Conventional Mixing Research Articles

Field Performance of Asphalt Mixture Modified with Reactive Isocyanate Based Modifier

The reactive isocyanate-based modifier chemically reacts with asphalt components, overcoming the issues of increased viscosity and phase separation encountered with conventional modified binders. It can be used to modify binders to meet the highest performance grades currently specified by state highway agencies. This project aimed to demonstrate the constructability of an asphalt mixture modified with the reactive isocyanate-based modifier in the field and compare its performance with that of a control mixture. The project involved milling an approximately 5.0-cm (2-in) thick surface layer of two 30.5-m (100-foot) sections with similar foundation support. One section was resurfaced with a reactive isocyanate-modified mixture and the other with a conventional SBS-modified mix. The mixtures have shown no significant difference in field performance and laboratory performance test results. This study has provided insights into the field applicability of reactive isocyanate-based modifiers in asphalt mixtures, facilitating the ongoing efforts to develop durable road surfaces.

Experimental studies on strength and workability of mineral admixture modified cement-based fibre-reinforced self-compacting concrete

ABSTRACT Mineral admixtures such as fly ash (FA), ground granulated blast furnace slag (GGBS), metakaolin (MK), and silica fumes (SF) derived from industries are often referred to as secondary cementitious materials, as partial replacements for cement. Also, the use of fibres significantly enhances the flexural behaviour of concrete. Various kinds of literature highlight the performance of concrete with one or two types of admixtures. In this study, an attempt is made to explore the effect of the use of more than two admixtures viz. FA, GGBS and MK as a partial replacement to cement and fibrofor fibre (FF) on workability and strength properties of based Fibre-Reinforced Self-Compacting Concrete (FRSCC). The FF in Self-Compacting Concrete (SCC) is varied from 1.0 to 2.0 kg/cum. The SCC samples are tested for three curing durations. Based on the experimental investigations, the workability of all the mixes is found to be within the EFNARC limits. The variation in the compressive strength of SCC for various fibre dosages is within 10%, after 28 days of the curing period. It is noted that A-10 mix with fibre dosage of 1.0 Kg/cum yielded the highest compressive, split tensile, and flexural strengths after 56 days of curing, as compared to that of all other variations including conventional SCC mix.

Study on the unique separation effect of emulsion in the stirring-induced turbulent flow field

Much attention has been gained to treat organic pollution dominated by oil pollutants in water with the frequent discharge of wastewater in industries. Liquid–liquid emulsion is a typical existence form of water and oil pollutants. The relative stable flow field is a necessary condition to separate the emulsion, while turbulence of the flow field is required for homogeneous mixing. For centuries, stirring-induced turbulent flow has been used for mixing, with a limited number of separation cases achieved by the stable part of the container at low Reynolds numbers (Re). In this study, the separation of liquid–liquid emulsions in a fully turbulent system for Reynolds number values above 10,000 was observed for the first time. Besides the turbulent flow influenced by the stirring speed, the additional dispersed phase, which was the same as the emulsified dispersed phase, played a critical role in the separation performance. The turbidity of oil-in-water emulsion could be decreased to less than 5 NTU (nephelometric turbidity unit) from 500 NTU under the optimal conditions in this study, with a separation efficiency of over 99%. This peculiar and wonderful characteristic of the turbulent flow and the study of the parameters and constraint conditions for separation may extend the application field of the turbulent flow field from conventional mixing to oil pollutants separation from water in environmental engineering.

Mechanical and economical feasibility of LDPE Waste-modified asphalt mixtures: pathway to sustainable road construction

