Control Concrete Research Articles

Assessment of Galvanized Iron Fiber and Waste Tire Composite Concrete

The traditional method of disposing of tire debris is now a huge worldwide problem and presents serious environmental risks. Because of this, using waste tires in concrete not only lowers its density but also guarantees an economical and environmentally responsible alternative for the building sector. However, because of their superior ductility and tensile strength, galvanized iron (GI) wire fibers are now more frequently used in plain concrete. Different amounts of waste tire fiber (WTF) with different coarse aggregate replacement ratios (0, 3, 6, and 9%) and different percentages of GI fiber (GIF) (0, 1, 3, and 5%) of concrete volume were examined in this study under axial compression in concrete grades M25, M30, and M35 respectively. According to the test results, GI fiber and waste tire composite concrete demonstrated ductile failure behavior in comparison to control concrete, in addition to delaying the propagation of cracks. On the other hand, the workability of concrete decreased as the percentage of mixed fiber increased. In addition, higher-strength concrete's ductility and compressive strength considerably improved as fiber percentages rose in comparison to lower-grade concrete. The specimen that contained 1% GIF and 3% WTF performed the best under peak load conditions for higher-strength concrete, according to the data.

An Innovative Approach to Enhancing Concrete Sustainability: Utilising Unprocessed Steel Slag with Low CaO and High SiO2 Content

As a non-biodegradable material and a major environmental hazard due to its discharge into the environment, by-products like steel production steel slag (SS) are disposed of in open spaces, agricultural lands, and close to residential areas. This by-product is now considered to have qualities that make it a potential substitute for cement and natural aggregates in the manufacturing of concrete or clinker in the cement manufacturing sector. The effects of using a novel type of SS made in an induction furnace (IF) in place of Portland cement and natural coarse aggregate in concrete were investigated experimentally. Steel slag powder (SSP), low-density steel slag (LDSS) aggregate, and high-density steel slag (HDSS) aggregate were all physically and chemically examined in this study. Each of these three replacement materials was added to concrete in weight proportions of 20%, 40%, and so on. The performance of the resultant mixtures was compared to that of the plain concrete, and the mechanical properties such as split tensile strength, flexural strength, and compressive strength were examined, along with the durability properties of water absorption (WA) and freeze–thaw, and the non-destructive testing of ultrasonic pulse velocity (UPV) of the concrete mixtures were also evaluated. The results indicated that adding HDSS to the concrete increased its mechanical and durability properties, while adding LDSS and SSP resulted in a small and a significant drop in mechanical properties, respectively, when compared to the plain concrete. The increase in compressive strength and the decrease in water absorption at the standard age of 28 days reached 5.2% and 2.1%, respectively. The percentage decrease in compressive strength (8.95–21.74%) of SS concrete mixtures after freeze–thaw cycles was greater than that of the control concrete. Additionally, a concrete mixture containing 40% HDSS yielded the best results.

Valorization of Douala Car Tyres Steel Fibers Waste in Concrete at Cameroonian Coast: Effect of Lengths and Fibers Content

In developing countries such as Cameroon, the sale and use of second-hand tyres from European and Asian countries is booming; most vehicle owners cannot afford new tyres. These tyres obviously have a very short life (less than 3 months) and end up in the wild or in fire, with for both cases, a serious environmental impact: this often means that these countries are the garbage of the West. In order to make a useful valorization of these wastes, this work makes a contribution by incorporating the steel fibers from worn-out tyres into concrete. The study showed the impact of fiber lengths and their proportion, in quantity, on the mechanical behavior of concrete. To do this, the concrete was reinforced with steel fibers from used tyres collected from tyre operators in Douala 5th specifically in Ndogbong - Douala. The sand used in this work comes from the river Sanaga - Edéa. We made test pieces according to four fiber grades (0%, 0.4%, 0.6% and 0.8%) and three different lengths of steel fibers (2 cm, 3.5 cm and 5 cm), in accordance with previous works. Subsequently, three-points bending tests, compression tests, water absorption rate and density tests were carried out on concrete samples at 7, 14 and 28 days of cure. Test pieces of dimensions 40 x 40 x 160 (in accordance with EN 196) were used to determine the rate of water absorption, density and tensile strength by three points bending in a first step; then those of dimensions 40 x 40 x 80 (following the NF P 18-406 standard) allowed to determine the compressive strengths. Analysis have shown that the density of steel fiber reinforced concrete is higher than that of control concrete in all cases. The introduction of steel fibers into concrete reduces the rate of absorption of concrete. In addition, compared with the control concrete, the bending limits and compression stresses of the different proportions increased for all lengths and fiber contents. However, it was observed that concrete specimens with a dosage of 0.6% steel fibers and a length of 2 cm (BFA2-6) had an optimum physical and mechanical properties and was more elastic.

