One-part Geopolymer Research Articles

Utilizing raw phosphogypsum to prepare one-part geopolymer: Mechanical properties, optimization, and hydration mechanisms

The accumulation of phosphogypsum (PG) poses environmental risks. This study investigates the feasibility and performance of one-part geopolymers derived from a ternary system, where raw phosphogypsum (PG) partially replaces ground blast furnace slag (GBFS) in combination with fly ash (FA). The effects of raw PG on geopolymerization kinetics, mechanical properties, and efflorescence were examined. PG addition affected compressive strength, gel formation, and efflorescence. An optimal PG replacement rate of 10–20 % for GBFS was identified to balance the positive effect on ettringite formation and the negative impact on gel phase formation. Using a composite alkali activator, combining NaOH and Na2SiO3, promotes strength development and enhances the anti-efflorescence properties of one-part geopolymers synthesized with PG. One-part PG-incorporated geopolymers demonstrate excellent performance in the fixation of heavy metal contaminants in raw PG, offering a more convenient and safer alternative to conventional two-part synthesis methods.

Sodium metasilicate-activated one-part geopolymer concrete: Impact strength assessment with bottom ash substitution and fiber reinforcement

This study aims to investigate the effect of fibers on the impact strength of fibrous one-part geopolymer concrete (OPGC) to mitigate its brittleness. This research examines the impact strength of OPGC activated with sodium metasilicate pentahydrate, utilizing fly ash as a precursor material. The study uniquely explores the effects of bottom ash, substituted at varying levels (25 % to 100 %) for sand, within the OGPC matrix. Additionally, incorporating two distinct fiber types, polypropylene and kenaf, individually at 0.5 % and in a hybrid combination at 0.25 % each, offers a fresh perspective on fiber reinforcement in OGPC. Scanning electron microscopy and X-ray diffraction provide critical insights into the microstructural and mineralogical properties of the developed OPGC. The impact strength of OPGC with this specific combination of materials has not been previously investigated by any researchers, establishing the novelty of this study. Results revealed that the combination of fibers with 25 % BA exhibited a synergistic effect, leading to a notable enhancement in impact strength. Conversely, the impact strength declined with other combinations of materials. Polypropylene fibers demonstrated the highest performance in terms of impact strength for OPGC, followed by the hybrid fiber combination, with kenaf fibers exhibiting the lowest performance in this regard.

A Prefatory Sustainability Assessment of One-Part Geopolymers

A Prefatory Sustainability Assessment of One-Part Geopolymers

Preparation of solid alkali activator for geopolymer synthesis using vanadium-bearing shale tailing

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na2SiO3 and Na15.6Ca3.8Si12O36. During the synthesis of one-part geopolymer (OPG), Na2SiO3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na15.6Ca3.8Si12O36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers.

Performance Assessment of One-Part Self-Compacted Geopolymer Concrete Containing Recycled Concrete Aggregate: A Critical Comparison Using Artificial Neural Network (ANN) and Linear Regression Models

Geopolymer concrete, a cement-free concrete with recycled concrete aggregate (RCA), offers an eco-friendly solution for reducing carbon emissions from cement production and reusing a significant amount of old concrete from construction and demolition waste. This research on self-compacted, ambient-cured, and low-carbon concrete demonstrates the superior performance of one-part geopolymer concrete made from recycled materials. It is achieved by optimally replacing treated RCA with a unique method that involves coating the recycled aggregates with a one-part geopolymer slurry composed of fly ash, micro fly ash, slag, and anhydrous sodium metasilicate. The research presented in this paper introduces predictive models to assist researchers in optimising concrete mix designs based on RCA rates and treatment methods, including the incorporation of coated recycled concrete aggregates and basalt fibres. This study addresses the knowledge gap regarding geopolymer concrete based on recycled aggregate, various RCA rates, and novel RCA treatments. The novelty of the paper also lies in presenting the effectiveness of Artificial Neural Network (ANN) models in accurately predicting the compressive strength, splitting tensile strength, and modulus of elasticity for self-compacting geopolymer concrete with various rates of RCA replacement. This addresses a knowledge gap in existing research on ANN models for the prediction of geopolymer concrete properties based on RCA rate and treatment. The ANN models developed in this research predict results that are more comparable to experimental outcomes, showcasing superior accuracy compared to linear regression models.

