Low-calcium Fly Ash-based Geopolymer Research Articles

Effect of initial curing conditions on the durability performance of low-calcium fly ash-based geopolymer mortars

Geopolymer composite production has become an indispensable product to reduce carbon dioxide emissions, which have become an important problem today, and to provide green sustainability. Concerns about the global climate change problem have also accelerated geopolymer studies. This research investigated the mechanical and durability characteristics of low-calcium fly ash (LCFA) based geopolymer mortars with different curing temperatures and times. Two forms of curing conditions were applied; the first one was standard curing at room temperature (20±3°C and RH 65±10%) and the second one was cured in the hot air at 40°C, 60°C, and 80°C for 24h, 48h, and 72h followed by standard curing. After all curing processes, compressive strength, flexural strength, water absorption, void ratio, resistance to elevated temperatures, and freeze–thaw conditions were determined experimentally. In addition, SEM analysis was performed before and after durability tests for comparison purposes. Also, XRD and TGA analyzes were performed. According to test results, curing specimens at longer times and higher temperatures has been shown to increase compressive strength results. The highest compressive strength value was reached at 80°C after 72h of curing. Geopolymer specimens subjected to elevated temperatures (600°C and 900°C) lost a significant part of their strength value. After the freeze–thaw test, LCFA-based geopolymer specimens showed more than 70% resistance. The freeze–thaw resistance of geopolymer samples was positively affected on long-term curing at high temperatures, but high-temperature resistance was impacted negatively.

Enhancing the properties of geopolymer concrete using nano-silica and microstructure assessment: a sustainable approach

Nowadays low calcium fly ash-based geopolymer concrete can be replaced with cement-based concrete to avoid the adverse effect of manufacturing cement on the environment. Utilization of geopolymer concrete instead of traditional concrete using low calcium fly ash and nano silica reduces a significant amount of CO­2 emission towards the atmosphere. However, the performance of geopolymer concrete is less than that of Portland cement concrete. To improve the performance of geopolymer concrete nano silica was used in the present study. In this work, geopolymer concrete was made utilizing fly ash, ground granular blast furnace slag (GGBS), and sugarcane bagasse ash. In the first instance, binary combinations i.e. fly ash and GGBS were employed as cementitious materials for the production of geopolymer concrete. In the second instance, a ternary mixture of pozzolanic material was prepared by taking 25% GGBS, 65% Fly ash, and 10% bagasse ash. In the third instance, varying percentages of nanoparticles were used for the above ternary mixture. The mechanical and durability properties of the geopolymer composite that was made earlier were tested. The compressive strength and split tensile strength of geopolymer composites were assessed for mechanical properties and a rapid chloride permeability test, water absorption test, and acid attack test were done to know about the porosity of concrete. Results showed that, with a dose of 4% nanoparticles, the durability and strength properties of the concrete had improved the most. The GCBA-N4 mixture had the highest split tensile and compressive strength was measured to be 2.91 MPa and 41.33 MPa and the rapid chloride permeability test, water absorption rate, and percentage of mass loss due to sulfate attack were found as a minimum for GCBA-N4 specimen.

Durability performance of low calcium Flyash-Based geopolymer concrete

This investigation aims to systematically evaluate the durability performance of 30 MPa grade of low calcium fly ash-based geopolymer concrete. The geopolymer concrete with fly ash as binder is manufactured using an alkaline activator solution (of 14 Molar and Na2Sio3/NaOH ratio of 2.5). The results were also compared with the Portland cement concrete of similar grade. The concrete samples were subjected to water absorption, water permeability, sorptivity, acid resistance, sulphate resistance, and rapid chloride penetration tests. Water absorption study findings revealed less water absorption by low calcium fly ash-based geopolymer concrete than Portland cement concrete. Also, the water permeability tests on geopolymer concrete indicated lower water penetration depth compared to Portland cement concrete. Sorptivity test results depict lower sorptivity by geopolymer concrete over ordinary Portland cement concrete. Geopolymer concrete shows better acid resistance and sulphate resistance performance than Portland cement concrete in terms of residual compressive strength. Rapid chloride penetration test results indicated moderate chloride penetrability of geopolymer concrete and low chloride penetrability by Portland cement concrete. In general, low calcium fly ash based geopolymer concrete outperformed Portland cement concrete in most durability indices, which led to the conclusion that low calcium fly ash based geopolymer concrete durability performance was superior to that of concrete of a similar grade made of Portland cement concrete.

