High Fly Ash Content Research Articles

Aerated Concrete Made of MSW Incineration Ash: Effect of Blending Materials and CO2 Curing Condition

Municipal solid waste (MSW) incineration ash is used to produce aerated concrete blocks (ACB). To reduce cement usage and improve ACB quality, steel slag and blast-furnace slag were tested as cement substitutes, and CO2 mineralization technology was applied to cure ACB. The effect of steel blending ratios (MSW incineration ash, cement substitutes, water, aluminum powder) and CO2 curing conditions (temperature, pressure) on ACB properties was investigated. Under different conditions, the compressive strength, CO2 uptake and microstructure of ACB were determined. Higher fly ash content in ACB increases CO2 uptake but reduces compressive strength; ACB shows better mechanical properties when the cement is completely replaced by blast-furnace slag, but steel slag will cause ACB to fail to form; the optimal water-to-solid ratio enhances carbonation rate and compressive strength, and reducing aluminum powder content improves compressive strength. As the CO2 curing temperature increases from 25 to 105ºC, the carbonation rate and compressive strength of the ACB initially increase and then decrease, with the maximum CO2 uptake ratio of 20.0% and peak compressive strength occurring at 65ºC. When CO2 pressure increases from 0.2MPa to 1MPa, the carbonation rate rises to 23.4%, and the compressive strength first increases and then decreases, reaching 1.86MPa at a curing pressure of 0.6MPa, meeting the GB/T 11968-2020 B03 A1.5 grade standard. Approximately 0.58 tons of CO2 emissions can be reduced for every ton of ACB produced. This study established an innovative method to produce an environmentally friendly, low-carbon building material.

Enhancing wear resistance of aluminum 6061 composites with fly ash: A sustainable approach for industrial applications

This study investigated the benefits of adding fly ash as a reinforcement material. The benefits included cost-effectiveness, improved quality, isotropic behavior, and environmental advantages. To improve self-lubrication and wettability behavior, Al6061 alloy composites were fabricated with different amounts of fly ash (0%, 2%, 4%, 6%, and 8% by weight), along with a fixed amount of graphite (3wt.%) and magnesium (2wt.%). Wear tests were conducted using Taguchi’s Design of Experiment (DoE) approach on the composites. The optimized composition with 6% fly ash exhibited the least wear rate under the test conditions of load = 10 N, sliding velocity = 3 m/s, and sliding distance = 2 km. SEM images revealed a uniform distribution of fly ash and graphite reinforcement in the matrix, contributing to enhanced wear resistance. The composites exhibited fewer scratches and plastically deformed surfaces, indicating a decrease in wear rate and increased wear resistance with higher fly ash content. ANOVA were used, and four parameters were identified to be critical, Composition at 34%, Sliding Distance at 27%, load at 23%, and Sliding Velocity at 12% contribution with a statistical confidence of 95%. This research contributes to developing cost-effective and environmentally sustainable materials with improved mechanical properties. It makes them suitable for various industrial applications, such as the automotive industry, where wear resistance is essential.

Hydration and Hardening Properties of High Fly-Ash Content Gel Material for Cemented Paste Backfill Utilization.

As more and more mines utilize the cemented paste backfill (CPB) mining method, the demand for reducing backfill cost and carbon footprint is increasing and becoming more critical. In this work, a new backfill gel binder made with 40 wt.% of low-quality Class F fly ash (FCM) is proposed to replace ordinary Portland cement (OPC). The binder hydration and gel hardening properties were experimentally investigated through X-ray diffraction, Mercury intrusion porosimetry, uniaxial compression, and thermogravimetric analysis. Three different mine tailings were used to verify the FCM's applicability. Results show that the strength performance of FCM-CPB is 72% of that of OPC-CPB, while FCM production cost is almost less than half of OPC. The hydration process of the FCM-CPB can be divided into five stages, and the main hydration products are ettringite and gel-like hydrates. The 31.2% porosity of FCM-CPB at 28-day curing is higher than that of 7-day curing, while the average pore size is lower, and the structure is denser. The FCM can meet the strength requirement of three different mine tailings regarding different subsequent filling and cut-and-fill mining methods. The proposed FCM provides a feasible alternative with economic and environmental benefits.

