Low Calcium Fly Ash Research Articles

Effect of silica fume on compressive strength of ultra-high-performance concrete made of calcium aluminate cement/fly ash based geopolymer

The study on geopolymers blended with silica fume is scant. This study investigates the effects of silica fume (SF) on the compressive strength of geopolymer-based ultra-high-performance concrete (G-UHPC) subject to ambient curing. Low-calcium fly ash (LCFA) and calcium aluminate cement (CAC) were activated by a combination of sodium hydroxide and sodium silicate solution to produce geopolymer binders. Effects of the CAC content, alkaline solution to binder (A/B) ratio, and sodium hydroxide (SH) concentration on the flowability and compressive strength of geopolymer binders were studied. The SF dosage varied from 5% to 30% of the total binder weight, and the Taguchi method was used to determine the optimum mix proportions. The incorporation of SF showed a complicated influence on the compressive strength, depending on the CAC content. For mixes with 20% CAC content, the compressive strength increased with increasing SF dosage. But for mixes with 10% CAC content, a high SF dosage (>10%) negatively influenced the compressive strength. The mechanisms for this contradictory behavior were discussed based on the X-ray diffraction and scanning electron microscopy analyses. The inclusion of steel fibers has a positive influence on the mechanical properties of G-UHPC. The G-UHPC mix with 1.5 vol% steel fibers achieved a compressive strength of 139.1 MPa and flexural strength of 13.5 MPa at 28 days. • Geopolymer-based UHPC was developed by incorporating calcium aluminate cement. • Taguchi analysis was used to optimise mixture compositions for geopolymer-based UHPC. • Effects of silica fume on the strength were explained via SEM and XRD analyses. • Effects of steel fiber on the mechanical properties were evaluated.

Development of Low Calcium Fly-Ash Based Geopolymer Concrete Using Marble Powder

If you compare geopolymer concrete to cement concrete, it is a novel and rising trend in today's concrete business. It can be used as a good substitute for cement concrete and has a variety of benefits over cement concrete, including greater durability. Geopolymer concrete is a kind of green concrete that was created by repurposing waste materials from various power generation companies and thermal power plants. Because of the presence of alkaline activators in geopolymer concrete, it has strong heat resistance capabilities and provides firm bonding between particles, which may result in superior mechanical properties. Geopolymer concrete is also more durable than plain cement concrete. When exposed to acids in a maritime environment, it demonstrates exceptional resistance to corrosion. When low calcium fly ash is used in place of cement, the strength is increased to 40 N/mm2. The amount of marble powder used as a filler was varied as a percent of 0, 5, 10, 15, 20, and 25% to achieve the desired strength of 40 N/mm2. The highest strength was observed when fly-ash was used as a 20% replacement for cement.The molarity of NaOH was employed as 12 molarity at a 2.5 alkaline liquid ratio, which is a good value. They were kept consistent throughout all of the mixes.

Steel Wire Wrapped Bamboo – As a Sustainable Reinforcement in Alkali Activated Fly Ash-Slag based Concrete

The cost ratio of steel to concrete exceeding 100 in most of the RCC structures, alternative materials for replacing steel are underway to develop a sustainable built environment. Bamboo has been in housing industry since time memorial as a standalone structural member for lighter loads of roofing and wall cladding units. It has been tested for its use as reinforcement in OPC based cement concrete structures replacing steel reinforcement with appreciable performance while requiring serious attention on serviceability and durational aspects. The alkali activated low calcium fly ash & slag-based concrete with steel reinforcement as structural components cured at ambient temperature (RGPC) are being popularized in the most consumed sector of concrete construction industry.

The impacts of calcium acetate on reaction process, mechanical strength and microstructure of ordinary Portland cement paste and alkali-activated cementitious paste

The gentle corrosion of acetic acid is frequently utilized to modify recycled concrete aggregates for improving concrete performance, but there is a lack of research on the effect of its process product, calcium acetate (CA), on the properties of cementitious materials. The reason for this work is to discover the role of CA in ordinary Portland cement, alkali-activated low-calcium and high-calcium cementitious materials, and to investigate its possibility as chemical admixture. The impacts of CA on the reaction process, compressive strength, and microstructure of diverse cementitious materials were mainly studied. The results appeared that the impacts of CA on diverse cement are different. The performance of ordinary Portland cement paste depended on the content of calcium acetate. The content of 0.25 wt% CA can increase the reaction degree of cement, improve strength and microstructure of cement paste. In alkali-activated low-calcium fly ash paste, the positive impact of Ca2+ dissolved from calcium acetate was obvious. With the increment of CA content, their strength improvement and microstructure characteristics were optimized. The reaction process of alkali-activated high-calcium slag paste was hindered by calcium acetate, which resulted in the deterioration of strength, the increase of porosity and pore fractal dimension, as well as the relatively uncompacted microstructure. Based on the results, calcium acetate can be used as an admixture, but the content needs to be controlled according to the characteristics of cementitious materials.

