Geopolymer Cement Research Articles

Developing interpretable machine learning-Shapley additive explanations model for unconfined compressive strength of cohesive soils stabilized with geopolymer.

This paper seeks to develop an interpretable Machine Learning (ML) model for predicting the unconfined compressive strength (UCS) of cohesive soils stabilized with geopolymer at 28 days. Four models including Random Forest (RF), Artificial Neuron Network (ANN), Extreme Gradient Boosting (XGB), and Gradient Boosting (GB) are built. The database consists of 282 samples collected from the literature with three different types of cohesive soil stabilized with three geopolymer categories including Slag-based geopolymer cement, alkali-activated fly ash geopolymer and slag/fly ash-based geopolymer cement. The optimal model is selected by comparing their performances with each other. The values of hyperparameters are tuned by Particle Swarm Optimization (PSO) algorithm and K-Fold Cross Validation. Statistical indicators show the superior performance of the ANN model with three metrics performance such as coefficient of determination R2 = 0.9808, Root Mean Square Error RMSE = 0.8808 MPa and Mean Absolute Error MAE = 0.6344 MPa. In addition, a sensitivity analysis was performed to determine the influence of different input parameters on the UCS of cohesive soils stabilized with geopolymer. The order of feature effect can be ordered in descending order using the Shapley additive explanations (SHAP) value as follows: Ground granulated blast slag content (GGBFS) > Liquid limit (LL) > Alkali/Binder ratio (A/B) > Molarity (M) > Fly ash content (FA) > Na/Al > Si/Al. The ANN model can obtain the best accuracy using these seven inputs. LL has a negative correlation with the growth of unconfined compressive strength, whereas GGBFS has a positive correlation.

Enhancement of kaolin clay soil for civil engineering application using rice husk ash and sawdust ash geopolymer cements

These days, good quality road construction materials are scarce and their haulage to the construction site is expensive. When unsuitable materials are encountered during flexible pavement construction, the most technical and economical option is always to improve them to meet design standards. One of these deficient materials mostly encountered in tropical regions is kaolin clay soils. Cement and lime that are traditional deficient soil improvement agents are on high demand therefore have kept the cost of engineering construction financially high. Thus, the use of agricultural wastes such as sawdust and rice husk as alternative construction materials will considerably reduce the cost of construction and as well mitigate the environmental hazards caused by the wastes and cement production. This study investigated and compared the performance of rice husk ash (RHA) and sawdust ash (SDA) geopolymer cements in improving the geotechnical properties of kaolin clay soil used for flexible pavement construction. All laboratory experimental tests were carried out in accordance with British Standard (BS) 1377 and BS 1924 for natural and modified kaolin clay soil samples respectively. Soil samples were mixed with geopolymer cement at stepped concentrations of 0, 4, 8, 12, 16 and 20% by dry weight of soil. Results indicated that the plasticity index value of the natural kaolin clay of 18.52% was reduced to 7.24% at 20% RHA geopolymer cement content. The unconfined compressive strength of the natural soil was improved by 600 and 400 % by RHA and SDA geopolymer cements respectively. It was concluded that the use of up to 20% RHA and SDA geopolymer cements can efficiently and eco-friendly improve kaolin clay for flexible pavement foundation purpose.

Pemanfaatan Lusi dan Fly Ash Sebagai Material Bautan Berdasarkan Nilai Berat Jenis Agregat Halus dan Porositas

Sidoarjo mudflow (Lusi) still occurs today, various efforts to stop and reduce the eruption have been made but have not stop able to stop the Sidoarjo mud. To help reduce the mud being ejected, it is necessary to utilize Sidoarjo mud. Researchers aim to reduce the mud caused by Sidoarjo mud by utilizing artificial materials as substitutes for natural materials. Utilization is also carried out for fly ash which is waste from the PLTU. Sidoarjo mud and fly ash are combined with an alkaline activator to form geopolymer paste and cement paste. The geopolymer paste specimen were tested for specific gravity of fine aggregate and its porosity. The result show Sidoarjo mud has a specific gravity of fine aggregate of 2.519 and fly ash of 2.525 which is greater than specific gracity of water, namely 1. The porosity of the geopolymer paste is 3% and that of cement paste is 3.8%.