Hydration and Mechanical Properties of High-Volume Fly Ash Cement under Different Curing Temperatures.

This study aimed to investigate the effects of different curing temperatures on the hydration and mechanical properties of high-volume fly ash (HVFA) concrete. The key variables were curing temperature (13 °C, 23 °C, 43 °C) and fly ash (FA) content (0%, 35%, 55%). The hydration characteristics of HVFA cement were examined by evaluating the setting time and heat of hydration under different curing temperatures. The mechanical properties of HVFA concrete were analyzed by preparing concrete specimens at various curing temperatures and measuring the compressive strength at 7, 28, 56, and 91 days. The results indicated that concrete with high FA content was more sensitive to curing temperature compared to ordinary Portland cement.

Sulfate resistance of mortars under semi-immersion condition: Impact of environmental humidity and fly ash content

Fly ash can effectively improve the sulfate resistance of immersed concrete by refining the pore size. However, increase of capillary pores may not be a good thing for salt crystals. In this paper, the effects of fly ash contents and environmental humidity on the sulfate resistance of semi-immersed mortars was investigated by appearance, mechnical strength, and microstructure. Capillary adsorption capacity, ingressed sulfate concentration and erosion productes were further investigated to analyze damage mechanism of mortar under semi-immersion condition. Lower environmental humidity and higher fly ash content were not conducive to the sulfate resistance of semi-submerged mortar, when the humidity was lower than 55 %, the fly ash content should be further reduced. The migration of sulfate ions in capillary pores and the physical salt crystallization in the region of humidity change are the main reasons for the damage.

Behavior of controlled low-strength material incorporating industrial by-products fly ash, quarry waste and concrete waste

The widespread generation of concrete waste from demolished structures presents a significant challenge in construction waste management. However, its integration into Controlled Low Strength Material (CLSM) presents a promising avenue for sustainable construction for utility fill or backfilling applications when suitable granular fills are not available. A low strength flowable fill mix necessitates a mix design that achieves a compressive strength below 0.7 MPa after 28 days for easy excavatability using hand tools. This study delves into the feasibility of replacing fly ash by incorporating concrete waste and quarry waste into CLSM formulations with minimal amounts of cement through laboratory investigations to engineer CLSM blends optimized for easy excavation, particularly for utility fills. Results indicate that the inclusion of concrete waste reduces the water demand and mitigates bleeding in CLSM, thereby enhancing the overall stability of the mix. Moreover, CLSM compositions exhibit densities akin to the density of sand. The addition of 10 % and 20 % of concrete waste led to substantial increases in unconfined compressive strength (UCS). The impact was more pronounced at lower cement contents, with significant early strength development observed when concrete waste was included.The split tensile strength was found to have a linear correlation with the UCS and the dry density of the mix. The formation of pozzolanic hydration products, particularly in mixes with higher fly ash content, was identified as a key factor contributing to strength development, while increased friction between particles of quarry waste further increased the strength and the same has been confirmed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The findings also revealed that a CLSM blend composed of, 30 % fly ash, 50 % quarry waste and 20 % concrete waste supplemented with an extra 3 % cement at 250 mm flowability could be used for backfilling applications where sufficient strength and excavatablity with hand tools is required.

Experimental study and prediction of the long-term strength development of high-flowability concrete made of mixed sand and high-content fly ash

To comprehensively utilize the abundant solid wastes of superfine river sand and fly ash, a mixed sand of superfine river sand with coarse manufactured sand and high-flowability concrete made of mixed sand and high-content fly ash were developed. To address the critical question about the long-term strength of this new concrete, this paper presents an experimental study on the long-term development of cubic compressive and tensile strengths of the concrete over a curing age from 7 days to 360 days. In the study, the mixed sand was a hybrid of 40 % superfine river sand and 60 % coarse manufactured sand, and the fly ash content varied from 30 % to 75 % of the total binders by weight. The law of strength development of concrete with fly ash content was analyzed, combined with explanations of the mechanism and observations of hydration exotherms and microstructures of the concrete. Equations were proposed for predicting the long-term development of cubic compressive and tensile strengths, incorporating coefficients to reflect the effects of fly ash on the binder’s compressive strength and the development tendency of concrete strength. The validity of the proposed prediction equations was verified against the test results and compared with the extended application of the equation specified in CEB-FIP MC 2010.

