Properties Of Fly Ash Concrete Research Articles

Fresh, Setting, and Hardened Properties of Fly Ash Concrete with Nano-Silica

AbstractNano-silica (NS) may counteract the drawbacks of fly ash (FA), such as delayed setting and low early strength, by accelerating hydration and providing higher early strength in concrete. In this study, concrete mixtures having 4 different FA replacement ratios (0%, 20%, 35%, and 50% by vol.) and 3 different NS dosages (0%, 1.7%, and 3.4% by vol.) were prepared. Effect of NS on the rheology, setting times and temperature evolution during the setting period, microstructure, compressive strength, and modulus of elasticity (MOE) of concrete at constant slump (20 ± 1 cm) were investigated. Plasticizers influenced the rheological and setting properties of concrete designed at constant consistency. In terms of these properties, although there have been cases where the use of NS has shown controversy results compared to the common knowledge in literature, this situation has been associated with the demand for the plasticizers consumed to obtain constant slump. In general, NS accelerated the setting times of concrete, however, it could not completely tolerate the delay caused by FA. According to 7-day mechanical test results, using 3.4% NS almost fully recovered the 20% strength loss caused by 20% FA replacement. Even if compressive strength close to NS-free REF mixture could not be achieved with high volume FA replacement (50%), at 7 days, MOE results, comparable to NS-free REF concrete, could be achieved using 3.4% NS. At later ages, although the compressive strength varied over a wide range, i.e., from 30 to 75 MPa, MOE of FA concrete have become almost independent of the strength.

Influence of magnetization of water on mechanical and durability properties of fly ash concrete

This study looked at the effects of magnetic water and fly ash on the mechanical and durability characteristics of concrete. To estimate the effect of magnetization on the properties of water, Numerous experiments on treated and untreated water, such as “pH, acidity, alkalinity, chlorides, and total solids”, have been carried out with the assistance of a neodymium rare earth magnet with a strength of 1.5 Tesla. Fly ash has been replaced with cement in weight amounts of 10, 20, 30, and 40%. Moreover, the present study investigated the “compressive strength, split tensile strength, water absorption, sorptivity and corrosion resistance tests” of concrete mixes after 28 days of curing. It was discovered that including magnetized water in the concrete mix has shown an increase of 38.46% in compressive strength and that the optimal proportion of fly ash is 30%. Similarly, the magnetized water in concrete has the potential to really boost the durability of concrete.

Influence of curing system on static and dynamic mechanical properties of fly ash concrete

This paper investigates the effect of curing conditions on the static mechanical properties of fly ash concrete such as compressive strength and stress–strain behavior, and utilizes the split Hopkinson pressure bar (SHPB) device to characterize the dynamic mechanical responses of steam-cured concrete under different strain rates. Experimental results reveal that the strength of static concrete decreases with the increase of fly ash (FA) content and increases first and then decreases with the increase of steam curing temperature. The substitution of fly ash for cement reduces water consumption, weakens the hydration degree of cement, and affects the development of static concrete strength. The steam curing temperature plays a role in promoting cement hydration within a certain range, but high temperature leads to the destruction of concrete microstructure, thus inhibiting the development of strength and leading to the instability of concrete performance. The steam curing temperature effects on the dynamic compressive strength of concrete is receded with the increase of strain rate. When the steam curing temperature is constant, the dynamic compressive strength of concrete increases gradually with the increase of strain rate, and the influence of strain rate on the dynamic compressive strength of concrete is greater than that of steam curing temperature. The analysis of the scanning electron microscope (SEM) confirmed that the decrease of concrete strength was due to the change of temperature and fly ash content, which increased microstructure pores, thus affecting the development of strength. This study has important guiding significance to improve the safety of engineering facilities and adapt to the development of modern engineering towards heavy load, long span, and harsh environment.