Magnesium sulphate resistance of fly ash one-part geopolymers: Influence of solid alkali activators on physical, mechanical and chemical performance

The commitment to promoting circular economy and durable construction materials has led to the advocacy for one-part geopolymer (OPG), as an eco-friendly substitute for traditional ordinary Portland cement (OPC). Solid alkali activator is the fundamental component of OPG and significantly influences the sulphate resistance. To identify the types of solid alkali activators best suited for the development of sulphate-resistant OPGs, OPGs activated with Na2SiO3 (M-OPG), Na2SiO3+Na2CO3 (MC-OPG), Na2SiO3+NaOH (MH-OPG) and Na2SiO3+NaAlO2 (MA-OPG) were exposed to 5 % and 10 % of MgSO4 solutions for 28 days. The fine pore structures of MH-OPG and MC-OPG mitigated deterioration from the more concentrated MgSO4 solution, resulting in higher residual compressive strengths after exposure to the 10 % MgSO4 compared to the 5 %. Exposure to the 5 % MgSO4 solution resulted in strength deterioration for M-OPG, MH-OPG and MC-OPG due to the discontinuity of the aluminosilicate structure, as evidenced by the diminished Q4(3Al) sites. Conversely, the MA-OPG exhibited a 24.1 % increase in compressive strength, accompanied by the emergence of sodium magnesium aluminium silicate hydrate ((N,M)-A-S-H) gel. Hence, Na2SiO3+NaAlO2 should be acknowledged as the primary candidate for solid alkali activators in the development of sulphate-resistant OPGs.

Advancing the Sustainability of Geopolymer Technology through the Development of Rice Husk Ash Based Solid Activators

Rice husk ash (RHA), an agricultural waste byproduct, has already been tested as a component in geopolymeric binders, typically as part of the precursor solid mix, alongside materials like fly ash (FA), slag, and cement. This study presents a novel approach where RHA is employed to create a solid activator, aimed at entirely replacing commercial sodium silicates. The synthesis process involves mixing RHA, NaOH (NH), and water by applying a SiO2/Na2O molar ratio equal to 1, followed by mild thermal treatment at 150 °C for 1 h, resulting in the production of a solid powder characterized by high Na2SiO3 content (60–76%). Additionally, microwave treatment (SiO2/Na2O = 1, 460 W for 5 min) increases the environmental and economical sustainability of alkali silicates production from RHA since this processing is 12 times faster than conventional thermal treatment reducing at the same time the final product’s embodied energy. The efficacy of this new material as a sole solid activator for the geopolymerization of Greek FA is investigated through various techniques (XRD, FTIR, SEM). One-part geopolymers prepared with RHA-based solid activators demonstrated mechanical performance comparable to those prepared with commercial products (~62 MPa at 7 days). This research contributes to the advancement of sustainable construction practices emphasizing the importance of local materials and reduced environmental impact in achieving long-term sustainability goals.

Effect of multi-factors on the performance of one-part geopolymer mortar against magnesium sulfate erosion

Effect of multi-factors on the performance of one-part geopolymer mortar against magnesium sulfate erosion

Flexural behaviour of reinforced one-part geopolymer concrete beams

The recent development of “one-part geopolymer” has significantly improved construction safety and convenience, establishing it as a highly promising new type of low-carbon binder with performance comparable to traditional cement. This study investigated the flexural performance of reinforced concrete (RC) beams made from one-part geopolymer concrete (OPGC), in comparison to conventional ordinary Portland cement (OPC) concrete beams. The microstructure of OPGC and conventional concrete were firstly compared. Four-point bending tests were then conducted on nine beams, including three OPC concrete beams and six OPGC beams. The influence of longitudinal reinforcement ratio on the flexural performance of OPGC beams was examined, and the bending performance of OPGC beams and OPC concrete beams was compared. Experimental results revealed that OPGC beams exhibited similar flexural performance to those cast with OPC concrete in terms of cracking development, failure modes, load-deflection curves, and strain distribution. In addition, an analytical model for estimating the flexural capacity of OPGC beams was proposed and validated against experimental results. Finally, the environmental and economic indices between the OPGC and OPC concrete beams were compared and analysed. This research provides valuable insights for the design and analysis of OPGC structural members.

