Sustainable Geopolymer Research Articles

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.

Impact Resistance Enhancement of Sustainable Geopolymer Composites Using High Volume Tile Ceramic Wastes

The need for sustainable concrete with low carbon dioxide emissions and exceptional performance has recently increased in the building industry. Many distinct types of industrial byproducts and ecologically safe wastes have shown promise as ingredients for this kind of concrete. Meanwhile, as industrialization and lifestyle modernization continue to rise, ceramic waste becomes an increasingly serious threat to the natural environment. It is well known that free cement binder that incorporates tile ceramic wastes (TCWs) can significantly improve the material’s sustainability. We used this information to create a variety of geopolymer mortars by mixing TCWs with varied proportions of ground blast furnace slag (GBFS) and fly ash (FA). Analytical techniques were used to evaluate the mechanical properties and impact resistance (IR) of each designed mixture. TCWs were substituted for binders at percentages between 50 and 70 percent, and the resultant mixes were strong enough for real-world usage. Evidence suggests that the IR and ductility of the proposed mortars might be greatly improved by the addition of TCWs to a geopolymer matrix. It was found that there is a trend for both initial and failure impact energy to increase with increasing TCWs and FA content in the matrix. The results show that the raising of TCWs from 0% to 50, 60 and 70% significantly led to an increase in the failure impact energy from 397.3 J to 456.8, 496.6 and 595.9 J, respectively.

Optimization and utilization of waste fly ash and silica fume based eco-friendly geopolymer mortar using response surface methodology

Cement is the primary ingredient in concrete, which is one of the crucial building materials. The evolution of greenhouse gases, particularly carbon dioxide, which is produced during the hydration stage, has increased because of excessive use of concrete. Geopolymer, an alumina-silicate based bonding substance is made up of waste materials such as Fly ash (FA) or Silica Fume (SF) in the presence of alkaline solutions has been developed to reduce the effect of carbon emissions on the environment. This paper studied the optimization and utilization of FA and SF replacement as pozzolanic materials for the development of sustainable geopolymer mortar and to achieve optimal mechanical strength using response surface methodology (RSM). According to the study, with the addition of 90% FA and 10% SF content to the geopolymer design mix significantly improves their mechanical properties. When SF and sodium hydroxide are combined to create geopolymer mortar, they work as an alkaline catalyst, dramatically reducing carbon emission of the waste materials and providing it an edge over cement-based mortar. The construction of self-sustaining infrastructures ensuring human safety and eco-friendly practices will be encouraged by the multi-objective approach of RSM.

Mechanical and physical properties of synthetic sustainable geopolymer binders manufactured using rockwool, granulated slag, and silica fume

The substantial target of this work is to manufacture sustainable geopolymers by recycling low cost industrial wastes (granulated slag, GS; rockwool, RW; and silica fume, SF). To reveal the mineral and chemical compositions of these industrial solid wastes, they were investigated using X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). The granulated slag, rockwool and silica fume were blended with the convenient quantity of alkaline reactor to formulate a hydrated pattern of geopolymers. The phase configuration, physico-mechanical effects [compressive strength (CS), porosity and bulk density] and the microstructural form of the geopolymers were studied via the X-ray diffraction, hydraulic mechanical testing device, helium pycnometer, and Field emission Scanning electron microscope (FE-SEM), respectively. The results declared that the partial substitution of RW by various ratios of SF in presence of GS affect successfully on the physico-mechanical properties of hardened geopolymers. Implication of 2 % SF boosts the physico-mechanical features of the 50GS-48RW hardened geopolymers at all curing ages especially at the age of 28 days. Therefore, the geopolymer 50GS-48RW-2SF displayed the best physico-mechanical characteristics especially the CS at 28-days (39.12 MPa) owing to the formation of diverse hydration products like CSHS, CAHS and NASHs. These results were confirmed via FE-SEM/EDX images that exhibited compact and dense microstructure rod-like crystals of CSHs and three dimensional framework structures of NASHs.

