Sustainable Geopolymer Research Articles

Sustainable geopolymer concrete for thermoelectric energy harvesting

Concrete is a widely used material that presents vast opportunities for energy harvesting applications. Among these, thermoelectric concrete shows promising potential for harvesting waste heat generated in urban and industrial environments. However, the development of thermoelectric concrete poses several challenges that need to be addressed, such as the need to accurately account for the intrinsic voltage. This factor is frequently disregarded, but it has a significant impact on the measurement of thermoelectric properties in improving the intrinsically low electrical conductivity and Seebeck coefficient. In this context, this study evaluates the performance of industrially scalable geopolymer-based concrete that incorporates recycled aggregates as low-cost and environmentally friendly additives for thermoelectric energy harvesting applications. The concrete exhibited an intrinsic voltage of 15 mV, and a new test protocol was proposed to exclude its impact on thermoelectric measurements. The geopolymer concrete demonstrated a significantly high Seebeck coefficient of 570 µV/k, surpassing all previously reported values for geopolymer-based materials. Furthermore, it was discovered that the thermoelectric behavior of geopolymer-based concrete is of ionic origin, indicating that further improvements can be made by adjusting the pore solution chemistry. This finding suggests that there is ample opportunity for innovation and optimization in the development of thermoelectric concrete.

Recycled Surgical Mask Waste as a Resource Material in Sustainable Geopolymer Bricks

With the advent of the COVID-19 pandemic, the global consumption of single-use surgical masks has risen immensely, and it is expected to grow in the coming years. Simultaneously, the disposal of surgical masks in the environment has caused plastic pollution, and therefore, it is exigent to find innovative ways to handle this problem. In this study, surgical masks were processed in a laboratory using the mechanical grinding method to obtain recycled surgical masks (RSM). The RSM was added in doses of 0%, 1%, 2%, 3%, and 4% by volume of geopolymer bricks, which were synthesized with ground granulated blast furnace slag (GGBS), rice husk ash (RHA), sand, and sodium silicate (Na2SiO3) at ambient conditions for a duration of 28 days. The developed bricks were tested for compressive strength, flexural strength, density, water absorption, efflorescence, and drying shrinkage. The results of the study reveal that compressive strength and flexural strength improved with the inclusion of RSM in the bricks. The highest values of compressive strength and flexural strength were 5.97 MPa and 1.62 MPa for bricks with 4% RSM, respectively. Further, a reduction in the self-weight of the bricks was noticed with an increase in RSM. There was no pronounced effect of RSM on the water absorption and efflorescence properties. However, the RSM played a role in reducing the drying shrinkage of the bricks. The sustainability analysis divulges the catalytic role of RSM in improving material performance, thereby proving to be a potential candidate for low-carbon material in the construction industry.

Optimization of constituent proportions for compressive strength of sustainable geopolymer concrete: A statistical approach

Geopolymer concrete (GPC) is an environmentally friendly and sustainable concrete produced through the geopolymerization process, involving the combination of alumino silicate materials with alkaline solutions. It has unique advantage of being carbon-negative which helps reduce carbon dioxide levels in the atmosphere. One challenge with making GPC is the significant variation in compressive strength that arises from differences in constituent proportions, specimen ages, andcuring conditions. There is a need to optimize the GPC constituents to achieve the desired compressive strength. To address this issue, a comprehensive dataset comprising 1242 data points from existing literature on fly ash-based GPC (FA-based GPC) was compiled for the purpose of optimizing the constituent proportions of GPC using statistical analysis. Nine independent variables were selected to develop the predictive models for compressive strength using linear (LRA), multilinear (MRA), and non-linear (NRA) regression analyses. The models were assessed using scatter plots between experimental and predicted responses and adopting the performance criteria such as the statistical significance of the model unknowns, R2 values, root mean square error (RMSE), mean absolute error (MAE), and scatter index (SI). LRA revealed that the compressive strength of GPC is not dependent on any single independent variable. Therefore regression analysis with multiple independent variables was conducted. From MRA, ±15 % error for training dataset and (15–20) % error for validating dataset was estimated. The R2, RMSE, MAE, and SI values were found to be 0.8086, 6.11, 5.35, and 0.21. NRA predicted the compressive strength more efficiently because it provides the error ±10 % for both training and validating datasets with R2, RMSE, MAE, SI values of 0.8321, 5.46, 4.77, and 0.19. Further, curing temperature, specimen age, Na2SiO3/NaOH ratio, I/b ratio, and aggregate content were found as the most significant independent variables. The time and cost-effective design mix for FA based GPC can be prepared using the regression models presented in the current work.

