Geopolymer Concrete Specimens Research Articles

Influence of GGBFS and alkali activators on macro-mechanical performance and micro-fracture mechanisms of geopolymer concrete in split Hopkinson pressure bar tests

With superior low-carbon emission and low-resource consumption, geopolymer concrete (GPC) is receiving increasing attention as an optimal alternative to conventional building materials for cleaner and sustainable construction. However, the practical application of GPC poses great challenges since its dynamic mechanical performance remains far from well understood. In this study, via a split Hopkinson pressure bar (SHPB) system, a series of dynamic compression tests at strain rates of 45 s-1 to 150 s-1are conducted on GPC specimens with different alkaline activators (AAS)-binder mass ratios (i.e., 10%, 15%, 20%, and 25%) and ground granulated blast furnace slag (GGBFS)-binder mass ratios (i.e., 0%, 30%, 50%, 70%, and 100%). Our testing results comprehensively explored the influence of mix proportions and loading rates on the dynamic mechanical performance of GPC, including the dynamic strength and deformation characteristics, energy evolution and utilization, and progressive failure behavior. The permanent strain, energy dissipation density, and dynamic strength of GPC specimens generally increase with increasing strain rate, while the average fragment size decreases. Under higher loading rates, GPC specimens are featured by denser microcracks, shorter propagation paths, and more prominent stepwise fractures. In addition, GGBFS has a greater impact on dynamic strength, strain rate sensitivity, and energy utilization than AAS. Micro-fracture effect of GPC with different mix proportions is investigated. An appropriate content of alkaline activator (i.e., 20%) and higher GGBFS content (i.e., 100%) promotes the binder depolymerization-aggregation reaction, reduces initial defects inside concrete specimens, and facilitates a more compact block structure.

Mechanical properties of geopolymer concrete specimens exposed to fire retrofitted with glass and basalt fiber reinforced polymer laminates

AbstractExposure of concrete to elevated temperature affects its mechanical and physical properties. One of the important reasons for the use of fiber‐reinforced polymer (FRP) composite materials is because of its superior mechanical properties. These mechanical properties include impact resistance, strength, stiffness, flexibility, and also it is enhanced ability to carry loads. The high strength–weight ratio, and corrosion resistance of FRPs made them suitable for repair. For strengthening and retrofitting of concrete structures confinement with FRP has received considerable attention in recent years. Geopolymer concrete (GPC) can be expressed as “concrete without cement.” GPC is environmentally friendly and an inventive way to replace the conservative concrete which contributes 7%–8% of total CO2 production in the world. “The concrete which entails of the source materials and the alkaline solution.” The composite material made of fiber‐reinforced polymer (FRP) has recently gained attention as a potential repair method for concrete structures that have been damaged. This study investigates the performance of glass and basalt fiber‐reinforced polymer (GFRP and BFRP) laminates as a retrofit solution for fire‐damaged GPC specimens. The specimens were subjected to temperatures of 200°C, 400°C, 600°C, and 800°C for a period of 1, 2, and 3 h, followed by retrofitting with FRP laminates. The results indicated an increase in the ultimate load‐carrying capacity of GPC specimens when subjected to 200°C for 1 h, beyond which it decreased. However, a fall in ultimate load capacity was observed for higher ranges of temperature and duration of the fire. In this project, geopolymer specimens that had been damaged by fire are wrapped with GFRP and BFRP laminates to study the effect of confinement on the strength of GPC specimens. The fiber laminate used was bi‐directional glass and bi‐directional basalt. Based on the analysis of test data, there was the conclusion that the fire‐damaged GPC was strengthened when retrofitted with GFRP and BFRP laminates was attainable.

Potential for Recycling Metakaolin/Slag-Based Geopolymer Concrete of Various Strength Levels in Freeze-Thaw Conditions.