Compressive Strength Prediction of Fly Ash Concrete Using Machine Learning Techniques

It is time-consuming and uneconomical to estimate the strength properties of fly ash concrete using conventional compression experiments. For this reason, four machine learning models—extreme learning machine, random forest, original support vector regression (SVR), and the SVR model optimized by a grid search algorithm—were proposed to predict the compressive strength of fly ash concrete on 270 group datasets. The prediction results of the proposed model were compared using five evaluation indices, and the relative importance and effect of each input variable on the output compressive strength were analyzed. The results showed that the optimized hybrid model showed the best predictive behavior compared to the other three models, and can be used to forecast the compressive strength of fly ash concrete at a specific mix design ratio before conducting laboratory compression tests, which will save costs on the specimens and laboratory tests. Among the eight input variables listed, age and water were the two relatively most important features with superplasticizer and fly ash being of weaker relative importance.

Effect of ceramic tile waste as a fine aggregate on compressive strength, permeability, and microstructural properties of fly ash concrete

Effect of ceramic tile waste as a fine aggregate on compressive strength, permeability, and microstructural properties of fly ash concrete

Study of Fly Ash Concrete Exposed to Elevated Temperature

The ability to improve the tendency of hardened concrete in compression at elevated temperature was studied. Five mixes of fly ash were cast with a replacement amount of 0%, 10%, 20%, 30%, and 40% by cement mass. They were exposed to 400°C and held for 2 hours after water curing. The specimens have been cooled down to room temperature and then undergo a compressive test. This research aims to study the physical and mechanical properties of fly ash concrete after being exposed to elevated temperatures. A digital microscope was used to analyse the formation mechanism of microstructure in concrete. Fly ash was used to produce high fire resistance concrete with 100 mm x 100 mm x 100 mm concrete cube. Sample 4 with 30% fly ash has the highest compressive strength with 26 MPa after 28 days and 21 MPa after exposed to 400°C. The results show that concrete containing a high amount of fly ash has several improvements when exposed to elevated temperature. The concrete specimens were used to validate an interfacial transition zone (ITZ) in concrete. The microstructure features were discussed concerning their influence on the strength development of concrete.

Experimental and numerical model for mechanical properties of concrete containing fly ash: Systematic review

Increasing use and need for cement have forced researchers to build alternative building materials that are environmentally friendly in nature and help manage less waste. Using waste materials to produce the structural concrete needs theoretical models for implement application for construction. Fly ash as a byproduct of coal-fired electric generating plants showed many advantages in improving the properties of concrete due to its pozzolanic feature. Therefore, this study intends to review previous studies and propose new models to determine the elastic moduli, compressive and tensile strengths of concrete produced by fly ash as a replacement of cement. For this aim, wide-range experimental results were evaluated and provided from previous studies. The disadvantage of the previous study is not covering all elastic moduli, compressive and tensile strengths together. Therefore, a total of 263 concrete mixtures were also produced in this study and the gap of the previous investigations was filled. Therefore, highly accurate machine learning models were used in MATLAB software to predict the mechanical properties of concrete produced by fly ash including radial basis function, multilayer perceptron, support vector regression, adaptive-network-based fuzzy inference system and deep neural network. Additionally, the experimental results were compared with existing models and new highly accurate models were developed to determine the modulus of elasticity, compressive and tensile strengths of concrete produced by various fly ash contents. Experimental results showed that the optimal content for fly ash was obtained by 10% in terms of the maximum mechanical properties of concrete. In addition, used Artificial Neural Networks, particularly deep neural networks showed a highly accurate prediction. Moreover, the proposed models by a high agreement with experimental results (R2>0.98) could be used as highly efficient and accurate tools to determine the mechanical properties of fly ash concrete.

Tensile mechanical properties of fly ash concrete at early age for thermal stress analysis

The present study investigates tensile properties of concrete with and without fly ash at early age, such as tensile Young’s modulus, strength and creep. Some Young’s modulus of fly ash concrete for thermal crack analysis was compared with the tensile Young’s modulus, secant modulus, initial tangent modulus and linear modulus obtained from the direct tension test and compression test. The tensile creep test was also performed to obtain the specific creep behavior considering decrease in elastic strain due to stiffness development at early age during creep test. The results show that the Young’s modulus for crack evaluation can be obtained from the compression test based on the stress range less than the splitting tensile strength, while the compressive secant modulus was smaller than the tensile Young’s modulus. The decrease of the elastic strain at early age contributes more to the evaluation of the tensile creep than the use of the fly ash mixing.

