Geopolymer Concrete Mixes Research Articles

RETRACTED: Fresh and mechanical performances of recycled plastic aggregate geopolymer concrete modified with Nano-silica: Experimental and computational investigation

Concerning environmental concerns, it has become crucial to invent and develop alternative construction materials that can replace ordinary Portland cement and use waste materials instead of natural aggregates in the production of concrete. An important advancement in this area is the utilization of recycled plastics to create geopolymer concrete, which helps reduce plastic waste and minimize the environmental impact of construction materials. Since plastics have become a significant environmental issue, it is imperative to find ways to recycle them for a sustainable future. Thus, this study was conducted involving the preparation of seventeen different mixtures of geopolymer concrete (GPC) in three stages. In the first stage, five GPC mixes were created with varying amounts of nano-silica (NS) ranging from 0 % to 4 %. The main objective of this stage was to determine the optimal NS content that could enhance the performance of the GPC matrix. In the second stage, recycled plastic aggregates (RPA) were introduced to replace a portion of the fine aggregates, ranging from 0.05 to 0.5 volume percentages. This aimed to assess the impact of RPAs on the fresh GPC and its mechanical properties. The third stage involved an analysis to improve the performance of the GPC compound incorporating RPAs. The optimal NS content identified in the first stage was utilized for all mixtures with RPA. Lastly, several modeling techniques, including artificial neural network, M5P tree, multiple linear regression, full quadratic, multi-expression programming, and linear regression, were employed to predict the compressive strength of the GPC compound. The results demonstrated that the addition of nano-silica increased the compressive strength of the GPC mixtures by 6.3 %, 13.4 %, 20.5 %, 21 %, and 21.9 % at curing ages of 3, 7, 28, 90, and 180 days, respectively, when using 3 % NS content compared to the control GPC mixture. However, the inclusion of NS had a negative impact on the workability of the GPC mixes. Furthermore, incorporating RPAs reduced both the workability and compressive strength of the GPC compound. In the end, the results obtained from the modeling analysis revealed that the compressive strength of GPC could be predicted with a high degree of accuracy by taking into account the mixture proportions of its constituents. Among the various techniques used, it was found that the artificial neural network model outperformed other methods in accurately forecasting the compressive strength of GPC. This indicates that the neural network model is a superior and reliable approach for estimating the strength characteristics of GPC, providing valuable insights for optimizing its composition and enhancing its overall performance.

Strength, life cycle analysis, embodied energy and cost-sensitivity assessment of sugarcane bagasse ash-based ternary blends of geopolymer concrete

The sustainability of cement concrete is always a subject of concern and hence, less polluting concrete alternatives are being explored. Geopolymer concrete can be an alternative, which may be partly or fully cement-free. However, there exists a huge gap in the knowledge of quantification for ecological advancements that can be achieved. This study reports on the life cycle assessment (LCA) of five different geopolymer concrete mixes made up of ternary blends of sugarcane bagasse ash, blast furnace slag and fly ash. The results coupled with 28-day mechanical test results were compared with traditional cement concrete of similar grade. Correlation analysis was carried out among the obtained results to determine Pearson’s coefficient and Spearman’s rho factor. The aspect of cost and embodied energy was also studied simultaneously. The analyses showed that conventional concrete is more harmful in all ecological impact categories as compared to other alternative concretes except majorly Ozone layer depletion, Carcinogens and Mineral extraction. The sugarcane bagasse ash-based geopolymer concrete mixtures were also found to be cost and embodied energy-effective as compared to traditional concrete.

Mechanical and bond behaviour of high volume Ultrafine-slag blended fly ash based alkali activated concrete

The development of Geopolymer concrete (GPC) mixes by employing large volume of ultrafine ground granulated blast furnace slag (UBFS) blended with Fly ash (FA) and activated by sodium hydroxide (SH) has been presented in this study. Several GPC mixes has been prepared to investigate the effect of varying alkali content, fine aggregate to total aggregate ratio (s/a) and molar concentration (M) of alkali activator on the fresh and hardened characteristics, including the bond strength with Portland cement concrete (PCC). The properties of the GPC mixes are assessed by workability test, compressive strength test, split tensile strength test and slant shear test, including the microstructure through FESEM (Field Emission Scan Electron Microscopy) and X-ray diffraction (XRD). The test result shows that s/a ratio is a crucial factor in controlling segregation and bleeding in GPC. However, an ideal GPC mix with s/a ratio 0.41 provides a better packing resulting in improved mechanical properties. Application of high volume UBFS in the GPC exhibits better reaction products as shown by the microstructure at a relatively lower alkali concentration which ultimately leads to higher strength. Superior bond strength is achieved between the GPC and old PCC substrate; however, the molarity of SH significantly affects the adhesion property of GPC.