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.

Mechanical and durability properties of alkali-activated binders based paver blocks derived from secondary sources

In this research study, low calcium fly ash (FA) and Ground granulated blast furnace slag (GGBS) are used as precursors activated with the solution of sodium hydroxides (SH) and sodium silicates (SS) for the development of geopolymer(GP) paver blocks. A total of 12 FA-GGBS based GP concrete mixes are developed by varying the ratio of SS solution to SH solution (0.25,0.67 and 2.33) along with the binder variation of FA: GGBS (80:20,70:30,60:40 and 50:50) under ambient curing conditions. From the synthesised FA: GGBS and alkalinity ratio, the required GP mixes for paver blocks suitable for medium traffic (M40) and heavy traffic (M50) conditions are formulated. The properties of the GP paver blocks such as mechanical and durability properties are evaluated as per the codal recommendations. All the GP paver blocks satisfy the minimum breaking load criteria with respect to flexural strength and split tensile strength and fall within the allowable abrasion resisting limits. The research findings affirm that the FA-GGBS blend GP paver blocks perform well as per specification requirements. Hence, these GP paver blocks can be adopted for various pavement applications thereby contributing to the adoption of sustainable construction practices.

Effect of high temperatures on the properties of lightweight geopolymer concrete based fly ash and glass powder mixtures

Given the large manufacturing and consumption of concrete globally, there has been widespread speculation that it is a significant source of greenhouse gas emissions. Consequently, scientists are looking for sustainable and beneficial solutions to the environment. The influence of adding expanded clays (Leca) and crushed recycled bricks clay lightweight aggregates (RBA) on the fly ash and glass powder-based geopolymer concrete were investigated at ambient and high temperatures. High temperature influences the significant characteristics of mortar and lightweight aggregate geopolymer concrete. Low calcium fly ash was utilized as a binder in the concrete paste with a 10% replacement rate of Glass Powder. The concrete specimens were heated to 200, 400, 550, and 800 °C at a 7 °C/min rate for 60 min. Lower coarse aggregate strength is a contributing factor to concrete compressive strength reductions. The influences of high temperatures on geopolymer concrete were studied in terms of mass loss, cracking, water absorption, and microstructure. The research outcomes show that the geopolymer concrete suffered damage and dehydration at a heating temperature of 550 °C and above. Acceptable correlation between the temperature degree and Ultrasonic Pulse Velocity UPV with the compressive strength of the lightweight concrete. The test results showed the residual compressive strength 110.2%, 92.9%, 71.9%, and 55.6% as well as 109.2%, 91.5%, 79.6%, and 52.6% in addition to the density reduced 0.17%, 2.56%, 7.29%, and 12.18%, and 0.74%, 3.97%, 6.31%, and 13.25% in 200,400,550, and 800 °C for Leca and RBA type respectively. The equations showed acceptable results with experimental data. The impact of replacing waste glass powder with fly ash on the development of microstructures and gels was also investigated.

Engineering properties and pore structure of lightweight aggregates produced from off-spec fly ash

