Increase In Fly Ash Content Research Articles

Effects of High-volume Fly Ash on the Properties of Roller Compacted Concrete: A Review

Roller compacted concrete (RCC) is a kind of dry and water-poor concrete, which has the advantage of less water consumption, fast construction speed using roller compaction machine compaction and low cost. RCC is often used in water conservancy projects. This paper outlines the effects of fly ash on the impact of compacted concrete in terms of compressive properties, flexural properties, dynamic modulus of elasticity, impermeability performance and crack resistance based on the working mechanism of fly ash in concrete. In a certain range, the performance of RCC is improved with the increase of fly ash content. Finally, this paper puts forward some suggestions for the further research of RCC.

Effect of Fly Ash Content in Shotcrete on Mechanical Properties

As one of the key technologies of NATM (New Austrian Tunnel Method) construction, shotcrete has advantages such as simple, fast and adaptable technology, and becomes an indispensable modern construction method in tunnel construction. Adding some fly ash into shotcrete can reduce cracks, compensate shrinkage and improve workability. In this paper, raw materials are selected for mix design, and the mechanical properties of shotcrete with different fly ash content are experimentally studied. The test results show that the 28d compressive, flexural and tensile properties of sprayed concrete shotcrete gradually decrease with the increase of fly ash content. In order to avoid too much strength reduction and ensure structural safety, the fly ash ought to be controlled within a certain amount in the actual construction process.

Study on Triaxial Mechanical Properties and Micro Mechanism of Fly Ash Reinforced Cement Calcareous Sand

In order to study the mechanical properties and micro-mechanism of industrial waste fly ash-reinforced cement calcareous sand (FCS), the triaxial unconsolidated undrained (UU) test and scanning electron microscope tests (SEM) were carried out on it. The results of UU test show that the peak stress and energy dissipation of the FCS sample first increase and then decrease with the increase in fly ash content. Fly ash enhances the cement calcareous sand by increasing both the cohesion and internal friction angle, and adding 10% content of fly ash gives the largest values. The SEM test results shows that the hydration products of cement and fly ash filled the pores and cracks on the surface of the calcareous sand, which increased the compactness and structure of the FCS samples. The porosity of cement calcareous sand can be reduced from 27.6% to 12.8% by adding 10% fly ash. A brittleness evaluation index based on energy dissipation is proposed to quantitatively characterize the brittleness of FCS samples. The results show that when the content of fly ash is 5%, the brittleness of FCS samples is the lowest. This study shows that the mechanical properties of cement calcareous sand can be effectively enhanced by adding the appropriate amount of fly ash.

Predicting compressive strength of concrete with fly ash, metakaolin and silica fume by using machine learning techniques

The compressive strength (CS) is the most important parameter in the design codes of reinforced concrete structures. The development of simple mathematical equations for the prediction of CS of concrete can have many practical advantages such as it save cost and time in experiments needed for suitable design data. Due to environmental concerns with the production of cement, different supplementary cementitious materials are often used as partial replacements for cement such as fly ash (FA), metakaolin (MK), and silica fume (SF). However, little work has been done for developing simple mathematical equations for the prediction of CS with FA, MK and SF by using the M5P algorithm. Moreover, the M5P algorithm is not compared with other modelling techniques such as linear regression analysis, gene expression programming (GEP) and response surface methodology. It is established that, for concrete with FA and SF, M5P showed superior prediction capability as compared with other modelling techniques, however, GEP gave the best performance for concrete with MK: CS decrease by increasing FA content, while it increases by increasing MK and SF content.

Improving mechanical properties and shrinkage cracking characteristics of soft clay in deep soil mixing

Deep soil mixing is a ground improvement method that enhances the characteristics of soft soils by mechanically mixing the soil with cementitious binders such as cement and fly ash (FA). The objective of this paper is to investigation the post-treatment mechanical properties and shrinkage cracking characteristics of soft Bangkok clays treated with ordinary Portland cement (OPC) and FA. Unconfined compressive strength, modulus of elasticity, and shrinkage cracking after 7 and 28 days of mixture curing were measured. The effects of wet/dry cycling on the durability of mixtures were examined. Microstructures of treated soft clays were examined using scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) techniques. Test results showed that strength and stiffness improvements of stabilised soft clays increased with OPC content but decreased with FA content, while the extent of sample shrinkage decreased with increasing FA content. Based on these results, we propose the preliminary guideline of applying 15% replacement of OPC with FA to obtain the optimal mixture ratios that allows FA to act as a shrinkage-reducing agent for deep soil mixing purposes. By adding OPC and 15% FA at a binder-per-water ratio (B/wc) of 0.4, the stabilised soft clay satisfied both strength and shrinkage cracking criteria for deep soil mixing purposes. SEM/EDX analyses further supported these experiment results. In addition, correlations between the mechanical properties and the chemical compositions of stabilised soft clay were derived and presented.