This research study evaluates the impact of low-density polyethylene (LDPE) modified asphalt binder on the mechanical performance and economical feasibility of asphalt concrete (AC) mixtures. LDPE-modified mixtures were compared with conventional mixes prepared with various binders commonly used in India, i.e., VG 30, VG 40, Polymer-Modified Binder (PMB), and Crumb Rubber Modified Binder (CRMB). LDPE-modified mixtures exhibit superior mechanical performance, increasing the stiffness of AC mixtures by 171% and 125% at 25 °C and 35 °C, respectively, compared to VG 30 base binder. Additionally, the indirect tensile strength (ITS) improved by 51% over VG 30. LDPE-modified mixtures also showed improved resistance to permanent deformation, with RTIndex values up to 133.46% higher than VG 30, and higher fatigue resistance, as indicated by increased CTIndex values compared to VG 30 and CRMB. However, the CTIndex values for LDPE-modified mixtures were 26.32% and 56% lower than those for VG 40 and PMB, respectively. Pavement analysis using 3D-Move showed lesser deflections at pavement layer interfaces, resulting in higher rutting and fatigue life for LDPE-modified pavements. Furthermore, LDPE-modified pavements showed up to 57% higher fatigue life (Nf) and up to 42.33% higher rutting life (Nr) than other pavements. The economic analysis showed that the cost of LDPE-modified pavements is comparable to VG 40 and around 10% more economical than pavements containing PMB. Using LDPE also offers environmental benefits by repurposing up to 750 kg for every kilometer of single-lane pavement section having 50mm thick surface course. Overall, LDPE-modified asphalt mixtures present a sustainable and high-performance solution for asphalt pavement construction.

Optimization of Rotational Hydrodynamic Cavitation Reactor Geometry

A Rotary-Pulsation Apparatus (RPA), also known in the literature as a Rotational Hydrodynamic Cavitation Reactor (RHCR), is a device which typically consists of a rotating mechanism that generates pulsations or vibrations within a fluid. This can be achieved through various means such as mechanical agitation, pneumatic pulses, or hydraulic forces. It is widely used in food, chemical, pharmaceutical, and microbiological industries to improve the mixing of different fluids, dispersion, pasteurization, and sterilization. In the present paper, a CFD study was conducted to develop and optimize the geometry of the RPA’s rotor and stator to induce cavitation in the fluid flow. The effect of cavitation has the potential to improve dispersion and emulsion properties and to significantly reduce operation pressure, in comparison to conventional mixing systems.

Mesoscale modelling of recycled aggregate concrete: A parametric analysis of properties of mesoscopic phases of RAC

This paper analyses the relative effects of ten parameters of recycled aggregate concrete (RAC) mix design on its mechanical properties. Research on the effect of the source concrete and of the quality of the interfacial transition zones (ITZ) on the properties of RAC is scarce and additional knowledge would guide RAC mix design towards efficiency and understanding of the effect of recycled aggregates (RA) on concrete. Therefore, this paper presents the outcomes of parametric numerical analyses on this topic. Within the range of parameters commonly found in conventional concrete mix design, it is found that: (1) the quality of both the old and new mortar substantially influences the mechanical behaviour of RAC. High-quality RAC can be produced with RA sourced from, at least, medium quality concrete (C40); (2) a poor-quality ITZ results in a significant decrease in concrete properties, particularly decreasing the tensile strength up to 58%, since micro-cracks that initiate in weak ITZ can readily develop into mortar; (3) the most relevant factors that determine the strength of RAC are the quality of mesoscopic phases, with the relative effects that range from 8% to 53% for compressive strength and from 22% to 59% for tensile strength; (4) the concrete mix design was less relevant, with a maximum influence of 23%; (5) the previous two observations imply that the most efficient way to improve the properties of RAC is to use RA of better quality; (6) a high proportion of coarse aggregates and a lower replacement ratio of natural aggregate with RA can effectively improve the stiffness of RAC by 16% and 15%. This paper contributes to understanding the influence of mix design and raw materials on the properties of RAC and determines the limiting factors that prevent a concrete mix from reaching its intended performance.

Strength and Durability Studies on Concrete Utilizing Sewage Sludge Ash and Treated Sewage Water

The effects of incorporating sewage sludge ash and treated sewage water on the strength and durability of concrete, with the goal of evaluating their viability as sustainable alternatives in construction materials. The sewage sludge ash was used as a replacement material to cement after burning of sewage sludge with high temperature of 800oC. So obtained sewage sludge ash was analysed for chemical, physical and morphological properties. Burning sewage sludge at high temperatures imparts pozzolanic properties to the resulting ash, which, when used as a cement replacement, improves concrete's compressive and tensile strengths. Various SSA replacement levels (5%, 10%, 15%, 20%, and 25%) were tested, with 15% SSA showing the highest strength gains. SSA affects setting time and workability, but treated sewage water does not significantly impact concrete properties. Concrete with SSA showed superior strength compared to conventional mixes with both fresh and treated water. Durability tests revealed that while SSA concrete experienced minor efflorescence in saltwater, it resisted acid attacks better than conventional concrete, indicating its good durability.

