Strength Of Concrete Research Articles

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.

Economical design strategies for reinforced concrete one-way slabs: a parametric approach considering material strength and rebar size

Despite the rapid advancements in optimization algorithms for economical reinforced concrete (RC) structures, their application to RC slabs has been significantly limited. The primary constraint is slab depth, governed only by deflection control criteria, which impedes further depth reduction—a key factor in cost optimization. The deflection check relies solely on one design parameter—span length, which is often fixed. This constraint limits the effectiveness of even advanced algorithms, which have consistently failed to deliver substantial cost savings in slab design. To address this issue, this study presents a detailed parametric investigation of three key cost-reducing factors in RC one-way slabs: steel strength, concrete strength, and reinforcing bar sizes, in accordance with the ACI 318–19 code. By bypassing algorithmic constraints, the study formulates optimal design strategies through extensive manual design iterations, providing novel trend-based solutions for cost-effective slab design. The findings indicate that for lower live loads, grade 280 steel offers a 20–30% cost reduction compared to higher-grade steel, despite the latter's strength advantage. However, for higher loads, grade 420 or 500 is recommended. Additionally, optimal bar sizes and concrete strengths are recommended for varying load conditions, offering practical design strategies. This approach provides designers with actionable insights to achieve cost-efficient designs without relying on traditional optimization algorithms.

Effect of steam curing on strength, durability and microstructure of concretes with and without mineral admixtures

This research explores the effect of steam curing on the strength, durability and microstructure of concretes with and without mineral admixtures of fly ash (FA) and ground granulated blast-furnace slag powder (SL). Two types of C55 strength grade concretes (one was pure cement concrete, the other was a concrete made by replacing part of the cement with 12% FA and 18% SL) were prepared and their compressive strength, chloride diffusion coefficient and carbonation depth under standard and steam-curing conditions were measured and compared. The phase composition and microstructure of the concretes under the two curing conditions were tested by X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry. The results showed that, on the one hand, compared with standard curing, steam curing is beneficial to the early strength, but not conducive to the later strength development and chloride permeability resistance of both types of concretes. Furthermore, for the steam-cured concrete, the 28 days carbonation depth of the forming surface is higher than that of the bottom surface. In addition, steam curing can reduce the carbonisation resistance of pure cement concrete and improve the carbonisation resistance of concrete mixed with FA and SL. On the other hand, composite mineral admixtures of FA and SL reduce the early strength and the carbonisation resistance of concrete cured by standard curing, but improve the later strength, the carbonisation resistance and chloride permeability resistance of concrete cured by steam curing. FA and SL are thermally activated under steam curing and can react with the calcium hydroxide formed by cement hydration in the early stage, which produces a larger amount of secondary hydration products to improve the pore structure and interfacial microstructure of the concrete with FA and SL. In this way, the adverse effects of steam curing on later strength and durability of concrete are significantly restrained by composite mineral admixtures of FA and SL.

Study on the properties of recycled concrete mixed with coal gangue: Mechanics, workability and microstructure

Coal gangue is a by-product in the process of coal mining. Calcined coal gangue powder and coal gangue aggregate are used to prepare concrete, which can not only enhance the utilization rate of coal gangue, but also improve the performance of coal gangue concrete. In this study, calcined coal gangue powder (CCGP) was employed as an auxiliary cementation material, and coal gangue was employed as coarse concrete aggregate (CCA). Different mix proportions were designed to prepare 180 concrete specimens, and slump, cube compressive strength, splitting tensile strength and SEM test were carried out, respectively. The results show that after standing for 120min, the slump of CP0CA0 group is 53 mm, while the slump of CP30CA0 group is only 48 mm. CCGP can reduce the slump loss of concrete over time. The incorporation of CCGP into coal gangue concrete (CGC) can improve the late strength of concrete. When the substitution rate of CCA is constant, the CGC whose substitution rate of CCGP is 20 % will have the best mechanical properties: the compressive strength values are 49.67 MPa, 39.22 MPa and 27.35 MPa; the splitting tensile strength values are 2.92 MPa, 2.59 MPa and 1.92 MPa. In addition, how CCGP affects the mechanical properties of CGC was analyzed from the microscopic level in this paper. Through the regression analysis of the test data, the conversion relationship between the compressive strength and the splitting tensile strength of the concrete mixed with CCGP and CCA was obtained, which can be used to predict the splitting tensile strength. The results of this study can provide a new research idea for the efficient utilization of coal gangue.