A study on development of pavement quality geopolymer concrete for low volume roads

The world's rural roads are extensively interconnected with all conventional OPC (Ordinary Portland cement) concrete roads and with little traffic. The main ingredient in concrete pavements is ordinary Portland cement which has serious environmental issues like CO2 emissions during the production. A replacement for traditional cement-based concrete is available in the form of geo-polymer concrete (GPC). The current work mainly emphasis on the mix development of Fly Ash (FA)-Ground Granulated Blast Furnace Slag (GGBFS) based GPC for rigid pavements application in low volume concrete roads (LVCR). The study consists of preparing GPC mixes with total of 8 combinations comprising GGBFS and fly-ash as binders (GGBFS-40% and 50% replacement to FA), two different alkaline solution/binder ratio (As/Bi = 0.45 and 0.50) and sodium hydroxide (NaOH) solutions of 8 and 10 Molarities with a constant proportion of sodium silicate (Na2SiO3) by sodium hydroxide (NaOH) is 2.5 by 1. All the specimens were kept under outdoor curing only. The guidelines by IRC:SP:62-2014 recommended that the characteristic compressive strength of concrete at 28 days used to pave ruralcountry roads be at least 30 MPa, while the 28 days flexural strength should not be less than 3.8 MPa. From the experimental study it was noticed that, when the GGBFS content and NaOH molarity increases, the mix’s workability is getting reduced and mechanical properties were improved significantly whereas when the As/Bi increases from 0.45 to 0.50, the mix workability increases and also mechanical properties too. And also concluded that, the FA-GGBFS based GPC mix for low volume concrete roads is attained with GGBFS content 40% to 50% replacement for fly ash and NaOH Concentration of 10 M with a binder content of 400 kg/m3 at an As/Bi ratio of 0.45 and 0.50 are adequate to meet the requirements for low volume concrete road standards.

Physico-Mechanical Evaluation of Geopolymer Concrete Activated by Sodium Hydroxide and Silica Fume-Synthesised Sodium Silicate Solution

Commercial sodium hydroxide (NaOH) and sodium silicate (SS) have remained two of the leading alkaline activators widely used in producing geopolymer concrete, despite some identified negatives regarding their availability and additional CO2 emissions relating to the overall manufacturing process. This study reports the viability of developing geopolymer concrete using a laboratory-synthesised silica fume (SF)-derived SS solution in combination with NaOH at a molarity of 10M as an alternative binary alkali-alkaline activator to Ground Granulated Blast Furnace slag (GGBS). The use of SF in the development of geoolymer activators will pave the way for the quality usage of other high-silica content by-products from nature, industry, and agriculture. In the currently reported proof of concept, four geopolymer concrete batches were produced using different alkaline activator/precursor-A/P ratios (0.5 and 0.9) and SS to NaOH-SS/SH volume ratios (0.8/1.2 and 1.2/0.8), to establish the impact on the engineering performance. Two controls were adopted for ordinary and geopolymer concrete mixes. The engineering performance was assessed using slump and compaction index (CI) tests, while the Unconfined Compressive Strength (UCS) and tensile splitting (TS) tests were measured at different curing ages in accordance with their appropriate standards. The results indicated a reduction in slump values as the A/P ratio decreased, while the CI values showed a reversal of the identified trend in slump. Consequently, mix GC2 attained the highest UCS strength gain (62.6 MPa), displaying the superiority of the alkali activation and polymerisation process over the CSH gel. Furthermore, the impact of A/P variation on the UCS was more pronounced than SS/SH due to its vital contribution to the overall geopolymerisation process.

