Levels Of Fly Ash Research Articles

Mechanical properties and microstructure of brick aggregate concrete with raw fly ash as a partial replacement of cement

In response to environmental concerns, researchers explore fly ash as a cement replacement material, and crushed bricks as a cost-effective and load-reducing aggregate, particularly where stone chips are scarce. Therefore, this study investigates the mechanical properties and microstructure of brick aggregate concrete (BAC) with raw fly ash (FA) as a partial replacement of cement. The research involved casting raw FA based BAC (FBAC) cylinders (100 mm diameter and 200 mm height) and prism (100 × 100 × 500 mm) with varying levels of FA (0–25%) using a constant mix proportion by volume of 1:1.5:3 (cement : fine aggregate : coarse aggregate) with a water to binder (w/b) ratio of 0.50 and three curing ages (7, 28, and 90 days). Tests for mechanical properties, including compressive strength, split tensile strength, flexural strength, modulus of elasticity, and Poisson's ratio were conducted to assess the behavior of FBAC, and microstructure were then investigated at 28 days. The results indicated that increasing the FA content up to 15% led to gradual improvement in compressive strength and tensile strength values. At 28 days, the highest values of compressive strength and split tensile strength were observed at 10% FA, with 7.9% and 14.2% increase, respectively, compared to the control concrete. However, the flexural strength of FBAC decreased gradually with cement replacement. On the other hand, modulus of elasticity and Poisson's ratio increased gradually up to 20% and 25% cement replacement, respectively. Up to 15% FA enhanced a more uniform and compact microstructure than that of control concrete. Several equations have been developed to express relationship between compressive strength and other mechanical properties of FBAC. Hence, up to 15% raw FA as a partial replacement of cement improved the mechanical properties and microstructure of BAC.

Investigation on the metallurgical and welding characteristics of AA7075/Fly ash composites

This study reinforces aluminium alloy AA7075 with industrial byproduct fly ash (FA) to improve the material's metallurgical and tribological qualities. Variable amounts of fly ash were included into a high-temperature vacuum stir casting process to create metal matrix composites (viz. 0, 6, and 12 wt%). From 60 BHN (AA7075) to 80 BHN (for 12 wt% FA), the hardness of the reinforced Al alloy was pointedly increased. Although there was only a little shift in values from 263 to 251 J for impact strength, this was in direct contrast to the upward trend shown in hardness. Different process factors, including FA concentration, sliding velocity, and applied load, were examined to see how the composites worn against an EN31 hardened steel disc. Extreme abrasive grooves and brittle fracture were observed at low levels of FA (between 0 and 6 wt%), whereas mild abrasive tracked by crumbling of the protective tribo-layer was observed at higher levels of fly ash (12 wt%). Taguchi design of trials was used to find the sweet spot between the several process parameters that would result in the least amount of sliding wear. Sliding at 1 m/s with an applied load of 20 N yielded the lowest wear rate for a composite with 12 % fly ash reinforcement.

Identifying the microstructure and mechanical properties of expansive soil stabilized using fly ash and waste foundry sand

Expansive soil causes road construction damage in the form of cracks or deformations due to changes in moisture content. One method to address this issue is soil stabilization using additive materials. Special additives can sometimes be expensive; hence it is necessary to use additive materials based on industrial waste as a waste management solution to solve the problem of expansive soil as a road construction subgrade. This study aims to analyze the effects of adding two types of industrial waste, namely fly ash (FA) and waste foundry sand (WFS), regarding the microstructure, physical, and mechanical properties of expansive soil. The method of stabilizing expansive soil involves mixing the soil with 9 % FA and various levels of WFS (0 %, 7.5 %, 10 %, 15 %) based on the dry weight of the soil. Microstructure testing includes quantitative X-ray diffraction and scanning electron microscopy. Physical property testing includes specific gravity, Atterberg limits and sieve analysis. Mechanical testing, i.e. compaction, California Bearing Ratio, swelling, and Triaxial tests were conducted. Soil stabilized with 9 % FA and 15 % WFS shows a significant increase in the internal friction angle and cohesion, reducing swelling by 67.18 % compared to the original soil swelling. The addition of 9 % fly ash and 15 % WFS to expansive soil reduces the content of montmorillonite. Natural expansive soils have a very poor soaked CBR of 0.94 %, while stabilized soils with 9 % FA and 15 % WFS have a soaked CBR of 6.46 %. This means that the soaked CBR of the stabilized soil meets the minimum CBR required for road subgrade construction. A mixture of 9 % FA and 15 % WFS in expansive soil can be recommended as a material for stabilizing expansive soil due to its ability to improve microstructure and mechanical properties

