Slag-based Geopolymer Research Articles

Post-fire performance of slag-based geopolymer concrete exterior beam–column joint

The post-fire performance of slag-based geopolymer materials in structures under cyclic loading has yet to be reported and the condition of the rebars inside such structures remains unexplored. In the present work, cyclic tests were conducted on exterior beam–column joints made with a slag-based geopolymer after exposing the specimens to natural fire. The mechanical properties of the reinforcement embedded in fire-exposed specimens were also determined and analysed. The cyclic test results indicated that deterioration of the geopolymer and rebar altered the failure pattern of the fire-exposed specimen from the desired beam-end hinging to joint shear failure. The peak load, stiffness, ductility and energy dissipation reduced significantly in the fire-exposed specimens compared with the unheated control specimens.

Effect of mechanical activation on reaction mechanism of one-part preparation fly ash/slag-based geopolymer

One-part geopolymers are a greener alternative to Portland cement and are more suitable in engineering applications compared with two-part geopolymers. The effects of mechanical activation on the properties and the mechanism of the pozzolanic reaction of fly ash (FA)/slag-based geopolymer paste prepared using the one-part method were studied. Simple mixing was used for the control group and the effect of mechanical activation on the macroscopic properties of geopolymers was studied using tests for compressive strength, fluidity and setting times. The effect of mechanical activation on the pozzolanic reaction of geopolymers was assessed using isothermal calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. The results showed that the 28-day compressive strength of the geopolymer formed by mechanical activation was 26% higher than that of the geopolymer prepared using simple mixing. Workability and fluidity were also enhanced. The reactivity of the precursor was improved by mechanical activation, particularly for the FA. The mechanically activated FA experienced a pozzolanic reaction within 7 days, while the undisturbed FA produced pozzolanic activity after 14–28 days. In addition, mechanical activation lessened the carbonisation of the one-part FA/slag-based geopolymer The implications of these results in terms of the influence of mechanical activation on pozzolanic activity are discussed.

Strength and durability properties of expansive soil treated with geopolymer and conventional stabilizers

This paper reports the strength and durability properties of expansive soil treated with slag-based geopolymer, hydrated lime, and Portland cement. The slag content in the soil-slag mix is varied as 5%, 10%, and 20% by dry weight of soil and activated with NaOH solutions of 2 M, 6 M, and 8 M concentrations, respectively. Whereas cement and lime contents in the mix are varied as 4%, 12%, and 15%. The plasticity and compaction properties of the mixes are evaluated. Further, the unconfined compressive strength of specimens, compacted to their respective maximum dry density at optimum moisture content, is determined after 0, 3, 7, and 30 days of curing. Durability studies such as freezing-thawing, slaked durability, modified durability, and resistance to water immersion are determined on 30-days cured stabilized soil specimens. X-ray diffraction and scanning electron microscopic analysis are carried out for identifying the reaction products and microstructure of the stabilized specimens. The results indicate that the expansive soil can be effectively stabilized with slag-based geopolymer. The geopolymer stabilized soil has superior strength and durability compared to the conventional stabilizers. Geopolymer stabilized soil attains dense and compact structures with the better formation of cementitious products.

Slag-based geopolymer microspheres as a support for CO2 methanation

Reducing the emission of CO2 and converting it into energy are the key issues researchers are concerned about. Geopolymers with the advantage of alkali metal synergistic catalysis and excellent ability to adsorb metals are promising catalyst supports. To prove this point, KOH-activated chemically synthesized slag (CaO-MgO-Al2O3-SiO2) and ground granulated blast furnace slag were used as the raw materials in this study to prepare CO2 methanation catalysts. Ni metal (15 wt%) was loaded onto the slag-based geopolymers using the incipient wetness impregnation method. The as-synthesized slag-based geopolymer and real slag-based geopolymer catalysts were prepared and denoted as Ni-P-SGS and Ni-S-SGS, respectively. The results showed that the Ni-P-SGS catalyst showed better Ni dispersion, more alkaline sites, and stronger CO2 adsorption capacity, and hence higher catalytic activity for CO2 methanation than the Ni-S-SGS catalyst. Therefore, the Ni-P-SGS catalyst showed a CO2 conversion of 80.2% and a CH4 selectivity of 99.2% at 400 °C/0.1 MPa and a weight hourly space velocity of 12000 mL g-−1h−1. This performance is superior to that of the Ni-S-SGS catalyst, which showed a CO2 conversion of 72.8% and CH4 selectivity of 98.3%. In addition, the hydrogenation of formate seemed to be the rate-limiting step for the formation of CH4. This work provides sufficient evidence that geopolymers are promising catalyst supports.

