Activated Fly Ash Research Articles

The Role of Pozzolanic Activity of Siliceous Fly Ash in the Formation of the Structure of Sustainable Cementitious Composites

The following article introduces, in a thorough manner, how the chemical pozzolanic reaction takes place in cement composites containing the fly ash (FA) additive. In the research part, however, the development of phases in the structure of the cement paste in the initial period of its curing and after 28 days from its preparation was traced. For this purpose, a Scanning Electron Microscope (SEM) was used. In order to accurately highlight all the characteristic stages of the formation of the structure of the composite containing FA, an analysis of the cement matrix was carried out between 0.5 and 28 days of their curing. Microstructural studies were complemented by tests of pozzolanic activity of FAs used. In order to conduct a full analysis of this feature, experiments were carried out using two types of research methods, i.e., chemical and physical. On the basis on the conducted studies it was found that: in cement composites with the addition of FA, in the period until the third day of curing, the development of the material structure is mainly the result of the hydration reaction, and between the seventh and fourteenth day after sample preparation, the first signs of the pozzolanic reaction on FA grains are visible; however, in the period between 14 and 28 days, there is a clear homogenization of the structure of the cement composite with the addition of FA, resulting from the change of disordered phases into compact and homogeneous forms and filling in the composite of porous places with pozzolanic reaction products. The use of cement composites based on materials whose application makes it possible to reduce GHG emissions to the atmosphere, reduce energy consumption, and reduce industrial waste landfills leads towards the development of ecological and sustainable building engineering.

The effect of reinforcement ratio on the flexural performance of alkali-activated fly ash-based geopolymer concrete beam

Alkali activated fly ash (AAFA) based geopolymer concrete structure is getting attention due to its eco-friendly construction characteristics and improved engineering properties. However, comprehensive studies on the structural performance of hardened properties of AAFA geopolymer concrete is not well addressed, especially on non-linear fracture behavior. This paper aims to present the reinforcement ratio effect on the flexural performance and non-linear fracture characteristics of alkali activated fly ash based geopolymer concrete beams. Sixteen finite element (FE) and four experimental models were used to study the effect of reinforcement ratio on the flexural performance and non-linear fracture characteristics. Four groups of concrete specimens with an average compressive strength of 19.30 MPa, 32.60 MPa, 38.2,0 MPa, and 41.70 MPa were utilized under this study. To investigate the effect of reinforcement ratio on flexural performance of the beams, reinforcement ratios of 0.03, 0.042, 0.045, and 0.063 were used for each compressive strength class. The result showed that the ultimate load carrying capacity of the beam showed significant improvement by about 36.38% by increasing of reinforcement ratio from 0.03 to 0.063 by keeping the compressive strength of concrete constant. However, it was observed that the effect of compressive strength was not such substantial as reinforcement ratio in enhancing the ultimate load bearing capacity. The experimental result showed that the increase in ultimate load by keeping the reinforcement ratio constant is about 12.20% for different compressive strength. Furthermore, the crack formation in the concrete was highly associated with the tensile reinforcement ratio, i.e., smaller reinforcement ratio led to higher strain growth in the concrete. Moreover, the validation study between the numerical simulation and test results showed a good agreement.

Comparing Permeability and Drying Shrinkage of the Concrete Containing Mineral Admixtures under the Equal Strength Grade

Fly ash (FA) and ground granulated blast-furnace slag (GGBS) are the most widely used mineral admixtures in engineering. However, their roles in concrete under the equal strength grade, a common comparison method in engineering, were seldom reported. This study investigated the chloride ion permeability and drying shrinkage of concrete samples containing FA or GGBS under an equal strength grade. The samples’ strengths and slumps maintained the same levels by adjusting the water-to-binder ratios and superplasticizer dosages. The results show that both FA and GGBS can promote the resistance to chloride ion penetration and decrease the chloride diffusion coefficients, especially at late ages, due to the hydraulicity of GGBS and pozzolanic activity of FA. Compared with FA, GGBS presents a greater reduction in the concrete permeability due to its higher reactivity. Forty percent replacement levels of FA and GGBS can decrease the penetration level from “high” of plain cement concrete to “moderate” and “low”, respectively. In addition, FA and GGBS can decrease the drying shrinkage of concrete at high replacement levels (30% and 40%). This decrease is more significant in the FA-containing concrete, with the shrinkage decreasing from approximately 400 με to 350 με at a 40% replacement level. The findings can provide scientific guidance for applying FA and GGBS in practical engineering.

