Slag Geopolymer Research Articles

Experimental study on the characteristics, rheological factors, and flowability of MK-GGBFS geopolymer slurry

In this study, we investigated the effects of concentration and modulus of alkaline activator, liquid–solid (L/S) ratio, and sand volume fraction on rheological properties and flowability of metakaolin (MK)–ground granulated blast furnace slag (GGBFS) geopolymer slurry (pastes and mortars). The rheological property of geopolymer slurry was consistent with the Bingham model. A decrease in the modulus and the L/S ratio, or an increase in the concentration increased the plastic viscosity of geopolymer paste. The geopolymer pastes with higher plastic viscosity exhibited a lower fluidity. The yield stress of geopolymer paste was negatively correlated with concentration, modulus, and L/S ratio. An increase in the sand volume fraction increased the plastic viscosity and yield stress of geopolymer mortar, and decreased the consistency and fluidity of that. Moreover, the correlation between rheological parameters of the geopolymer mortar and paste, and the relationship between the flowability parameters and rheological parameters of geopolymer slurry were constructed.

Utilization of coal-based synthetic natural gas slag as road base construction material through geopolymerization

The development of the Coal-based synthetic natural gas industry inevitably produced lots of slags. The application of coal-based synthetic natural gas slag (CSNGS) to road base not only effectively alleviated the accumulation and pollution of CSNGS, but also reduced the consumption of resources, which had significant economic and social benefits. However, CSNGS has a higher crushing value and water absorption, thus its mix design, mechanical properties and pavement performance must be further investigated when applied as the raw material of novel cementing material and aggregate. The purpose of this study is to investigate and comparatively analyze the optimal mixing ratio and mechanism of the strength of CSNGS applied in road base. For this, this study prepared the precursor of geopolymer by milling CSNGS into powder and mixing it with 20% cement. Then sodium hydroxide and sodium silicate were used as alkali activators to activate CSNGS, and the 7d unconfined compressive strength was used as the evaluation index to develop the optimal mix ratio of coal-based synthetic natural gas slag geopolymer (CSG). CSNGS with particle sizes ranging from 0 to 4.75 mm and 0 to 9.5 mm were used as aggregates to replace natural stones, then the cement and CSG were selected respectively to stabilize the slags-aggregates, and the relevant tests were carried out to investigate the mechanical and road properties. The results showed that the performance of CSG stabilized aggregates was lower than cement stabilized aggregates in the tests of unconfined compressive strength, splitting strength, unconfined compressive modulus of resilience, dry-wet cycles, and freeze–thaw cycles. The performance of the mixture deteriorated with the incorporation of CSNGS when the cementitious material was cement. The temperature shrinkage test found that the shrinkage of CSG stabilized specimens was less than cement stabilized specimens, which indicated that CSG had excellent anti-cracking potential. In addition, the temperature shrinkage coefficients of mixtures with different CSNGS dosages varied with temperature when the cementitious material was cement. Finally, to further verify the macroscopic test results, this study combined with scanning electron microscope (SEM) test to deeply analyze the strength formation mechanism of several mixtures.

Study on the influence mechanism of micro-mechanical properties of heterogeneous geopolymer gels

Geopolymers are inorganic, environmentally friendly cementing materials, and they exhibit broad application prospects in geotechnical engineering. These are formed by alkali activation and solidification with silicon- and aluminum-rich minerals or wastes as raw materials. Previous studies have revealed that the physical and mechanical properties of geopolymers from various raw materials differ significantly, which is closely aligned with those of geopolymer gels produced by alkali-activated hydration. However, no current systematic theory can explain these differences, so the design of mix proportions of raw materials and activators is particularly blind when preparing geopolymers. To solve this problem, this paper studies the composition and mechanical properties of the slag geopolymer by nano-indentation tests. On this basis, Raman mapping and SEM-EDS tests revealed the information of the polymerization degree and elemental composition of calcium silicoaluminate hydrate (CASH) in the heterogeneous gel phase. Finally, we carried out a verification test combined with ion implantation technology. The results revealed that the direct source of the difference in the mechanical properties of gel phases was the polymerization degree of CASH, and a secondary reason was the atomic ratio of active silicon to aluminum in CASH. Furthermore, the micro-mechanical properties of the gels could be improved by appropriately increasing the concentration of Al element. The results demonstrated the influence mechanism of mechanical properties of heterogeneous gel phases on the molecular scale, which helped evaluate the potential of raw materials to form specific gel phases and thus guided the scientific preparation of high-performance geopolymer materials.