Comparative Analysis of Regression and ANN Algorithm for Predicting Compressive Strength of Sustainable Geopolymer Concrete at Varying NaOH Concentration and Curing Temperature

Comparative Analysis of Regression and ANN Algorithm for Predicting Compressive Strength of Sustainable Geopolymer Concrete at Varying NaOH Concentration and Curing Temperature

Investigation on the impact of elevated temperature on sustainable geopolymer composite

Geopolymer concrete (GPC) is an eco-friendly, sustainable, cementless and green concrete. It could be an alternative to the conventional concrete. In alkaline circumstances, the alumina and silica concentration in geopolymer concrete creates the geopolymer bond, while regular concrete creates C-S-H (calcium silicate hydrate bond). The final result of the geopolymer bond does not include any water. At elevated temperatures, geopolymer concrete would thus be more stable. Due to its greater strength and durability quality, geopolymer concrete may be the ideal replacement for ordinary portland cement (OPC) concrete. This research intends to examine how specimens of geopolymer concrete and regular concrete respond to exposure to increased temperatures between 100°C and 800°C. Mass loss, ultrasonic pulse velocity, compressive strength, X-ray diffraction, thermogravimetric analysis and derivative thermogravimetric analysis were all examined throughout the experimental examination. Both concrete specimens lose mass or weight as the exposure temperature rises; OPC concrete samples spalls at 600°C, while GPC sample fail at 800°C. GPC specimens lose around 12% of their original mass after being exposed to temperatures of 800°C, while OPC specimens lose about 7%. The GPC specimens maintained 60% of their initial compressive strength after being exposed to a temperature of 700°C, but the OPC concrete specimens only kept 52%. With each increase in exposure to extreme temperatures, the peaks of quartz and cristobalite are lowered. Only the form or structure of the mineral oxide would change; the chemical linkages would remain. The GPC samples subjected to temperatures of 100°C exhibit effective thermal stability than all other specimens exposed to extreme temperatures. As the exposure temperature rises, the GPC specimens become more thermally stable. According to the experimental findings, the GPC specimens’ bonding structure makes them more resistant to high temperatures than regular concrete specimens. Micropores are present in the voids of the geopolymer matrix, while mesopores and micropores are present in the voids of the OPC matrix. While OPC bonding is C-S-H formed by the hydration of lime and silica contained in the cement, the geopolymer bonding did not include the water content in the final or end result of geopolymerisation for strengthening.

Influence of various fibers on the physico-mechanical properties of a sustainable geopolymer mortar-based on metakaolin and slag

Recently, studies on sustainability and ecology have become widespread in almost all sectors. One of the most important reasons for this spread is the rapid increase in industrialization and, thus, the increase in waste caused by industries. In this context, significant efforts are being made to evaluate some of these wastes. One of these efforts is the production of geopolymers. In this research, metakaolin and slag-based geopolymer mortar samples were manufactured, and polyvinyl Alcohol, basalt, and macro synthetic polypropylene fibers were used to enhance the physical, mechanical, and high-temperature resistance of the sample. Physical and mechanical tests of the produced samples were performed after 28 days. Then, elevated-temperature experiments were conducted to evaluate the behavior of the fibers under the influence of high temperature. Following the high-temperature test, physical, mechanical and microstructure tests of the samples were performed. As a result, basalt fiber enhanced the compressive strength of 800 °C-exposed samples by 7.72% compared to the fiber-free sample. Also, polyvinyl Alcohol fiber increased the energy absorption capacity of the samples by increasing Charpy impact values to 72.22% compared to fiber-free sample. Moreover, macro synthetic polypropylene fiber reduced capillary water absorption value up to 12.44% compared to fiber-free sample.

