Geopolymer Concrete Samples Research Articles

Bond behavior of reinforcing steel bars in metakaolin – calcium carbide residue-based geopolymer concrete

The bond property of concrete is a key characteristic of concrete that affect the structural activity of reinforced concrete beams. Concrete produced from geopolymer has the prospect to replace concrete produced from ordinary Portland cement (OPC) for structural applications. Therefore, this research evaluates the bond behavior of metakaolin-calcium carbide residue (CCR)-based geopolymer concrete for use in in situ structural applications. Comparative studies were carried out on concrete made of geopolymer and OPC. The embedment lengths (5ϕ and 7ϕ) and reinforcing bar diameters (14 and 16 mm) were varied and the bonding activity of the different concrete types was studied. Additionally, the qualities of the concrete produced were assessed, including density, ultrasonic pulse velocity, and compressive and flexural strengths. Generally, the metakaolin-CCR-based geopolymer concrete samples had the best mechanical properties, followed by metakaolin-based geopolymer and OPC concrete, respectively. Bond activity enhanced when embedment length and diameter of reinforcement were reduced in all types of concrete. Thus, with a reinforcing bar diameter of 14 mm and an embedment length of 5ϕ, the average bond strength of the metakaolin-CCR-based geopolymer concrete was 14.3MPa, which was 18.87% and 105.46% higher than that of the metakaolin-based geopolymer and OPC concrete, respectively. Influenced by experimental conclusions, it can be established that the metakaolin-CCR-based geopolymer concrete has the capacity to be used in place of OPC concrete in bond applications where steel reinforcing bars are employed.

The mathematical model for the optimization of compressive strength of sawdust ash geopolymer concrete

Geopolymer concrete offers an eco-friendlier option compared to traditional cement, as it lowers greenhouse gas emissions during production. It consists of an alkaline solution with sodium or potassium silicate and sodium or potassium hydroxide, as well as a source material abundant in silica and alumina. For this study, thirty geopolymer concrete samples were produced in the lab using a mix design approach from Scheffe’s (5,2) model. The focus of the research was on maximizing the compressive strength of the concrete, especially when incorporating sawdust ash as the source material. The findings indicated that subjecting sawdust ash to pyrolysis in the absence of oxygen significantly impacts its pozzolanic properties and, consequently, the characteristics of the concrete. The research determined the optimal compressive strength of geopolymer concrete incorporating sawdust ash to be 21.673 MPa, along with specific concentration ratios of NaOH, Na2SiO4 to NaOH, sawdust ash in the binder, water to binder, and activator to sawdust ash at 10.5415, 2.0446, 38.6307, 0.0363, and 2.5882 respectively. Furthermore, MATLAB-based computer programs were utilized to optimize and forecast the ideal mixture proportions for sawdust ash-based geopolymer concrete.

Evaluation of self-compacting geopolymer concrete properties containing different water glass solutions

This research investigates how water glass solutions (Ms 1.99 and Ms 2.92) impact the standard consistency, setting time, rheological properties, and mechanical and microstructural characteristics of self-compacting geopolymer concrete (SCGC) with various amounts of fly ash, ground granulated blast furnace slag (GGBFS), and rice husk ash (RHA). Six Self compacting geopolymer concrete (SCGC) samples were prepared from each of the two glass water solutions. Mechanical properties, such as compressive, split tensile, and flexural properties, were evaluated for the blends. Compared to Ms 1.99, concrete using water glass solution Ms 2.92 had a standard consistency of 49%, and the setting time was increased from 1100 to 1250 min. The Ms. 2.92 combine improves workability. Mechanical properties revealed that 28-day-cured concrete with Ms 2.92 water glass solution had the highest compressive strength of 55.6 MPa and achieved the highest split tensile and flexural strengths, 6.67 MPa and 10 MPa, respectively. XRD, SEM, EDX, and FTIR are used to investigate SCGC's microstructures.