Performance evaluation and cost analysis of ternary blended geopolymers for sustainable built environment under different curing regimes

Geopolymer technology provides ecological and monetary benefits in supporting waste management. This study examines the influence of different aluminosilicate materials (85–100 % ground granulated blast furnace slag (GGBS), 0–15 % fly ash (FA), and 0–15 % waste glass powder (WGP)) and curing regimes (water and steam curing) on the mechanical and durability properties and production cost of geopolymers. The water-binder ratio, binder-fine aggregate, and alkaline activator-binder ratios were kept constant, whereas different amounts of superplasticizer were used in all the samples to achieve the target strength of 250 mm. The results revealed that the compressive and flexural strengths of specimens containing FA and WGP outperformed those of GGBS-based geopolymers. The compressive and flexural strength results demonstrated that the optimal FA and WGP replacement levels in ternary blended geopolymers were 10 % and 0–15 %, respectively; subsequent increases or decreases in FA and WGP replacement levels in most of the specimens resulted in mechanical properties similar to those of GGBS-based geopolymers without a significant increase in the production cost. Moreover, exposing specimens to freeze–thaw cycles led to higher compressive strength, ultrasonic velocity values, and weight irrespective of the curing regime, which can be credited to the continued geopolymerization reaction. Contrary to freeze–thaw cycles, only some specimens exhibited higher compressive and flexural strength once exposed to magnesium sulfate (MgSO4) solution. Like compressive and flexural strengths, the resistance of ternary blended geopolymers against freeze–thaw and sulfate attack is higher than that of GGBS-based geopolymers. It is also revealed that water- and steam-cured specimens provide better early- and later-age mechanical and durability properties; therefore, the choice of curing regime should be based on potential application. The positive results of this study indicate that ternary blended geopolymers have the potential to solve environmental challenges while also being futuristic and cost-effective in the production of eco-friendly and structural-grade materials.

Elucidating the role of fly ash in root-knot nematode (Meloidogyne incognita) suppression on okra (Abelmoschus esculentus L.): Insights into cellular viability and host defence system

In the present era of climatic shift, due to many natural and anthropogenic activities, it is imperative to use eco-friendly products to improve the soil quality and production of food crops, including okra (Abelmoschus esculentus L. Moench). As chemical nematicides are damaging to the environment, there is a need for developing alternate eco-friendly measures for the management of root-knot nematodes (Meloidogyne spp.) which cause major losses to vegetable crops globally. In this regard, a pot experiment was performed under optimal environmental conditions to study the nematicidal properties of fly ash (FA) on okra. Various grades of fly ash were applied in pots containing autoclaved soil before seed sowing. Results indicated that the application of 20% FA level (80:20 w/w field soil: fly ash) was found most beneficial for soil health, improving growth and yield traits, physio-biochemical attributes, and antioxidant properties of okra by alleviating the harmful effects of root-knot nematode (Meloidogyne incognita Kofoid and White, 1919; Chitwood, 1949) compared to other treatments. Stomatal attributes of okra also improved at 20% FA level, as demonstrated by scanning electron microscopy. Galls, egg mass formation and reproduction factor of M. incognita was significantly reduced at 20% FA level. Moreover, laser confocal microscopy combined with scanning electron microscopy revealed that 20% FA application enhanced root cell viability and detoxifies the accumulation of reactive oxygen species.