Effects of teff straw ash on the mechanical and microstructural properties of ambient cured fly ash-based geopolymer mortar for onsite applications

Although geopolymer cement (GPC) is a substitute for Portland cement, its application is restricted due to the need for high-temperature curing (40–90 °C), which makes it challenging to utilise for onsite applications. To address this issue, the current study examined the potential of substituting fly ash (FA) with teff straw ash (TSA) in geopolymer mortars cured at ambient temperature. The findings revealed that substituting FA with TSA can eliminate the need for high-temperature curing, and the compressive strengths of FA-TSA-based geopolymer mortar mixtures cured for 28 days ranged from 45 to 53 MPa. Further, increasing the TSA content enhanced the mortar's flexural and direct tensile strengths. A teff straw ash level of 10% increased compressive, flexural, and direct tensile strengths by 40%, 59%, and 30% at 28 days, respectively. Furthermore, the mineralogical phases of the mortar after 28 days confirmed the presence of gismondine coexisting with other phases, and microstructural analysis indicates that the inclusion of TSA resulted in a denser structure. These findings suggest that TSA could be a potential substitute for FA in GPC applications to lower energy usage and environmental impact.

Alkali-bauxite fusion method of synthesizing ambient-cured volcanic ash geopolymer cement mortars

The plain volcanic ash-based geopolymer cement (VA-GPC) system typically exhibits weak strength development under ambient temperature curing, thereby limiting its potential application in engineering construction. This study aimed at synthesizing an improved VA-GPC binder using a highly reactive sodium aluminate material as an admixture for enhancing geopolymerization.Bauxite was fused with sodium hydroxide alkali at 750 °C to prepare the sodium aluminate admixture (faBX). The faBX admixture composition was varied to different amounts of sodium oxide comprising 20, 30, 40, 50 and 60 % Na2O by weight of bauxite. A combined solution of sodium silicate and sodium hydroxide was used as the alkaline activator reagent. In the study, the VA-GPC binder was synthesized by blending volcanic ash with 0 or 10 wt% faBX admixture. Mortar mixtures were then made by mixing the synthesized VA-GPC binder with fine aggregate, followed by curing at ambient temperature. Setting time, workability, compressive strength, drying shrinkage, pore volume and water absorption properties of the geopolymer specimens, were evaluated. Analytical studies were done using XRD, FTIR and SEM/EDS. It was found that the 28-day compressive strength results gave values of up to 26.9 MPa, representing 1500 % strength increase over that of the control. The initial and final setting times were significantly shortened as Na2O content of faBX increased. Microanalysis results showed that an amorphous geopolymeric gel was produced, consisting mainly of poly(silicate-siloxo) and poly(ferro-silico-aluminate) phases. Evidently, incorporation of faBX in VA-GPC enables the binder system to develop suitable normal or rapid hardening geopolymer cement properties under ambient curing conditions.

Immobilization Approach as a Creative Strategy to Remove Reactive Dye Red 195 and Cu2+ Ions from Wastewater Using Environmentally Benign Geopolymer Cement

Water is a resource that is essential to almost all phases of industrial and manufacturing operations globally. It is important to handle the wastewater generated professionally. The textile industry is one of the major global polluters, with textile producers responsible for one-fifth of all industrial water pollution worldwide. In contrast, heavy metal contamination has developed into a critical, expanding global environmental problem. Geopolymer is a cementitious constituent of amorphous aluminosilicates derived from natural or industrial wastes. It is produced using the polymerization of aluminosilicate raw ingredients in an alkaline atmosphere. The aim of this study is to evaluate the application of eco-friendly geopolymer cement in the immobilization technique for the treatment of wastewater including heavy metals and dyes. Geopolymer cement pastes were organized using slag and fly ash as an aluminosilicate source, (1:1) sodium silicate and sodium hydroxide 15 wt.% as an alkali activator in the presence of organic dye pollutant reactive red 195, and Cu2+ ions (700 ppm) at different hydration times for up to 28 days. The physicochemical and mechanical properties of the prepared geopolymer cement mixes were further examined in relation to reactive dye pollutant and Cu2+ ions. The hydration characteristic was examined using the compressive strength and % of total porosity tests, as well as FTIR and XRD studies. Our findings support the 100% immobilization of both Cu2+ ions and organic dye pollutants in prepared geopolymer pastes for up to 28 days of hydration. Additionally, adding both Cu2+ ions and dye pollutants to the prepared geopolymer paste improves its mechanical properties, which is also supported by FTIR data. XRD and FTIR studies showed that the Cu2+ ions and dying bath effluent addition have no influence on the kind of hydration products that are produced. On the other hand, the geopolymerization process is negatively impacted by the presence of Cu2+ ions alone in the geopolymer paste.

