Fly Ash Replacement Level Research Articles

Durability of concretes exposed to high concentrations of CaCl2 and MgCl2.

In cold regions, calcium and magnesium chloride deicing salts damage concrete pavements due to the formation of certain deleterious chemical phases, including calcium oxychloride. While there is much research at a cement paste-scale, damage in concrete has been less studied. In this study, we evaluate concrete damage due to calcium and magnesium chloride and explain the roles of supplementary cementitious materials (SCM) replacement level, air entrainment, salt type, and exposure conditions in damage development. Various non-destructive test methods including bulk resistivity, mass change, and visual damage assessment were used to monitor the damage over time. Damage was reduced as the SCM replacement level and air content increased, regardless of exposure conditions. Bulk resistivity and visual assessment were promising indicators of damage. The product of 91-day bulk resistivity and the air content predicted concrete performance when exposed to concentrated deicing salts. Based on several criteria, mixtures with 20% fly ash replacement level or 35% slag mitigated damage significantly when the air content was greater than 5% by concrete volume. Damage mitigation mechanisms of SCM and air are discussed.Supplementary InformationThe online version contains supplementary material available at 10.1617/s11527-022-01992-y.

Development of a Screening Tool for Rapid Fly Ash Evaluation for Mitigating Alkali Silica Reaction in Concrete

Performance-based approaches to evaluate fly ash effectiveness in suppressing alkali silica reaction (ASR) require testing for a range of replacement levels to determine optimum fly ash dosage. Current approaches of ASR evaluation, that is, determining optimum fly ash dosage for ASR mitigation, are impractical as a mix design tool for new concrete construction. Therefore, in the present work a screening tool is developed to predict optimum fly ash dosage to suppress ASR in concrete mixes. The screening tool uses water-soluble (readily available) alkali from fly ash and cement to determine pore solution alkalinity (PSA) of concrete mixes for different fly ash replacement levels. The optimum fly ash dosage in concrete to mitigate ASR is estimated based on the PSA and aggregate threshold alkalinity (THA) relationship, that is, PSA should be ≤THA to make the mix ASR mitigated. Results from the screening tool demonstrate an 82% reliability in predicting fly ash dosage necessary to keep expansions below 0.04% based on AASHTO TP 142 tests for ASR expansion. In addition, a multiple non-linear regression model was developed to predict water-soluble alkali from fly ashes in place of testing using 50 experimental data points from laboratory measurements and literature studies. Overall, the screening tool presents a rapid and reliable approach to determine the optimum fly ash content required for ASR mitigation based on pore solution composition of mixes and aggregate reactivity.

Application of machine learning algorithm to assess the efficacy of varying industrial wastes and curing methods on strength development of geopolymer concrete

The contribution of geopolymer concrete is irrefutable and imperative in the context of sustainable construction practices. The current study highlights the relevance of red mud and glass powder in conjunction with fly ash as the aluminosilicate source material for geopolymer concrete production. The performance of the designed binders was evaluated accentuating the function of fly ash replacement levels (10%-40%), curing time, and curing method (ambient, external exposure, and oven curing). Experimental results affirm that the mix containing 10% red mud and glass powder in equal proportions depicted the highest compressive strength at 28 days under external exposure (48 MPa) and oven curing (75 MPa). The study also revealed allowable leachability of geopolymer composites as per relevant standards. Analysing the 28 days compressive strength data using machine learning algorithms showed that the relationship between the dependent and the set of independent variables could be best predicted by a non-linear model, substantiated by the highest level of accuracy (98.79%).