Tensile performance of cast-in headed anchors in ambient-temperature cured fly ash-based geopolymer concretes with varying fracture energies

The performance of cast-in headed anchors subjected to tensile loading in ambient-temperature cured fly ash-based geopolymer concrete was investigated in this research. Varying sizes of anchors were installed in geopolymer concrete at effective embedment depths ranging between 40 mm and 90 mm. The new experimental results were compared with those of a previous study on the tensile performance of anchors in geopolymer concrete with similar compressive and tensile strengths, but different fracture energy and elastic modulus. The influence on the concrete cone capacity and its angle due to the varying anchor head size ratio and fracture energy were evaluated in detail. A 43% difference in fracture energy between the two geopolymer concrete mixes translated to 17% increase in concrete cone capacity of the tested anchors. Moreover, the obtained results were compared with the existing prediction models, the Linear Fracture Mechanics (LFM), and Concrete Capacity Design (CCD) models, as well as the design models by ACI 318 and AS 3850.1. The results showed that most of the existing models overestimate the concrete cone capacity of anchors tested in this study and the test-to-prediction ratios depend on the effective embedment depth of anchors. After statistical analysis of experimental results, a new modified equation was proposed to extend the use of the existing CCD model to anchors installed in geopolymer concrete studied in this article.

Evaluating the Impact of Inclusion Metakaolin and Silica Fume on the Green and Mechanical Properties of Low Calcium Fly Ash Concrete

Generally, low calcium fly ash concretes (FFACs) subjected to ambient temperatures exhibit low initial strengths. Thus, FFACs require higher temperatures to improve the monomer dissolutions, but that increases the energy consumption. Thus, this paper aims to evaluate the influence of the incorporation of different dosages of silica fume (SF) and metakaolin (MK) on the green and hardened properties of FFACs cured at room temperature of 21 ˚C. Slump and air content tests were applied to evaluate the green characteristics of the designed geopolymer concrete mixes (GPCMs). The hardened properties of FFACs were assessed in terms of compressive, flexural, and splitting tensile strengths at different curing ages. Outcomes revealed that the slump and air content of GPCMs declined with improving SF or MK percentages. The 28 days flexural, compressive, and splitting tensile strengths of FFACs manufactured with the optimum dosages of 20% MK and 10% SF cured at 21 ˚C were evidently higher than those of FFACs (100 % FFA) subjected to curing temperatures ranging from 10-to-50 ˚C. Also, the strength enhancement of MK was relatively comparable to those of SF with less requirement for superplasticizers.

Physical characteristics and mechanical properties of a sustainable lightweight geopolymer based self-compacting concrete with expanded clay aggregates

Geopolymer Concrete (GPC) is a unique and sustainable building material that has the potential to be transformed into a self-compacted lightweight composite for industrial applications. This paper investigates the sustainability of self-compactable lightweight geopolymer concrete (SCLGC) made from Expanded Clay Aggregate (ECA) to further explore this front. In this study, the physical properties of SCLGC, such as slump flow test, T500 test, V-funnel, and J-ring tests, are examined. Furthermore, the density, Ultrasonic Pulse Velocity (UPV), compressive strength, splitting tensile strength, and impact resistance are also tested to evaluate the mechanical properties of SCLGC mix with various concentrations of Sodium Hydroxide (SH) cured under different curing regimes. The aforenoted properties are examined following the American, Indian and European guidelines. In addition, microstructural analysis is conducted to assess the compactness and internal structure of SCLGC blends with varying SH concentrations cured under different curing regimes. Finally, the sustainability aspects of GPC and SCLGC mixes are analyzed through the Life Cycle Assessment (LCA) and Environmental Impact Assessment (EIA) to evaluate the energy requirement and CO2 emission and cost. The Sustainability analysis was performed to evaluate the energy requirement and CO2 emission of SCLGC in the production of 1 m3 concrete based on the previous literatures. The significance of the proposed research work emphasizes the utilization of ECA as an aggregate material for the development of SCLGC. The cost, carbon and energy efficiency of the SCLGC's mixes were estimated. Mix with ECA requires higher energy demand and emits high CO2 in the open atmosphere. Based on the present analysis it can be concluded that an increase in the concentration of activator solution increases the energy demand and emits more amount of CO2. The inference from the present study reveals ECA can be employed for the production of SCLGC with the replacement percentage not exceeding 50%.