Finite element analysis of beam-column joint behaviour utilizing glass fiber reinforced polymer bars and geopolymer concrete

The important areas in an earthquake-prone reinforced concrete building are the beam-column joints. Therefore, the design of beam-column joints requires for extremely ductile materials, because during an earthquake, the moment carrying capacity and shear strength of the beam-column joint are reduced, which leads to failure. There has been a lot of interest from around the world in using bars made of glass fibre reinforced polymer (GFRP) as internal reinforcement for concrete constructions working in severely difficult situations. In addition, geopolymer cement is currently gaining a lot of attention as a possible replacement for conventional portland cement (OPC), because there are no CO2 emissions produced during its manufacture. But there hasn't been enough scientific investigation to demonstrate the advantages of combining these materials in actual infrastructure, which is the primary motivation behind this study. From the earlier research work till now, it is observed that analysis of beam column joints is done using FRP-RC and S-RGC systems which are usually over reinforced. So the aim of this research work is to study the benefits of the Glass Fibre Reinforced Polymer Bars and Geopolymer Concrete (GFRP-RGC) system in actual infrastructure. The experimental study is very costly and time consuming. Nowadays, it is becoming increasingly important to analyse different structural components using finite element analysis (FEA). In this study, finite element method is used to analyze the beam column joint. For that, the published experimental results first compared with finite element results of beam using Glass Fibre Reinforced Polymer Bars and Geopolymer Concrete (GFRP-RGC) system. Based on this, it was cleared that experimental results and finite elements are approximately equal. Then analysis of RCC building was done in Etabs software for Dead load, live load, and Earthquake load to identify critical joints. Further study was undertaken for critical joints for axial forces, shear forces and bending moment in ANSYS using GFRP-RGC system by the same process.

Characterizing a Local Sewage Sludge Ash for Developing Alkali-Activated Geopolymer Mortar

Production of ordinary Portland cement (OPC) has significant adverse effects on the environment and accounts for 5%–7% of CO2 emissions globally. Geopolymer cement is potentially a sustainable alternative to OPC and is created by the activation of aluminosilicate materials with an alkaline solution that induces geopolymerization, causing gelation of the materials. Sewage sludge ash (SSA) contains relatively high contents of aluminosilicate materials and can be a precursor for geopolymers. This study aims to characterize a local SSA as a precursor to develop geopolymer mortar. Chemical and leaching analysis found no significant adverse environmental implications of the SSA. Strength activity index tests showed that the SSA has a moderate pozzolanic activity. The SSA was then utilized to develop a geopolymer mortar in conjunction with an alkaline solution consisting of sodium hydroxide and sodium silicate. Factors that influence the geopolymerization and strength gain of geopolymers were examined, including the molar ratio between silicon dioxide and sodium oxide and the activator/binder ratio. An optimal activator/binder ratio of 0.22 and a SiO2/Na2O molar ratio of 0.80 were determined to yield the highest compressive strength of the geopolymer mortar.

Evaluation of the Potential of Metakaolin, Electric Arc Furnace Slag, and Biomass Fly Ash for Geopolymer Cement Compositions.