Development of hybrid machine learning-based carbonation models with weighting function

Carbonation of concrete has significant influence on the service life of constructions and great effort has been made to establish an accurate and efficient model of carbonation that incorporates both internal and external factors. We present a hybrid machine learning (ML) approach that combined two single ML models: artificial neural network (ANN) and support vector machine (SVM). A literature survey generated a database containing 532 records of accelerated carbonation depth measurements for concrete mixtures inclusive of fly-ash blends. Six inputs comprising cement content, fly-ash replacement level, water–binder ratio (w/b), CO2 concentration, relative humidity and exposure time were selected for modeling, justified by grey relational analysis. The four ML models had excellent accuracy in predicting the carbonation depth of concrete, with the correlation coefficient ranging from 0.9788 to 0.9946, but the two hybrid ML models achieved superior performance to the single ANN and SVM models with characteristic higher correlation coefficients, lower mean value for the absolute error and lower standard deviation for its distribution. In addition, compared with other commonly known empirical carbonation models, the hybrid ML models showed more accurate carbonation depth prediction with smaller root mean square error. Furthermore, the weightings of the contributions of six selected factors to carbonation depth disclosed that CO2 concentration, w/b and binder content had higher relative importance to carbonation depth and should be given greater weighting in future carbonation model development.

Recycled Aggregate Pervious Concrete: Analysis of Influence of Water-Cement Ratio and Fly Ash under Single Action and Optimal Design of Mix Proportion

Pervious concrete is recommended, which is of great benefit to the ecological environment and human living environment. In this paper, the influences of five water-cement ratios and four fly ash contents to replace the cement by mass with a water-cement ratio of 0.30 on the properties of Recycled Aggregate Pervious Concrete (RAPC) were studied. Following this, based on the Grey relational-Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) optimization method, the strength, permeability, abrasion loss rate, and material costs of RAPC were adopted as evaluation indices to establish a mix proportion optimization model. The results show that the increase of water-cement ratio and fly ash replacement level of RAPC leads to decreased compressive strength while an increase in the permeability and abrasion loss rate. According to test results based on the optimal model 0.30 was identified as the best mix proportion. In addition, ecological-economic analysis of RAPC raw materials was carried out by comparing different natural aggregates. The results of EE (embodied energy) and ECO2e (embodied CO2 emission) pointed out that the combination of recycled aggregate and fly ash leads to significant ecological and economic benefits.

Effects of sodium oxide content on the durability of alkali-activated mortar utilizing botswana copper mine tailings and fly ash

This investigation aims to provide experimental data on the performance of alkali-activated mortar made of copper mine tailings (CMT) and fly ash (FA) exposed to acid-sulphate attacks and elevated temperature environments as a measure of durability. FA was used as a replacement material, substituting 20 to 40% of the CMT by mass, and sodium hydroxide was the alkaline activator, which was added in terms of Na2O content by mass of the total binder at 5%, 10%, and 15%. The durability performance of alkali-activated mortar was evaluated against 5 % and 10% concentrations of sulphuric and hydrochloric acids, and magnesium and sodium sulphates up to 180 days of exposure, as well as elevated temperature environment. The specimens were first visually examined, and weight change was measured before being exposed to an elevated temperature environment and the residual compressive strength was measured. It was observed that Na2O content and elevated temperature environment influence the residual compressive strength of alkali-activated mortar. Increasing the Na2O content for all CMT-FA-based mortar samples performed well in sulphates and acids mediums in terms of durability, but with a slight reduction in its durability performance in terms of residual compressive strength. However, these effects were more profound in samples exposed to acids, particularly those with lower FA replacement levels and sodium oxide content. For the high-temperature exposure, the residual compressive strength of all CMT-FA samples was much higher than the initial values. The findings also revealed that the partial replacement of CMT by FA significantly improved the residual compressive strength in terms of the durability performance of the alkali-activated mortar

Reaction mechanism of sulfate attack on alkali-activated slag/fly ash cements

In this work, the effects of slag/fly ash ratios, Na2O concentration, and silicate modulus (Ms) of activators on the reaction mechanism of sulfate attack on alkali-activated slag/fly ash cements are elucidated by XRD, FTIR, and TG/DTG analysis. To accelerate the sulfate attack process, the alkali-activated cements (AACs) were crushed into particle samples before immersion in the Na2SO4 and MgSO4 solutions. The results show that upon the Na2SO4 attack, the C-A-S-H gel structures of AACs do not change basically. However, the MgSO4 attack on AACs is severe due to the dissolution of alkali and the intrusion of Mg2+. Gypsum is the main product in AACs upon the MgSO4 attack, and the amount of brucite decreases with the incorporation of fly ash. The NaOH-activated slag (Ms = 0) has a relatively higher MgSO4 resistance compared with the Na2SiO3-activated slag, while it is the opposite when the fly ash replacement level increases to 80%.