Exploring the impact of pretreatment and particle size variation on properties of rubberized concrete

This study comprises the influence of particle sizes of discarded tire rubber with and without pre-treatment to check the hardened properties of rubberized concrete (RC) in analogy to control concrete. Fine aggregates from concrete are volumetrically substituted using untreated and pre-treated rubber particles of three different sizes up to 20% in part, with an increment of 5%. Pre-treatment using two different pre-treatment methods i.e., sodium hydroxide (NaOH) and silica fume and NaOH was adopted. Properties of fresh concrete-i.e., density, workability, and toughened concrete strengths as compressive, flexural, and indirect tensile strengths were assessed with the control concrete. Along with these, unconventional properties like cylindrical compressive strength and abrasion, resistance to impact, and water absorption are compared. The mechanical properties of RC were found to be similar to conventional concrete, as the compressive strength for RC with pretreated rubber fibers up to 10% obtained was 61.5 MPa while flexural and split tensile strength was above 5.6 MPa. The abrasion resistance was obtained for RC with rubber fibers from 0.98 to 1.46 mm up to 20% substitution against 1.34 mm of control concrete. Modified concrete with pre-treated rubber particles showed better performance than concrete with untreated rubber particles with coarser sizes.

AN EXPERIMENTAL INVESTIGATION ON RECYCLED CONCRETE AGGREGATE

A similar investigation of the trial aftereffects of the properties of new and solidified cement with various supplanting proportions of normal with reused coarse total is introduced in the paper. Reused total was made by smashing the waste cement of research facility test 3D shapes and precast solid sections. Three sorts of solid blends were tried: concrete made altogether with characteristic total (NAC) as a control concrete and two kinds of cement made with regular fine and reused coarse total (half and 100% substitution of coarse reused total). Ninety-nine examples were made for the testing of the essential properties of solidified cement. Burden testing of fortified solid bars made of the researched solid sorts is likewise introduced in the paper. Notwithstanding the substitution proportion, reused total cement (RAC) had an agreeable exhibition, which didn't contrast fundamentally from the presentation of control concrete in this exploratory examination. Be that as it may, for this to be satisfied, it is important to utilize quality reused concrete coarse total and to observe the particular guidelines for plan and creation of this new solid sort. KeyWords: pre-engineered; conventional steel building; design; built-up sections; optimizations; minimum weight

Radiological safety assessment of blended cement concrete

Maintaining the qualities of supplementary cementitious materials (SCMs) used as Portland limestone cement (PLC) replacement in concrete manufacturing for the safety and durability of buildings is essential. This study produces concrete from cement modified with SCMs such as seashell powder (SSP), shea nutshell ash (SNA), and aluminium dross (AD) at 0–15 wt. % substitution with 0 wt. % SCMs substitution serving as control concrete. Mix proportions were designed using C25 MPa concrete grade, prepared, and tested for compressive strength after 28 curing age. The activity concentrations of radionuclides (ACRs) in raw materials and concrete samples were determined using a NaI (Tl) detector coupled with a Canberra MP2-2U as the detecting device for gamma-ray spectrometry. The results showed that all concrete samples incorporated with SCMs attained the design compressive strength, and their ACRs (226Ra, 232Th, and 40 K) were reduced at 5–15 wt. % of SSP, SNA, and AD substitutions. The mean values of 226Ra, 232Th, and 40 K in the raw materials (concrete constituents) were 28.06 ± 0.48, 17.91 ± 0.31, and 1007.75 ± 10.27 Bq kg−1. The mean values of 226Ra, 232Th, and 40 K in the concrete samples were 16.29 ± 0.17, 5.47 ± 0.12, and 1145.65 ± 10.92 Bq kg−1 compared to control concrete with mean values of 27.29 ± 0.73, 7.92 ± 0.12, and 1368.51 ± 12.32 Bq kg−1. All radionuclides were below the standards' recommendations, except for 40 K in granite. Therefore, SSP, SNA, and AD can be utilized safely at 5–15 wt. % of PLC substitution for concrete manufacturing without endangering prospective users with radioactivity.

