Class-F Fly Ash Research Articles

Utilisation of Class-F fly ash in xanthan gum–amended neutral or acidic soils

Xanthan gum (XG) is an eco-friendly biopolymer with potential applications in soil amendment. However, in acidic soil environments, the pyruvate groups and glycosidic bonds in XG molecules tend to hydrolyse, thereby weakening the efficacy of soil improvement. In this study, the feasibility of utilising alkaline Class-F fly ash (FA) to assist XG in reinforcing acidic soils was evaluated through proctor compaction, unconfined compression, and one-dimensional consolidation. With the increasing soil acidities, the beneficial effect of FA on the geotechnical performances of XG-amended soils grew. The improvement in both mechanical strength and compressibility of XG-amended acidic soils might be caused by the crossing-linking of XG molecular strands and the mitigated hydrolysis of XG hydrogels due to the presence of FA. Based on the findings, it is suggested to use FA in combination with XG for treating the acidic soils and use XG alone for treating the neutral soils. The research outcomes will promote the reuse of solid waste Class-F FA in sustainable geotechnical engineering practices, for example, biopolymer-based soil amendment in acidic soils.

Highly efficient radium removal from mine wastewater with fly ash NaP1 zeolite

This study investigates the application of NaP1 zeolite, synthesized hydrothermally from F-class fly ash, for treating radium-contaminated mine water. The objective was to assess the efficiency of NaP1 zeolite in removing radium ions from real mine water samples. Three samples with high concentrations of 226Ra and 228Ra and total dissolved cation contents ranging from 48.9 to 89.0 g/L were treated using sequential batch and fixed bed experiments. The NaP1 zeolite demonstrated high treatment efficiency for radium-sulfate and radium-strontium water, with removal rates of 97 % and 82 % for the 1st liter, and 54 % for the 53th and 9th liters, respectively. However, for radium-barium water, the maximum treatment efficiency was 45 % for the 1st liter, dropping to 0 % after 4th liter. This decline was attributed to the competitive adsorption of barium ions, which reduced the radium removal efficiency more rapidly than in the other water types. An additional experiment with synthetic barium water confirmed that 10 g of NaP1 zeolite adsorbed 1 g of Ba from one liter of distilled water. These results highlight the potential of NaP1 zeolite for radium removal in certain contexts, although its efficiency may be hindered by the presence of competing ions such as barium.

Geotechnical and microstructural analysis of high-volume fly ash stabilized clayey soil and machine learning application

The weak soil stabilization using solid wastes is one of the most common solutions for improving geotechnical characteristics as well as for problematic waste dumping in landfills. The present experimental study aims to examine the effect of high-volume Class-F fly ash on the geotechnical and microstructural properties of clayey soil by adding them in ranges between 5 % and 50 %. The results show that as the amount of fly ash in clayey soil increases, properties like the specific gravity, plasticity index, permeability, optimum moisture content, maximum dry density and free swelling index improves. Moreover, these geotechnical properties were analyzed to develop machine learning models using three different algorithms, namely K-nearest neighbor regression, random forest, and support vector regression, for obtaining the optimum amount of fly ash contents in weak expansive soils. The predicted and experimental results found to be in close-relation for predicting the geotechnical behavior of modified clayey soil. Furthermore, the performance of the ML models degrades as the number of components reduces, with KNN regression consistently outperforming SVR and RF but suffering significantly with fewer components. The results of the testing set in the case of four components are MSE of 77, R² of 0.896, RMSE of 0.846, MAE of 0.327, and SEE of 0.858, indicating precise and consistent predictions. However, the prediction accuracy considering lesser components shows MSE as 262, R² as 0.648, MAE as 5.606, SEE as 16.707, and GPI as 1.056, confirming the elevated error rates. Overall, it has been concluded that combining comprehensive experimental work and machine learning techniques outperforms in enhancing geotechnical data processing, optimized waste contents in weak soils, improves sustainability in construction, saves resources, reduces the possibility of human mistakes, and increases reliability.