The widespread use of geopolymer cement (GPC) has been hindered by a lack of scientific knowledge that still exists regarding its synthesis process. Key points, such as the release of aluminosilicate species from the raw materials and its link to the properties of GPC, have still not been completely studied. As a result, most of the GPC formulations covered in the literature are based on precursors' elemental analysis using XRF (X-ray Fluorescence), or other equivalent analysis methods, and consider that the total aluminosilicate content of the precursors is available for participating in the geopolymerization process, which seems very unlikely. In this study, the amounts of aluminate and silicate species released from metakaolin (MK), electric arc furnace slag (EAFS), and biomass fly ash (BFA) in alkaline dissolution tests were determined by simple spectrophotometric methods. It was found that MK yields the highest aluminosilicate dissolution amount, about 2.1 mmol of silicate + aluminate per gram of MK, while EAFS and BFA yield about 0.53 and 0.32 mmol/g precursor, respectively. These results were used to estimate the total amounts of dissolved aluminosilicates in a series of GPC mortars prepared from these raw materials, which were thereafter subjected to mechanical tests. It was shown that the mortars' compressive strength (which ranged from 1 to 63 MPa) is linearly correlated with their estimated total amount of dissolved aluminosilicates, with the best linear fit yielding a coefficient of determination above 0.99. It was concluded that by using the results of the dissolution tests, the estimation of compressive strength is greatly improved when compared to using the elemental analysis obtained by XRF, which yields a coefficient of determination of 0.88 and a larger dispersion of data points. The results reveal the usefulness of this simple method for evaluating the potential of inorganic industrial waste streams as precursors for GPC.

Role of CO2 in enhancing geopolymer properties formulated with fluidized bed combustion ash

Fluidized bed combustion coal ash was used together with conventional coal ash and alkaline materials to synthesize geopolymer cement. The production process was performed in a carbon dioxide-rich environment to integrate carbon dioxide into the cement. The presence of carbon dioxide was found to enhance the formation of crystalline carbonates during the hydration reaction yielding an enhanced geopolymer matrix with improved binding characteristics. The non-crystalline (metastable) carbonates formed undergo crystallization processes that complement the hydration reactions, and yield carbonate with beneficial binding effects. Experimental optimization was designed and implemented to select the desired formulation of raw materials for achieving high levels of carbon capture and engineering properties. The optimized formulation produced a geopolymer cement with 7.4 wt% CO2 content, which produced concrete materials with a flow table of 68 cm, an initial set time of 34 min, and 28-day compressive strength reaching 28.2 MPa with acceptable residual compressive strength.

A state-of-the-art review of the structure and properties of laterite-based sustainable geopolymer cement

Portland cement is the primary material in the field of construction. Despite its importance, its production remains an energy-consuming and polluting operation. Research on alternatives to Portland cement has become an international concern, and these alternatives include geopolymers. With the evolution of the research on geopolymers during the last decade, it is necessary to work on raw materials that are abundant in nature and less expensive and provide sustainable construction materials. The present paper reviews the research on the use of laterites as a precursor in synthesizing sustainable geopolymers. The effect of the nature of activators, the calcination temperature of laterites, and the effect of additives on the properties of laterite-based geopolymers are also examined. The characterization results of laterite-based geopolymers show that laterite is a promising precursor for synthesizing sustainable geopolymers with high physical-mechanical characteristics. Finally, perspectives and recommendations for advancing laterite-based geopolymers are discussed at the end of the paper.

Assessment of Natural Radioactivity and Radon Exhalation in Peruvian Gold Mine Tailings to Produce a Geopolymer Cement

Mining generates significant amounts of waste that can represent a source of contamination for areas close to the extraction area, generating a negative impact both on the environment and the health of people. This study aims to evaluate the radiological risk derived from exposure to natural radionuclides contained in tailings from Peruvian gold mines and to establish whether the tailings can be used as raw materials in building materials. The mine tailings come from a mining project in the northern highlands of Peru. Radon exhalation was measured using Rad7 in a closed chamber and activity concentration of 226Ra, 232Th, and 40K radioisotopes by gamma spectrometry using NaI 3” × 3” detector. Maximum activity concentrations measured for 226Ra and 232Th were 15.38 Bq kg−1 and 11.9 Bq kg−1, respectively; meanwhile, activity concentration for 40K ranged from 182.7 Bq kg−1 to 770.8 Bq kg−1. All activity concentrations were below the worldwide average except for 40K. The radon exhalation rate varied from 2.8 to 7.2 mBq kg−1 h−1. The gamma index (Iγ), and radiological parameters, including the Radium equivalent activity (Raeq), and the external hazard index (Hex), being below the recommended levels by UNSCEAR, ensure the safe use of these mines tailing to produce a geopolymer cement.