Sawdust Ash as a Sustainable Binder in Geopolymer Concrete: A Study on Split Tensile Strength

Geopolymer concrete can serve as a more environmentally friendly alternative to traditional cement by reducing the release of greenhouse gases during production. It is composed of an alkaline liquid containing sodium or potassium silicate and sodium or potassium hydroxide, along with a source material rich in silica and alumina. In a recent investigation, thirty geopolymer concrete samples were created in the laboratory using a mix design approach. The study focused on optimizing the split tensile strength of the concrete, particularly when using sawdust ash as the source material. The research revealed that subjecting sawdust ash to pyrolysis in the absence of oxygen significantly affects its pozzolanic characteristics and, consequently, the properties of the concrete. The study determined the optimum split tensile strength of sawdust ash-blended geopolymer concrete to be 2.9899 MPa. The specific concentration ratios of NaOH, Na₂SiO₄ to NaOH, sawdust ash in the binder, water to binder, and activator to sawdust ash were found to be 9.75, 1.8750, 37.5, 0.025, and 2.5, respectively. Additionally, computer programs developed using MATLAB were employed to optimize and predict the ideal mix proportion of sawdust ash-based geopolymer concrete.

The Behavior of Ceramic Fiber Geopolymer Concrete under the Effect of High Temperature

Geopolymer concrete (GC), also known as green concrete, contains slag, silica fume, and fly ash as binders. The absence of cement in concrete is critical to protect the world from the environmental impacts of cement production. In addition, exposure to high temperatures is a critical parameter that causes loss of strength in concrete. In this study, Geopolymer concrete samples were prepared with 10 different samples containing different proportions of slag, silica fume, and porous ash and subjected to various physical, mechanical, and optical tests. The sample (GS90) with optimum workability and compressive strength, which also showed high performance in water absorption, freeze-thaw, and UPV tests, was used in high-temperature tests. Portland cement concrete (PCC) was used as a control sample. This study investigated the effect of high temperatures on the physical and mechanical properties of fiber-free GCs containing 2%, 5%, and 10% by volume of ceramic fibers. Therefore, fiber-reinforced, fiber-free, and PCC specimens were subjected to high-temperature tests at 100, 300, 600, and 900 °C. As a result of the observation of crack growth, color changes, and compressive strength parameters in the samples subjected to high-temperature tests, the thermal resistance of the 10% ceramic fiber geopolymer concrete sample was 2.5% higher than other samples. There is no study in the literature that examines the behavior of ceramic fiber-reinforced geopolymer concrete at high temperatures. This research revealed an important finding by proving that ceramic fiber reinforcement increases the compressive strength of geopolymer concretes at a remarkable rate after high-temperature impact.

Reuse of Industrial By-products in Construction using Geopolymerization

This study explores the reuse of industrial by-products in construction through geopolymerization, positioning it as a sustainable alternative to conventional construction materials. In light of the growing demand for environmentally friendly building practices, this research aims to evaluate geopolymer concrete made with industrial by-products as a viable substitute for traditional concrete. The introduction highlights the importance of sustainable construction and the potential of geopolymer technology in reducing environmental impacts. A comprehensive review of the composition, properties, and previous studies on geopolymer concrete using industrial waste materials is provided. The research methodology outlines the objectives, materials used, experimental framework, and testing protocols. Results on compressive strength, flexural strength, and durability of the geopolymer concrete samples are discussed in detail in the results and analysis section. The discussion interprets the findings, focusing on the enhanced strength and durability achieved through the incorporation of industrial by-products. The study concludes with a summary of key outcomes, implications for the construction industry, and recommendations for future applications and research on geopolymer concrete using industrial waste.

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

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

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.

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.