Comparative study of Pb2+, Ni2+, and methylene blue adsorption on spherical waste solid-based geopolymer adsorbents enhanced with carbon nanotubes

• Carbon nanotube/geopolymer spheres were obtained by spheroidization. • Pore structure and phase evolution of the spheres were affected by carbon nanotubes. • Adsorption performance was enhanced by carbon nanotubes. Spherical porous carbon nanotube-reinforced geopolymer (CNTs/GP) adsorbents were spheroidized in polyethylene glycol 400 solvent by combing carbon nanotubes (CNTs) with a fly ash and slag-based geopolymer slurry. The effects of CNTs on the phase evolution and pore structure of the CNTs/GP spheres and their adsorption behavior for methylene blue (MB) and heavy metals (Pb 2+ and Ni 2+ ) were evaluated. The CNTs/GP spheres had a perfect spherical shape and mesoporous structure. The spheres were composed of an amorphous phase and had a high BET surface area of 73.06 m 2 /g with 3 wt% CNTs. The addition of CNTs into the spheres enhanced the removal efficiency for the pollutants (Pb 2+ , Ni 2+ and MB). The calculated q m of the sphere with 3 wt% CNTs was 25.549 mg/g for MB, 52.743 mg/g for Pb 2+ ; and 8.915 mg/g for Ni 2+ . The adsorption data of the spheres were well obeyed the Langmuir isotherm model and pseudo-second-order kinetics model, suggesting that multiple mechanisms such as physisorption, chemisorption and ion exchange were involved. The CNTs/GP spheres also presented good cyclic regeneration properties; hence, they can be applied as potential adsorbents for the treatment of hazardous wastewater.

Assessment of recycling use of GFRP powder as replacement of fly ash in geopolymer paste and concrete at ambient and high temperatures

Environmental issues caused by glass fiber reinforced polymer (GFRP) waste have attracted much attention. The development of cost-effective recycling and reuse methods for GFRP composite wastes is therefore essential. In this study, the formulation of the GFRP waste powder replacement was set at 20–40 wt%. The geopolymer was formed by mixing GFRP powder, fly ash (FA), steel slag (SS) and ordinary Portland cement (OPC) with a sodium-based alkali activator. The effects of GFRP powder content, activator concentration, liquid to solid (L/S) ratio, and activator solution modulus on the physico-mechanical properties of geopolymer mixtures were identified. Based on the 28-day compressive strength, the optimal combination of the geopolymer mixture was determined to be 30 wt% GFRP powder content, an activator concentration of 85%, L/S of 0.65, and an activator solution modulus of 1.3. The ratios of compressive strength to flexural strength of the GFRP powder/FA-based geopolymers were considerably lower than those of the FA/steel slag-based geopolymers, which indicates that the incorporation of GFRP powder improved the geopolymer brittleness. The incorporation of 30% GFRP powder in geopolymer concrete to replace FA can enhance the compressive and flexural strengths of geopolymer concrete by 28%. After exposure to 600 °C, the flexural strength loss for geopolymer concretes containing 30 wt% GFRP powder was less than that of specimens without GFRP powder. After exposure to 900 °C, the compressive strength and flexural strength losses of geopolymer concretes containing 30 wt% GFRP powder were similar to those of specimens without GFRP powder. The developed GFRP powder/FA-based geopolymers exhibited comparable or superior physico-mechanical properties to those of the FA-based geopolymers, and thus offer a high application potential as building construction material.

Setting Time, Microstructure, and Durability Properties of Low Calcium Fly Ash/Slag Geopolymer: A Review

Ordinary Portland cement (OPC) is known for its significant contribution to carbon dioxide emissions. Geopolymer has a lower footprint in terms of CO2 emissions and has been considered as an alternative for OPC. A well-developed understanding of the use of fly-ash-based and slag-based geopolymers as separate systems has been reached in the literature, specifically regarding their mechanical properties. However, the microstructural and durability of the combined system after slag addition introduces more interactive gels and complex microstructural formations. The microstructural changes of complex blended systems contribute to significant advances in the durability of fly ash/slag geopolymers. In the present review, the setting time, microstructural properties (gel phase development, permeability properties, shrinkage behavior), and durability (chloride resistance, sulfate attack, and carbonatation), as discussed literature, are studied and summarized to simplify and draw conclusions.

Evaluation of the Effect of Granite Waste Powder by Varying the Molarity of Activator on the Mechanical Properties of Ground Granulated Blast-Furnace Slag-Based Geopolymer Concrete.