Tailoring high ductility cementitious composite incorporating recycled fine aggregate based on shrinkage and mechanical properties

High ductility cementitious composite (HDCC) is recognized as an ideal structural bonding and repair material due to multiple steady-state cracking and strain-hardening properties. However， higher shrinkage strains and low economic and environmental friendliness limit its wide application. To promote the application of HDCC, recycled high ductility cementitious composite (R-HDCC) was prepared by using recycled fine aggregate (RFA) to replace natural fine aggregate (NFA), and the effects of RFA substitution rate and fly ash content on the mechanical and shrinkage properties of R-HDCC were thoroughly investigated. The results showed that the compressive strength of R-HDCC gradually decreased with the increase of RFA substitution, but its tensile strain was enhanced. R-HDCC, with 100 % RFA substitution, still maintained a tensile strength of 2.66 MPa and a tensile strain capacity of 2.46 %. The high fly ash content improved the matrix ductility, resulting in a 54.19 % increase in tensile strain over natural HDCC. In addition, the incorporation of RFA and fly ash reduced the autogenous shrinkage of R-HDCC due to the internal curing effect, but the total drying shrinkage of the matrix increased with increasing RFA substitution rate. R100-70 showed optimal environmental benefits and engineering application value through environmental impact assessment and economic analysis. Finally, this paper is expected to guide the design of ecological, economical, and high-performance R-HDCC.

The Influence of Recycled Coarse Aggregate Content on the Properties of High-Fly-Ash Self-Compacting Concrete

In Vietnam, solid waste from construction activities significantly impacts environmental pollution. Recycled concrete aggregate (RCA), derived from waste concrete, can serve as a coarse aggregate in concrete production. However, compared to natural aggregates, RCA exhibits distinct characteristics, including lower strength, higher water absorption, and an increased angular and rough surface. These properties may influence concrete’s workability, compressive strength, and durability. This research investigates the influence of RCA on the properties of High-Fly-Ash Self-Compacting Concrete (SCC). The study explores various replacement levels of natural coarse aggregate with RCA (0%, 50%, 75%, and 100%), alongside a 50% volume fraction of fly ash. Key concrete properties evaluated include workability, compressive strength, flexural strength, and chloride ion permeability. The findings reveal that using 100% RCA in combination with a high fly ash content (50%) produces SCC that meets workability requirements according to EFNARC standards. However, there are trade-offs: the compressive strength decreases by 4.61%, the flexural strength decreases by 3.1%, and chloride ion permeability increases by 57.57% compared to the control sample (using natural aggregates). Notably, the chloride ion permeability of SCC using 100% RCA falls into the category of low permeability. Doi: 10.28991/CEJ-SP2024-010-04 Full Text: PDF

Enhancing the self-healing performance of engineered cementitious composites in harsh environment through cementitious matrix optimization and crack width controlling

The fragile cementitious materials can be easily cracked under service in the harsh environment, which can reduce the loading capacity of concrete structures and its expected service life. The self-curing ability of cementitious materials is thus essential for the resilience of the concrete structures in harsh environments. The purpose of the study is to enhance the self-healing ability of Engineered Cementitious Composites (ECC) in harsh environment though cementitious matrix optimization and crack width controlling. The cementitious matrix containing cement, silica fume, and fly ash is optimized based on the Simple Centroid Method. The Ultra-high Molecular Weight Polyethylene (UHMWPE) fibers have been selected as reinforcing materials due to their superior mechanical performance. The results show that the compressive strength of the ECC samples generally increases with the silica fume content, and the tensile strength rises with both the silica fume and cement content. Meanwhile, the ultimate tensile strain of the ECC samples increases and declines with the fly ash and silica fume content, respectively. The self-repairing properties of the pre-damaged ECC specimens with 5 % strain are examined through exposure in the simulated harsh environment. It is found that the exposure to the groundwater environment can improve the self-curing ability of the pre-damaged ECC specimens, while the self-curing ability can be deteriorated under exposure to the marine environment. Furthermore, the crack sealing and strength recovery ability of cementitious materials can be enhanced with higher fly ash content and lower silica fume content. Finally, the self-curing mechanism of the ECC samples is analyzed by means of the phase and microstructure analysis. Exposure to groundwater environments can promote the generation of the C–S–H gel and calcium carbonate in the self-curing product, and thus enhance the self-healing efficiency. This study can contribute the resilience enhancement of the concrete structure in harsh environments.