Efficient adsorption of antibiotics using MXene nanosheet delaminated by Taylor vortex flow

MXenes are emerging as a promising class of two-dimensional (2D) adsorbents suitable for various environmental applications. The present study explores the use of Ti3C2Tx MXene nanosheet, delaminated by Taylor vortex flow (TVF), namely d-MXene-CT, as an efficient adsorbent for fluoroquinolones (FQs). The TVF induced in the gap between two coaxial cylinders of the Couette-Taylor reactor enhances the delamination process, yielding larger and thinner MXene nanosheets with a specific surface area 12 fold higher than that of nanosheets delaminated by turbulent eddy flow (TEF), namely d-MXene-MT in a conventional mixing tank (MT) reactor. As a result, the d-MXene-CT exhibited superior adsorption performance, with removal capacity for ciprofloxacin (CIP) of 349 mg/g and for levofloxacin (LEV) of 290.51 mg/g, representing 40 ∼ 60 % improvement over d-MXene-MT (249 mg/g for CIP and 180.22 mg/g for LEV). The adsorption process follows the pseudo-second-order kinetics model and fits the Langmuir isotherm, indicating the involvement of a monolayer chemisorption mechanism. Further investigation revealed that the removal of CIP and LEV was mainly driven by electrostatic attraction between oxygen functionality of MXene and protonated nitrogen group of FQs. The study highlights the potential of d-MXene-CT as a promising adsorbent for treating (FQs) from contaminant water.

EVALUATION OF BITUMINOUS MIXES WITH EPOXY-MODIFIED ASPHALT BINDERS

Road surfaces have long been made with bituminous mix because of its low cost and versatile applications. However, environmental variables, traffic loads, and ageing frequently affect its endurance. Many additives have been introduced to overcome these problems, and epoxy resin has shown great promise. This study evaluates bituminous binder and bituminous mixes with different percentages of epoxy modification. Epoxy asphalt binder's (EAB) rheological properties were described. Following that, an evaluation was conducted on the engineering properties of an epoxy asphalt mixture (EAM). The results demonstrated that the rheological properties of EAB outperform those of neat binders. Furthermore, the outcomes demonstrated that EAM had better moisture damage performance in terms of static immersion test and retained Marshall stability test than the conventional hot dense graded bituminous mixes. According to the results, the ideal content for both VG 30 and VG 40 binders is 2% epoxy modification. Out of all the mix permutations, bituminous mixes with 2% epoxy modification yielded the best results. Comparing blends with control mixes or unmodified bituminous mixes, on the other hand, revealed a lower resistance to moisture damage than mixes with 3% epoxy modification with both binders. The study concludes that epoxy resin can significantly improve the performance and longevity of asphalt concrete roadways, offering benefits to the road construction industry.

Investigating the effect of polypropylene fibres and curing parameters on the workability and mechanical properties of concrete

Polypropylene fibers possess certain characteristics that make them an ideal counterpart to attain explicit advantages when used for building works, more specifically, when added to concrete. In this investigation, polypropylene fibers were added by weight of cement (0.25%, 0.5%, and 0.75%) in M20 grade of concrete and their impact on workability, compressive strength, and flexural strength were assessed and analyzed. The slump test revealed that as the polypropylene fiber loading in the concrete mix was increased, the workability of the mixture continued to decrease; the workability decreased by 11.11%, 19.44%, and 45.83% upon the addition of 0.25 %, 0.5%, and 0.75% fibers respectively in the concrete. The compressive strength, as well as the flexural strength of the concrete, increased monotonously with an increase in the curing time and fiber loading. For instance, in the case of acidic water curing, the compressive strength enhanced from 19.08 MPa to 22.85 MPa upon increasing the fiber content from 0.25% to 0.75%. Adding 0.25% polypropylene fiber resulted in an increase in the flexural strength of conventional concrete mix by 15.78% and 10.29% when cured in normal water for 28 days and 56 days, respectively. Both the compressive and flexural strength of the samples cured in normal water was found to be higher than the samples cured in acidic water and it was observed that the fibre-reinforced concretes were more resistant to acids than the normal unreinforced concrete.