• High- and low-calcium off-spec fly ash based lightweight aggregate (LWA) was produced. • Engineering properties and pore structure of LWA was characterized. • Small dose of NaOH as fluxing agent can result in off-spec fly ash based LWA with desired engineering properties. This study characterizes the engineering properties of lightweight aggregate (LWA) manufactured from low calcium (F-FA) and high calcium (C-FA) waste fly ash that were designed using a previously-developed thermodynamics-guided process. LWA properties that were characterized include specific gravity, vacuum water absorption, water absorption over time, water desorption, porosity, pore size distribution, and permeability. The LWA studied had a low oven dry specific gravity ranging from 1.22 to 1.45. The vacuum absorption and total open porosity of F-FA LWA decreased as the fluxing agent (NaOH) concentration increased while the values for C-FA LWA varied with increasing amounts of fluxing agent. All LWA passed the ASTM C1761 water absorption/desorption requirements for application to the internal curing of concrete. X-ray computed tomography (XCT) and dynamic vapor sorption analyzer (DVSA) techniques were used to characterize the LWA pore structure. It was found that for F-FA LWA the normalized porosity, counting only pores smaller than 50 nm (gelpores + mesopores), ranged from 4 % to 11.5 %, while for C-FA LWA, this same pore size range had porosity ranging from 1.7 % to 2.8 %. Pore size distribution measurements of F-FA LWA using XCT showed that the pores became larger and the predicted permeability coefficient increased as the fluxing agent concentration increased. For C-FA LWA, the predicted permeability increased with increasing NaOH concentration. Since the pore size distribution had greater variability and did not follow a specific increasing trend, the increase in C-FA permeability could only be due to an increase in pore connectivity.

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.

An assessment on the durability performance of fly ash-clay based geopolymer mortar containing clay enhanced with lime and GGBS

The increased demand for cement as a construction material led to its humongous production and hence the emission of carbon dioxide. The geopolymer binder is an alternate binder which make use of aluminosilicate surplus industrial and agricultural waste and hence completely devoid of cement. The current study primarily aims at investigating the durability performance of low calcium fly ash based geopolymer mortar containing clay blends. Two types of clay treated with lime, ground granulated blast furnace slag (GGBS) and lime-GGBS combination was used in the study. The optimization tool used was the central composite design in response surface methodology by which a set of trial mixes were obtained. The design trial that exhibited maximum compressive strength and lower water absorption was taken as the optimum mix. The durability characteristics of the optimum mix in terms of water absorption, sorptivity, abrasion resistance, acid attack resistance and sulfate attack resistance were analyzed. Combination of lime-GGBS incorporated clay-based specimens exhibited better durability characteristics. The test results were discussed with microstructural characterization techniques such as X-ray Diffraction analysis (XRD) and Fourier Transform Infrared Spectroscopy (FTIR).

Effect of Ultrafine Fly Ash and Water Glass Content on the Performance of Phosphorus Slag-Based Geopolymer.

Phosphorus slag (PS), an industrial waste slag, has been used in geopolymers because it is rich in silicon and calcium. The poor performance of phosphorus slag-based geopolymer is due to its aluminum deficiency. In this work, low-calcium fly ash, treated by a wet-grinding process, named wet-grinding ultrafine fly ash (WUFA) was used as an Al supplement to replace some of the phosphorus slag, and the wet-grinding, ultrafine fly ash-phosphorus slag (WUFA-PS)-based geopolymer was prepared. The effects of the substitution amount of WUFA and the activator dosage on the hydration properties, mechanical properties, pore structure and SEM of the WUFA-PS geopolymer were discussed in detail. The results indicate that WUFA and more activators contribute to the Al and high alkalinity environment, which positively induces the production of more geopolymer gels, thus releasing more heat and optimizing the pore structure of the matrix. The compressive strength increased by up to 28.1%. The enhanced performance of the WUFA-PS-based geopolymer may also arise from the filling effect and activity improvement of WUFA. This study has proved the feasibility of preparing a geopolymer by blending wet-grinding ultrafine fly ash and phosphorus slag and has provided references for the ratio and performance evaluation of WUFA-PS-based geopolymer concrete.

Flexural Behavior of Low Calcium Fly Ash Based Geopolymer Reinforced Concrete Beam

Pioneering studies have been conducted on alternative cementitious material in the manufacturing of conventional concrete to reduce carbon emission and improve the overall efficacy. However, there are limited studies on eco-friendly materials with low calcium fly ash. This study aims to examine the strength fly ash geopolymer concrete and reduce carbon emission. In this investigation, flexural test is done for conventional and geopolymer concrete (GPC) beam samples after the fulfillment of rest period and 24 h steam curing at 60 °C. The experimental results prove that the initial characteristics of both specimens are almost similar. When GPC specimens reached the service, yield, and failure stages, the load carrying capacity, deflection increased up to 21.5 and 8.75%, respectively and better load bearing capacity, moment resistance, and crack propagation were observed more than in conventional cement. Fresh property test results indicated the achievement of standard workability without the addition of any admixture. Our study show that low calcium based geopolymer can be used as an efficient material for the alternate of cement in cement-based industries with eco-friendly nature.