One-part geopolymer based on micronized sediments and fly ash mix: Mechanical, microstructural and leaching assessment

This study aims to investigate the leaching behavior of one-part geopolymer based on micronized sediments and fly ash. Four mixtures optimized in terms of mechanical performance and contain 0, 15, 30 and 50 % of sediments were studied. Mixtures characterization indicated that adding sediments increases compressive strength from 19 MPa to 29 MPa and increases mesoporosity (less than 50 nm) from 1.6 % to 3.5 %, with C-A-S-H and N-A-S-H gels coexistence. Given the use of dredged sediments in mixtures, it was important to study their environmental impact. The batch leaching test (0–4 mm) was carried out to study the environmental impact of mixtures at the end of their life cycle. Next, the potential for the release of chemical elements during the life cycle of the mixtures was studied through leaching tests on monolithic samples. The findings show that geopolymerization is effective for the chemical and physical immobilization of several contaminants contained in aluminosilicate sources. The geopolymer binders synthesized proved effective for the chemical immobilization of large metallic and metalloid trace elements (MMTEs) and anions (sulfate, chloride and fluoride). However, immobilization of oxy-anions MMTEs such as arsenic occurs by physical rather than chemical trapping, due to the low porosity of geopolymers. The concentration of arsenic (As) and selenium (Se) were below the non-hazardous wastes (NHW) threshold for all aluminosilicate sources but after activation the results show that these elements are mobilized due to elevated pH. This shows an effect of alkalinity on element mobilization/immobilization. It was demonstrated that carbonation could be a solution for immobilizing arsenic at the end of the mixtures' life cycle, as it reduced its concentration for all mixtures (between 20 and 51 % depending on the mixtures). In addition to these findings, the pH assessment (less than 12.5) showed that these binders can be considered as non-hazardous materials and can be assimilated to an ordinary non-corrosive binder.

Low-carbon metakaolin precursor for one-part and two-part geopolymer activation of demolition wastes

A critical part of civil engineering infrastructure works is to develop innovative construction materials for a low-carbon future development. This study delved into the feasibility of using metakaolin (MK) as a low-carbon precursor for one-part and two-part geopolymer stabilization of recycled demolition wastes. In this research, the effects of MK precursor were evaluated in combination with construction and demolition (C&D) waste aggregates such as crushed brick (CB), reclaimed asphalt (RAP) and recycled concrete (RCA) using one-part and two-part geopolymer activation. Various geotechnical tests were performed including compaction tests, repeated triaxial loading tests (RLT), unconfined compressive strength tests (UCS) and microstructural analysis. Results from this study indicated significant strength development of MK mixtures for both one-part and two-part geopolymer options. Furthermore, one-part geopolymer also showed better activation than two-part geopolymer under 7 days and 20℃ curing condition. Additionally, 30 % MK mixtures were optimal for road construction applications based on the obtained results. At 28 days or 40 ℃, MK mixtures performed best with RCA and CB as main aggregates, showing strength improvement of up to 250 % compared to 7 days and 20 ℃ curing condition. Resilient modulus (Mr) results indicated that the optimal mixtures experienced good resilient behavior with average Mr values ranging from 150 MPa to 200 MPa. Overall, MK precursor was found to be a suitable material for stabilizing demolition aggregates using geopolymer under various curing conditions.