Evaluation of early-age thermal cracking resistance of high w/b, high volume fly ash (HVFA) concrete using temperature stress testing machine

Fly ash (FA) is an environmentally hazardous industrial solid waste. High FA replacement levels on properties of concrete with low w/b have been widely investigated, however, studies on the thermal cracking behavior of HVFA concrete with high w/b are lacking. This paper investigated the effect of high volume fly ash (HVFA) on mechanical properties and thermal cracking resistance of concrete with a high w/b of 0.45 using temperature stress testing machine (TSTM). An adiabatic curing condition during the temperature rise stage and a rapid cooling during the temperature drop stage were applied on test specimens. The effectiveness of concrete with different FA replacement levels (0%, 20%, 50% and 80%) on the thermal cracking potential of concrete under a restraint degree of 100% has been addressed. Results showed that the mechanical properties of concrete mixture decreased with the increasing FA replacement level; the ratio of creep-to-free strain (i.e., relaxation behavior) of concrete mixture decreased when the FA replacement level reached 20%, and converted to increase for the FA replacement level ranging from 50% to 80%; FA replacement level with 50% showed a desirable effect on the thermal cracking resistance enhancement of high w/b concrete mixture regarding restrained cracking control.

Influence of Particle Packing Theories on Strength and Microstructure Properties of Composite Cement–Based Mortars

Supplementary cementitious materials (SCMs) have become a part of cementitious composites in the manufacturing of cement for improved performance and sustainability. Composite cement is one such type of cement in which ordinary Portland cement (OPC) is partially replaced with fly ash and granulated blast furnace slag (GBFS). In this study, the replacement levels of fly ash and GBFS are optimized to 20% and 30%, respectively, with a 50% OPC content. Apart from the superior properties of these binding materials, a better packing of aggregate comes in handy for improved properties. In this study, the modified Taufer model (MTM) and J. D. Dewar (JDD) model of proportioning the fine aggregates are adopted for improved packing density to obtain better mixes, and a comparison is made with proportions recommended by Indian standard (IS) 383 and IS 650. The packing density obtained in proportioning fine aggregates using the MTM, JDD, IS 650:2008, and IS 383:2016 methods are 0.6814, 0.6737, 0.6238, and 0.6008, respectively. The aggregate sizes recommended based on particle packing models (PPM) particularly, the MTM method tends to improve the packing by reducing the voids content. A direct influence of such effective packing can be observed from the microstructure studies conducted on different samples. MTM samples evidenced better packing compared to other methods of proportioning the mixes. The compound phase changes and development of microstructure were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), a back scattered electron (BSE), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Also, the quantification of portlandite and calcium carbonate available in the samples was determined using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) for different proportions. At 28 days, the specimens cast using MTM showed 11.11% and 15.5% higher compressive strength than the specimens prepared using IS 650:2008 and IS 383:2016, respectively. At every stage of curing, MTM mixes exhibited superior compressive strength.

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.

