Self-compacting ultra-high-performance geopolymer concrete: influence of alkaline activator and curing regime

Environmental impact assessment of fly ash and silica fume based geopolymer concrete

In this study, the effects of magnesium sulfate on the mechanical performance and the durability of confined and unconfined geopolymer concrete (GPC) specimens were investigated. The carbon and basalt fiber reinforced polymer (FRP) fabrics with 1-layer and 3-layers were used to evaluate the performances of the specimens under static and cyclic loading in the ambient and magnesium sulfate environments. In addition, the use of FRP materials as a rehabilitation technique was also studied. For the geopolymerization process of GPC specimens, the alkaline activator has selected a mixture of sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) with a ratio (Na2SiO3/NaOH) of 2.5. In addition to GPC specimens, an ordinary concrete (NC) specimens were also produced as a reference specimens and some of the GPC and NC specimens were immersed in 5% magnesium sulfate solutions. The mechanical performance and the durability of the specimens were evaluated by visual appearance, weight change, static and cyclic loading, and failure modes of the specimens under magnesium sulfate and ambient environments. In addition, the microscopic changes of the specimens due to sulfate attack were also assessed by scanning electron microscopy (SEM) to understand the macroscale behavior of the specimens. Results indicated that geopolymer specimens produced with nano-silica and fly ash showed superior performance than the NC specimens in the sulfate environment. In addition, confined specimens with FRP fabrics significantly improved the compressive strength, ductility and durability resistance of the specimens and the improvement was found higher with the increased number of FRP layers. Specimens wrapped with carbon FRP fabrics showed better mechanical performance and durability properties than the specimens wrapped with basalt FRP fabrics. Both FRP materials can be used as a rehabilitation material in the sulfate environment.

Geopolymer concrete has developed as a potential alternative to ordinary Portland cement-based concrete, wherein various industrial by-products have been converted as beneficial spin-offs. Apart from appropriate compressive strength in the construction sector worldwide, the durability, sound absorption, thermal conductivity, and weight of concrete are also major concerns. Lightweight geopolymer concretes have gained attention because of their superior strength, durability, lower environmental impact, and sustainable characteristics. In this view, the current study examined the feasibility of using sawdust as a natural fine and coarse aggregate substitution in fly ash (FA)-granulated blast furnace slag (GBFS) based geopolymer concrete. Four mixes with a different percentage of sawdust (25, 50, 75, and 100) substituting natural aggregate were designed to examine the effects of sawdust on fresh and hardened features of geopolymer concrete compared to those conventional FA-GBFS-based geopolymer concrete with natural aggregate. Sodium silicate (NS) and sodium hydroxide (NH) (with NS/NH ratio of 0.75) were utilized to dissolve the alumina silicate from FA and GBFS. Informational models were developed using an experimental dataset to estimate the compressive strength of geopolymer concrete mix designs. Besides, using the weight of the developed network, a global sensitivity (GS) analysis was developed to identify the sensitivity of compressive strength to the waste sawdust content. Test results confirmed that by substituting natural aggregate with 100% sawdust, there was around a 35% decrease in compressive strength. Nevertheless, the sound absorption coefficient was increased by an average of 38% in frequencies range between 1800 and 2500 HZ, and thermal conductivity decreased by around 4.5 times once the natural aggregate was substituted by 100% sawdust.

This study explores the potential of calcium carbide residue (CCR) as an alternative activator for ground granulated blast-furnace slag (GGBS) to reduce reliance on ordinary Portland cement (OPC) in mortar production. A series of OPC-GGBS-CCR ternary binders were prepared and evaluated for their fresh and mechanical properties over various curing periods. The findings showed that mortars’ fresh and mechanical characteristics were significantly improved with longer curing times, suggesting CCR’s potential to efficiently activate GGBS, thereby benefiting the environment and economy. Significant enhancements in compressive strengths were observed after 7 days of curing, with increases of 44%, and 69–144% for OPC and OPC-GGBS-CCR ternary binders, respectively, while the utilization of activated binders led to flexural strength growth compared to three days of curing, with improvements of 70–173% for OPC-GGBS-CCR ternary binders, respectively. Microstructural analyses confirmed accelerated hydration and increased product formation due to CCR’s calcium content. An optimal mix ratio of OPC:GGBS:CCR = 1:1:0.5 demonstrated mechanical properties comparable to OPC mortars after 28 days, highlighting CCR’s potential for sustainable cementitious materials.