Investigating the Properties of Foamed Fly Ash and Metakaolin-based Geopolymer Concrete

A study has been carried out to produce environmentally friendly lightweight concrete by total replacement of cement with fly ash and metakaolin as binder material by adopting the pre-formed foam method. In this research, a geopolymer paste was produced by mixing fly ash or metakaolin with an alkali solution of sodium silicate and sodium hydroxide. Five mixes were produced at a density of 1000 kg/m³ as four foamed geopolymer concrete and one conventional foamed concrete made with cement paste as a binding medium. During the laboratory work, many trials were carried out to solve the segregation of the cellular structure from the mortar. From the results, it was noticed that the pore merging is more evident in foamed concrete mixes rather than in foamed geopolymer concrete mixes. In addition, the pore structure of fly ash-based geopolymer concrete is finer than that of metakaolin-based concrete geopolymer. The greater degree of pore merging resulted in forming of larger irregular voids and wider distribution of pore sizes and finally reducing strength. In general, the permeation, mechanical and thermal properties of foamed mixes made with geopolymer pastes are better than those of foamed mix made with cement paste. For a geopolymer paste, using metakaolin and fly ash C in combination helped in achieving the best properties i.e. reduction in water absorption by 34%, increasing strength by 78% and decreasing thermal conductivity by 44%.

Enhancement of the Mechanical Properties of a Geopolymer Concrete Due to Chemical and Microstructural Interaction of the Binder Material

Many experimentation and researchers were made in the recent decades in concrete and advancement in the field of concrete technology were given a major focus. In the years of research, many new replacement materials were identified and further details studies over the materials were made to have a clear and better idea about the material. In this study, the binder which is to be cement basically is replaced with a combination of Alccofine-1203(A), Metakaolin (MK), and Ground Granulated Blast-furnace Slag (GGBS) in different ratios to arrive a geopolymer concrete mix. In addition, the study also focuses on the chemical interaction of the replacement material and its microstructure interaction. The liquid binder (l/b) ratios varied between 0.48 to 0.54, and about seven geopolymer concrete mixes were arrived and experimental investigation done for mechanical property. The maximum compressive strength obtained from the mix proportions G50M35A15 at an l/b ratio of 0.50 was taken as a mix design for the Geopolymer mix. The identified combination of Granulated Blast-furnace Slag, Metakaolin, Alccofine-1203 (GMA) is used for further study. In general, when finer particles were replaced or added to the material, the finer particle will reduce the voids and thereby increasing the strength of the concrete by developing a denser material combination. Experimentally, results proves that there is a significant hike in the mechanical behaviour of the concrete. The microstructure investigation is carried out through SEM analysis and energy dispersive X-ray analysis (EDAX) which indicated a good interlocking characteristics of the materials which inturn directly impacts the mechanical properties of the concrete.

Multi-response optimization of ceramic waste geopolymer concrete using BWM and TOPSIS-based taguchi methods

This study examines the effect of using ceramic waste (CW) and granulated blast furnace slag (GBFS) as a blended binder on the mechanical and durability characteristics of geopolymer concrete. The experimental design was carried out following the Taguchi approach for five factors, each having four levels, to produce an L16 orthogonal array. The factors included the binder content, CW replacement by GBFS (CW:GBFS), ratio of alkaline solution to binder (AS:B), ratio of sodium silicate solution to sodium hydroxide solution (S:H), and sodium hydroxide (NaOH) solution concentration. The quality criteria were compressive strength, elastic modulus, splitting tensile strength, flexural strength, abrasion resistance, water absorption, sorptivity, ultrasonic pulse velocity, and bulk resistivity. The proportions of CW-GBFS geopolymer concrete mixes were optimized using the best-worst method and TOPSIS approach considering 9, 5, and 2 quality criteria in three scenarios. Experimental test results revealed that the optimum mix was the same for both optimization techniques irrespective of the number of quality criteria considered. The optimum mix comprised a binder content of 450 kg/m3, CW:GBFS ratio of 2:3, AS:B ratio of 1:2, S:H ratio of 3:2, and NaOH solution concentration of 10 M. The anticipated results of the optimum mix were validated through experimental testing. Its experimental test results included compressive, flexural, and splitting tensile strengths of 58.9, 5.72, and 3.81 MPa, respectively. Meanwhile, it had a water absorption of 3.45%, elastic modulus of 27.4 GPa, sorptivity of 0.025 mm/s0.5, bulk resistivity of 4652 Ω•cm, abrasion resistance of 8.98%, and UPV of 6745 m/s.