Molten salt synthesis of mullite whiskers entirely derived from fly ash for electronic packaging toughening ceramic applications

Preparation of mullite from high-alumina coal fly ash (CFA) has become one of the most important ways for high-value utilization. However, low Al2O3/SiO2 ratio, poor reaction activity and various impurities in fly ash led to poor quality of mullite products. Conventional sintering method requires addition of aluminum sources and sintering additives, and high synthesis temperature. This paper proposes a new technical route for preparation of mullite whiskers entirely from fly ash by molten salt method based on additive activation-acid leaching process. The growth process and synthesis mechanism of mullite whiskers in Na2SO4 molten salt from fly ash were systematically investigated, and the application of fly ash-derived mullite whiskers in electronic packaging toughening ceramic was also explored. The results show that leaching liquor containing Al3+, Na+, and SO42−, and amorphous silica slag can be separated and obtained after acid leaching of activated fly ash at 80 °C, and the fly ash-derived mullite whiskers with a length of about 1 μm can be synthesized from the mixture of crystalline products and silica slag by the proposed method under the optimal synthesis conditions. Using amorphous silica slag with higher dissolution activity as the silicon source, the nucleation of mullite whiskers with homogeneous nucleation process is promoted and highly monodispersed mullite whiskers derived from fly ash form. The fly ash-derived mullite whiskers can improve the mechanical strength, reduce the dielectric constant and dielectric loss of the composite ceramic substrates, and the dielectric constant and dielectric loss of the composite ceramic are the lowest 5.16 and 0.006, respectively, when the mullite addition content is 20 wt.%, indicating that they could be used as electronic packaging materials. This paper provides a novel pathway for synthesis of mullite whiskers and high-value utilization of fly ash.

Reduction of pavement thickness using a subgrade layer treated by different techniques

A range of stabilisers for poor quality subgrade soils have been developed to promote road constructions. Many of them are becoming more popular depending on their effectiveness. The purpose behind this research is to identify the relative efficacy of many physical and chemical stabilisation techniques for enhancing the properties of three types of local Iraqi subgrade soils. The comparison of the samples is based on the CBR tests. The AASHTO (1993) flexible pavement design was used to compute the pavement thickness requirements. The soil samples A, B and C have a natural CBR values of 3.8, 3.9 and 4, respectively, on which the physical stabilisers of Powdered rock (PR), grained recycled concrete (GRC), and recycled crumb rubber grains (CR) were employed, while Quicklime (QL) and activated fly ash (AFA) were both utilised as chemical stabilisers. The stabilisation with 15 % of AFA proved to be the most applicable method for soil types A and B for reducing the pavement thickness requirements by 51 % and 32 %, respectively, with a reasonable financial feasibility for both. The same feasibility is proven when stabilising soil type C with 15 % of GRC, which reduces the pavementthickness by 25.7 %.

Mechanochemically Assisted Coal Fly Ash Conversion into Zeolite.

Mechanically treated fly ash (FA) was utilised to provide Al and Si atoms for zeolite synthesis. A combination of mechanical fly ash activation and classical hydrothermal synthesis led to favourable dissolution of activated fly ash and improved crystallization of zeolites. The milling activation step induced structural changes in FA to promote its reactivity in alkaline solution. The conversion of milled FA into zeolite materials was finally completed in the second step, during hydrothermal synthesis. The effect of such factors as crystallization temperature, milling time, and solution conditioning were systematically studied. The physicochemical properties characterising the obtained zeolite materials were determined via particle size distribution (PSD), nitrogen adsorption–desorption, X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD). As a result, the best samples achieved a high degree of crystallinity and an extensive specific surface area of 292 m2/g, 87.4 m2/g, 41.9 m2/g for Na-X, Na-P1, and Na-A, respectively. The obtained results provide new and useful data for utilising fly ash resources and synthesising other practical zeolites through an innovative, mechanochemically assisted, and template-free approach.