Investigation of freeze-thaw performance for sustainable rubberized concrete composites with different water to cement ratios

This research aimed to evaluate the freeze-thaw performance of waste rubber substituted concretes with two different water/cement ratios. Different ratios of waste rubber were used in concrete by substituting fine and coarse aggregates. The weight and compressive strength losses of rubberized concrete and control concretes subjected to freeze-thaw were experimentally examined. The changes in the microstructure of the concrete were analyzed by using a Scanning Electron Microscope (SEM). Furthermore, ANOVA was used to test the significance of the selected parameters statistically. The control concrete with a 0.5 water/cement ratio had eight times higher mass loss compared to the rubberized concrete. The SEM analysis results were consistent with the freeze-thaw test results. ANOVA that the waste rubber substitution ratio had a significant effect on the freeze-thaw performance of rubberized concrete. Water/cement ratio, together with the waste rubber substitution ratio, is an effective parameter on the freeze-thaw resistance of rubberized concrete.

Effect of waste water bottle and treated sisal fibers on the durability and mechanical properties of concrete

Globally, the disposal of waste plastic bottles is challenging. However, many researchers reported the importance of incorporating waste polyethylene-based waste water bottles (WWB) as a fiber and treated sisal fiber separately in the concrete mixture. However, it is novel to reinforce concrete by WWB fiber and treated sisal fiber together for more production of sustainable concrete. So the present study investigated the effect of using different doses of WWB fiber with and without treated sisal fiber on the physical and mechanical properties of concrete. Also, it is detail discussed its effect on concrete durability like in different elevated temperatures and acidic environments. As the result indicates, the reinforcement of concrete by WWB and treated sisal fibers lessens the fresh density and in 5% of HCl solution, it give higher strength and lower mass loss compared to the control concrete. Also, concrete WF25 increased compressive strength by 34.6%, 7.42%, and 3.6% respectively at 28, 56, and 180 days of concrete age, while concrete sample WF100 highly increased the splitting tensile strength of concrete by 26.67% compared to the control concrete mixture. Concrete having only WWB without treated sisal fiber reduced water absorption, increased mass loss, and lessened strength at 200, 300, and 400 °C elevated temperatures. So, this study is significant for implementing improved construction material performance by WWB and treated sisal fibers, as well as supporting the reduction of plastic bottles from the environment.

Thermal and acoustic performance of solid waste incorporated cement based composites: an analytical review

Extensive reviews have been conducted on the mechanical, structural, and durability properties of cementitious composites incorporating waste materials. However, a significant knowledge gap exists regarding a comprehensive analysis of their thermal insulation and sound absorption properties. This review seeks to bridge that gap by examining the effects of various waste materials, such as rubber, plastic, glass, ceramic, wood, construction waste, and bio-waste, on these properties in concrete. Incorporating these waste materials improves thermal insulation and sound absorption mainly by increasing porosity and creating interconnected micro and macro pores, leveraging the waste materials’ inherent high porosity and low density. Key findings from the review include a 77% reduction in thermal conductivity with 45% volume replacement of dry materials with plastic compared to control concrete. In addition, maximum sound absorption of 60% at 2000 Hz was achieved with a combination of fly ash and rubber at 30% weight replacement of coarse aggregate. Optimizing the thermal insulation and sound absorption properties of concrete is critically dependent on effective particle size, as it directly influences the concrete’s pore structure. Finer rubber particles (0.1–4 mm) significantly enhance thermal insulation by reducing thermal conductivity to 0.28 W/mK, compared to 0.44 W/mK for coarser particles (5–10 mm). In contrast, coarser particles improve sound absorption, achieving a peak absorption of 32% at 1000 Hz, compared to 27% for finer particles. This dual optimization strategy demonstrates the potential for tailored particle sizes to improve the necessary properties of concrete. The review also outlines future research directions and practical applications, highlighting the potential of recyclable waste materials in the building construction and insulation industry.