Development of sustainable geopolymer materials made with ground geopolymer waste powder as renewable binder up to 100%

Reusing ground geopolymer waste powder (GWP) as renewable binder in sustainable geopolymer offers a valuable approach for recycling geopolymer waste. This study investigated the micro–macro characteristics of fly ash (FA)-based geopolymer, including the replacement of FA with GWP up to 100%. The GWP comprised the GWPG from GGBS-based geopolymer paste, the GWPGF from GGBA-FA-based geopolymer paste, and the GWPF from FA-based geopolymer paste, respectively. The findings revealed that GWPG exhibited higher alkali-activated reactivity compared to GWPGF and GWPF. The geopolymer made with 100% GWPG demonstrated a better microstructure than FA-based geopolymer, but the microstructure of geopolymer deteriorated with the inclusion of GWPGF and GWPF. The average pore diameter of geopolymer made with 100% FA, 100% GWPG, 100% GWPGF, and 100% GWPF was measured at 18.06, 15.69, 116.50, and 92.62 nm, respectively. Mixing GWP led to an increase in drying shrinkage. The strength and permeability resistance of eco-friendly geopolymer initially decreased and subsequently improved with increasing substitution of GWPG, with geopolymer made with 100% GWPG exhibiting superior strength and permeability resistance compared to FA-based geopolymer. However, the strength and permeability resistance of eco-friendly geopolymer exhibited a continuous decline with the increasing replacement of GWPGF or GWPF, up to 100%. When the content of GWP was identical, GWPG blended geopolymer exhibited superior micro-structure and macro-properties compared to GWPGF or GWPF blended geopolymer. Thus, it is recommended to substitute GWPG for 100% FA in fully recycled geopolymer owning good strength and permeability resistance. However, caution should be exercised when incorporating high volumes of GWPGF or GWPF in eco-friendly geopolymer.

Microstructural analysis of environment friendly sustainable geopolymer concrete

Microstructural analysis of environment friendly sustainable geopolymer concrete

Waste-to-energy agricultural wastes in development of sustainable geopolymer concrete

The building industry, which generates many greenhouse emissions, is under much pressure because of how communities are being affected by climate change. Due to the environmental issues associated with traditional cement production, geopolymer concrete has emerged as a feasible alternative. In recent years, Portland cement has been replaced with industrial or agricultural byproducts as precursors in the environmentally friendly building material known as geopolymer concrete. Fly ash, powdered granulated blast furnace slag, and metakaolin were all employed as precursors in geopolymer concrete, with fly ash being the most popular. This study examined the compressive strength of geopolymer concrete with various dosages of rice husk ash (RHA) and ground granulated blast furnace slag (GGBS). Additionally, geopolymer concrete blends' micro-structure and energy efficiency with different RHA were assessed and contrasted with regular plain Portland cement concrete. According to the findings, using agricultural wastes in geopolymer concrete has three advantages: it improves compressive strength, creates a waste-to-energy nexus, and lessens the environmental effect.

Effective utilization of agricultural ashes in development of sustainable geopolymer concrete

The use of concrete is widespread in the construction industry due to its successful and desirable properties. As industrial and urban development rapidly increases, the demand for concrete is also reaching new heights compared to other materials. In this regard, there is a pressing need for alternative materials to replace cement and industrial by-products. This paper proposes the effective utilization of agricultural ashes, including rice husk ash (RHA), bagasse ash (BA), and palm oil ash (PA), in geopolymer concrete. The study evaluates fly ash-based geopolymer concrete's compressive strength and microstructural performance by replacing fly ash with varying percentages of agricultural ashes. The results show that including agricultural ashes in the fly ash-based geopolymer blends yields higher strength than the 100% fly ash-based geopolymer concrete. However, using higher dosages of agricultural ashes decreases strength and forms micro-cracks in the geopolymer phases. Therefore, using 20% RHA or 15% BA or 15% PA as a precursor in fly ash-based geopolymer concrete can produce sustainable construction material and contribute to greener construction. Green concrete can help advance the circular economy and promote environmental protection.