ДОСЛІДЖЕННЯ СТРУКТУРУВАЛЬНОЇ ЗДАТНОСТІ МІНЕРАЛЬНОГО ПОРОШКУ РІЗНОГО ПОХОДЖЕННЯ

Introduction. Mineral filler is an important component of asphalt mixture which plays an important role in ensuring the quality of asphalt mixtures. The specific surface of mineral filler is about 90 % of the specific surface of aggregates in asphalt mixture. Being a part of asphalt mixture, mineral filler performs two roles: it fills the pores between fine grained and coarse-grained aggregate and structurizes bitumen. Recently, a significant amount of works has been devoted to the study of industrial waste as a raw material for the production of mineral filler. First of all, these studies are related to the evaluation of the direct effect of mineral filler mainly on the volumetric properties of asphalt concrete or on its strength properties. Since one of the purposes of mineral filler is structurizing of bitumen, it is reasonable to pay considerable attention when studying the alternative raw materials, to the structurizing ability of the obtained mineral filler, as insufficient structurizing ability of mineral filler can cause plastic deformations, and too high structurizing ability causes the decreasing of its low-temperature crack resistance. Problem statement. In order to evaluate the structurizing ability of the mineral filler, the «ring and ball method» is preferably used, in which the structurizing ability is evaluated by ane increase in the softening point of bitumen after mixing with the mineral filler. However, this method characterizes only the effect of mineral filler on the properties of bitumen at high operating temperatures, but it does not consider the possible change in the properties of bitumen at low operating temperatures and at process temperatures. Objective. This study explores the evaluation of the effect of mineral filler of different origin on the structuring of bitumen at low and high operating temperatures, as well as at process temperatures for the production of asphalt mixtures. Materials and methods. Mineral filler of limestone, granite, quartzite, fly ash, mechanically activated fly ash, the ash from hydraulic waste disposal, blast furnace slag and cement had been used for research. Results. The results of researches showed a significant effect of the mineral filler origin on its structurizing capacity. The structurizing capacity of mineral filler increases with growing temperature; so at low operating temperature mineral filler has almost no effect on the properties of bitumen, and with the increase of temperature to the values of high operating temperature and process temperatures of asphalt mixtures production, the effect of mineral filler on bitumen properties becomes much more significant. Conclusions. Studies of the structurizing capacity of mineral filler of different origins by changing the softening point had shown the possibility of using the raw materials of different origins for the production of mineral filler namely: raw materials from rock (sedimentary, erupted and metamorphic), raw materials from industrial by-products (fly ash, ash from hydraulic waste disposal, blast furnace slag), and also practically finished construction product (cement). For evaluation of the effectiveness of mineral filler, it is possible to study its structurizing capacity by changing the brittleness temperature, as during determination of this indicator, it is possible to evaluate the effect of structuring, which consists in maintaining the homogeneity of asphalt binder during the preparation of plates.

Preparation of non-sintered lightweight aggregate ceramsite based on red mud-carbide slag-fly ash: Strength and curing method optimization

The utilization of such solid wastes as red mud (RM), carbide slag (CS), and fly ash (FA) in the production of environmentally friendly and cheap construction materials is a challenging task. This study produced red mud-carbide slag-fly ash (RCF) lightweight aggregate ceramsite by disc pelletizer. The effects of the preparation and curing method on the cylinder crush strength, apparent density, bulk density, water absorption, and softening coefficient of RCF ceramsite samples were experimentally investigated. The curing method was optimized based on XRD, FTIR, TG-DTG, and SEM analyses. The mechanical properties and internal pore structure of ceramsite samples were significantly improved by increasing steam curing temperature, steam curing time, and standing curing time. The optimum curing method implied a 24 h curing at the standing time and 12 h at 80 °C steam curing temperature. RCF ceramsite samples obtained by this method featured an apparent density of 1400 kg/m3, bulk density of 770 kg/m3, and softening coefficient of 0.95. Their cylinder crush strength was increased by 114.3%, and a 1 h water absorption dropped by 17.0% compared to RT-produced samples. This was due to high temperature accelerating the activation of FA and promoting the dissolution of inner spherical beads. This, in turn, accelerated the hydration reaction and increased the amount of C-(A)-S-H gel, which filled the pores and improved the overall density. The increased length of standing curing time improved the ability of RCF ceramsite samples to withstand structural damage caused by high temperatures. This product can be used to prepare light partition walls and light non-load-bearing structural prefabricated members instead of natural gravel. The results provide a theoretical basis for engineering the application of light aggregates produced from solid wastes.