Geopolymer concrete (GPC) represents an innovative green and low-carbon construction material, offering a viable alternative to ordinary Portland cement concrete (OPC) in building applications. However, existing studies tend to overlook the recyclability aspect of GPC for future use. Various structural applications necessitate the use of concrete with distinct strength characteristics. The recyclability of the parent concrete is influenced by these varying strengths. This study examined the recycling potential of GPC across a spectrum of strength grades (40, 60, 80, and 100 MPa, marked as C40, C60, C80, and C100) when subjected to freeze-thaw conditions. Recycling 5-16 mm recycled geopolymer coarse aggregate (RGAs) from GPC prepared from 5 to 16 mm natural coarse aggregates (NAs). The cementitious material comprised 60% metakaolin and 40% slag, with natural gravel serving as the NAs, and the alkali activator consisting of sodium hydroxide solution and sodium silicate solution. The strength of the GPC was modulated by altering the Na/Al ratio. After 350 freeze-thaw cycles, the GPC specimens underwent crushing, washing, and sieving to produce RGAs. Subsequently, their physical properties (apparent density, water absorption, crushing index, and attached mortar content and microstructure (microhardness, SEM, and XRD) were thoroughly examined. The findings indicated that GPC with strength grades of C100, C80, and C60 were capable of enduring 350 freeze-thaw cycles, in contrast to C40, which did not withstand these conditions. RGAs derived from GPC of strength grades C100 and C80 complied with the criteria for Class II recycled aggregates, whereas RGAs produced from GPC of strength grade C60 aligned with the Class III level. A higher-strength grade in the parent concrete correlated with enhanced performance characteristics in the resulting recycled aggregates.

Optimisation Investigation and Bond-Slip Behaviour of High Strength PVA-Engineered Geopolymer Composite (EGC) Cured in Ambient Temperatures

Engineered geopolymer composite (EGC) is becoming an uprising product in the civil industry as a substitute and solution for conventional geopolymer concrete (GPC) as GPC exhibits brittleness and has poor cracking resistance. In this paper, we explored high strength engineered geopolymer composite (EGC) made of polyvinyl alcohol (PVA) fibre and without coarse aggregate constituents characterised as high-performance geopolymer concrete. Varying alkaline solution to fly ash ratio (AL/FA) was investigated. Bond-slip behaviour and the mechanical properties, including compressive, tensile, and flexural strengths, were studied. PVA-EGC mix designs in this research was optimised using response surface methodology (RSM). Various parameters, including the amount of ground granulated blast slag (GGBS) and silica fume, were included in the parametric and optimisation study. Based on the RSM study, the use of quadratic studies found the responses to be well-fitted. Next, the optimised mix design was utilised for the casting of all the samples for the mechanical and bond-slip tests in this study. The main parameters of bonding behaviour include multiple embedment lengths (7 d, 10 d, 12 d and 15 d) and various sizes of rebar diameter used for pull-out tests. Moreover, the mechanical properties and bond behaviours of EGC were compared with those of conventional geopolymer concrete (GPC). The compressive strength of EGC and GPC at 28 days were designed to be similar for comparison purposes; however, EGC shows higher early compressive strength on day 1 compared to GPC. In addition, results indicate that EGC has superior mechanical properties and bond performance compared to GPC, where EGC is approximately 9 and 150% higher than GPC in terms of flexural and tensile strength, respectively. Pull-out tests showed that EGC samples exhibited higher ductility, as evidenced by the presence of multiple cracks before any exhibited failure in tension and flexure. Ductile failure modes, such as pull-out failure and pull-out splitting failure, are observed in EGC. In contrast, GPC specimens show brittle failure, such as splitting failure.

Durability Performance of Ferro Geo Polymer Concrete

The expansion of the building sector is ultimately driving up the manufacturing of Portland cement, which rises pollution. Consequence of this is global warming. Sustainable alternatives are being used in concrete on a large scale to minimise the impact of greenhouse gases. Concrete made of geo-polymers is one of such alternative. Since Geo Polymer Concrete (GPC) is inherently known for its resistance to aggressive environment, to add to its characteristics, steel wire mesh was incorporated into geo polymer concrete which can largely be termed as “Ferro Geo Polymer Concrete” (FGPC). In the current study, durability properties of FGPC such as resistance to acid attack, Half-Cell Potential (HCP) and resistance to abrasion have been studied. Welded square wire mesh has been used in the specimens with different number of layers. FGPC specimens were compared to GPC specimens of same grade without mesh. Double layered FGPC specimens have shown better resilience to acid attack having weight loss and strength loss of 0.44% and 17.24% when immersed in H2SO4 and 0.45% and 8.4% when immersed in HCL correspondingly. Double layered FGPC has better resistance towards abrasion of concrete with PWL of 2.43% and ADA of 1.07 mm.

