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Article

Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials

by
Ebrahim Sharifi Teshnizi
1,*,
Jafar Karimiazar
2 and
Jair Arrieta Baldovino
3,*
1
Department of Geology, Faculty of Science, Ferdowsi University of Mashhad, Mashhad 9177948974, Iran
2
Department of Civil Engineering, Faculty of Engineering, Seraj Higher Education Institute, Tabriz 5166616471, Iran
3
Civil Engineering Department, Universidad de Cartagena, Cartagena de Indias 130014, Colombia
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(19), 14407; https://doi.org/10.3390/su151914407
Submission received: 24 July 2023 / Revised: 14 September 2023 / Accepted: 24 September 2023 / Published: 30 September 2023
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Abstract

:
This research examined how changing the ratios of certain substances affected the strength and durability of a specific type of building material when exposed to acid and heat. This study used various combinations of zeolite, metakaolin, slag, and Portland cement as primary materials. It also used different amounts of potassium hydroxide (KOH) to make the geopolymer mortar. The concentrations of KOH used were 8 M, 12 M, 14 M, and 16 M. The cement-based material had the highest water absorption. A total of 240 tests were conducted, including 20 samples for each mix design tested at curing times of 7, 14, 21, 28, and 90 days. The results showed that the samples made with slag base material and 8 M mixing design had the highest average compressive strength at 28 and 90 days in the acidic environment test, and the zeolite and metakaolin base material samples had the highest corrosion and weight loss, possibly due to their high specific surface and aluminosilicate origin. The samples made with slag-based material had better resistance and the highest average compressive strength in the 300 °C and 500 °C thermo-mechanical tests. The lowest average compressive strength in the thermal and mechanical stress test was related to the samples made with a metakaolin base material. The tests performed on the samples made with slag base material had better compressive strength than the three other base materials in the acid and heat tests. The zeolite-based mortar lost the most weight under 30% acidic sulfuric water. The findings suggest that changes in the molar ratios of alkaline activators can significantly affect the durability properties and strength of geopolymer mortar, and the slag-based material with an 8 M mixing design had the best performance; also, SEM analysis verified this mechanism.

1. Introduction

Making cement uses a lot of power, water, and materials. It also creates harmful gases, like CO2, SO2, and NOx. The cement industry releases between 0.7 and 1 ton of carbon dioxide for every ton of cement it makes. This happens in three stages: 50% during the heating of limestone, 40% when burning fuel in a furnace, and 10% when transporting the cement [1,2]. Although concrete is cheap and uses readily available materials, it has weaknesses in harsh conditions and hurts the environment. As a result, researchers are looking for other options [3,4,5,6]. Meanwhile, many industrial by-products and wastes, including pneumatic sand, rice husk ash, and blast furnace slag, are currently unused and are buried in the environment [7,8,9,10,11,12,13,14,15,16].
New technologies like alkaline activation offer a way to use waste materials from industries, such as sand from coal-fired power plants and slag from blast furnaces, that were previously added to concrete. These leftover materials, like geopolymer cement, are essential in creating new cement [17,18,19,20,21,22,23]. There has been a growing interest in recent studies of geopolymer cement as an alternative to conventional cement [24,25,26]. Hardjito and Rangan reported that 2.5 cubic meters of geopolymer concrete can be produced using 1 ton of low-calcium sand (class F), which is less expensive than conventional Portland cement concrete [27].
The strength of geopolymer samples made with puffed-up sand and tested by Hardjito and Ragan [27] was influenced by the amount of liquid that made it alkaline. This was true regardless of how hot or cold the samples were kept and how long they were kept before testing. The 14 M solution could handle more pressure than the 8 M solution [28,29,30,31,32,33].
The preparation process of sodium hydroxide releases a significant amount of heat, and therefore, it is recommended to allow the activator solution to reach room temperature before mixing [34,35]. Geopolymerization or alkaline activation is a chemical process that converts the glassy structure of raw materials, which is partially or generally amorphous or unstable, into a fully compacted and cementitious composite [36]. During the polymerization process, a strongly alkaline medium is necessary to dissolve silica and alumina and disperse the surface hydrolysis of the raw material particles [30]. The compressive strength of geopolymer samples made of aerated sand and tested by Hardjito and Ragan [27] was dependent on the concentration of the alkalizing solution, regardless of the curing temperature and the sample’s life. The 14 M solution was found to withstand more significant pressure than the 8 M solution [27]. The most significant factor determining the strength of the aerated sand geopolymers, as established by Bakharev et al., was the amount of sodium hydroxide solution utilized [37].
Similarly, Topark-Ngarm [38] found that the activator concentration significantly affects the strength of geopolymer samples, and they determined the ideal concentration that increases the geopolymer strength. The presence of OH-free in the alkali-activated matrix at higher concentrations can be a factor in the loss of material mechanical properties, which may alter the structure of the geopolymer material. The sample life and processing temperature are also significant factors that can affect the mechanical properties of geopolymers. However, other factors will be practical only if the activator concentration is sufficient to advance the geopolymerization process [39,40,41,42,43].
Materials like slag, sandstone, and metakaolin can combine with a special liquid to form alkaline-activated materials. A mix of sodium silicate and sodium hydroxide solutions is often used as a robust alkaline solution. The ratios of sodium silicate to sodium hydroxide and water to cement, as well as the solution concentration, all affect how the alkaline-activated materials develop over time [44,45,46,47]. Metakaolin differs from other pozzolanic materials in its contact surface, high water absorption, fineness, and high reactivity. The addition of metakaolin to conventional concrete reduces its permeability to liquids. Studies found that parameters such as precursor solids, alkaline solution, and curing process significantly impact geopolymer materials’ strength, chemical reaction, and permeability [48,49,50,51,52,53,54,55,56,57].
Studies showed that the processing of materials at ambient temperature gradually increases strength and low hardness. In contrast, high temperatures cause an accelerated increase in strength [21,58]. Moreover, the permeability of alkaline-activated wind sand is higher than that of ordinary Portland cement [59,60,61]. Aerated sand mainly comprises alumina, silica, iron, magnesium, and lime. The reaction between alumina and silica in aeolian sand occurs during geopolymerization when using a unique liquid containing alkali. This process results in the formation of a gel-like substance known as alumino-silicate hydrate [62]. Steel furnace slag is left over from making steel, while blast furnace granular slag (GGBFS) is made by quickly cooling melted slag in water to turn it into a glassy substance, then breaking it up into tiny pieces and cooling it. Using slag with more calcium in alkaline conditions creates a gel called calcium silicate hydrate that contains a large amount of organic matter [63,64,65].
Several studies demonstrated that geopolymer materials incorporating ground granulated blast furnace slag (GGBS) can be utilized in cementitious mixtures to achieve high strength and durability. The polymerization process involves dissolution, orientation or transfer, and polycondensation, which leads to high compressive strength percentages in the mortar matrix. The results indicate that GGBS, with sufficient calcium reacting well in the mortar matrix, can contribute to high compressive strength [18]. There have been significant advances in geopolymer mechanisms based on various aluminosilicate minerals. Neupane et al. [66], Naghizadeh and Ekolu [67], and Abdellatief et al. [68] are among the researchers who contributed to these advancements. Extensive research was conducted to understand the physical, microstructural, mechanical, and mixing design aspects of geopolymer concrete using different raw materials. Also, research looked at how different things added to geopolymer concrete and mortar can affect its qualities. These investigations were carried out and verified by some other researchers [69,70,71,72].
The compressed strength of a specific sand–cement composite formulated using air bubbles and a sodium solution was superior to similar combinations incorporating potassium or lime solutions, as concluded by Nematollahi et al. in a 2015 study. The study showed that the compressive strength of the potassium-based activator in wind-blown sand geopolymer was promising, while applying a lime-activating solution resulted in meager resistance. Tensile strength tests on potassium and lime-activated sand-geopolymer mortar samples showed a 30% lower strength than sodium-based activators, as reported by Nematollahi et al. [73].
A study was done by Sata et al. [74] to test how well bottom ash (BA) geopolymer mortar, aerated sand mortar, and ordinary Portland cement mortar could resist the damaging effects of sulfuric acid and sulfate solutions. The compressive strength of BA geopolymer mortar increased as the particle surface area (fineness) increased. BA geopolymer mortar was 5% less susceptible to sodium sulfate solution attacks than base-cement mortar. Lower ash geopolymer mortars (BA) immersed in 3% sulfuric acid solution deteriorated less than conventional Portland cement mortars. Mortars containing 40% fine sand (FA) and fine-grained sand (FBA) also performed better. Additionally, all geopolymer mortars lost less than 3.6% mass loss in 120 days, according to Sata et al. [74].
Cement is a widely used material for mortar to meet the minimum strength requirement worldwide. However, geopolymer materials, such as zeolite and slag, are not commonly utilized to enhance mortar. Therefore, this study aimed to investigate the compressive strength and weight loss of geopolymer mortar made from different base materials (slag, metakaolin, cement, and zeolite) under critical environmental conditions (acidity) and high temperatures. The experiments conducted in this study include examining the resistance of samples to 30% acid attack and the effects of elevated temperatures (300 °C and 500 °C) on their durability.
Additionally, this study highlights the impact of KOH concentration and eco-friendly materials (slag, metakaolin, cement, and zeolite) content on the compressive strength of geopolymer mortar before and after exposure to high temperatures. Scanning electron microscopy (SEM) analysis was also performed to investigate the morphological structure of geopolymer mortar.