Vapor-liquid equilibria for the CO2 + trimethoxymethylsilane and CO2 + triethoxymethylsilane systems under high-pressure conditions

New binary isotherms are crucial for designing chemical separation processes within supercritical carbon dioxide (CO2) + trialkoxysilane systems. Vapor-liquid equilibria (VLE) were investigated for two-component systems, trimethoxymethylsilane + CO2 and triethoxymethylsilane + CO2, at five temperatures (313.2, 333.2, 353.2, 373.2, and 393.2 K) and pressures up to 14.07 MPa using a synthetic high-pressure phase equilibria apparatus. The pressure-temperature (P-T) plot indicates that the critical mixture curve lies between the critical points of CO2 and the trialkoxysilane compounds. The solubility of trimethoxymethylsilane and triethoxymethylsilane in CO2 increased with increasing temperature at constant pressure, following a type-I phase behavior characteristic. The experimentally observed VLE values of the CO2 + trialkoxysilane systems were correlated using the Peng-Robinson equation of state with binary parameters (kij and ηij) in the conventional mixing rule. The model accuracy was validated by calculating the average relative deviation percentage for the pressure of the binary systems, resulting in values of 4.98% for the trimethoxymethylsilane + CO2 system and 3.64% for the triethoxymethylsilane + CO2 system. The estimated variables fell within reasonable limits and showed no significant differences between the predicted and observed VLE data for both systems.

Moisture susceptibility of HMA containing high siliceous quartzite aggregates: a comparative study of different hydrated lime addition methods

ABSTRACT Hydrated lime (HL) has been used in asphalt mixtures to enhance the resistance to moisture damage in three ways, viz, as a filler, bitumen additive, and coating to aggregates. Quartzite aggregates are weaker in adhesion to asphalt binder due to higher silica content in chemical composition. This study compared three HL addition mechanisms to improve moisture-induced damage in hot mix asphalt made with high siliceous quartzite aggregates. Extensive experimental investigations were carried out, such as indirect tensile strength (ITS), tensile strength ratio (TSR), and fracture energy (FE), to compare the effects of HL addition with respect to conventional mixes. The ITS and TSR results found that HL-additive and HL-coating methods improved the resistance to moisture damage. Compared to control mixtures, HL-treated mixtures showed 20–25 percent higher TSR values. Meanwhile, the HL-filler method showed better resistance to fracture than the other two methods, offering better resistance to fracture in the field.

Experimental Research on the effect of Structural glass fibre in the Tensile Strength Ratio and Retained Stability of VG40 Bituminous mix

Abstract The tensile characteristics of bituminous mix are a major concern for pavement engineers due to the cracking issues. The cracking infuses moisture into the pavement layers which affects the stability of the pavement. The measures to reduce the fatigue tensile cracks have to be taken in the design stage rather than the maintenance stage. The tensile properties and the stability are evaluated using the indirect tensile strength and retained stability tests. While fibers improve the tensile properties of pavement, the S-glass fiber possessing superior mechanical strength has been found to have less scope in past studies. Thus, the current study primarily focuses on examining how Structural Glass fiber reinforced in VG-40 bituminous concrete mix improves the tensile and moisture susceptibility characteristics. The Marshall technique of bituminous mix design was used to establish the ideal bitumen content for casting the bituminous concrete specimens. At the ideal bitumen content, the attributes of bituminous mixes were established. Tensile strength ratio (TSR), Indirect Tensile Strength (ITS), and Retained Stability of modified bituminous concrete mix were assessed. It is observed that the bituminous mix prepared by adding the S-Glass fibre of 8mm length by 3% weight of aggregates exhibited higher ITS, TSR, and Retained stability. The bituminous mix with glass fiber incorporated had higher retained stability (95.36%) than the conventional mix (91.17%). The results of the Indirect Tensile Strength Test revealed that the mix with glass fiber added had a higher Tensile Strength Ratio (92%) compared to the mix with conventional fiber (87%). A noteworthy outcome that creates opportunities for more study in this field is the rise of 5% TSR and 4.66% maintained the stability of the glass fiber-modified bituminous mix.