Effect of Coarse Aggregate Type on the Fracture Toughness of Ordinary Concrete

This research work aims to compare the strength and fracture mechanics properties of plain concretes, obtained from different coarse aggregates. During the study, mechanical parameters including compressive strength (fcm) and splitting tensile strength (fctm), as well as fracture parameters involving critical stress intensity factor (KIcS) and critical crack tip opening displacement (CTODc) were evaluated. The effect of the aggregates used on the brittleness of the concretes was also analyzed. For better understanding of the crack initiation and propagation in concretes with different coarse aggregates, a macroscopic failure surfaces examination of the tested beams is also presented. Crushed aggregates covered were basalt (BA), granite (GT), and limestone (LM), and natural peeble gravel aggregate (GL) were used in the concrete mixtures. Fracture toughness tests were performed on an MTS 810 testing machine. Due to the high strength of the rock material, the rough surface of the aggregate grains, and good bonding in the ITZ area between the aggregate and the paste, the concretes with crushed aggregates exhibited high fracture toughness. Both of the analyzed fracture mechanics parameters, i.e., KIcS and CTODc, increased significantly in the case of concretes which were manufactured with crushed aggregates. They amounted, in comparison to concrete based on gravel aggregate, to levels ranging from 20% for concrete with limestone aggregate to over 30% for concrete with a granite aggregate, and to as much as over 70% for concrete with basalt aggregate. On the other hand, the concrete with gravel aggregate showed the lowest fracture toughness because of the smooth surface of the aggregate grains and poor bonding between the aggregate and the cement paste. However, the fracture process in each series of concrete was quasi-plastic in the case of gravel concrete, semi-brittle in the case of limestone concrete, and clearly brittle in the case of the concretes based on granite and basalt aggregates. The results obtained help to explain how the coarse aggregate type affects the strength parameters and fracture toughness at bending.

Progress Analysis of Bonding Performance of GFRP Reinforcement to Concrete

The article briefly summarizes the latest progress of research on the bonding properties of GFRP bars to concrete at home and abroad. It analyzes three test methods for studying the bond properties of GFRP bars, namely: losberg test, standard specimen test, and beam test, and briefly introduces the pullout test device for the pullout test. The bonding mechanism and the influence of the surface form of GFRP bars, concrete strength, diameter size, anchorage length, protective layer thickness and other influencing factors on the bond strength are analyzed and summarized, among which the diameter size and anchorage length have a greater influence on the bond strength. Suggestions are also made to address the shortcomings of the existing research, which provide a basis for a more in-depth study of the bond strength of GFRP bars in the future.

Finite element analysis of ductility and flexural capacity of FRP and steel bars hybrid reinforced concrete beams

AbstractTo study the flexural behavior of hybrid reinforced concrete (hybrid‐RC) beams with FRP and steel bars, this paper used ABAQUS finite element (FE) software to model and nonlinear analyze the hybrid‐RC beams and investigate the effects of effective reinforcement ratio, concrete strength, and FRP bars type on the flexural behavior of hybrid‐RC beams. In addition, the FRP bars stress, flexural bearing capacity, and ductility formulas for hybrid‐RC beams were fitted based on the FE results, and existing literature data were used to verify their accuracy. The FE model results indicated that the effective reinforcement ratio, FRP bars type, and concrete strength significantly impacted the flexural bearing capacity and deformation performance of hybrid‐RC beams. Increasing the strength of concrete improved the flexural bearing capacity and ductility of hybrid‐RC beams; increasing the effective reinforcement ratio and the elastic modulus of FRP bars increased the flexural bearing capacity of the hybrid‐RC beams but decreased its ductility. In addition, the fitted FRP bars stress, flexural bearing capacity, and ductility calculation formulas can quickly and conveniently predict the flexural bearing capacity and ductility of hybrid‐RC beams.