Evaluation of Pozzolanic Activity of Mineral Additives for Hydraulic Concrete

High the quality and reliability of hydraulic engineering construction is the basis of civil engineering technology. The use of mineral additives in hydraulic concrete decreases heat dissipation, contribute to a reduced adiabatic rise in the temperature of concrete, improve its performance characteristics and increase durability. Application of such materials will reduce binder consumption without the decrease of concrete properties and mostly even impoving the properties of mortar and concrete. An indirect method of pozzolanic activity evaluation of low-calcium fly ash, volcanic slag, volcanic tuff and waste basalt powder was applied in the study. The investigation shows that volcanic slag is additive with the least volume increase at age of 30 days and it has high pozzolanic properties. The results show that it can be used as base pozzolanic additive for economically and technologically effective hydraulic concrete, superior to non-additive concrete. Use of pozzolanic additives will positively affect the environment due to Portland cement use decrease and the utilization of waste dumps, decrease cost of concrete and a more rational use of natural resources and sustainable development.

Development of cementless ultra-high performance fly ash composite (UHPFC) using nucleated pozzolanic reaction of low Ca fly ash

This study developed ultra-high performance fly ash composite (UHPFC) by enhancing the pozzolanic reactivity of low-calcium fly ash (FA). Although it did not include Portland cement, the composite exhibited outstanding performance in workability, mechanical properties, and strength development. At room temperature (20 °C), the hydrated lime-activated FA containing silica fume showed a distinct acceleration period. Moreover, 3 days of steam curing at 60 °C guaranteed its final strength (∼110 MPa) before 7 days because of the synergistic effect between the ultrafine filler and steam curing. At 60 °C, the reactivity of FA was dramatically improved only when nucleation sites were provided by silica fume. Furthermore, increasing the curing temperature reciprocally affected FA and silica fume in the reaction; while FA was a leading participant in the pozzolanic reaction, silica fume mostly played a role as a physical filler, providing the nucleation site for reaction products.

Effects of compound mineral admixtures on the properties of magnesium oxysulfate cement

Adding mineral admixtures is a green, economic and effective way of improving the properties of magnesium oxysulfate cement (MOSC). Based on MOSC modified with low-calcium fly ash (L-FA), high-calcium fly ash (H-FA) and granulated blast-furnace slag (G-BS), the effects of L-FA, H-FA and G-BS and silica fume (SF) double mixing on the properties of MOSC were studied by characterising the compressive strength, water resistance, hydration heat, hydration products and micropore structure characteristics. The modification mechanism of the mineral admixtures was also investigated. The results showed that L-FA, G-BS and SF double mixing optimised the hydration product composition and the micropore structure of the MOSC, thus improving its compressive strength and water resistance. The hydration reaction rate of MOSC and 5.1.7 phase content in the hydration products was increased by H-FA and SF double mixing, but the micropore structure was not further optimised, which is why the water resistance of MOSC with H-FA and SF was not improved. The research results enrich the basic theory of mineral admixtures for improving the properties of MOSC and provide theoretical guidance for practical applications.

Kinetics and phase transformation of low-calcium coal fly ash (CFA) under hydrofluoric acid leaching

ABSTRACT The content and depolymerization degree of the glass phase in coal fly ash (CFA) is positively correlated with the activity of CFA, which is one of the key factors in the comprehensive utilization of this ash. At present, the most common and accurate method for quantitative analysis of fly ash is selective dissolution. However, more experimental data are needed to specify the effect of HF concentration on reaction kinetics, the dissolution rate of amorphous phases, and the formation of new amorphous and crystalline phases. In this study, the effects of reaction temperature, reaction time, and hydrofluoric acid concentration on the leaching rate of CFA were investigated with a single-factor condition experiment and orthogonal experiment. Phase composition and transformation of CFA under different conditions were observed with XRD and SEM. The results show that with increasing reaction time (5–120 min), temperature (20–80°C), and HF concentration (5% to 30%), the leaching rate of CFA also increased from 29.4% to 90.2%. The phase transformation of CFA in acid solution is as follows: in 5% hydrofluoric acid concentration solution, the original glass phase disappears totally and a new glass phase is formed; in 15% hydrofluoric acid concentration solution, quartz disappears and a new phase named ralstonite [Na0.5Mg0.5Al1.5F4(OH)2 · (H2O)] is formed; and when the hydrofluoric acid concentration reaches 30%, mullite disappears and a new phase named potassium aluminum fluoride (KAlF4) is formed. Also, when the temperature rises to 80°C, the f-CaO in CFA participates in the reaction to form creedite (Ca3Al2SO4F7.5(OH)2.5 · 2H2O) and fluorite (CaF2). Reaction kinetics demonstrate that the leaching reaction to the glass body of CFA is a diffusion-controlled process, and the apparent activation energy of the Si and Al leaching reaction in glass phase is 11.62 kJ/mol and 26.039 kJ/mol, respectively.