Early Age Strength of Development Ultra High-Performance Concrete Using Class-F Fly Ash and Local Materials for Repair

Early Age Strength of Development Ultra High-Performance Concrete Using Class-F Fly Ash and Local Materials for Repair

Comparative Analysis of Woody Biomass Fly Ash and Class F Fly Ash as Supplementary Cementitious Materials in Mortar.

Biomass fly ash is a sustainable, eco-friendly cement substitute with economic and performance benefits, being renewable compared to coal fly ash. This study examines using biomass fly ash (BFA) as a sustainable cement substitute, comparing it with Class F fly ash (CFA). With a water-binder ratio of 0.5 and replacement rates of 10%, 15%, 20%, 25%, and 30% (by mass), the research highlights BFA's promising applications. BFA and CFA were mixed into cement paste/mortar to analyze their reactivity and properties, with hydration products CH and C-S-H evaluated at 7, 28, and 91 days. Compressive strength, micro-pore structure, and drying shrinkage (assessed from 7 to 182 days) were tested. Results showed BFA had similar pozzolanic reactions to CFA at later stages. While compressive strength decreased with higher BFA replacement rates, early-stage performance matched CFA; growth was CFA-10 (18 MPa) and BFA-10 (17.6 MPa). BFA mortars exhibited slightly better deformation properties. BFA-30 cement had superior performance, with a lower drying shrinkage rate of 65.7% from 14 to 56 days compared to CFA-10's 73.4% and a more stable shrinkage growth rate decrease to 8.4% versus CFA-10's 6.4% after 56 days. This study concluded that BFA, usable without preprocessing, performed best at a 10-15% replacement rate.

Enhancing Concrete Performance through Sustainable Utilization of Class-C and Class-F Fly Ash: A Comprehensive Review

Integrating class-C and class-F fly ash (FA) as supplementary cementitious materials (SCMs) in concrete offers a promising pathway for sustainable construction practices. This study explores the pivotal role of FA in reducing carbon dioxide (CO2) emissions and improving concrete’s durability and mechanical properties through a comprehensive life cycle analysis (LCA). By blending FA with cement, significant reductions in CO2 emissions are achieved, alongside enhancements in the workability, compressive strength, and permeability resistance of the concrete matrix. This research elucidates the pozzolanic reaction between FA and calcium hydroxide (CH) during cement hydration, highlighting its contribution to concrete strength and durability. Through a range of comprehensive analysis techniques, including mechanical testing and environmental impact assessment, this study demonstrates the substantial benefits of prioritizing the utilization of class-C and class-F FA in sustainable construction. The findings underscore the industry’s commitment to environmentally conscious practices, promoting structural integrity and reducing ecological impacts. Overall, this research emphasizes class-C and class-F FA as critical components in achieving sustainable construction goals and advancing towards a more environmentally responsible built environment.

Induction furnace slag as fine and coarse aggregate in quaternary blended self-compacting concrete: A comprehensive study on durability and performance

This research explores the innovative use of Induction Furnace slag Aggregate (IF-slag) as both fine and coarse aggregates in Quaternary Blended Self-Compacting Concrete (QBSCC) mixes, an area that has received limited attention in previous studies. The primary aim is to compare the durability characteristics of QBSCC mixes containing natural aggregate versus those incorporating IF-slag aggregate. A total of 18 SCC mixes were prepared in two groups: one using natural aggregate and the other using IF-slag aggregate. Each group consisted of eight optimized QBSCC mixes alongside a reference SCC mix. The QBSCC mixes were formulated using Ordinary Portland Cement (OPC) with Supplementary Cementitious Materials (SCM) such as Silica Fume (SF), Class F-Fly Ash (FAF), and Ground Granulated Blast Furnace Slag (GGBFS). Previous work by the authors analysed the fresh and mechanical properties of these QBSCC mixes. This study assesses various durability properties, including water absorption, permeable pore volume, absorption coefficient sorptivity, ultrasonic pulse velocity, resistance to chloride ion penetration, electrical resistivity, and thermal conductivity. Experimental findings indicate that SCC prepared with IF-slag exhibited inferior durability performance compared to natural aggregate. However, regardless of aggregate type, QBSCC mixes outperformed the SCC mix containing 100% OPC. Notably, the SCC-47.5 (OPC)/52.5(SCM) QBSCC mix demonstrated significant improvements in durability properties, achieving a reduction of 25% in water absorption, 24% in permeable pore volume, 48% in absorption coefficient, and 46% in sorptivity. QBSCC mixes also exhibited resistance to chloride ion penetration and enhanced electrical resistivity. Moreover, using quaternary blends reduced the thermal conductivity and improved the energy efficiency.