An Experimental Investigation on the Effect of Incorporating Natural Fibers on the Mechanical and Durability Properties of Concrete by Using Treated Hybrid Fiber-Reinforced Concrete Application

This research explores the use of treated hybrid natural fibers—wheat straw and bamboo—as reinforcements in concrete for pavement applications. Motivated by environmental and economic benefits, the study investigates how these fibers can enhance the mechanical and durability properties of concrete. Wheat straw fibers, abundant in Ethiopia due to extensive wheat farming, help control micro-cracks and increase the tensile strength of concrete, while bamboo fibers, also locally available, reduce macro-crack propagation and improve concrete toughness. To prepare these fibers, wheat straw was cut to 25 mm in length and bamboo fibers were treated with a 5% sodium hydroxide solution before being cut into lengths of 30, 45, and 60 mm. A concrete mix targeting a cube compressive strength of 30 MPa incorporated 0.1% wheat straw fibers, with varying bamboo fiber contents (0.5%, 1%, and 1.5%) by weight of cement. The results indicate that the uniquely treated hybrid natural fiber-reinforced concrete mix exhibits noticeable enhancements in mechanical properties, with approximate increases of 4.16%, 8.80%, and 8.93% at 7, 28, and 56 days, respectively. Furthermore, the split tensile strength, flexural strength, and durability properties of the concrete were significantly improved by the proposed fiber concentration and length compared to the control concrete mix design. This treatment also shifted the failure mode of the concrete from brittle to ductile and enhanced its energy absorption capacity up to 7.88% higher than that of the control concrete. Based on the AASHTO 1993 pavement design guidelines, this fiber-reinforced concrete reduces pavement thickness by 11% compared to the control concrete while improving post-cracking behavior. This hybrid natural fiber-reinforced concrete presents a promising, sustainable, and eco-friendly alternative for rigid pavement construction.

An investigation on the mechanical and microstructural properties of pigeon pea stalk ash concrete: an approach towards environmental sustainability.

The concept of sustainability in agricultural residue management has gained significant attention worldwide in recent years. After harvesting, large volumes of waste are generated, often dumped into the environment, contributing to pollution. However, these wastes can be used in the concrete industry to reduce the depletion of mineral resources, thus preventing environmental degradation. This approach supports sustainable development. In this investigation, the effect of pigeon pea stalk ash (PPSA) as a partial cement replacement in concrete was evaluated through a series of experimental tests. The results indicate that compressive strength increases when 4 to 8% of the cement is replaced with PPSA. However, beyond 8% replacement, the strength decreases. Based on the experimental findings, concrete with 8% PPSA demonstrated a 6.96% increase in compressive strength. Further increases in PPSA content led to a reduction in compressive strength. Although the split tensile strength of 8% PPSA concrete was similar to that of the control concrete, it outperformed other replacement levels. Additionally, concrete with 8% PPSA exhibited higher flexural strength compared to the control concrete. PPSA concrete, prepared with up to 8% pigeon pea stalk ash as a cement substitute, also showed reduced permeability and greater resistance to acid attack. All strength and durability test results confirmed that PPSA concrete was superior to control concrete in terms of mechanical properties and durability. This study highlights the improved economic and environmental benefits of using pigeon pea stalk ash in concrete, pointing to the significant potential for incorporating agricultural wastes like PPSA in sustainable, green concrete.

Preparation of phosphogypsum ecological concrete and study on its phytogenic properties

In this study, vegetative eco-concrete was prepared based on electrolytic manganese slag/phosphogypsum composite cementitious material as binder and clayey ceramic grains as aggregate. Based on the conditions of porosity and water-cement ratio, the optimal proportion of phosphogypsum-based eco-concrete was investigated, and concrete specimens with good performance were prepared (14 days compressive strength: 3.49 MPa, permeability coefficient: 1.37, total porosity: 24.5%, Improved compressive strength by 15% and water retention by 20%). The nutrient matrix of vegetative eco-concrete with different phosphogypsum/electrolytic manganese slag ratios was designed and modified, and the vegetative performance of the eco-concrete was investigated using four-season grass, ryegrass, clippings and clover as the grass species. The results showed that the eco-concrete based on phosphogypsum as raw material was rich in nutrients such as nitrogen, phosphorus and potassium, which could meet the requirements of plant growth, Supporting plant growth with a 30% increase in root length and 25% improvement in biomass compared to control concrete. The addition of improvers had a good passivation effect on heavy metals such as As, Cu, Cr, Zn, Sb and Pb in the phytogenic substrate. The adaptability of different grass species to the planting substrate was Four Seasons > ryegrass > shepherd’s purse > clover, alfalfa, dogbane; the application of electrolytic manganese slag substrate had the best performance of planting, and the planting substrate with the application of improver inhibited the growth of plants. The study addresses the challenge of using phosphogypsum as a binder in concrete, which has traditionally faced issues with strength and stability. By optimizing the mix ratio and curing process, we were able to achieve a concrete material that not only performs well mechanically but also supports plant growth.