Engineering attributes of alkali-activated mortars containing ceramic tiles waste as aggregates replacement: Effect of high-volume fly ash inclusion

Fast depletion of the natural aggregates and an ever-increasing carbon footprint in environment has enforced humanity to take an immediate remedial measure. Meanwhile, the wastes generated from ceramic materials by various industries worldwide became responsible for growing landfill problems. Several alkali-activated mortars mortars containing ceramic tiles waste as natural aggregates replacement have been designed and evaluated to assess the effectiveness of such waste on the engineering characteristics, such as compressive strength, drying shrinkage, abrasion resistance and water absorption performance of the obtained mortars. The prepared mortars enclosed high volume Fly Ash (FA), Ceramic Tiles Waste (CTW) and Ground Blast Furnace Slag (GBFS). It has been observed that the use of 100% of CTW as fine aggregates replacement was shown to achieve strengths comparable to the control specimen, whereas the inclusion of high volume of FA contents as GBFS substitute in the proposed mix design was discerned to affect significantly on their early strength, thus enhanced the durability performance in term of reducing the total drying shrinkage. However, the results showed that the porosity and abrasion resistance are negatively affected due to increasing FA level. The grinding depth and waster absorption percentage of the mortars was found to increase with the increase of FA content as GBFS replacement.

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.

Shear strength of eco-friendly self-compacting concrete beams containing ground granulated blast furnace slag and fly ash as cement replacement

It is becoming essential to find solutions to preserve the environment from emissions related to cement manufacture. One of the most effective solutions and techniques is using supplementary cementitious materials (SCMs) as cement substitutes to produce eco-friendly concrete. This experimental work primarily aimed to investigate the impact of ground granulated blast furnace slag (GGBFS) and fly ash (FA) as cement substitutes on the shear behavior of SCC beams. Six SCC mixtures with binary and ternary binders based on cement, FA, and GGBFS were manufactured. Twelve SCC beams (two beams for each mixture) with and without shear reinforcement were cast and tested under simply supported four-point loading conditions. Test variables were different substitute levels of GGBFS and FA (0 %, 25 %, and 50 %) of the total weight of cement and shear reinforcement ratio. The findings indicated that the addition of GGBFS and FA had a negative impact on the mechanical characteristics of SCC. The stiffness, ultimate shear strength, and toughness of SCC beams decrease with the increase of GGBFS and FA contents. The ultimate shear strength of tested beams without stirrups comprising GGBFS and FA up to 50 % was reduced by about 12.1 % and 19.3 %, respectively. The ultimate shear strength, shear ductility, and stiffness of tested beams comprising up to 50 % GGBFS were reduced by about 10.5 %, 36.4 %, and 9.1 %, respectively. Based on the experimental results, from both an environmental and engineering perspective, a combination of ternary binders based on 50 % cement, 25 % FA and 25 % GGBFS can be considered the optimum substitute ratios that can be used on the SCC mixture. Whereas it contains a high level of SCMs causing a minimal impact on shear strength with the improvement of the ductility of SCC beam. Lastly, the experimental ultimate shear strength of test specimens was compared with those predicted from different international design codes.

Effect of Crumb Rubber, Fly Ash, and Nanosilica on the Properties of Self-Compacting Concrete Using Response Surface Methodology.

Producing high-strength self-compacting concrete (SCC) requires a low water-cement ratio (W/C). Hence, using a superplasticizer is necessary to attain the desired self-compacting properties at a fresh state. The use of low W/C results in very brittle concrete with a low deformation capacity. This research aims to investigate the influence of crumb rubber (CR), fly ash (FA), and nanosilica (NS) on SCC’s workability and mechanical properties. Using response surface methodology (RSM), 20 mixes were developed containing different levels and proportions of FA (10–40% replacement of cement), CR (5–15% replacement of fine aggregate), and NS (0–4% addition) as the input variables. The workability was assessed through the slump flow, T500, L-box, and V-funnel tests following the guidelines of EFNARC 2005. The compressive, flexural, and tensile strengths were determined at 28 days and considered as the responses for the response surface methodology (RSM) analyses. The results revealed that the workability properties were increased with an increase in FA but decreased with CR replacement and the addition of NS. The pore-refining effect and pozzolanic reactivity of the FA and NS increased the strengths of the composite. Conversely, the strength is negatively affected by an increase in CR, however ductility and deformation capacity were significantly enhanced. Response surface models of the mechanical strengths were developed and validated using ANOVA and have high R2 values of 86–99%. The optimization result produced 36.38%, 4.08%, and 1.0% for the optimum FA, CR, and NS replacement levels at a desirability value of 60%.