Valorization of biomass bottom ash in alkali-activated GGBFS-fly ash: Impact of biomass bottom ash characteristic, silicate modulus and aluminum-anodizing waste

Growing production of green energy from biomass has led to a surge in biomass bottom ash (BBA) generation, often relegated to landfills due to high leachable heavy metal content. This study proposed solidifying BBA in alkali-activated granulated ground blast furnace slag (GGBFS) and class F fly ash (CFA) blended binders. Investigations into the influence of BBA content, fineness, silicate modulus of activators, and aluminum-anodizing waste (AAW) on solidification performance were conducted, focusing on reaction mechanisms, phase assemblages, mechanical properties and leaching behavior. Results indicate relatively low reactivity of BBA and high leachable chloride (Cl-), sulphate (SO42-), chromium (Cr), molybdenum (Mo), lead (Pb) and zinc (Zn) contents from BBA. Increased BBA substitution leads to strength deterioration, while ground biomass bottom ash (GBBA) improves the mechanical performance slightly. This improvement is attributed to the increased reactive aluminosilicate content and an enhanced packing system resulting from finer particles. However, GBBA induces an increased heavy metals leaching. Higher silicate modulus activators enhance mechanical properties and reduce the leaching of Mo and Cl-, while lower silicate modulus activator accelerates the reaction process, promoting the formation of hydrotalcite-like phases and reducing the leaching of Cr and SO42-. Incorporating 0.5 wt% aluminum-anodizing waste improves immobilization efficiency of toxic ions, but further increases in dosage lead to higher leaching due to weakened mechanical performance. Overall, hybrid binders with 10 wt% G/BBA exhibit desirable mechanical properties, along with sufficient immobilization of leachable heavy metals, enabling their use as potential construction materials.

Impact of SCMs and fibres in ECC on the fire resistance of hot-jointed SCC/ECC composites

The influence of various supplementary cementitious materials (SCMs) and fibres on the fire resistance of composite systems that combine engineered cementitious composites (ECCs) in tension with self-compacting concrete (SCC) in compression was examined. The study was designed to determine the ideal ECC formulation for optimising mechanical properties and bonding performance at ambient and elevated temperatures. The SCC and ECC were hot-joined without vibration or surface preparation, using a fresh-to-fresh casting method. Modifications to the chemical composition of the ECCs included the addition of class F fly ash (FAF), class C fly ash (FAC) or slag, as well as polyvinyl alcohol (PVA) fibres or steel fibres. The samples were exposed to temperatures of 200°C, 400°C, 600°C and 800°C, followed by comprehensive testing to evaluate their flexural strength, tensile strength and interfacial properties. The results indicate that the incorporation of an ECC layer within the SCC system significantly improved mechanical strength and thermal stability, both at ambient temperatures and under high-temperature conditions. Notably, the addition of FAF (rather than FAC or slag) in the ECC layer offered superior thermal stability and ensured the retention of desirable residual mechanical properties. Moreover, steel fibre reinforcement greatly improved the SCC/ECC bonding, outperforming PVA reinforcement at elevated temperatures.