Metakaolin‐based geopolymer concretes for nuclear protection: On the perspective of physicochemical, durability, and microstructure

AbstractAs a striking contribution of metakaolin to geopolymer concretes, the varying contents of metakaolin with quartz powder are included the mixtures with ground granulated blast furnace slag, and quartz sand to observe the mechanical, physical, transport, microstructure, and nuclear protection parameters of the samples, within this study. The geopolymer concrete samples are tested for the mechanical transport and physical properties depending on the curing time, curing temperature, and the raw/by‐product material type. The results show that the samples containing the most metakaolin performed well with a 24‐h compressive strength of 131.78 MPa. Increasing the curing temperature and curing time affected both mechanical, physical and transport properties. In addition, the microstructure of the samples was analyzed by scanning electron microscopy, x‐ray diffraction, and Fourier transform infrared spectroscopy. Moreover, the effect of increasing metakaolin reinforcement on the nuclear protection capacity of the produced geopolymer concretes with experimental gamma transmission and neutron dose measurements was investigated. The M3 sample with high content of both metakaolin and granulated blast‐furnace slag showed the highest resistance to gamma photons in the energy range of 0.081–0.383 MeV. The produced geopolymer samples absorbed almost 40% of the fast neutrons with 4.5 MeV energy. Neutron removal cross sections of the produced geopolymer concretes are in the range of 0.0952–0.0949 cm−1 and are larger than those of B4C, graphite, and boric acid. The findings of this study revealed that the addition of metakaolin improved the mechanical, nuclear shielding and structural properties of geopolymer concretes.

Mechanical Strength and Microstructure of GGBS-SCBA based Geopolymer Concrete

This paper deals with the attempt to develop and study the performance of ground granulated blast furnace slag (GGBS) and sugarcane bagasse ash (SCBA) based sustainable geopolymer concrete. NaOH (8M, 10M, and 12M) and Na2SiO3 were used as alkaline activators with a ratio of 2.5. SCBA mainly acted as amorphous silica and has been utilized as a substitute material for GGBS. The effect of SCBA contents (0%, 5%, 10%, 15% & 20% by the mass of binder) in terms of fresh, hardened, microstructural, and correlation properties of geopolymer concrete developed have been evaluated. Different tests such as the slump cone test, compression test, split tensile test, flexure test, and ultrasonic pulse velocity test were conducted. Scanning electron microscopy, Energy dispersive analysis, and X-ray diffraction analysis were investigated for understanding the microstructural properties. The research findings have shown that with an increase in molarity from 8M to 12M there is an increase in the strength properties of geopolymer concrete. The results in this current study show that 28 days compressive strength was found to increase by 4–15% when the NaOH molarity was increased from 8M to 10M and 8–21% when the NaOH molarity was increased from 8M to 12M. The geopolymer concrete developed with 20% SCBA and 80% GGBS with 8M NaOH solution and SS/SH ratio of 2.5 can be used for a target strength of 30–35 MPa. Scanning electron microscope images show a packed and dense matrix, which clearly outlines the reason behind the attainment of higher strength in higher molarity of GGBS-SCBA based geopolymer concrete samples and the presence of CASH gel confirmed this in the geopolymer matrix. Furthermore, there is a strong correlation between the experimental findings and the model equations proposed. These presented models will be useful in improving the strength of geopolymer concrete incorporating agricultural and industrial wastes.

Microstructure Studies on the Effect of Alkaline Activators to Flyash Ratio on Geopolymer Concrete

Abstract: Fly ash-based geopolymers are new binding materials produced to replace the ordinary Portland cement used in concrete. In this research, the effect of alkaline activators to flyash ratio on the compressive, split tensile, flexural strength and microstructural study of fly ash-based geopolymers were studied. Alkaline activators to fly ash ratios of 0.30, 0.35, 0.40 and 0.45 and ratio of sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) maintained constant throughout the study. The alkaline activator solution was prepared by mixing sodium silicate (Na2SiO3) with a 12M NaOH solution. The samples were casted and cured at a temperature 60° C for 24 hours in Dry oven and kept at room temperature till the testing (7days and 28 days). The test results indicated that the compressive, split tensile and flexural strength increased when the ratio of alkaline activator to fly ash was decreased. The ratio of 0.30 produced the maximum compressive strength, which was 68.02 MPa at 28 days curing. SEM (Scanning Electron Microscope) test conducted on geopolymer concrete samples and observed that alkaline activators to fly ash ratio of 0.30 and 0.35, geopolymer samples has the continuous, homogenous matrices and less porous structure because of the high dissolution of the fly ash particles in the alkaline activator solution.