Alkali-fused lithium slag as a substitute for slag in one-part geopolymers: Mechanism of reactivity enhancement and microstructure

Alkali-fused lithium slag as a substitute for slag in one-part geopolymers: Mechanism of reactivity enhancement and microstructure

Comparative study on the prediction of the unconfined compressive strength of the one-part geopolymer stabilized soil by using different hybrid machine learning models

With the development of green, low-carbon, and sustainable economic systems, the issues of high pollution and energy consumption in construction materials have become increasingly prominent. This study focuses on adopting one-part geopolymer (OPG) in soil stabilization for underground engineering, which exhibits environmental and low-carbon advantages. The unconfined compressive strength (UCS) serves as a crucial parameter for assessing stabilized soil’s performance. However, it is necessary to conduct a large number of experiments, inducing high costs and time consumption. In this study, one multiple linear regression model, one Decision Tree (DT) model, five ensemble machine learning (ML) models (i.e. Random Forest [RF], Extra Tree [ET], Gradient Boosting [GB], Gradient Boosting Decision Tree [GBDT], and Extreme Gradient Boosting [XGBoost]), and hybrid models of those single ensemble models with Particle Swarm Optimization (PSO) (i.e. PSO-RF, PSO-ET, PSO-GB, PSO-GBDT, and PSO-XGBoost) were adopted and compared to achieve better prediction on the UCS of the OPG-stabilized soil. Furthermore, the interpretable method including SHAP and PDP (1D and 2D), was employed to investigate the precise mechanisms by which input parameters influenced the output label. The results revealed that the multiple linear regression model delivered the lowest accuracy, and PSO-XGBoost and PSO-ET exhibited the best performance on the prediction of the UCS with R2 value of 0.9964 and 0.9928, respectively. In addition, Curing time exerted the most significant impact on the UCS, followed by FA/GGBFS, Molarity, Water/Binder, and NaOH/Precursor. Compared to the SHAP method, the PDP offered a more intuitive approach to reveal the relationship between the inputs and output. The outcome of the study shed new light on the application of ML models in the prediction of the OPG-stabilized soil’s performance in underground engineering.

Dynamic mechanical properties of one-part ultra-high performance geopolymer concrete

Geopolymer has been recognized as a promising construction material offering performance comparable to traditional cementitious materials while significantly reducing carbon dioxide emissions. Notably, the recent development of “one-part geopolymer”, which transforms the alkaline activator solution into a solid activator powder, has greatly enhanced construction convenience. One-part ultra-high performance geopolymer concrete (OP-UHPGC), which has mechanical properties comparable to ultra-high-performance concrete (UHPC), has been developed recently. This study investigates the dynamic compressive and splitting tensile properties of OP-UHPGC using a split Hopkinson pressure bar (SHPB). The damage progression, failure mode, dynamic stress and strain, dynamic increase factor (DIF), and energy absorption of OP-UHPGC specimens were systematically studied. Test results showed that OP-UHPGC exhibited strain rate sensitivity. Both compressive and splitting tensile DIFs increased with the strain rate, and empirical formulas were proposed to predict the DIFs of OP-UHPGC. The DIFs of OP-UHPGC were comparable with those of steel fibre-reinforced geopolymer or cementitious composites, yet smaller than those of plain geopolymers or conventional concrete reported in the existing literature. In addition, the energy absorption of OP-UHPGC under dynamic compression and splitting tension both increased with the strain rate. This study provides a valuable reference for the dynamic mechanical properties of OP-UHPGC.

