Alkali-activated Blast Furnace Slag Research Articles

Investigating the impact of foundry by-product sand as an activator on workability improvement and strength development in alkali-activated blast furnace slag mortar

The substitution of alkali-activated furnace slag significantly reduces the necessity of cement manufacture and mitigates the continuous growth of carbon emissions. In addition, it shows superior mechanical properties compared to traditional concrete materials. However, rapid setting issues hinder its widespread applications. This study investigated the innovative use of zero-carbon waste sodium silicate-bonded sand as a substitute for the fine aggregate and sodium silicate in traditional alkali-activated blast furnace slag mortar. The primary objective is to analyze the impact of waste sodium silicate-bonded sand on the workability and mechanical properties of the mortar. The key properties such as flowability, setting time, temperature measurement, compressive strength, and microstructural were analyzed to determine the improvement in workability and the strength development of alkali-activated blast furnace slag mortar resulting from the use of waste sodium silicate-bonded sand. The research showed the integration of waste sodium silicate-bonded sand results in an eco-friendly and cost-effective material, which addresses limitations in traditional activated blast furnace slag mortars. The finding revealed that substituting fine aggregate and sodium silicate with waste sodium silicate-bonded sand significantly improved the mechanical and workability properties of alkali-activated mortars. Notably, the compressive strength of mortars incorporating waste sodium silicate-bonded sand exceeded that of traditional Portland cement and effectively mitigated rapid setting issues. In addition, this approach led to an environmentally friendly mortar with satisfactory workability. The research emphasizes the practical benefits of utilizing waste sodium silicate-bonded sand and offers new insights into its effects on mortar performance. This has provided more details for future exploration and refinement in the field of alkali-activated materials.

Effect of Inorganic Anions on the Structure of Alkali-Activated Blast Furnace Slag

Analyzing the effect of anions on the structure of geopolymers is crucial because anions can significantly influence the material’s chemical stability, mechanical properties, and long-term durability. Understanding these effects helps optimize geopolymer compositions for various applications, such as construction materials and waste encapsulation. This research report describes the effects of nitrate, sulfate, and phosphate anions on alkali-activated blast furnace slag’s structural integrity and properties. Advanced techniques like XRD, FT-IR, Raman spectroscopy, and XPS have been employed to analyze structural modifications caused by anions, providing insights into their interactions and effects. These anions generally decrease compressive strength by disrupting geopolymerization and altering microstructure. For example, sulfate ions lead to the formation of ettringite, while phosphate ions bind calcium into separate phases. We can also observe microstructural changes, such as increased porosity with phosphate, which significantly reduces strength. Nitrate’s effect is less detrimental but still influences the overall structural dynamics.

Effect of glass and nylon fibers on drying shrinkage of alkali activated blast furnace slag mortars

The environmental consequences of Portland cement (PC) manufacturing have prompted the exploration of alternative binders, such as the alkali activation of blast furnace slag (BFS), which is generated as a byproduct during the extraction of iron. While alkali-activated blast furnace slag (AAS) binders have some benefits over regular PC binders, they also suffer from disadvantages such as significant drying shrinkage. The study investigated the impact of Na dosage and curing conditions on alkali-activated blast furnace slag mortar (AASM). The consistency of the specimens was tested for fresh, hardened properties, and was conducted. The optimum Na dosage and curing conditions were selected. In the second stage, 0.1% and 0.2% glass and nylon fibers were added to the selected optimum mortar. Consistency, fresh, mechanical, and durability properties tests were conducted on the fiber mortars. The results showed that increasing the Na content increased the compressive and flexural strengths of AASM specimens. Thermal curing provided high compressive and flexural strengths, whereas fiber addition reduced water absorption and drying shrinkage. The drying shrinkage value was reduced by 26.82 % for AASM specimens with 0.2 % nylon fibers by volume compared to AASM without fibers.