Influence of recycled steel fiber on the properties of self-compacting concrete with high fly ash content


 
 
 The recycled steel fibers from waste steel cables have properties suitable for enhancing the load-bearing capacity, impact resistance, and shrinkage reduction of Self-Compacting Concrete (SCC). The use of a high content of fly ash in SCC reduces production costs and is environment friendly by minimizing the amount of cement in the mix. This article presents the experimental research results on the influence of the content of recycled steel fibers on the properties of high-fly-ash SCC. The research utilized recycled steel fibers from elevator steel cables with volume percentages of 0%, 0.5%, 1% and 1.5% respectively in SCC, with a fly ash content in the SCC mix of 50% by volume of powder. The evaluated properties included workability, plastic shrinkage, drying shrinkage compressive strength, and tensile strength. The results indicate that using recycled steel fibers with a maximum content of 1% enables the production of SCC that meets European standards for workability. In addition, when comparing SCC with 0.5% and 1% recycled steel fiber content to control SCC samples (without steel fibers), the compressive strength of SCC increased by 5.04% and 7.56% respectively, the tensile strength increased by 2.99% and 5.97% respectively, plastic shrinkage decreased by 27.34% and 30.47% respectively, and 28-day drying shrinkage decreased by 3.2% and 4.6% respectively. Using recycled steel fibers combined with high-volume fly ash is a reasonable solution to save production costs and be environmentally friendly. Additionally, this solution not only improves the compressive and tensile strength but also limits plastic and drying shrinkage deformations of SCC. As a result, the durability of SCC is enhanced.
 
 

Development of Eco-friendly Particleboard Composite using Fly Ash

This study explores the development of eco-friendly particleboard composite by integrating fly ash (FA) as a partial substitute for wood particles, aiming to promote resources conservation and sustainability. The physical and mechanical properties of fly ash particleboard (FAPB) were systematically examined. Both FA and wood particles used in this research were sieved through a 2 mm sieve. FAPB samples were produced with FA content at 30%, 40% and 50% as replacement for wood particles. The particleboards were produced in the dimension of 300 mm x 300 mm x 15 mm (thickness). These samples underwent a series of test including density, color, scratch resistance, water absorption, compression and flexural tests. Results revealed that increasing FA content led to a rise in the density of the FAPB. The color tests indicated a darker hue with higher FA content, while scratch resistance and surface durability improved correspondingly. Water absorption tests showed a reduction in water uptake with increased FA replacement. The compression test result demonstrated that the FAPB with 40% FA replacement exhibited the highest compressive strength of 3.49 MPa. However, flexural strength decreased as the FA content increased. This research concludes that, incorporating 40% FA into particleboard creates a sustainable, eco-friendly material and promoting waste reduction.

Study on the adsorption performance of modified high silica fly ash for methylene blue.

Presently, there are several issues associated with solid waste fly ash, such as its accumulation and storage, low comprehensive utilization rate, lack of high-value utilization technology, environmental risk and ecological impact. Thus, based on the high silica content and adsorption characteristics of fly ash, two novel adsorbents, namely mesoporous silica-based material (MSM) and sodium dodecyl sulfate-modified fly ash (SDS-FA), were prepared using an ultrasound-assisted alkali fusion-hydrothermal method and surface modification method. Furthermore, effects of adsorbent dosage, initial pH, contact time, and initial concentration of the solution on the adsorption of the organic pollutant methylene blue (MB) by fly ash, MSM, and SDS-FA were investigated to select the optimal modified high silica fly ash adsorbent. Based on the adsorption isotherms and adsorption kinetics, together with SEM, XRD, FTIR and BET analyses, the adsorption mechanism of MSM for MB was revealed. The results showed that under the conditions of an adsorbent dosage of 2 g L-1, initial pH of 9, contact time of 150 min, and initial concentration of 100 mg L-1, MSM and SDS-FA exhibited removal efficiencies of 92.69% and 84.64% for MB, respectively, which were significantly higher than that of fly ash alone. The adsorption of MB by MSM and SDS-FA followed the Langmuir model and pseudo-second-order kinetics, indicating monolayer adsorption with chemical adsorption as the dominant mechanism. The mechanism of the adsorption of MB by MSM is mainly the result of the synergistic effect among its increased specific surface area, hydrogen bonding, ion exchange, and electrostatic interactions. After five cycles of adsorption-desorption process, the removal efficiency of MSM for MB consistently remained above 80%. Therefore, MSM can serve as a valuable reference for the resource utilization of fly ash and remediation of dye-polluted wastewater.