Industrial waste such as Ground Granulated Blast-Furnace Slag (GGBS) and Granite Waste Powder (GWP) is available in huge quantities in several states of India. These ingredients have no recognized application and are usually shed in landfills. This process and these materials are sources of severe environmental pollution. This industrial waste has been utilized as a binder for geopolymers, which is our primary focus. This paper presents the investigation of the optimum percentage of granite waste powder as a binder, specifically, the effect of molar and alkaline to binder (A/B) ratio on the mechanical properties of geopolymer concrete (GPC). Additionally, this study involves the use of admixture SP-340 for better performance of workability. Current work focuses on investigating the effect of a change in molarity that results in strength development in geopolymer concrete. The limits for the present work were: GGBS partially replaced by GWP up to 30%; molar ranging from 12 to 18 with the interval of 2 M; and A/B ratio of 0.30. For 16 M of GPC, a maximum slump was observed for GWP with 60 mm compared to other molar concentration. For 16 M of GPC, a maximum compressive strength (CS) was observed for GWP with 20%, of 33.95 MPa. For 16 M of GPC, a maximum STS was observed for GWP, with 20%, of 3.15 MPa. For 16 M of GPC, a maximum FS was observed for GWP, with 20%, of 4.79 MPa. Geopolymer concrete has better strength properties than conventional concrete. GPC is $13.70 costlier than conventional concrete per cubic meter.

Strength and Microstructural Characterization of Ferrochrome Ash- and Ground Granulated Blast Furnace Slag-Based Geopolymer Concrete

Strength and Microstructural Characterization of Ferrochrome Ash- and Ground Granulated Blast Furnace Slag-Based Geopolymer Concrete

Highly efficient Cd(II) removal using macromolecular dithiocarbamate/slag-based geopolymer composite microspheres (SGM-MDTC)

The Si-O-Si moiety present in low-cost, easy-to-prepare geopolymers forms a part of the skeletal structure and does not participate in adsorption. In this work, a novel composite adsorbent (SGM-MDTC) was synthesized by grafting macromolecular dithiocarbamate (MDTC) on slag-based geopolymer microspheres (SGM), and the SiOSi in SGM was activated to enhance the Cd(II) adsorption performance of the geopolymer adsorbent. The SGM-MDTC was synthesized successfully and characterized using the XRD and FT-IR techniques. The Si-O-Si unit present in SGM was activated after anchoring MDTC. The activation was confirmed using the XPS technique. It was observed that the morphology of SGM and SGM-MDTC changed significantly, and the specific surface area of SGM increased from 52.99 to 72.36 m2/g following the process of MDTC anchoring. The effects of pH, the dosage of SGM-MDTC, contact time, and initial concentration during static adsorption on the adsorption performance of Cd(II) on SGM-MDTC were studied. It was observed that the process followed the pseudo-second-order kinetics, Langmuir, and Sip models and was primarily controlled by the process of intra-particle diffusion. The adsorption capacity of the synthesized SGM-MDTC (205.8 mg/g) material was nearly twice as high as that of SGM (106.7 mg/g) under conditions of static adsorption. Dynamic adsorption is more suitable for practical application than static adsorption. The adsorption capacity of SGM-MDTC was as high as 382.8 mg/g. This revealed that the synthesized SGM-MDTC material exhibited excellent Cd(II) purification performance and high application value.

Coal fly ash-slag and slag-based geopolymer as an absorbent for the removal of methylene blue in wastewater

The fly ash and slag from coal burning were attractive byproducts to prepare geopolymers for the adsorption of methyelen blue in wastewater due to their availability and low cost. Various mixing amounts between them were conducted during geopolymerization with a Na2SiO3/NaOH ratio of 10 M of 2.5 and a curing temperature of 60°C for 24 h. When the amount of coal slag in the geopolymer composition was increased from 0 to 51 %, the surface structures of the resultant geopolymers were much softer and more porous due to the lack of initial material, causing a reduction in the surface area of geopolymers to 119,23 m2/g for 0 % and 5,29 m2/g for 51 %. The adsorption amount of methylene blue performed at pH 12 showed different tendencies on the dependence of contact time for the indivually prepared geopolymer. The uptake amount decreased from 36.2 mg/g to 34.2 mg/g with the enhancement of coal slag in the geopolymer from 0 to 51 % after 180 minutes of immersion in methylene blue solution. In addition, the adsorption mechanism evaluated by FT-IR spectroscopy was observed to involve electrostatic forces formed by hydrogen bonding between hydroxyl groups (Si–OH) and nitrogen atoms in the structure of methylene molecules. This study indicated that coal slag could be a potential material to prepare geopolymers for removing dye pollutants.