Mechanical properties of basalt fiber reinforced ambient-cured lightweight expanded polystyrene geopolymer concrete

This study investigated the mechanical properties of ambient-cured lightweight expanded polystyrene (EPS) geopolymer concrete (LEGC) specimens with densities ranging from 1321 to 1912 kg/m3 (i.e., EPS dosing of 40%, 30%, 20%, and 10%) by dosing basalt fiber (BF) with volume contents of 0.2%, 0.4%, 0.6%, and 0.8%. First, density, workability, quasistatic compression, splitting tensile, flexural and ultrasonic pulse velocity (UPV) tests were carried out with the LEGC specimens. Based on the test results, the quasistatic compressive strength enhancement rates of LEGC specimens dosed with EPS volume contents of 10%, 20%, 30% and 40% under the effect of optimal dosing of BF were 10.39%, 19.71%, 16.61%, and 15.18%; the split strength enhancement rates were 14.08%, 21.54%, 26.83% and 19.44%; the flexural strength enhancement rates were 7.35%, 17.82%, 22.56% and 17.34%; and the UPV enhancement rates were 2.82%, 1.90%, 3.12% and 2.95%, respectively. Consequently, empirical formulas were established for predicting the quasistatic compressive strengths, splitting tensile strengths, flexural strengths, and UPV values of the LEGC specimens. The prediction equations were also compared with the empirical equations proposed by previous researchers. Finally, to characterize the damage mechanisms of the LEGC specimens, computerized tomography (CT) and scanning electron microscopy (SEM) analyses were also performed on damaged LEGC specimens.

Mechanical properties prediction of geopolymer concrete subjected to high temperature by BP neural network

High temperatures can deteriorate the mechanical properties of geopolymer buildings. Rapid prediction of the residual mechanical properties and failure mode of geopolymer concrete (GPC) after thermal treatment is important to ensure the safety of buildings. In this study, a method combining BP neural network with numerical simulation is proposed to predict the residual mechanical properties and failure mode of GPC subjected to high temperature simultaneously. 15 GPC specimens with 65 % aggregate content were prepared by mixing metakaolin-based geopolymer and limestone aggregates. These GPC specimens were divided into 5 groups and heated at 25 °C, 200 °C, 400 °C, 600 °C and 800 °C, respectively. The uniaxial compression tests were conducted on the GPC after thermal treatment. The variation in the peak stress, peak strain and elastic modulus of GPC with temperature was further analyzed. The prediction method by combining the BP neural network with numerical simulation was constructed to predict the mechanical properties and failure mode of GPC subjected to high temperature. The reliability of the prediction method was verified by comparing the predicted results and the experimental results. The results show that as the temperature increases, the peak stress and elastic modulus decrease and the peak strain increases, showing a deterioration of the mechanical properties of GPC after thermal treatment. The prediction method combining the artificial neural networks and numerical simulation has high accuracy, with prediction errors of less than 10 % for peak stress and less than 20 % for peak strain and elastic modulus. The results also show that under uniaxial compression load, the predicted failure mode of GPC after thermal treatment is consistent with the experiment results. The method proposed in this study can simultaneously predict the mechanical properties and failure mode of GPC with low error, which have potential application prospects in building safety assessment.

Investigation on residual bond strength and microstructure characteristics of fiber-reinforced geopolymer concrete at elevated temperature

Fiber-reinforced geopolymer concrete has been attracting attention and interest worldwide due to its sustainable properties. However, few studies have reported the pull-out behaviour of fiber-reinforced geopolymer concrete (GPC) at elevated temperatures. In order to bridge this knowledge gap, a series of detailed investigations aimed to investigate the effect of elevated temperatures on the mechanical and microstructure properties of fiber-reinforced geopolymer concrete. In the present investigation, crimped steel fibers (SF), polypropylene fibers (PF), basalt (BF), and hybrid fibers such as SF:PF and PF:BF is employed to develop the GPC. Alkaline activators such as sodium hydroxide (NaOH) of 8 M and 10 M and Na2SiO3/NaOH ratios of 2.5 are used in the production of M35 and M40 grade GPC. Compressive strength, weight loss, crack pattern, bond strength, and microstructure of fiber-reinforced GPC specimens have been evaluated, after exposing to higher temperature following ISO 834 standard fire curve. Results from the conducted tests show that adding various types of fibers improves the compressive strength and bond strength of the GPC specimens. More specifically, amongst all tested specimens, the exposed GPC-BF shows lesser weight loss and higher residual compressive strength with fewer cracks on the surface of the specimens. on the other hand, GPC with SF shows higher residual bond strength than other fiber-reinforced GPC specimens. Microstructure analysis (SEM/EDAX) confirms the extent of damage and contribution of fiber in the temperature-exposed GPC. A statistical relationship and correlation has been obtained between compressive and bond strength.