Effect of magnesium sulfate on properties of low calcium fly ash based-geopolymer- treated hemp shiv bio-concrete

Sulfate attack is one of the major threats to concrete structures. In this study, strength degradation, by magnesium sulfate (MgSO4) reaction, of low-calcium fly ash geopolymer-hemp shiv concrete was carefully investigated. The hemp shiv was pretreated with AlCl3-KOH to prevent water absorption. Air and water curing were also performed to elucidate the effects of air and water degradation that might have co-contributed to the degradation of the geopolymer concretes. After the MgSO4 treatment, the strength reductions of the geopolymer-hemp shiv concretes were 1.5–2.5 MPa in flexural mode and 0.2–0.6 MPa in compressive mode while the strength reduction of the geopolymer matrix was around 2 MPa in both strength modes. The results suggested the ability to prevent sulfate attack of the AlCl3-KOH pre-treatment and thus degradation was primarily from the geopolymer matrix. However, the TGA and XRD analyses did not observe relevant phase changes or significant occurrences of the strength detrimental phase such as brucite (Mg(OH)2) in the matrix bulk after the MgSO4 treatment, suggesting that the degradation was not according to these factors. Besides, similar degradation was observed in the water-cured samples. Strength degradation was suggested to be due to the migration of sodium ions from the geopolymer gel structure in the aqueous-curing system causing structural disintegration.

Experimental modal analysis of fly ash-based geopolymer concrete specimens via modal circles, mode indication functions, and mode shape animations

The polymerization process of geopolymer concrete is entirely different from the hydration process of ordinary Portland cement concrete. Therefore, it is necessary to re-examine this new material's engineering properties from the ground up. To date, researchers have investigated many engineering properties, but in the whole literature, the available information about the modal characteristics is minimal. Additionally, since the evaluations in the literature are made only on the A ratio (sodium silicate to sodium hydroxide ratio), no significant relationship has been reported between damping and activators. So, this study is conducted to draw attention to this gap in the literature and examine the effect of fundamental geopolymer concrete component ratios on modal characteristics. For these purposes, large-scale heat-cured low-calcium fly ash-based geopolymer concrete mix variations are produced and investigated by performing experimental modal analysis via the advanced modal circle method and mode indication functions. It is found that individually analyzing the total amount of water from the activators and the pure chemical dosages provides more meaningful results than the traditional A ratio. According to the analysis from this perspective, increasing the dosage of pure sodium silicate in the mixture generally increases the damping; on the other hand, it decreases the resonance frequency and dynamic elasticity modulus. Obtained findings of this study reveal some of the methods and benefits of appropriately designing this sustainable material against dynamic loads.

Development of Mix Design Guidelines for Low Calcium Fly Ash-based Geopolymer Concrete – A Quantitative Approach

Development of Mix Design Guidelines for Low Calcium Fly Ash-based Geopolymer Concrete – A Quantitative Approach

Development of Detailed Mix Design Methodology for Low Calcium Fly Ash Based Geopolymer Concrete Incorporating OPC and Crumb Rubber

This experimental study proposes a systematic mix-design procedure to develop rubberized geopolymer concrete (RGPC). The developed method is meant to identify the mix ratios for the production of high-strength, low-calcium fly ash-based geopolymer concrete, with OPC as a supplementary binder and crumb rubber as a partial replacement for the fine aggregates. The binder (80% fly ash + 20% OPC) content (350, 375, and 400 kg/m3), crumb rubber percentage (0, 5, 10, and 15%), and NaOH molarity (8, 10, and 12 M) are identified as key variables, with the focus on attaining the targeted compressive strength and workability under heat curing (60 °C). Thirty-six mix designs were tested for their compressive strength after 7 and 28 days, and their graphical relationship with the chosen variables is presented (CR-GPC graphs). A trial experiment with an example is performed to establish the validity of the developed mix-design procedure. It was found that the targeted compressive strength and slump of the rubberized GPC can be achieved with conviction.

Study on the Light Weight Geopolymer Concrete Made of Recycled Aggregates from Lightweight Blocks