On-the-fly spectral unmixing based on Kalman filtering

This work introduces an on-the-fly (i.e., online) linear spectral unmixing method which is able to sequentially analyze spectral data acquired on a spectrum-by-spectrum basis. After deriving a sequential counterpart of the conventional linear mixing model, the proposed approach recasts the linear unmixing problem into a linear state-space estimation framework. Under Gaussian noise and state models, the estimation of the pure spectra can be efficiently conducted by resorting to Kalman filtering. Interestingly, it is shown that this Kalman filter can operate in a lower-dimensional subspace to lighten the computational burden of the overall unmixing procedure. Experimental results obtained on synthetic and real Raman data sets show that this Kalman filter-based method offers a convenient trade-off between unmixing accuracy and computational efficiency, which is crucial for operating in an on-the-fly setting. The proposed method constitutes a valuable building block for benefiting from acquisition and processing frameworks recently proposed in the microscopy literature, which are motivated by practical issues such as reducing acquisition time and avoiding potential damages being inflicted to photosensitive samples. The code associated with the numerical illustrations reported in this paper is freely available online at https://github.com/HKouakou/KF-OSU.

Pavement performance and model studies with modified bitumen binder

Flexible pavements experience premature deterioration due to several factors, such as high volumes of traffic, repeated wheel loads, overloading, adverse weather conditions, inferior quality of materials, and other related issues. One of the most commonly found types of distress is rutting, which severely affects pavement performance; hence, the prediction of rutting behaviour is crucial. Research has been done by adding various industrial wastes, chemicals, additives, and modifiers such as rubber, natural rubber, polymers, and waste plastic into the bitumen. These materials are expected to have a substantial impact on enhancing the strength, durability, and performance of pavement while simultaneously reducing the cost of construction. The present research deals with a laboratory investigation of bituminous mixes using both Marshall stability and rutting tests. The performance tests were carried out by Roller Compactor cum Rut Analyzer (RCRA) equipment and Finite Element (FE) analysis in ABAQUS. The experimental findings show that the modified bitumen exhibits 48% greater strength and 20% more resistance to rutting than the conventional bituminous mixes. The model analysis was successfully validated by experimental results. The findings of the research resulted in the development of a mathematical equation that helps to calculate in-service pavement rut depth.

Solution infiltrated lanthanum nickelate–GDC composite cathode via flash-light sintering for intermediate temperature solid oxide fuel cells

Solid oxide fuel cells (SOFCs) require high operating temperatures to minimize the oxygen reduction reaction resistance at cathode and increase the ionic conductivity of oxygen. However, at high operating temperatures, their stability during long-term operation degrades because of material deterioration and the mutual chemical reactions occurring at the interfaces. Herein, an electrode–electrolyte composite is fabricated by solution infiltration of lanthanum nickelate (LNO) electrode material into a GDC electrolyte layer to ensure more reaction sites compared with the conventional powder mixing of the electrode and electrolyte material. Further, the conventional thermal sintering process is replaced with the flash-light sintering process. Thus, the performance of the LNO–GDC cathode cell manufactured by flash-light sintering improves owing to suppression of grain growth of the infiltrated LNO particles. The microstructures of the infiltrated solution and composite layer of the electrolyte material are analyzed using field-emission scanning electron microscopy, and the crystallinity of the LNO nanoparticles is analyzed using high-resolution transmission electron microscopy. A maximum power density of 1.1 W/cm2 is achieved, an improvement of 58 % over the LSCF cell without infiltration at 750 ℃. This study is expected to contribute to the commercialization of SOFCs by replacing conventional thermal sintering.

Investigation on structural and functional behavior of open and dense graded asphalt mixes in mitigating urban floods

Urbanization has led to extensive pavement construction, which, coupled with improper drainage infrastructure, exacerbates urban flooding. Conventional bituminous pavements exacerbate flood risks due to their impermeability, leading to safety hazards and infrastructure damage. To address these challenges, this study investigates the efficacy of Porous Asphalt Concrete (PAC) as a sustainable solution for flood mitigation and pavement durability enhancement. Through laboratory evaluations and flood simulation analyses, the study compares PAC with conventional bituminous mixes in terms of structural, functional, and permeability characteristics. Results indicate that PAC exhibits superior permeability, facilitating effective stormwater management and reducing surface runoff by up to 40%. Furthermore, PAC demonstrates comparable or enhanced performance in Marshall Properties, including stability, flow, and air voids, when compared to conventional mixes. The incorporation of Induction Sensitive Fibers (ISF) enhances pavement durability and moisture resistance, leading to improved tensile strength and reduced abrasion. Binder performance analysis reveals that CRMB-55 exhibits superior stability and durability, making it a promising option for sustainable pavement construction. Flood simulation analyses using QSWAT software demonstrate the effectiveness of PAC in mitigating urban flooding, with notable reductions in surface runoff and discharge. Overall, this research underscores the potential of PAC as a viable solution for sustainable pavement construction, offering both flood mitigation benefits and enhanced pavement durability in urban environments.Graphical