Data‐driven approach for investigating and predicting of compressive strength of fly ash–slag geopolymer concrete

AbstractFly ash–slag geopolymer concrete is an intangible material that does not use conventional Portland cement, thereby reducing CO2 emissions into the environment, and helping to increase sustainable development. However, compared with conventional concrete, the compressive strength of fly ash–slag geopolymer concrete is complexly dependent on many factors. Using the data‐driven approach for investigating and predicting fly ash–slag geopolymer concrete compressive strength is a suitable choice. This study introduces 11 easily accessible machine learning models in open‐source libraries of the Python programming language such as support vector machine, random forest (RF), gradient boosting (GB), AdaBoost, decision trees, light GB machine, extreme GB (XGB), K‐nearest neighbors, multivariable regression, Gaussian process regression, and CatBoost (CatB). Based on a dataset of 158 samples, 14 inputs, and 1 output variable compressive strength, the performance of 11 machine learning models was evaluated through 4 criteria including coefficient of determination, root mean square error, mean absolute error, and mean absolute percentage error combined with 10 repeats of 10‐fold cross‐validation. Four models have the best performance based on the above four criteria value in determining compressive strength for testing dataset sorted descending is CatB > XGB > RF > GB. Global Shapley (SHAP) value‐based CatB and XGB indicates three groups of factors with decreasing influence on compressive strength of geopolymer concrete: group I (slag, molarity, coarse aggregate, curing temperature, and alkaline activator/binder) > group II (Na2SiO3 content, NaOH content, fine aggregate, fly ash content), curing period > group III (extra water added, NaOH/Na2SiO3, superplasticizer content, rest period). Extra water added, NaOH/Na2SiO3, superplasticizer content, rest period have insignificant influence on the compressive strength value of geopolymer concrete. The greater the slag content in the slag–fly ash mixture, the greater the compressive strength of geopolymer concrete. The optimum molarity of NaOH concentration is about 14–16 M for designing the compressive strength of geopolymer concrete. SHAP values partial dependence plots (PDP) and PDP indicate that alkaline activator/binder optimal values exist to achieve high compressive strength. The compressive strength increases with curing temperature between 20 and 100°C. PDP values show that the tendency to increase compressive strength with increasing coarse aggregate content from about 750 to 1250 kg/m3.

Triaxial Stress-Strain Behavior of a Novel Basalt Rock Waste and Ground Granulated Blast Furnace Slag Geopolymer

Triaxial Stress-Strain Behavior of a Novel Basalt Rock Waste and Ground Granulated Blast Furnace Slag Geopolymer

Transformation of rice husk modified basic oxygen furnace slag into geopolymer composites

Synergistic use of industrial and agricultural by-products can be solution of carbon emission from construction industry. The whole world is facing a crisis in finding ways to dispose of waste material. Hence, this study attempts to use rice husk and rice husk ash in geopolymers. Thus the study aims to develop a rice husk/basic oxygen furnace slag based geopolymer and study the factors affecting the performance of the binder. The developed geopolymer specimens were characterized using mechanical testing, physical and chemical techniques. The expansive nature of the organic matter in rice husk resulted in the geopolymer expanding and cracking. For this reason, rice husk ash was used to replace basic oxygen furnace slag. The rice husk was calcined at 600 °C to produce rice husk ash. The amount of rice husk ash as a replacement for basic oxygen furnace slag geopolymer varied from 0% to 50%. The effect of NaOH concentration, solid/liquid ratio, Na2SiO3/NaOH ratio, and the curing temperature was also studied to investigate the optimum parameter. The unconfined compressive strength is used to determine the performance of the binder. The results indicated an uptrend in unconfined compressive strength when increasing the rice husk ash content from 5% to 10%, and the optimum was 10%. Specimen with 8 M NaOH concentration had the highest unconfined compressive strength of 6.285 MPa. Moreover, it was also found that curing at 80 °C is an optimum condition for curing. Efflorescence formation and alkali leaching increased with the increase in rice husk ash content.