Experimental and Simulation Study of Water Absorption in Unsaturated Concrete

The aim of this research is to investigate the sorptivity and capillary coefficient in unsaturated concrete using the capillary water absorption experiment. The effects of water-binder ratio, fly ash content, and aggregate content on the water absorption performance in concrete are compared. The decrease of water-binder ratio, aggregate content, and the increase of the initial degree of water saturation can lead to a decrease in the water absorption ability. With the increase of fly ash content, the water absorption ability first decreases and then increases; the 40% fly ash content had the worst water absorption ability. To forecast the water transport process, an unsaturated flow theory was used to predict the water content distribution in concrete during transport, this theory can well reveal the water distribution in concrete during water transport and the law of water content distribution is consistent with that of the water absorption experimental.

Effect of Fly Ash on Leaching Characteristics of Cement-Stabilized Macadam Base.

To study the leaching characteristics of a cement-stabilized macadam base with fly ash, a calcium leaching test, using varying cement and fly ash dosages in an ammonium chloride solution, was designed to obtain the rate of calcium ion leaching, porosity, and permeability coefficient of cement-stabilized macadam with leaching time. The results showed that the number of leached calcium ions increased with the cement dosage in the leaching of cement-stabilized macadam. With an increase in the cement dosage, the leaching rate of calcium ions decreased, and the leaching process of the material was delayed. The incorporation of fly ash could effectively slow down the degree of calcium ion leaching. The permeability coefficient increased gradually with the extension of leaching time, and the increase in fly ash content had a more significant effect on the improvement of the permeability coefficient than the increase in cement dosage did.

Effect of high volume fly ash and micro-steel fiber on flexural toughness and durability properties in self-compacting lightweight mortar (SCLM)

In this study, high volumes of fly ash and micro-steel fiber were used to improve lightweight aggregate mixes' strength and durability properties that can be used in the prefabrication industry. The developed composite can be used in roof truss flooring of steel structures and bridge decks. Although the unit weight of the mixtures was reduced below 2000 kg/m3, micro steel fibers were used to improve the behaviour against seismic effects. The increase in fly ash content increased the porosity, water absorption, and water penetration depths of the mixes. The increase in the steel fiber content created a micro-filter effect, reducing the water absorption and water penetration depths. The hardened unit weights of the mixes vary between 1305–1723 kg/m3, while their 91-day compressive strength varies between 30.9 and 46.4 MPa. It has been observed that the mixes using steel fiber are in the medium and good class in the residual strength factors specified in ASTM C 1018. The carbonation depth of the mixes using 50% fly ash increased more than 5.5 times compared to the reference mix. After the freeze–thaw effect, spills occurred on the surfaces of the mixes due to fiber corrosion.

Development and mechanical properties of low fired bricks from drinking water sludge and fly ash

Demand for water and energy supply has dramatically increased the amount of drinking water sludge (DW) and fly ash (FA) annually. These wastes should be properly managed and disposed to protect any potential contamination to surrounding ecosystem. Both by-products can be potentially recycled as raw material for brick development. This study aimed to examine the influence of fly ash content on mechanical properties of drinking water sludge brick at low firing temperature of 500°C. Different ratios of FA content were added to the DWS ranged between 0 and 45%. Brick sample was moulded in 215 mm x 102.5 mm x 65 mm dimension. Samples were air-dried prior to firing at 500°C for 3 hours in a furnace. Basic characterization of DW and FA showed pH of 5.76 and 10.1 with organic contents of 8.42% and 1.14%, respectively. Clay and silt fractions were dominant in DWS while silt more apparent than sand and clay in FA. The volume changes and water absorption of the brick samples decreased with increasing FA content. For the water absorption of the brick increased back as 40% of FA content. The density and compressive strength dropped with the increasing amount of FA. The compressive strength of brick experienced with sulphate attack also decreased with increasing FA content. The results suggested that further study are needed to improve the compressive strength of the studied bricks.

