Effect Of High Volume Fly Ash Research Articles

Understanding the effect of high-volume fly ash on micro-structure and mechanical properties of cemented coal gangue paste backfill

The utilization of coal gangue and fly ash to produce cemented paste backfill is an effective strategy to mitigate the environmental impact of such bulk solid wastes. In this study, we aimed to investigate the hardening properties of cemented coal gangue paste backfill (CCGPB) containing high-volume fly ash using macroscopic and microscopic characterization techniques. Specifically, uniaxial compressive strength (UCS) and slump were measured to evaluate the hardening properties of CCGPB, while Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) were used to characterize the internal microstructure and internal pores. A total of 216 mixture proportions were designed through variations in the contents of cement, fly ash, water, and curing time. The resulting experimental data were used to develop a random forest model. This model was subsequently employed to evaluate the impact of different variables on the development of UCS in CCGPB. The results revealed that the slump increased with increasing fly ash contents and mass concentration. The maximum UCS was achieved at the mass concentration of 0.81 and the fly ash-cement replacement ratio of 0.42, which was also verified by the SEM showing a more compact interfacial transition zone with hydration products of calcium silicate hydrates, calcium aluminosilicate hydrates, and ettringites. The MIP results showed that the addition of fly ash had slight effect on the pores less than 1 μm, while pores larger than 1 μm increased with increasing fly ash content. The porosity ratio decreased by only 4% when fly ash was increased from 30% to 50%. The simulation results by the developed RF model indicated that the curing age had the highest relative importance (47.7%), while the UCS gain was less sensitive to the fly ash content compared with the cement. Overall, this study provides valuable insights into the application of fly ash and coal gangue to cemented paste backfill.

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.

Systematic multiscale models to predict the effect of high-volume fly ash on the maximum compression stress of cement-based mortar at various water/cement ratios and curing times

Advances in technology and environmental issues enable the building industry to use more high-performance materials. In this analysis, the hardness of cement mortar with high-volume fly ash has been evaluated and modeled using different model techniques. To establish systematic multiscale models to predict the compressive strength of cement mortar containing a high volume of fly ash (FA) and to be used by the construction industry with no theoretical restrictions. For that purpose, a wide experimental data (a total of 450 tested cement mortar modified with FA) from different academic research studies have been statistically analyzed and modeled. For that purpose, Linear and Nonlinear regression, M5P-tree, and Artificial Neural Network (ANN) approaches were used. In the modeling process, the most relevant parameters affecting the strength of cement mortar, i.e. fly ash (class C and F) incorporation ratio (0–70% of cement's mass), water-to-binder ratio (0.235–1.2), and curing ages (1 to 365 days). According to the correlation coefficient (R), Mean Absolute Error (MAE), and the Root Mean Square Error (RMSE), the compressive strength of cement mortar can be well predicted in terms of w/b, fly ash, and curing time using various simulation techniques. The sensitivity investigation concludes that the curing time is the most dominating parameter for the prediction of the compressive strength of cement mortar with this data set.

Effect of High Volume Flyash on Fiber Strengthened Concrete

Fly Ash (FA) is being utilized as a pozzolonic material when connected as a valuable cementitious material for cement. Fiber Reinforced Concrete (FRC) is a solid having sinewy material which manufactures its helper uprightness. It contains short discrete strands that are reliably scattered and aimlessly arranged. The expansion of Steel Fibers in cement essentially expands its flexural strength; vitality retention limit, malleable conduct before a definitive disappointment, decreased breaking, and improved toughness. Basalt fiber is an elite non-metallic fiber produced using basalt shake dissolved at high temperature. In High Volume Fly Ash Concrete (HVFAC), increment in the amount of cementitious C-S-H stage and calcium aluminium hydrates improves the long haul qualities and lessens the porousness. Therefore improves the solidness properties. The primary point of this examination is to consider the mechanical properties of HVFA cement fortified with half and half filaments. Tests are directed according to the Indian norms and test outcomes are broke down and contrasted and the control example that contains crossover fiber fortified HVFA concrete, HVFA concrete without any strands (non-stringy cement), and Conventional cement. With the fitting understanding of the got outcomes, it is possible to decide the ideal fiber rate in HVFA concrete.