Effective Utilization of Copper Slag for the Production of Geopolymer Concrete with Different NaOH Molarity under Ambient Curing Conditions

In spite of the considerable research on the mechanical and durability properties of geopolymer concrete, its widespread applicability is hindered due to the difficulties involved in achieving ambient curing conditions and awareness of the effective utilization of industrial by-products. This study investigates the physical and microstructure characterization of sustainable geopolymer concrete (GPC) developed with copper slag as a replacement for fine aggregate. In total, forty-four geopolymer concrete mixtures were prepared to examine their fresh and hardened properties. Four different NaOH molarities (10, 12, 14 and 16) and the replacement levels of copper slag, ranging from 0 to 100% with an increase of 10%, were considered as variables in this research. The study parameters examined includes the fresh (slump) and hardened concrete properties. Additionally, the microstructural characterization for different mixes were studied using the Fourier Transform Infrared Spectroscopy (FTIR), Electron Dispersive Spectrum (EDS) analyses and Scanning Electron Microscope (SEM). Results indicated that replacing fine aggregate with copper slag up to 100% showed no strength reduction. Increasing the molarity of the NaOH solution to 16M led to an increased strength of about 35% compared to the concrete with 10 M in all the mixes. The microstructural analysis performed using SEM/EDS and FTIR showed that a cohesive and fully compact geopolymer matrix was achieved together with the use of low-calcium fly ash and copper slag under ambient curing conditions.

Role of industrial by-products and metakaolin in the development of sustainable geopolymer blends: Upscaling from laboratory-scale to pilot-scale

In this experimental work, the geopolymer blends were synthesized from metakaolin, fly ash, and sugarcane bagasse ash based on their low cost and easy availability to improve the strength and durability of the newly developed product. In this research, a multilevel investigation has been carried out in two phases i.e., initially at the laboratory-scale which was then upscaled to pilot-scale. In the laboratory-scale study, the precursors namely, metakaolin, fly ash, and sugarcane bagasse ash were used in the multilevel materials investigation i.e., these materials were tested at mono level, binary level, and ternary level. Cylindrical specimens with 500 mm diameter and 100 mm height in size were cast by applying a constant pressure of 10-MPa. The samples were prepared with 10 M solution of NaOH and a Na 2 SiO 3 /NaOH ratio of 1.5 and were cured under normal room temperature. Upscaling of the optimized mixes, as revealed from the laboratory-scale investigation, was carried out at the pilot-scale by simulating the laboratory conditions for casting the full-sized brick specimens. The mechanical properties and durability aspects of the upscaled-brick specimens were investigated and compared with the standard codes of practice for conventional burnt clay bricks, leading to satisfactory results overall. The strength and durability of the developed product were enhanced due to the formation of the sodium- and calcium-based aluminosilicate hydrates i.e., N-A-S-H and C-A-S-H, which were validated through FTIR and SEM analysis. Interestingly, multilevel investigation of the blends helped in identification of the geopolymerization potential of these materials at different levels (mono, binary, and ternary level in this study). • Utilization of calcined clay and ashes to develop a geopolymer blends. • Quantification of their reactivity through dissolution process of Metakaolin, Fly Ash and Sugarcane Bagasse Ash in alkali environment. • Multilevel testing (mono-level, binary-level and ternary-level composites) for identification of individual material role. • Synthesis of eco-friendly geopolymer bricks by using metakaolin, fly ash and bagasse ash from optimized laboratory findings. • Comparison of mechanical and durability properties of developed geopolymer bricks with the standards. • Characterization of selected geopolymer blends through FTIR and SEM.

Synergetic effect of ethylene glycol for production of hybrid sustainable geopolymer concrete

Synergetic effect of ethylene glycol for production of hybrid sustainable geopolymer concrete

The effect of various fibers on the red mud additive sustainable geopolymer composites

In this paper, an experimental research was conducted to investigate some mechanical and microstructural properties of geopolymers composites based on red mud-metakaolin reinforced with four different fiber types and filled with brick dust-recycle aggregate filling material. Polypropylene, glass, polyvinyl alcohol and basalt fibers were used. The effect of fiber reinforcements on the strength properties and abrasion resistance of geopolymer composites was investigated, and microstructural analysis was performed to reveal the geopolymeric matrix composition, structure and bonding of the fibers. The results revealed that fiber reinforcement to metakaolin red mud-based geopolymers with brick waste powder and recycling aggregate improved the strength properties. For example, the presence of glass and polyvinyl alcohol fibers increased the flexural strength of geopolymer composites by 39% and 61%, respectively, compared to the control sample. Microstructural analysis revealed that the fibers gave an acceptable interfacial bond with the geopolymeric binder. The findings of the current article show a potential solution to becoming a sustainable geopolymer by presenting the successful use of red mud, recycling aggregate, and brick dust waste with different fibers as important asset materials.