Potential utilization of natural zeolite, fly ash and rice husk ash for geopolymer concrete production

Purpose. The experimental research purpose is to study the potential use of natural zeolite, fly ash, and rice husk ash for geopolymer concrete production based on the effect of the Al/Si ratio on microstructure properties and compressive strength. Methods. The formulation process is based on the ratio of Al/Si contained in the raw material, the selection of raw material grain size, mixing and molding of the geopolymer concrete. The geopolymer concrete properties are analyzed in terms of compressive strength and microstructure properties. Findings. Fly ash, natural zeolite and rice husk ash can be used to produce new functional materials in the form of geopolymer concrete with a compressive strength of up to 16.74 MPa. The mixing formula is based on the ratio of Al/Si contained in the raw materials, and their ratio is 1:2; 1:2.5; 1:3; 1:3.5 and 1:4. Geopolymer concrete specimens showed the required physical and mechanical properties. Originality. The originality of this research lies in the utilization of natural zeolite, fly ash, and rice husk ash as raw materials for geopolymer concrete production. This approach offers a practical solution by utilizing these common and readily available materials, rich in silica and alumina, to produce functional and environmentally friendly building materials. Practical implications. This research can provide a practical solution to the problem of natural zeolite, fly ash, and rice husk ash rich in silica and alumina, which can be utilized for geopolymer concrete production. Thus, geopolymer concrete can mainly be utilized as a building material for laying walls and floors in pedestrian areas and parks or for other purposes.

Development of alkali activated paver blocks for medium traffic conditions using industrial wastes and prediction of compressive strength using random forest algorithm

Geopolymer is an environment friendly construction material that could be synthesized using either the natural source or the industrial byproducts such as flyash and GGBS. The characteristics of the Geopolymer rely on the proportion of the flyash and GGBS and the concentration of the activator solution used. In this research work, the effect of partial replacement of flyash with GGBS in proportions such as 0, 10, 20, 30 and 40% is investigated. Also Molarity of NaOH are tested from 8 to 14 M and both the parameters are optimized. In this optimized Geopolymer concrete, the utilization of iron slag as a partial substitute for river sand in various proportions such as 10, 15, 20, 25, 30 35, 40 and 45% are investigated. The optimized Geopolymer concrete with iron slag is investigated for its performance as a paver block with incorporation of banana fiber in proportions such as 0, 0.5, 1 and 1.5 and is compared with conventional cement concrete paver block. The results show that there is a significant enhancement in the properties of Geopolymer concrete with the different levels of optimization and the utilization of natural banana fiber. The developed sustainable paver block was found to with stand medium traffic conditions as per IS 15658:2006. Further this study employed random forest (RF) algorithm for the prediction of compressive strength of geopolymer concrete specimens for the variable parameters such as molarity of alkaline solution, Flyash/GGBS ratio and partial replacement of river sand with iron slag. The performance evaluation parameters represented high accuracy of developed RF model. This research work unleashes a heft potential of Geopolymer concrete to develop economical eco-friendly sustainable paver blocks to the society through mitigation of environmental strain on the ecosystem.

Strengthening mechanism of polyvinyl alcohol fibers on mechanical properties of geopolymer concrete subjected to a wet-hot-salt environment

