Low-calcium Fly Ash-based Geopolymer Concrete Research Articles

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.

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.

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.

Prediction of the Compressive Strength from Resonant Frequency for Low-Calcium Fly Ash–Based Geopolymer Concrete

AbstractThis study focuses on using fly ash to produce a cement-free geopolymer concrete. The combination of potassium hydroxide (KOH) and potassium silicate solution (K2SiO3) was used as the alkal...

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.

Suitability of Ambient-Cured Alccofine added Low-Calcium Fly Ash-based Geopolymer Concrete

Objective:To develop geopolymer concrete (GPC) using 100% industrial waste as a binder at ambient temperature. Methods/Analysis:The low calcium fly ash based GPC was prepared with different percentage (0%,5%, and 10%) of alccofine and fly ash content (350,370,400kg/m3), to examine the fresh and hardened properties of alccofine activated GPC like density, workability, water absorption, permeable voids, water permeability, compressive and split tensile strengths using international standards. Nine mixes were prepared and investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) for the determination of their phase, composition and microstructural properties. Findings: The result shows that alccofine enhances the mechanical properties and significantly reduces the transport properties of GPC. Furthermore, GPC specimens prepared with alccofine emerge to improve the densification process. The results of investigations conducted reveal that higher percentage of alccofine and fly ash content has a significant effect on the polymerisation of the GPC, which in turn improves the strength and microstructural features. A maximum compressive strength of 42 MPa is achieved with 10% alccofine without elevated heat curing. Novelty/Improvement:Alccofine plays a significant role in improving the mechanical and transport properties of low calcium fly ash based geopolymer concrete at ambient conditions providing as an alternative to heat cured GPC.

Influence of Curing Condition on Compressive Strength of Low-calcium Fly Ash-based Geopolymer Concrete

This paper aims to investigate the influence of curing condition on compressive strength of low-calcium fly ash-based geopolymer concrete (FAGC) by preparing six mixtures. The results also show that the specimens cured at room temperature for one day and then cured at high temperature will be helpful to obtain materials with higher strength than that of directly cured specimens at high temperature. Additionally, cured at room temperature for one day and then cured at high temperature would weaken the adverse effect of wet curing on the growth of compressive strength.

Compressive stress-strain model for low-calcium fly ash-based geopolymer and heat-cured Portland cement concrete

This research focuses on elucidating the present knowledge gaps in geopolymer concrete's engineering properties, specifically its stress-strain behaviour. Geopolymer concrete (GPC) is an emerging alternative to ordinary Portland cement concrete (OPCC), and is produced via a polycondensation reaction between aluminosilicate source materials and an alkaline solution. As a relatively new material, many engineering properties of geopolymer concrete are still undetermined. In this paper, the compressive strength, modulus of elasticity and stress-strain behaviour of ambient and heat-cured GPC and OPCC have been studied experimentally. A total of 195 geopolymer concrete cylinders and 210 Portland cement concrete cylinders were tested for the above mentioned characteristics. Based on the experimental results, constitutive models describing the complete stress–strain behaviour in uniaxial compression have been developed for the low-calcium fly ash-based geopolymer concrete and the heat-cured Portland cement concrete.

Chloride-induced corrosion of reinforcement in low-calcium fly ash-based geopolymer concrete

Geopolymer concrete (GPC) has significant potential as a more sustainable alternative for ordinary Portland cement concrete (PCC). However; as a rather new engineering material, there are some concerns over the durability aspects of geopolymer-based binders. In this study, the performance of chloride-contaminated reinforced GPC specimens manufactured using a blended low-calcium fly ash and slag cement is investigated by long-term monitoring of corrosion parameters such as open circuit corrosion potential, polarization resistance and Tafel slopes. The electrochemical results are validated by contrasting the electrochemical mass losses with the mass losses obtained from the gravimetric measurements. The investigated low-calcium fly ash-based GPC exhibit a comparable electrochemical performance to a similar strength PCC during the propagation phase of corrosion. Additionally, some of the conventional classifications which are commonly used to assess the severity of corrosion in Portland cement-based corroding systems might need some recalibration to be used for low-calcium fly ash-based corroding systems.

The effect of heat-curing on transport properties of low-calcium fly ash-based geopolymer concrete

The aim of this study is to evaluate the transport properties of class F fly ash-based geopolymer concrete cured at various conditions. Twelve different heat curing regimes including three temperatures of 60, 75 and 90°C and four curing durations of 8, 12, 18 and 24h, as well as ambient curing, were imposed to the specimens. The material properties such as compressive strength, elastic modulus, ultrasonic pulse velocity, absorption, volume of permeable voids, pore size distribution and resistivity were evaluated against the reference Portland cement (OPC) concrete. Experiments showed that proper curing conditions such as curing at 75°C for 18–24h yield a geopolymer concrete with low volume of permeable voids and low sorptivity coefficient. The reduced volume of permeable voids and less continuous capillaries, attained by applying the proper curing regime, leads to an increased electrical resistivity and compressive strength of the low-calcium fly ash-based GPCs.

Suitability of heat-cured low-calcium fly ash-based geopolymer concrete for precast applications

This paper discusses the advantages of using low-calcium fly ash (FA)-based geopolymer concrete (GPC) for precast applications when high early-age strength is required. Heat curing is known to be the reaction accelerator for both Portland cement (OPC) concrete and the newly emerged GPC. Here, the influence of 12 different heat-curing regimes, as well as internal curing, on mechanical properties of an FA-based GPC is investigated. The curing regimes include three temperatures of 60, 75 and 90°C, and four curing durations of 8, 12, 18 and 24 h. Results are compared with that of OPC concrete counterpart, with the same amount of binder and aggregate. Test results show that, in optimum heat-curing conditions, GPC can achieve more than 90% of its 28 d compressive strength after 1 d, compared to only 55% to 71% for normal concrete. The optimum heat-curing regime for GPC, combining best performance and energy efficiency, is found to be 75°C for 18 h. Contrary to conventional concrete, heat curing has no detrimental effect on the long-term compressive strength of GPC. It is concluded that, for precast applications, FA-based GPC appears to perform better than OPC concrete in terms of both early and long-term compressive strength using the same amount of binder.