Effective utilization of agricultural waste in synthesizing activator for sustainable geopolymer technology

The creation of one-part geopolymer mixtures is necessary to increase the economic feasibility of geopolymers in practice. The utilization of extremely corrosive alkali solutions that are often used as activators in the development of standard geopolymers hinders the sustainability nature of geopolymers. Hence, to overcome the sustainability issues related to sodium silicate, a novel method of developing sodium silicate from rice husk ash (RHA) and using it as an activator in the development of one-part geopolymer binders has been proposed in this research. This novel sodium silicate has been produced in a thermo-mechano-chemical technique by agglomerating RHA with sodium hydroxide. The developed binders were characterized by mineral composition and phase, morphology, and strength parameters. The compressive strength results were in the range of 58.08 MPa to 88.23 MPa and varies with respect to the modulus of silica of the derived powdered activator. The enhanced polycondensation process and better gel structure, as seen by microstructural tests, are what account for the increase in mechanical strength. By this, it can be concluded that the activator powder derived in this research can be used to produce a geopolymer binder that can be handled similarly to Portland cement with less potential for global warming.

Investigation of using waste marble powder, brick powder, ceramic powder, glass powder, and rice husk ash as eco-friendly aggregate in sustainable red mud-metakaolin based geopolymer composites

Geopolymers are an important composite material alternative to cement with high CO2 emission, which allows the use of waste materials in its structure. However, which waste material contributes to the geopolymer composite structure to what extent is still an ongoing research area. This study has been prepared to contribute to closing the gap in this field. In this study, industrial waste materials (waste marble powder (MP), waste brick powder (BP), ceramic waste powder (CW), waste glass powder (GP), and rice husk ash (RHA)) were used 25%, 50%, and %75 percentage as aggregate instead of recycled concrete (RC) on red mud-metakaolin based geopolymer mortars. Mechanical properties (ultrasonic pulse velocity (UPV), splitting tensile, compressive, and flexural strengths), physical properties (void ratio, water absorption, unit weight, and workability properties), abrasion test, and microstructure analyzes (SEM-EDS and XRD) were performed. The highest compressive strength results were in seen the 25% brick powder substitution, with an increase of 74.01% compared to the control sample. Also, the compressive strength results increased in the case of increasing the use of ceramic waste. High silica and alumina contents in both materials were effective in these cases. In terms of the abrasion test, the highest performance was seen as a 49.2% decrease in the mass loss in 75% marble powder replacement. As a result, substitute materials have shown a successful performance, creating significant potential in the production of a sustainable geopolymer.

Effect of waste concrete powder on slag-based sustainable geopolymer composite mortars

In this study, the effect of waste concrete powder (WCP) on slag-based geopolymer composite mortars was investigated. Blast furnace slag (BFS) and WCP were used as binders in geopolymer mortars. WCP was substituted into the geopolymer mortar composites at rates of 10%, 20%, 30%, and 40% by weight of slag. Sodium hydroxide (NaOH) solution was used as the alkali activator in the mixtures and the solution activator concentration was chosen as 16 molars (M). After the prepared mortars were cured at 100°C for 24 hours, they were subjected to flexural strength (ffs), compressive strength (fcs), and ultrasonic pulse velocity (UPV) tests. When the obtained results were examined, it was observed that ffs, fcs, and UPV results decreased with the increase in WCP replacement ratio. These decrements were seen clearly, especially after the 20% replacement ratio. However, despite these decrements, the compressive strengths of all groups were found to be above 50 MPa. In addition, it is thought that environmental pollution can be reduced by using WCP in geopolymer composite mortars.

Enhancing the Durability Properties of Sustainable Geopolymer Concrete Using Recycled Coarse Aggregate and Ultrafine Slag at Ambient Curing