Subbase stabilization with fly ash

Due to increased activities in civil engineering, and especially in the transport infrastructure, and thus an increase in the use of additional construction materials, innovative solutions are needed in finding alternative materials for the preservation of natural resources. One of the solutions for preserving natural building materials is the application of recycled material, which will also meet the required standards in civil engineering. In the transport infrastructure, there is a great opportunity for the use of recycled material, starting from the subbase, through the embankment and all the way to the superstructure and the concrete structures. One of the recycled materials that can be used in construction is fly ash. Fly ash is the most promising waste material when it comes to the wide range of applications in construction. Fly ash is obtained by burning coal in thermal power plants to produce electricity. Due to variations in the composition and characteristics of fly ash, several divisions and classifications have been created. One of the main classifications is according to the American standard ASTM C 618-05 where it is divided into class C and class F fly ash. This research aims to investigate the application of fly ash for subgrade stabilization and to determine the difference from a financial and environmental perspective for the application of fly ash compared to natural stone aggregate. The main research was carried out in connection with the increased use of natural stone aggregate, which appeared as a need during the rehabilitation of state road R1206, section Karpalak - Zelino. Apart from the use of large quantities of stone aggregate for the stabilization of the subgrade, it also had an impact on the financial framework for the realization of the road project. In Macedonia, an analysis of the chemical composition of 4 samples of fly ash obtained in REC Bitola was carried out. From the obtained results, it can be concluded that it belongs to the classification of F-class fly ash and with the use of an activator (lime or cement) it can be used in the stabilization of the subgrade.

Mechanical and microstructural properties of pavement quality concrete using both Class-F fly-ash and copper slag

This research deals with the improvement in the mechanical properties of pavement quality concrete (PQC) when mixed with Class-F Fly-Ash (FA) and Copper Slag (CS) as replacements for ordinary Portland cement (OPC) and river sand (RS), respectively. Forty-eight different PQC mixes of M40 and M50 grades were prepared, in which RS is replaced by CS to the extent of 100%, and OPC is replaced by FA to the extent of 30%, with each replacement done at a certain increment. The combined effects of CS and FA on fresh and hardened concrete properties such as workability, density, water absorption, volume of voids, cube compressive strength, split tensile strength, flexural strength, cylinder compressive strength and ultrasonic pulse velocity (UPV) are experimentally investigated. All mixes containing up to 20% FA and up to 100% CS replacements showed increased strength compared with that of the control mix. The PQC mix containing 20% FA and 60% CS resulted in superior strength properties at a 90-day curing period. However, PQC mixes with 30% FA showed a decrease in strength properties with respect to the control mix. X-ray diffraction (XRD) and scanning electron microscope (SEM) studies were employed for the characterisation of selected PQC samples. Furthermore, multiple linear regression equations were established to predict all the strength parameters. The PQC mixes made with FA and CS provide superior strength, reduce waste disposal problems and preserve natural resources for future generations, making such developed mixes sustainable.

A STUDY ON CONCRETE CONTAINING THE SANDSTONE SLURRY AND FLY ASH PARTIALLY REPLACED WITH SAND AND CEMENT

Now a day’s the waste is produced in immense amounts during construction and coal burning, this study mainly focused on the utilization of sandstone slurry produced during sandstone cutting and Class-F fly ash produced by coal-burning. In this study a deep analysis is taken after 28 days’ testing, six concrete mixes were prepared one is conventional as M20, and trial mix batches are a total of five, three specimens were taken from each concrete mix separately to determine the engineering properties of the prepared specimen. Fly ash partly replaced with the cement in % of 5%,10%,15%,20%,25% and Sandstone slurry partially replaced with sand in % of 10%,20%,30%,40%,50%. Water cement ration took .4-.7%, after 28 days specimens were tested of water curing at ±2, 270C. Sulfate bath is prepared for durability test with 5% Na2SO4 and prepared specimen left for 28 days curing in prepared sulfate bath after completion of 28 days’ normal water curing, the specimen was tested after 56-day curing, acidic nature was maintained for prepared bath, on daily basis pH value has been noted if found more than 6.9 pH than sulphuric acid is added to keep the acidic nature of prepared bath. Only 5% FA and 10% SSS specimen show strength increment up to 14.477% and after sulfate bath, no change was found in specimen’s volume. In compressive strength maximum strength increased up to 19.39%, from 5% FA and 10% SSS replacement. In splitting tensile strength maximum strength increased 11.37% with 10% FA and 20% SSS.