Ecological concrete by partially substitution of cement with Cameroonian corn stover ash.

Ecological concrete by partially substitution of cement with Cameroonian corn stover ash.

Characteristics of natural sponge fibres and their effects on the properties of cement-based materials

Literature indicates that natural fibre-reinforced concrete (NFRC) can effectively serve as an alternative to conventional fibre concrete for reducing brittleness. Yet, there are limited studies on how natural sponge fibre (NSF) affects the properties of concrete. Hence, this study aims to assess the properties of reinforced concrete containing non-chemically (NonC) and NaOH (N)-treated NSF, along with their composite’s potential for structural advantage and environmental sustainability. In the experimental method, mass concrete was prepared by adding NonC and N-treated NSF in varied ratios of 0.00%, 0.75%, 1.00%, and 1.25% by mass. The impact of NonC and N-treated NSF on the physical and mechanical properties of NSFRC was evaluated. Scanning electron microscopy (SEM) was used to observe the effects of treatments. It was observed that the strength and durability properties of the N-treated NSFRC composites improved; however, the workability was reduced compared to the NonC-treated NSFRC and the control concrete. The strain at peak stress (ε2) of N-treated composites was more than 0.002 in conventional concrete. Also, the SEM validation supported the mechanism, which led to the results of this study. In conclusion, the strength of N-treated NSFRC makes it a potential construction material for structural advantage.

Effect of Abaca Fiber and Basalt Fiber in Mono and Hybrid Incorporating in Improving the Mechanical Properties of Self‐Compacting Concrete

To address the growing demand for environmentally friendly building materials, increasing attention is being given to adding natural fibers to concrete. While incorporating natural fibers enhances stability by reducing flow, their use in self‐compacting concrete (SCC) presents challenges in maintaining flowability. This study investigates the impact of mono and hybrid natural fibers on the fresh and mechanical properties of SCC, aiming to create more sustainable and cost‐effective concrete by identifying optimal dosages without using mineral admixtures. Abaca fiber (AF) of 50 mm length at a dosage of 0.25% and 0.5% and basalt fiber (BF) of 12 mm length were incorporated in SCC from 0.25% till 2% at 0.25% increment, and the optimum level of usage was identified based on the fresh property tests like slump flow diameter, T500 test, and mechanical tests like compressive strength and split tensile strength after 7 and 28 days of normal water curing. It was observed that AF of 0.25% was considered the optimal dosage, as its compressive strength and tensile strength at 28 days was 4.25% and 8.03%; 11.42% and 6.84% greater than conventional concrete, and AF of 0.5% mix. BF with 0.25%, 0.75%, 1.25%, and 1.75% provided good strength in all parameters, and 1.25% was its optimum dosage. In hybrid fiber mixes, the optimal dosages from mono fiber mixes were combined, and their mechanical behavior like compressive strength, split tensile strength, impact strength, and flexural strength was tested, and the selected specimens were analyzed for microstructural changes using scanning electron microscopy (SEM) to validate the results. The finding indicated that 0.25% AF and 0.25% BF mix achieved better flowability and the highest compressive strength compared to other combinations. In addition, the mix of 0.25% AF and 1.75% BF demonstrated tensile, impact, and flexural strength improvements of 21.42%, 8.21%, and 94.19%, respectively, over control concrete. It is concluded that AF‐based SCC (A‐SCC) and BF‐based SCC (B‐SCC) could not comply with EFNARC norms requiring increased superplasticizer for flow, but the strength parameter was higher in FR‐SCC than the conventional SCC.

