Production of geopolymer concrete using natural pozzolan: A parametric study

Abstract. The manufacturing of cement for use in construction sites all over the world has resulted in tonnes of carbon dioxide being released. It is better to replace an alternative material such as geopolymer which contributes less carbon footprint than traditional Portland cement. Concrete is the most versatile building material, yet it has drawbacks in mechanical and physical properties, such as limited ductility, high water absorption, and low compressive strength. This study aims to determine the effect of the addition of composite fibers on the mechanical and physical properties of geopolymer concrete. In this research, the physical and mechanical properties of geopolymer concrete were investigated by mixing Class F fly ash with an alkaline activator consisting of sodium hydroxide and sodium silicate. Steel fiber and polypropylene cut into 2 mm fiber were added into the geopolymer concrete as reinforcement. Various volume percentages ranging from 0% to 2% are used. Density, water absorption, workability, and compression testing were performed on all geopolymer concrete reinforced with steel and polypropylene fiber with varying volume percentages. The density of geopolymer concrete is similar to that of Ordinary Portland Cement (OPC), which is around 2400 kg/m3, and it has gradually increased with the inclusion of steel fiber, while more polypropylene fiber causes lesser density. With an increment of steel fiber and a decrement of polypropylene fiber, the result of water absorption percentage shows a decrement. Besides, the inclusion of steel fibers reduces the workability of geopolymer concrete. However, the addition of polypropylene fibers shows a higher workability. Plus, the inclusion of steel fiber and the reduction of polypropylene fiber improve the compressive strength.

Ferrochrome slag (FS) and ground granulated blast furnace slag (GGBFS) were used as resource material in geopolymer concrete mixtures. A mixture of 10 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as the activator. After the two different slag‐based geopolymer concrete (SGC) mixtures were prepared and molded. They were kept at 80°C for 24 hr, and then the SGC samples were cured in 23 ± 1°C water for 27 days. Samples that completed the curing times were exposed to the 300 freeze–thaw (F–T) cycles. The compressive strength, ultrasonic pulse velocity, relative dynamic elasticity modulus values, weight changes, and appearances of the SGC samples were examined at the end of every 50 F–T cycles. Scanning electron microscopy analysis was performed to examine the microstructure changes of the samples after 300 F–T cycles. As the GGBFS proportion in the SGC mix increased, the mechanical properties of the samples against the F–T effect increased. Samples containing 100% FS and 75% FS fell apart at the end of 150 and 200 F–T cycles, respectively. The deterioration of the geopolymer gel structures of the samples exposed to F–T was decreased with increasing GGBFS ratio in the mix.

The reliability of the Rapid Chloride Permeability Test (RCPT), ASTM C1202, for geopolymer concrete (GPC) is often debated, particularly due to the use of 60 V and the lack of a standardised rating scale tailored to GPC. Although prior studies have noted problems with RCPT in GPC and proposed partial remedies, a fully validated framework tailored to GPC is still lacking. Standardised testing conditions and clear links between RCPT results and chloride transport behaviour remain undeveloped. To this end, this study examines the effect of applied voltage on RCPT results and recommends a modified methodology to establish a suitable rating scale for GPC. Sixty GPC mixtures, characterised by varying mix designs and strengths, were assessed, and their key properties – compressive strength, conductivity, formation factor, and charge passed – were analysed in relation to chloride diffusion coefficients. The formation factor was incorporated to normalise pore solution conductivity, thereby enabling assessment of microstructural transport behaviour. Findings confirm that voltages above 10 V often cause premature test termination; therefore, 10 V is identified as the recommended upper operating voltage for reliable RCPT testing in GPC under the investigated conditions. Following these results, performance criteria for the modified RCPT and formation factor are proposed, providing a reliable basis for assessing chloride permeability in GPC. Additionally, prescriptive requirements are outlined to guide the selection of suitable GPC mixtures for specific applications. This study delivers a validated framework for reliable RCPT use in GPC, defining voltage, rating scale, and formation factor limits to enable standardisation and adoption in design codes. • Validated guidelines established for voltage selection in RCPT tailored to GPC • RCPT performance-based testing framework developed and validated for GPC • Introduced formation factor from pore conductivity as durability indicator • Proven OPC pore chemistry–RCPT relation inapplicable to GPC

This research discusses the compressive strength of geopolymers made from coffee grounds as an additional material in geo-polymer fly-ash based concrete. The research aims to design a geopolymer concrete mix based on coffee grounds and fly ash, determine the compressive strength of geopolymer concrete based on coffee grounds and fly ash, and identify the optimal percentage of coffee grounds in geopolymer concrete production. The study has limitations, such as a concrete strength of 35 MPa, testing at 7, 14, and 28 days, and the use of an alkali activator with a molarity of 8. The research method employed involved experiments conducted in the material and concrete laboratory with the variable percentage of coffee grounds ranging from 0% to 20%. The use of coffee powder in the geopolymer concrete mixture as a replacement for fly ash has an impact on reducing the slump value by up to 18.52 % and reducing the specific gravity of the concrete by up to 6.55%. However, the use of up to 10% coffee powder still produces compressive strength values above the minimum requirement for structural concrete compressive strength, namely 20 MPa. Thus, a mixture with 10% coffee grounds can still be used as an alternative construction material that is more economical and sustainable.