Rheological properties, strength characteristics and flexural performances of engineered cementitious composites incorporating synthetic wollastonite microfibers with two different high aspect ratios

In this study, synthetic wollastonite microfiber (SWM) with high aspect ratio (44:1/SWM-I) developed with a special technique was used in different proportions instead of cement (C), fly ash (FA) and cement + FA (C-FA) in Engineered Cementitious Composites (ECC). SWM-I decreased the workability as a result of interlocking during flow due to its acicular particle structure. When SWM-I was used instead of C, it was determined that the compressive strength decreased and the ductility improved significantly due to the increased SWM-I content. The use of SWM-I instead of FA improved the mechanical performance up to 6% in terms of compressive strength and flexural performance. However, the mixtures prepared by using SWM-I instead of C-FA provided optimum data, considering both ''increasing deformation capacity'' and ''maintaining the bearing strength by fiber bridging after crack''. Therefore, the effect of SWM-II (30:1) was tested by using instead of C-FA. SWM-I with a higher aspect ratio has been improved the mechanical properties of ECC and reduced the workability of ECC more than that of SWM-II. Increasing FA content in ECC has been provided higher ductility but decreased significantly the compressive strength. The bearing strength and deformation capacity of the ECC designed with finer aggregate has been achieved the higher levels compared to larger aggregate size. As a result of all obtained findings, the data of the optimum mixture has been determined as follows: the compressive strength, flexural strength and ductility of ECC incorporating 6% SWM-I instead of C-FA have been reached higher levels than that of 19.0%-12.5%, 12.0%-8.2% and 56.2%-25.5% at 7–28 days, respectively.

Rheological properties of cemented coal gangue backfill based on response surface methodology

In order to study the different mix proportions on rheological properties of cemented coal gangue backfill (CGB). Firstly, by single-factor test, the appropriate dosage ranges of mass concentration, fly ash content and fine gangue ratio were determined. Then on this basis, by response surface methodology, the quadratic polynomial regression models of yield stress and plastic viscosity were constructed respectively. The results show that the rheological model of fresh CGB accorded with rheological behavior of the Bingham fluid. With the increase of mass concentration, the yield stress of fresh CGB increases significantly. With the increase of fly ash content, the plastic viscosity of fresh CGB increase significantly. With the increase of the fine gangue ratio, the yield stress of fresh CGB decreases first and then increases, and the plastic viscosity increases slowly. This study will provide theoretical support for practitioners to predict the rheological properties of fresh CGB with different material compositions, and optimize the pumping performance in order to guide the engineering application more accurately.

Dynamic compressive properties of high volume fly ash (HVFA) concrete with nano silica

High Volume Fly Ash (HVFA) concrete enables the utilization of fly ash (FA) to diminish greenhouse gas emission by decreasing the demand of ordinary Portland cement. Structures made of HVFA concrete, such as roadside barriers, tunnel cushions and building walls could be subjected to impact and blast loads during service life. Thus, dynamic performance of HVFA concrete is worthy of investigating for better analysis and design of concrete structures. This paper presents the quasi-static and dynamic properties of HVFA concrete containing FA contents of 40 and 60% (by wt.) as partial replacement of cement. The effect of 2% (by wt.) nano silica (NS) on the quasi-static and dynamic properties of HVFA concrete is also studied. The dynamic compressive tests are carried out by using a split Hopkinson pressure bar (SHPB) with 100 mm diameter. The failure processes and patterns as well as stress–strain curves of plain and HVFA concretes under different strain rates are compared. The strain rate effects on the compressive strength, modulus of elasticity and energy absorption capacities are analysed. The experimental results show that quasi-static and dynamic performances of HVFA concrete are enhanced by the addition of NS. With the increase of FA content, the damage level becomes more severe, and modulus of elasticity and energy absorption capacities of HVFA concretes become lower at the similar strain rate. Dynamic increase factors (DIF) of compressive strength for HVFA concretes are quantified and compared with the empirical formulae recommended by Euro-International Committee for Concrete (CEB) for normal concrete. Adding NS leads to lower DIF for compressive strength of HVFA concrete. Empirical formulae for DIF of compressive strength, modulus of elasticity and energy absorption capacity of HVFA concretes with and without nano silica as a function of strain rate are proposed. It is worth noting that the NS modified HVFA C60F38N2 in this study has higher compressive strength, modulus of elasticity and energy absorption capacity than the plain concrete (PC), which shows the potential to replace the normal concrete as a sustainable construction material.

