Fly Ash Based Geopolymer Mortar Research Articles

Efflorescence of fly ash-based geopolymer mortars under quasinatural conditions: the relationship between curing temperature, ion transport, and compressive strength

This investigation reports the effect of curing temperatures ranging from 20 °C to 80 °C on the efflorescence of fly ash-based geopolymer mortars under quasinatural conditions. The microstructures of the geopolymers before and after efflorescence were characterized by SEM and MIP, respectively. These characterizations are adopted to further explain the change in compressive strength. The micromorphology and phase assemblage of the efflorescence products were identified by SEMEDS and XRD, respectively, indicating that the significant ions involved in the efflorescence include Ca2+, Na+, and CO32-; then, the concentrations of those ions in the leachate were detected by ICP, AAS, and acidbase neutralization titration, respectively. The results show that low curing temperatures (≤ 50 °C) promote the diffusion of ions into the leachate, while high curing temperatures (> 50 °C) contribute to the transportation of ions towards the drying part for the formation of hollow structured Na2CO3·7H2O. Although the increase in the compressive strength of the geopolymers resulting from efflorescence decreased with increasing curing temperature, the 50 °C-cured geopolymer exhibited the highest compressive strength during efflorescence. This study provides a reference for mitigating efflorescence and improving practicability in the hydraulic engineering of geopolymers.

Properties of Basalt Fiber-reinforced Lightweight Geopolymer Mortars Produced with Expanded Glass Aggregate

Geopolymers are new-generation construction materials that have attracted attention recently and can be an alternative to cement. In the production of these materials, aluminosilicate powder materials are used together with alkali or acid solutions. Geopolymers have different types of superiorities, such as rapid strength gain, high mechanical properties and good durability. This experimental study investigated the properties of expanded glass aggregate-bearing Class F fly ash-based lightweight geopolymer mortars. The fresh unit weight, water absorption capacity, compressive strength and high-temperature resistance (upon exposure to 900°C) of the mortars were determined. In addition, basalt fiber addition's effects on these properties were investigated. The inclusion ratios of basalt fiber were 0.1%, 0.2% and 0.4% by volume. The compressive strengths of fiber-free lightweight mixture and mixtures, including 0.1%, 0.2% and 0.4% basalt fiber, were found to be 8.2, 8.9, 9.0 and 8.0 MPa, respectively. The compressive strength of all lightweight mortars increased between 61.3% and 76.4% after the high-temperature effect. The results proved that it is possible to produce expanded glass aggregate-bearing lightweight geopolymer mortars with acceptable mechanical properties.

Bacteria-based crack healing of 3D printed PVA fiber reinforced geopolymer mortars

Geopolymers have been regarded as a promising environmentally friendly alternative to cementitious materials in 3D printing. In this study, 3D-printed fly ash based geopolymer mortars containing silica fume were produced with PVA fiber at 0%, 0.5%, 1%, and 1.5% ratios. Cracks were created in the specimens using flexural strength test after 28 days. Then, bacterial self-healing process was applied to the half of cracked samples and the remaining cracked samples were used as control samples. Sporosarcina pasteurii was used for healing. Lastly, the visual inspection, flexural strength, compressive strength, and water absorption analyzes were conducted mechanical properties to evaluate the healing performance of 3D-geopolymer samples containing PVA. In addition, the samples were subjected to microstructural examination using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) to determine the changes in the microstructural of bacterial based healing. As a result, CaCO3 precipitates, which are the bacterial healing output, filled the cracks and boosted the mechanical characteristics of 3D-geopolymer. The application in 3D-printed PVA fiber reinforced geopolymer mortars of bacterial healing resulted in a significant 36.23% improvement in flexural strength and an 11.57% reduction in the capillary water absorption coefficient compared to the non-healed samples.