Performance Optimization of FA-GGBS Geopolymer Based on Response Surface Methodology.

Many scholars have focused on the workability and mechanical properties of fly ash (FA)- ground granulated blast furnace slag (GGBS) geopolymer. To enhance the compressive strength of geopolymer, zeolite powder was added in the present study. A series of experiments were carried out to investigate the effect of using zeolite powder as an external admixture on the per-formance of FA-GGBS geopolymer, 17 sets of experiments were designed and tested to deter-mine the unconfined compressive strength based on the response surface methodology, and then, the optimal parameters were obtained via modeling of 3 factors (zeolite powder dosage, alkali exciter dosage, and alkali exciter modulus) and 2 levels of compressive strength (3 d and 28 d). The experimental results showed that the strength of the geopolymer was the highest when the three factors were 13.3%, 40.3%, and 1.2. Finally, a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and 29Si nuclear magnetic resonance (NMR) analysis was used to conduct micromechanical analysis and explain the reaction mechanism from a microscopic perspective. The SEM and XRD analysis revealed that the microstructure of the geopolymer was the densest when the zeolite powder was doped at 13.3%, and the strength increased accordingly. The NMR and Fourier transform infrared spectroscopy analyses revealed that the absorption peak wave number band shifted toward the lower wave number band under the optimal ratio, and the silica-oxygen bond was replaced by an aluminum-oxygen bond, which generated more aluminosilicate structures.

Research on Reducing Shrinkage Behavior of Ground Granulated Blast Furnace Slag Geopolymers Using Polymer Materials

Geopolymers are a new type of environmentally friendly cement-based material with serious drying shrinkage problems. In order to overcome this problem and improve the engineering performance and durability of geopolymers, in this study we added 0%, 0.3%, 0.5%, 0.7%, and 0.9% polymer materials, namely, polyacrylamide, sodium polyacrylate, and sodium tetraborate, respectively, to geopolymers to reduce their degree of shrinkage. We also assessed changes in their length and durability to determine how the addition of polymer materials could reduce their degree of shrinkage. The results indicate that 0.7% sodium tetraborate yielded the most favored shrinkage, and, through imaging technology, the crack change at the age of 0–3 days was measured, during which polyacrylamide (PAM) effectively slowed down the dimensions of crack propagation by 0.47% compared with the control group.

Influence on Rheology and Microstructure of Nanosilica and Modified Polycarboxylate in Water‐Glass‐Activated Fly Ash/Ground Granulated Blast Furnace Slag Geopolymers

AbstractThis study establishes the effect of nano silica (NS) in the alkali activator on the behaviour of rheology and microstructure of Alkali activated material. The rheological behaviour of the Fly ash (FA)‐Ground granulated blast furnace slag (GGBS) (4 : 1) activated using water glass of Ms 1.1 (SiO2/Na2O), with nano silica (NS), Modified Poly carboxylate (MPC) was studied and the link between the composition and fundamental behaviour are reported. A total of 12 mortar mixtures were cast by varying the dose of NS from 0–3 %, and MPC 0–2.5 % and their fresh properties were obtained from the slump, setting time and flow value. The compressive strengths of mortars showed an increasing trend from 40 to 55 MPa with NS addition from 0–2.5 wt% at an optimal dose of 1 % MPC. The suspensions with and without NS fit well with Herschel‐Bulkley model, in the hysteresis cycle. The incorporation of NS at a threshold value below 2 % leads to a drastic change in viscosity with increasing time at a constant shear rate, implying. a thixotropy with yield‐type behaviour that are associated with the rebuilding of the flocculated structure with time. The nucleating effect of NS progressively improved the strength of the mix, due to the formation of compact gel microstructure which was confirmed by SEM micrograph with fewer pores. NS improves CSH gel and gelatinous silica phase in the matrix as is evident from the formation of the SiQ4 structural unit as it is absent in control. The poly (Sialate) structural unit in geopolymer ascertained from 29Si, 27Al MAS NMR chemical shift corresponds to Alq3(3Si) with the absence of remnant Al(IV) peak of Fly ash in NS (2.%) activated samples.

