potential in low carbon cementitious materials. • Superfine slag was activated by sodium carbonate. • Marble powder was used as partial replacement of superfine slag. • Marble powder increased the fluidity but decreased the strength of mortars. • This kind of binders showed low carbon emissions.

Development and research of the influence of the composition and concentration of activators on the strength of phosphorus slag binders

The paper discusses various ways of activating phosphorus slags by introducing additives for the development of phosphorus slag binders (PSB), replacing cement. Considering that pseudowollastonite is the main mineral of phosphorus slags and without activating components does not possess the binding properties necessary for the production of building materials based on them, we used compositions of small amounts of sodium hydroxide with alkali metal salts, the anions of which form poorly soluble compounds with calcium. When choosing activating components, scarce alkaline additives were replaced by waste from chemical plants, which allows a passing solution of their practical use and environmental problems. The strength at a sodium hydroxide content of 1–4 % after curing of slag samples of various batches was in the range of 50.0–70.0 MPa. Samples of binders of normal hardening at the age of 28 days with a sodium hydroxide content of 0.5; 1.0, 2 and 4 % had the strength of 20.3; 35.4; 45.6; 55.8 MPa, respectively. The effect of the combined presence of alkali and salt is especially noticeable for small amounts of sodium hydroxide. Binders containing a composition of cement with salts under normal conditions and after curing showed a slightly lower strength than in an alkaline medium. With a constant cement content (4 %), the strength indicators increase with an increase in the proportion of the salt additive, reaching at 4 % its maximum value. The effect of the nature of activators on pH was determined. The data obtained indicate the advantages of using PSB and various industrial wastes with a low content of alkaline compounds in the production

Experimental comparisons between one-part and normal (two-part) alkali-activated slag binders

One-part alkali-activated slag (AAS) binders are more promising in large-scale constructions because one-part mixing procedure is safer and easier to handle compared to normal two-part method. Thus, this study aims at investigating different properties of one-part AAS binders and control samples prepared using the two-part method. Experimental results of the former suggested the hardening time was greatly extended, but the workability showed little difference. Besides, compared to the control, one-part AAS binders had similar early compressive strength (within 7 days) and flexural strength in all tested curing stages but lower later compressive strength (from 28 days). The characterisation of the porous structures suggests that there were fewer C-A-S-H gels for one-part binders evidenced by less volume of mesopores but with larger amount of bigger pores. In addition, mineralogical and microstructural analyses imply that there was no hydrotalcite formed in the one-part AAS binders. Moreover, one-part AAS binders are more susceptible to efflorescence, presumably further affecting their surface and long-term durability.

Calcium carbide residue as auxiliary activator for one-part sodium carbonate-activated slag cements: compressive strength, phase assemblage and environmental benefits

Sodium carbonate (Na2CO3) has the potential to become an efficient solid activator for preparing one-part alkali-activated ground granulated blast furnace slag cements. However, the Na2CO3-activated slag binders usually exhibit the delayed hardening time and slow early-age strength development. In this study, calcium carbide residue (CCR), an industrial waste mainly composed of Ca(OH)2, was applied as a type of auxiliary activator to accelerate the reaction kinetics of Na2CO3-activated slag binders. Effects of CCR additions on the compressive strength and phase assemblage of the binders were investigated, and the environmental benefits from the use of CCR were evaluated. The results showed that the initial reaction between CCR and Na2CO3 removed CO32- ions and meanwhile produced OH- ions in the aqueous phase to enhance the alkalinity. The Ca2+ ions released from the dissolved CCR particles promoted the polymerization of C-A-S-H type gel, associated with the formation of other calcium-containing products of calcite, calcium hemicarboaluminate and calcium monocarboaluminate. Hydrotalcite-like phase was identified in the inner product layer formed around the slag particles. The CCR addition promoted the hardening and consequently enabled the pastes to set within 7 h. As the optimum mixture in terms of strength development, the binder with 8% Na2CO3 and 2.5% CCR exhibited the maximum 1-day and 28-day compressive strengths of 21.8 and 37.7 MPa, respectively. When compared with the PC paste, production of this CCR-modified Na2CO3-activated slag cements had considerable savings of 94%, 87% and 20% in CO2 emissions, energy consumption and cost, respectively.