Synergic effect of some waste pozzolans on the mechanical and shielding properties of geopolymer concretes

This work aimed to investigate the effect of raw materials to geopolymer concrete; such as silica fume, metakaolin, ground granulated blast-furnace slag, and quartz powder on mechanical (compressive strength, flexural strength), physical, transport, and nuclear radiation shielding properties. The silica fume, metakaolin, ground granulated blast-furnace slag, and quartz powder used singly and/ or in combination for geopolymer mixture along with sodium-based solutions. Four different geopolymer mixtures were prepared and cured at three different temperatures (30°C, 60°C and 90°C) for three curing periods (5, 7 and 9 h). Then, the mineralogical and morphological properties were considered with X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM) tests. Based on the findings, the use of metakaolin in the geopolymer mixture increased both the compressive and flexural strengths. In addition, the compressive strength of 137.5 MPa was reached in the mixture using metakaolin at 90°C and in a short period of curing, like 9 h. The metakaolin (MK) is decreased the sorptivity coefficient of the geopolymer concrete samples. Withal, extensive experimental measurements were performed to investigate the gamma-ray and fast neutron shielding properties of fabricated concretes. The mass attenuation coefficient enjoyed values such as 0.2078, 0.2078, 0.2079 and 0.2081 cm2/g for M1, M2, M3 and M4 geopolymer concretes, respectively. It was reported that the geopolymer concretes attenuated the fast neutron flux with the energy of about 4.5 MeV by 35%. All inspected geopolymer concretes exhibited excellent neutron attenuation properties, as their values ΣR greater than those of commonly used ones as the neutron absorbers.

Behaviour of geopolymer concrete at elevated temperature- a comprehensive review

In comparison to conventional materials made of concrete, geopolymer materials are sustainable, durable and strong. Geopolymer used should not only be sustainable but also fire-resistant for the necessary amount of time. The properties of geopolymer materials after high-temperature exposure, such as weight loss, thermal expansion, thermal conductivity, mechanical properties, and microstructure are reviewed and discussed in detail in the current study. In addition, the behaviour of Geopolymer concrete (GPC) at high temperatures with different recycled fibre additions as well as additions of crumb rubber is also examined in this article. The use of recycled fibres made from industrial wastes offers additional advantages, including resource conservation, waste reduction, lower costs of processing than normal fibres, and the removal of waste disposal in landfills. The latter offers a sustainable method for recycling tyres and helps slow down the depletion of natural aggregates. From the literature, it is revealed that at 800–1000 °C, compared to the OPC concrete specimens, the GPC samples had less cracking damage and also substantial spalling was seen in the OPC samples, but not in the GPC samples. GPC with recycled fibres has higher crack-resistant characteristics at elevated temperatures. Meanwhile, in a study at 800 °C, rubberized geopolymer showed more cracks compared to control GPC. This work also provides comprehensive reviews on the type of recycled fibres and rubber aggregates, spalling mechanisms, physical inspection and properties of rubberized geopolymer and recycled fibre-reinforced GPC. It also demonstrated the influence of elevated temperature on the characteristics of recycled fibre-reinforced GPC and rubberized geopolymer after high-temperature exposure.