Need of construction is increasing due to increase in population growth rate. The geopolymer concrete is eco‐friendly than ordinary concrete. Current experimental investigation was conducted on ordinary and geopolymer concrete using nondestructive testing (NDT) tests like ultrasonic pulse velocity (UPV) test and rebound hammer (RH) test. Cube specimens of dimensions 150 mm × 150 mm × 150 mm are used to conduct these tests at 7, 14, and 28 days. Proportions considered for concrete are cement‐fly ash‐river sand (100‐0‐100% and 60‐40‐100%), cement‐fly ash‐robo sand (100‐0‐100% and 60‐40‐100%) whereas geopolymer concrete fly ash‐metakaolin is taken in proportions of 100‐0%, 60‐40%, and 50‐50%. Alkaline activators (sodium hydroxide and sodium silicate with molarity 12M) were used in preparing geopolymer concrete. The major objective of the current study is to obtain relation between compressive strength of concrete and UPV values.

This paper describes the research on bond behavior of plain reinforcing bars in geopolymer and normal concrete. The geopolymer concrete in this research was made of class F fly ash taken from Tanjung Jati Electric Steam Power Plant (PLTU) with Sodium Hydroxide (NaOH) and Sodium Silicate (Na2SiO3) as alkaline activator, added in the mixture. The effect of bar size was studied by varying the bar diameter in range 10 mm to 19 mm. Each bar was casted in the center of concrete blocks made of geopolymer as well as normal concrete. Pull-out tests were carried out to the specimens that have reached 28 days of age. The test results show that the bond behavior of geopolymer concrete differs substantially from normal concrete, where geopolymer concrete has a higher bond strength when compared to normal concrete with identical concrete strengths.

Strength development and durability of alkali-activated fly ash mortar with calcium carbide residue as additive

One of the most important challenges in developing the concrete industry is to use sustainable materials that are able to improve concrete properties. Magnetized water (MW) is a type of water that can replace tap water (TW) in conventional concrete and enhance its mechanical properties. However, the performance of MW in geopolymer concrete has not been well investigated up to now. The goal of this study is to measure the effect of using an alkaline activator (AA) made of MW on the mechanical properties and durability of fly ash (FA)-based geopolymer concrete. The AA was a mixture of sodium hydroxide (SH) solution and sodium silicate (SS) solution. Eighteen geopolymer concrete mixes were tested for several fresh, hardened, and durability properties. Of these mixes, nine were prepared with AA made of MW and the other nine were the same but prepared with AA made of TW. The preparation of MW was simply carried out by passing TW across permanent magnets of 1.6 Tesla, and then 1.4 Tesla intensities for 150 cycles. The MW-based AA properties were analyzed and compared to those of the conventional TW-based AA. Several mechanical and durability properties were measured. Scanning electronic microscopy (SEM) analysis was also conducted on selected mixes. The outcomes of the hardened concrete tests demonstrated that while using MW to prepare AA solution contained SH with a molarity of 16 M, an SS/SH ratio of 2, an AA/C ratio of 0.4, a W/C ratio of 10%, and a curing temperature of 115 °C could display the best outcomes in this study when used in geopolymer concrete. Using MW in a geopolymer concrete AA could increase its slump by up to 100% compared to that made of TW. Using MW in the AA enhanced the compressive strength by up to 193%, 192%, and 124% after 7, 28, and 56 days, respectively. The SEM analysis showed that using MW clearly enhanced the surface morphology of geopolymer concrete. The proposed geopolymer concrete made using the MW-based AA in this study sheds the light on a new class of eco-friendly concrete that could possibly be used in many structural applications.