Design of Low Alkali activator Geopolymer Concrete Mixtures

<p class="Abstract">This paper presents the results of research on the design of geopolymer concrete mixes. The main objective of this research is to develop an efficient and easy design of low-alkaline activator geopolymer concrete mixture, which until now has been the biggest obstacle in the use of geopolymer concrete. The variables reviewed were the amount of alkaline activator was quite low at 4%, room temperature and 60oC ratio of alkaline activator/fly ash (AAS/FA) were 0.35, 0.4, 0.5, 0.6. The test results show the parameters of geopolymer concrete with low alkali activator 4%, sodium silicate/sodium hydroxide ratio 2.5%, sodium hydroxide molarity 14M, type F fly ash and the discovery of the relationship model of compressive strength and the ratio of alkali activator/fly ash with a very high correlation as basic development of geopolymer concrete mix design. The design of the geopolymer concrete mix developed is easy because it is application-based and efficient because it only requires 4% alkaline activator.</p>

Performance evaluation of sodium silicate waste as a replacement for conventional sand in geopolymer concrete

Excessive exploitation and increased demand for conventional sand made an unbalanced ecosystem; a suitable and sustainable alternative has to be adopted to preserve the ecosystem. The present investigation examines the performance of Sodium Silicate Waste (SSW), an industrial by-product of 100% sand replacement in geopolymer concrete (GPC). The investigation's significance lies in employing industrial waste SSW as an alternative for regular mining sand. The densities of all GPC mixes fall between 2136.7 kg/m3 and 1750.28 kg/m3. Following EN 206-1, the SSW blended GPC can be termed as lightweight concrete, which falls under energy-efficient and sustainable construction practices. The test results show that the percentage increase in industrial waste SSW from 25% to 100% improves the Compressive Strength (CS) to peak at 45.01 MPa. Comparative analysis between River Sand (RS) and SSW mixes shows that SSW blended GPC mixes produced higher strength with the increasing SSW content than GPC mixes with RS. From the Eco-efficient performances, it is concluded that replacing RS with SSW with 25%–100% may lead to sustainable GPC production in terms of cost, carbon, and energy efficiencies.

Development and characterization of ceramic waste powder-slag blended geopolymer concrete designed using Taguchi method

• Taguchi L16 matrix was used to design the experiments with five factors and four levels. • Taguchi method optimized the mix design of CWP-slag blended geopolymer concrete. • The compressive strength of the optimum mix reached 58.9 MPa. • Mechanical and durability properties were correlated using analytical regression models. • Scanning electron microscopy highlighted the formation of C-A-S-H and N -A-S-H gels. The ability to utilize industrial by-products in the production of cement-free geopolymer concrete is a promising technology. However, the development, characterization, and optimization of geopolymer concrete made with ceramic waste powder (CWP) and ground granulated blast furnace slag (or simply slag) have not been examined yet. This paper investigates the mechanical and durability properties of geopolymer concrete incorporating CWP and slag. Taguchi method was employed to design sixteen CWP-slag blended geopolymer concrete mixes. Five factors with four levels were considered in the design, including binder content, CWP replacement percentage by slag, alkali-activator solution to binder ratio (AAS/Binder), sodium silicate (SS) to sodium hydroxide (SH) ratio (SS/SH), and SH solution molarity. Results showed that geopolymer concrete properties remarkably degraded when CWP served as the sole binding material. However, combining 40 % CWP and 60 % slag yielded superior performance than the control mix made with 100 % slag. Correlations between mechanical and durability properties were developed in the form of regression models. The optimal compressive strength response (58.9 MPa) of CWP geopolymer concrete was attained using 450 kg/m 3 of binder content, 60 % of CWP replacement by slag, 0.5 of AAS/Binder, 1.5 of SS/SH, and 10 M of SH solution molarity. Scanning electron microscope and energy-dispersive X-ray spectroscopy highlighted the formation of calcium aluminum silicate hydrate and calcium silicate hydrate gels. Experimental findings provide evidence of the ability to utilize CWP in the production of structural grade geopolymer concrete.

Experimental and Artificial Neural Network-Based Study on the Sorptivity Characteristics of Geopolymer Concrete with Recycled Cementitious Materials and Basalt Fibres

The environmental concerns regarding the production of the most widely consumed cement construction material have led to the need for developing sustainable alternatives. Using recycled industry waste products such as fly ash and slag via geopolymerisation has led to the development of geopolymer cement—an efficient replacement for ordinary Portland cement (OPC). Adopting geopolymer cement and concrete as a construction material reduces greenhouse gas and promotes the recycling of waste products. This study explores the suitability of a unique geopolymer concrete mix made of recycled cementitious materials including industry waste products such as fly ash, micro fly ash and slag for use in aggressive environments. Sorptivity tests are conducted to assess the durability of concrete and indicate the cementitious material’s ability to transmit water through the capillary forces. This study thus reports on the sorptivity characteristics of a newly developed self-compacting geopolymer concrete and two other fibre geopolymer concrete mixes containing 1% (by weight) of 12 mm- or 30 mm-long basalt fibres. The addition of basalt fibres indicated less water absorption and moisture ingress than the mix without fibres. The study used 18 specimens from three geopolymer concrete mixes, and the results showed that adding fibres improved the durability performance in terms of resistance to moisture ingress. Finally, an artificial neural network model is developed to predict the absorption rates of geopolymer concrete specimens using MATLAB. The prediction models reported excellent agreement between experimental and simulated datasets.