Experimental studies on behavior of one-part geopolymer composite slabs subjected to blast loading

Over the past two decades, geopolymer has emerged as a noteworthy alternative to traditional cementitious materials in construction, offering comparable performance with reduced carbon dioxide emissions. The recent development of one-part geopolymer composites, which transform the alkaline activating solution into a solid powder form, has significantly enhanced the scalability and applicability of geopolymer in construction contexts. This study investigates the mechanical behavior of one-part geopolymer composite slabs when subjected to blast loading. Four slab specimens were constructed using the one-part geopolymer composite. Two of these specimens were reinforced with steel wire mesh, while the other two used PVA fibers for reinforcement. These slabs were tested under various blast loading induced by a shock tube. Employing three-dimensional digital image correlation techniques, the dynamic responses and damage mechanisms exhibited by these slabs were analyzed and discussed. The experimental results reveal that the fiber-reinforced geopolymer composite (FRGC) slabs demonstrate superior blast resistance compared to those reinforced with steel wire mesh. In particular, the one-part geopolymer matrix combined with PVA fibers exhibited a synergistic effect, indicating an enhanced capacity for energy dissipation. The findings suggest that one-part geopolymer concrete reinforced with PVA fibers holds significant potential for applications in the field of protective engineering, marking a step forward in the development of sustainable and resilient construction materials.

Biochar-geopolymer composite for structural capacitors

This study introduces a novel biochar-geopolymer composite (BGC) electrode designed for structural supercapacitors. Employing a one-part geopolymer system with varying biochar volume fractions, BGC electrodes were fabricated, and their electrochemical performance was assessed. The BGC electrode with a 70 % composition demonstrated enhanced dispersion of biochar, leading to significantly improved electrochemical performance, which was shown as increased peak-measured current and capacitance. The experimental results validate the feasibility of directly mixing biochar with geopolymer binder to create multifunctional supercapacitor electrodes. Promising results demonstrate the potential usage of biochar as a sustainable supercapacitor material.

Optimizing toughness and cost-effectiveness in one-part geopolymers via fiber reinforcement: A comprehensive investigation of PVA, PE, and glass fibers

This study explores developing and characterizing a one-part geopolymer, an innovative and sustainable construction material. The effects of incorporating polyvinyl alcohol (PVA), polyethylene (PE), and glass fibers (GF) on the toughness of slag and fly ash-based one-part geopolymer mortars were investigated through compressive, three-point flexural, and four-point bending tests. The findings demonstrate that fiber incorporation reduces fluidity and compressive strength due to increased porosity, lower elastic modulus of fibers, and weak interfacial bonding. However, fibers significantly enhance damage resistance and toughness via crack bridging and load transfer mechanisms. Formulations with 2 % PVA fibers and combinations of 1 % PVA with 1 % PE fibers and 1 % PVA mixed with 0.5 % PE and 0.5 % GF demonstrate excellent toughness. Notably, the latter two fiber blends achieve 14 % and 10 % cost reductions, respectively, compared to using only PVA fibers, making them economically viable for large-scale applications. Scanning electron microscopy and X-ray diffraction provided insights into the toughening mechanisms, including crack bridging, fiber pull-out, and enhanced stress distribution within the geopolymer matrix. Digital image correlation techniques further elucidated the fibers' role in improving the post-cracking behavior and structural resilience under load.

Effect of silica fume on the efflorescence, strength, and micro-properties of one-part geopolymer incorporating sewage sludge ash

The application of sewage sludge ash (SSA) in alkali activated cementitious material, i.e., geopolymer, was one of the effective measures to dispose of and recycle the sewage sludge. However, the geopolymer efflorescence could be aggravated due to elevated alkali content, especially for one-part geopolymer, where the dissolution reaction of solid alkali activator was less sufficient. This study focused on the efflorescence of GGBS-SSA based one-part geopolymer, as compared to two-part geopolymer, and the effect of silica fume on the efflorescence, strength and micro-properties of the one-part geopolymer. The results showed that the extent of efflorescence crystallization and the concentration of leached Na+ ions in the one-part geopolymer were more severe than the two-part geopolymer, due to the lower degree of geopolymerization reaction and the heterogeneous dense microstructure of the one-part geopolymer. After adding silica fume to the one-part geopolymer, the extent of efflorescence crystallization and the concentration of leached Na+ ions reduced significantly, and the compressive strength increased from 41.6 MPa to 57 MPa when the silica fume content was 10 %, but then decreased slightly. Adding the silica fume reduced the release rate of reaction heat, which helped to increase the solubility of solid alkali activator and improve the geopolymerization reaction, thus significantly reducing the content of mobile alkali ions and enhancing the compressive strength. Moreover, the silica fume with tiny spherical particle had better ball effect and micro-aggregate filling effect, which refined the pore size and reduced the connectivity of pore network, significantly reducing the diffusion rate and leaching of mobile alkali ions.