Concrete with clinker‐efficient cements ‐ Robustness to variations in water content and temperature

AbstractThe use of multi‐component cements (CEM II‐CEM VI), which contain main constituents other than Portland cement clinker in significant quantities, can significantly help to reduce the CO2 footprint of the cement or concrete industry. Clinker‐efficient cements (CEM II/C‐M) have been standardized in the current version of DIN EN 197‐5. In a systematic experimental program, the influence of water content variations and temperature on the robustness of concrete with clinker‐efficient cements with high contents of granulated blast furnace slag or fly ash and limestone (CEM II/C‐M (S‐LL) and CEM II/C‐M (V‐LL)) was studied. As a reference, concretes representative for construction elements used indoor (XC1) or in protected outdoor environment (XC3) with standard Portland composite cement (CEM II/A‐M) and blast furnace slag cement (CEM III/A) were investigated. The influence of variations in water content and temperature on fresh (rheological properties, bleeding) and mechanical concrete properties (compressive strength, elastic modulus) were investigated. The results obtained show similar performance and robustness of such concretes with clinker‐efficient cements compared to the reference concretes.

Properties of alkali-activated slag and fly ash blended sea sand concrete exposed to elevated temperature

Alkali-activated slag and fly ash (FA)-blended seawater sea sand concrete (AASC) is a new type of concrete produced without Portland cement or river sand. The advantages of utilising industrial waste and marine resources are that they are not only eco-friendly but cost-saving. This study aimed to investigate the properties of AASC exposed to elevated temperatures. Slag and FA were activated using NaOH and water glass solutions for mixing AASC. Heating and compressive tests were conducted to analyse the thermal and compressive properties of the AASC. The results showed that the AASC with higher FA content (Type II) had fewer flaky structures and more integral interfacial transition zones than the other type of AASC (Type I) after exposure to 600 °C. Type I AASC had better mechanical performance at temperatures below 400 °C but was inferior to Type II AASC beyond 600 °C. A compressive constitutive model was proposed for AASC.

Investigation of different ways of activation of fly ash–cement mixtures: part 2—mechanical activation

AbstractIntroducing supplementary cementitious materials (SCM), e.g. fly ash, into cement composite results in ecological benefits. However, in the case of high amount of SCM used as a replacement of a part of cement, there are problems related to the development of the desired properties of the final composite. Such mixtures often require activation. In the first part of this series of publications, the results of chemical activation (using Na2SO4 and Ca(OH)2) of a mixture with a very high content of fly ash were discussed. The aim of this work was to investigate the influence of mechanical activation on hydration and microstructure of the binder composed of 80% of fly ash and 20% of cement. Mechanical activation was performed using a planetary ball mill. The following instrumental methods were used to investigate the activated fly ash-cement pastes: calorimetry, TG/DTG, FTIR spectroscopy, X-ray diffraction and scanning electron microscopy (SEM) coupled with EDS. It was shown that concomitant grinding of cement and fly ash is more effective compared to separate grinding. Mechanism of hydration/activation of such mixtures was discussed in detail.

Improving the Mechanical Properties of Fly Ash Reinforced Polyester Composites for New Household Uses

Abstract Fly ash, which is industrial waste, has become an excellent material for use as a reinforcing material in composite materials. In addition, this material is a geopolymer material that is used to replace traditional ceramic materials, as it allows the production of high-quality composite materials with excellent properties, lightness, and lower cost. The engineering applications of such composites require high tensile strength, low density, and high wear resistance. In this article, various mechanical tests and fracture surface analyses have been carried out. The surface properties, represented by hardness and elasticity, increased with increasing fly ash content, which is also evidenced by high impact strength. Modification of the surface of the fly ash particles in depth led to an optimal increase in the plastic properties, represented by ultimate strength. The wear tests have shown that high fly ash content can improve wear resistance. The analysis of the fracture and wear surfaces showed that the particles are distributed efficiently. Finally, this composite is intended for use in new buildings as the building block of the future, the design of which was reported in this article.