Use of waste glass powder toward more sustainable geopolymer concrete

The influence of waste glass powder (WGP) with fly ash in certain proportions on geopolymer concrete (GPC) was investigated by exchanging different proportions of molarity and WGP percentages in GPC. For this objective, fly ash was altered with WGP having percentages of 10%, 20%, 30%, and 40%, and the effect of molarity of sodium hydroxide (NaOH) was examined. The compressive strength tests, splitting tensile tests, and flexural strength tests were conducted. The workability and setting time were also evaluated. With the addition of WGP, the workability for molarities (M) of 11, 13, and 16 NaOH reduced by an average of 17%, 10%, and 67%, respectively. The findings showed that the slump values decreased as the molarity and WGP percentages increased. Molarity significantly affected the setting time, but WGP had no effect on the setting time. Although high molarity increased the capacity, this had a noticeable negative effect on the setting time and workability. This study demonstrated that WGP had a slight negative effect on the capacity and workability. Furthermore, when the combined effects of WGP and NaOH molarity were taken into account, the use of 10% WGP with M13 NaOH was recommended to obtain the optimum sustainable GPC considering both fresh and hardening properties. Scanning electron microscopy (SEM) analysis was done on the samples, too.

Mechanical Strength and Microstructure of GGBS-SCBA based Geopolymer Concrete

This paper deals with the attempt to develop and study the performance of ground granulated blast furnace slag (GGBS) and sugarcane bagasse ash (SCBA) based sustainable geopolymer concrete. NaOH (8M, 10M, and 12M) and Na2SiO3 were used as alkaline activators with a ratio of 2.5. SCBA mainly acted as amorphous silica and has been utilized as a substitute material for GGBS. The effect of SCBA contents (0%, 5%, 10%, 15% & 20% by the mass of binder) in terms of fresh, hardened, microstructural, and correlation properties of geopolymer concrete developed have been evaluated. Different tests such as the slump cone test, compression test, split tensile test, flexure test, and ultrasonic pulse velocity test were conducted. Scanning electron microscopy, Energy dispersive analysis, and X-ray diffraction analysis were investigated for understanding the microstructural properties. The research findings have shown that with an increase in molarity from 8M to 12M there is an increase in the strength properties of geopolymer concrete. The results in this current study show that 28 days compressive strength was found to increase by 4–15% when the NaOH molarity was increased from 8M to 10M and 8–21% when the NaOH molarity was increased from 8M to 12M. The geopolymer concrete developed with 20% SCBA and 80% GGBS with 8M NaOH solution and SS/SH ratio of 2.5 can be used for a target strength of 30–35 MPa. Scanning electron microscope images show a packed and dense matrix, which clearly outlines the reason behind the attainment of higher strength in higher molarity of GGBS-SCBA based geopolymer concrete samples and the presence of CASH gel confirmed this in the geopolymer matrix. Furthermore, there is a strong correlation between the experimental findings and the model equations proposed. These presented models will be useful in improving the strength of geopolymer concrete incorporating agricultural and industrial wastes.