Heat of hydration of cement pastes containing high-volume fly ash and silica fume

This paper reports the effect of high-volume fly ash (low and high calcium types) with and without silica fume as Portland cement replacement on the heat of hydration of binary and ternary cement mixes. Both low and high calcium fly ash types were used to replace part of Portland cement at 50%, 60% and 70% by mass as binary cement mixes. The combination of fly ash and silica fume at 10% by mass as ternary cement mixes was also studied. The results indicated that low calcium fly ash retarded the rate of heat evolution more than high calcium fly ash at the same cement replacement levels. The total released heat reduction of about 70% can be achieved as Portland cement was replaced up to 70 mass% with low calcium fly ash. Total released heat of high calcium fly ash when compared to low calcium fly ash at 50%, 60% and 70% by mass of Portland cement replacement levels were higher by approximately 35%, 24% and 63%, respectively. The results confirmed that CaO content in fly ash had a significant effect on the hydration reaction of these cement mixes. In ternary cement mixes, in both low and high calcium fly ash, silica fume acted as a nucleation site that results to acceleration in the rate of heat evolution and total released heat more so than binary mix cement pastes, which contributed to the increase in early age compressive strength.

Evaluation of the effects of high-volume fly ash on the flexural behavior of reinforced concrete beams

High-volume fly ash (HVFA) concrete represents a promising solution for the construction industry to deal with the issues related to the global emissions of greenhouse gases. Although numerous studies were dedicated on the material properties of HVFA concrete, need is to study the flexural behavior and performance of structures using HVFA concrete in order to promote further field applications. Therefore, this study presents the results of a series of tests conducted on reinforced concrete beam specimens with various fly ash replacement ratios of 0%, 35% and 50%, various tensile steel ratios and concrete compressive strengths to evaluate their flexural behavior. Moreover, based upon the experimental results, an analysis model is proposed to predict the behavior of the reinforced concrete beams. The comparison with the test data verifies that the analytic results predict accurately the behavior of the beams for all the considered replacement ratios in fly ash.

Effect of early-age freeze-thaw exposure on the mechanical performance of self-compacting repair mortars

Abstract Self-compacting repair mortar (SCRM) is a functional material for repair or retrofit applications. Industrial byproducts, such as fly ash (FA) or ground granulated blast furnace slag (GGBFS), can be used to reduce cement dosage and to obtain an eco-friendly material. However, these waste materials may cause durability problems at early ages as a result of curing sensitivity. In this study, the effects of high-volume FA and GGBFS replacement on early-age freeze-thaw (F-T) resistance of SCRM with and without steel microfibers were investigated. The mechanical properties, including fracture energy, were determined after F-T cycles. The fresh state properties and volume stability of the hardened specimens were studied. The results demonstrated that prolonged curing is essential to avoid the loss in mechanical properties due to F-T exposure. SCRM containing high-volume byproducts seem vulnerable to the effect of F-T at early ages, and this negative effect cannot be overcome with steel microfibers.

Freeze–thaw resistance and transport properties of high-volume fly ash roller compacted concrete designed by maximum density method

Abstract The aim of this study is to evaluate the effect of high-volume fly ash on some durability characteristics of roller compacted concrete (RCC). In addition to a control mixture without fly ash, two different series of mixtures were prepared by partial replacement of either cement or aggregate with fly ash. The mixtures were designed by a maximum density method. A total of 28 mixtures having four different water/binder ratios (0.30, 0.35, 0.40 and 0.45 by mass) were prepared to determine the optimum water/binder ratio. Among these, seven mixtures containing the optimum water content were selected for further experimental study. It was observed that in the mixtures where cement was substituted with fly ash, increasing the fly ash content adversely affected the durability performance up to 90 days. However, fly ash substitution for a part of the aggregate improved the durability characteristics of the mixture as the amount of fly ash increased.

Effect of High-Volume Fly Ash on Shear Strength of Concrete Beams

Every year concrete production exceeds 6.5 billion tons worldwide, nearly 1 ton for every man, woman, and child on the planet. In fact, concrete is used 10 times more than any other building material in the world, primarily because of its incredible versatility, availability, and relatively low cost. Unfortunately, the production of portland cement—the key ingredient in concrete—generates approximately a pound of carbon dioxide for every pound of cement produced. One method of reducing concrete's carbon footprint is to replace a significant amount of the cement with fly ash, a by-product of coal-burning thermal power stations. This paper presents the results of an investigation of the shear strength of full-scale reinforced concrete beams constructed with both high-volume fly ash concrete (concrete with at least 50% of the cement replaced with fly ash) and conventional concrete. A test matrix of 16 beams included 12 beams without shear reinforcing and four with shear reinforcing in the form of stirrups; eight beams were constructed from each concrete type. Evaluation of the test results included a comparison with U.S. and international design codes, an examination based on AASHTO load and resistance factor design provisions of the longitudinal strains and angle of the critical flexure-shear crack, a comparison with an extensive database of shear tests on conventional concrete, and a detailed statistical study. The results revealed that the high-volume fly ash concrete beams had higher shear strengths than the conventional concrete beams tested in this investigation.