This study aimed at investigating the durability characteristics of the ambient-cured geopolymer concrete (GPC) developed using recycled coarse aggregate (RCA) and ultrafine slag (UFS). Two series of mixes were prepared. Natural aggregates (NAs) were replaced by RCA at different volume levels of 0, 25, 50 and 100% in both series. Meanwhile, UFS was added as a replacement by volume of fly ash at varying levels of 0, 15, and 30% in the first series, while UFS was used in addition to fly ash by percentage weight of fly ash at the levels of 0, 15, and 30% in the second series. The compressive strength, water absorption, chloride ion penetration, and carbonation depth of the developed ambient-cured GPC were studied. In addition, creep and drying shrinkage of the specimens were also examined. It was found that the compressive strength increased with the UFS content, while the opposite trend was observed with increasing RCA%. The highest compressive strength obtained with 100% RCA was 40.21 MPa (at 90 days), when 30% UFS was used in addition to fly ash. The addition of UFS not only helped in improving the strength characteristics but also provided an alternative to heat curing, which is a major drawback of GPC. Furthermore, the negative effects of RCA can also be minimised by adding UFS, which can be used as a compensator to RCA to improve the durability characteristics. The experimental results prove that susceptibility to chemical, water and chloride attacks can be mitigated by incorporation of UFS, and durable GPC can be produced by using RCA and UFS.

Durability properties of copper slag and coal bottom ash based I-shaped geopolymer paver blocks

Geopolymer mortar was prepared with aluminate and silicate-bearing minerals with caustic activators like fly ash (FA), and copper slag (CS). The impression focused on the entire replacement of extensive and energy-intensive Portland cement and traditional natural fine aggregates with coal bottom ash and CS in manufacturing of sustainable geopolymer paving blocks suitable for both rural and urban infrastructure. The designed paver blocks were tested for various durability tests such as water absorption, chemical resistance, abrasion resistance, efflorescence and initial rate of absorption. In overall, the findings indicate the recommendation of geopolymer paving blocks containing 70% of CS and 30% of CBA with different concentrations of alkali activators. Also, the aforesaid geopolymer paver blocks, were found to be efficient compared to conventional (FA and PC) based paver blocks as the same were resulted in reduced water absorption (up to 15%). Similarly GPC mixes, resulted in better resistance (as the same were yielded up to 15% and 70%) against abrasion and chemical attack compared to conventional paver blocks respectively. Based on experimental findings, irrespective of the cost, the designed GPC mixes demonstrated excellent resistance towards aforementioned durability aspects compared to the conventional mix based paver blocks.

Geotechnical characterization of sustainable geopolymer improved soil

Abstract Geopolymer (GP) has recently emerged as a novel and environmental friendly alternative to conventional soil stabilization products like lime and Ordinary Portland Cement (OPC), which adversely affect the environment. This article emphasizes GPs produced from high calcium class C fly ash (CFA) and an alkali activator comprising sodium hydroxide and sodium silicate solution for sand stabilization. The experimental program includes a series of unconfined compressive strength (UCS), flexural strength, tensile strength, and microstructural analyses using scanning electron microscopy. Results revealed that UCS, flexural strength, and tensile strength of GP-treated soil were in the range of 2–10, 0.5–2.0, and 0.4–1.2 MPa, respectively (depending on the ratio of fly ash and activator). These strengths were even higher than those of cement-stabilized soil. The microstructural analysis revealed that the formation of dense calcium–sodium alumina–silicate hydrated gel (C, N–A–S–H) is the reason for strength improvement. According to the findings of this study, using a CFA-GP binder for soil improvement is a viable alternative to OPC in geotechnical applications.

Reusing recycled powder as eco-friendly binder for sustainable GGBS-based geopolymer considering the effects of recycled powder type and replacement rate

Utilizing recycled powder (RP) as binder for geopolymer reduces the construction waste and contributes to the development of sustainable geopolymer materials, but the effects of RP type and replacing rate on the characterization of sustainable geopolymer with RP received less consideration in previous investigations. Therefore, this investigation showed the upcycling of various RPs as an eco-friendly binder for sustainable GGBS-based geopolymer, and the micro-characteristics, mechanical strength and transport performance of geopolymer containing RP up to 100% were measured. The results indicated that RP from various construction waste mainly consisted of hydrated products, un-hydrated cement particle, quartz and calcite. Incorporating high-volume RP enlarged the pore structure of GGBS-based geopolymer, and substituting RP for 100% GGBS resulted in relatively loose micro-structure of sustainable geopolymer. Incorporating RP decreased the autogenous shrinkage of GGBS-based geopolymer, but the mix of high-volume RP increased the drying shrinkage of GGBS-based geopolymer. The mechanical strength and resistance to water ingress of GGBS-based geopolymer decreased as the RP replacing rate was increased, and substituting RP for 100% GGBS led to a significant reduction of mechanical strength and water absorption resistance. However, the mechanical strength of geopolymer with 100% RP from hardened cement paste waste was much better relative to geopolymer with 100% RP from mortar waste or concrete waste, because hydrated cement particle in RP has relatively high polymerization activity. Optimizing RP type and replacing rate can prepare sustainable geopolymer with good performance, and the upcycling of 100% RP for fully recycled geopolymer is feasible and sustainable.