A statistical models to predict strength development of eight molarity geopolymer concrete

Geopolymer concrete has emerged as a viable alternative to traditional concrete. Geopolymer is amorphous to semi-crystalline materials synthesized from materials generally containing SiO2 and Al2O3 compounds as a source of aluminosilicates. This study aims to develop and validate statistical models to predict the strength development of Geopolymer concrete with 8 molarity of NaOH using data from current experimental work as well as experimental data gathered from local and international literature with different R ratios; SiO2/Al2O3. The present experimental study used binary and ternary systems of source materials, Fly ash FA, Ground Granulated Blast-furnace Slag GGBS, and Metakaolin MK, to achieve different percentages of R ratios ranging from 1.42 to 3.6. Seven Geopolymer concrete mixes with varied R ratios were used in the current experimental portion of the inquiry. Compressive, splitting, and flexural strengths were the characteristics determined. Based on the findings of the trials, it was found that the R ratio has a considerable impact on the mechanical performance of the final product. Results showed that; the compressive strength, splitting tensile strength, and flexural strength at the highest value of R ratio of 3.6 used increased by 362%, 272%, and 333%, respectively, compared with those strengths at the lower R ratio of 2.01 used. Linear and non-linear regression analyses were performed by the Statistical Package for the Social Sciences (SPSS) software version 25 to generate the developed models. The statistical models indicated that the R ratio could reasonably estimate the geopolymer's strength with a statistical correlation coefficient of 0.86, 0.93, and 0.86 for compressive, splitting, and flexural strengths.

Experimental investigations on mechanical properties of normal and high strength high calcium geopolymer concrete

Alkali activated (Geopolymer) concrete is an excellent and viable alternative to Portland cement based concrete as it can be produced using industrial by-products such as Ground Granulated Blast Furnace Slag (GGBS) and fly ash (source of reactive alumino-silicates) along with less energy craving ingredients such as alkali activators. In this study, slag based geopolymeric concrete mixes of M40 and M80 grade were prepared using GGBS and fly ash in proportion of 70:30 by weight. Geopolymeric binder was activated using combination of Sodium hydroxide and Sodium Silicate. Activator modulus (i.e. SiO2 / Na2O) was maintained as 1 and Na2O was kept as 7% and 8% by weight of total binder respectively for M40 and M80 grade geopolymeric concrete mixes. Both the concrete mixes were evaluated for fresh properties of concrete (slump and air content) along with mechanical properties of hardened concrete. Performance of geopolymeric mixes was compared with two conventional concrete mixes of equivalent grade (i.e. M40 and M80) in terms of aforementioned mechanical properties. Study concludes that slag based geopolymer concrete mixes of a particular strength were developed at significantly lower total binder content in comparison to cementitious binder required for development of conventional Portland cement based concrete of equivalent strength. Early age compressive strength of normal strength geopolymeric concrete mixes is higher in comparison to conventional concrete mix. Modulus of elasticity and Poisson’s ratio of geopolymeric mixes of both normal and high grade are observed to be lower in comparison to their corresponding conventional concrete mixes of equivalent strength.

Development and strength assessment of eco-friendly geopolymer concrete made with natural and recycled aggregates