Management of root-knot nematode infection by using fly ash and Trichoderma harzianum in Capsicum annum plants by modulating growth, yield, photosynthetic pigments, biochemical substances, and secondary metabolite profiles

A nematicide is a type of chemical pesticide used to kill plant-parasitic nematodes. Nematicides have tended to be broad-spectrum toxicants, possessing high volatility or other properties that promote migration through the soil. In addition, the nematicides used are more expensive and have adverse effects on health and the environment, so it must use more eco-friendly and less expensive alternative methods to control root-knot nematodes (Meloidogyne incognita). Chili (Capsicum annum) suffers from nematode infestation, which reduces its quality and quantity. Therefore, the goal of this research was to assess the effect of different doses of fly ash (FA) mixed soil (5%, 10%, 15 and 20% FA) with two doses of Trichoderma harzianum (1 g and 2 g) for the management of root-knot nematode infection in chili crop. The results showed that significant enhancement in plant growth, yield, chlorophyll, and carotenoid content, protein, carbohydrate, amino acid, tryptophan, indole acetic acid, phenolics, flavonoids, proline, and nitrate reductase content of chili plants was recorded at 10% fly ash with 2 g of T. harzianum (T6). The inoculated plants registered the greatest damage with galling indexes. The lowest galling index was estimated at the T6 treatment. At higher levels of FA + combined with both doses of T. harzianum, nematode could not survive that’s why eighter galls or egg masses were observed. Nematodes may have ceased to function, lost their activity, and hence been unable to resist the stress of fly ash and T. harzianum set. The application of T. harzianum with a lower dose (10%) of fly ash to control the nematode favored plant growth in general. In conclusion, 10% fly ash and 2 g of T. harzianum have the ability to operate as growth promoters and biocontrol agents for M. incognita.

Effects of Sulfate and Sulfuric Acid on Efficiency of Geopolymers as Concrete Repair Materials.

Various geopolymer mortars (GPMs) as concrete repairing materials have become effective owing to their eco-friendly properties. Geopolymer binders designed from agricultural and industrial wastes display interesting and useful mechanical performance. Based on this fact, this research (experimental) focuses on the feasibility of achieving a new GPM with improved mechanical properties and enhanced durability performance against the aggressive sulfuric acid and sulfate attacks. This new ternary blend of GPMs can be achieved by combining waste ceramic tiles (WCT), fly ash (FA) and ground blast furnace slag (GBFS) with appropriate proportions. These GPMs were designed from a high volume of WCT, FA, and GBFS to repair the damaged concretes existing in the construction sectors. Flexural strength, slant shear bond strength, and compatibility of the obtained GPMs were compared with the base or normal concrete (NC) before and after exposure to the aggressive environments. Tests including flexural four-point loading and thermal expansion coefficient were performed. These GPMs were prepared using a low concentration of alkaline activator solution with increasing levels of GBFS and FA replaced by WCT. The results showed that substitution of GBFS and FA by WCT in the GPMs could enhance their bond strength, mechanical characteristics, and durability performance when exposed to aggressive environments. In addition, with the increase in WCT contents from 50 to 70%, the bond strength performance of the GPMs was considerably enhanced under sulfuric acid and sulfate attack. The achieved GPMs were shown to be highly compatible with the concrete substrate and excellent binders for various civil engineering construction applications. It is affirmed that the proposed GPMs can efficiently be used as high-performance materials to repair damaged concrete surfaces.

Compressive Strength of Mortar with Partial Replacement of Cement by Fly Ash and GGBFS.