Effect of Different Ceramic Waste Powder on Characteristics of Fly Ash-Based Geopolymer

The escalating demand for construction materials driven by rapid population growth has heightened the reliance on cement binders, resulting in increased CO2 emissions from the cement industry. Geopolymers, considered environmentally friendly alternatives, have been explored in various studies to address this challenge. This research specifically investigates the impact of different types of ceramic waste bricks (BT), floor tiles (FT), roof tiles (RT), and sanitary ceramics (ST) on the physical and mechanical properties of fly ash-based geopolymer mortar. To provide a comprehensive understanding, this research examines the compressive strength, mineral phase, chemical bonds, and microscopic evolution of fly ash geopolymer mortar incorporating varying proportions of each ceramic waste type (25% and 50% fly ash replacement). A consistent mixture of Na2SiO3and NaOH was used for the alkaline solution in all formulations. The curing process was carried out at room temperature for 7, 14, and 28 days prior to the compressive strength test. The result revealed that the inclusion of 25% BT experienced higher strength compared to the control sample after 14 days, but the strength became comparable after 28 days at 40.24 MPa. A reduction in strength was evident with the addition of other ceramic components. Moreover, higher incorporation of CWP correlated with a faster setting time for fresh geopolymers. This was also linked to the degree of gel formation, as indicated in the microstructure images. The emergence of plagioclase minerals was evident in all formulations of the geopolymer products under XRD analysis, while the bond of the geopolymer signature, Si-O-T (T = Si or Al), was identified from the infrared spectra. The microstructure of the binder showed a geopolymer matrix alongside unreacted fly ash particles. Overall, CWP replacement up to 25% can be potential in fly ash geopolymer without sacrificing significant strength loss and remaining in the range of normal strength mortar. Doi: 10.28991/CEJ-2024-010-02-06 Full Text: PDF

Effect of initial curing conditions on the durability performance of low-calcium fly ash-based geopolymer mortars

Geopolymer composite production has become an indispensable product to reduce carbon dioxide emissions, which have become an important problem today, and to provide green sustainability. Concerns about the global climate change problem have also accelerated geopolymer studies. This research investigated the mechanical and durability characteristics of low-calcium fly ash (LCFA) based geopolymer mortars with different curing temperatures and times. Two forms of curing conditions were applied; the first one was standard curing at room temperature (20±3°C and RH 65±10%) and the second one was cured in the hot air at 40°C, 60°C, and 80°C for 24h, 48h, and 72h followed by standard curing. After all curing processes, compressive strength, flexural strength, water absorption, void ratio, resistance to elevated temperatures, and freeze–thaw conditions were determined experimentally. In addition, SEM analysis was performed before and after durability tests for comparison purposes. Also, XRD and TGA analyzes were performed. According to test results, curing specimens at longer times and higher temperatures has been shown to increase compressive strength results. The highest compressive strength value was reached at 80°C after 72h of curing. Geopolymer specimens subjected to elevated temperatures (600°C and 900°C) lost a significant part of their strength value. After the freeze–thaw test, LCFA-based geopolymer specimens showed more than 70% resistance. The freeze–thaw resistance of geopolymer samples was positively affected on long-term curing at high temperatures, but high-temperature resistance was impacted negatively.

The influence of microwave curing on the strength of silica fume-added fly ash-based geopolymer mortars

Geopolymer concretes a substitute for traditional Portland cement as a more environmentally sustainable alternative. In addition, one of the most significant advantages of geopolymer concrete is the high setting speed that can be achieved with thermal curing, that is, the short curing period. Research on geopolymer concrete has focused on curing, where curing is usually done with conventional ovens. Microwave curing initiates heat generation at the molecular level, which results in a minimal heat increase on the surface of the specimens compared to traditional thermal curing methods. In addition, it provides internal, rapid, and homogeneous heating and rapid strength development. This study is based on research that examined the effect of microwave cure on the compressive strength of silica füme-modified geopolymer mortar. In the study, sodium silicate and sodium hydroxide were used for activation, and first of all, fly ash substituted geopolymer mortar specimens were subjected to conventional thermal curing in an oven. On the other hand, the mortar specimens with the same composition were subjected to short-duration (10 minutes) microwave curing at power levels of between 200-600 W. When the results were compared regarding compressive strength, void and percent water absorption, UPV, and SEM-internal structure examination, it was revealed that microwave curing could be used faster than the conventional oven curing method in silica füme-added fly ash-based geopolymer mortars. This research can be considered an essential step for further optimizing and popularising geopolymer concrete and microwave curing and proposes a method that should be considered in the future development of more sustainable construction materials.

Impact of Low-Reactivity Calcined Clay on the Performance of Fly Ash-Based Geopolymer Mortar

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications.