2. Materials and Methods

2.1. Materials

This study used sodium silicate (Na2SiO3) as a solid powder. It is important to acknowledge that powdered sodium silicate, which was chosen as an activator in this study due to its relevance in geopolymerization, exhibits relatively lower solubility at room temperature. While solubility is an essential aspect, the effectiveness of an activator in geopolymerization encompasses multiple factors beyond solubility alone, including dissolution kinetics, reactivity, and subsequent reaction pathways. Despite the solubility characteristic, our choice was rooted in its significance to real-world applications and aligns with our study’s objectives. Our experimental design accounted for this by assessing the geopolymer mortar’s behavior under specific conditions, such as exposure to a 30% acidic environment and elevated temperatures up to 500 °C. This controlled approach enabled us to comprehensively evaluate the material’s performance.
Potassium hydroxide was used with the chemical formula of KOH. Slag is a synthetic and ancillary product formed during the separation of iron in iron furnaces from impurities in iron ore. Type 1 cement was used in this study. Another substance used was metakaolin, which is one of the active pozzolans used in recent decades. This material obtained from baking kaolin clay is used to increase the reliability and mechanical strength of concrete and, in some cases, improve the appearance of decorative concrete. Also, zeolites, crystalline alumina-silicates, and hydrates are alkaline earth metals, especially calcium, barium, strontium, sodium, and magnesium. The crystal lattice of zeolites is based on a three-dimensional SiO4 quadratic lattice in which adjacent quadrilaterals share all four oxygens. The chemical properties of metakaolin, zeolite, slag, and cement in this study are shown in Table 1. River sands are an example of the sands used in this research. The physical properties of the aggregate used in this study are listed in Table 1. Natural limestone sand was used in this investigation as aggregate in this research. The aggregate specifications were determined according to the requirements of ASTM C33/C33M-18 [75], as presented in Table 2.

2.2. Mix Design and Sample Preparation

Figure 1 illustrates the sodium silicate powder (glass water, Na2SiO3), potassium hydroxide powder (KOH) (Figure 1), water (drinking water), washed sand (sieve 03) (Figure 1), and the use of 4 base materials of metakaolin, zeolite, slag, and cement (Figure 1), which were first placed into test molds with the dimensions of 5 × 5 × 5 cm (Figure 1). One must take care that the material of the mold does not deform the mortar when it is poured into the mold. To begin the experiment, we must consider a mixing plan (Figure 1). The mixing plans considered in this experiment were the 8 M, 12 M, 14 M, and 16 M mixing plans, which are fully described in Table 2.
The authors first used an eight-molar mixing scheme to make a mortar with a zeolite base material. In the mixing plan, 8 M (800 g) of zeolite, potassium hydroxide powder (KOH) (202 g), sodium silicate powder (glass water) (105 g), washed sand (2200 g), and water 105 g. First, water (105 g) was poured into a glass container, and then glass water powder was mixed in. Note: when the authors added the powder to the water, the water temperature rose by about 70 °C, and then the authors waited for the temperature of the sodium silicate powder solution to drop.
After the sodium silicate solution had cooled, the potassium hydroxide powder (KOH) was added and mixed. This was then poured into the container where the sand was poured and mixed. First, a metal container was used but this caused the metal container to corrode, and thus, the authors used a plastic container. Furthermore, after compacting the mortar, the authors put them in a typical environment, and after 24 h, the authors took the samples out of the mold and put them in a suitable place.
The number of samples made in each design was 24 samples, with 12 samples for acid testing and 12 samples for heat testing (i.e., 96 samples were made from each base material), for a total of 240 samples. Only the potassium hydroxide powder (KOH), whose weight was varied, is given in the following explanations (Table 3).

2.3. Details of the Testing Procedure

Two tests were conducted to evaluate the performance of the materials: the compressive strength of mortar samples produced in an acidic environment and under thermal conditions. In the acidic environment considered for this research, the samples with different KOH ratios were immersed in a pond made up of 30% acid (sulfuric acid), and it was processed at room temperature at 7 days, 14 days, 21 days, 28 days, and 90 days of curing time [69]. In order to explore the varying levels of severe acid environments, several concentrations, such as 30% sulfuric acid (0.5 M of H2SO4) can be used [76]. It is important to note that the pH of the 0.5 M sulfuric acid solution was approximately 0.3, indicating a high degree of acidity and resulting in a severe corrosive condition. However, the 30% sulfuric acid solution presented an even more potent acidic environment, potentially surpassing the corrosive nature of the 0.5 M solution. Considering the potential for reduced material durability in the face of this higher concentration, the decision was made to focus on the 30% sulfuric acid scenario for this project’s scope. This approach allowed us to comprehensively investigate and assess the implications of a particularly severe acidic condition.
In addition, the other samples made with different concentrations of 8 M, 12 M, 14 M, and 16 M were heated to 300 °C and 500 °C in a furnace at a rate of 4 degrees per minute in order to investigate the effect of temperature on the resistance parameters of geopolymer mortar [19,21].

2.3.1. Compressive Strength

The authors tested the strength of the geopolymer mortar samples that were cured for 28 days and 90 days. The samples were 50 × 50 × 50 mm in size. The authors followed the guidelines of the ASTM C109/C109M standards to measure their compressive strength. The tests were performed using a machine called DYE-2000, which uses electricity and hydraulic pressure. The machine applied a force at 1 kilonewton per second [77].

2.3.2. Acid Attack

To check how well acid can be resisted, tests were done following a specific standard called ASTM C267 [78]. Samples were kept in water for one day and then put into a solution of HCl with a strength of 0.5 M for different amounts of time (7, 14, 21, 28, and 90 days) after being aged for 28 days. The acid mixture was replaced every 7 days up to one month, then monthly up to the end of immersion according to ASTM C 1012-04 and ASTM C267 [78,79]. After contacting the acid solution, the samples were taken out and cleaned with purified water. Small pieces of dirt and dust were gently removed, and the samples were dried quickly by pressing them with paper towels. After keeping the samples in a room with a temperature of 18–22 °C and humidity level of 55–65% for an hour, the authors tested them to see how much force they could withstand and whether they had lost any weight using the guidelines set by ASTM C267 [78].

2.3.3. Thermal Deformation

Geopolymer mortars and cement mortars (measuring 5 × 5 × 5 mm) that had been cured for 28 days and 90 days were molded in accordance with the ASTM C157 standard [80]. The authors tested the samples at hot temperatures in a special oven called a muffle furnace. It could reach up to 1175 °C (Figure 2). The furnace’s temperature went up by 10 °C every minute. The desired temperatures were 300 °C and 500 °C. The samples were kept at the planned temperature for 3 h before cooling slowly in the furnace. The authors tested the strength of the samples as soon as they were cooled down to room temperature.
To stop the cement mortar from bursting when it got too hot, it was dried in a hot place for three days before putting it in the furnace. However, the geopolymer samples did not need to be dried beforehand because they were already cured in the oven.

2.3.4. SEM Analysis

The authors used SEM to study paste samples made in the same way as the mortar mixtures. The authors conducted these analyses to study the shape and structure of the material and the products formed during geopolymerization. To obtain the SEM pictures, the authors looked at the broken surface of the paste samples. The pastes had a thin layer of gold–palladium (80:20) on their surfaces. This layer was 7 nm thick and was applied using a sputter coater device. Pictures were captured using either a 10- or 20-kilovolt energy level and were magnified 1000 times.