Abstract: This study studied the properties of lightweight geopolymer concrete that contained recycled lightweight block aggregate. The recovered blocks are classified as coarse aggregates after being crushed.To reduce greenhouse gas emissions, geopolymers have the potential to be used to create new, environmentally beneficial materials. A new class of building materials called geopolymer concrete (GPC) has a replacement for regular Portland cement concrete (OPCC) and are capable of revolution in the construction sector. The impact of On the strength characteristics, alkaline activators have been investigated. Used fly ash was obtained for this study from a nearby thermal power plant. Samples were produced from low-calcium fly ash through activation with a combination of sodium silicate solution and sodium hydroxide. Fly ash was added to the concrete with a ratio of 0.5. Using a mix proportion and 5,10,15 Molar of sodium hydroxide solution, geopolymer specimens were cast. The samples underwent compression testing. test with ambient temperatures for curing. From the analysis ofLiterature suggests that the combination of the aforementioned ingredients is healing. FromAccording to a review of the literature, the amalgamation of the aforementioned elementshas a favorable effect on the strength properties of geopolymer concrete. Since fly ash is viewed as a waste product, geopolymer concrete made from low-calcium fly ash costs less than Portland cement concrete as a result. Lowcalcium fly ash-based geopolymer concrete has good compressive strength, very little drying shrinkage and minimum creep, great resistance to sulphate attack, and superior acid resistance.

Comparative Study on Strength Characteristics of Fly Ash Based Geopolymer Concrete with 8, 10 & 12 Molar Naoh Activator

Ordinary Portland cement is a major construction material worldwide. Cement manufacturing industry is one of the carbon dioxides emitting sources besides deforestation and burning of fossil fuels. The global warming is caused by the emission of greenhouse gases, such as CO2, to the atmosphere. Among the greenhouse gases, CO2 contributes about 65% of global warming. The cement sector accounts for around 7% of worldwide greenhouse gas emissions of the earth’s atmosphere. In order to address environmental effects associated with Portland cement, Alternative binders for concrete production are needed. Low-calcium (Class F) fly ash-based geopolymer from Vijayawada was used in this study. Geopolymer concrete was made with the help of a thermal power plant. The combination of sodium silicate solution and sodium hydroxide solution was used as alkaline solution for fly ash activation. Alkaline solution to fly ash ratio was varied as 0.45. The concentration of sodium hydroxide solution was maintained as 8M, 10M & 12M (Molars). The curing condition of geopolymer concrete was varied as ambient curing. The compressive strength, Split Tensile Strength of the geopolymer concrete was tested at various ages such as 7 and 28days. From the test results it was found that as the alkaline solution to fly ash ratio increases, the strength of geopolymer concrete also increases.

Development of low-calcium fly ash-based geopolymer mortar using nanosilica and hybrid fibers

Fly ash has been widely explored in alkali-activated concrete technology as a precursor; however, it suffers sudden brittle failure and requires heat activation for early-strength development. Previous studies have demonstrated that these shortcomings can be overcome by adding nanosilica and various types of fibers. However, they were mainly focused on improving the mechanical properties, but there is no clear understanding of the durability and microstructural changes. Therefore, this study systematically addresses the effects of nanosilica sol and hybrid fibers (steel and polypropylene fibers) on the workability, porosity, flexural/compressive strength development, flexural toughness, crack resistance, and durability (subjected to sulfuric acid of pH = 1, 5% sodium sulfate, and 3.5% seawater attacks) of fly ash-based mortars cured at ambient environments. The results demonstrate that nanosilica and hybrid fibers have acceptable simultaneous effects on the properties of mortar. Although they both reduce fluidity, nanosilica improves the pore enlargement caused by fiber materials; thus, it greatly improves the mechanical properties of mortar. The flexural toughness of the mortar with nanosilica and hybrid fibers was approximately 200% higher than that of the pure-fly ash. Only approximately 58.25 mm2 microcracks were observed during the early crack detection, and the residual strength also improved under chemical solution attack. The microstructures were studied by field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction/Rietveld method, and nanoscale 3D X-ray microscopy. The nanosilica enhanced the reactivity of the precursors and refined the pore structure of the mortar due to the changes in the crystalline and amorphous phases, and the hybrid fibers produced composites with good internal characteristics and strong fiber/matrix interfacial bonding.

Alkali-Silica Reaction Resistance and Pore Solution Composition of Low-Calcium Fly Ash-Based Geopolymer Concrete

Low-calcium fly ash-based geopolymer concrete is generally reported to be less vulnerable to alkali-silica reaction (ASR) than conventional ordinary Portland cement concrete. However, the lack of understanding of pore solution composition of the low-calcium fly ash-based geopolymer limits the investigation of the underlying mechanisms for the low ASR-induced expansion in the geopolymer concrete. This study presents a systematic investigation of the pore solution composition of a low-calcium fly ash-based geopolymer over a period of one year. The results show that the pore solution of the fly ash geopolymer is mainly composed of alkali ions, silicates, and aluminosilicates species. The lower expansion of the geopolymer concrete in the current study is most probably due to the insufficient alkalinity in the geopolymer pore solution as the hydroxide ions are largely consumed for the fly ash dissolution.