The single and hybrid use of steel and basalt fibers on high‐temperature resistance of sustainable ultra‐high performance geopolymer cement mortars

AbstractThis paper primarily examines the flowability, physical appearance, mass loss, residual compressive strength (RCS), and residual flexural strength (RFS) properties of steel (ST) and basalt (BA) fiber‐added sustainable ultra‐high performance geopolymer cement (UHPGPC) mortars exposed to high‐temperature effects. According to the results obtained, ST and BA fibers adversely influence the workability properties of UHPGPC mortars and thus significantly reduce the spreading diameters of the mortars. However, ST and BA fibers substantially improve the RCS and RFS capacities of UHPGPC specimens exposed to high temperatures because they have a powerful bonding effect with the matrix and effectually restrict the development of micro‐ and macro‐cracks with their bridging effect. Furthermore, this phenomenon is slightly more effective in hybrid form than using ST and BA fibers.

Valorization of phosphogypsum waste through acid geopolymer technology: synthesis, characterization, and environmental assessment

Phosphogypsum (PG) constitutes the principal by-product of the phosphate industry which largely restricts its wide development. The incorporation of PG as a reinforcement agent into geopolymer cement, can play however a significant role to enhance their mechanical and microstructural properties and to develop a sustainable geopolymer–PG based circular economy. In this study, geopolymer reinforced PG composites were prepared at different PG content according to PG/MK ratio in the range of 0–1. The mechanical properties of the composites were tested under compressive and flexural strength. The results show a significant enhancement of compressive and flexural strength from 40.14 MPa to 48.43 MPa and 5.13 MPa to 9.1 MPa respectively with addition of 20.6 % and 77.3 % compared standalone geopolymer. This improvement was linked systematically with crack self-healing mechanism due to PG rod-like morphology and its high adhesion to the geopolymer matrix. The heavy metals leaching test show that most of the developed acidic geopolymer– PG composites have a leaching value lower than the international recommendations. Thus, geopolymer– PG composites can constitute an efficient and sustainable alternative to conventional building materials and can be extended to divers’ industrial applications.

Valorization of limestone powder as an additive for fly ash geopolymer cement under the effect of the simulated tidal zone and seawater attack

Generally, buildings and constructions subjected to the harsh marine environment, especially tidal zone, are usually more susceptible to deterioration than others. Therefore, choosing the type of cement is important to limit this degradation. Limestone powder is widely used as a cementitious material in traditional Portland cement systems due to its availability and low cost. Unlike in the geopolymers, using limestone powder is still in its growth stage, especially in fly ash geopolymer cement. The recent article is the first attempt to enhance fly ash geopolymer cement with limestone powder aiming to limit the deterioration caused by seawater attack and the simulated tidal zone. For this reason, the fly ash was partially replaced with limestone powder at levels oscillating from 10 % to 60, by weight, with a stride of 10 %. After initial curing, the specimens were exposed to seawater attack and the simulated tidal zone for 3, 6 and 12 months. Other specimens were exposed to the air and tap water for the same periods for comparison purposes. Compared to the specimens cured in the air, the results disclosed that the specimens subjected to the simulated tidal zone showed the highest impairment ratios followed by those submerged in seawater, whilst the specimens submerged in tap water came in last place. The incorporation of limestone powder up to 20 % into fly ash geopolymer cement showed a positive effect in enhancing the compressive strength and limiting the deterioration caused by the harsh environment, whilst higher ratios than 20 % showed a negative effect.

Development and optimization of phosphogypsum-based geopolymer cement

Phosphogypsum (PG) is a solid waste product that is generated in the phosphoric acid manufacturing process, most of which is currently sent to landfills rather than reused. In this study, beta-hemihydrate phosphogypsum (β-HPG), slag, fly ash (FA) and alkali activator were mixed to form a phosphogypsum-based geopolymer (PBG) cement. The effects of the slag and FA content, citric acid (CA) dosage, sodium metasilicate (SM) dosage, and water addition process were investigated. The results indicated that the 28-day unconfined compressive strength (UCS) of the cement can exceed 60 MPa when a reasonable mix proportion is adopted. The hydration products and strength formation mechanism of the PBG cement were assessed using XRD-Rietveld and SEM-EDS. The micro-analysis results indicated that the main hydration products were dihydrate phosphogypsum, ettringite, and CSH gel, which jointly provided the strength for the PBG cement. The PBG cement may improve the utilisation prospects of PG waste.