The compressive strength characteristics of mortar containing Ground Granulated Blast Furnace Slag (GGBFS) and Fly Ash (FA) in mortar by partial substitution of cement are investigated in this work. The increased demand for cement in the construction industry is a concern for environmental degradation; in this case, waste materials such as GGBFS and FA are used to replace cement. The optimal level of GGBFS and FA was determined using a percentage range of 0% to 40% for different curing days. Compressive strength tests were performed on the replaced mortar. For all mixes, the binder-to-water ratio was kept at 0.4. The compressive strength tests were conducted for 7, 28 and 90 days of curing on a Mortar. The result obtained that as the curing time increased the compressive strength of mortar containing GGBFS and FA increased. In comparison to M1 (cement only), the compressive strength improved by 13.15 percent and 15.5 percent at M3 (20%FA) and M8 (30%GGBFS), respectively. The results showed that adding GGBFS and FA to mortar improve compressive strength, which is improves the mechanical properties of the mortar.

Experimental investigation of eco-friendly high strength fiber-reinforced concrete developed with combined incorporation of tyre-steel fiber and fly ash

Simultaneous addition of waste fibers and supplementary cementitious materials is a novel and eco-friendly approach to resolve the issues related to brittleness and environmental impact of plain-concrete (PC). This study examines the concrete mixes incorporating different levels of recycled-tyre steel fiber (RTSF) (0, 0.25, 0.5 and 1% by volume fraction) and low-calcium fly ash (FA) (0, 10, 15, 25, and 35% by volume replacement of cement). The studied properties include compressive strength-fCS (28 and 120-days), splitting-tensile strength-fSP (28-days), modulus of rupture-MOR (28-days), water-absorption-WA (28-days), ultrasonic pulse velocity-UPV (28-days) and electrical resistivity-ER (28-days). The experimental results showed that the simultaneous addition of 10–15% FA and 0.25%-0.5%RTSF can enhance the ductility and imperviousness of concrete. The maximum efficiency of RTSF in fSP and MOR was noticed in the concrete mix containing 10% FA. Whereas rise in FA content beyond 15% decreased the overall mechanical strength and efficiency of RTSF. The high strength concrete mix containing 10%FA and 0.5%RTSF showed 83%, 49% and 19% higher MOR, fSP and fCS, respectively than the reference concrete mix. FA at all levels and RTSF at 0.25–0.5% volume was beneficial to the imperviousness of high strength concrete. All FA levels (i.e., 10–35%) can minimize the electrical conductivity of RTSF-reinforced concrete mixes with respect to the reference mix.

Influence of Various Design Parameters on Compressive Strength of Geopolymer Concrete: A Parametric study by Taguchi Method

Global warming is one of the severe environmental effects, faced by the current generation. Studies show that, Carbon di-oxide (CO2) is the major cause for the global warming and is mainly due to huge production of Ordinary Portland Cement (OPC). Supplementary cementitious materials can reduce this effect by reducing the requirement materials instead of OPC for the construction purposes. Geopolymer Concrete (GPC) is a new generation concrete, which does not require OPC. In this study, Fly Ash (FA) was used to produce GPC. Various parameters are considered in the present study. Taguchi’s method is used for analyzing the parameters. An empirical relation is developed to predict the compressive strength of GPC based on the different parameters. Thirty-six mixes were casted to determine the effect of curing temperature, curing time, rest period, ratio of Alkaline Activator solutions (AAs), ratio of activators to FA, molarity of NaOH and replacement level of FA with OPC on the compressive strength. Contribution of each parameter was estimated by ANOVA. Results show that, addition of OPC had a significant effect on the compressive strength of GPC. The mix with 20% OPC, 14M NaOH, curing temperature of 60oC, curing time of 36hrs, rest period of 48hrs, AAs to FA ratio 0.3 and ratio of alkaline solutions 2.5 was found to have the maximum compressive strength. A regression equation is developed to determine the compressive strength of GPC with respect to the parameters considered.