Bacterial healing of geopolymer concrete exposed to combined sulfate and freeze-thaw effects

In this study, metakaolin-based colemanite and red mud substituted geopolymer concrete were exposed to combined sulfate and freezing-thawing effects to simulate the effects of cold locations with a sulfate environment. Firstly, samples were exposed to a 5% sodium sulfate solution for four days for combined sulfate and freezing-thawing effects. Then, these samples were subjected to freezing-thawing according to TS EN 15177. Finally, cracks formed on the samples exposed to combined sulfate and freeze–thaw effect. Then, the bacterial healing process was applied to heal the cracks. Sporosarcina pasteurii bacteria were used to form CaCO3 in the cracks. The capillary water absorption, weight measurements, splitting tensile strength, ultrasonic pulse velocity, microstructural analyzes, and visual assessment of bacterial-healed geopolymer concrete samples were performed. As a result of this study, the healing ability of Sporosarcina pasteurii was successfully demonstrated by filling cracks caused by the combined durability effect with CaCO3 precipitates. Also, the recovery percentage of splitting tensile strength of the bacterial-healed samples was obtained as 61.71%.

Assessment of environmental, economic and technical performance of geopolymer concrete: a case study

Although several studies report the CO2 reduction obtained from alkali-activated materials/geopolymers, only a few investigate their engineering, environmental and economic aspects. The present paper provides an evaluation approach to address these three major aspects of geopolymer concrete by choosing three scenarios for industrial precast applications. Using the analytical hierarchy process, a single sustainability score was determined for three scenarios using technical, environmental and economic parameters. Such sustainability sensitivity analysis led to decision-making for various scenarios. This case study provides an example of reaching these parameters for choosing suitable concrete mixtures for a given application or requirements. The technical and environmental results showed that a wide range of late and early age compressive strength could be achieved by changing the mix composition and proportions. However, all the geopolymer concrete samples exhibited a lower environmental footprint than OPC concrete.

Experimental evaluation of compressive, tensile strength and impact test in blast furnace slag based geopolymer concrete, under high temperature

Today, the use of nanoscale additives in the concrete industry with the aim of reducing the negative effects of Portland cement and improving the mechanical properties of concrete has received much attention. Also, in order to reduce the harmful environmental effects and increase the mechanical properties and durability of concrete, particles with high pozzolanic properties are used as a suitable alternative to ordinary cement in concrete. In this regard, geopolymer concrete using materials containing aluminosilicate materials with adhesive properties and filler, as an alternative to cement, has attracted the attention of researchers. Concrete resistance to high heat is of particular importance. Geopolymer concrete has a good performance against heat due to its strong structure. In the current study, slag-based geopolymer concrete was used with 0-2% polyolefin fibers and 0-8% nano-silica to improve its structure. After curing the specimens under dry conditions at a temperature of 60°C in an oven, they were subjected to Compressive strength, Tensile strength, and Drop weight hammer tests to evaluate their mechanical properties. all tests were performed at 90 days of age under ambient temperature (20 ℃) and high temperature (500 ℃). The addition of nano-silica enhanced the whole properties of the slag-based geopolymer concrete. Addition of up to 8% nanosilica to the geopolymer concrete composition at 20% temperature improved the compressive strength test results up to 21.94%, tensile strength up to 15.19% and impact energy up to 36.36%. Addition of up to 2% of polyolefin fibers to the geopolymer concrete composition improved the tensile strength up to 11.76%, the impact energy up to 8.26 times and the compressive strength drop up to 22.49%. Applying high heat to geopolymer concrete samples reduced the compressive strength up to 16%, tensile strength up to 21% and impact energy up to 72.72%. The effect of heat on the drop in results in control concrete is more than geopolymer concrete. In the following, by conducting the SEM test, a microstructure investigation was carried out on the concrete samples. In addition to their overlapping with each other, the results indicate the geopolymer concrete superiority over the regular concrete. Besides, it demonstrated the positive influence of nano-silica addition on the concert microstructure.