Concrete materials are subjected to a complex coupled environment of temperature, humidity, and salt ions when in a coastal area during the summer. Geopolymer concrete (GPC), as one of the best alternatives to ordinary silicate concrete, was explored in this study to investigate its mechanical damage under wet-hot-salt environment, and to understand the strengthening mechanism of its mechanical properties by polyvinyl alcohol fibers (PF), which are crucial for the application of GPC in coastal engineering. To achieve this, a series of experiments were conducted to investigate the effect of wet-hot-salt coupled environment and PF content on the mechanical properties of fiber-reinforced geopolymer concrete containing nano-SiO2 (PF-GPC). In the experimental design, a coupled environment of 45 °C temperature, 100% humidity, and 5% NaCl solution content was firstly established for simulation acceleration test by an environmental simulation test chamber. Then different PF volume contents (from 0% to 0.8%) were considered for the cube compressive strength test, split tensile test, elastic modulus test and impact test. The results indicated that the wet-hot-salt environment significantly weakened the mechanical properties of GPC specimens, while the addition of appropriate content of PF effectively mitigated the degradation caused by the wet-hot-salt environment. The compressive strength, splitting tensile strength and elastic modulus of PF-GPC reached their maximum value at a PF content of 0.6%. Particularly, the addition of PF significantly improved the impact resistance of PF-GPC in wet-hot-salt coupled environment, with the highest impact resistance indices observed at a PF content of 0.4%. Moreover, the correlation between the elastic modulus and compressive strength of PF-GPC in wet-hot-salt environment was established by using the power function equation. And based on the applicability of the two-parameter Weibull distribution in the impact life model, an impact damage evolution equation of PF-GPC was established and validated under the wet-hot-salt conditions, which can provide valuable guidance for the design of GPC structures under different damage probabilities. The findings of this study indicated that PF-GPC can be applied in the wet-hot-salt environment, which is important for the low-carbon sustainable development of building materials.

Investigation on the impact of elevated temperature on sustainable geopolymer composite

Geopolymer concrete (GPC) is an eco-friendly, sustainable, cementless and green concrete. It could be an alternative to the conventional concrete. In alkaline circumstances, the alumina and silica concentration in geopolymer concrete creates the geopolymer bond, while regular concrete creates C-S-H (calcium silicate hydrate bond). The final result of the geopolymer bond does not include any water. At elevated temperatures, geopolymer concrete would thus be more stable. Due to its greater strength and durability quality, geopolymer concrete may be the ideal replacement for ordinary portland cement (OPC) concrete. This research intends to examine how specimens of geopolymer concrete and regular concrete respond to exposure to increased temperatures between 100°C and 800°C. Mass loss, ultrasonic pulse velocity, compressive strength, X-ray diffraction, thermogravimetric analysis and derivative thermogravimetric analysis were all examined throughout the experimental examination. Both concrete specimens lose mass or weight as the exposure temperature rises; OPC concrete samples spalls at 600°C, while GPC sample fail at 800°C. GPC specimens lose around 12% of their original mass after being exposed to temperatures of 800°C, while OPC specimens lose about 7%. The GPC specimens maintained 60% of their initial compressive strength after being exposed to a temperature of 700°C, but the OPC concrete specimens only kept 52%. With each increase in exposure to extreme temperatures, the peaks of quartz and cristobalite are lowered. Only the form or structure of the mineral oxide would change; the chemical linkages would remain. The GPC samples subjected to temperatures of 100°C exhibit effective thermal stability than all other specimens exposed to extreme temperatures. As the exposure temperature rises, the GPC specimens become more thermally stable. According to the experimental findings, the GPC specimens’ bonding structure makes them more resistant to high temperatures than regular concrete specimens. Micropores are present in the voids of the geopolymer matrix, while mesopores and micropores are present in the voids of the OPC matrix. While OPC bonding is C-S-H formed by the hydration of lime and silica contained in the cement, the geopolymer bonding did not include the water content in the final or end result of geopolymerisation for strengthening.

Optimizing the strength of geopolymer concrete incorporating waste plastic

In this work, we systematically examine several factors in an effort to maximise the strength of geopolymer concrete that includes recycled plastic. Geopolymer concrete specimens with varying amounts of plastic content, particle size distribution, alkaline activator concentration, mix design, additional materials, additives, and fibre properties were subjected to water absorption and compressive strength tests. Compressive strength was increased to 40 MPa, while water absorption was decreased to 1.5%, all as a consequence of raising the plastic content to 15%. In addition to the ideal concentration of 8 M sodium hydroxide and 3 wt% sodium silicate, the use of coarse plastic particles helped boost the material's mechanical qualities. The employment of a superplasticizer and fibre additives, in addition to the incorporation of silica fume, increased the strength and durability of geopolymer concrete. These results provide light on how to better incorporate waste plastic into the design and formulation of geopolymer concrete, a key ingredient in the development of environmentally friendly and functional building materials.