Performance, cost, and ecological assessment of fiber-reinforced high-performance mortar incorporating pumice powder and ground granulated blast furnace slag as partial cement replacement

The production of cement and concrete is a significant source of greenhouse gas emissions. Hence, recent governmental regulations have brought the attention of industry and academia to the environmental impact of these materials. Recognizing the pressing need to address the environmental footprint of the widely used construction materials, there is a growing focus on strategic initiatives that involve incorporating alternative waste materials to partially substitute ordinary Portland cement (OPC). It is also noteworthy that high-performance concrete and mortar emits significantly less CO2 per unit of strength. Therefore, this study aims to develop high-strength mortar mixes incorporating pumice powder (PP) and ground granulated blast-furnace slag (GGBS) as substitutes for OPC. To this end, nine different mixes, with varying levels of OPC replacement ranging from 0% to 60%, were produced. These mixes underwent a comprehensive experimental evaluation to assess their physical, mechanical, and durability properties. Scanning electron microscopy analyses were conducted to examine the microstructural characteristics of the mixes as well. Furthermore, the embodied energy, embodied carbon, and cost of the prepared mixes were calculated. The experimental findings suggest that high-strength mortar, with a compressive strength varying between 64 and 82 MPa at 28 days of curing, can be successfully produced with reduced embodied carbon and embodied energy compared to conventional mortar mix while maintaining a comparable cost.

Timescale dependent homogeneous assembly of lipid-polymer hybrid nanoparticles in laminar mixing for enhanced lung cancer treatment

The homogeneity of core–shell structure lipid-polymer hybrid nanoparticles (HNPs) is crucial for efficient intracellular cargo delivery. While microfluidic techniques have been recognized for their capabilities in precisely controlling the size and drug encapsulation efficiency, there is little research exploring the impact of mass transfer behavior within microchannels on the homogeneous assembly process of HNPs. Here, we manipulated the laminar flow state within TrM device to achieve controlled assembly of HNPs and explored a timescale dependent assembly technique to ensure the homogeneity of folate modified HNPs (FHNPs). Our founding indicate that this method enabled the control over the growth kinetics of PLGA cores within a timescale (τgrow) of 1–15 ms. The homogeneous ligand assembly on the surface of FHNPs can only be achieved when τgrow exceeds the timescale of functional lipid coating (τcoating). Compared to conventional bulk mixing methods, this strategy significantly reduces the risk of heterogeneous assembly in FHNPs fabrication and ensures consistent reproducibility across batches. The homogeneous FHNPs (HFHNPs) fabricated through this method exhibit precise control over particle size (ranging from 75 nm to 150 nm), low polydispersity index, and consistent core–shell structure. Furthermore, this strategy enhances the density of available folate ligands on the surface of FHNPs. In subsequent in vitro and in vivo anti-tumor assays, the icariside Ⅱ (IS) loaded HFHNPs (IS@HFHNPs) exhibited enhanced cellular uptake and tumor accumulation behavior. the timescale dependent homogeneous assembly method for HNPs developed in this research presents a promising avenue for maintaining quality in the synthesis of self-assembly composite nanomecidine.

Aspekti prikladnosti trostupanjskog miješanja gotove betonske smjese

Several studies have indicated that three-stage mixing (TM) methods improve the mechanical strength and slump of concrete compared to those of normal mixing methods, particularly when a recycled concrete aggregate is used. However, most studies did not address the technological aspects of ready-mixed concrete, including continuous mixing during site delivery. In this study, the properties of concrete (slump and compressive strength) based on the time lapse after mixing via the TM method (i.e. immediately, 45 min, and 90 min after mixing) were investigated, and the samples were tested after three years of curing. The results indicate some positive effects of TM on ready-mixed concrete and its characteristics on a delivery to the construction site, particularly a less severe loss of consistency compared to that of conventional mixing, as well as a positive effect on the compressive strength when fly ash is used as an aggregate coating additive in the first stage of concrete mixing.