Commercial sodium hydroxide (NaOH) and sodium silicate (SS) are commonly used as alkaline activators in geopolymer concrete production despite concerns about their availability and associated CO2 emissions. This study employs an alternative alkaline activator (AA) synthesized from a sodium silicate alternative (SSA) solution derived from rice husk ash (RHA) and a 10 M sodium hydroxide solution. The initial phase established an optimal water-to-binder (W/B) ratio of 0.50, balancing workability and structural performance. Subsequent investigations explored the influence of the alkali/precursor (A/P) ratio on geopolymer concrete properties. A control mix uses ordinary Portland cement (OPC), while ground granulated blast-furnace slag (GGBS)-based geopolymer concrete—GPC mixes (GPC1, GPC2, GPC3, GPC4) vary the A/P ratios (0.2, 0.4, 0.6, 0.8) with a 1:1 ratio of sodium silicate to sodium hydroxide (SS: SH). The engineering performance was evaluated through a slump test, and unconfined compressive strength (UCS) and tensile splitting (TS) tests in accordance with the appropriate standards. The geopolymer mixes, excluding GPC3, offer suitable workability; UCS and TS, though lower than the control mix, peak at an A/P ratio of 0.4. Despite lower mechanical strength than OPC, geopolymers’ environmental benefits make them a valuable alternative. GPC2, with a 0.4 A/P ratio and 0.5 W/B (water to binder) ratio, is recommended for balanced workability and structural performance. Future research should focus on enhancing the mechanical properties of geopolymer concrete for sustainable, high-performance mixtures.

Strength performance of alkali activated structural lightweight geopolymer concrete exposed to acid

This study summarised the recent achievement in developing fiber reinforced geopolymer concrete. The factor of replacing Ordinary Portland Cement (OPC) which is due to the emission of carbon dioxide that pollutes the environment globally is well discussed. The introduction towards metakaolin is presented. Besides, the current research trend involved in geopolymer also has been reviewed for the current 20 years to study the interest of researchers over the world by year. Factors that contribute to the frequency of geopolymer research are carried out which are cost, design, and the practicality of the application for geopolymer concrete. Besides, the importance of steel fibers addition to the geopolymer concrete is also well discussed. The fundamental towards metakaolin has been introduced including the source of raw material, which is calcined kaolin, calcined temperature, chemical composition, geopolymerisation process, and other properties. Alkali activators which are mixing solution between sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) have been reviewed. The mechanical properties of fibers reinforced metakaolin-based geopolymer concrete which is compressive and flexural are thoroughly reviewed. The compressive and flexural strength of fiber-reinforced metakaolin geopolymer concrete shows some improvement to the addition of steel fibers. The reviews in this field demonstrate that reinforcement of metakaolin geopolymer concrete by steel fibers shows improvement in mechanical performance.

A comprehensive review of nano materials in geopolymer concrete: Impact on properties and performance

This study aims to reduce the usage of ordinary Portland cement and to improve the usage of the other by-product such as fly ash. This product helps in reducing the carbon emissions caused by the conventional concrete. This also produces high strength concretes with the use of nominal mixes when compared to conventional concrete. An experimental work conducted by casting fourteen trial geopolymer concrete mixes. Those are designed to study the effects of various parameters on properties of fly ash-based geopolymer concrete especially the compressive strength. These parameters were alkaline liquid to fly ash ratio, the ratio of sodium silicate solution to the sodium hydroxide solution, the concentration of sodium hydroxide solution, the dosage of superplasticizer, rest period and temperature degree. All these parameters studied on compressive strength in three ages (1, 7, & 28) days. Study the microstructure of geopolymer concrete and compare the results with normal concrete by conducted the tests SEM increasing of curing temperature, concentration of sodium hydroxide, sodium silicate solutions, and rest period, lead to increase in compressive strength. While the increase, by dosage of superplasticizer, alkaline liquid to fly ash, leads to decrease compressive strength. Also, SEM test results show the difference in microstructure between geopolymer and normal concrete.