Unsupervised deep learning framework for ultrasonic-based distributed damage detection in concrete: integration of a deep auto-encoder and Isolation Forest for anomaly detection

This study presented an unsupervised anomaly detection-based framework for distributed damage detection in concrete using ultrasonic response signals. A deep fully connected auto-encoder was employed to reconstruct the ultrasonic response signals. This model was trained on the intact specimen’s responses. The auto-encoder demonstrated a relatively high prediction error encountering the damaged specimen’s responses. Two time-domain features (mean squared error and reconstructed-to-original signal ratio) and one frequency-domain feature (fundamental amplitude ratio) were defined to measure the reconstruction error of the auto-encoder (the damage-sensitive features). Finally, the Isolation Forest algorithm was implemented for anomaly (damage) detection. The beauty of this framework is that it requires a few numbers of data only from the intact specimen for training the auto-encoder and collecting the binary decision trees of the Isolation Forest. The framework was successfully implemented for damage detection in five geopolymer concrete specimens with different mix proportions. Using all three introduced damage-sensitive features, the framework demonstrated an average prediction accuracy of 95.0% and 93.0% for damaged and intact stages, respectively.

Evaluating the Influence of Palm Kernel Shell Ash on Ire Clay Geopolymer Concrete Cured at Ambient Temperature

There is an abundance of clay deposit in Ire Ekiti which can serve as geopolymer source material and Palm kernel shell exists as a massive agro waste in South Western Nigeria. This study evaluates the effect of palm kernel shell ash (PKSA) as an additive on the compressive strength of Ire clay geopolymer concrete. The objective of the study is to determine the selected properties of the obtained concrete at room temperature. Palm kernel shell was burned at 650oC for 2 hours in a furnace. Natural clay collected from Ire Ekiti was manually pulverized, air dried and calcined in a furnace at 750o for 2 hours. The geopolymer concrete was prepared at a mixing ratio of 1:2:3. The material constituents were calcined clay (source material), 12M of NaOH and Na2SiO3 (ratio of NaOH to Na2SiO3 was 2:5), river sand and 12.5mm granite were the fine and coarse aggregates respectively while PKSA of 0%,7.5% and 15% of the calcined Ire Clay content were used as additive in preparing the geopolymer concrete. geopolymer concrete specimens were cured at ambient temperature till testing at different maturity ages of 7, 14 and 28 days. It was generally observed that increasing the percentage of PKSA as additive strongly improved the compressive strength gain with maturity of the Ire clay geopolymer concrete. At 28 days maturity, 7.5% PKSA addition improved the compressive strength by 166% while 15% PKSA addition improved the strength by 181% increase. The highest compressive strength was 7.67N/mm2 at 15% PKSA addition on 28 day. Conclusively, Ire clay and PKSA are viable source material and additive respectively for geopolymer concrete production. The Ire clay geopolymer concrete can be practically applied like conventional concrete in structural work especially in a rural community like Ire Ekiti where cement needs to be transported over kilometers. Also, the concrete performing well at ambient temperature makes it cost effective compare to most geopolymers that require heating at high temperature. It is recommended that further study on the durability should be done.

Axial compressive behaviour of GPC filled FRP Tubes: Experimental and analytical investigations

The production of Ordinary Portland Cement (OPC) releases carbon dioxide (CO2), which is one of the main contributors in the rising level of Greenhouse Gases (GHG) into the atmosphere and adversely effecting the environment and subsequently causing the climate change. In this study, the fly ash (FA) an alternative of OPC is used to produce environmental friendly cementless geopolymer concrete (GPC). This study investigates the axial compressive behavior of GPC filled fiber reinforced polymer (FRP) tubes. Two types of FRP tubes, i.e., carbon FRP (CFRP) tubes and glass FRP (GFRP) tubes were prepared by the wet lay-up procedure using CFRP and GFRP sheets, respectively. A total of forty-five GPC specimens of 150 mm diameter and 300 mm height were prepared with five different molarity of NaOH (8–16 M) with Na2SiO3 to NaOH ratio of 1.5. The unconfined GPC (Control), GPC filled CFRP tube (GCT) and GPC filled GFRP tube (GGT) specimens exhibited a significant increase in the peak axial stress (fc) with the increase in the molarity of NaOH. The scanning electron microscopic investigation also exhibited a reduced number of unreacted fly ash particles in the GPC with increasing the molarity of NaOH. The fc and corresponding axial strains (∊c) of GCT and GGT specimens were significantly higher than those of unconfined GPC specimens. The GCT specimens exhibited higher fc and corresponding ∊c than the GGT specimens. The analytical axial stress–strain (fc-∊c) curves of GCT and GGT specimens developed using available fc-∊c models of FRP confined ordinary Portland cement (OPC) concrete matched well with the experimental fc-∊c curves of GCT and GGT specimens.