Effect on Mechanical Properties of Fly Ash Concrete Using Iron Slag as Partial Replacement of Sand

Effect on Mechanical Properties of Fly Ash Concrete Using Iron Slag as Partial Replacement of Sand

Impact of Splitting Tensile Properties and Dynamic Constitutive Model of Fly Ash Concrete

This paper studies the impact of splitting tensile properties of fly ash concrete with a split Hopkinson pressure bar device. Three different water-cement ratios (0.45, 0.55, and 0.6) and six different fly ash contents (0%, 5%, 10%, 15%, 20%, and 30%) were designed in the experiment. Both quasi-static and impact tests were conducted to study the influence of strain rate, water-cement ratio, and fly ash content on the dynamic mechanical properties of concrete. The test results show that the dynamic splitting tensile strength and dynamic incremental factor of fly ash concrete have an obvious strain rate enhancement effect. Under impact load, the dynamic splitting tensile strength of fly ash concrete with a water-cement ratio of 0.45 and 0.6 achieves its maximum value when fly ash content is 10%, and that of fly ash concrete with a water-cement ratio of 0.55 achieves its maximum value when fly ash content is 5%. Finally, the constitutive model considering dynamic damage was established to fit the test curve. The results show that the constitutive model has a good fitting effect on the test curve.

Properties of fly ash concrete containing tropical soil bacteria

The autonomous crack healing process using microbiologically induced calcium carbonate precipitation (MICP) is a sustainable alternative to overcome propagation of micro-cracks and restore the durability of concrete. This paper presents the potential use of tropical soil bacteria as a self-healing agent for fly ash concrete. A solution of 107 cells/mL Lysinibacillus sphaericus (L. sphaericus), was selected to be the self-healing agent by replacing partially the amount of water. Concrete cube specimens with 30% fly ash, were cured under two conditions, which are water and air curing. The potential effects of the self-healing agent was evaluated in terms of the ultrasonic pulse velocity (UPV), initial surface absorption test (ISAT) and compressive strength. The initial results show an improvement of UPV and between 12% and 54% improvement on the compressive strength for the bacterial concrete compared to the control specimen. It was probably due to the presence of the microbial calcium carbonate that fills the concrete pores through the inclusion of bacteria in the concrete. However, based on the ISAT value, the direct addition of bacterial solution increased the concrete’s permeability. Thus, further investigation is suggested to assess the self-healing effect towards permeability and compressive strength of bacterial concrete.

Effect of Colour Pigment on Selected Properties of Fly Ash Concrete. Part 1: Compressive Strength and Water Absorption

Concrete has not only fulfilled the load-bearing function, but also its aesthetic function comes to the fore. It is precisely coloured concrete that performs this function best. The second phenomenon of today is "green concrete". In the paper, the properties of coloured concrete are compared with its "greener" alternative - coloured concrete with fly ash as a binder substitution. Experimental samples were measured for compressive strength and water absorption over a period of 7 days to 2 years. The results showed that the combination of coloured pigment and fly ash has an interesting synergistic effect, as evidenced by a 45MPa compressive strength and a 15% decrease of water absorption.

The Mechanical Properties of Fly Ash Concrete Reinforced with Bamboo Fibers

In addition to the economic advantages, using fly ash in cement has enormous effect on the mechanical properties of the concrete. Moreover, Researchers have identified that the addition of fibers to concrete increases its mechanical properties. Therefore, Better concrete product using both fly ash and fibers especially natural fibers which are more economical and eco-friendlier than the other fibers for an improved concrete strength production is the major aim of this research. This experimental investigation had been undertaken to study a fly ash concrete reinforced with bamboo fibers. The optimum percentage of fly ash to replace cement was first determined by compressive strength test for different percentages by weight of fly ash substitution. After that, mechanical properties of the fly ash concrete were studied with the addition of three different percentages of bamboo fibers. Mix designs were formulated for all percentage and then, Specimens were casted and tested for computing compressive strengths, indirect tensile strengths and flexural strengths for 7th and 28th day period. In the experiments, non-fibrous 25% fly ash substituted with cement concrete (the optimum percentage which was first determined using compressive strength) were compared with the 25% flyash substituted with cement for the individual fibers percentages. The standard 150mm cube compressive strength of bamboo fiber reinforced Fly Ash Concrete (BFRFAC) with 0.10% addition of bamboo fiber by weight of concrete showed an increment of 12.44%, Whereas bamboo fiber reinforced Fly Ash Concrete with 0.2% and 0.30% addition of bamboo fiber by weight of concrete showed a compressive strength reduction of 9.33% and 33.03% respectively compared to non-fibrous fly ash concrete. Bamboo fiber reinforced Fly Ash Concrete with 0.10% and 0.20% bamboo fiber addition by weight of concrete showed an increment in mean split tensile strength of 5.81% and 0.12% respectively; whereas 0.30% additions of bamboo fiber by weight of concrete showed split tensile strength reduction of 14.54% compared to non-fibrous fly ash concrete. Mean Flexural strength of bamboo fiber reinforced Fly Ash Concrete with 0.10%, 0.20% and 0.30% addition of bamboo fiber by weight of concrete showed an increment by 2.48%, 5.98% and 7.80% compared to non-fibrous fly ash concrete respectively.