The construction industry significantly contributes to global carbon emissions, primarily due to the extensive use of Ordinary Portland Cement (OPC) in conventional concrete (CC). Cement manufacturing is energy-intensive and responsible for substantial CO₂ emissions, leading to environmental degradation and climate change. Additionally, conventional concrete exhibits durability challenges when exposed to aggressive environmental conditions such as sulfate attack, acid exposure, and high temperatures. In this context, Geopolymer Concrete (GPC), synthesized using industrial by-products such as fly ash and Ground Granulated Blast Furnace Slag (GGBS) activated by alkaline solutions, has emerged as a promising sustainable alternative. This research presents an AI-based research and experimental analytical assessment of the environmental and economic impacts of fly ash utilization in building projects by comparing GPC with conventional M-30 grade concrete. The experimental methodology involves the design and development of M-30 grade GPC using fly ash and GGBS as binder materials activated with sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃) solutions. Mechanical performance will be evaluated using compressive, split tensile, and flexural strength tests on cube, cylinder, and beam specimens. Durability assessment will include water absorption tests to evaluate porosity and permeability, acid and sulfate resistance tests to analyze chemical durability, and thermal resistance tests to assess performance under elevated temperatures. Furthermore, a comprehensive Life Cycle Assessment (LCA) will be conducted to quantify CO₂ emissions, embodied energy, and environmental impacts associated with both GPC and CC. AI-based analytical modeling techniques will be employed to predict performance trends, optimize mix proportions, and evaluate sustainability indicators. The proposed work aims to establish a comparative framework for assessing strength, durability, carbon footprint, and cost-effectiveness of GPC and CC. Expected outcomes include significant reduction in CO₂ emissions due to partial or complete replacement of OPC, improved resistance to aggressive environments, enhanced thermal stability, and long-term economic benefits through reduced maintenance and lifecycle costs. AI-driven analysis is anticipated to improve predictive accuracy and decision-making for sustainable construction practices. The study concludes by proposing geopolymer concrete as a technically viable, environmentally sustainable, and economically feasible alternative to conventional concrete for structural applications, particularly in M-30 grade construction, without compromising mechanical performance and durability.

SummaryThis paper presents the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures of 200, 400, 600 and 800 °C. The source material used in the geopolymer concrete in this study is low‐calcium fly ash according to ASTM C618 class F classification and is activated by sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solutions. The effects of molarities of NaOH, coarse aggregate sizes, duration of steam curing and extra added water on the compressive strength of geopolymer concrete at elevated temperatures are also presented. The results show that the fly‐ash‐based geopolymer concretes exhibited steady loss of its original compressive strength at all elevated temperatures up to 400 °C regardless of molarities and coarse aggregate sizes. At 600 °C, all geopolymer concretes exhibited increase of compressive strength relative to 400 °C. However, it is lower than that measured at ambient temperature. Similar behaviour is also observed at 800 °C, where the compressive strength of all geopolymer concretes are lower than that at ambient temperature, with only exception of geopolymer concrete containing 10 m NaOH. The compressive strength in the latter increased at 600 and 800 °C. The geopolymer concretes containing higher molarity of NaOH solution (e.g. 13 and 16 m) exhibit greater loss of compressive strength at 800 °C than that of 10 m NaOH. The geopolymer concrete containing smaller size coarse aggregate retains most of the original compressive strength of geopolymer concrete at elevated temperatures. The addition of extra water adversely affects the compressive strength of geopolymer concretes at all elevated temperatures. However, the extended steam curing improves the compressive strength at elevated temperatures. The Eurocode EN1994:2005 to predict the compressive strength of fly‐ash‐based geopolymer concretes at elevated temperatures agrees well with the measured values up to 400 °C. Copyright © 2014 John Wiley & Sons, Ltd.