Sustainable Pond-Fly Ash Geopolymer Mortar Technology that Eliminates CO2 Emission and Replaces Natural Sand

Sustainable Pond-Fly Ash Geopolymer Mortar Technology that Eliminates CO2 Emission and Replaces Natural Sand

Synthesis of industrial solid wastes based geopolymer foams for building energy conservation: Effects of metallic aluminium and reclaimed materials

Thermal insulation materials with less energy consumption and low CO2 emissions have been paid great attention. This study was devoted to assessing the feasibility of utilizing industrial solid wastes for the preparation of sustainable geopolymer foams to make up for the weak link of using industrial solid waste in green low-carbon building energy-saving materials research. Efforts were made to investigate the effects of aluminium powder content and substitution ratio of reclaimed materials on slurry performance, physic-mechanical properties and formation of gel species by a series of characterization methods. Results revealed that the geopolymer foams characterized by compressive strength of 2.83 MPa, bulk density of 507 kg/m3 and thermal conductivity of 0.167 W/(m·K) were successfully produced by external incorporation of 0.17 % dosage of Al powder. 10 % substitution ratio of reclaimed materials presented no obvious negative effect on fluidity, initial setting time, bulk density, compressive strength, thermal conductivity, pore structure and microstructure of the specimens. The pore structure, morphology and polymeric gels of pore partition matrix co-determined the macroscopic properties of geopolymer foams. The existence of semi-crystalline zeolite precursors in reclaimed materials may induce the formation of zeolite-like grains on the inner surface of pores. The present work was in agreement with the strategic objective of resources recycling, solid waste utilization, lower carbon emission and building energy saving, which was conducive to the development of the circular and green economy.

Physical and mechanical properties of metakaolin-based geopolymer mortars containing various waste powders

In this paper, it was aimed to evaluate the effectiveness of four different types of filler materials with particle sizes below 63 μm in sustainable geopolymer mortars. For this purpose, 25%, 50%, and 75% limestone powder (LSP), basalt powder (BP), waste marble powder (WMP), and recycled aggregate powder (RAP) were substituted with river sand and 13 different mixtures including reference were obtained. Metakaolin was used as the main binder material, and sodium hydroxide/sodium silicate was used in a ratio of 1:2 as an activator. In addition, blast furnace slag was added to the mixture as a reaction accelerator at a rate of 13% of the amount of metakaolin. To determine the mechanical properties of the produced geopolymer mortars, compressive strength, flexural strength, splitting strength, porosity, ultrasonic pulse velocity (UPV), and abrasion tests were performed. Also, SEM and XRD analyses were performed to examine the microstructures of the specimens. The satisfactory results obtained proved that all four types of filler materials can be used in metakaolin-based geopolymer mortars. Optimum rates for limestone powder, basalt powder, waste marble powder, and recycled aggregate powder were obtained as 50%, 50%, 25%, and 25%, respectively.

Strength, Durability, and Microstructures characterization of sustainable geopolymer improved clayey soil

Geopolymer has been emerged as an innovative and eco-friendly alternative to traditional soil improvement products such as Ordinary Portland Cement (OPC) and lime, which have negative environmental consequences. Geopolymer has been employed in various geotechnical applications as alternative lightweight backfill in highway barriers and/or behind retaining walls, providing technical, environmental, and economic benefits. The present study aims to evaluate the mechanical, durability, and Microstructure properties of clayey soil (with different percentages of sand) stabilized using coal-fired fly and a sodium hydroxide/sodium silicate solution alkali activator. Stabilized soils exhibited high strength of 1–8 MPa compared with less than 0.3 MPa for untreated soils. Moreover, adding sand to clay soil reduced the optimum ratio of alkaline activator from 0.8 for clayey soil with 5% sand to 0.6 for clayey soil with 10, 20, 30% sand. The geopolymer treated samples also showed high resistance to the acidic environments and chlorides. Finally, SEM results revealed a clay fabric modification caused by inter-particle contacts and the resulting bonding caused by gel formation and hardening. According to the outcomes of this study, it can be concluded that using a fly ash geopolymer binder for soil stabilization is a viable alternative to cement in geotechnical applications.