Alkali-activated aerated blends: interaction effect of slag with low and high calcium fly ash

Alkali-activated aerated blends: interaction effect of slag with low and high calcium fly ash

High-Temperature Performance of Low-Calcium Fly Ash–Based Geopolymers

High-Temperature Performance of Low-Calcium Fly Ash–Based Geopolymers

Shrinkage behavior and mechanical properties of alkali activated mortar incorporating nanomaterials and polypropylene fiber

Blended ground granulated blast slag (GGBS), low-calcium fly ash (FA), nano silica (NS), and nano alumina (NA) with/without polypropylene fiber (PPF) had a significant effect on the development length of alkali activated mortar (AAM) cured at various humidity levels and curing ages. This paper presents the behavior of alkali activated mortar with 50% FA and 50% GGBFS binder materials and the alkali ratio of sodium silicate to sodium hydroxide (SS/SH) is 2.5. The molar concentration of sodium hydroxide (NaOH) used was 12 M. Feasibility Comparisons between the different humidity 60%–98% of at 23 ± 3 C° were examined. The strength behavior of alkali-activated mortar with different curing ages was also evaluated. Scanning electron microscopy (SEM) analysis and X-ray diffractions (XRD) were also conducted to clarify the effect of nanomaterials and PPF on the microstructures of AAM. It was found that the shrinkage values of AAM were decreased with the addition of polypropylene fiber and nanomaterials. The combined use of both nanomaterials had better performance than the use of nano SiO2 and/or nano Al2O3 alone. The combined use of PPF with nanomaterials had a superior reduction in shrinkage and expansion and increment on strength values; the minimum shrinkage, expansion values, and maximum strength were found at AAM mix incorporating 2%NS-1%NA-0.5%PPF. The SEM analysis and XRD evaluation indicates the significant effect of nanomaterials on the microstructures and bond strength of AAM. The microstructure of the mixes incorporating both nanomaterials and PPF was denser than other mixes without nanomaterials and/or PPF and showed lower micro cracks.

Capturing the early-age physicochemical transformations of alkali-activated fly ash and slag using ultrasonic pulse velocity technique

Research has shown that reaction kinetics and physical transformation during alkali-activation of aluminosilicate materials are sensitive to both the compositions of raw precursors and the alkaline solution. Methods that allow for early observations relating to reaction kinetics, and that capture early-age physicochemical transformations with sufficient accuracy, can assist design engineers in bringing this new generation of binders to market. In this study, reaction heat and ultrasonic pulse velocity (UPV) evolutions of low calcium fly ash activated with alkaline solutions of different concentrations, and substituted with various dosages of ground granulated blast furnace slag (GGBFS), were systematically monitored using isothermal calorimetric and portable ultrasonic testing facilities. The incorporation of slag in a fly ash-based system influences the reaction kinetics, rate of physical transformation and morphological features. The study shows that UPV can capture the effect of slag addition on the microstructure densification, which is confirmed by measurements of heat evolution and SEM-EDS microstructural observations. A linear correlation of UPV was identified with the heat evolved. It was further shown that UPV tests can successfully capture workable time of alkali-activated fly ash paste blends that contain at least 10% of slag, noting that mixtures without any slag did not set within the first 24 h of activation. Further, improved dissolution of species, leading to an increased heat evolution, was observed with increasing activator alkalinity. SEM-EDS microstructural characterisation reveals an advanced dissolution of particles in a more alkaline environment, while higher silicate content leads to a more homogeneous morphology. The findings of this research will assist in the utilisation of alkali-activated materials in construction practice.