Compressive Strength and Microstructure of Carbide Slag and Alkali-Activated Blast Furnace Slag Pastes in China

The alkali-activated blast furnace slag is attracting significant attention in replacing Portland cement due to several characteristics similar to cement hydration. However, there are a few practical problems with commercial alkali activators, such as the fast setting time, relatively high costs, and significant CO2 emissions during preparation. Thus, discovering industrial residues possessing inherent alkalinity are urgent. This study proposes the use of carbide slag at levels of 0%, 5%, 10%, 15%, 20%, and 30% and alkali at levels of 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10% activated blast furnace slag. The compressive strength and microstructure of carbide slag and alkali-activated blast furnace slag (CAB) pastes were examined using X-ray diffraction analysis (XRD), Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TG), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). The results revealed that the addition of carbide slag produced more hydrotalcite-like phase as well as decreased the content of ettringite (AFt) and the calcium–silicate–hydrate (C-S-H) gel, which decreased the compressive strength of the CAB pastes. At the age of 28 days, when the dosage was 5%, 10%, 15%, 20%, and 30%, the compressive strength of CAB mixes decreased by 2.1%, 7.1%, 9.2%, 9.8%, and 28.1%, respectively. The addition of NaOH promoted the formation of AFt, and there was an optimum level of NaOH corresponding to the high compressive strength of paste. At the age of 3 days and 7 days, the compressive strength reached its maximum at the dosage of 6% NaOH, which was 24.8 MPa and 36.3 MPa, respectively. However, at the ages of 14 days and 28 days, the compressive strength increased as the dosage of NaOH increased to 5%, which was 43.3 MPa and 44.5 MPa, respectively. The water curing could both enhance the early and later strength, the compressive strength of 23.3 MPa was gained at 3 days, and this increased by 16.3%, 24.0% and 36.9% at 7 days, 14 days and 28 days, respectively. Therefore, water curing was suitable for the strength development of CAB pastes.

Effect of Silica Addition on Lead Ion Adsorption Ability of Alkali-Activated Blast Furnace Slag

Effect of Silica Addition on Lead Ion Adsorption Ability of Alkali-Activated Blast Furnace Slag

Adsorption of methylene blue by composite foams containing alkali-activated blast furnace slag and lignin

Adsorption is a promising method to remove dyes, such as methylene blue, from wastewater. In this study, a dynamic adsorption set-up was used to treat synthetic wastewater containing methylene blue by using alkali-activated blast furnace slag and lignin composite foam. The structure of the foam without lignin was first optimized by comparing cationic and non-ionic surfactants in the preparation of the foam via the direct foaming method. The selection of the surfactant affects the porosity and pore structure of the foam through different abilities to stabilize the gas–liquid interface and changes in the viscosity of the fresh-state paste. The foam prepared with non-ionic Triton X-114 surfactant had the highest adsorption performance and was selected for the optimization of adsorption conditions. The optimized conditions were 5 mg/L influent concentration of methylene blue, pH of 7, and flow rate of 1.0 L/h (corresponding to ~ 9 min empty bed contact time). To further enhance the methylene blue adsorption performance, a composite containing lignin was prepared. The optimum lignin amount in the foam was 0.8 wt% and it resulted a ~ 93% higher adsorption amount compared to the foam without lignin. The highest cumulative adsorption capacity in this dynamic adsorption setup was 39.5 mg/g, which is among the highest reported values for methylene blue removal by monolithic adsorbents. The present study provides a proof of concept for the enhancement of adsorption performance of alkali-activated materials by introduction of lignin into the structure.

Preparation and characterisation of alkali-activated blast furnace slag and Na-jarosite catalysts for catalytic wet peroxide oxidation of bisphenol A

ABSTRACT In this study, cost-effective alkali-activated materials made from industrial side streams (blast furnace slag and Na-jarosite) were developed for catalytic applications. The catalytic activity of the prepared materials was examined in catalytic wet peroxide oxidation reactions of a bisphenol A in an aqueous solution. All materials prepared revealed porous structure and characterisation expressed the incorporation of iron to the material via ion exchange in the preparation step. Furthermore, the materials prepared exhibited high specific surface areas (over 200 m2/g) and were mainly mesoporous. Moderate bisphenol A removal percentages (35%–37%) were achieved with the prepared materials during 3 h of oxidation at pH 7–8 and 50°C. Moreover, the activity of catalysts remained after four consecutive cycles (between the cycles the catalysts were regenerated) and the specific surface areas decreased only slightly and no changes in the phase structures were observed. Thus, the prepared blast furnace slag and Na-jarosite-based catalysts exhibited high mechanical stability and showed good potential in the removal of bisphenol A from wastewater through catalytic wet peroxide oxidation.