Development of a novel rapid repairing agent for concrete based on GFRP waste powder/GGBS geopolymer mortars

The use of waste glass fiber-reinforced polymer (GFRP) powder as a binding agent in the synthesis of geopolymers offers an eco-friendly solution for managing GFRP waste. The aluminosilicate present in GFRP powder can be activated by an alkaline solution to produce a sustainable geopolymer. In this study, a novel rapid repairing material was developed from partially-replaced ground granulated blast furnace slag (GGBS) by GFRP waste powder as precursors in geopolymer mortar (GM). The effect of GFRP powder replacement and mix proportions on the fresh and hardened properties of GMs were evaluated. It was found that an increase in GFRP powder replacement led to an increase in the setting time and a decrease in workability. The highest 28-day compressive strength was obtained at a 20% replacement of GGBS with GFRP powder. At this optimal mixture, the GMs achieved a compressive strength of 15.2 MPa after 6 h and 35.7 MPa after 1 day. Results from the slant shear test revealed that the failure pattern of the GM-repaired concrete samples changed from interface failure to monolithic failure and explosive spalling in the concrete substrate (CS), when the test duration increased from 3-days to 7-days and 28-days, respectively. This was attributed to the formation of a compact interfacial zone with prolonged testing duration, leading to increased bond strength. The developed GMs demonstrate a short setting time, excellent flowability, high early mechanical strength and superior bond properties, and thus can be applied as rapid concrete repair materials or as protective coatings for concrete in corrosive environments.

Sustainability of pre-treated and nano-fly ash powder on the thermal stability and environmental impact of green mortars under ambient conditions

Safety during fire exposure conditions paid a lot of attention in today's modern construction activities which demands the exploration of thermally stable and eco-friendly building materials. During the elevated temperature conditions, the building with Portland cement construction experienced large rate of decomposition and heavy spalling. To achieve the thermal stability and sustainability in the building construction, an alternative zero cement geopolymer system was developed by using pre-treated and cost-effective nano-fly ash powder. The thermal stability of the developed nano-fly ash impregnated geopolymer mortar was assessed under various temperatures in terms of weight loss, visual observation and the post fire residual strength. Also, the results were validated by means of conducting Thermo Gravimetry Analysis, Fourier Infrared Spectroscopy and Scanning Electron microscopic analysis. From the results, it was observed that the geopolymer mortars with 1% nano-fly ash impregnation exhibited the highest compressive strength at all the temperature conditions. Also, the nano-fly ash added geopolymer mortars retained with 67% of its original strength even after the maximum temperature exposure of 900 °C. The use of pre-treated and nano-fly ash completely eliminates the need of superplasticizer and oven curing due to the improved reactivity. Also, the developed green mortar resulted in 46% reduced green house gas emission and 18.3% reduced cost of construction which paves the way to the development of cost-effective and sustainable geopolymer construction under fire explosive environments.

Mechanical characteristics and solidification mechanism of slag/fly ash-based geopolymer and cement solidified organic clay: A comparative study

Geopolymers have recently received intensive research interests in the solidification of various soft soils due to their low-carbon footprint and environmentally friendly. However, understanding of the solidification characteristics of geopolymers in organic clay is still limited. In this study, a range of unconfined axial compression, pH value, moisture content, phase analysis, micromorphology, element composition and pore structure tests was conducted to comparatively investigate the physical properties and micromechanism of slag/fly ash-based geopolymer solidified organic clay (GSO) and cement solidified organic clay (CSO). Furthermore, the reinforcement effect of different parameters (geopolymer content and alkali-activator content) on the mechanical characteristics of GSO in the presence of humic acid was also investigated. The results show that the moisture content of CSO and GSO gradually increases with the content of humic acid, but the pH value and strength gradually decrease. Sustainable geopolymer is proven to be superior to cement in improving the physical-mechanical properties of organic clay. The unconfined compressive strength (UCS) of 28-day cured GSO2 containing 6% humic acid can reach 1.31 MPa, about 1.96 times of CSO1 containing 3% humic acid. The UCS of GSO can be significantly increased by the reasonable content of geopolymer and alkali-activator. Specifically, the 28-day UCS of GSO6 containing 20% geopolymer is 1.92 times and 2.68 times that of GSO2 (15%) and GSO5 (10%), respectively. The analysis of microscopic characteristics confirms that the strength formation of CSO and GSO is mainly affected by the number of cementitious products and the cementation degree of clay particles, which is attributed to the compactness of the matrix structure. The research results provide insights for a more comprehensive understanding of the application potential of geopolymers in organic clay solidification.