Use Recycled Glass As Fine Aggregate in Slag-Blended Fly Ash-Based Geopolymer Mortar

Geopolymer has emerged as the potential alternative to Portland cement in recent years. In addition, fly ash and recycled glass are abundant by-products derived from the industry. The purpose of this study was to evaluate the potential of using recycled glass to replace the sand aggregate in slag-blended fly ash-based geopolymer mortar. For geopolymer synthesis, the mixture of water glass (Na2SiO3) and sodium hydroxide (NaOH) solution with a NaOH concentration of 14 mol/l was used as an activator. In the mortar mixture, the recycled glass's investigated replacement level of the sand aggregate was up to 100 %. Using recycled glass (RG) as fine aggregate was seen to increase the mechanical strength compressive strength and flexural strength of mortar after 28 days of curing. Otherwise, there was a reduction in the drying shrinkage of mortar samples with a high recycled glass content of 80 and 100 %.

Time Dependence of Viscosity of Alkali-Activated Fly Ash Based Geopolymer Mortar

FA was used as the raw material, and the net slurry of FA base Geopolymer was set as the control group to study the influence of sand content, gradation, reaction temperature and time on the time dependence of the viscosity of alkali-activated fly ash based geopolymer mortar. The experimental results show that the curing reaction of alkali-activated fly ash based geopolymer mortar was affected by the temperature dependence of fluid viscosity and the activation energy of the chemical reaction, which is relatively complex. This paper will divide the whole polymerization process into three stages to elaborate. The increase of sand cement ratio will increase the viscosity of FA base polymer mortar. If the sand is too coarse or too fine, the viscosity of FA base polymer mortar will increase significantly, and the fine sand has a greater impact on the viscosity of FA base polymer mortar than the coarse sand. Increasing temperature will significantly accelerate the reaction speed and increase the influence of chemical reaction activation energy on the viscosity of the system while the too high temperature will make the viscosity of the system decrease more significantly in the reaction. This study will reveal the intrinsic relationship between the viscosity of geopolymer and the reaction process, the reaction mechanism of the curing process so that the reaction stage can be represented by the viscosity state of the slurry.

Effect of GGBS on Fly Ash Based Geopolymer Mortar at Ambient and Heat Curing

AbstractThis study investigates and shows the effect of incorporation of ground granuated blast furnace slag (GGBS) content in fly ash (FA) based geopolymer mortar by assessing the strength properties of geopolymer mortar in both ambient (25 °C) and heat (60 °C) curing. The percentage of GGBS is varied from 0% to 50% with FA in geopolymer mortar. Sodium silicate (SS) and sodium hydroxide (SH) solutions are used to activate the main binders. For all the mixes the alkali/binder ratio, molarity (M), and sodium silicate (SS)/sodium hydroxide (SH) ratio are fixed to 0.45, 12 M, and 2, respectively. The fresh property in terms of slump flow and other properties like compressive strength, water absorption, and dry density of the geopolymer mortar are determined. The result of this study shows that the inclusion of GGBS content in FA‐based geopolymer mortar significantly increases the compressive in both the curing conditions. Maximum compressive strength of 44.33 MPa is obtained when 50% GGBS is added to the mixes at a curing temperature of 60 °C.

Performance of eco-friendly fly ash-based geopolymer mortars with stone-cutting waste

In this study, the physical and mechanical properties of the geopolymers formed by substituting red (RSW) and yellow (YSW) stone-cutting wastes into geopolymer mortars based on class F fly ash at 10–40 wt% rates were investigated. Sodium hydroxide (NaOH) solution was used as an activator in the production of the mortars. Produced samples were thermally cured at 90 °C for 24 h. Workability, unit weight, flexural strength, compressive strength, water absorption, porosity, and elevated temperature resistance tests (400, 600, and 800 °C) were applied to the produced geopolymer mortars. In addition, the chemical analysis (XRF), crystal phase analysis (XRD) of wastes/selected mortars, and microstructural analysis (SEM) of before and after elevated temparature resistance tests were carried out to investigate the effect of stone-cutting wastes on geopolymer mortars. SW up to 40% enhances mechanical strength up to 26–30.7 MPa from 16.4 MPa due to its high Si/Al ratios and Ca content and needle-like crystals formed by stone-cutting waste. The crystalline phases are determined to be mullite, quartz, anorthite, and zeolite derived from stone-cutting waste in the selected mortars. As a result, it was seen that the use of stone-cutting wastes up to 40% improved the physical, mechanical, and microstructural properties of fly ash-based geopolymer mortars.