Use of Time–Temperature Superposition and Stepped Isothermal Method for Estimating Long-Term Properties of Recycled Aggregate Roller-Compacted Concrete

Abstract Although the use of recycled materials in civil engineering construction is a desirable option from a sustainability standpoint, the questionable long-term performance of these materials often hinders their widespread use in practice. The primary focus of this study was to perform accelerated aging and testing for estimating long-term properties of a roller-compacted concrete composed of crushed recycled aggregate, Type-I portland cement, and ASTM Class-F fly ash replacing up to 50 % of cement by weight. Accelerated aging was accomplished by curing cylindrical specimens at three different elevated temperature regimes for specific time durations. At the end of each time–temperature regime, the residual stiffness of the specimen was measured in a nondestructive fashion. Series of stiffness–time master curves were then constructed for each mix using the time–temperature superposition (TTS) technique and the stepped isothermal method (SIM). While the TTS method uses different sets of specimens for each elevated time–temperature regime, SIM uses a single set of specimens that are stepped up in temperature and held at each regime for a specified duration. Results indicated that for all mixes, the material stiffness degraded with time. Based on the Arrhenius equation, stiffness–equivalent age master curves were developed. Stiffness prediction was accomplished up to an equivalent age of almost 600 days, although the actual short-term test lasted only up to 6 days. It was also found that SIM and TTS provided comparable results, thus implying that the testing time and the number of specimens can be significantly reduced by using the SIM.

The characteristics of alkali-activated slag-fly ash incorporating the high volume wood bottom ash: Mechanical properties and microstructures

The main objective of this study was to evaluate the mechanical properties and microstructure of alkali-activated material (AAM) incorporating the high volume of wood bottom ash (WBA) for the production of paste samples (AAWP). WBA was used to replace 0 %, 30 %, 50 %, and 70 % of the mass of a blend of ground granulated blast furnace slag (GGBFS) and class-F fly ash (FA) with a mass ratio of GGBFS/FA of 1:1. These paste mixtures were activated by an alkaline solution of sodium hydroxide (NaOH) 10 M and sodium silicate (Na2SiO3), with an alkali concentration Na2O of 4 % and varied silica modulus (Ms) ratios of 0.5, 0.75, and 1.0. A series of tests were performed following the relevant standards, including slump flow, setting time, compressive strength, and ultrasonic pulse velocity (UPV) to evaluate the mechanical properties of paste samples, while the microstructure of hardened paste was examined by X-ray diffraction (XRD), scanning electronic microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). The compressive strength of AAWP ranged from 14.6 to 50.0 MPa at 56 days of curing age. The results revealed that using 30 wt% WBA significantly improved compressive strength and microstructure compared to the reference mixture. Meanwhile, the AAWP with 50 wt% WBA replacement performed the compressive strength of approximately 30 MPa, and the replacement by 70 wt% WBA exhibited a significant reduction in strength. Moreover, increasing the Ms ratio slightly increased the compressive strength and qualities of the paste samples in all levels of WBA replacement. The C-(A)-S-H/Calcite gel and the Ht-like phase were the main hydration products of the paste samples.

Influence of calcium sulfate dihydrate as chemical activator on compressive strength of hardened fly ash-cement pastes

The present study focuses on evaluating influence of calcium sulfate dihydrate (CaSO4.2H2O) as a chemical activator on compressive strength of hardened pastes containing fly ash and cement as cementitious materials. A high amount of Class-F fly ash used to replace Portland cement ranged from 85 to 93% by mass of cementitious materials. For all the pastes, a low water-to-cementitious materials ratio of 0.20 was prepared. The amounts of CaSO4.2H2O added to the mixtures were 0.0, 1.5, 2.0, and 2.5% by mass of cementitious materials. Experimental results showed that at the age of 3 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was higher 1.21–2.15 times than that of the control paste specimen without CaSO4.2H2O. At the age of 7 days, the compressive strength of hardened paste specimens using CaSO4.2H2O still continued to be higher 1.03–2.06 times than that of the control paste specimen without CaSO4.2H2O. At the ages of 14 and 28 days, the compressive strength of hardened paste specimens using CaSO4.2H2O was approximately equal to that of the control paste specimen without CaSO4.2H2O. Consequently, the addition of CaSO4.2H2O improved the early-age compressive strengths of the fly ash-cement pastes, and the CaSO4.2H2O content of 2.0% by mass of the cementitious materials was effective in increasing the compressive strength of such pastes.