Effect of Retarders on the Reactivity and Hardening Rate of Alkali-Activated Blast Furnace Slag Grouts.

Sodium silicate-activated slags have the potential to harden quickly, which limits their practical use in grouting and deep soil mixing works. The open time of grouts is defined as the time period when their rheological properties allow their storage, pumping, and injection into the soil. In this work, the impact of the H2O/Na2O ratio and two acids (citric and boric acid) on the reactivity and hardening rates of slag-based grouts was studied. The H2O/Na2O ratio had a minimal impact on the open time but prolonged the setting time, as observed by ultrasonic characterization. Both acids were effective in delaying the structuration time, as revealed by oscillatory rheology and reaction advancement; however, they caused a decrease in the elastic modulus. Adding the acids resulted in a decrease in the pH of the medium, which may be linked to the extended open time. The analysis of the ion concentration of Ca, Si, and Al disclosed the mode of action of the two retarders.

An experimental study on the development of self-compacting alkali-activated slag concrete mixes under ambient curing

This study was carried out to develop alkali-activated blast furnace slag concrete having self-compacting properties under ambient curing. Ground Granulated Blast Furnace Slag was used as the binder, and the blended sodium silicate liquid and sodium hydroxide pellets were added to activate the GGBFS. Fine aggregate and coarse aggregate were replaced by unprocessed blast furnace slag and electric arc furnace slag. There were a huge number of parameters, such as binder content, water-binder ratio (w/b), Na2O% and activator modulus (Ms), that influence the fresh and hardened properties of self-compacting alkali-activated Slag concrete. Taguchi’s Design of Experiments (DOE) method was used to minimize the possible number of mixes to perform experiments. Taguchi’s DOE method uses a specific design based on the orthogonal arrays to understand the entire parametric space with a less number of possible experiments. Therefore, based on Taguchi’s DOE method, detailed experiments were carried out corresponding to only nine mixes known as calibration mixes. Mix-7 shows higher compressive strength (at 28 days), modulus of elasticity, split tensile and flexural strength are 46.2 M of 46.2 MPa, 30.27 GPa, 4.43 MPa and 5.31 MPa, respectively. The results of this study show that the 28 days mechanical strength of SCAASC mixes is most controlled by Na2O% followed by binder content (GGBFS), Ms value and w/b ratio.

Mechanical Strengths of Alkali-Activated Blast Furnace Slag Powder with Different Alkali Activators and Plant Fibers

In this paper, the influence of water glass types, the modulus of water glass, the alkali content, the water consumption, and plant fibers on the mechanical strengths of alkali-activated blast furnace slag powder (BFS) is investigated. Moreover, the fiber types and pretreatment on the plant fibers and the measuring temperature on the performance of alkali-activated BFS are further considered. Results indicate that BFS activated by potassium silicate shows higher mechanical strengths than that activated by sodium silicate. The alkali-activated BFS with alkali treatment on fibers is the most advantageous. The modulus of alkali leads to decreasing the compressive strength. A total of 35% water consumption is the most beneficial to the specimens’ flexural and compressive strengths. Samples with 14% potassium silicate show the maximum mechanical strength. Alkali-activated BFS with 1% wheat straw fibers in addition by total volume represents the maximum mechanical strength. The alkali-activated BFS with alkali treatment on fibers is the most advantageous. The addition of potassium silicate can improve the flexural and compressive strengths by the maximum values of 30.4% and 16.8% compared to specimens with sodium silicate. A total of 35% water consumption can increase the flexural and compressive strengths by 33.8% and 32.7%.