Artificial neural network and soft computing models to predict the compressive strength in self-compacting green concrete

Artificial neural network and soft computing models to predict the compressive strength in self-compacting green concrete

Strength, durability, and heat development characteristics of high-performance concrete containing ground coal bottom ash with low and high calcium

Currently, the availability of fly ash has reduced continuously due to the shutdowns of coal-fired power generating plant as climate change concerns have increased. Therefore, the aim of this paper is to find an alternative pozzolan by examining the employment of low- and high-calcium oxide (CaO) ground bottom ash which has been abandoned rather using in concrete production. The bottom ashes were blended with fly ash as a partial substitution of cement (OPC) by observing their generic effects on the compressive strength, cumulative heat generation, chloride ion penetration, and water sorptivity of high-performance concrete. The samples of bottom ash were prepared by oven drying, particle size cutting, and grinding to enhance the reactivity and consistency. High-performance concretes were made at a water-to-binder (W/B) ratio of 0.27 and partial replacement of OPC up to 50 % by weight of the binder. The results indicated that the concretes with 28-day compressive strengths of 101.0 and 109.0 MPa (21.6 % and 28.2 % stronger than OPC concrete) were produced with 50 wt% OPC replacement with high- and low-calcium ground coal bottom ashes (HCBA and LCBA), respectively. These findings suggest that HCBA and LCBA have high pozzolanic reactivity and high possibility for utilization as pozzolan or supplementary cementitious materials in concrete. In addition, the binary blended binders (OPC-HCBA and OPC-LCBA) and ternary blended binders (OPC-HCBA-FA and OPC-LCBA-FA) produced had better chloride ion penetration resistance, less cumulative heat evolution, and lower water sorptivity than 100 % OPC as a cementitious material. Partial OPC replacement by HCBA and LCBA improved the chloride ion penetrability class of OPC concrete from “very low” to “negligible.” The cumulative heat generation due to the pozzolanic reaction of HCBA and LCBA from the partial replacement of OPC up to 50 % reduced 30–44 % relative to the OPC-based mixture throughout during 72 hours after mixing. The CaO content strongly influenced early compressive strength development and cumulative heat evolution but had less impact on chloride ion penetration resistance and water sorptivity.

The study on bond‐slip constitutive model of recycled concrete under different loading rates

AbstractIf recycled concrete is to be widely, reasonably, and safely applied in practical engineering, the study of bond‐slip performance between steel bars and concrete is crucial. In this paper, the central pull‐out test of recycled concrete under different loading rates was conducted. The characteristics of failure mode and crack directions of the specimens were observed and analyzed. The ultimate bond strength and slip displacement between rebar and concrete were analyzed. The effects of three parameters, namely concrete strength grades, replacement percentage of recycled coarse aggregate, and loading rates on the failure modes and bond‐slip mechanical properties of recycled concrete, were analyzed and summarized. The experimental results showed that there were significant differences in the influence trend and amplitude of the above three parameters on the ultimate bonding strength, slip amount, and slip curve. Based on the above experimental and theoretical analysis, a reasonable bond‐slip constitutive model was established in this paper and was in good agreement with the experimental results.

Experimental and Theoretical Study on Local Damage of Reinforced Concrete Column under Rectangular Charge

During an explosion, a building’s stability is directly impacted by reinforced concrete (RC) columns. However, there is currently no theoretical analysis model that can precisely predict damage to RC columns after close-in/contact explosions. In the present study, the local damage response of RC columns under a rectangular charge was experimentally and numerically investigated, and a theoretical analysis model for predicting local damage after a contact explosion was developed. The experimental results verify the effects of concrete strength, standoff distance, transverse reinforcement spacing, and axial load on damage to RC columns. When the standoff is 100 mm, increasing the axial load can effectively reduce the damage to the center of the column surface. Numerical simulations were carried out to study the effect of different parameters on concrete damage, showing that the damage span of reinforced concrete increases with increased stirrup distance; however, when the stirrup distance decreases to 70 mm, the distance between the stirrups and the explosives is too close to limit the damage. The prediction model innovatively considers the attenuation of steel cross-section transmission and the characteristics of rectangular charges. Compared with traditional semi-empirical calculation models, it can accurately calculate local damage caused by contact explosions on reinforced concrete columns.