3. Results and Discussion

3.1. Acid Attack

Concrete structures need to stay strong against acid for a long time if we want our economies to be sustainable. When acid comes into contact with repair binders, it can make them work less effectively and weaken the connection. Therefore, it is essential to consider how well concrete structures can withstand acids to last a long time and be sustainable.
As shown in Figure 3, in the samples made with metakaolin base material in all four mixing designs, as well as zeolite base material, at 90 days of age, the materials experienced weight loss. Most weight loss in the 7-day zeolite samples was treated in an acidic environment with 12 M of KOH, which resulted in 66% weight loss of the grout samples. Moreover, the highest weight gain was related to slag with 14 M of KOH, which increased by 11% (Figure 3a).
The highest weight loss of the zeolite samples over 14 days was processed in an acidic environment in 12 M of KOH, which had a 44% weight loss of the grout samples. Furthermore, the highest weight gain was related to slag mixing with 14 M of KOH, which increased by 11% (Figure 3b). The highest weight loss of the zeolite samples over 21 days was processed in an acidic environment in 12 mol of KOH, which had a 50% weight loss of the grout samples. Furthermore, the highest weight gain was related to slag in 14 M of KOH, which increased by 11% (Figure 3c). Also, the highest weight loss in the 28-day zeolite samples was treated in an acidic environment with 12 mol of KOH, which had a 50% weight loss of the grout samples. Moreover, the highest weight gain was related to slag with 14 M of KOH, which increased by 9% (Figure 3d). The highest weight loss of the zeolite treatment samples over 90 days in an acidic environment was in 12 M of KOH, which had a 57% weight loss of the grout samples. Additionally, the highest weight gain was related to cement with 12 M of KOH, which increased by 6% (Figure 3e).
As shown in Figure 3, in the samples made with zeolite base material, in contrast to the samples made with cement base material and slag base material, the samples showed severe weight, volume, and corrosion loss at the age of ninety days, which was reduced by almost 40%. The primary material of zeolite in these four tested designs reacted very weakly to acidic environments. The maximum weight loss was in the mixing design with 12 M with a weight loss of 105 g, and the lowest weight loss was in the mixing design with 14 M with a weight reduction of 74 g.
Zeolite geopolymer may not react appropriately in acidic water compared with slag and cement due to its chemical composition and structural differences. Zeolites are aluminosilicate minerals with a unique framework structure, high surface area, and porosity, which can trap and release water and other molecules. They are used in geopolymer materials as a source of alumina and silica, which are the main components of the geopolymer matrix.
Zeolites have a high silica content, making them vulnerable to dissolution in acidic solutions. This can result in the silica framework’s breakdown, lowering the strength, durability, and weight of the zeolite geopolymer. In contrast, slag and cement contain calcium compounds that can react with acidic water to form C-S-H gel, strengthening and protecting the material. This pozzolanic reaction is essential for the long-term durability of concrete. Therefore, the difference in susceptibility to dissolution in acidic water between zeolite geopolymer and slag or cement may be due to variations in their chemical composition and the absence of calcium compounds in zeolite geopolymer. As shown in Figure 3, the samples made with slag-based material had less water absorption than the cement. The lowest water absorption was with the 16 M mixing plan, which not only did not increase in weight but also (−2 g) decreased in weight.
As shown in Figure 3, in samples made with cement-based material, the authors saw an increase in weight in both the mixing design with 14 M (16 g), which had the highest water absorption, and the mixing design with 8 M, where the weight increased by about (8 g). The authors found that when the cement samples were in acid for longer periods, their compressive strength decreased compared with the control samples.
Figure 4a,b show how an acid attack affected the strength of the geopolymer samples. These samples were made with different materials (metakaolin, zeolite, slag, and cement) and tested in acidic and tap water. The strength was measured after 28 days and 90 days. The strength of the geopolymer materials soaked in acidic water after 28 days and 90 days was less than that of control samples soaked in tap water. For example, the strength of the geopolymer sample made with metakaolin after 28 days was 5.29 megapascals (MPa) when using a KOH concentration of 16 M.
In comparison, the strength of the sample when exposed to acid was 2.6 MPa, while the control sample had a strength of 2.6 MPa. Acidic water can damage the geopolymer structure by dissolving the bonds that hold it together, which are important for the material to stay strong. This breaking up leads to more Al-OH and Si-OH groups in the structure and more silicic acid ions and dimers in the acidic liquid. This process of dissolving usually causes the geopolymer samples to lose mass and become less strong when compressed. In addition, the acid attack can also cause the wearing away and drying out of C-(A)-S-H gels, which makes the material less stable. Therefore, the acid water can break down the geopolymer structure and make it lose mass, erode, and dehydrate. This weakens the geopolymer and makes it less strong.
The study examined how different amounts of KOH affected the strength of geopolymer samples made from different materials (metakaolin, zeolite, slag, and cement) after 28 days and 90 days. The results can be seen in Figure 4a,b for samples not exposed to any additional factors other than being soaked in tap water with an acidic pH. The strength of the geopolymer samples increased when the concentration of KOH was higher, except for the metakaolin geopolymer sample. The strength of the geopolymer samples made with slag, zeolite, and cement increased when they were soaked in tap water and higher KOH concentrations were used. This was because KOH, which is an ingredient used to activate geopolymer materials, helps them form and harden. The KOH solution starts and makes the chemical reaction happen to create the geopolymer matrix. Increasing the KOH concentration can strengthen the reaction and help create a stronger geopolymer. This makes the geopolymer more compact and long-lasting, which increases its strength when compressed.
The strength of geopolymer samples made with metakaolin did not get stronger when more KOH was added, which was not the case with geopolymer samples made with slag. This is because metakaolin can react quickly and has a large surface area, which helps to form a more robust geopolymer structure, even with less KOH. If we increase the amount of KOH too much, it can weaken the geopolymer matrix. This can cause the material to be less resistant to pressure. The amount of KOH concentration affects the strength of geopolymer materials differently depending on the type of aluminosilicate material used. The ideal KOH concentration may also vary for different types of geopolymer materials.
The geopolymer made from slag showed stronger compressive strength after 28 days and 90 days, regardless of the concentration of KOH used. In simpler terms, when a strong chemical called KOH (potassium hydroxide) was used in high concentrations and applied to the geopolymer sample, its compressive strength after 28 days was 539% higher than that of metakaolin, 332% higher than zeolite, and 314% higher than cement. This was because the C-(A)-S-H gels and Si-O-Al bonds helped to make the structure of metakaolin, zeolite, and slag geopolymer more tightly packed, which made it stronger. In a geopolymer, the dissolution of silicate occurs through the leaching of non-framework alkaline ions (e.g., the substitution of Na+ by H3O+) and the removal of Al species via the hydrolysis of Si-O-Al bonds. This process was studied by Oelkers [81], Chen et al. [82], Hartman et al. [83], Hartman et al. [84], Jamieson et al. [85], Bakharev [86], Ariffin et al. [87], Deb et al. [88], and Mohammadifar et al. [25].
Based on the research by Sturm et al. [89], their study found that when something acidic comes into contact with certain materials, it can make sodium, aluminate, and silica come out into the liquid. This ends up causing a thin layer of silica gel to form on the damaged surface. This layer can stop things from breaking apart and losing much weight. Furthermore, silica particles that have not undergone a reaction in the material can serve as solid fillers, enhancing the ability of the geopolymer to withstand acids and prevent dissolution. The damaged parts of the material can create a safe layer that stops the material from breaking down more until the movement of particles is limited. This layer helps to protect geopolymer mortars and keep them from losing too much mass and strength when exposed to acid for 28 and 90 days.

3.2. Effect of High Temperature

The strength of the geopolymer samples with different materials (metakaolin, zeolite, slag, and cement) after being heated for 28 days and 90 days are shown in Figure 5 and Figure 6. The 28-day curing time compressive strength of the 16 M KOH metakaolin, zeolite, slag, and cement geopolymer samples at 300 °C and 500 °C were 4.8, 4.3, 19.1, and 5.7 MPa and 3.5, 3.1, 16.9, and 4.9 MPa, respectively, which were decreases of 0.27, 0.9, 0.49, and 0.52% and 0.74, 1.64, 0.68, and 0.77% compared with those at room temperature.
Figure 5 and Figure 6 illustrate the compressive strengths of geopolymer mortars before and after exposure to high temperatures (300 °C and 500 °C) with 28-day and 90-day curing times. When subjected to high temperatures, the decline in compressive strength and increase in weight loss of geopolymer materials like slag, zeolite, cement, and metakaolin can be attributed to physical and chemical changes within the material. One of the primary reasons for the decrease in compressive strength is the loss of water from the geopolymer matrix. Geopolymers contain significant amounts of adsorbed water within their structure, contributing to their strength and durability. When the geopolymer samples are subjected to high temperatures, this adsorbed water evaporates off, causing the geopolymer matrix to become prone to cracking and more brittle, which can reduce the compressive strength. In addition, the high temperatures in the oven can also cause chemical changes within the geopolymer matrix. For example, the thermal decomposition of calcium carbonate (CaCO3) and other minerals may occur at high temperatures, forming new phases and releasing carbon dioxide (CO2) gas. This can create pores and cracks within the geopolymer matrix, further reducing its strength.
Furthermore, geopolymer materials may undergo phase transformations or structural changes at high temperatures, which can also contribute to the loss of strength and an increase in weight loss. For instance, the amorphous aluminosilicate phases in geopolymer materials may crystallize or transform into other phases at high temperatures, leading to a loss of structural integrity and increased weight loss. Therefore, when geopolymer materials, like slag, zeolite, cement, and metakaolin, are exposed to high temperatures in an oven, their strength decreases and they lose weight. This is because both physical and chemical changes are happening inside the materials due to the heat treatment. As the temperature increased, all the geopolymer mortars became weaker over time. However, the geopolymer mixtures maintained high compressive strengths, even when heated to temperatures between 300 °C and 500 °C [21,35,90].
According to Figure 5 and Figure 6, the higher weight loss of metakaolin and zeolite-based geopolymer materials compared with slag and cement-based geopolymer materials at high temperatures of 500 °C may be due to chemical composition and thermal stability differences. Metakaolin and zeolite are aluminosilicate materials with a high surface area and reactivity, making them more susceptible to thermal degradation at high temperatures. At high temperatures, the geopolymer matrix can undergo structural changes, such as dihydroxylation, decarboxylation, and deaminization, which can cause the release of water, carbon dioxide, and other volatile compounds, leading to a higher weight loss. In contrast, slag- and cement-based geopolymer materials contain calcium compounds that can stabilize the geopolymer matrix at high temperatures. The calcium compounds can react with the aluminosilicate materials to form calcium silicate hydrate (C-S-H) gel, which can enhance the thermal stability and reduce the weight loss of the geopolymer material. Therefore, the higher weight loss of metakaolin- and zeolite-based geopolymer materials compared with slag- and cement-based geopolymer materials at high temperatures of 300–500 °C may have been due to chemical composition and thermal stability differences.