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.

Characteristic properties of fly ash-based self-compacting geopolymer mortars with synthetic wollastonite microfiber produced from silica and calcite

This study investigated the fresh, physical, and mechanical properties of self-compacting geopolymer mortars (SCGs) with synthetic wollastonite microfiber (SWM). SCGs were designed with Class F fly ash (FA) as a binder by activating it with Na2SiO3 and NaOH solutions. First, SWM was produced in the laboratory. Alkali ratios were determined as 1.5, 2.0, and 2.5, whereas SWM percentages were utilized as 0%, 4%, 8%, and 12% by weight of the binder. After geopolymer mortars were cured at 80 oC and 100 oC for 24 hours, respectively, they were kept at room temperature until testing age. The compressive strength, flexural strength, ultrasonic pulse velocity, dynamic modulus of elasticity, water sorptivity coefficient values, and physical characteristics of SCGs were tested at the end of the 28th day. The highest compressive strength value was obtained as 28.9 MPa for SCG-1.5-8 cured at 100 oC, while 6.5 MPa was measured as the highest flexural strength for SCG-2-12 cured at 80 oC.

Experimental Study on the Compressive Strength of Masonry Blocks with Geopolymer Mortar

Masonry units are the major building materials used in construction work. There are several masonry units available in the market today. Some of the widely used masonry units are burnt clay bricks, concrete blocks, fly ash blocks, compressed stabilized soil/earth blocks, geopolymer mud blocks, geopolymer concrete blocks, and so on. These blocks are used for the construction of load bearing structure. To bond two masonry units together, mortar plays a vital role. Fly ash based geopolymer mortar has been used in this study. The strength of masonry units namely bricks, concrete blocks and stabilized geopolymer blocks masonry with geopolymer mortar has been individually studied and the results have been tabulated. From this study, it was found that the stabilized geopolymer mud blocks are suitable in the construction of load bearing walls and for other structural purposes. The failure pattern revealed visible vertical fissures and ultimately spalling of brick prism blocks.

The study on various temperature condition of fly ash based geopolymer mortar

The present research investigated the curing conditions (ambient and heat curing) and the duration of heat curing which is considered as significant criteria affecting the mortar strength. The geopolymer (GP) sample was cured at several heating temperatures, which were ambient, 60, 80, and 100 °C for a curing time of 24 h in the oven. The samples were then stored at room temperature until the day of testing. Compressive strength (CS) was used to evaluate the mechanical characteristics of GP mortar. Mortar control specimens that hardened at room temperature were used for comparison. The outcomes were established using specimens ages 3, 7, 28, 56, and 90 days after the curing procedure. The study reveals that the CS of GP mortar under heat curing conditions develops polymerization faster as the temperature rises. Comparing curing at ambient temperature to elevated temperatures, it can be determined that temperature has a significant effect in promoting the GP mortar strength increase. In comparison to all other curing conditions, oven curing at 80 °C for 24 h obtained the highest CS (32 MPa) at the age of 90 days. The partial replacement of GGBS under ambient curing conditions yielded a maximum CS of 35 MPa.

Investigation of the effect of metakaolin substitution on physicomechanical properties of fly ash-based geopolymer mortars

In this study, geopolymer mortar samples were prepared with metakaolin (MK) substitution in fly ash-based geopolymer mortar. A vibration table was used in the production of the geopolymer mortars, and the samples were shaped to 4 × 4 × 16 cm prismatic size. The samples were placed in a laboratory-type oven and subjected to thermal curing processes at different temperatures and times. After curing, the samples were kept in an open laboratory environment for seven days until the related tests. In conclusion, it was determined that NaOH molarity did not significantly affect the physical properties but significantly affected the mechanical properties. It was also observed that the strength values increased with an increase in MK replacement and curing temperatures. The mechanical properties of the samples are increased by decreasing the porosity of the samples with the MK substitution ratio. At the same time, the results also show that relatively high curing temperatures and extended periods of curing times are unnecessary for this type of production.