Multiscale study of the effect of fly ash geopolymer on the fatigue cracking of cement stabilized macadam

Understanding of the correlation between the micro-composition and macro-mechanics of cement stabilized macadam (CSM) is crucial to an optimized design of cement-treated base (CTB) with improved crack resistance. In this study, acoustic emission (AE) technique was used to monitor the crack propagation of plain cement stabilized macadam (P-CSM) and fly ash geopolymer cement stabilized macadam (FAG-CSM) under cyclic loading. Experimental tests and characterizations, including such as nanoindentation, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS), were further performed. The test results show that FAG-CSM has better fatigue performance than that of P-CSM; the AE counts, risetime/AE amplitude values (RA) and b-value can be used to assess the damage degree, cracking mode as well as the bulk modulus of cement composites. Interfacial transition zone (ITZ) is the weakest modulus area in CSM and the incorporation of fly FAG can effectively increase the indentation modulus of ITZ. The volcanic ash reaction of fly ash leads to the hydration of cement to produce more hydration products, which reduce the voidance within ITZ and thus improve the bonding between the aggregate and mortar, which supports the findings of the macro-mechanical analysis and AE monitoring of CSM.

Reaction mechanism and mechanical properties of geopolymer based on kaolinitic coal tailings

Valorization of coal tailings as supplementary cementitious material is vital for green development, including their application as aluminosilicate in geopolymer materials. Coal tailings from southern Brazil were activated mechanically and thermally. This work analyzed the effect of calcium addition via Portland cement and flue gas desulfurization on the reaction mechanism of geopolymer using setting times and semi-adiabatic calorimetry. Additionally, un-calcined coal gangue was added to geopolymer cement to evaluate the effect of sulfur in the microstructure of geopolymer. The experimental results showed kaolinitic coal sludge was transformed into a metastable phase with higher reactivity, while X-ray pyrite reflection was observed for un-calcined coal gangue. The findings showed that calcium modified the reaction mechanism by accelerating the monomers' condensation and increasing the energy released, promoting the hardening of the geopolymer at 24 h. In addition, a solid matrix of geopolymer was developed compounded mainly by an amorphous inorganic polymer and C-A-S-H gel as a secondary phase. The thermodynamic simulation confirmed the addition of coal gangue reduced the pH of the pore solution and increased the content of SO42− and Fe2+. These results evidenced that partial oxidation of pyrite in an alkaline medium releases iron and sulfate ions and this process can lead to acidification of the pore solution resulting in internal degradation.

Bioinspired brick-and-mortar geopolymer composites with ultra-high toughness

Geopolymer cement is a promising alternative to ordinary Portland cement as it offers comparable mechanical properties and greater durability with lower carbon emissions. Despite its advantages, the brittleness of geopolymer hinders its application as a structural material. In this work, a bioinspired brick-and-mortar structure is explored as a design paradigm to overcome this brittleness and to further augment geopolymer mechanical performance. To this end, composites were prepared with geopolymer as the brick phase and 3D-printed polymers as the mortar phase, with focus on the influence of the mortar phase stiffness. Bending and fracture results reveal strong and tough geopolymer composites can be achieved through a bioinspired brick-and-mortar structure. The geopolymer based composites showed up to 830 times greater toughness with simultaneous gains of 48% in strength compared to the bulk geopolymer. This composite exceeds bending strength and toughness of both its constituents. Stiffer soft phases generate tougher composites compared to more compliant soft phases. Various toughening mechanisms, including brick interlocking, crack bridging and crack deflection, triggered by the bioinspired design, were revealed through Digital Image Correlation, indentation, and microscopy.

Decolorization of Reactive Dyes, Part VIII: Eco-Friendly Approach of Reactive Red 195 Dye Effluents Decolorization Using Geopolymer Cement Based on Metakaolin backed by slag

Decolorization of Reactive Dyes, Part VIII: Eco-Friendly Approach of Reactive Red 195 Dye Effluents Decolorization Using Geopolymer Cement Based on Metakaolin backed by slag