Mechanical properties and durability of concrete containing coal mine waste rock, F-class fly ash, and nano-silica for sustainable development

Natural resources such as river sand and rock used for producing concrete tend to be depleted. Thus, it is necessary to find a new material for substituting the natural aggregate in concrete production. Waste materials such as coal mine waste rock, if these wastes are not treated properly, they negatively affect the environment and human health. Therefore, utilizing waste rock from coal mining to partially substitute aggregate in concrete manufacturing for sustainable development is urgent. In this study, crushed sand from coal mine waste rock (CSM) has partially replaced river sand and combined with F-class fly ash (FFA) and nano-silica (NS) to produce concrete with a minimum compressive strength of 35 MPa. Specifically, 40% of cement was replaced by 38% of FFA and 2% of NS, and river sand (RS) was replaced by CSM at contents of 0%, 10%, 20%, 30%, 40%, and 50%. Mechanical properties, durability, and environmental impact were conducted to evaluate the application of CSM in concrete for sustainable development. The results showed that the synergistic effects of fly ash and nano-silica in concrete helped CSM more environmentally friendly. The mechanical properties and durability of concrete using CSM were close to those of normal concrete using conventional aggregates with the required compressive strength of 35 MPa. The use of mine waste in concrete production has shown its effectiveness in replacing traditional aggregates (river sand), which can minimize environmental impact for sustainable development.

Understanding reactive amorphous phases of fly ash through the acidolysis

It is well understood that the reactive components of fly ash (FA) in alkali cement are mainly donated by amorphous phases. The acidolysis method is typically employed to dissolve these amorphous phases for separate analysis; however, such method is not truly convincing, especially the testing and analysis processes. This paper investigates the hydrofluoric acid (HF, 1%) dissolution process (from 0.5 h to 20 h) of two Class-F FAs with different physical and chemical characteristics. The time-dependent quantitative analysis results indicate that in addition to amorphous phases, some crystalline phases are also dissolved in 1% HF solution. Further, the chemical statistics on the dissolved amorphous phases was extracted from the scanning electron microscopy images. Amorphous aluminosilicates in FA can be quantitatively classified into six groups, of which the three reactive amorphous aluminosilicates are defined.

Effect of Activator Type on Geopolymer Mortars Containing Different Types of Fly Ash

In this study, the influence of the activator type on the physical and mechanical properties of the geopolymer mortars was analyzed. C and F-class fly ash (FA), blast furnace slag (BFS), sodium hydroxide (NH), sodium metasilicate (NS), standard sand, and distilled water were used in the production of mortar specimens. All specimens were cured at room temperature. C and F-class fly ash usage ratios are 0%, 15%, and 30%. NH was used as an activator in the 1st group of the produced geopolymer mortars, and NS with NH was used in the 2nd group. 5 series were produced and a flow-table test, ultrasonic pulse velocity test, flexural strength test, compressive strength test, and Scanning Electron Microscope-Energy Dispersive Spectrometry (SEM-EDS) microstructure analysis were applied to the samples. The addition of NS increased the compressive strength and the greatest increase occurred in the reference sample by 113%. It also increased the compressive strength of FAF30 by 60% in comparison to FAC30. Following the results of the SEM examination, when the reference samples were compared, the addition of NS inhibited the formation of cracks. According to the SEM-EDS analysis results, an increase in the F and C-class FA ratio improved the crack formation. Compared to F-class FA, FAC30 has more cracks due to the lower SiO2 content in C-class FA. High K content and SiO2 ratio, as determined by EDS analysis, boost the alkalinity and positively impact the strength.