Compressive stress-strain relationship for fly ash concrete under thermal steady state

The paper presents an experimental study on the mechanical properties of fly ash concrete during thermal exposure. The tests were carried out on an apparatus specially designed for studying “hot” mechanical properties of concrete materials. The results presented include the compressive strength, strain at peak stress point, Young's modulus, and stress-strain relation at temperature ranging from ambient to 900 °C. It was found that 25% replacement of ordinary Portland cement with fly ash in concrete would yield less decrease of compressive strength and more linear stress-strain response at high temperatures due to the further reaction between the reactive silica in fly ash and calcium hydroxide under hydrothermal conditions. Based on the experimental results, an advanced temperature-dependent stress-strain model for fly ash concrete under thermal steady state is proposed. Compared with previous models, the present model has the advantage of considering the variation of the curvature of stress-strain relationship with the increase in temperature. The results are not only a supplement to existing experimental data but also provide the basis for the continuous research on the fly ash concrete under thermal transient state.

Study on properties of bacteria-embedded fly ash concrete

This paper focuses on adopting a new biotechnology tool for enhancing the property of fly ash concrete. Much of the coal fly ash generated from power plants is being dumped regularly. However, environmental situations do not permit dumping of fly ash in huge quantity. To cope with this problem, biotechnology tool is being implemented in the current research work for the utilization of fly ash in concrete. Strength and durability properties of bacteria-embedded fly ash concrete are examined for various ratios of bacterial solution to water. Experimental results show that incorporating alkaliphilic endospore-forming bacteria into fly ash concrete exhibited higher strength and durability than conventional concrete for bacterial solution to water ratios of 0.3 and 0.6. Interestingly, the ratio of compressive strength to split tensile strength of bacteria-embedded fly ash concrete was lower than that of ordinary concrete. It was observed that fly ash replacement up to 30% exhibited better strength and durability properties than normal concrete. Scanning electron microscopic analysis revealed direct involvement of the strain in precipitating calcite and was confirmed by XRD.

TENSILE CREEP OF FLY ASH CONCRETE AT EARLY AGE CONSIDERING THE YOUNG'S MODULUS DEVELOPMENT

Tensile properties are important for predicting tensile stress which causes thermal cracking. Fly ash, a by-product from coal-fired power plants, has been recently used to reduce such thermal cracks. However, investigations dealing with tensile properties of fly ash concrete are still limited. This study focuses on the tensile properties of concrete mixed with fly ash at an early age. Fly ash was mixed in general purpose concrete with a cement-replacement ratio of 20% by mass to simulate fly ash concrete used in Japan. To examine tensile Young's modulus and tensile creep, direct tension test was conducted using dog-bone shaped specimens. The tensile creep tests were conducted at the age of 3 days or 7 days, and the loading (30% of splitting tensile strength at the loading age) was sustained for 14 days. Past investigations usually assumed a constant elastic strain during creep test. It should be noted however that elastic strain at early age decreases with the age of concrete as hydration continues. This study takes a consideration of Young's modulus development during creep test to distinguish actual creep and elastic strains. Test results show that creep strain has been underestimated when assuming constant elastic strain.