Impact of Fly Ash on Time-Dependent Properties of Agro-Waste Lightweight Aggregate Concrete

The utilization of by-products and waste materials to substitute for the natural or manufactured resources is considered as a practical way to obtain green building materials. In concrete mixtures, amongst the many available options, Fly Ash (FA) as a by-product pozzolan has been used as a partial replacement of cement. As for the aggregates, lightweight agro-waste oil palm shell (OPS) can be used as a replacement to conventional aggregate for the production of lightweight aggregate concrete. The present communication aims to investigate the impact of FA on time-dependent development properties of OPS lightweight aggregate concrete, including density, water absorption, compressive strength up to 120-days, and drying shrinkage up to the age of 365-days under standard moist curing, partially early curing, and non-curing conditions. Additionally, drying shrinkage crack development was investigated. In this study, two series of concrete mixtures with different substitution levels of OPS (0%, 50%, and 100%) and FA were tested. From the obtained results, it was concluded that the incorporation of fly ash in OPS concrete reduces the density and compressive strength values. Dually, the initial and final water absorption values plus the rate of drying shrinkage at early and long-term ages increased. On top of that, a high potential of drying shrinkage crack, especially for mixtures with 100% OPS, was identified.

Sustainability of Excavation Soil and Red Brick Waste in Rammed Earth

Sustainable construction is an urgent theme in both industrial and developing countries where the construction sector consumes 36% of worldwide energy usage and 40% of the natural resources. Moreover, it causes a hug adverse impact on the environment. One of the major practices to achieve sustainability in construction sector is the use of waste and recycled materials as building materials. The use of waste reduces the consumption of natural resources, energy consumption and carbon emissions. This study is carried out on three types of waste and by-product materials; excavation waste, crushed red brick, and fly ash (FA) which emits from coal-fired thermal plants. The study aims to assess these materials to produce rammed earth as sustainable solution reduces resource consumption, energy consumption, and the environmental pollutants caused by building activities and industrial waste. In order to achieve that, five FA levels 0%, 5%, 10%, 15%, and 20% were mixed with excavation waste of natural soil, and crushed red brick to prepare five rammed earth mixtures. The samples were tested for compressive strength, dry shrinkage, erosion resistance, and microstructure analysis using the scanning electron microscope. The obtained results show that the aforementioned materials can be utilized to produce rammed earth comply with the standard requirements. Also, the observed results indicate that the better properties were measured for mixture prepared using 20% fly ash.

Accumulation of metals, antioxidant activity, growth and yield attributes of mustard (Brassica juncea L.) grown on soil amendments with fly ash together with inorganic nitrogen fertilizer

The study was accompanied to assess the effect of varying levels (0, 20, 40 or 60 t ha−1) of fly ash (FA) and nitrogen (N) (0, 60 or 80 kg ha−1) on Cd, Cr and Pb accumulation, antioxidant activity and yield traits of two mustard cultivars (Brassica juncea cv. ‘Varuna’ and ‘Pusa Bold’). The results showed that antioxidant activity increased concurrently as the FA levels increases. The dose of FA60 accompanied with N60 and N80 lowers enzymatic activity, photosynthetic pigments level, and yield; however, FA at the rate of 40 t ha−1 together with N60 significantly enhanced the crop productivity followed by N80. These results suggest that FA40N60 proved optimal for enhancing crop growth and yield, whereas a high concentration of FA (FA60) caused oxidative stress in both mustard cultivars. Oleic and linoleic acid contents were increased; however, erucic acid content decreased by the application of FA40N60.

Mechanical, durability and economic performance of concrete incorporating fly ash and recycled aggregates