Ensemble machine learning models for compressive strength and elastic modulus of recycled brick aggregate concrete

This study delivers an in-depth analysis of predicting the compressive strength and elastic modulus of recycled brick aggregate concrete (RBAC). It assembles an extensive database of 633 compression test results and develops five ensemble learning models—random forest (RF), gradient boosting regression trees (GBRT), extreme gradient boosting (XGB), light gradient boosting machine (LGBM) and stacking (St). These models are evaluated against existing empirical formulas with respect to their effectiveness. The findings reveal that machine learning (ML) models outperform existing formulas: for compressive strength prediction, traditional models achieve a maximum determination coefficient R² of 0.38, whereas ML models attain an R² range of 0.91–0.94. For elastic modulus, the highest R² values are 0.44 for traditional models and 0.97 for ML models. Notably, the LGBM and St models excel in predicting compressive strength and elastic modulus, respectively. The study also identifies critical parameters influencing RBAC’s compressive behavior and highlights their impact trends. Remarkably, while the mass-weighted water absorption of coarse aggregates and the replacement ratio of recycled brick aggregates (RBAs) have less impact on compressive strength compared to the effective water-to-cement ratio, they become more influential for elastic modulus. Additionally, the decrease in elastic modulus due to higher RBA replacement ratios or increased mass-weighted water absorption of coarse aggregates exceeds the corresponding reduction in compressive strength. This research not only deepens the understanding of RBAC’s mechanical properties but also provides valuable predictive tools for civil engineering applications.

Chemical interference between graphene oxide and polycarboxylate superplasticizer, and the resulting impact on the concrete strength, workability, and microstructure

Graphene oxide (GO) nanoreinforcement is shown to significantly improve the strength and durability of concrete at the expense of mix workability. While polycarboxylate superplasticizers (PCSP) addition has improved GO-cement/mortar strength and workability in existing literature, this article examines if this improvement is translated to concrete with lower cement and water contents. PCSP and GO showed colloidal instability and particulate aggregation through surface charge measurements, presumably caused by divalent Ca 2 + ion interbridging between the GO and PCSP. This chemical interference results in a 26% reduction in 28-day compressive strength and a 20% decrease in the workability of PCSP-treated GO-concrete. Microstructural examination reveals significantly larger pores in PCSP+GO cement than in GO-cement or PCSP-only cement due to the chemical interference induced by PCSP-GO interactions in cement and concrete. Hence, PCSP and GO interactions must be further researched for practical use in concrete structures.

Splitting behavior of polyvinyl alcohol fiber reinforced iron ore tailings concrete

To promote solid waste reutilization and reduce natural river sand consumption, iron ore tailings (IOT) are expected to be used in concrete production as a potential substitute for river sand under the premise of comparable material properties with ordinary concrete. In this study an IOT concrete reinforced by Polyvinyl Alcohol (PVA) fiber has been proposed and the slump and splitting behavior under various IOT substitution rates and PVA fiber contents has been experimentally investigated. Slump tests reveal that the optimal PVA fiber content is 0.1 % and IOT substitution rate is 60 % from the view of workability. Splitting tensile tests show a monotonous strength growth with PVA fiber content increase. The incorporation of IOT has increased concrete splitting tensile strength but the strength is smaller than that of normal concrete as soon as IOT substitution rates exceed 50 %. A regression model and Back Propagation (BP) neural network model have been adopted to establish splitting tensile strength prediction model. Compared to regression model, the BP model has exhibited better accuracy which is suitable to predict the splitting tensile strength of PVA-IOT concrete with PVA content less than 0.3 %.