Development of sustainable geopolymer composites for repair application: Workability and setting time evaluation

One of the most used construction materials worldwide is concrete. It has a lot of advantages over the other construction materials. However, the production process of concrete produces a huge amount of carbon dioxide. Geopolymer composites are gained attention as eco-friendly alternative to traditional cement. In this research an attempt has been done to optimize a sustainable geopolymer mortar made of ground-granulated blast furnace slag (GGBS) and fly ash (FA). The optimized geopolymer mortar is designed to be convenient and practical for repairing damaged reinforced concrete members. Accordingly, this research is focused on improving setting time and workability of an ambient cured geopolymer mortar. In this research an attempt has been done to study the impact of using different superplasticizer dosages, different GGBS percentages, and different alkaline activator solution ratios on the setting time and flowability of an ambient cured geopolymer mortar. The obtained findings of this study showed that, alkaline activator ratio is one of the most significant parameters that affect workability and setting time of the geopolymer mortar. In this study, fifteen different mixes were tested and evaluated. Modified Vicat apparatus and Flow Table test were used to evaluate setting time and workability for the mortars. The outcome of the optimization showed that, the most convenient and practical mix which provided the highest setting time and reasonable flowability contained of 25% GGBS, 75% FA and 5% superplasticizer. The obtained workability for the optimum mix was about 156.25 mm and the achieved setting time was about 30 min.

Study on Mechanical and Durability Characteristics of Sustainable Geopolymer Concrete

Abstract: The concentration of greenhouse gases in the atmosphere has increased quickly as a result of anthropogenic activities that cause global warming. To solve this issue, Portland cement-free geopolymer concrete is created by using ground granulated blast furnace slag (GGBS) as the primary binder and micronized biomass silica (MBS) in varying proportions in composition of GGBS. The outcomes of this experimental investigation demonstrate the mechanical properties and robustness of geopolymer concrete. In the creation of MBS, rice husk is utilized. Besides from compression, flexural, split tensile strength, and elastic modulus testing, further measurements of water absorption, water sorptivity and rapid chloride permeability test were also carried out. It is found that a geopolymer concrete mix with 10% MBS and 90% GGBS as a binder had the best strength and durability. Also, the compressive strengths of each geopolymer concrete mixture exceeded the required design strength. This experimental investigation shows the possibility of employing MBS as a binder raw material in the production of geopolymer concrete.

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.

Recycled waste glass as precursor for synthesis of slag-based geopolymer

The current study assesses the effectiveness of recycled waste glass as a precursor in the synthesis of slag-based geopolymer. Fractional substitution of slag was made with powdered waste glass (WG) with 10%, 20%, 30% and 40%-part replacement. The early age, hardened and microstructural properties of slag-waste glass-based binary geopolymer synthesized with 6 M sodium hydroxide solution were assessed. The hardened and microstructural properties were examined on the 28 days cured specimens subjected to 24 h initial heat curing at 60 °C. The presence of alkali cations in the WG speeds up the setting time of the binary geopolymer as slag is partly replaced with WG. The mix proportion with 10% WG achieved a peak 28-day compressive strength of 42.7 MPa. Further, it also attains a low pore volume in the hardened matrix, confirming sorptivity index values and microstructural images. However, the incorporation of higher WG contents causes a significant decrease in mechanical strength with high pore volumes. The energy dispersive spectroscopic analysis showed an enhancement in Si/Al ratio with the incorporation of WG. In addition, the development of calcium silicate hydrates and sodium aluminosilicate hydrates in slag-WG geopolymer was identified from mineralogical studies. These results confirm that WG has a substantial influence on the gel formation mechanism in the matrix and alters the mechanical behaviour. The outcomes of the present study encourage the incorporation of WG as a fractional substitute of slag in the manufacturing process of sustainable geopolymer binders.

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.