3.3. Comparing the Standard Mortar with Geopolymer Mortars

Figure 7a,b show the loss of unconfined compressive strength (UCS) in mortar subjected to elevated temperature and acidic environments; a common trend emerged, where mortar composed solely of cement and lacking alkaline activators generally experienced a greater reduction in strength compared with geopolymer mixtures that incorporated cement, slag, zeolite, and metakaolin.
For instance, in the case of standard mortar, the initial unconfined compressive strength (UCS) after a 90-day curing period stood at 47.2 MPa. However, subjecting it to 500 °C reduced the UCS to 19.4 MPa, signifying a decrease of 2.4 times relative to its original strength. Conversely, for the slag-based geopolymer with 8 M NaOH, the UCS reduction under the same conditions was comparatively milder at about 1.5 times. Shifting the focus to immersion tests, the slag-based geopolymer achieved a 31 MPa UCS in tap water after 90 days, which decreased to 22 MPa in an acidic sulfuric environment, reflecting a reduction ratio of 1.45 times. In contrast, standard mortar exhibited a higher initial UCS in tap water (47.2 MPa) but faced more pronounced degradation in an acidic setting (21 MPa), leading to a reduction ratio of 2.24 times, notably surpassing the geopolymer’s reduction in acidic conditions. Therefore, the geopolymer mortar had better resistance against elevated temperatures and acidic environments than standard mortar. This observed trend can be attributed to the differing chemical reactions and binding mechanisms at play in these two categories of mortar.
The decreased UCS in cement-only mortar arose from the hydration process of the cement particles. Hydration leads to the formation of a matrix within the mortar that contributes to its strength. However, under elevated temperatures and exposure to acidic conditions, the chemical stability of this matrix can be compromised. High temperatures can accelerate the breakdown of hydrated compounds, leading to the loss of strength. Additionally, the acidic environment can facilitate the dissolution of certain minerals within the matrix, further contributing to strength reduction.
Conversely, geopolymer mortars, encompassing cement, slag, zeolite, and metakaolin, offer a more durable and resilient response to elevated temperature and acidic challenges. The geopolymerization process creates a three-dimensional network structure that inherently possesses enhanced thermal and chemical degradation resistance. The supplementary materials contribute to this resilience by forming additional reaction products that reinforce the geopolymer matrix against adverse conditions.
In summary, while the initial UCS of cement-only mortar might be higher, it exhibits a greater loss of strength when subjected to elevated temperatures and acidic environments. This is attributed to the susceptibility of the cement-based matrix to chemical alterations and structural breakdown. On the other hand, geopolymer mortars showcase a more gradual reduction in UCS due to their durable binding mechanism, which enables them to maintain their structural integrity and strength even under challenging conditions.
These trends underscore the advantage of geopolymer mortars when aiming to mitigate the loss of strength in the face of elevated temperatures and acidic environments. This research elucidates the complex interplay between composition, binding mechanisms, and environmental stressors, offering insights that are vital for selecting and optimizing mortar formulations to ensure robustness in diverse construction scenarios.
Also, Figure 7b reveals that standard mortar made only with cement, without the extra ingredients, tends to lose less weight in these harsh conditions compared with the special mixtures with cement, slag, zeolite, and metakaolin.
The reason for this lies in how the two types of mortar are built. The cement-only mortar forms a dense structure due to how cement reacts with water. This makes it more resistant to weight loss under challenging conditions. On the other hand, the mixtures with extra ingredients (geopolymer mortars) have a different structure. They might lose more weight because their special binding process can be more sensitive to these conditions.
Therefore, in simple terms, while the cement-only mortar was better at resisting weight loss, the mixtures with unique ingredients (geopolymer mortars) offered other benefits, like durability, even though they might lose a bit more weight. It is a trade-off between these different qualities that builders need to consider when choosing the correct mortar for a specific project.
In summary, above 200 °C, the degradation of the mechanical properties of geopolymers could be attributed to crack development and degradation of material properties. From 200 °C to 800 °C, with increasing temperature, the compressive strength of GM-NaNa and GM-NaK groups decreased because of material degradation (i.e., sintering and crystallization) and internal structural changes (i.e., pore structure and cracks). Previously, studies demonstrated that the reduction in compressive strength was due to the different thermal expansions of the aggregate and the geopolymer binder and the formation of cracks.

3.4. SEM

Figure 8 shows the SEM (scanning electron microscopy) images of different geopolymer samples after the thermal test. SEM analysis can provide information on the microstructure and morphology of geopolymer materials, which can be used to infer their mechanical properties and strength. The surfaces of slag and cement reveal a dense composition with cracks present. In contrast, metakaolin and zeolite exhibited conspicuous cracks and a visible decline in the integrity of their aluminosilicate gel and polymerization structure. This occurrence within the microstructure can be attributed to the breakdown of geopolymerization and the associated calcium silicate hydrate (CSH) gel. As the temperature rose to 500 °C, the thermal stress compounded, expanding the crack size [91,92,93].
The impacts of 500 °C temperature on the geopolymer metakaolin and zeolite microstructures were striking, resulting in pronounced cracks that strongly influenced their mechanical performance. These observable cracks significantly contributed to a reduction in mechanical properties. Through SEM analysis, the correlation between the intensity of elevated temperature and these cracks became evident, portraying a direct link between temperature and structural changes.
Further insights stemmed from the resilience of slag-based geopolymers when exposed to heightened temperatures. Despite the cracks, the SEM images demonstrate that slag specimens exhibited comparatively lower signs of deterioration. This resilience arose from the distinct behavior of slag when subjected to thermal influences and its interaction with other components. This finding holds significance for civil engineering applications, offering a path toward crafting robust, sustainable construction materials capable of enduring temperature fluctuations.
SEM analysis unveils a narrative of the interplay between temperature, microstructural transformation, and mechanical properties. The process involves the gradual weakening of geopolymerization, resulting in prominent cracks. The effects of these mechanisms resonate within the broader realm of civil engineering, providing insights into how eco-friendly geopolymer mortars respond to thermal challenges. Also, the SEM showed that some of the metakaolin and zeolite were unreacted in the geopolymerization, leading to a more porous structure and cracks in the mortar matrix [94].
Payakaniti et al. [95] suggested that geopolymers become weaker when heated above 400 °C due to thermal stress. Scientists also mentioned that when the temperature reaches 800 °C or higher, new structures are formed in the material, which causes internal tensions that can lower its ability to withstand compression. Also, the heating period (h) and different raw geopolymer materials can be the other factors that can affect the structure of the matrix of samples. Rashad [96] and Klima et al. [97] reported that when water in a geopolymer evaporates, it creates pressure inside and damages the structure. Additionally, when the water is lost, the geopolymer shrinks, and this reduction in water weakens the strength. In contrast, Liu et al. [90] said that when the temperature increases, the substance can start to melt slightly. This melted substance can go into the holes, break the material, and fix them.
The SEM images are shown in Figure 7 for both the control specimens and specimens exposed to 500 °C. The internal structure of the samples underwent significant changes after being subjected to high temperatures, regardless of the type of geopolymer used. All samples displayed signs of deterioration, as evidenced by porous structures with numerous microcracks. Among all the samples, the ones made with metakaolin mortar had the most significant microcracks.