EXPERIMENTAL APPROACH FOR DEVELOPMENT OF SUSTAINABLE HYBRID GRADED FIBER REINFORCED CONCRETE BY CONSUMING LATHE WASTE STEEL FIBERS WITH GLASS FIBERS FOR ENHANCED MECHANICAL PROPERTIES

Local workshops generate large quantities of industrial lathe waste steel fibers, which the steel manufacturing industries find difficult to recycle because of their sharp edges. The utilization of lathe waste steel fibers as fiber reinforcement is sustainable in concrete because these fibers have the same properties as steel fibers. Furthermore, using combinations of ductile and elastic fibers improves strain capacity and resistance to pre- and post-cracking. This research employs hybrid fiber reinforcement technology, utilizing industrial lathe waste steel fibers and glass fibers in varying proportions, to bridge the micro and macro cracks in concrete specimens. This research was done to examine the physical (workability) and mechanical properties (compressive and flexural strength) of hybrid fiber-reinforced concrete. In this research different mixtures of hybrid fiber-reinforced concrete were cast and designated as M0, M1, M2, M3, M4, M5, and M6. The mixtures included lathe waste steel fibers at 0%, 0.50%, 1%, 1.5%, 2%, 2.5%, and 3%, and glass fibers at 0%, 0.15%, 0.25%, 0.45%, 0.60%, 0.75%, and 0.90%, respectively. The ASTM-standardised protocols were followed for all laboratory testing. The physical property results showed a decrease in the workability of concrete mixes as the percentage of lathe waste steel and glass fiber increased. This suggests that a higher percentage of lathe waste steel and glass fibers leads to a lower slump value. Consequently, the mechanical property results showed a gradual enhancement in the compressive and flexural strengths of hybrid fiber-reinforced concrete up to 2.5% lathe waste steel fibers and 0.75% (M5). Further incorporation causes a reduction in strength. The physical examination of fractured samples of hybrid fiber-reinforced concrete confirms that the lathe waste steel fibers yield a maximum strain before breaking down in the concrete matrix. Furthermore, lathe waste steel fibers broke rather than being pulled out, indicating a good bond with the concrete. It is recommended that up to 2.5% lathe waste steel fibers and 0.75% of glass fibers by the total weight of the concrete can be used as hybrid fiber reinforcement for optimum strength achievement.

DURABILITY CHARACTERISTIC OF COCONUT FIBER AGGREGATE CONCRETE BOND IN LIGHTWEIGHT FOAM CONCRETE

The research paper probes into coconut fibre used as lightweight aggregate in concrete for thermal conditioning, specifically on durability. The durability properties of coconut fibre and coconut fibre lightweight aggregate concrete were examined on the thermal conditioning. The use of coconut fibre aggregate in construction was tested and verified. It ascertained the moisture content and water absorption capacity found to be 4.20% and 24% respectively. These values can be compared to the conventional aggregate used in normal times. The density of coconut fibre was found to be in the range of 550 -650 kg/m3. They are within the specified limits of lightweight aggregate standards. The study conducted a related hydration test on coconut fibre fines with cement. The coconut fibre-cement ratio has been optimized to satisfy the criteria of structural lightweight concrete for insulation and thermal conditioning to ensure durability. The experiments for long-term investigation continued for 365 days on the compressive strength of coconut fibre aggregate concrete for three different curing conditions.

Back-propagation neural network model enhanced by transfer learning for the prediction method of compressive strength of alkali residue-based foamed concrete