This paper studies the impact of replacing natural coarse aggregates (NCA) with recycled coarse aggregates (RCA) and cement (OPC) with fly ash (FA), on properties and economy of concrete. RCA was obtained by crushing old concrete specimens. FA of low calcium type was used to partially replace OPC. A total of nine concrete mixes (including a reference mix) were prepared using 50% RCA, and 100% RCA with four different levels of FA (0% FA, 10% FA, 20% FA, 30% FA). Workability, fresh density, compressive strength, apparent porosity, and bulk density was measured to evaluate the performance of each mixture. Mixes with optimum levels of both RCA and FA reaching the compressive strength potential of reference mix at 90 days, were subjected to chloride migration testing. To ascertain the combined impact of RCA and FA on economic and strength performance of concrete, a cost to strength ratio (CSR) analysis was also performed on all mixes. Results of testing indicate that FA compensates the loss in workability of fresh concrete and improve the compressive strength of RCA concrete at 28 and 90 days. Negative influence of RCA on density and porosity is minimized by consumption of FA in concrete. Mixes with 50% RCA and 20–30% FA show better resistance against chloride penetration compared to that of the reference mix. CSR analysis suggests that FA must be used along with RCA in concrete in order to minimize the negative influence of RCA on both cost and strength.

Capric Acid Hybridizing Fly Ash and Carbon Nanotubes as a Novel Shape-Stabilized Phase Change Material for Thermal Energy Storage.

Capric acid (CA) is one of the most promising phase change materials to be used in reducing the energy consumption of buildings due to its suitable phase change temperature and high latent heat. In this paper, a novel shape-stabilized phase change material (SSPCM) is fabricated by “hazardous waste” fly ash (FA) via simple impregnation method along with CA and carbon nanotubes (CNTs). In this composite, raw FA without any modification serves as the carrier matrix to improve structural strength and overcome the drawback of the leakage of liquid CA. Simultaneously, CNTs act as an additive to increase the thermal conductivity of composites. The results of leakage tests indicate that CA was successfully confined as 20 wt % in the composite. Then, various characterization techniques were adopted to investigate the structure and properties of the prepared SSPCM of CA/FA/CNT. Scanning electron microscopy and Fourier transform infrared spectroscopy results showed that CA was well adsorbed into the microstructure of FA, and there was no chemical interaction between the components of the composites. Thermogravimetric analysis results demonstrated that the SSPCM presented good thermal stability. Differential scanning calorimetry results indicated that the melting temperature and freezing temperature of CA/FA/CNT were 31.08 and 27.88 °C, respectively, and the latent heats of CA/FA/CNT during the melting and freezing processes were 20.54 and 20.19 J g–1, respectively. Moreover, compared to the CA and CA/FA, the heat transfer efficiency of CA/FA/CNT was significantly improved by doping 1, 3, 5, and 7 wt % of CNT. All of the results suggest that CA/FA/CNT possessed comfortable melting and freezing temperatures, excellent thermal stability, high latent heat value, and favorable thermal conductivity, and therefore, it is a suitable thermal storage material for building applications. Simultaneously, CA/FA/CNT can improve the comprehensive utilization level of FA.

Combined Influence of Fly Ash and Recycled Coarse Aggregates on Strength and Economic Performance of Concrete

Recycled coarse aggregates (RCA) and fly ash (FA) are materials with least to very low global warming potential. Considering long term strength and durability, various studies have suggested to use RCA in concrete with FA. This research paper deals with the strength and economic performance of concrete made with individual and combined incorporation of FA and RCA. Nine different mixtures of concrete were prepared by varying the incorporation levels of RCA and FA. 0% RCA, 50% RCA and 100% RCA were used in concrete with three different levels of FA (0%FA, 20%FA, and 40%FA). The compressive strength of each mixture of concrete was determined at the age of 3, 28, 90 and 180 days. To evaluate economic performance cost of 1 m3 of each mixture of concrete was compared to that of the control mixture having 0% RCA and 0% FA. Results showed that RCA was detrimental to the compressive strength of concrete at all ages, whereas, FA reduced early strength but improved the strength at later ages of testing i.e. 90 and 180 days. FA plus RCA mixes also showed lower early age strength but gained higher strength than conventional concrete at the age of 180 days. RCA did not reduce the cost of concrete effectively. FA despite having a very high transportation cost, it reduced the cost of concrete efficiently. FA did not only reduce the cost of binder but also lower the demand of plasticizer by improving workability. Cost to strength ratio (CSR) analysis also indicated that FA significantly improve the combined economic and strength performance of RCA concrete mixes.