Purpose This study aims to develop geopolymer concrete (GPC) using manufactured sand (M-sand) and recycled concrete aggregate (RCA) under different curing conditions. GPC is a sustainable construction material developed with industrial waste products such as fly ash to eliminate the use of cement in the production of concrete. GPC requires heat curing for the attainment of early age strength. The development of GPC under heat curing conditions is a hard process in practice. To overcome such circumstances, an attempt was made to develop the GPC under different curing conditions with the aid of coarse aggregate (CA) and RCA. The influence of different curing conditions on strength gain and microstructural characteristics of GPC is investigated. Mechanical properties of GPC such as compressive strength, tensile strength, flexural strength and elastic modulus are reported and discussed. Design/methodology/approach This study focuses on the assessment of mechanical and microstructure characterization of eco-efficient GPC developed with natural CA and RCAs. The required optimum quantity of binder, alkali activator, alkaline liquid to binder ratio and aggregates was determined by appropriate trials. Three types of curing methods, namely, ambient, oven and water, were used for the development of GPC mixes. Following the properties of RCA, it is realistic to substitute up to 40% of coarser aggregates as the resulting aggregate mix falls within the requirements of the analyzed mix. Findings Special attention is required for the mix with RCA because the mix’s consistency is affected by the high water absorption of the RCA mix. GPC specimens cured at ambient and water conditions exhibited marginal variation in the compressive strength for both CA and RCA. The compressive strength of GPC mixes prepared with RCA was marginally higher than that of the GPC made with CA under different curing regimes. RCA can be used as a sustainable material in lieu of CA in GPC. Originality/value The main significance of this research work is to develop the optimal mix design with appropriate mix proportion. The present study proposes a satisfactory methodology that enhances the mechanical strength of GPC as the guidelines are not available in the standards to address this problem. Effective use of waste materials such as fly ash and recycled aggregate for the development of GPC is another major research focus in the proposed investigation.

Behavior evaluation of sustainable high strength geopolymer concrete based on fly ash, metakaolin, and slag

The environmental challenge such as high energy demand, consuming raw materials, large CO2 emissions, and many other reasons associated with ordinary Portland cement manufacturing-led us to search for alternatives such as green concrete or geopolymer concrete. In this paper industrial wastes like fly ash, metakaolin, and granulated blast furnace slag were used as a base for high strength geopolymer concrete (HSGC). Four high strength concrete (HSC) mixes with Portland cement were produced for comparison with fifteen different geopolymer concrete mixes. All mixes were cast, cured, and tested. Slump and air content were measured as fresh properties for both HSC and HSGC mixes. Compressive strength at 3, 7, 28, and 91 days, splitting tensile strength, flexural strength, and modulus of elasticity were also measured and analyzed as mechanical properties. Durability properties like water permeability coefficient, drying shrinkage at 3, 7, 14, 21, 28, 56, and 91 days and temperature studies from 100 ° to 700 ° were investigated. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy analysis of cement and geopolymer concrete mixes were conducted. Regarding fresh properties results showed that the geopolymer concrete based on slag with 500 kg/m3 showed 225 mm slump, while in hardened properties, the mix contained 200 kg of metakaolin with 300 kg of slag had the greatest compressive strength in both early and late age 63.3, 82.6 MPa, respectively, also had the greatest splitting tensile strength 6.2 MPa, flexural strength reached 9.2 MPa and modulus of elasticity was 37.68 GPa. Also, the coefficient of permeability decreases as the granulated blast furnace slag increases. The mineral additives contributed to reducing the dry shrinkage of geopolymer concrete. SEM images exhibited that the geopolymer matrix contained more dispersed small-sized pores which indicate a higher compressive strength absolutely than other experimental mixes.

Calibration of a stress-strain response for geopolymer concrete under axial compressive load

The use of geopolymer concrete (GPC) in common load-bearing structures is still limited, mainly due to the lack of specific design procedures and limited understanding of the stress–strain behavior under uniaxial loading. The present work investigates the mechanical responses of GPC under axial compressive load by conducting a large number of experiments. For this purpose, 198 samples with three GPC mixes were designed, including concrete grades of 30, 40, and 50 MPa. The samples were prepared following the ASTM standards to determine the stress–strain relationship under compression. The results showed that fly ash-based GPC had average elastic modulus values of 30.424, 31.497, and 33.650 GPa, respectively, for G30, G40, and G50, lower than estimated using formulae for Ordinary Portland Cement (OPC) concrete, such as ACI standard 318-11, AASHTO-2007, and others. Furthermore, a novel model of GPC stress–strain response was proposed, mainly based on the empirical formulation suggested by Sargin using a modified factor D. Besides, the deformation of GPC was observed larger than that of OPC with similar strength, for instance, the strain at peak stress [Formula: see text]. The GPC was also found to have better plasticity behavior than OPC while conducting the axial stress–strain response, with the obtained values of [Formula: see text]. The findings of this work might lead to additional in-depth research into GPC's mechanical characteristics, particularly its structural behavior.