Mechanical behaviour of Hong Kong marine deposits stabilized with high content of coal fly ash

Dredged marine deposits are a major source of solid wastes in Hong Kong, which need suitable sites to dump. This study investigates the potential of using dredged marine deposits stabilized with coal fly ash as construction materials for reclamation to enhance sustainability. A series of unconfined compression tests were performed on sandy and clayey Hong Kong marine deposits stabilized with high content of coal fly ash, to reveal their stress–strain behaviour and failure modes, and to evaluate the factors affecting their unconfined compressive strength (qu). Results show that the stress–strain behaviour of the stabilized soil shifts from ductile to brittle with increasing fly ash content, curing period and decreasing water content. The qu increases marginally by further increasing the fly ash content from 30% to 40% and it attains much higher values (maximum 2.29 MPa) in the sandy samples than those (maximum 0.29 MPa) in the clayey ones. In general, brittle samples with higher strength fail in axial splitting mode while ductile samples with lower strength fail in shear or multiple shear fractures mode. The qu is inversely proportional to the water to cementitious materials ratio (W/C). For a given W/C, the qu increases with the soil to cementitious materials ratio (S/C).

Shear behavior of fiber reinforced concrete beams with high fly ash content

The shear behavior of Fiber Reinforced Concrete (FRC) beams with high Fly Ash (FA) content is investigated experimentally. Despite greater understanding of FRC shear behavior for the design of structural elements such as beams, the practicality of FRC with a high FA content has yet to be determined. Despite the fact that substantial study has been undertaken to establish the optimal usage of FA as a cement and fine aggregate replacement in concrete while investigating the shear behavior of conventional concrete, only a few studies have focused on the influence of FA in the FRC on concrete's shear behavior. The findings of shear tests performed on the FRC concrete beams of dimension 900 mm long by 80 mm wide by 120 mm high containing a high FA content up to 50 % are presented in this study. This study's principal goal is to investigate the impact of factors such as FA replacement level with fine aggregate and fiber volume on the shear behavior of concrete beams. Concrete mix with different combinations of 50 % FA by weight, as a replacement for fine aggregate, and steel fiber 1 % by volume is investigated. A four-point loading setup was used to test each of the beams. The results on FRC shear resistance capacity at failure load, as well as the effect of fiber volume and high FA content on ultimate load, have been presented and discussed. Mid-span deflection and crack patterns are also investigated during testing. The test results reveal that FRC overperforms in the presence of FA at a level of 50 % fine aggregate replacement with FA. Fibers, as expected, delayed crack formation and significantly reduced their width. As a result, it can be concluded that 50 % fine aggregate replacement with FA can be used effectively in concrete construction with no significant loss in shear strength, both in the presence and absence of steel fibers.

A survey of shear strength behavior of high content fly ash reinforced concrete beams

Fly ash (FA) is a significant industrial byproduct that causes environmental problems. It is utilized in a range of application fields, including as the filling of down regions, mine filling, bricks, and the partial replacement of cement in concrete building, in an effort to lessen the environmental concerns it poses. Numerous studies have been conducted to determine the best way to use FA as a substitute for cement and fine aggregate in concrete and how it affects the mechanical and structural performance of modified concrete. In this view, the current study provides an overview of prior experimental outcomes on the behavior of high content fly ash (HCFA) reinforced concrete (RC) beams under shear. The effect of partially replacing cement in concrete with HCFA ranging from 0% to 70% on several factors pertaining to beam resistance in shear, such as the ratio between shear span and depth of the beam, concrete mix proportions, and concrete reinforcement, has been evaluated. The results on the shear resistance capacity of RC beams under shear at first crack and failure load, as well as deflection at ultimate load, have been presented and discussed. According to the available test results, up to 50% FA can be employed efficiently in concrete construction with no substantial reduction in shear strength. A review of the literature reveals that there is limited data on the influence of HCFA on the shear strength of beams, and more experimental studies are required to understand the shear performance of reinforced concrete members containing FA at the ultimate load and the resulting failure criteria.