Microstructural and thermal characterization of concretes prepared with the addition of raw and milled fly ashes

The influences of mechanically activated fly ash on the microstructure and thermal behaviour of atmospheric-cured concrete panels have been evaluated. For this purpose, comparative analyses of concretes prepared with and without addition of raw and milled fly ashes were performed. The raw fly ash was activated with an attrition mill for 1 h. Cylindrical concrete specimens with and without 20% fly ash substitution and large concrete panels with the same compositions were prepared. Mechanical properties of the concrete specimens were measured after 3, 7, 28 days, 2 and 4 months. After preparation the cylindrical specimens were cured in water while the concrete panels were kept in an open atmosphere outside the building for 1 year.The 28-day compressive strengths of the non-fly ash added cylindrical concrete specimen was 61.1 MPa, raw and mechanically activated fly ash added specimens were 54.4 and 64.7 MPa, respectively. Microstructural and thermal studies of the concrete panel were performed in the core drilled specimens after 1 year curing. The compressive strength of the core drilled specimens was 26.6, 25.4 and 35.9 MPa for the non-fly ash added, raw and mechanically activated fly ash added concrete panels.A beneficial pozzolanic reaction and improved mechanical properties of the milled fly ash-substituted concrete cured under harsh weather conditions were observed and determined by differential thermal analysis-thermogravimetry and mercury intrusion porosimetry. Improved mechanical properties of the milled fly ash added panel indicates its potential applicability in industrial practice due to the simplicity of the process.

Effect of fly ash with or without mechanical activation on early-age cement hydration: A comparative case study by boundary nucleation and growth model

In this study, the modified boundary nucleation and growth (BNG) model is adopted to elucidate the effect of fly ash, with or without mechanical activation, on early-age cement hydration kinetics. Results show that compared with ordinary Portland cement paste, as-received fly ash has impaired the nucleation density. This might be attributed to the aluminate ions in the pore solution, released from the dissolution of cement and fly ash, which have passivated the surface of particles and suppressed nucleation and growth of the main hydration products, i.e., calcium-silicate-hydrate (C-S-H) at the early age. However, mechanical activation towards fly ash has improved its specific surface area, further boosting its reactive area fraction in the nucleation and growth process. The increased boundary area per unit volume for mechanically activated fly ash is less affected by the hindering effect of aluminate ions, and favors the C-S-H nucleation in the paste, which causes the nucleation density for the paste containing mechanically activated fly ash to be higher than the one containing as-received fly ash.

Immobilization of Dithizone on Coal Fly Ash in Alkaline Medium as Adsorbent of Cd(II) Ion

Immobilization of dithizone on activated fly ash (AFA) has been carried out in water medium and used as adsorbent for Cd (II) metal. Some parameters that influences the efficiency of Cd (II) adsorption such as solution pH, adsorbent mass, contact time and initial adsorbate concentration were optimized. The concentration of Cd (II) ion before and after adsorption or desorptiom were determined by AAS. Results of the study suggest that immobilization of dithizone on AFA has successfully accomplished in water/base medium. Adsorption of Cd (II) on AFA and dithizone-immobilized fly ash (DIFA) reaches its maximum value at pH 7 and contact time of 60 minutes using 0.02 g of adsorbent mass. Kinetics and isotherm adsorption studies indicate that the adsorption of Cd (II) on both adsorbent follows pseudo 2nd-order kinetics model and Langmuir isotherm adsorption model. Based on desorption data, it is revealed that the interaction between metal ion Cd (II) and AFA is dominated by ion exchange, while the interaction between Cd (II) metal ion and DIFA mostly occurs via the formation of complexes.