Highly esthetic, deodorant, and antibacterial tile with natural zeolite set via a blast furnace slag-based geopolymer

Highly esthetic, deodorant, and antibacterial tile with natural zeolite set via a blast furnace slag-based geopolymer

Sulfate and chloride resistance of bottom ASH doped slag-based geopolymer composites

Within the scope of this study, while the performance of slag (S)-based geopolymer mortars with bottom ash (BA) reinforcement was examined, chloride and sulfate attack tests were also carried out to investigate their durability properties. For the durability tests of geopolymer composites, sodium chloride (NaCl) and sodium and magnesium sulfate (Na2SO4 and MgSO4) solutions were preferred for a period of 10 months and a 15% solution percentage. The performance of geopolymer composites after the effect of durability was determined by flexural and compressive strengths, SEM and XRD analyses, weight changes, and visual inspection. When the results obtained were evaluated, it was seen that 15% BA substitution provided the highest compressive strength. There was variation in durability tests. At the end of the 2-month period, there was an increase in the compressive strength, while a decrease was observed at the end of the 6-month period. The main factor that created these fluctuations was that alkali ions migrated from sample to solution while the solutions were diffusing into the matrix. Gypsum and ettringite formed in the pores were effective in the losses that occurred in the 6-month period. In addition, the alkali ions leaving the sample and passing into the solution effectively accelerated the formation of micro cracks. Thus, strength losses were observed.

Slag-based geopolymer microsphere-supported Cu: a low-cost and sustainable catalyst for CO2 hydrogenation

Recent studies on the exploration of sustainable approaches by utilizing large-scale waste materials as potential catalysts in the field of heterogeneous catalysis have attracted much attention.

Experimental Investigation of Soft Soil Stabilization Using Copper Slag-Based Geopolymer

Experimental Investigation of Soft Soil Stabilization Using Copper Slag-Based Geopolymer

Mechanical properties and strengthening mechanism of silty sands stabilized with steel slag-based geopolymer binder

Geopolymer binder has the advantages of early strength, fast solidification, high volume stability, and low permeability. It is beneficial to improve the mechanical performance of silty sands, saving cement consumption and being environmentally friendly. However, the strength improvement of silty sand stabilized with steel slag-based geopolymer was significantly controlled by their material composition and technical parameters. This study conducted a series of unconfined compression tests to investigate the material composition of steel slag-based geopolymer binders and their reasonable mixing ratio for silty sand stabilization. The optimum mixing ratio of precursor (steel slag) to alkaline activator (the combination of Na₂SiO₃ and CaO) and the optimum dosage of steel slag-based geopolymer for silty sand stabilization were explored. The strengthening mechanism of geopolymer-stabilized silty sands was discussed based on microstructural images and elemental concentrations of primary components observed by SEM and EDS. The results show that when the mass ratio of Slag : Na₂SiO₃ : CaO was 80:35:21, and the steel slag-based geopolymer material was 15%, the silty sand could achieve the best mechanical performance improvement. The microstructural characteristics of geopolymer-stabilized silty sands at different curing ages illustrated that the compactness and integrity of silty sand structures were enhanced over the curing age. The improving cementitious contact among particles and enlarging particle size was responsible for the strength improvement of silty sand. This research can provide a reference for applying steel slag-based geopolymer in silty sand stabilization in engineering practices.

Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution.

Mineral geopolymer binders can be an attractive and more sustainable alternative to traditional Portland cement materials for special applications. In geopolymer technology the precursor is a source of silicon and aluminium oxides, the second component is an alkaline solution. In the synthesis of geopolymer binders the most commonly used alkaline solution is a mixture of sodium or potassium water glass with sodium or potassium hydroxide or silicate solution with a low molar ratio, which is more convenient and much safer in use. In this paper, we present the influence of sodium or potassium silicate solution on the physical and mechanical properties of fly ash and ground granulated blast furnace slag-based geopolymer mortars. Mercury intrusion porosimetry and microstructural observation allowed for comparing the structure of materials with a different type of alkaline solution. The evolution of compressive and flexural tensile strength with time determined for composites using 10%, 30% and 50% slag contents (referring to fly ash mass) was analysed. The tests were performed after 3, 7, 14 and 28 days. It was observed that, as the amount of slag used increases in the precursor, the strength of the material grows. Mortars with the sodium alkaline solution were characterised by a higher strength at a young age. However, the values of strength 28 days were higher for geopolymers with potassium alkaline solution reaching 75 MPa in compression. Geopolymer mortar microstructure observation indicates a high matrix heterogeneity with numerous microcracks. Matrix defects may be caused by the rapid kinetics of the material binding reaction or shrinkage associated with the drying of the material.