Model for compressive strength development of OPC concrete and fly ash concrete with time

Towards promoting the use of higher percentage levels of fly ash in concrete in order to reduce its carbon dioxide footprint, rational models for estimating the mechanical properties of fly ash concrete (FAC) are required. A simple model for predicting the mean compressive strength development with age of both FAC and ordinary Portland cement concrete (OPCC) is proposed. The model is applicable to concrete containing 0–75% class F fly ash, type I cement and normal-weight aggregates and having a 28 d average compressive strength up to 65 MPa. The model was developed based on two-stage regression analyses of the experimental data of 512 concrete mixtures collected from the literature. The predictions made using the model were found to be in good agreement with the results of experimental investigations carried out at CSIR-Structural Engineering Research Centre and additional experimental data collected from the literature. From a comparison with a reaction-kinetics-based strength development model available in the literature, it was noted that the proposed model is able to reflect the reaction kinetic processes involved in strength development in both OPCC and FAC. The proposed model should help in developing specifications related to strength development for FAC similar to that given in fib Model Code 2010 for OPCC.

The mechanical properties of fly ash concrete prepared and cured at high temperatures

Results of an experimental investigation on the effect of fly ash content, water cement (w/c) ratio of concrete prepared and cured at temperatures of ambience, 40°C and 60°C are presented in this paper. The mechanical properties investigated here include its workability, its behaviour under compression and splitting tension. Microscopic investigations were also carried out using SEM micrographic images to gain understanding of concrete at its microstructural level.The results indicate that high temperature increases early compressive strengths of concrete, but has decreasing effects on the strengths at later ages. The use of fly ash in concretes cast and cured at elevated temperatures improves the physical and mechanical properties of fresh as well as those of hardened concrete.Various mathematical models describing the properties of such concretes are considered at the end of this paper. The strength properties of high temperature fly ash concrete were best represented by a simple exponential function of time, while its stress-strain relationship could be best described by an exponential function of strain of a more complicated form.

Experimental Comparison of Methods to Assess the Durability of Concrete Pavement Deteriorated from Scaling and Freeze–Thaw Effect

In cold climates, deicing agents are used to reduce traffic problems due to ice and snowdrifts. However, the use of deicing salts results in accelerated scaling of concrete surfaces on account of damage caused by salt combined with rapid freeze–thaw cycles. These cycles reduce user safety and the service life of concrete pavement. Moreover, scaling is the deterioration of concrete due to the general loss of surface mortar or the mortar surrounding aggregates in concrete. Numerous methods have been proposed and evaluations have been conducted to predict the degree of deterioration caused by scaling and freeze–thaw cycles. In the present study, several previously proposed test methods were experimentally investigated and their differences were examined. Although the watertightness and durability properties of fly ash concrete were observed to be excellent, the scaling resistance decreased. Therefore, it is considered that scaling resistance has a direct effect on cement paste strength. Furthermore, measurement of the scaling resistance varies according to the saline solution, surface finishing treatment, and freeze–thaw environments. In this study, saline solutions that combined the deicing agents NaCl and CaCl2 were used. The surfaces of the test specimens were given the same finish as the field samples using a stiff brush after bleeding. It was determined that these conditions must be considered to simulate conditions that are similar to those of roads, and a critical experimental assessment must be undertaken.

Effects of pore water saturation on the mechanical properties of fly ash concrete

This paper investigates the effects of pore water saturation on the ultrasonic pulse velocity, rebound value, compressive strength, and elastic modulus of fly ash concrete. Fly ash concrete was placed in an artificial climate chamber to achieve different degrees of pore water saturation. Effects of the level of fly ash replacement and the degree of pore water saturation were examined on the concrete rebound value, ultrasonic pulse velocity, compressive strength and elastic modulus. The results showed that the influence of fly ash replacement on rebound values, ultrasonic velocity and elastic modulus was basically the same as on compressive strength. For the range of 0–45% for the level of fly ash replacement, the rebound value, the ultrasonic velocity, the elastic modulus and the compressive strength all reached their maximum value corresponding to the fly ash replacement level of 15%. As the degree of pore water saturation increased, the rebound value of fly ash concrete was increased first and then decreased, the compressive strength was decreased, but the ultrasonic velocity and the elastic modulus were increased.