Uticaj sedimentnih aditiva na mehaničko ponašanje betona armiranog vlaknima u agresivnim sredinama

Introduction/purpose: The use of supplementary cementitious materials (SCM) in construction has gained popularity due to their ability to improve the mechanical properties and environmental sustainability of concrete. This study aimed to investigate the potential of utilizing waste materials, specifically marble powder (MP) and dam sediment (DS), as partial replacements for cement in self-compacting concrete (SCC). The primary objectives were to recycle these waste materials and assess the durability and strength of SCC exposed to aggressive chemical environments. Methods: In this study, cement was partially replaced with 40% MP, 40% DS, and a combination of 20% MP and 20% DS. The performance of such concrete was evaluated through compressive strength tests conducted for 28 days. Durability was assessed by exposing the concrete to chemical attacks from hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and sodium sulfate (Na₂SO₄) solutions. Mass loss due to these chemical attacks was also measured. Results: The concrete incorporating MP demonstrated compressive strengths similar to that of the control concrete, achieving 37.61 MPa at 28 days. The concrete with DS exhibited lower strength (31.81 MPa) and showed higher resistance to HCl (ML = 38.78%) compared to the MP concrete (ML = 40.74%). Additionally, all concrete samples exhibited good resistance to sulfuric acid due to the formation of expansive ettringite which protected the concrete from further degradation. Conclusions: The results indicated that both marble powder and dam sediment are viable supplementary materials for improving the mechanical properties and durability of SCC. The concrete with marble powder showed superior strength, while dam sediment contributed to enhanced acid resistance. The combination of these materials offers a sustainable solution for concrete exposed to aggressive environments.

LOCAL FORMULATION OF HIGH PERFORMANCE CONCRETE USING CALCINED KAOLIN: CASE OF CHAD

The main aim of the work carried out in this article is to investigate the local formulation and characterization of metakaolin and superplasticizer-based high-performance concretes (HPCs) in Chad. Five types of concrete were formulated, including one control and four others containing metakaolin as a cement substitute in proportions of 5, 10, 15 and 20%. Four concrete properties were evaluated: fresh concrete (density and slump test) and hardened concrete (density and compressive strength at 3, 7, 14 and 28 days), in order to assess the influence of metakaolin in the different compositions. The results obtained show that: (1) the concretes tested have almost identical workability, with a standard deviation of 0.62 (2) in the fresh state, the control concrete has a higher density, justifying the lower mass of the metakaolin, whereas in the hardened state, the density of the high-performance concrete with 20% metakaolin is higher (3) the high-performance concretes show greater kinetics in the evolution of compressive strengths. Simple compressive strengths are observed on HPCs with a maximum of 70.2 MPa on 15% metakaolin concrete, compared with a minimum value of 51.4 MPa on control concrete. Overall, the present work has highlighted the pozzolanic activity between metakaolin and lime released during cement hydration to produce hydrated calcium silicates, and the deflocculating activity of cement grains by the superplasticizer, with the joint aim of improving concrete mechanical strengths and durability.

Clustering Analysis of Compressive Strength of Structural Recycled Aggregate Concrete

Clustering analysis primarily highlights the in homogeneity of data and can be utilized in structural engineering to demonstrate strength irregularity. It is well-known that strength irregularity between neighboring floors within a structure or among structural elements can lead to non-holistic behavior. Therefore, the clustering of compressive strength holds significant importance. Despite the relevance, only a few studies have addressed the clustering of compressive strength in recycled aggregate concrete (RAC) and proposed potential solutions for clustering issues. This paper aims to investigate the clustering of compressive strength in RAC and explore viable solutions. In this experimental study, four concrete groups were produced under standard conditions. The first group included natural aggregate concretes (NAC) designed with the Absolute Volume Method (AVM) as control concretes. The second group, comprised of RAC, was designed with the equivalent mortar volume method (EVM) as the control RAC. The third group consisted of RAC treated with silica fume (SF) and designed using AVM, while the fourth group included RAC designed with EVM. Statistical analyses were conducted on the 28-day compressive strength test results. The results indicated that the strength class of compressive strength clusters varied among the four groups. The clustering of test results was influenced by the type of concrete components used and the design method employed. Additionally, using silica fume and adopting the Absolute Volume Method reduced strength fluctuation and regulated the strength class of clusters by bringing them closer together. In contrast, the Equivalent Mortar Volume Method resulted in a greater dispersion of strength classes. The clustering effect of recycled aggregate (RA) was more pronounced than that of natural aggregate (NA). Given these findings, it is essential to implement measures when utilizing RAC in sustainable structures to address potential clustering issues.