Influence of chemical composition of soda ash activated fly ash and copper slag geopolymer pastes on compressive strength

The effect of the chemical composition of geopolymer pastes on compressive strength was investigated in high-calcium fly ash and copper slag blends. In synthesizing the pastes, soda ash at activator to binder ratio of 0.4 was used. The characterization of material samples and the hardened fly ash-copper slag pastes was conducted through X-ray fluorescence (XRF), and X-ray diffraction (XRD) for the major oxide and phase composition. The hardened paste cubes which were cured at 80 °C were tested for compressive strength at ages 3, 7, and 28 days to obtain the mechanical performance property of each respective mix. The findings establish the impact of variation in the individual material and paste composition on the compressive strength of fly ash-copper slag geopolymer. The result shows that increase in the SiO2/Al2O3 and Na2O/Al2O3 ratios of paste products of samples corresponded to an increase in compressive strength. Whilst Fe2O3 wt.% increase in products from slag addition and positively influenced the compressive strength as fillers. However, CaO had no positive influence on the matrix of the activated product. The optimal blend mix design was 40 wt.% of copper slag which achieved a 28-day compressive strength of 24.66 MPa.

Effect of Organic Polymers on Mechanical Property and Toughening Mechanism of Slag Geopolymer Matrix.

In this work, two series of chemically reactive polymers, silane coupling agents (SCAs) and water-soluble polymers, were specifically designed as an additive to improve the ductility of slag geopolymer paste by vibration pressure technique. The influences of organic polymers on the fluidity, rheological behavior, mechanical property, porosity, and toughening mechanism of slag geopolymer were investigated. The polycondensation and bonding characteristics of organic–inorganic products were calculated by 1H liquid nuclear magnetic resonance (NMR) technology and Fourier transform infrared (FT-IR). The polymerization degree of composite geopolymer was evaluated by 29Si NMR and X-ray photoelectron spectroscopy (XPS). The microscopic morphology of the geopolymer matrix was analyzed using scanning electron microscopy (SEM). The results showed that the dosage of the KH570 and PAA-Na with 5 wt% behaved best in improving the flexural strength and the compressive strength of geopolymer in their corresponding organic series, respectively. The addition of polymers decreased the fluidity and the fluidity loss ratio of geopolymer slurry but reduced the harmful pores of hardened geopolymer. The organic polymers acting as bridge-fixed water molecules weakened the repulsion force, and formed a three-dimensional network through molecular interweaving in a geopolymer matrix. Methacryloxy in silane coupling agents and carboxyl group in water-soluble polymers may contribute to the improvement of hydration product structure through strong bonding with C-A-S-H. Microscopic measurements indicated that the addition of KH570 and PAA-Na in geopolymer could form 73.55% and 72.48% Si-O-Si with C-A-S-H gel, higher than the reference, and increase the polycondensation degree of C-A-S-H phase, reflected by the increased generation of Q2 and Q2(1Al) and the longer chain length, leading to a higher densified geopolymer matrix with high ductility.

Microstructural investigation of lithium slag geopolymer pastes containing silica fume and fly ash as additive chemical modifiers

Lithium slag is an industrial by-product obtained after lithium extraction from spodumene ore. The higher concentration of sulfate ions (SO4−2) in the form of gypsum/anhydrite makes it a chemically unviable binder. This research investigates the dilution of the sulphatic component in pore solution by additive incorporation of silica fume and fly ash as chemical modifiers in the lithium slag geopolymer. The setting behavior, detailed microstructural properties, mineral phase quantitative analysis, and compressive strength of lithium slag geopolymer containing fly ash and silica fume were studied. The increasing silica to alumina ratios (Si/Al) by incorporating silica fume in sodium tetraborate added geopolymer resulted in the set retardation after the setting accelerated at Si/Al ratio of 3.5. Similarly, the set retardation was observed for all fly ash replaced lithium slag geopolymers marked by the lower dissolution of SO4−2 ions in pore solution. The fragmented and porous N-(C)-A-S-H gel in lithium slag geopolymer densified by additive incorporation of silica fume and fly ash due to suppressed formation of SO4−2 in pore solution, thus increasing the compressive strength. The main binding zeolite phases quantified in mineral and crystal phase analysis of fly ash replaced geopolymer were mordenite, anorthite, analcime, and calcium chabazite, whereas for silica fume incorporated geopolymer were mordenite, anorthite, analcime, and sodium clinoptilolite. Thus, the lithium slag can be a promising geopolymer precursor along with other supplementary cementitious materials. However, further research is suggested for its chemical viability as a sole geopolymer binder.