Biomass ash waste from agricultural residues: Characterisation, reactivity and potential to develop one-part geopolymer cement

Biomass is burned to generate heat and electricity. The use of biomass fuel has acquired great importance in the last years owing to its carbon-neutral nature. As a result, there is a massive build-up of biomass ash that will keep growing for decades to come. This study uses biomass ash waste to fabricate cements for construction and it presents a “zero fossil energy consumption and zero waste generation" approach to cement production. We measure the reactivity of crop biomass ash (CBA) from a power plant and the properties of one-part, CBA-slag geopolymer cements made with it. CBA has pozzolanic reactivity and potential as precursor for geopolymer fabrication. Up to 30% of CBA can be blended with ground granulated blast furnace slag (GGBS) to produce sound, one-part geopolymers activated with sodium carbonate and/or sodium silicate. Beyond this ash threshold, the geopolymer matrix experiences a strength reduction due to insufficient cement content. A one-part geopolymer consisting of 30% CBA and 70% GGBS activated with 10% sodium carbonate achieved a compressive strength of 30.70 MPa at 28 days of curing at ambient temperature. However, it exhibited a prolonged setting, taking up to 5 hours to initially set and 8 hours to finally set. Adding a sodium silicate activator significantly improved mechanical performance and accelerated setting. A formulation activated with 20% sodium silicate and 5% sodium carbonate reached a compressive strength of 46.09 MPa at 28 days, with setting times reduced to 57 minutes for the initial setting and 1 hour 15 minutes for the final setting. The sodium silicate activator enhanced hydrate formation and facilitated polymerization thereby accelerating the set and enhancing mechanical performance. Owing to the low carbon emission factor of CBA, the one-part CBA-GGBS has a low carbon footprint, which can reduce carbon emission by 80% in comparison to PC-GGBS (CEM II) mortar with a similar compressive strength. The CBA-GGBS geopolymer is economically feasible, applicable, and market attractive due to its low cost compared with equivalent PC products.

Mechanical and microstructural properties of one-part geopolymer-solidified soil attacked by Na2SO4

In the construction of traffic engineering, a large amount of waste soils was generated. These soils have poor engineering properties, cannot be used as subgrade fill, so they were solidified treatment, commonly used cement curing agent have adverse effects on the environment. One-part geopolymer (OPG), as a green and new type of soil stabilizer, not only provides a new idea for the solidification of engineering waste, but also offers an effective way for the disposal of industrial solid waste, and reduces the consumption of cement. In order to evaluate the durability of geopolymer solidified soil, in this paper, with fly ash (FA) and ground granulated blast furnace slag (GGBS) as raw materials, solid NaOH and Na2SiO3 as solid alkali-activator to prepare OPG, which was used as a solidifier to solidify the waste dredged silt to produce one-part geopolymer-solidified soil (OPGSS). The variation patterns of mass, unconfined compression strength (UCS) and elasticity modulus of OPGSS with attack time under 0%, 5% and 10% Na2SO4 solutions were investigated. The changes in the phase composition, micro-morphology and pore size distribution of OPGSS were characterized by XRD, SEM-EDS and nuclear magnetic resonance (NMR). The results showed that: Under both 5% and 10% Na2SO4 solutions, the UCS of OPGSS decreased in two stages with attack time, and the number of large pores and total pores of OPGSS increased in two stages. The inflection points appeared on day 8 under 5% Na2SO4 solution; the inflection points appeared on day 5 under 10% Na2SO4 solution. This was mainly due to the expansion of corrosion products formed by OPGSS under Na2SO4 attack, which destroyed the microstructure of OPGSS and led to a reduction in the UCS of the OPGSS.