The Effect of High Temperatures on the Compression and Flexural Characteristics of Recycled Fiber-Reinforced Concrete

The objective of this experimental study is to examine the behavior of concrete reinforced with metallic fibers (CMF) and polypropylene fibers (CPPF) subjected to high temperatures, as well as the effect of temperature variations on their mechanical properties, by evaluating the residual mass loss as well as the residual compressive and flexural strength. Two optimal fiber contents were selected for this study: W = 0.2% in compression and W = 0.8% in flexure, while a control concrete (W=0%) of the same composition serves as a reference. The fibers are characterized by their mechanical strength and pull-out resistance. The concrete composition is determined using the experimental method known as the "Dreux-Gorisse" method. Compression tests are carried out on cylinders with a diameter of Ø16 cm and a height of H32 cm, while flexural tests are performed on prismatic specimens with dimensions [10x10x40] cm³. Fiber-reinforced concretes are subjected to different heating-cooling cycles, reaching maximum temperatures of 600°C and 800°C at 28 days of age. This study revealed that the residual compressive and flexural strength of fiber-reinforced concretes exposed to very high temperatures of 600°C and 800°C decreases compared to concretes not exposed to such temperatures (20°C). For all temperatures studied, concrete reinforced with metallic fibers (CMF) showed significantly higher strength than concrete reinforced with polypropylene fibers (CPPF). At 800°C, both metallic fiber concretes and polypropylene fiber concretes exhibited networks of microcracks, but no spalling occurred.

THE EFFECT OF PARTIAL REPLACEMENT OF CEMENT WITH FLY ASH ON THE STRENGTH OF CONCRETE FOR TRANSPORTATION STRUCTURES AND ROAD PAVEMENTS

The effect of replacing part of the cement with fly ash on the strength of concrete for transportation structures and road pavements has been determined. Portland cement CEM II/A-S 500, crushed stone (5–20 mm fraction), quartz sand with fineness modulus of 2.3, the superplasticizer Polyplast SP-1, and fly ash from the Darnytsia Thermal Power Plant were used in concrete production. The properties of three concrete compositions were investigated. Composition No. 1 (without fly ash) served as the control, with 300 kg/m³ of Portland cement used as the binder. In composition No. 2, 10% of the Portland cement was replaced with 75 kg/m³ of fly ash. In composition No. 3, 20% of the Portland cement was replaced with 150 kg/m³ of fly ash. All concrete compositions included 2.4 kg/m³ of superplasticizer. All concrete mixtures exhibited equal workability (S1), with the water/cement ratio (W/C) depending on the composition. For the control composition No. 1, the W/C ratio was 0.390. For composition No. 2, the actual W/C ratio, calculated as the total binder content (cement and fly ash), was 0.333. For composition No. 3, the W/C ratio was 0.308. Thus, as the proportion of fly ash in the binder increased, the W/C ratio of the mixtures decreased. The average density of the control concrete (composition No. 1) and composition No. 2 was approximately equal (2441 kg/m³ and 2446 kg/m³, respectively), while composition No. 3 exhibited a slightly lower density (2423 kg/m³). This can be explained by the fact that replacing part of the cement with a larger mass of fly ash reduces the W/C ratio while simultaneously increasing the spacing of coarse aggregates. Compressive strength was measured at 7 and 28 days. At 7 days, the compressive strength of composition No. 2, where 30 kg/m³ of cement was replaced with 75 kg/m³ of fly ash, was 6.8% lower than that of the control (composition No. 1). However, at 28 days, the compressive strength of composition No. 2 was 3.8% higher than that of the control. For composition No. 3, replacing 60 kg/m³ of cement with 150 kg/m³ of fly ash resulted in a 28.3% decrease in compressive strength at 7 days and a 14.0% decrease at 28 days compared to the control. Thus, concretes containing fly ash demonstrated slower strength gain compared to concrete using only Portland cement as the binder. Replacing 10% of the Portland cement with a rational amount of fly ash produced concrete with strength comparable to that of the control composition. However, replacing 20% of the Portland cement was not fully compensated by the fly ash. Therefore, the use of fly ash in concrete for transportation structures and road pavements is both feasible and effective. The introduction of a rational amount of fly ash reduces binder consumption, which has significant ecological benefits and is economically viable.