Comparative Study on Impact of Rice Husk Ash and Fly Ash in Concrete Mix Design for Different Grades of Concrete

Influence of engineering fibers on fresh and mechanical properties of geopolymer concrete

Geopolymer is an inorganic alumino-silicate product that shows good bonding properties. Geopolymer binders are used together with aggregates to produce geopolymer concrete which is an ideal building material for infrastructures. A by-product material such as fly ash is mixed together with an alkali to produce geopolymer. Current research on geopolymer concrete has shown potential of the material for construction of reinforced concrete structures. Structural performance of reinforced concrete depends on the bond between concrete and the reinforcing steel. Design provisions of reinforced concrete as a composite material are based on the bond strength between concrete and steel. Since geopolymer binder is chemically different from Ordinary Portland Cement (OPC) binder, it is necessary to understand the bond strength between geopolymer concrete and steel reinforcement for its application to reinforced concrete structures. Pull out test is commonly used to evaluate the bond strength between concrete and reinforcing steel. This paper describes the results of the pull out tests carried out to investigate the bond strength between fly ash based geopolymer concrete and steel reinforcing bars. Beam end specimens in accordance with the ASTM Standard A944 were used for the tests. In the experimental program, 24 geopolymer concrete and 24 OPC concrete specimens were tested for pull out. The concrete compressive strength varied from 25 to 55 MPa. The other test parameters were concrete cover and bar diameter. The reinforcing steel was 500 MPa steel deformed bars of 20 mm and 24 mm diameter. The concrete cover to bar diameter ratio varied from 1.71 to 3.62. It was found from the test results that the failure occurred by splitting of concrete in the region bonded with the steel bar, in both geopolymer and OPC concrete specimens. Comparison of the test results shows that geopolymer concrete has higher bond strength than OPC concrete. This suggests that the existing design equations for bond strength of OPC concrete with steel reinforcing bars can be conservatively used for calculation of bond strength of geopolymer concrete.

The information and communication revolution in the twentieth century has brought about massive changes in the living style and also economy. Although the quality of lives has been enhanced by these spectacular developments undoubtedly during the modern times, they have led to manifold problems in disposal of e-wastes. The annual generation of e-wastes globally is about 50 million tons, and according to recent studies, the quantity of e-wastes generated in India is 18.5 lakhs MT/year. Therefore, in order to protect the environment and create a sustainable livelihood, proper management of e-wastes is indispensible. Efforts are underway in the construction industry to use the non-metallic components of e-wastes, especially Printed Circuit Boards, as partial replacement for aggregates in concrete. A large portion of non-metallic materials in printed circuit boards (PCBs) are disposed off by disposal in landfill or combustion but it may lead to secondary pollution and wastage of resources. Geopolymer concretes have proved to greatly immobilise hazardous and radioactive wastes, thereby reducing their concentration and the impact on human and environment. Hence, this study aims to identify the possibilities of utilising the crushed PCBs as partial replacement for fine aggregates in Geopolymer concrete. It was observed that up to 30% replacement of crushed PCBs, the mechanical properties improved after which they were found to decrease. This increase in strength was significant at increased percentages (50–75%) of GGBFS replacement in Geopolymer concrete. It is thereby suggested from this study that utilisation of crushed PCBs in Geopolymer concrete will not only reduce the requirement for conventional fine aggregates but will also help in immobilising the heavy metals thereby affecting the conservation of natural resources.