Application of Group Method of Data Handling via a Modified Levenberg-Marquardt Algorithm in the Prediction of Compressive Strength of Oilwell Cement with Reinforced Fly Ash Based on Experimental Data

SummaryThe experimental design of well cement with durable compressive strength (CS) is challenging and time-consuming. The current research predicts CS using the enhanced group method of data handling via a modified Levenberg-Marquardt algorithm (GMDH-LM) with experimental data. Class F fly ash (CFFA) is used as a supplementary material to cement at various proportions. Experimental tests of CS, thermogravimetric (TG) analysis, rheology, and scanning electron microscopy (SEM) are applied. Experimental findings revealed that the addition of fly ash (FA) enhances CS with curing time as an outcome of pozzolanic action. CS for 20% FA reinforcement after curing for 28 days was 42.95 MPa, compared with 41.53 MPa for 50%. This indicates that a higher addition of FA lowers CS. The rheological findings revealed that FA enhanced the viscosity of the cement slurry. The SEM images demonstrated that the incorporation of CFFA with cement modified the contexture of hardened cement. Cement, water, oilwell cement (OWC), curing time, dispersant, and FA were assigned as input variables for GMDH-LM while CS from the experimental analysis was set as output. Machine learning (ML) findings indicated that GMDH-LM can effectively estimate the CS of OWC. GMDH-LM performed better than backpropagation neural network (BPNN), support vector machine (SVM), and normal GMDH models in predicting CS; it provided higher linearity during training as GMDH-LM gave R2 = 0.958, GMDH = 0.946, SVM = 0.925, BPNN = 0.897, and the least loss functions of mean square error (MSE) = 0.238, MSE = 1.685, MSE = 2.567, and MSE = 4.032, respectively. Similarly, good results were ascertained during testing GMDH-LM provided R2 = 0.928, GMDH = 0.907, SVM = 0.895, BPNN = 0.878, and the lowest loss functions of MSE = 0.304, MSE = 2.650, MSE = 3.494, and MSE = 5.678, respectively. Therefore, the comparative results of all experiments and predictions reveal that GMDH-LM can be deployed as an advanced approach for the estimation of cement hydration in oil and gas wells.

Comparison of the performance of class-C and class-F fly ash concrete mixtures produced with crushed stone sand

The use of fly ash as partial replacement of cement in the production of environmentally-friendly concrete is now an established fact. This study investigated the effects of class-C and class-F fly ash at 20 wt% replacement of Portland cement (PC) on the strength and durability characteristics of concrete mixtures incorporating crushed stone sand as fine aggregate. Experimental investigations were carried to compare the effects of class-C and class-F fly ash as partial replacement of cement on the rheology, compressive strength, moisture sorption, abrasion resistance, and microstructural characteristics of the resulting concrete mixtures at various concrete ages.Test results showed that the use of class-C fly ash lowers the workability (slump value) by 26% and entrained air by 33% of the fresh concrete, while the class-F fly didn’t not affect these characteristics when compared with that of control mixture. On the other hand, the use of class-C and class-F fly ash enhanced the later age compressive strength of the resulting mixtures by 23% and 35%, respectively in comparison to control concrete mixture. At 56 days of concrete age, 20% and 29% reduction in the 8-day cumulative moisture sorption and 14% and 19% reduction in mass loss due to abrasion of class-C and class-F based concrete mixtures, respectively, was recorded as compared to that of control mixture. Scanning electron microscopic (SEM) analyses showed enhancement in the microstructure of the concrete mixtures as results of the inclusion of fly ash as partial replacement of PC. Test results also showed superior performance of class-F fly ash on the strength and durability characteristics of resulting concrete mixture as compared to class-C fly ash at equivalent replacement level. The outcome of this study provides insight into the comparative performance of class-C and class-F fly ash based concrete mixtures in fresh and hardened states.