Effect of fibre characteristics on physical, mechanical and microstructural properties of geopolymer concrete: A comparative experimental investigation

AbstractThe main aim of this work is to comparatively reveal the effect of fibre type, length and content on compressive strength and microstructure of structural geopolymer concrete (GPC) produced under constant mixture and curing parameters in order to address the significant gap in present literature. Firstly, GPCs with different NaOH concentrations (i.e., 6, 9, 12 and 15 M) and activator solution/binder (a/b) ratios (i.e., 0.45 and 0.55) were produced in ambient curing condition, and optimum production parameters were determined based on the preliminary evaluations. Then, glass and polypropylene fibres in 6‐mm length (GS6 and PP6) and polyamide and polypropylene fibres in 12‐mm length (PY12 and PP12) were included in GPCs at ratio of 0.4%, 0.8% and 1.2% (by volume). Compressive strength, apparent porosity, bulk density, ultrasonic pulse velocity (UPV), X‐ray diffraction (XRD) and scanning electron microscope (SEM) analysis of GPC samples were carried out comparatively. The inclusion of GS6 fibre enhanced the compressive strength thanks to fibre surface being covered by geopolymer gel and the strong adhesion between GS fibre and geopolymer matrix. SEM images of fibre reinforced GPC (FRGPC) also confirmed the experimental findings, which were attributed to improvement in compressive strength. Regardless of the fibre type, the maximum compressive value strength was obtained from GPC specimens with 0.4% fibre and then decreased. Higher fibre inclusions led to poor compaction, workability issues and inhomogeneous fibre dispersions. A very good relation (R2 = 0.98) was acquired between UPV and compressive strength values of GPC/FRGPC samples.

The influence of low alkaline activator on the compressive strength and workability of geopolymer concrete

This paper presents the results of research on geopolymer concrete using a reasonably low alkaline activator. The key objective concerning this research is to investigate whether a low alkaline activator is still qualified to produce a concrete compressive strength that fulfills the structural requirements. The experimental program is carried out by making geopolymer concrete specimens, where the variables reviewed represented the amount of alkaline activator (4% and 5%), the ratio of alkaline activator to fly ash (AAS/FA) was 0.35, 0.4, 0.5, 0.6. The treatment temperatures of the specimens were room temperature (33°C) and 60°C. The experimental results of the compressive strength test have shown that the compressive strength of low alkaline geopolymer activator concrete still meets the requirements as a structural material (i.e. Indonesian Concrete Code). The weight of the resulting specimen is included in the category of normal weight concrete. The workability of geopolymer concrete with low alkaline activator tends to be better if the ratio AAS/FA also increases, but the compressive strength of concrete tends to decrease.

Effects of Cementitious Material Content and Sand Ratio on Mechanical Properties of the Dry-Mixing Geopolymer Concrete

The paper investigates the 7-day, 28-day and 56-day compressive & splitting tensile strength of thirty geopolymer concrete specimens using the dry mixing method. The cementitious material content, sand ratio, along with the water binder ratio were chosen as the variables. Influences of the parameters on the mechanical behavior of the dry mixing geopolymer concrete are discussed in the paper.

One-Year study of restrained shrinkage and creep behaviours of geopolymer concrete

The viability of geopolymer concrete (GPC) for industrial applications has been increasing in recent years by utilising solid alkali activators and curing at ambient temperature. With higher viability and desirability for engineering applications, their dimensional stability and serviceability properties remained a focal point for investigation. The one-year dimensional stability of GPC was studied using standard shrinkage and creep tests. Furthermore, a novel photogrammetry technique was introduced and utilised to measure the shrinkage of concrete slabs in restrained conditions. The 56-day drying shrinkage of GPC specimens was between 280 and 600 microstrain, which is suitable for most structural engineering applications. GPC experienced a slightly higher drying shrinkage in free condition than conventional concrete when the fly ash/slag mix ratio was 60/40. However, GPC displayed 38–57% lower shrinkage in restrained conditions than the conventional counterpart. GPC specimens also experienced lower creep strain and coefficient when compared to normal concrete. The GPC shrinkage and creep performance revealed that slag content played a crucial role, as the free shrinkage and creep strains in slag-dominant GPC were the highest.