Improvements of Flexural Properties and Thermal Performance in Thin Geopolymer Based on Fly Ash and Ladle Furnace Slag Using Borax Decahydrates.

This paper elucidates the influence of borax decahydrate addition on the flexural and thermal properties of 10 mm thin fly ash/ladle furnace slag (FAS) geopolymers. The borax decahydrate (2, 4, 6, and 8 wt.%) was incorporated to produce FAB geopolymers. Heat treatment was applied with temperature ranges of 300 °C, 600 °C, 900 °C, 1000 °C and 1100 °C. Unexposed FAB geopolymers experienced a drop in strength due to a looser matrix with higher porosity. However, borax decahydrate inclusion significantly enhanced the flexural performance of thin geopolymers after heating. FAB2 and FAB8 geopolymers reported higher flexural strength of 26.5 MPa and 47.8 MPa, respectively, at 1000 °C as compared to FAS geopolymers (24.1 MPa at 1100 °C). The molten B2O3 provided an adhesive medium to assemble the aluminosilicates, improving the interparticle connectivity which led to a drastic strength increment. Moreover, the borax addition reduced the glass transition temperature, forming more refractory crystalline phases at lower temperatures. This induced a significant strength increment in FAB geopolymers with a factor of 3.6 for FAB8 at 900 °C, and 4.0 factor for FAB2 at 1000 °C, respectively. Comparatively, FAS geopolymers only achieved 3.1 factor in strength increment at 1100 °C. This proved that borax decahydrate could be utilized in the high strength development of thin geopolymers.

The Durability and Leaching Behavior of Granulated Blast Furnace Slag, Fly Ash, and Waste Foundry Sand Geopolymers

Waste generation and management in industries is a major problem worldwide. In this study, granulated blast furnace slag (GBFS), fly ash (FA) + cement (CM), and de-silicated foundry sand (DFS) based geopolymers were developed and their leachability studied. The elemental composition showed that the raw materials studied had the highest compositions in SiO2 and Al2O3, which are the constituents desired for the formation of a geopolymer. The GBFS geopolymer had the highest unconfined compressive strength (UCS) of 30.977 MPa, followed by the FA + CM geopolymer with 16.704 MPa. The DFS geopolymer recorded the lowest strength. The mineralogy of GBFS geopolymer showed the presence of an amorphous phase which consisted predominantly of grossite. The FA + CM-based geopolymer had an amorphous and crystalline phase predominated by sillimanite. The DFS-based geopolymer consisted mainly of sodium silicate hydrate. The leaching tests showed that the concentrations of the elements in the leachates were all below the regulatory limits. All of the developed geopolymers were considered environmentally friendly. This study showed that GBFS geopolymer and fly ash + CM-based geopolymers have good durability and leaching behavior, with DFS-based geopolymers possessing poor durability but good leaching behavior. The studied geopolymers are suitable for use as building wall materials and paving bricks without compromising and polluting the environment.

Effect of Sodium Hydroxide Molarity on the Alkali-Activated Fly Ash and Granulated Slag Geopolymer Binders with Water Glass – Part I

Effect of Sodium Hydroxide Molarity on the Alkali-Activated Fly Ash and Granulated Slag Geopolymer Binders with Water Glass – Part I

Performance assessment of mechanical and durability properties of cupola slag geopolymer concrete with fly and rice husk ashes

Research into substituting recycled materials for cement and aggregates can yield beneficial natural resource conservation, waste management, cost savings, and reduced embodied energy in concrete. Hence, this research investigates the potential adoption of coal fly ash (CFA) and rice husk ash (RHA) as geopolymer binders to partially substitute cement in varying proportions up to 25%. However, cupola furnace slag (CFS) was also used as a partial substitute of crushed granite from 0% to 35% in steps of 5% in the production of geopolymer concrete (GPC). The selected geopolymer binders were synthesized using an alkaline solution. Workability, compressive strength, and rapid chloride penetration tests on fresh and hardened normal concrete (NC) as control and GPC containing CFS were evaluated at different water-binder ratios. The findings revealed that integrating 15%CFA, 20%RHA, and 30%CFS with w/b of 0.50 and 0.65 improved the workability by 180% and 105.7%, respectively, but compressive strength is significantly reduced. The findings further showed that combining 75%OPC, 20%CFA, 5%RHA, 100%RS, 20%CFS, and 80%CG results in optimal compressive strength of 19.68 N/mm2 and, 21.49 N/mm2 at 28 days and 56 days with w/b of 0.50, respectively, as contrasted to the lowest possible strength requirement. The Rapid Migration Test (RMT) was used to determine the chloride ions permeability in various concrete mixes. The results show that GPC produced with the combination of 15%CFA, 20%RHA 65%OPC, 30%CFS, and 70%CG with w/b of 0.65 is more durable and has higher chloride ion penetration resistance than most other mix proportions.