Effects of alccofine and curing conditions on properties of low calcium fly ash-based geopolymer concrete

In order to employ the waste from plants, geopolymer concrete was manufactured with low calcium fly ash, alccofine, sodium silicate and sodium hydroxide as main ingredients. This study investigates the effect of alccofine percentages on the properties of fresh and hardened low-calcium fly ash-based geopolymer concrete. Alccofine was utilized in geopolymer concrete mixtures in 0%, 5% & 10% as partial replacement of fly ash (by weight) and cured at ambient (27 °C) as well as heat (90 °C) temperatures. The results of this study revealed that alccofine enhanced the slump, compaction, density and strength values in comparison to standard geopolymer concrete values with 0% alccofine, in contrary, air voids decreased. Further, X-ray diffraction and Scanning electron microscope results indicated better polymerization in the presence of alccofine which led to the formation of CSH, CASH, NASH products and better densification. Thus, geopolymer concrete produced using low calcium fly ash with different percentages of alccofine can be used for cast in situ practices and at ambient temperature.

Creep and shrinkage of synthetic fibre-reinforced geopolymer concrete

This paper presents the results of an investigation on the use of synthetic polypropylene (PP) and polyolefin (PO) fibres to improve the creep and shrinkage performance of low-calcium fly ash-based geopolymer concrete. Three PP fibres of 18, 19 and 51 mm length and two PO fibres of 48 and 55 mm length with a volume fraction of 0·5% were added to geopolymer concrete. The mechanical properties of the resulting material, such as compressive and splitting tensile strength, modulus of elasticity and modulus of rupture, have been studied. The drying shrinkage and creep of plain and fibre-reinforced geopolymer concrete were examined for a period of 1 year. The results revealed that the inclusion of PP and PO fibres in a volume fraction of 0·5% decreased the drying shrinkage and increased the compressive creep of fly ash-based geopolymer concrete at both early ages and in the long term.

Experimental Developments on Corrosion Resistivity of Low Calcium Fly Ash-Based Geopolymer Concrete

Portland cement production is an main component in making of “concrete, which contributes significant amount of greenhouse gas, because in the process of production of Portland cement also releases about one ton of carbon dioxide gas into the atmosphere. Therefore, the introduction of a novel binder called ‘geopolymer’ by Davidovits promises a good prospect for application in the concrete industry as an alternative binder to Portland cement”. In terms of reducing global warming, the technology based on geo-polymer could reduce the C02 emission to the atmosphere caused by aggregates and cement industries by 80%.Fly ash-based geopolymer concrete “manufactured using fly ash as its source material and does not use Portland cement at all. Not only fly ash, alkaline solution is being utilized to make geopolymer paste which binds the aggregates to form geopolymer concrete. The geopolymer concrete possess excellent mechanical characteristics and better durability characteristics like permeability, resistance against sulphate and acids.” In reinforcement the corrosion is the single most common source of damage and it is usually clear that lack of concrete, inadequate cover to the reinforcement or the available impurities (and sometimes all three) is the prime cause. In the present work, Open Circuit Potential(OCP) method was able to determine the corrosion activity in the reinforced beams. The effect of corrosion on the tensile behavior of reinforcement under different rates of corrosion was compared. The test results reveals that the Geopolymer concrete performs superior to OPC concrete.

Behaviour of fly ash geopolymer binders under exposure to alkaline media

Alkaline agents are primary binder components of geopolymer systems. In the converse, however, the hardened geopolymer binders can be adversely affected under exposure to strong alkalis. This paper presents an investigation conducted to evaluate the effects of highly alkaline exposure environment on fly ash geopolymer binders. In the study, a combination of sodium silicate and 12 M NaOH solution was used as the alkali activator to prepare a low calcium (Class F) fly ash-based geopolymer binder. Fly ash geopolymer pastes or mortars were cast into 50 mm cubes and 25 × 25 × 285 mm prisms, then immersed in different media consisting of water or 1–3 M NaOH solutions maintained at varied temperatures of 23, 38, and 80 °C. The tests done include compressive strength, expansion, and weight changes. Analytical studies were done using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy. Leaching analysis of storage solutions was also conducted. Results showed that alkali attack occurred when the concentrations of storage solutions exceeded 1 M NaOH. The severity of attack increased with increase in NaOH concentration and in storage temperature. It was found that the alkali attack causes damage to the polymeric structure of the binder, leading to release of Al and Si. A gel-like substance is formed, causing expansion and microcracking. New crystalline zeolite phases comprising phillipsite, zeolite-P and chabazite, also formed under exposure of the fly ash geopolymer binder to elevated alkali concentrations.