The influence of fly ash content on ITZ microstructure of coal gangue concrete

Coal gangue is the main solid waste produced in coal mining, and the resource utilization of coal gangue has become a popular topic in the industry. It is gradually applied that coal gangue concrete (CGC) prepared by replacing crushed stone with coal gangue in a certain proportion. Further, adding fly ash (FA) to CGC improves not only the performance of CGC, but also the resource utilization rate of coal-based solid waste, and this helps meet low carbon and environmental protection requirements. The effect of FA on the macro performance of CGCs has been investigated extensively; however, only few studies have examined microinterface structure changes, interface transition zone (ITZ) characteristics, and mortar microcharacteristics, which are closely related to the macro performance of concrete. Therefore, exploring the effect of FA on the microstructure performance of CGC has great scientific value and engineering significance. In this study, concrete with a 40% replacement rate of coal gangue, which is widely used in engineering practice, is considered the research object. The effect of 0%, 10%, 20%, 30%, and 40% FA on ITZ thickness, mortar pore structure, and micromorphology of CGC aggregates and the relationship between the microstructure parameters and mechanical properties of concrete are analyzed using microhardness tests, mercury intrusion porosimetry, and scanning electron microscopy. The research results indicate that, (1) with an increase in FA content, the decreasing range of the ITZ thickness of gangue concrete first increases and then decreases, and the total porosity of the mortar area increases, but the proportion of serious damage pores decreases; (2) the thickness of the coal gangue ITZ is smaller than that of crushed stone ITZ, which is attributed to the refinement of FA and the filling of ITZ pores; and (3) FA has a dual improvement effect on the ITZ performance of the gangue concrete and the pore structure of the mortar area. These research results provide a reference for further research on the influence of mineral admixtures on concrete ITZ and theoretical guidance for the modification methods of CGC.

Study on Preparation and Performance of Fly Ash Used in Clay Fluidized Backfill Materials

The problem of insufficient compaction of traditional fillers is difficult to solve in the backfilling project. It is a new solution to prepare backfill materials with self-leveling and self-compacting properties by using excavated clay, cement and water as raw materials. Adding fly ash to the backfill materials to replace part of the cement can effectively improve the utilization of industrial waste. Through a series of laboratory tests, the fluidity, bleeding and compressive strength of the mixture were studied respectively, and the influence of fly ash content on the performance of the mixture was preliminarily grasped. The test results show that the increase of fly ash content can reduce the fluidity of the mixture. Compared with the strength of the mixture without fly ash, when the amount of fly ash replacing cement is less than 10%, the strength of the mixture increases, and when the amount of fly ash replacing cement is more than 15%, the strength of the mixture decreases.

EFFECT OF FLY-ASH ON THE STRENGTH DEVELOPMENT OF COASTAL SOILS-A CASE STUDY FOR THE SOUTHERN COASTAL ZONE OF BANGLADESH

The rapid demand for urbanization expands the requirements of infrastructures and owing to the scarcity of available firm land; people are now built structures on soft soils. However, the application of a deep foundation for a low-rise structure may not be economically feasible for developing countries. The economic, as well as safe foundation, can be ensured by adopting traditional ground stability approaches. However, replacement of the industrial by-product, which possess minimum environmental threat may be a plausible option for ground stability. Therefore, an attempt is taken in this research to study the improvement of soft coastal soil by replacing with eco-friendly fly ash. The eastern bank of the river Karnaphuli, which has increasing industrial and residential demand is taken as a case study in this research. A series of experimental set-ups have been conducted to evaluate the strength development with different fly ash contents. It is found that the strength of fly ash treated soils increases with fly ash content up to a threshold value, and beyond that, the strength decreases. In addition, compaction and plasticity characteristics are also investigated through experimental observations and show better performance criteria with increasing fly ash contents. In a nutshell, this approach of replacing fly ash is suitable for coastal soil, and the experimental investigation reveals that an optimum 20% of fly ash content is justified.