Preparation of non-sintered sewage sludge based ceramsite by alkali-thermal activation and hydration mechanism

The recycling of sewage sludge (SS) and fly ash (FA) is significant for the disposal of increasing solid waste. In this study, SS and FA were used as raw materials, and sodium hydroxide (NaOH) and calcium oxide (CaO) were used as alkali activators to prepare non-sintered ceramsite under room temperature curing, and the optimal preparation conditions for the ceramsite were determined through single-factor experiments. Alkaline-thermal activation (ATA) was used to enhance the activity of SS and FA, and the results showed that the activities of SS and FA after ATA were largely improved, and composite activation by CaO and NaOH is more effective than that by either CaO or NaOH. The formed abundant sodium silicate hydrate (N-A-S-H) gels and few hydrated calcium silicate (C-A-S-H)/hydrated silicate (C–S–H) gels can bind well with the particles inside the ceramsite to form the denser structure. In addition, the cylindrical compressive strength of the ceramsite can reach 7.43 MPa, while the apparent density, bulk density, and water absorption are 2603 kg/m3, 852 kg/m3, and 8.37%, respectively under the conditions that the ratio of SS to FA is 8: 2, 9 wt% NaOH and 6 wt% CaO and 600 °C thermal activation, which can meet the standard of ceramsite (GB/T 17431.1–2010). This study provides an effective way for the utilization of SS and FA.

Top-Down Production of Nano-Seeds from Activated Fly Ash Tuned for Enhancing the Early Strength in Blended Cements.

To achieve the new level of blended cement performance, the slurries of Class C and F fly ash were mechano-chemically activated in a vibro-mill with superplasticizer and nanosilica. The resulting activated products were tested in mortars replacing up to 30% portland cement. The activation process resulted in the formation of nano-seed clusters and micronized ash particles that both significantly improve the early strength of mortars as well as allow for the replacement of portland cement with industrial by-products. A small amount, 0.1% (of a binder weight), of nanosilica was used in selected compositions to improve the process of activation and facilitate the formation of nano-seeds. Due to an intensive activation of fly ash in the vibro-mill and the formation of nano-seed hydration products, the increase in the heat of the hydration flux and improvement of the mechanical properties such as compressive strength, especially in the early stages of hardening, were achieved. It is envisioned that fly ash activation and the use of supplementary cementitious materials as a precursor can induce a denser structure of cementitious matrix due to better particle packing realized with the application of the nano-seed product, nanosilica, ultra-fine particles of fly ash, and the formation of a refined C-S-H structure realized with the incorporation of the nano-seed particles.

Analysis of the isothermal hydration heat of cement paste containing mechanically activated fly ash

Fly ash is a widely used supplementary cementitious material in the world. Mechanical activation, as a potential approach, can realize maximum bulk utilization of fly ash. In this study, the isothermal hydration heat flows of cement paste containing fly ash with or without mechanical activation are tested and modelled by Avrami equation, reaction order model and three-parameter exponential function at different stages. The results indicate that addition of 20% as-received fly ash retards the cement hydration at the nucleation and growth stage, because the aluminate ions in the pore solution might decrease heterogeneous nucleation sites of C-S-H and suppress its growth. Moreover, as-received fly ash impairs the reaction rate of the whole system at final tail stage owing to its low heat release. However, compared with as-received fly ash, mechanically activated fly ash has promoted cement hydration at the very early age due to the enhanced filler effect. More surface area supplied by mechanically activated fly ash promotes C-S-H growth and partially offsets the retarding effect of aluminate ions. The reaction rate of the whole cementitious system at the deceleration stage is also promoted by the improvement of pozzolanic reactivity after mechanical activation. Furthermore, three different mathematical calculation approaches have been adopted to calculate the ultimate hydration heat Qmax of the cementitious systems. In spite of different values for Qmax, the consensus can be achieved that mechanical activation towards fly ash can promote the reaction degree of the system.