Study on the flexural properties and fiber‐selection method of fiber‐reinforced geopolymer concrete

AbstractIn order to study the effect of different types of fibers on the bending properties of geopolymer concrete (GPC), a series of fiber‐reinforced geopolymer concrete (FRGPC) samples were prepared, and their flexural properties were evaluated by four point bending test and bending toughness evaluation index. Then, based on the fiber characteristic value (λ), a new bending strength prediction model and a three‐dimensional (3D) curved surface prediction model of the bending toughness of FRGPC are proposed and fitted. Finally, a new method for the selection of fibers in GPC is designed by calculating the derivative of the quadratic relationship between fiber reinforcement factor (S) and λ. The results show that all types of fibers have a certain effect on improving the bending strength of GPC samples, and the lifting rate is end‐hook steel fiber (SF), basalt fiber (BF), and short polyethylene polypropylene fiber (SPPF), from high to low. Mixing the above types of fibers with long polypropylene fibers (LPPF) will produce better performance. Among them, the hybrid fiber‐containing SF has the best performance. The bending performance prediction model deduced in this paper has a good correlation coefficient, which can be used to predict the bending performance of FRGPC. By making dS/dλ = 0 can calculate the optimal λ, and this λ can maximize the parameter S and guide the selection of optical fibers.

Effect of binder dosage and the use of waste rubber fiber on the mechanical and durability performance of geopolymer concrete

This paper was designed to find solutions to the fact that the availability of natural aggregates in accordance with the standards used in concrete is gradually decreasing, the environmental problems caused by cement threaten our future, and the recycling of used tire waste is very difficult. The effects of three different binder dosages (300, 400 and 500 kg/m3) on the mechanical and durability properties of geopolymer concrete (GPC) samples were investigated in binder contents consisting of 98% granulated blast furnace slag (GBFS) and 2% nano silica. As for the aggregate composition, natural sand was used as the fine aggregate, while the waste rubber fibers (WRF) were substituted in different proportions (0%, 5%, 10% and 15%) of the coarse aggregate by volume. Following the solid part was obtained as described, the alkaline activation of GPC specimens was provided using a 12 M NaOH solution. At the end of 28-day curing period, compressive strength, flexural strength, splitting tensile strength, impact resistance, capillary permeability and elevated temperature performance properties were investigated in detail and the results obtained from the mentioned tests were also confirmed by microstructural analysis. Experimental findings revealed that the increase in binder dosage resulted in significant increases in all of the mechanical properties, and it was speculated that this was due to the formation of a denser and more compact microstructure compared to their counterparts produced using lower binder dosage. Besides the negative effects of WRF usage on compressive strength and resistance of elevated temperature, the other performance criteria such as flexural strength, impact resistance and splitting tensile strength values of GPC samples significantly improved with the usage of WRF. As a result, experimental findings demonstrated that the usage of waste rubber fibers in the production of GPC was advantageous in terms of some mechanical and durability properties.

Effect of fibre addition on the static and dynamic compressive properties of ambient-cured geopolymer concrete

This paper presents an experimental study on the static and dynamic compressive properties of ambient-cured fibre reinforced geopolymer concrete (FRGPC) containing mono steel, mono polypropylene (PP) or hybrid steel-PP fibres. A Split Hopkinson Pressure Bar (SHPB) was used to carry out dynamic compressive tests under different strain rates up to 130.5 s−1. The effects of fibre addition on static compressive strength, splitting tensile strength, dynamic failure process and damage mode, dynamic compressive strength, specific energy absorption and dynamic increase factor (DIF) were investigated and analysed. The results revealed mono steel fibre as the most effective in improving static compressive and splitting tensile strengths, which increased by 21.92% and 21.05% respectively, compared to plain geopolymer concrete (GPC). The dynamic compressive strength of both plain GPC and FRGPC increased with the increase of strain rate. There is a positive relationship between DIFs of compressive strengths and strain rates for all GPC and FRGPC samples. The samples containing mono PP fibres showed the most strain rate sensitivity with respect to compressive strengths and specific energy absorption within the tested strain rates. Furthermore, empirical formulae are proposed accordingly to predict the DIFs and specific energy absorption of ambient-cured GPC and FRGPC.