Experiment on the Effect of Freezing–Thawing Cyclic on Mechanical Properties of Solidified Sludge

The solidification technology of sludge can effectively solve the problem of environmental pollution and resource shortage. Whereas, the current study lacks the exploration of the durability of solidified sludge. The freeze–thaw cycle test and the moisture transfer test were carried out to test the freeze–thaw resistance and the failure mechanism of the solidified sludge. The results showed that the content of fly ash has a significant effect on the freeze–thaw cycle of the mechanical properties of the solidified sludge. The stress–strain relationship of different dosage samples tends to approach the number of freeze–thaw cycles increases. The stress–strain curve of the samples under all confining pressures is strain-hardening type, which failure mode is ductile failure. The incorporation of fly ash can improve the failure strength and cohesion of cement–lime solidified soil, and gradually increase with the increase of fly ash content. The freeze–thaw cycle test is carried out under the closed system. The moisture in the sample migrates under the temperature load, causing the water content to increase and decrease the partition distribution. The sample with lower fly ash content has smaller static pressure density, which is beneficial to water migration. And increasing the range of water increase zone, the effect of the sample on the freeze–thaw cycle is relatively small. However, the influence of the number of freeze–thaw cycles on the internal friction angle of each soil sample depends largely on the distribution of water in the soil sample, it does not appear regular changes. During the freezing and thawing process, the effects of fly ash content and water redistribution on the mechanical properties of the solidified sludge are simultaneous. In short, the samples with different ratios and freeze–thaw cycles have different factors influencing the change of strength.

Comparison of test methods to determine resistance to chloride penetration in concrete: Sensitivity to the effect of fly ash

There are several methodologies for assessing the entry of chlorides into the concrete. This article aims to compare four test methods to determine the concrete resistance to chloride penetration. The sensitivity of these methods to the effect of three levels of fly ash was investigated. Besides, three ranges of compressive strength were evaluated. The sensitivity of the fly ash effect was different in each test. The physical effect of pore refinement caused by fly ash was identified in all tests, while the chemical effect was suppressed in the accelerated C1202 migration procedure. This reduced the correlation of this last test with the other procedures. The chloride depths between the different tests are closer as the fly ash content increases. New ranges of chloride penetration for each test from the silver nitrate spray were suggested, using the charge passed or the non-stationary chloride diffusion coefficient as reference.

Effect of various parameters on the workability and strength properties of geopolymer concrete

In the present study, effect of various molarities of NaOH, various fly ash content and alkaline activator solution (AAS) / fly ash(FA) ratios on the workability of geopolymer concrete(GPC) are studied along with the effect of use of Na2SiO3/NaOH and K2SiO3/KOH as alkaline activator solutions and various fly ash contents on the compressive strength of geopolymer concrete mixes. Observations shows that both Na2SiO3/NaOH and K2SiO3/KOH gives better performance for different molar, AAS/FA and oxide ratios. Class C GPC has better performance than Class F GPC. It was found that the increase in molarity decreases workability of geopolymer concrete. Also, the workability increases with increase in fly ash (FA) content and AAS/FA ratio in geopolymer concrete. Compressive and split tensile strengths decrease with increase in fly ash content.

Effect of Fly Ash Content on Properties of Fibre Reinforced Cementitious Composites

The effects of 20%, 30% and 40% fly ash on the properties of fibre reinforced cementitious composites were studied. The results showed that the fresh slurry changed from shear thinning to shear thickening with the increase of fly ash content. The flexural strength of specimens increased slightly, but the compressive strength of specimens decreased with the increase of fly ash amount. Moreover, the flexural strength of all specimens showed different degrees of shrinkage over time. With the increase of the content of fly ash, the elastic modulus of specimens decreased.

SIFAT-SIFAT MEKANIK MATERIAL KOMPOSIT BERBAHAN DASAR FLY ASH DAN PASIR HALUS

Soil stabilization using fly ash is an attractive alternative to be developed. Besides reducing industrial waste, it is also economical in terms of costs. With the presence of water, the lime contained in fly ash would be decomposed and undergone a cementation process and a pozolan reaction which would bind the sand grains. In this study, the effect of fly ash content and curing period on the amount of compressive strength and shear strength was observed using an unconfined compressive and direct shear test, respectively. The stress-strain relationships due to shear loads between sand without fly ash and sand with fly ash were compared to see an increase in shear strength due to the addition of fly ash. The results show that the unconfined compressive strength and shear strength of the composite material increase with the addition of fly ash and curing period. But the opposite happened in compressive strain. It was confirmed that the strain to achieve maximum compressive strength decreased with increasing fly ash content and curing period. The fly ash bond was getting brittle with the increasing compressive strength of the composite material made from fly ash and fine sand.