Removal of Reactive Yellow 4R Azo Dye from Synthetic Aqueous Solution by Alkali Hydrothermally Activated Fly Ash

Dye-containing wastewater affects the aesthetic quality, transparency and gas solubility of natural water bodies, hence colored wastewater must be treated before being discharged. Physical removal of dyes from wastewater can be achieved using activated carbon. However, this technique is expensive, so there is a need to find less expensive alternatives. A waste product generated from coal-fired plants known as fly ash is a sorbent that can be used to remove pollutants from solution. This study investigated the effectiveness of using alkali (NaOH) hydrothermally activated fly ash to remove Reactive Yellow 4R azo dye from synthetic aqueous solution. Na2O in alkali hydrothermally activated fly ash increases thirteen-fold. SEM observations revealed that the raw fly ash consisted of smooth round shaped particles, whereas the activated fly ash was composed of granular crystalline particles. Batch adsorption experiments of the dye at 25 °C showed that increasing the activated fly ash quantity (0.5 to 3.5 g) increased the removal efficiency from 30% to 39.3%. The Freundlich isotherm adsorption model best described the adsorption of Reactive Yellow 4R dye by alkali hydrothermally activated fly ash with KF = 1.49 x 10-21 mg/g. The dye adsorption kinetics by activated fly ash followed the Lagergren pseudo second order model, with calculated qe = 2.65 mg/g; k2 = 0.06 g/mg; and calculated h = 0.42 mg/g min‑1. Dye removal occurred primarily through surface adsorption and very little through intra-particle diffusion.

The compressive and tensile behavior of polypropylene fibers and activated fly ash incorporated concrete at elevated temperatures

The major problem with the fly ash concrete is lower early strength because of the addition of fly ash. The main objective of the present investigation is to improve the compressive and tensile properties of polypropylene fiber-reinforced concrete at elevated temperatures by adding activated and inactivated fly ash. Polypropylene (PP) fibers (0.5% by volume of concrete) with fly ash (40% replacement of cement) were utilised to check the compressive strength and split tensile strength both at normal and elevated temperatures. No spalling of concrete occurred with testing temperature ranging between 100 and 650 °C by using PP fibers. By using an activator with fly ash in concrete, the compressive strength of activated fly ash concrete (CAF) was 52% and 29.8% greater than inactivated fly ash concrete (CIF) at 7-days and 28-days, respectively. The use of fly ash enhanced the concrete strengths at elevated temperatures especially up to 200 °C. For elevated temperatures up to 650 °C, the compressive strength of PP fiber reinforced concrete with activated and inactivated fly ash was higher than that of the control concrete at normal temperature. A similar trend of amelioration was observed for the split tensile strength of CIF and CAF. Up to 650 °C, the PP fiber reinforced concrete with activated and inactivated fly ash reported a greater tensile strength than the control model. The statistical analysis using the ANOVA test reported that the activation of fly ash along with the amalgamation of PP fibers ameliorated the compressive and tensile strength results of concrete efficiently.

Mechanical property and microstructure development in alkali activated fly ash slag blends due to efflorescence

Efflorescence of alkali activated materials (AAMs) is caused by alkali leaching and precipitation of carbonated salts, which occurs concurrently with leaching and natural carbonation. Efflorescence is specifically driven by precursor and activator variability in AAMs vis-à-vis phase changes, microstructure, and mechanical properties are not well understood. To that end, this study analyses the effects of long-term (90 days) efflorescence on AAMs with eight varied calcium and activator contents and correlated with compressive and splitting tensile strengths. Microstructural features including N-A-S-H/C, N-A-S-H gel change are analysed using Fourier-transform infrared spectroscopy (FTIR), magic-angle spinning nuclear magnetic resonance (MAS-NMR) and thermogravimetric analysis (TGA). AAMs with 9 wt% Na2O and Ca/(Si + Al) ratio of 0.0 to 0.25 exhibit enhanced efflorescence and dealumination of Al[IV] in N-A-S-H/C,N-A-S-H gels, higher mobility of Na+ ions, and natural carbonation. AAMs with 5 wt% Na2O and Ca/(Si + Al) ratio of 0.0 to 0.25 exhibit lower efflorescence and higher stability, in contrast. Under efflorescence, the binder with 5 wt% Na2O and Ca/(Si + Al) ratio of 0.25 exhibited dealumination and carbonation, and the binders with 5 wt% Na2O and Ca/(Si + Al) of 0.0 to 0.10 showed less dealumination and higher concentration of Al[IV] in aluminosilicate gel, indicative of greater phase stability. This study highlights the criticality of calcium and activator doses in controlling the stability of phase composition and mechanical property, which is essential for the industrial application of AAMs.