This study introduces a novel artificial intelligence method for predicting the compressive strength (CS) of alkali residue-based foamed concrete (A-FC). The goal was to accurately predict the CS of A-FC in data-limited scenarios using key parameters such as density, water-to-cement ratio (W/C), and sand-to-cement ratio (S/C). This research employed a back-propagation neural network initially trained on CS data from 190 conventional foamed concrete (C-FC) groups (source domain data: W/C from 0.26 to 0.85, S/C from 0 to 4.29, and density from 0.43 to 2.00 g/cm³). The model then underwent transfer learning (TL) to improve its predictive capabilities. After adapting to 30 A-FC datasets (target domain data: W/C from 0.75 to 2.00, S/C from 0.25 to 2.33, and density from 0.35 to 0.90 g/cm³), the model demonstrated remarkable accuracy with new data. Its robustness was further validated by predicting the CS of an additional 12 A-FC groups. The results show a strong alignment between the model’s predicted values and the experimental data, highlighting its excellent predictive accuracy and generalization capabilities. Compared to traditional experimental methods, this approach significantly reduces both time and costs. The study examines the factors influencing the CS of C-FC and A-FC, improving the accuracy and efficiency of A-FC CS predictions and providing theoretical support for its large-scale application.

Effects of bamboo leaf ashes on concrete compressive strength, water absorption, and chloride penetration

Bamboo leaves are an agro-waste from the bamboo industry that carries a significant environmental impact, primarily due to its phytotoxic activity. In this paper the pozzolanic potential of bamboo leaf ashes are assessed. Bamboo leaves were calcined at five different temperatures - 500, 600, 700, 900, and 1000 °C. The obtained ashes were characterized using X-ray diffraction, X-ray fluorescence, differential thermal gravimetric analysis, Modified Chapelle's method, and Pozzolanic Activity Index. The ash calcined at 600 °C, exhibiting the highest pozzolanic activity, was used in concrete production as a partial replacement for Portland cement at levels of 5 %, 10 %, and 15 %. Concrete compressive strength, water absorption, and chloride diffusivity were assessed. The results indicate that the use of BLA significantly improves the concrete performance, increasing 28-day compressive strength by up to 18 % and reducing the non-steady state chloride penetration by up to 71.2 %. Overall, the use of bamboo leaf ashes obtained at 600 °C leads to significant improvements in mechanical and durability-related properties of concrete, indicating the viability of using this agro-waste as a supplementary cementitious material.

Experimental Study on the Shear Behavior of HTRCS-Reinforced Concrete Beams

High-toughness resin concrete steel mesh (HTRCS) composites, as a novel reinforcement material, are extensively employed, yet there has been a lack of comprehensive quantitative studies on them, and our knowledge about them predominantly relies on experimental investigations. To delve into the shear performance of reinforced concrete beams fortified with HTRCS, this research executed four-point bending static load experiments on a benchmark of two standard beams and six HTRCS-reinforced beams. The results demonstrate that the shear bearing capacity of the reinforced concrete beams was notably enhanced with HTRCS, ranging from approximately 10% to 65%. Further examination revealed that the stiffness of the specimens is significantly influenced by the HTRCS thickness, shear–span ratio, and concrete strength, with the shear–span ratio exerting the most notable impact on stiffness. This analysis furnishes a solid theoretical foundation for the utilization of HTRCS.

Experimental investigations on strength and microstructural characteristics of air-cell impregnated light weight concrete

Concrete structures have high massive building materials than steel structures and possess very low thermal conductivity and high specific heat capacity. However, an efficient approach to reducing high production cost and structural weight of concrete elements without impacting their strength evolve as a growing necessity that leads to innovation in the Light weight concrete (LWC) fields such as aerated concrete and foamed concrete. Those large bubbles seem highly likely to get a break, move upwards through buoyancy and may get lost, while concrete has been mixed, transported, placed and vibrated. Hence to prevent increased bubble spacing, and air loss and to increase concrete durability, a sort of micron-sized air-cells could be generated in aerosol form, by passing out compressed air to dense form generating surfactants. Therefore to circumvent certain drawbacks of conventional LWC, the study delineated to bring out an innovative air-cell impregnated concrete (AIC) material, with homogenous mixing of cement, sand, water and uniformly distributed micron-sized air-cells wherein course-aggregates were replaced with air-cells. This uniform air-cell distribution creates durable concrete with unique feature characteristics since the micron-sized air-cells will be stable and does not collapse. The suitable surfactant towards contributing the strength and durability of proposed AIC structure are assessed, based on results.