Sustainable concrete formulations to mitigate Alkali-Silica reaction in recycled concrete aggregates (RCA) for concrete infrastructure

The Alkali-Silica Reaction (ASR) is a Portland Cement Concrete (PCC) distress of greater relevance worldwide, and several authors have successfully mitigated ASR with improved concrete mixture formulations. These concrete mixtures are mainly associated with incorporating Supplementary Cementitious Materials (SCM), which usually involve recycled materials or co-products from other processes, thus contributing to concrete production sustainability. Due to global warming and irreversible impacts on the planet, the circular economy and sustainability concepts are now of particular concern in the cement and concrete industry. Different ways to reduce the environmental impacts of Portland cement concrete include using SCM and Recycled Concrete Aggregates (RCA) to replace natural aggregates. Despite there are no concrete structures made with RCA that have been reported showing signs of ASR, it is essential to check the potential reactivity of RCA to take the necessary corrections to use them safely. This paper includes a laboratory investigation on mitigating the ASR of RCA in PCC production by using several SCM (fly ash, slag, and silica fume) to achieve a more sustainable material, reducing the production cost and the environmental load associated. Results indicate that replacement levels of fly ash (FA, 20%), slag (SL, 40%), and silica fume (SF, 10%) were able to mitigate the alkali-silica reaction of one source of RCA successfully. The optimum dosage of RCA is suggested to be between 25 and 50% (by weight of total coarse aggregate) for mixes containing fly ash and 50–100% for silica fume and slag mixes, respectively. The work also involves a life cycle assessment (LCA) to quantify the environmental benefits depending on the SCM used and the aggregate portion replaced by RCA on PCC mixtures. SCM and RCA in concrete mixtures significantly reduced greenhouse gas (GHG) emissions and energy demand due to lower Portland cement contents.

Strength activity index and bulk resistivity index modifications that differentiate inert and reactive materials

The ASTM C311 strength activity index test is a potentially flawed test because inert materials are known to be able to pass the test. The early age of testing, low fly ash replacement levels, variable water-to-cementitious materials ratio, and low strength limits all contribute to the inability of the test to successfully distinguish inert and reactive materials. Test modifications utilizing higher replacement levels (50% by mass) and higher temperatures (50 °C) are evaluated in this study for three fly ashes and two inert materials. Bulk resistivity is also measured in addition to strength. Using higher replacement levels and higher temperatures provides improved differentiation of inert and reactive materials when using strength, however, the magnitude of differences is somewhat small, when considering variability in strength measurements. On the other hand, higher replacements and especially higher temperatures result in a very substantial increase in bulk resistivity for the fly ashes but not for inert materials. Therefore, a bulk resistivity index test carried out at higher temperatures provides for clear differentiation of inert and reactive materials and should considered for standardization/specification. The calcium hydroxide contents and heat release measured in corresponding cement pastes show that increased temperature enhances fly ash reaction but does not affect inert materials. At higher replacement levels, greater effects of fly ash reaction are manifested, resulting in better differentiation from inert materials than at lower replacement levels.

USING FLY ASH AS A PARTIAL REPLACEMENT FOR FINE AGGREGATE IN CONCRETE AND ITS EFFECTS ON CONCRETE PROPERTIES UNDER DIFFERENT CURING TEMPERATURES

A shortage of natural fine aggregates has occurred worldwide, especially due to excessive consumption of them in construction activities. For this, the availability of sustainable alternative materials for natural fine aggregate is researched. Fly ash is identified as one such material that can partially replace fine aggregate in concrete. The current study demonstrates the feasibility of using fly ash as a partial fine aggregate replacing material in concrete and its effects on the compressive strength and some significant durability properties when cured under different curing temperatures. Fine aggregate and cement were partially replaced with Class F fly ash in different percentages. The curing methods (used in this study) were isothermal heat curing at 30ºC, 50ºC, and 70ºC, and one-day accelerated heat curing. The compressive strength test, carbonation depth test, rapid chloride penetration test, and surface resistivity test were performed for concrete mixtures with different fly ash replacement levels and curing temperatures. Test results reveal that the use of fly ash as a partial fine aggregate replacing material in concrete gives higher compressive strength than that of concrete with fly ash as a partial cement replacing material at both an early age and a later age. One-day accelerated curing is the most beneficial curing method, regarding the compressive strength at all the tested ages. Moreover, concrete with fine aggregate replacement gives better results for carbonation resistance, chloride penetration resistance, and surface resistivity when compared with the control mixture and mixtures with fly ash as a partial cement replacing material.