Effect of sea sand and recycled aggregate replacement on fly ash/slag-based geopolymer concrete

Abstract The purpose of this study is to investigate the impact of recycled aggregate (RA) and sea sand (SS) replacement on fly ash (FA) slag-based geopolymer concrete (GPC). An orthogonal array design is employed to obtain the optimum mix proportions, and geopolymer mixes are prepared using slag percentages of 10%, 20%, and 30% slag in FA/slag-based GPC. Sodium hydroxide (NaOH) solution is prepared at three concentrations (8 mol/L, 12 mol/L, and 16 mol/L). The mechanical properties of the geopolymer mixes are determined based on the tensile strength, compressive strength, flexural strength, and elastic modulus. GPC is prepared using water-binder ratios of 0.3, 0.4, and 0.5 at 0%, 25%, 50%, 75%, and 100% of RA replacement. The results showed that the variation in the RA replacement ratio had little effect on the strength and elastic modulus of sea sand geopolymer concrete (SS–GPC), but it had a significant effect on river sand geopolymer concrete (RS–GPC). The RA replacement ratio also showed a noticeable change in the damage surface of the specimens. In addition, SS hinders the hydration reaction of the geopolymer in the early stage and reduces the early strength of the GPC; however, in the later stages, the effect becomes insignificant.

Mechanical behavior of fiber reinforced slag-based geopolymer mortars incorporating artificial lightweight aggregate exposed to elevated temperatures

The present research investigates the effects of artificial lightweight aggregate (ALWA) and polyvinyl alcohol (PVA) fiber utilization on the mechanical performance of slag-based lightweight geopolymer mortar (LGPM) specimens cured at ambient temperature. Also, the influence of elevated temperature (250 °C and 500 °C) on the resulting performance of LGPM samples was studied. For the production of LGPM specimens, 60% and 80% ALWA were utilized as a partial replacement of river sand. The slag-based LGPM samples were activated by a mixture of sodium silicate and 12 M sodium hydroxide solutions. The fresh and hardened state properties of LGPM specimens with and without fibers were assessed by workability, density, compressive strength, uniaxial tensile strength, and flexural strength tests. Also, the micro-scale variations were evaluated by scanning electron microscopy (SEM). The findings revealed that the incorporation of ALWA reduced the workability, density, and compressive strength of the LGPM, and the reductions in all these properties were more with 1% PVA inclusions. Meanwhile, inclusions of 1% PVA fibers significantly enhanced the uniaxial tensile and flexural behaviors of LGPM. After exposure to 250 °C, all mechanical strengths were improved due to the further geopolymerization, while mechanical strength reductions were observed at 500 °C due to the vapor impact and difference in thermal expansion. The uniaxial tensile strength of fiber-reinforced LGPM samples was improved from 1.47 MPa to 2.16 MPa at 250 °C, while uniaxial tensile strength reduced at 500 °C, and the samples exhibited a brittle failure mode due to the melting of PVA fibers. The results pointed out that tensile and flexural properties of LGPM significantly enhanced with ALWA and 1% PVA fiber utilization.

Mechanical, durability properties, and environmental assessment of geopolymer mortars containing waste foundry sand

Today, with the expansion of industries and construction activities, attention to environmental issues such as sustainable development, recycling, reuse, etc. becomes important. The global demand for cement production has been increasing. One ton of cement releases about one ton of carbon dioxide into the atmosphere. Also, after freshwater, sand is considered the second natural resource that is consumed.Due to the limited sand resources and the concerns around the environmental issues of cement production, in this study, the use of waste foundry sand (WFS) as an alternative to aggregate in slag-based geopolymer mortars as an alternative to cement has been considered. WFS is a by-product of the foundry industry, which is produced in large quantities and buried in landfills, and slag is the by-product of iron and steel making process which is highly cementitious and high in calcium silicate hydrates (CSH).In this study, the mechanical, durability properties, and environmental assessment of geopolymer mortars using WFS were investigated. The results show that the compressive strength of geopolymer mortars containing treated WFS at the age of 91days had an increase of 158% compared to cement-based mortars. The adhesion and flexural strength in geopolymer mortars containing treated WFS compared to untreated mortars increased by 145% and 18%, respectively. Toxicity characteristic leaching procedure (TCLP) results showed that the concentration of heavy metals in the leachate WFS, mortars containing treated and untreated WFS, and ground granulated blast-furnace (GGBF) slag was within the standard permitted limitations and WFS is not a hazardous waste.