Effect of green liquor dregs as an alkali source for alkali-activated blast furnace slag mortar

Sodium-rich green liquor dregs (GLD) are one of the main landfilled residues generated in pulp mills, and to date, no economically profitable ways to utilise GLD has been identified. In this study, GLD have been studied to be used as an alternative alkali source together with alkali-activator, sodium metasilicate (Na2SiO3), for blast furnace slag (BFS) mortar. Microsilica was used as an additional silica source to ensure steady Na2O:SiO2-ratio (0.16). In purpose to remove the remaining organic carbon and increase the suitability of GLD to be used in alkali-activated materials, it has been first thermally treated in 525 °C. The amount of GLD in the recipes varied from 0 to 45 wt%. Calorimetry measurements showed that increasing the amount of GLD reduced the hydration heat and postponed the reaction. With thermogravimetric analysis, X-ray diffractometry and scanning electron microscopy it was found that hydrated samples with more GLD contained more carbonate phases, which indicated that the reactivity of GLD was lower in comparison with that of other raw materials. Compressive and flexural strength measurements showed that increasing the amount of GLD affected the early strength gain (2 and 7 days) of the samples, but at the age of 29 days, the difference was not as high. The compressive strength of the reference sample at 29 days was 59 MPa, while the compressive strength of four sample recipes containing GLD (up to 36 wt%) was higher than 49 MPa. According to the results, green liquor dregs have potential to be used as a secondary alkali source in alkali-activated materials, but more detailed study should be conducted for the recipe in the future.

Effect of washing aggregate sludge waste on the properties of alkali-activated blast furnace slag

The growing production of aggregates in quarries leads to the generation of solid wastes and an expansion of energy footprint. Since these solid wastes are generally stored in landfills, they cause environmental and economic problems. This paper sought to provide a sustainable alternative for the valorization processes of one of these solid wastes, washing aggregate sludge (WS) obtained from a specific aggregate quarry, by investigating the possibility of its utilization as a supplementary precursor material in alkali-activated paste and mortars. The mixtures were produced by replacing the blast furnace slag (BFS) with WS by 0, 25, 50, and 75 wt%, and the effect of WS on the physical, mechanical, durability, and microstructural properties of samples was comprehensively studied. The results revealed that the incorporation of WS consistently extended the setting time of mixes, providing a suitable setting time range for ease of handling, and the setting time of mixtures was predominantly influenced by the initial SiO2/Al2O3 molar ratio. The mechanical and physical test results indicated that the increase in WS replacement ratios increased the water absorption, voids content, drying shrinkage, and sorptivity values, and reduced the compressive strength of alkali-activated mortar samples. On the other hand, an increase in WS ratio efficiently increased the residual compressive strength values of mortar specimens during wetting-drying cycles, indicating its suitability for warm and moist climatic areas. The microstructure analysis revealed that C-A-S-H type gels were mainly formed in the reference mix (100% BFS), whereas N-A-S-H along with C-A-S-H type gels were detected in the specimens produced with a higher WS ratio. The incorporation of WS up to 25% to produce BFS-based AAM as a construction material can be a competent method to efficiently utilize WS waste which may also protect the environment and ensure sustainability.

Optimal Constituent Mix Ratio for Improved Fresh Properties of Cementitious and Alkali-Activated Porous Concretes

This study focuses on the ideal mix of constituents (aggregate, binder, liquid phase, and admixtures) for porous concrete (PC) with optimal fresh properties to be used in pervious road pavements. Ordinary portland cement (CEM-I) and alkali-activated blast furnace slag (AA-BFS) were used as binders. This experimental investigation focused on finding the mix proportion that can best produce a consistent fresh mixture in which the mortar attaches strongly to the coarse aggregates. CEM-I and AA-BFS mortars and concretes were designed to meet the consistency criteria for PC mixtures and then tested to assess their volumetric and mechanical properties. The effect of mix composition on the consistency of fresh mixtures was adjudged through statistical analyses. In the case of AA-BFS mixtures, latex admixture (LA) and a polycarboxylate-ether-based superplasticizer (SP) both helped to achieve a higher level of consistency, and the addition of a viscosity-modifying admixture was necessary for CEM-I PC mixtures only. In terms of hardened properties, AA-BFS mortars exhibited slightly higher strengths than CEM-I ones independently of curing time. Although neither LA nor SP increased strength values at the mortar scale, in PC mixtures, the use of LA proved fundamental in the production of AA-BFS concrete with adequate strength values. This study recognizes that the optimization method as per the consistency assessment of fresh mixtures can be applied to PC with both cementitious and AA-BFS binders.