Predicting the compressive strength of fly ash concrete with the Particle Model

A novel approach called the Particle Model is used to predict the compressive strength of fly ash concrete. Thousands of fly ash particles are classified into the nine groups based on the chemical information of each particle. Predictive models for compression strength for 20% and 40% fly ash replacement levels are developed for seven different curing times between 3d and 180d. The R-squared value for the compressive strength prediction of the Particle Model is ≈ 0.99, while the Class C and F classification model is <0.50. Furthermore, the results show that the Particle Model can predict the compressive strength within ±10% for 95% of all measurements at 20% fly ash mass replacement and for 81% of all measurements at 40% mass replacement. The coefficients in the derived predictive models give important insights into the effectiveness of different fly ash particles over time.

Impact of aggregate type and size and mineral admixtures on the properties of pervious concrete: An experimental investigation

Balancing the permeability with the compressive strength of pervious concrete is essential to satisfy the requirements for pavement concrete. The aggregate type and size and mineral admixtures are important factors influencing the permeability and the compressive strength of pervious concrete. 56 groups of pervious concrete samples with different aggregate types and sizes and mineral admixtures were prepared. Test results show that higher compressive strength and permeability are obtained in pervious concrete with dolerite aggregate compared to pervious concrete with granite aggregate. The optimum porosity and w/c for pervious concrete with both dolerite and granite are 18% and 0.25, respectively, in the studied ranges. For granite aggregate, the permeability decreases as the particle size increases in the case of single size and the lowest permeability is observed for the combined gradation of granite aggregate. The compressive strength of pervious concrete increases with the increase of replacement level of silica fume while it decreases with the increase of replacement level of fly ash. The maximum permeability for single used of silica fume and fly ash is found at the replacement level of 6% and 10%, respectively. The maximum permeability for the combined used of silica fume and fly ash was observed in the case of 0% fly ash and 6% silica fume.

A Novel Durability Based Concrete Mix Design Using Supplementary Cementitious Materials and Modified Aggregate Band Gradation

This study focuses on proposing a novel mix design method giving emphasis to the durability of concrete and replacing cement with supplementary cementitious materials (SCMs) at certain percentages. It also includes band gradation of aggregate that merges fine and coarse aggregates to result in a single well-packed combined gradation. Two replacement levels (20% and 35%) of fly ash and three replacement percentages (20%, 65% and 90%) of slag by weight of cement were used to prepare a significant number of concrete mixes. Compressive strength, workability and durability of the prepared mixes were determined. Rapid Chloride Permeability Test (RCPT) was carried out for measuring durability of concrete. From the prepared mixes, it was possible to achieve 90-day RCPT value as low as 216-coulomb and 28-day compressive strength up to 46.5 MPa. Several contour plots were developed correlating the three mix design parameters (compressive strength, slump and durability) with cement and water contents. Finally, using the plotted contours, a mix design process has been organized into five simple steps that can easily be followed in order to proportion an optimized ratio of cement, aggregate and SCMs for preparing durable and economical concrete mixes.

Mechanical and electromagnetic performance of cement based composites containing different replacement levels of ground granulated blast furnace slag, fly ash, silica fume and rice husk ash

In this study, cement additives were replaced with cement in mortar mixtures by mass. Mortar specimens were prepared with different additives and dosages which were mechanically and electromagnetically tested. According to the compressive strength test results, mortars containing ground granulated blast furnace slag had weak early age strength and strong later age compressive strengths values, mortars containing fly ash had lower compressive strength value with increasing amount of additives in the mortar mixture for both 7 and 28-day samples, mortars containing silica fume had the maximum strength values at 20% replacement level and lastly the mortars including more than 10% rice husk ash showed weaker strength behaviors with increasing amount of rice husk ash. Besides, electromagnetic responses of the mortar samples were investigated in the frequency range of 3–18 GHz. The reflection and transmission values were measured and the absorption characteristics were calculated. According to the electromagnetic test results, it is revealed that the mortars including ground granulated blast furnace slag can be utilized in the applications of high stealth technology and electromagnetic shields in a wide frequency range of communication field. An increase in the ratio of fly ash in the mortars reduces the transmission of the electromagnetic wave. Mortars including silica fume had very low values of reflection and transmission. Hence, it is expected that the absorption values must be high due to dependency of absorption to reflection and transmission, and it can be said that mortar with rice husk ash exhibits a strong absorber behavior.