4. Practical Implications and Applications

The findings of this study have far-reaching practical implications for the field of geopolymer mortars [94], particularly in scenarios involving elevated temperature exposure and resistance to acidic environments. The conducted experiments yielded significant insights in guiding the real-world applications of various geopolymer compositions. In the realm of infrastructure, where durability is paramount, this research offers valuable insights. Regions facing high temperatures and exposure to corrosive agents, like sulfuric acid, can benefit from the understanding gained through this study. The responses of geopolymer mortars under such conditions guide the selection and optimization of construction materials, ensuring long-term performance in challenging environments. Industries operating in settings involving elevated temperatures or chemical processes also stand to gain from this research. This study’s insights into the behavior of geopolymer mortars under thermal and chemical stress provide valuable information for industries seeking reliable materials for applications in harsh environments. The observed resistance to degradation opens avenues for their use in industrial settings that demand materials capable of enduring rigorous operating conditions.
The enhanced resistance to sulfuric acid displayed by specific geopolymer compositions becomes particularly relevant in waste containment and treatment, where material stability is crucial. This study highlights their potential suitability for waste containment and treatment facilities, where materials that maintain their structural integrity and chemical stability are essential.
The energy sector, encompassing power generation and transmission facilities, also benefits from the findings of this research. Geopolymer mortars’ resistance to acidic environments and elevated temperatures positions them as potential candidates for use in energy-related projects. By contributing to the longevity and resilience of such facilities, geopolymer mortars can play a role in ensuring a consistent energy supply.
By weaving these practical implications into the manuscript, this study’s relevance is further solidified within the context of real-world applications. The insights from this research inform material selection and decision-making processes across different sectors, demonstrating the potential of geopolymer mortars to address critical challenges in diverse fields.

5. Conclusions

In summary, the culmination of our research provides a detailed panorama of the behavior of geopolymer mortars in response to varying conditions of elevated temperature and exposure to acidic environments. Through a meticulous investigation involving diverse base materials—slag, cement, metakaolin, and zeolite—coupled with a range of alkaline activator concentrations, the authors unearthed many insights that lend themselves to the advancement of sustainable civil engineering practices.
A pivotal facet that emerged from our study was the profound influence of composition on the mechanical integrity and durability of geopolymer mortars. Our experiments revealed that formulations incorporating slag and cement as base materials stood out with exceptional compressive strength, outperforming counterparts enriched with metakaolin and zeolite. This underscored the role of supplementary materials in shaping the matrix’s structural robustness, subsequently translating to superior performance in harsh conditions.
At the microstructural level, the SEM analysis was found to be invaluable in unraveling the intricate alterations brought about by the interaction between material composition and environmental stressors. The observed microcracks and porous structures in the SEM images corroborated the macroscopic degradation trends, providing visual evidence of the mechanisms driving the observed weight loss and reduced compressive strength. These microstructural insights furnish a deeper understanding of the underlying degradation processes and contribute to the holistic comprehension of material response.
Of noteworthy significance was the impact of elevated temperatures on the geopolymer mortars. While all the samples exhibited varying degrees of weight loss and compressive strength reduction, the extent of these effects hinged on the specific material composition. Particularly, geopolymer mortars comprising metakaolin and zeolite displayed heightened susceptibility to the combined temperature and acid exposure influences. In stark contrast, formulations enriched with slag and cement demonstrated remarkable resilience, showcasing less degradation and better retention of mechanical properties. This differentiation further reinforces the critical role of material selection in safeguarding the durability of construction elements under multifaceted challenges.
As we consider the broader implications of our findings, it becomes evident that our research can guide researchers, engineers, and industry stakeholders alike. The insights gleaned from this study can inform the selection of geopolymer materials tailored to the specific demands of various applications, whether in infrastructure development or other realms of construction. Moreover, the microstructural elucidation and degradation mechanisms uncovered in this research form the bedrock for future investigations, enabling a deeper dive into the intricacies of geopolymer behavior.
In a world characterized by evolving environmental considerations and sustainability imperatives, our research bolsters the knowledge foundation necessary for shaping resilient and ecologically responsible construction practices. By embracing the knowledge synthesized from our study, the authors collectively contribute to the evolution of construction materials that stand the test of time and the challenges of diverse environments.

Author Contributions

Conceptualization, E.S.T., J.K. and J.A.B.; methodology, E.S.T., J.K. and J.A.B.; software, E.S.T. and J.K., validation, E.S.T., J.K. and J.A.B.; formal analysis, E.S.T. and J.A.B.; investigation, E.S.T., J.K. and J.A.B.; resources, E.S.T. and J.K.; data curation, E.S.T.; writing—original draft preparation, E.S.T. and J.K.; writing—review and editing, E.S.T. and J.A.B.; visualization, E.S.T., J.K. and J.A.B.; supervision, E.S.T.; project administration, E.S.T.; funding acquisition, J.A.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data that support the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgments

The authors of this research are grateful to Haleh Rasekh, Soheil Jahandari, and Cherdsak Suksiripattanapong for their insights and assistance.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Bosoaga, A.; Masek, O.; Oakey, J.E. CO2 Capture Technologies for Cement Industry. Energy Procedia 2009, 1, 133–140. [Google Scholar] [CrossRef]
  2. Puertas, F.; Fernández-Jiménez, A. Mineralogical and microstructural characterisation of alkali-activated fly ash/slag pastes. Cem. Concr. Compos. 2003, 25, 287–292. [Google Scholar] [CrossRef]
  3. Naik, T.R. Sustainability of concrete construction. Pract. Period. Struct. Des. Constr. 2008, 13, 98–103. [Google Scholar] [CrossRef]
  4. Shaikh, F.U.A. Mechanical and durability properties of fly ash geopolymer concrete containing recycled coarse aggregates. Int. J. Sustain. Built Environ. 2016, 5, 277–287. [Google Scholar] [CrossRef]
  5. Aly, A.M.; El-Feky, M.S.; Kohail, M.; Nasr, E.-S.A.R. Performance of geopolymer concrete containing recycled rubber. Constr. Build. Mater. 2019, 207, 136–144. [Google Scholar] [CrossRef]
  6. Mirzababaei, M.; Karimiazar, J.; Sharifi Teshnizi, E.; Arjmandzadeh, R.; Bahmani, S.H. Effect of nano-additives on the strength and durability characteristics of marl. Minerals 2021, 11, 1119. [Google Scholar] [CrossRef]
  7. Belferrag, A.; Kriker, A.; Abboudi, S.; Tié Bi, S. Effect of granulometric correction of dune sand and pneumatic waste metal fibers on shrinkage of concrete in arid climates. J. Clean. Prod. 2016, 112, 3048–3056. [Google Scholar] [CrossRef]
  8. Belferrag, A.; Kriker, A.; Youcef, F.; Abboudi, S.; Tié Bi, S. Thermal Conductivity of Dune Sand Concrete Reinforced with Pneumatic Waste Metal Fibers. Int. J. Thermophys. 2022, 43, 140. [Google Scholar] [CrossRef]
  9. Qi, A.; Liu, X.; Wang, Z.; Chen, Z. Mechanical properties of the concrete containing ferronickel slag and blast furnace slag powder. Constr. Build. Mater. 2020, 231, 117120. [Google Scholar] [CrossRef]
  10. Amin, M.N.; Ahmad, W.; Khan, K.; Sayed, M.M. Mapping Research Knowledge on Rice Husk Ash Application in Concrete: A Scientometric Review. Materials 2022, 15, 3431. [Google Scholar] [CrossRef]
  11. Gerges, N.N.; Issa, C.A.; Sleiman, E.; Aintrazi, S.; Saadeddine, J.; Abboud, R.; Antoun, M. Eco-Friendly Optimum Structural Concrete Mix Design. Sustainability 2022, 14, 8660. [Google Scholar] [CrossRef]
  12. Sandanayake, M.; Bouras, Y.; Haigh, R.; Vrcelj, Z. Current sustainable trends of using waste materials in concrete—A decade review. Sustainability 2020, 12, 9622. [Google Scholar] [CrossRef]
  13. Karimizad, N.; Teshnizi, E.S.; Mahdad, M.; Karimiazar, J. Investigating the design features of CSG dams. JOJ Sci. 2020, 2, 60–66. [Google Scholar] [CrossRef]
  14. Sharifi Teshnizi, E.; Hoseini, Z.; Babakhani, P.; Mohamadi Anaie, H. Geodetic and Geotechnical Monitoring in Shallow and Urban Tunnels; Azarin Mehr: Tehran, Iran, 2021; ISBN 978-622-685544-0. [Google Scholar]
  15. Abharian, S.; Sarfarazi, V.; Rasekh, H.; Behzadinasab, M. Effects of concrete/gypsum bedding layers and their inclination angles on the tensile failure mechanism: Experimental and numerical studies. Case Stud. Constr. Mater. 2022, 17, e01272. [Google Scholar] [CrossRef]
  16. Ahmad, J.; Kontoleon, K.J.; Majdi, A.; Naqash, M.T.; Deifalla, A.F.; Ben Kahla, N.; Isleem, H.F.; Qaidi, S.M.A. A Comprehensive Review on the Ground Granulated Blast Furnace Slag (GGBS) in Concrete Production. Sustainability 2022, 14, 8783. [Google Scholar] [CrossRef]
  17. Cui, Y.; Gao, K.; Zhang, P. Experimental and statistical study on mechanical characteristics of geopolymer concrete. Materials 2020, 13, 1651. [Google Scholar] [CrossRef]
  18. Chithambaram, S.J.; Kumar, S.; Prasad, M.M. Thermo-mechanical characteristics of geopolymer mortar. Constr. Build. Mater. 2019, 213, 100–108. [Google Scholar] [CrossRef]
  19. Amin, M.; Elsakhawy, Y.; Abu el-hassan, K.; Abdelsalam, B.A. Behavior evaluation of sustainable high strength geopolymer concrete based on fly ash, metakaolin, and slag. Case Stud. Constr. Mater. 2022, 16, e00976. [Google Scholar] [CrossRef]
  20. Rashad, A.M.; Ezzat, M.; ElNagar, A.M.; El-Nashar, M.H. Valorization of limestone powder as an additive for fly ash geopolymer cement under the effect of the simulated tidal zone and seawater attack. Constr. Build. Mater. 2023, 369, 130616. [Google Scholar] [CrossRef]
  21. Gultekin, A.; Ramyar, K. Investigation of high-temperature resistance of natural pozzolan-based geopolymers produced with oven and microwave curing. Constr. Build. Mater. 2023, 365, 130059. [Google Scholar] [CrossRef]
  22. Tan, J.; Dan, H.; Ma, Z. Metakaolin based geopolymer mortar as concrete repairs: Bond strength and degradation when subjected to aggressive environments. Ceram. Int. 2022, 48, 23559–23570. [Google Scholar] [CrossRef]
  23. Lăzărescu, A.V.; Ionescu, B.A.; Hegyi, A.; Florean, C. Alkali-activated fly ash based geopolymer paving blocks: Green materials for future conservation of resources. Int. J. Conserv. Sci. 2022, 13, 175–186. [Google Scholar]
  24. Li, Z.; Lu, T.; Liang, X.; Dong, H.; Ye, G. Mechanisms of autogenous shrinkage of alkali-activated slag and fly ash pastes. Cem. Concr. Res. 2020, 135, 106107. [Google Scholar] [CrossRef]
  25. Mohammadifar, L.; Miraki, H.; Rahmani, A.; Jahandari, S.; Mehdizadeh, B.; Rasekh, H.; Samadi, P.; Samali, B. Properties of Lime-Cement Concrete Containing Various Amounts of Waste Tire Powder under Different Ground Moisture Conditions. Polymers 2022, 14, 482. [Google Scholar] [CrossRef] [PubMed]
  26. Hashemi, H.; Yazdi, A.; Teshnizi, E.S. Improvement of collapsing problematic soils on the sabzevar-mashhad railway route (northeast of Iran) using traditional additives. Nexo Rev. Cient. 2023, 36, 383–403. [Google Scholar] [CrossRef]
  27. Hardjito, D.; Rangan, B.V. Development and Properties of Low-Calcium Fly Ash-Based Geopolymer Concrete; Research Report GC 1; Faculty of Engineering Curtin University of Technology: Perth, Australia, 2005; p. 103. [Google Scholar]
  28. Hadi, M.N.S.; Al-Azzawi, M.; Yu, T. Effects of fly ash characteristics and alkaline activator components on compressive strength of fly ash-based geopolymer mortar. Constr. Build. Mater. 2018, 175, 41–54. [Google Scholar] [CrossRef]
  29. van Jaarsveld, J.G.S.; Van Deventer, J.S.J. Effect of the alkali metal activator on the properties of fly ash-based geopolymers. Ind. Eng. Chem. Res. 1999, 38, 3932–3941. [Google Scholar] [CrossRef]
  30. Van Jaarsveld, J.G.S.; Van Deventer, J.S.J.; Schwartzman, A. The potential use of geopolymeric materials to immobilise toxic metals: Part II. Material and leaching characteristics. Miner. Eng. 1999, 12, 75–91. [Google Scholar] [CrossRef]
  31. Alouani, M.E.L.; Alehyen, S.; Achouri, M.E.L.; Hajjaji, A.; Ennawaoui, C.; Taibi, M. Influence of the nature and rate of alkaline activator on the physicochemical properties of fly ash-based geopolymers. Adv. Civ. Eng. 2020, 2020, 8880906. [Google Scholar] [CrossRef]
  32. Panias, D.; Giannopoulou, I.P.; Perraki, T. Effect of synthesis parameters on the mechanical properties of fly ash-based geopolymers. Colloids Surfaces A Physicochem. Eng. Asp. 2007, 301, 246–254. [Google Scholar] [CrossRef]
  33. Sharma, P.K.; Singh, J.P.; Kumar, A. Effect of particle size on physical and mechanical properties of fly ash based geopolymers. Trans. Indian Inst. Met. 2019, 72, 1323–1337. [Google Scholar] [CrossRef]
  34. Kong, D.L.Y.; Sanjayan, J.G.; Sagoe-Crentsil, K. Factors affecting the performance of metakaolin geopolymers exposed to elevated temperatures. J. Mater. Sci. 2008, 43, 824–831. [Google Scholar] [CrossRef]
  35. Li, M.; Luo, R.; Qin, L.; Liu, H.; Duan, P.; Jing, W.; Zhang, Z.; Liu, X. High temperature properties of graphene oxide modified metakaolin based geopolymer paste. Cem. Concr. Compos. 2022, 125, 104318. [Google Scholar] [CrossRef]
  36. Palomo, A.; Grutzeck, M.W.; Blanco, M.T. Alkali-activated fly ashes: A cement for the future. Cem. Concr. Res. 1999, 29, 1323–1329. [Google Scholar] [CrossRef]
  37. Bakharev, T. Geopolymeric materials prepared using Class F fly ash and elevated temperature curing. Cem. Concr. Res. 2005, 35, 1224–1232. [Google Scholar] [CrossRef]
  38. Topark-Ngarm, P.; Chindaprasirt, P.; Sata, V. Setting time, strength, and bond of high-calcium fly ash geopolymer concrete. J. Mater. Civ. Eng. 2015, 27, 4014198. [Google Scholar] [CrossRef]
  39. Kuri, J.C.; Hosan, A.; Shaikh, F.U.A.; Biswas, W.K. The Effect of Recycled Waste Glass as a Coarse Aggregate on the Properties of Portland Cement Concrete and Geopolymer Concrete. Buildings 2023, 13, 586. [Google Scholar] [CrossRef]