Dependence of Lignosulfonate Plasticizer Efficiency on the Activator Concentration in Alkali-Activated Blast Furnace Slag Paste

Alkali-activated materials are a low carbon alternative for Ordinary Portland cement in the building industry. However, the effectiveness of commercially available cementitious plasticizers is often an issue. The present study deals with the workability, setting time, and mechanical properties of alkali-activated blast furnace slag (AAS) systems with different addition of lignosulfonate plasticizer (0; 0.5 and 1.0%) and various concentrations of alkaline activator (sodium hydroxide with concentration of Na+ ranging from zero to 12 mol∙dm−3 was used for these purposes). The workability of AAS was determined using the slump test according to EN 1015-3. Then the Vicat apparatus as described in EN 196-3 was used for measurement of the setting time. The effect of activator dose and plasticizer addition on the mechanical properties was determined using the determination of compressive and tensile strength in bending. A positive effect of the addition of a plasticizer in a certain concentration range on the workability was observed, but at the same time, the setting time is prolonged. The optimal concentration of NaOH seems to be of 2–4 mol∙dm−3 regarding the development of mechanical properties and workability.

The Influence of CaO and MgO on the Mechanical Properties of Alkali-Activated Blast Furnace Slag Powder.

CaO and MgO are both reported as effective activators for blast furnace slag. However, the synergistic effect of these two components on the mechanical properties of alkali-activated blast furnace slag remains unclear. In this study, the flexural and compressive strengths of alkali-activated blast furnace slag powder with MgO and CaO range from 0% to 30% by the mass ratio of alkali-activated blast furnace slag powder are investigated. Moreover, the dry shrinkage rate of alkali-activated blast furnace slag powder is measured. One percent refractory fibers by volume of binder materials are added in the alkali-activated blast furnace slag. Some refractory fibers are treated with water flushing, meanwhile, some refractory fibers are directly used without any treatment. Finally, the scanning electron microscope, the thermogravimetric analysis curves and the XRD diffraction spectrums are obtained to reflect the inner mechanism of the alkali-activated blast furnace slag powder’s mechanical properties. The water-binder ratios of the alkali-activated blast furnace slag powder are 0.35 and 0.42. The curing ages are 3 d, 7 d and 28 d. The measuring temperature for the specimens ranges from 20 °C to 800 °C. Results show that the flexural and compressive strengths increase with the increased curing age, the decreased water-binder ratio and the addition of refractory fibers. The water-treated refractory fibers can improve the mechanical strengths. The mechanical strengths increase in the form of a quadratic function with the mass ratio of MgO and CaO, when the curing age is 3 d, the increasing effect is the most obvious. A higher water-binder ratio leads to an increasing the drying shrinkage rate. The activated blast furnace slag powder with CaO shows a higher drying shrinkage rate. The mechanical strengths decrease with the increasing testing temperature.

Resistance of alkali-activated blast furnace slag to acids

In this paper, the resistance of alkali-activated blast furnace slag to degradation processes caused by the action of various acids was studied. The ground granulated blast furnace slag was alkali-activated using sodium hydroxide in 6% Na2O dosage by the slag weight and subjected to testing of acid resistance in both organic and inorganic acidic solutions (pH ≈ 3) for 84 days. Citric, acetic, hydrochloric, and sulphuric acids were used for these purposes. The reference samples were stored in water. The progress of degradation was studied using the phenolphthalein technique, compressive strength testing, and weight measurements. Moreover, the SEM-EDX was used for the characterization of the degradation processes and microstructure changes. The degradation of alkali-activated blast furnace slag occurred in both organic and inorganic acids; however, the action of organic acids appears to be much more deteriorating. The decrease in compressive strength of about 50% and 60% was observed for acetic and citric acid, while only of 32% and 23% in sulphuric and hydrochloric, respectively.