Effect of sulfate activator on mechanical and durability properties of concrete incorporating low calcium fly ash

The use of fly ash as a cement replacement material brings economy and sustainability in the concrete construction. Despite economic and environmental benefits, fly ash incorporation in concrete reduces its early age performance. Therefore, the main objective of this research is to increase the incorporation level of fly ash in the hybrid binder (cement plus fly ash) utilizing the sulfate activation technique to overcome the issue of inferior performance at an early age. Replacement levels of fly ash with cement were kept as 20 %, 40 %, and 60 %. 2 % sodium sulfate (Na2SO4) by weight of binder was utilized as an activator. Compressive strength and flexural strength tests on standard samples were carried out at the age of 3, 28 and 90 days. Durability tests namely apparent porosity, sorptivity coefficient and chloride penetration tests were also conducted. Experimental results showed sulfate activation increased the early age strength at all levels of fly ash. After activation, concrete mix with 20 % and 40 % fly ash showed better strength performance than that of the conventional concrete at all ages. Concrete with 20 % and 40 % fly ash upon activation showed lower sorptivity and porosity than control mix at all ages. Similarly, chloride penetrations of concrete with 20, 40 and 60 % activated fly ash was noticeably lower than that of the control concrete. Chemical activation is also beneficial in reducing the cost and carbon footprint per unit strength of the fly ash mixes.

Using the Particle Model to predict electrical resistivity performance of fly ash in concrete

The electrical resistivity performance of fly ash in concrete is not easy to predict due to the diverse sources of fly ash and their varying reactivity. Electrical resistivity gives direct evidence of the rate of corrosion within the concrete and provides indirect clues into the fluid transport into the material. This paper aims to develop predictive models for the electrical resistivity of fly ash concrete by applying the Particle Model. The Particle Model rapidly examines individual fly ash particles without human intervention and is used to derive predictive models for 20% and 40% fly ash replacement levels in concrete at seven different periods of hydration. The R-squared values of predictive models in the Particle Model show significant improvement over using the classification method based on Class C and F for both fly ash replacement at all investigated time periods. The derived predictive models are able to accurately estimate the electrical resistivity within +/- 10% for 80% of all measurements at 20% fly ash replacement and within +/− 10% for 75% of all measurements at 40% fly ash replacement. These investigations provide important insights into how the Particle Model can help predict the electrical resistivity of fly ash concrete even at different mixtures and hydration times.

Partial Replacement of Cement with Wood Ash &amp; Fly Ash in Pavement Quality Concrete

Pavement Quality Concrete (PQC) is a special type of concrete which is used for construction of rigid pavements in dense traffic regions. In this type of PQC higher percentage of cement content is added when compared with conventional concrete, and it is mostly designed for high strength concrete M40 to M50 grade of concrete. Cement production leads to emission of greenhouse gases in vast amount, which made researchers to look for an substitute material to incorpotate with cement. The current experimental work is done to study the effect of wood ash and fly-ash mixed in concete as a partial replacement of cement. The replacement levels of wood ash and fly ash are taken equally as 10, 20 and 30% by weight of cement. In this mainly focused on Compressive strength and split tensile strength according to IS Codal provisions. Experimental test results revealed that the replacement of wood-ash and fly ash as a cementitious material in Pavement Quality Concrete will improve compressive and split- tensile strength of concrete.