  40. Dai, W.; Wang, Y. Silica Fume Enhances the Mechanical Strength of Alkali-Activated Slag/Fly Ash Pastes Subjected to Elevated Temperatures. Fire 2023, 6, 252. [Google Scholar] [CrossRef]
  41. Wang, B.; Feng, H.; Huang, H.; Guo, A.; Zheng, Y.; Wang, Y. Bonding Properties between Fly Ash/Slag-Based Engineering Geopolymer Composites and Concrete. Materials 2023, 16, 4232. [Google Scholar] [CrossRef]
  42. Zhang, P.; Sun, X.; Wang, F.; Wang, J. Mechanical properties and durability of geopolymer recycled aggregate concrete: A review. Polymers 2023, 15, 615. [Google Scholar] [CrossRef]
  43. Zhang, Y.; Chen, J.; Xia, J. Compressive Strength and Chloride Resistance of Slag/Metakaolin-Based Ultra-High-Performance Geopolymer Concrete. Materials 2022, 16, 181. [Google Scholar] [CrossRef] [PubMed]
  44. Al Bakri, A.M.M.; Kamarudin, H.; Bnhussain, M.; Rafiza, A.R.; Zarina, Y. Effect of Na2SiO3/NaOH ratios and NaOH molearities on compressive strength of flyash- based geopolymer. ACI Mater. J. 2012, 109, 503. [Google Scholar]
  45. Arunachelam, N.; Maheswaran, J.; Chellapandian, M.; Ozbakkaloglu, T. Effective Utilization of Copper Slag for the Production of Geopolymer Concrete with Different NaOH Molarity under Ambient Curing Conditions. Sustainability 2022, 14, 16300. [Google Scholar] [CrossRef]
  46. Sherwani, A.F.H.; Younis, K.H.; Arndt, R.W.; Pilakoutas, K. Performance of Self-Compacted Geopolymer Concrete Containing Fly Ash and Slag as Binders. Sustainability 2022, 14, 15063. [Google Scholar] [CrossRef]
  47. Sharifi Teshnizi, E.; Reisi Dehkordi, M.S.; Moaiedi Kia, A.; Jamgohari, Y. The Strategic Management of Ballast (Design, Maintenance); Supreme National Defense University: Tehran, Iran, 2021; ISBN 978-622-6350-21-1. [Google Scholar]
  48. Alanazi, H.; Hu, J.; Kim, Y.-R. Effect of slag, silica fume, and metakaolin on properties and performance of alkali-activated fly ash cured at ambient temperature. Constr. Build. Mater. 2019, 197, 747–756. [Google Scholar] [CrossRef]
  49. Zhu, Y.; Longhi, M.A.; Wang, A.; Hou, D.; Wang, H.; Zhang, Z. Alkali leaching features of 3-year-old alkali activated fly ash-slag-silica fume: For a better understanding of stability. Compos. Part B Eng. 2022, 230, 109469. [Google Scholar] [CrossRef]
  50. Supit, S.W.M.; Pandei, R.W. Effects of metakaolin on compressive strength and permeability properties of pervious cement concrete. J. Teknol. 2019, 81. [Google Scholar] [CrossRef]
  51. Saboo, N.; Shivhare, S.; Kori, K.K.; Chandrappa, A.K. Effect of fly ash and metakaolin on pervious concrete properties. Constr. Build. Mater. 2019, 223, 322–328. [Google Scholar] [CrossRef]
  52. Mohd Nasir, N.A.; Abu Bakar, N.; Safiee, N.A.; Abdul Aziz, F.N.A. Permeation-durability properties of metakaolin blended concrete containing rubber. Eur. J. Environ. Civ. Eng. 2022, 26, 5113–5128. [Google Scholar] [CrossRef]
  53. Liang, X.; Ji, Y. Mechanical properties and permeability of red mud-blast furnace slag-based geopolymer concrete. SN Appl. Sci. 2021, 3, 23. [Google Scholar] [CrossRef]
  54. Moradikhou, A.B.; Safehian, M. Comparison of Mechanical Strengths and Resistance to Acidic Conditions, Permeability and Resistance to Elevated Temperatures of Geopolymer Concrete and Conventional Concrete. Adv. Res. Civ. Eng. 2021, 3, 27–37. [Google Scholar]
  55. Lim, Y.Y.; Pham, T.M.; Jangra, P.; Arora, S. Influence of Portland cement on performance of fine rice husk ash geopolymer concrete: Strength and permeability properties. Constr. Build. Mater. 2021, 300, 124321. [Google Scholar]
  56. Sharifi Teshnizi, E.; Arjmandzadeh, R.; Reisi Dehkordi, M.S.; Jollaie, A. Introduction to Building Materials and Concrete Technology; Sokhanvaran Publisher: Tehran, Iran, 2019; ISBN 978-622-215-207-9. [Google Scholar]
  57. Sharifi Teshnizi, E.; O’Kelly, B.C.; Karimiazar, J.; Moosazadeh, S.; Arjmandzadeh, R.; Pani, A. Effects of cement kiln dust on physicochemical and geomechanical properties of loess soil, Semnan Province, Iran. Arab. J. Geosci. 2022, 15, 1482. [Google Scholar] [CrossRef]
  58. Nath, P.; Sarker, P.K. Effect of GGBFS on setting, workability and early strength properties of fly ash geopolymer concrete cured in ambient condition. Constr. Build. Mater. 2014, 66, 163–171. [Google Scholar] [CrossRef]
  59. Wongpa, J.; Kiattikomol, K.; Jaturapitakkul, C.; Chindaprasirt, P. Compressive strength, modulus of elasticity, and water permeability of inorganic polymer concrete. Mater. Des. 2010, 31, 4748–4754. [Google Scholar] [CrossRef]
  60. Law, D.W.; Adam, A.A.; Molyneaux, T.K.; Patnaikuni, I.; Wardhono, A. Long term durability properties of class F fly ash geopolymer concrete. Mater. Struct. 2015, 48, 721–731. [Google Scholar] [CrossRef]
  61. Amran, M.; Debbarma, S.; Ozbakkaloglu, T. Fly ash-based eco-friendly geopolymer concrete: A critical review of the long-term durability properties. Constr. Build. Mater. 2021, 270, 121857. [Google Scholar] [CrossRef]
  62. Swanepoel, J.C.; Strydom, C.A. Utilisation of fly ash in a geopolymeric material. Appl. Geochem. 2002, 17, 1143–1148. [Google Scholar] [CrossRef]
  63. Ma, Y.; Ye, G. The shrinkage of alkali activated fly ash. Cem. Concr. Res. 2015, 68, 75–82. [Google Scholar] [CrossRef]
  64. Rangan, B.V. Mix design and production of flyash based geopolymer concrete. Indian Concr. J. 2008, 82, 7–15. [Google Scholar]
  65. Afshar, A.; Jahandari, S.; Rasekh, H.; Rahmani, A.; Saberian, M. Effects of Different Coatings, Primers, and Additives on Corrosion of Steel Rebars. Polymers 2023, 15, 1422. [Google Scholar] [CrossRef] [PubMed]
  66. Neupane, K.; Chalmers, D.; Kidd, P. High-strength geopolymer concrete-properties, advantages and challenges. Adv. Mater. 2018, 7, 15–25. [Google Scholar] [CrossRef]
  67. Naghizadeh, A.; Ekolu, S.O. Method for comprehensive mix design of fly ash geopolymer mortars. Constr. Build. Mater. 2019, 202, 704–717. [Google Scholar] [CrossRef]
  68. Abdellatief, M.; Alanazi, H.; Radwan, M.K.H.; Tahwia, A.M. Multiscale characterization at early ages of ultra-high performance geopolymer concrete. Polymers 2022, 14, 5504. [Google Scholar] [CrossRef]
  69. John, S.K.; Nadir, Y.; Girija, K. Effect of source materials, additives on the mechanical properties and durability of fly ash and fly ash-slag geopolymer mortar: A review. Constr. Build. Mater. 2021, 280, 122443. [Google Scholar] [CrossRef]
  70. Kotop, M.A.; El-Feky, M.S.; Alharbi, Y.R.; Abadel, A.A.; Binyahya, A.S. Engineering properties of geopolymer concrete incorporating hybrid nano-materials. Ain Shams Eng. J. 2021, 12, 3641–3647. [Google Scholar] [CrossRef]
  71. Shilar, F.A.; Ganachari, S.V.; Patil, V.B.; Khan, T.M.Y.; Almakayeel, N.M.; Alghamdi, S. Review on the relationship between nano modifications of geopolymer concrete and their structural characteristics. Polymers 2022, 14, 1421. [Google Scholar] [CrossRef]
  72. Abd, D.M.; Al-Khalid, H. Fatigue Characterization of WMA and Modeling Using Artificial Neural Networks. J. Mater. Civ. Eng. 2022, 34, 4021467. [Google Scholar] [CrossRef]
  73. Nematollahi, B.; Sanjayan, J.; Ahmed Shaikh, F.U. Tensile strain hardening behavior of PVA fiber-reinforced engineered geopolymer composite. J. Mater. Civ. Eng. 2015, 27, 4015001. [Google Scholar] [CrossRef]
  74. Sata, V.; Sathonsaowaphak, A.; Chindaprasirt, P. Resistance of lignite bottom ash geopolymer mortar to sulfate and sulfuric acid attack. Cem. Concr. Compos. 2012, 34, 700–708. [Google Scholar] [CrossRef]
  75. ASTM C33/C33M; Standard Specification for Concrete Aggregates. ASTM: West Conshohocken, PA, USA, 2017.
  76. Alanazi, H.; Yang, M.; Zhang, D.; Gao, Z. Bond strength of PCC pavement repairs using metakaolin-based geopolymer mortar. Cem. Concr. Compos. 2016, 65, 75–82. [Google Scholar] [CrossRef]
  77. C109/C109M; Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens). ASTM: West Conshohocken, PA, USA, 2016.
  78. ASTM C267-97; Standard Test Methods for Chemical Resistance of Mortars, Grouts and Monolithic Surfacings and Polymer Concretes. ASTM: West Conshohocken, PA, USA, 1997.
  79. ASTM C1012-95a; Standard Test Method for Length Change of Hydroulic-Cement Mortars Exposed to a Sulfate Solution. ASTM: West Conshohocken, PA, USA, 2004; pp. 450–456.
  80. ASTM C157; Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete. ASTM: West Conshohocken, PA, USA, 2010.
  81. Oelkers, E.H. General kinetic description of multioxide silicate mineral and glass dissolution. Geochim. Cosmochim. Acta 2001, 65, 3703–3719. [Google Scholar] [CrossRef]
  82. Chen, K.; Wu, D.; Yi, M.; Cai, Q.; Zhang, Z. Mechanical and durability properties of metakaolin blended with slag geopolymer mortars used for pavement repair. Constr. Build. Mater. 2021, 281, 122566. [Google Scholar] [CrossRef]