Incorporation of bioleached sulfidic mine tailings in one-part alkali-activated blast furnace slag mortar

Sulfidic mine tailings are potential waste materials from mining and mineral processing, and they can contain a high content of sulfur and metal(loid)s, even after bioleaching. Due to the large amount of tailings waste from historical mining, it is crucial to find alternative methods for utilizing such waste rather than permanent storage in tailings impoundments. One-part alkali-activated slag mortars are promising co-binder systems for the recycling of sulfidic mine tailings thanks to their practicability, easy transportation, and user-friendly production. In this work, up to 50 wt% mine tailings were incorporated into alkali-activated blast furnace slag mortars. C-(N)-A-S-H gels were formed in all final samples with hydrotalcite zeolites. Tailings hardly participate in alkali activation, but they do have a considerable influence on physical and chemical properties. The 20 wt% tailings-containing sample showed the highest compressive strength of 91.1 MPa after 90 days of curing. The results of isothermal calorimetry indicate that incrementally increasing the percentage of tailings promotes the pre-induction reaction but hinders the slag hydration process. In addition, the results of X-ray microcomputed tomography showed higher porosity when the mortar contains more tailings; thus, the sample with 10 wt% mine tailings showed the lowest porosity. According to the European Union batch leaching test, up to 20 wt% bioleached sulfidic mine tailings can be valorized in a co-binder system while remaining below the nonhazardous waste thresholds.

Structural transition to well-ordered phases of NaOH-activated slag-metakaolin cements aged by 6 years

The strength evolution and microstructural transition of reaction products of alkali-activated blast furnace slag (BFS) - metakaolin (MK) blends were investigated for up to six years of curing at 20 °C. The BFS-MK ratios were of 100–0, 80–20, 50–50, and 20–80, activated with 5, 10 and 15% wt. Na2O (relative to the mass of the precursors) using NaOH as the only activator. X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), thermal analysis and 27Al and 29Si nuclear magnetic resonance (NMR) indicated the formation of C,N-(A-)S-H gel, hydrotalcite, AFm phases of monocarboaluminate and calcite in 100% BFS binders. For pastes of BFS-MK (80–20, 50–50 and 20–80), the addition of MK gradually limited the formation of hydrotalcite and AFm phases, but enhanced the formation of crystalline type A and X zeolites, as well as sodalite syn and gobbinsite intermixed with C,N-(A-)S-H and N-A-S-H gel without producing microstructural alterations. This improved the compressive strength contrary to the reported for other NaOH-alkali activated materials.

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.

Comparison of Testing Methods for Evaluating the Resistance of Alkali-Activated Blast Furnace Slag Systems to Sulfur Dioxide.

Alkali-activated systems (AAS) represent an ecologically and economically sustainable inorganic binder as an alternative to ordinary Portland cement (OPC). One of the main benefits of AAS is their durability in aggressive environments, which can be equal or even better than that of OPC. In this paper, the influence of the type of alkaline activator in alkali-activated blast furnace slag (AAS) in terms of resistance to sulfur dioxide corrosion was investigated. The durability testing process was based on the CSN EN ISO 3231 standard and simultaneously compared with mortar samples prepared by using Blastfurnace cement CEM III/A 32.5R. The degradation progress was evaluated by employing several different methods such as observing the compressive strength development, weight change evaluation, non-destructive testing methods like ultrasound or impact echo technique, or visual phenolphthalein technique. Subsequently, fundamental characterization of samples by the XRD method was performed during the degradation test. The obtained results indicate that none of the testing methods used could be prioritized over others to determine the resistance of AAS against the action of sulfur dioxide. For this reason, the durability testing of AAS remains an issue, and the development of specific standards considering the behavior of AAS seems necessary.