Geopolymer concrete offers a promising alternative to traditional Portland cement concrete, exhibiting comparable mechanical and durability performance while reducing environmental impacts. However, achieving desirable properties in geopolymer concretes through heat curing remains challenging. This study proposes the use of an unsupervised Artificial Neural Network (ANN): Self-Organizing Map (SOM) to determine the optimal curing temperature of geopolymer concrete based on experimental datasets. The novelty of this study lies in utilizing SOM for clustering and pattern recognition to establish the relationship between curing temperatures and compressive strength, providing a novel data-driven methodology for enhancing material performance. Data on compressive strength at different curing temperatures were collected and used to train and validate SOM models. Fly ash based geopolymer concretes of size 100mm3 cubes were prepared in two sets of activators; sodium hydroxide (NaOH) and a combination of sodium silicate (Na2SiO¬3) with NaOH. These samples underwent curing under three conditions: ambient, 60° and 80° for 28 days. Clustering analysis generated by the SOM model provides valuable insights into the relationship between curing conditions, activator dosages, and compressive strength. Consequently, a cluster of mix proportion was developed, enabling the selection of specific curing conditions that result in targeted compressive strength. The results show that curing temperatures of 80°C offers optimal compressive strength ranging from 27MPa to 34MPa. This method introduces a novel "cluster mix proportion" for selecting curing parameters and demonstrates the potential of machine learning in advancing sustainable construction materials. The approach provides a distinct advantage by reducing reliance on trial-and-error methods, saving time and resources, and establishing a foundation for further exploration of data-driven techniques in cement and concrete research.

Mechanical properties of GPC are different compared over NSC; this is due to change in cracking behaviour under the application of load. Compressive strength, flexural strength, modulus of elasticity and in-plane shear strength are the important mechanical properties to be understood before it is used in practice. It has been observed that literatures available on in-plane shear strength of GPC are limited. The experimental investigation carried out in the present study is to study the in-plane shear strength of normal strength concrete (NSC) and geo polymer concrete (GPC) using push-off specimens. The grade of concrete and height of shear plane used are M30 and 100 mm, respectively. Dimensions of push-off specimen were 150 × 150 × 260 mm with two rectangular notches of 10 mm thick was cut, 100 mm apart along the longitudinal axis of loading and at equidistance from mid-depth. A total of 48 push-off specimens were tested (24 in each NSC and GPC, respectively), six push-off specimens with zero, one, two and three bars, respectively, crossing the shear plane. It was observed from experimental results that as the number of bars across shear plane increased the shear stress increased and in-plane shear strength of GPC was higher than NSC.

PurposeThe quest to reduce the cost of concrete which is a major construction input has prompted investigations into assessing the suitability of alternative sources of conventional materials. This paper aims to report the compressive strength and workability of lateritic gravel used as all-in aggregate for concrete production.Design/methodology/approachThree prescribed mixes from all-in aggregate concrete were compared with concrete from lateritic gravel. The paper investigated the variation in strength of four different mixes – 100: 0, 90: 10, 80: 20 and 70: 30 – when portions of the lateritic gravel were replaced with pit sand, respectively, using varying water cement ratios to achieve optimal workability.FindingsThe density and compressive strength of each cube was measured on the 7th and 28th test dates. An increase in slump and compressive strength was observed in the lateritic concrete, as portions of the lateritic gravel were replaced with sand. However, the rate of increase in the compressive strength tended to decrease with increase in part replacement of lateritic gravel with sand indicating that there was a threshold of percentage of sand increase after which the compressive strengths are likely to decrease. This work never reached this threshold, but it is estimated to be about 40 per cent.Research limitations/implicationsInvestigations focused on lateritic gravel sampled from two sites to represent samples from both the forest and savannah belt.Practical/implicationsLateritic gravel can be used as all-in aggregate for non-structural concrete.Originality/valueThe compressive strengths achieved were better than those for the available normal all-in aggregate used.

In this study, we investigated the feasibility of jarofix [a zinc (Zn) smelter by-product] as a potential geopolymer binder in soil stabilization for road applications. Different combinations of soil–jarofix (SJ) mixtures were prepared using sodium hydroxide (NaOH), sodium silicate (Na2SiO3), and a combination of NaOH + Na2SiO3 as alkali activators. Unconfined compressive strength (UCS) tests were performed to examine the mechanical performance of SJ mixtures, and the effects of the jarofix content, curing conditions, and curing time were investigated. Changes that occurred during the geopolymerization process were further corroborated using field-emission scanning electron microscope (FESEM) images and energy-dispersive X-ray spectroscopy (EDS) analysis. Durability tests were also performed to examine the weathering resistance of selected SJ mixtures against 12 cycles of alternating wetting and drying. Based on the experimental results, the compressive strength of bare soil was increased 8.8 times, from 0.31 to 2.75 MPa, under ambient curing (AC, at 27 ± 2°C) conditions and 6 times, from 1.1 to 6.55 MPa, under dry curing (DC, at 60°C) conditions. This increase in compressive strength was attributed to the formation of sodium alumino-silicate hydrate (N–A–S–H) gel structures during the geopolymerization process, which led to a compact soil matrix, as confirmed by the FESEM images. The specimens cured under DC conditions showed greater strength improvement than those cured under AC conditions owing to the faster rate of the geopolymerization reaction at elevated temperatures. In addition, the Na2SiO3 and NaOH + Na2SiO3 solutions were found to be the most efficient alkali activators for the SJ mixtures cured under AC and DC conditions, respectively. This durability study revealed that the alkali-activated SJ mixtures exhibit a significantly smaller loss in mass than bare soil when exposed to 12 cycles of alternating wetting and drying. Moreover, the specimens cured under DC conditions were found to be more resistant to weathering than those cured under AC conditions. Overall, soil amended with 15% jarofix (through alkali activation) satisfies the minimum strength and durability criteria recommended by Indian standards for its use as a subbase and subgrade material. The current study shows that jarofix has the potential to be used as a geopolymer binder for soil stabilization, which can help the mining sector in minimizing the volume to be stored in tailings storage facilities.