Chloride diffusion resistance and chloride binding capacity of fly ash-based geopolymer concrete

This study evaluated the chloride diffusion resistance of low-calcium fly ash-based geopolymer concrete through electrical and bulk diffusion techniques. The geopolymer concretes were prepared using 12 different heat curing conditions; three temperatures of 60, 75 and 90 °C and four curing durations of 8, 12, 18 and 24 h, as well as ambient curing. The mechanical and transport properties and microstructural characteristics of the geopolymer concretes were examined. NT BUILD 492 chloride migration and ASTM C1556 bulk diffusion tests were carried out. Results showed that the chloride diffusion resistance and the chloride binding capacity of fly ash-based geopolymer concrete is very low. The fly ash-based geopolymer concrete appears to be suitable for applications where there are little or no chloride-related durability concerns.

Effects of Portland cement addition on Young’s modulus of geopolymer concrete cured at ambient conditions

This paper presents the results of Young’s modulus and Poisson’s ratio tests conducted on samples made of low-calcium fly ash-based geopolymer concrete samples and on samples with a 10% addition of Portland cement, cured at ambient conditions. Furthermore, the measurement system, as well as sampling and sample preparation methodology, are discussed. Strain was tested concurrently using resistive strain gauges and extensometer on cylinder-shaped samples with a diameter of 150 mm and height of 300 mm. Keywords: engineering, construction materials, geopolymer concrete, Young’s modulus, Poisson’s ratio, alkali-activated concrete

Some Progresses in the Challenges for Geopolymer

Geopolymer is manufactured by chemical activation of industrial by-products, which include blast furnace slag, fly ash, steel slag, phosphorus slag etc, with alkali activators, such as the sodium silicate, sodium carbonate and sodium hydroxide and their mixtures. It has attracted worldwide attention due to its advantages of simple production process, low energy consumption, effective utilisation of industrial by-products and reduction of greenhouse gas emissions. However, as materials vary substantially in physicochemistry properties, hardening, workability and durability of deriving geopolymer products vary accordingly. Slag-based geopolymer usually set within a very short period of time (less than 30 min), while low calcium fly ash-based geopolymer takes long time (a couple of days) to set. Geopolymer binders cured at room temperature exhibited significantly higher shrinkage than Portland cement does, while thermal cured products are very volumetrically stable. Moreover, alkali-aggregate reaction can happen when alkali-reactive aggregates are used with geopolymer binders. These issues need to be considered in large scale applications. This paper reviews the current advance in the research of geopolymer.

Passivity of embedded reinforcement in carbonated low-calcium fly ash-based geopolymer concrete

This paper investigates the carbonation of two low-calcium fly ash-based geopolymer concretes to assess the effect of alkali concentration in the activator, and the carbon dioxide concentration on the pH drop and passivity of the reinforcement. Chemical adsorption of carbon dioxide at different concentrations into an aqueous NaOH solution, as representative of the pore solution, is studied to predict the distribution of carbonate species and pH drop. pH profiles were obtained during the exposure period. X-ray diffraction (XRD) was conducted to identify the carbonate phases. Half-cell potential and polarization resistance of reinforced concrete samples were monitored to assess the passivity of embedded reinforcement. The carbonated binders remained rather highly alkaline during the accelerated carbonation test which was in agreement with the predicted values. No sign of depassivation of reinforcement was observed, even for the lower strength grade concrete, during the long exposure time of 500 days to 1% carbon dioxide.

Predicting Relationship between Mechanical Properties of Low Calcium Fly Ash-Based Geopolymer Concrete

ABSTRACTThis paper presents the results of the experimental study carried out on geopolymer concrete with the inclusion of alccofine. Efforts have been made to achieve the required compressive strength at ambient temperature. In the present investigation alccofine, richer in silica and finer than fly ash, has been added up to 10% of fly ash content. In addition, geopolymer concrete with different fly ash contents has been produced. The results are encouraging, as required compressive strength even 40 MPa could be achieved at ambient temperature. Compressive and tensile strength were increased with increase in fly ash and alccofine content. It was observed that better geopolymerization occured in presence of alccofine, and strength continuously increased significantly up to 90%. Attempts were further made to relate the compressive strength with splitting tensile and flexural strengths in presence of alccofine. A relationship has been suggested which holds good for geopolymer concrete with and without alccofine at ambiently, and heat cured specimens.