The Mechanical Properties of Fly Ash and Slag Geopolymer Mortar with Micro Steel Fibers

In this study, experimental mortar combinations with 1% micro steel fibers, were examined to create geopolymer mortars. To test the effect of the fibers on the mortar's resistance, the geopolymer mortar was designed with various proportions of more environmentally friendly materials fly ash and slag. The percentage of fly ash by weight was 50, 60, and 70% of the slag. The best results were obtained when a 50:50 ratio of fly ash and slag were mixed with 1% micro steel fibers. The results showed that the mixtures containing fibers performed better in the considered tests (toughness index, ductility index, and resilience index). In the impact resistance test, the mixture contained 50% fly ash by weight of the slag with a temperature of 240°C and a curing period of 28 days, with and without micro steel fibers. Water absorption test results and void content increased when adding micro steel fibers after 7 and 28 days of curing at 24°C.

Thermo-mechanical behaviour of fly ash-ladle furnace slag blended geopolymer with incorporation of decahydrate borax

This paper elucidates the effect of adding decahydrate borax (1 and 2 wt%) on thermo-mechanical properties of fly ash-ladle furnace slag (FS) geopolymer at 29 °C – 1000 °C. Adding borax improved the compressive strength of unheated (40.5 MPa) and heat-treated (36.9 – 43.1 MPa) FS geopolymers by 8.4% and 21.2%, respectively. The higher crystallinity, incompact microstructure, and the presence of B-bonds and B-crystals contributed to the high-temperature resistance of FS-B geopolymer. The reduced sintering temperature by 75 °C due to addition of borax compared to FS geopolymer improved the thermal stability and structural integrity during high-temperature applications.

Comparison of thermal performance between fly ash geopolymer and fly ash-ladle furnace slag geopolymer

This paper compared the thermal stability between fly ash (FA) and fly ash-ladle furnace slag (FA-LS) geopolymers. FA-LS geopolymer was prepared by mixing FA and LS (FA:LS weight ratio of 80:20) with an alkali activator. Geopolymers were aged at room temperature for 28 days before being exposed to high temperatures (200 °C – 1000 °C). Unexposed FA and FA-LS geopolymers had a compressive strength of 38.9 MPa and 40.5 MPa, respectively. The FA and FA-LS geopolymers retained 61.6% and 91.3% compressive strength, respectively, when exposed to temperatures up to 1000 °C. FA-LS geopolymers experienced smaller variation in the density (2.6 – 5.5%) and pores (17.4 – 23.0%) compared to FA geopolymers (density and porosity of 2.9 – 25.2% and 19.0 – 30.0%, respectively). The formation of crystalline peaks, densification of matrix, pores and their connectivity, cracks and dimensional changes influenced the compressive strength of exposed geopolymers. FA-LS geopolymers could be potentially applied as heat-resistance material.

Freeze-thaw resistance of blast furnace slag alkali activated mortars

In this study, blast furnace slag geopolymer mortars were prepared in prism molds with the size of 4 x 4 x 16 cm by alkali activating powdered sodium meta silicate (Na2SiO3). The mortar mixtures prepared to contain sodium in different proportions were cured with 3 different curing methods, and 300 cycles of freeze-thaw were applied, and strength and weight losses were examined. Control samples prepared with PC were also exposed to freeze-thaw cycles and the results were compared with each other. It was observed that 8% sodium added geopolymer mortars significantly preserved their compressive strength and weight. Especially, the compressive strength of the samples produced with 8% sodium and exposed to freeze-thaw cycle after 28 days of air curing increased by around 32%.