  83. Hartman, R.L.; Fogler, H.S. Reaction kinetics and mechanisms of zeolite dissolution in hydrochloric acid. Ind. Eng. Chem. Res. 2005, 44, 7738–7745. [Google Scholar] [CrossRef]
  84. Hartman, R.L.; Fogler, H.S. Understanding the dissolution of zeolites. Langmuir 2007, 23, 5477–5484. [Google Scholar] [CrossRef] [PubMed]
  85. Jamieson, H.L.; Yin, H.; Waller, A.; Khosravi, A.; Lind, M.L. Impact of acids on the structure and composition of Linde Type A zeolites for use in reverse osmosis membranes for recovery of urine-containing wastewaters. Microporous Mesoporous Mater. 2015, 201, 50–60. [Google Scholar] [CrossRef]
  86. Bakharev, T. Resistance of geopolymer materials to acid attack. Cem. Concr. Res. 2005, 35, 658–670. [Google Scholar] [CrossRef]
  87. Ariffin, M.A.M.; Bhutta, M.A.R.; Hussin, M.W.; Mohd Tahir, M.; Aziah, N. Sulfuric acid resistance of blended ash geopolymer concrete. Constr. Build. Mater. 2013, 43, 80–86. [Google Scholar] [CrossRef]
  88. Deb, P.S.; Sarker, P.K.; Barbhuiya, S. Sorptivity and acid resistance of ambient-cured geopolymer mortars containing nano-silica. Cem. Concr. Compos. 2016, 72, 235–245. [Google Scholar] [CrossRef]
  89. Sturm, P.; Gluth, G.J.G.; Jäger, C.; Brouwers, H.J.H.; Kühne, H.C. Sulfuric acid resistance of one-part alkali-activated mortars. Cem. Concr. Res. 2018, 109, 54–63. [Google Scholar] [CrossRef]
  90. Liu, X.; Jiang, J.; Zhang, H.; Li, M.; Wu, Y.; Guo, L.; Wang, W.; Duan, P.; Zhang, W.; Zhang, Z. Thermal stability and microstructure of metakaolin-based geopolymer blended with rice husk ash. Appl. Clay Sci. 2020, 196, 105769. [Google Scholar] [CrossRef]
  91. Saridemir, M.; Severcan, M.H.; Ciflikli, M.; Celikten, S.; Ozcan, F.; Atis, C.D. The influence of elevated temperature on strength and microstructure of high strength concrete containing ground pumice and metakaolin. Constr. Build. Mater. 2016, 124, 244–257. [Google Scholar] [CrossRef]
  92. Hussin, M.W.; Bhutta, M.A.R.; Azreen, M.; Ramadhansyah, P.J.; Mirza, J. Performance of blended ash geopolymer concrete at elevated temperatures. Mater. Struct. Constr. 2015, 48, 709–720. [Google Scholar] [CrossRef]
  93. Akca, A.H.; Zihnioǧlu, N.Ö. High performance concrete under elevated temperatures. Constr. Build. Mater. 2013, 44, 317–328. [Google Scholar] [CrossRef]
  94. Alexander, A.E.; Shashikala, A.P. Studies on the microstructure and durability characteristics of ambient cured FA-GGBS based geopolymer mortar. Constr. Build. Mater. 2022, 347, 128538. [Google Scholar] [CrossRef]
  95. Payakaniti, P.; Chuewangkam, N.; Yensano, R.; Pinitsoontorn, S.; Chindaprasirt, P. Changes in compressive strength, microstructure and magnetic properties of a high-calcium fly ash geopolymer subjected to high temperatures. Constr. Build. Mater. 2020, 265, 120650. [Google Scholar] [CrossRef]
  96. Rashad, A.M. Metakaolin as cementitious material: History, scours, production and composition-A comprehensive overview. Constr. Build. Mater. 2013, 41, 303–318. [Google Scholar] [CrossRef]
  97. Klima, K.M.; Schollbach, K.; Brouwers, H.J.H.; Yu, Q. Enhancing the thermal performance of Class F fly ash-based geopolymer by sodalite. Constr. Build. Mater. 2022, 314, 125574. [Google Scholar] [CrossRef]
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Figure 1. Flowchart of experimental testing program.
Figure 1. Flowchart of experimental testing program.
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Figure 2. (a) Furnace with a capacity of 1175 °C, (b) applying an unconfined compression strength to sample after thermal heating in oven, and (c) broken samples.
Figure 2. (a) Furnace with a capacity of 1175 °C, (b) applying an unconfined compression strength to sample after thermal heating in oven, and (c) broken samples.
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Figure 3. (a) The weight loss percent after 7 days in acidic water with metakaoline, zeolite, slag, and cement. (b) The weight loss percent after 14 days in acidic water with metakaoline, zeolite, slag, and cement. (c) The weight loss percent after 21 days in acidic water with metakaoline, zeolite, slag, and cement. (d) The weight loss percent after 28 days in acidic water with metakaoline, zeolite, slag, and cement. (e) The weight loss percent after 90 days in acidic water with metakaoline, zeolite, slag, and cement.
Figure 3. (a) The weight loss percent after 7 days in acidic water with metakaoline, zeolite, slag, and cement. (b) The weight loss percent after 14 days in acidic water with metakaoline, zeolite, slag, and cement. (c) The weight loss percent after 21 days in acidic water with metakaoline, zeolite, slag, and cement. (d) The weight loss percent after 28 days in acidic water with metakaoline, zeolite, slag, and cement. (e) The weight loss percent after 90 days in acidic water with metakaoline, zeolite, slag, and cement.
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Figure 4. The compressive strengths of samples in acidic and tap water: (a) 28 days; (b) 90 days.
Figure 4. The compressive strengths of samples in acidic and tap water: (a) 28 days; (b) 90 days.
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Figure 5. The 28-day compressive strength and weight loss of samples in different concentrations of KOH: (a) 8 M; (b) 12 M; (c) 14 M; (d) 16 M.
Figure 5. The 28-day compressive strength and weight loss of samples in different concentrations of KOH: (a) 8 M; (b) 12 M; (c) 14 M; (d) 16 M.
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Figure 6. The 90-day compressive strength and weight loss of samples in different concentrations of KOH: (a) 8 M; (b) 12 M; (c) 14 M; (d) 16 M.
Figure 6. The 90-day compressive strength and weight loss of samples in different concentrations of KOH: (a) 8 M; (b) 12 M; (c) 14 M; (d) 16 M.
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Figure 7. The compressive strength of standard mortar in (a) elevated temperature and (b) sulfuric acidic for up to 90 days.
Figure 7. The compressive strength of standard mortar in (a) elevated temperature and (b) sulfuric acidic for up to 90 days.
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Figure 8. SEM images of mortar with (a) cement after 500 °C, (b) slag after 500 °C, (c) metakaolin after 500 °C, and (d) zeolite after 500 °C.
Figure 8. SEM images of mortar with (a) cement after 500 °C, (b) slag after 500 °C, (c) metakaolin after 500 °C, and (d) zeolite after 500 °C.
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Table 1. The chemical properties of metakaolin, zeolite, slag, and cement.
Table 1. The chemical properties of metakaolin, zeolite, slag, and cement.
Component (%)Al2O3SiO2CaOFe2O3Na2OMgOSO3K2OL.O.I *
Metakaolin40.4356.20.170.590.040.32-0.731.52
Zeolite8.958.8510.86.00.23-1.35.328.6
Slag11.3236.236.90.630.4211.312.730.49-
Cement5.5323.1358.953.510.331.182.190.854.33
* Loss of ignition.
Table 2. The physical properties of aggregates.
Table 2. The physical properties of aggregates.
Fineness ModulusDensity (g/cm3)Specific GravityCumulative Mass Percentage (%)
>2.38 mm2.38–1.181.18–0.60.6–0.30.3–0.15<0.15 mm
2.251.692.65019.554.568.180.1100
Table 3. The mix designs of the samples.
Table 3. The mix designs of the samples.
Mix DesignGeopolymer (gr)KOH
(Powder)
(g)		Na2SiO3
(Powder)
(g)		Water
(g)		Sand
(g)
MK-1Metakaolin8002021053602200
MK-28003031053602200
MK-38003541053602200
MK-48004041053602200
MZ-5Zeolite8002021053602200
MZ-68003031053602200
MZ-78003541053602200
MZ-88004041053602200
MS-9Slag8002021053602200
MS-108003031053602200
MS-118003541053602200
MS-128004041053602200
Standard mortarCement800--3602200
MC-138002021053602200
MC-148003031053602200
MC-158003541053602200
MC-168004041053602200
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Teshnizi, E.S.; Karimiazar, J.; Baldovino, J.A. Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials. Sustainability 2023, 15, 14407. https://doi.org/10.3390/su151914407

AMA Style

Teshnizi ES, Karimiazar J, Baldovino JA. Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials. Sustainability. 2023; 15(19):14407. https://doi.org/10.3390/su151914407

Chicago/Turabian Style

Teshnizi, Ebrahim Sharifi, Jafar Karimiazar, and Jair Arrieta Baldovino. 2023. "Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials" Sustainability 15, no. 19: 14407. https://doi.org/10.3390/su151914407

APA Style

Teshnizi, E. S., Karimiazar, J., & Baldovino, J. A. (2023). Effect of Acid and Thermo-Mechanical Attacks on Compressive Strength of Geopolymer Mortar with Different Eco-Friendly Materials. Sustainability, 15(19), 14407. https://doi.org/10.3390/su151914407

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