In many areas, natural soil does not have necessary resistance, some additives such as cement and microsilica are added to increase their resistance. In this research, the effect of microsilica on the strength and physical characteristics of fine sand stabilized with cement in sand samples containing cement and microsilica will be discussed. For this purpose, samples of fine sand with three different ratios of cement (2, 4, and 6 percent of soil weight) and four different ratios of microsilica (0, 0.5, 1, and 1.5 percent of soil weight) were mixed with optimal moisture, after Two curing periods of 1 and 7 days were subjected to compression and uniaxial compressive strength tests. The results of the experiments indicate that with the increase in the amount of cement and microsilica, the optimum moisture content in the density increases, the specific weight of the mixture of sand, cement and microsilica increases by adding these materials up to a certain amount, but after that it begins to decrease. . With increasing processing time, uniaxial compressive strength and rupture strain both increase. With a curing time of 1 day, for a fixed cement ratio, the compressive strength of sand-cement increases with the increase of microsilica up to about 20% of the cement weight, but after that, the resistance ratio decreases.
 With a curing time of 7 days for a constant cement ratio, the compressive strength increases with the increase of microsilica. It is also observed that in both curing times for different cement ratios, with the increase in the amount of microsilica, the relative deformation of the fracture increases.

This paper contains the experimental study of strength of geopolymer concrete for different molarities of sodium hydroxide solution. This paper also contains results of the laboratory tests conducted to find out the effect of sodium hydroxide concentration on the strength of the geopolymer concrete. In these days the world is facing a major problem i.e. the environmental pollution. We can use fly ash instead of cement in the construction in order to reduce environmental pollution. The Concrete made by using Fly ash and alkaline liquid mixture as a binder is known as geopolymer concrete. In this study for the polymerization process alkaline liquids used are Sodium Hydroxide (NaOH) and Sodium Silicate (Na2SiO3). Different molarities of sodium hydroxide solution i.e. 8M, 10M and 12M are taken to prepare different mixes and the compressive strength is calculated for each of the mix. The size of the cube specimens taken are 150mm X 150mm X 150mm. Curing of these cubes is done in an oven for 3 days and 28 days. The Compressive strength of these geopolymer concrete specimens is tested at 3 days and 28 days. The results show that there is increase in comp. strength of geopolymer concrete with increase in molarity of Sodium Hydroxide Solution. Ordinary Concrete Specimens are also manufactured with cement as binder. It is found that the Compressive strength of Geopolymer Concrete specimens is higher than the Compressive strength of Ordinary Concrete Specimens.

In recent years, the scale of China's marine engineering construction has increased year by year, and the demand and performance requirements of concrete are also getting higher and higher. Geopolymer concrete has higher stability and stronger corrosion resistance than ordinary silicate concrete. It is more suitable for application in marine engineering, and its fast hardening and early strength characteristics are more suitable for rapid construction at tidal water level seawalls. However, the self-shrinkage of geopolymer concrete is relatively large, and there is a risk of cracking during construction. In this paper, low-shrinkage geopolymer concrete was prepared, the shrinkage deformation characteristics and mechanical properties of geopolymer concrete were studied, and the engineering application of geopolymer was carried out in the seawall of Guangdong Province. The research results show that the self-shrinkage of the improved geopolymer concrete was greatly reduced, the temperature rise and the temperature difference between inside and outside were also smaller, and the risk of cracking was lower. The engineering application of geopolymer was carried out in the seawall of Guangdong Province of China. The self-shrinkage of the improved geopolymer concrete was greatly reduced. Geopolymer concrete had a small temperature rise and temperature difference between inside and outside, and the risk of cracking was low. The characteristics of rapid hardening and early strength of geopolymer concrete were more suitable for the rapid construction of seawalls at tidal water levels compared with ordinary cement concrete.