Study on the Characteristics of Grinding Activation of Fly Ash and Its Influence on Cement Cementitious System

This study takes fly ash of a coal-fired power plant as the research object, the pulverized and activated fly ash was processed by ball milling process. The difference of physical and chemical properties of fly ash before and after pulverized and activated treatment and its influence mechanism on cement cementitious system were studied by a series of characterization analysis methods. The results show that pulverized fly ash activation significantly reduces the particle size of fly ash, increases its specific surface area, and decreases the crystallinity of crystal minerals and anionic polymerization degree of internal silicon aluminate substance in fly ash, thus reaching the deep activation effect of fly ash activity. Fly ash powder can promote the compressive strength of test block more than fly ash original ash, especially the early compressive strength of test block. The experimental results of water absorption and thermogravimetry show that the effect of fly ash powder on test block is mainly to improve the compactness of test block, reduce its porosity. At the same time, accelerating the secondary hydration reaction of cement is bound to produce more C–S–H gel, thus improving the mechanical properties of test block.

Adoption of alkali-activated cement-based binders (geopolymers) from industrial by-products for sustainable construction of utility buildings-A field demonstration

There is an increasing interest towards using sustainable construction materials for reducing the consumption of natural resources and maximising the utilisation of industrial waste. Alkali activated alumina silicates sourced from industrial by products are environmentally friendly as they leave a low carbon footprint. In this research, performance-based mixes were designed in which a competitive cementitious binder (0% Ordinary Portland Cement) comprising a blend of fly ash–GGBSGround granulated blast furnace slag as a solid precursor and mixture of sodium hydroxide and sodium silicate was produced and utilised in the construction of a utility building after a comprehensive study. As a result of using the Alkali activated fly ash and slag (AAFS) binder, the formation of reaction product sodium-/calcium-containing alumino silicate hydrate gel of type N-A-S-H and C-A-S-Hnetworkyielded high compressive strength, good bond strength with steel and lower deterioration of the matrix on sulphuric acid exposure, which were confirmed from various test results. In-situ precast products of both structural and non-structural elements, viz. blocks, bricks, window/door frame and slabs of various sizes, were fabricated using local materials andproper training was provided to skill the workers to produce them. Different grades of concrete were produced (M20–M40) and utilised in different stages of the construction of the utility building rural children care centre. The field trials, testing methods, monitoring of various stages of the constructions and challenges are presented in this paper. The findings of this research would help in designing suitable user-defined geopolymer mixes in construction and if this technology becomes ubiquitous in the construction industry, it can contribute to reducing the adverse effects of climate change due to environmental degradation.

Phase Analysis of Alkali-Activated Slag Hybridized with Low-Calcium and High-Calcium Fly Ash

This paper investigates the hydrated phase assemblage, microstructure, and gel composition of sodium hydroxide (NaOH)-activated fly ash–slag blends with either low-calcium or high-calcium fly ash. The results show that the nature of precipitated calcium–aluminosilicate–hydrate (C-A-S-H) and alkali aluminosilicate-hydrate (N-A-S-H) depends on the fly ash composition and slag-to-fly ash ratio. However, regardless of fly ash composition and slag-to-fly ash ratio, a universal linear compositional relationship exists between Al/Ca ratio and Si/Ca ratio in precipitated gels. This indicates that there exists a structural limitation on the incorporation of Al3+ for Si4+ in the tetrahedral silicate of C-A-S-H, N-A-S-H, or metastable N-C-A-S-H gels. In a hybrid slag–fly ash system, the framework structure of precipitated gels is an assemblage of aluminosilicate units with heterogeneous Ca2+ and Na+ distribution. The amount and reactivity of calcium and alkalis seem to play a critical role in determining the structure and properties of precipitated gels in hybrid systems. The low cementitious capability in alkali-activated high-calcium fly ash may be attributed to the unstable N-C-A-S-H gel structure with concurrent high Na and Ca contents.