Effect of polypropylene fiber on workability and strength of fly ash-based geopolymer mortar

Geopolymers do not require Portland cement as a binder; hence, the binder is replaced by a material containing high SiO2 and Al2O3 reacted with an alkaline activator (NaOH and Na2SiO3). In addition, mortar or concrete is highly susceptible to cracking, requiring the addition of polypropylene fiber (PPF). This research belongs to an experimental study examining the addition of PPF with percentages from 0%, 0.25%, 0.5%, 0.75%, and 1% by utilizing coal fly ash (FA) as a precursor. This study also added a superplasticizer (SP) and extra water (EW) to maintain the flowability. The tests were carried out on the workability, strengths, and microstructure of geopolymer mortar. Workability obtained values of 140 - 220 mm. Furthermore, the highest compressive strength of 73.3 MPa and flexural strength of 9.92 MPa were identified in the geopolymer mortar with the addition of 0.5% PPF. In addition, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) tests were applied to investigate the geopolymer microstructure.

Chloride resistance of class C/class F fly ash-based geopolymer mortars with different strength grades

Chloride resistance is important for the durability of geopolymers used in construction applications, particularly in coastal and saline areas. In this study, the workability, mechanical performance, and chloride resistance of class C/class F fly ash-based geopolymer mortars were investigated. First, the effects of the water-to-fly ash ratio, class C fly ash content, and sand-to-ash ratio, on the fluidity, and mechanical properties of the geopolymers were examined. Second, based on the results, geopolymer mortars with three different strength grades were chosen for chloride resistance tests. After these were subjected to a NaCl solution, their weight change, ultrasonic flight-time, and compressive strength were determined. Moreover, corrosion products were evaluated by conducting microstructural analysis. The results indicated that a high class C fly ash content, small water-to-fly ash ratio, and small sand-to-ash ratio led to low fluidity and a high compressive strength of the specimens. The ultrasonic flight-time and the pore structures of the geopolymers were strongly related. Furthermore, after corrosion, the hydration products appeared as new crystalline zeolite phases in the low-strength samples. Compared with the high- and medium- strength mortars, the low-strength samples showed excellent chloride resistance.

Parametric investigation on the post-fire flexural behaviour of novel ferrocement panels with geopolymer mortar

To enhance the thermal durability and at the same time to achieve the sustainability in this paper, a novel approach of using fly ash based geopolymer mortar had been introduced to protect the steel wire mesh layer present in the ferrocement panels. Parametric study was done to study the influence of role of wire mesh, volume fraction from 0.8% to 1.96%, changes in temperature of heating and the application of geopolymer mortar on the ferrocement to analyse their effect on the post fire mechanical properties such as load-deflection behaviour, stress–strain behaviour, percentage of strength retained, moment of resistance and Young’s modulus. Although the cement mortar showed higher retained strength upto 600 °C, the geopolymer had the maximum retained strength after 900 °C due to the gradual improvement of geopolymerisation process. The retained strength ranged between 46.3–99.1% and 34.91–88.78% for the ferrocement panels with geopolymer and cement mortar respectively. Ferrocement panel with geopolymer mortar showed 12.9% improvement in the post fire flexural strength at 900 °C for the volume fraction of 1.8% as the geopolymer mortar possessed double the times enhanced retained compressive strength of cement mortar after fire exposure.

An assessment on the durability performance of fly ash-clay based geopolymer mortar containing clay enhanced with lime and GGBS

The increased demand for cement as a construction material led to its humongous production and hence the emission of carbon dioxide. The geopolymer binder is an alternate binder which make use of aluminosilicate surplus industrial and agricultural waste and hence completely devoid of cement. The current study primarily aims at investigating the durability performance of low calcium fly ash based geopolymer mortar containing clay blends. Two types of clay treated with lime, ground granulated blast furnace slag (GGBS) and lime-GGBS combination was used in the study. The optimization tool used was the central composite design in response surface methodology by which a set of trial mixes were obtained. The design trial that exhibited maximum compressive strength and lower water absorption was taken as the optimum mix. The durability characteristics of the optimum mix in terms of water absorption, sorptivity, abrasion resistance, acid attack resistance and sulfate attack resistance were analyzed. Combination of lime-GGBS incorporated clay-based specimens exhibited better durability characteristics. The test results were discussed with microstructural characterization techniques such as X-ray Diffraction analysis (XRD) and Fourier Transform Infrared Spectroscopy (FTIR).