Brittleness Of Concrete Research Articles

Circular concrete-filled double-skin steel tubular short columns under axial compression: An improved theoretical model and design

Existing theoretical analysis methods for concrete-filled double-skin steel tubular (CFDST) short columns generally ignore the reduction of concrete strength due to brittleness. As a result, these methods cannot accurately capture full range behavior for CFDST columns containing high-strength concrete. By focusing on the reduction effect of concrete strength in CFDST columns due to concrete brittleness, this paper proposes a reduction factor for use in design, for the first time. Based on this reduction factor, a theoretical model for axially compressed circular CFDST short columns considering non-uniform confinement effect of the sandwiched concrete is established. A substantial experimental database of 168 CFDST columns with carbon circular steel tubes is then compiled. By comparing with this database, the proposed theoretical model is shown to achieve greater accuracy than existing approaches. Utilizing this model, the influence of column parameters on the performance of the studied CFDST members are investigated and the results are discussed. It is shown that concrete strength, hollow ratio, yield strength of the outer tube, and the diameter-to-thickness ratio of the outer and inner tubes are influential to the ultimate strength and ductility of CFDST columns. However, the yield strength of the inner tube only affects the ultimate strength of CFDST columns but has a negligible influence on the ductility. Finally, utilizing the experimental and theoretical data presented, the accuracy of existing design codes for concrete-filled steel tubes for the design of CFDST members with or without considering the reduction effect of concrete strength is assessed. The results indicate that Eurocode 4 provides a more reasonable prediction result.

Experimental investigation of effects of multi-fissures on brittleness of ordinary Portland cement concrete and rubberized concrete

The Brittleness index of concrete is related to both confining pressure, ambient temperature, its components and internal defects, especially all types of fissures. In the paper, the experiments were conducted to investigate the relationships between brittleness index and concrete composition and flaws under uniaxial compression through the brittleness index of OPC (ordinary Portland cement concrete) and RC (rubberized concrete) containing multi-fissures. The results show that the relationship of brittleness index and concrete composition is positive to brittleness index change of OPC and RC containing multi-fissures. The brittle index of OPC is 18.3% higher than that of RC which replaced 10% sand by rubber power. As for OPC containing two fissures, the brittleness index is lower 48.8% than that of intact specimens and the specimens containing 45°angle has the lowest brittle index among counterpart of RC. As for RC with parallel and non-parallel fissures, the brittleness of the latter is 18.8% smaller than that of the former. The brittle index of the RC with non-parallel fissures declines the most and largest damage. Finally, OPC and RC containing fissures contribute to their toughness and ductility if permissible. The reliability of the new index of brittleness can nicely enrich and improve the existing evaluation methods of concrete brittleness.

Volume Stability and Frost Resistance of High-Ductility Magnesium Phosphate Cementitious Concrete.

To address the issue of pavement cracking due to brittle concrete in road and bridge engineering, this study explores the use of high-ductility magnesium phosphate cementitious concrete (HD-MPCC) for rapid repairs. The deformation and frost properties of HD-MPCC are analyzed to assess its suitability for this application. Deformation properties were tested for HD-MPCC specimens cured in both air and water. Subsequent tests focused on the frost performance and mechanical properties after freeze-thaw cycles. A mercury penetration technique was utilized to examine the pore structure. The findings reveal that the expansion deformation of HD-MPCC increases with curing age in both air and water conditions, and the quantitative relationship between the expansion deformation and curing age of HD-MPCC was analyzed. Additionally, the freeze-thaw cycles led to a decrease in mass loss, the relative dynamic elastic modulus, the ultimate tensile strength, the ultimate tensile strain, the flexural strength, and the peak deflection. The volume fraction of harmless and less harmful pores gradually decreased as the freeze-thaw cycle increased, while the volume fraction of more harmful pores increased, resulting in a decrease in the strength, ultimate tensile strain, and peak deflection.

Characterization of airborne dust emissions from three types of crushed multi-walled carbon nanotube-enhanced concretes

Dispersing Multi-Walled Carbon Nanotubes (MWCNTs) into concrete at low (<1 wt% in cement) concentrations may improve concrete performance and properties and provide enhanced functionalities. When MWCNT-enhanced concrete is fragmented during remodelling or demolition, the stiff, fibrous and carcinogenic MWCNTs will, however, also be part of the respirable particulate matter released in the process. Consequently, systematic aerosolizing of crushed MWCNT-enhanced concretes in a controlled environment and measuring the properties of this aerosol can give valuable insights into the characteristics of the emissions such as concentrations, size range and morphology. These properties impact to which extent the emissions can be inhaled as well as where they are expected to deposit in the lung, which is critical to assess whether these materials might constitute a future health risk for construction and demolition workers. In this work, the impact from MWCNTs on aerosol characteristics was assessed for samples of three concrete types with various amounts of MWCNT, using a novel methodology based on the continuous drop method. MWCNT-enhanced concretes were crushed, aerosolized and the emitted particles were characterized with online and offline techniques. For light-weight porous concrete, the addition of MWCNT significantly reduced the respirable mass fraction (RESP) and particle number concentrations (PNC) across all size ranges (7 nm – 20 μm), indicating that MWCNTs dampened the fragmentation process by possibly reinforcing the microstructure of brittle concrete. For normal concrete, the opposite could be seen, where MWCNTs resulted in drastic increases in RESP and PNC, suggesting that the MWCNTs may be acting as defects in the concrete matrix, thus enhancing the fragmentation process. For the high strength concrete, the fragmentation decreased at the lowest MWCNT concentration, but increased again for the highest MWCNT concentration. All tested concrete types emitted <100 nm particles, regardless of CNT content. SEM imaging displayed CNTs protruding from concrete fragments, but no free fibres were detected.

Enhancing the fire-resistant performance of concrete-filled steel tube columns with steel fiber-reinforced concrete

Due to their excellent mechanical features, concrete-filled steel tube (CFST) columns are usually employed in high-rise constructions; it is also significant to consider fire safety while designing buildings. The fire-resistance performance of fibre-reinforced CFST columns is superior to that of unreinforced CFST columns under identical conditions. The post-peak behavior of CFST columns can be enhanced by incorporating fibres to reduce the brittleness of concrete. The research on this topic is limited and considerable research gaps are available in the literature. This research examines the structural performance of steel fibre-reinforced concrete (SFRC) filled steel tubes exposed to ambient and elevated temperatures. For this purpose, fourteen CFST columns were investigated and separated into two groups. The first group of CFST columns was filled with three diverse grades of conventional concrete with and without fibres, which was subjected to ambient temperature. The second group is identical to the first group except all columns are exposed to a temperature of 1050 ℃. The parameters examined were the mechanical properties of concrete, load-carrying capacity, load-deflection response, axial load, and axial strain and ductility ratio. Furthermore, using different codes, a comparison was made for the column's empirically determined load-carrying capacity with the theoretical value. Besides, the morphological characteristics of concrete were examined using energy dispersive spectroscopy (EDS), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR) and X-ray powder diffraction (XRD). The findings show that the SFRC-filled column has superior structural qualities when subjected to elevated temperatures. At high temperatures, calcium hydroxide decomposes, and the steel tube yields, causing the column to fail by premature local bucking.

Experimental and Statistical Capacity of Rubberized Continuous Deep Beams under Monotonic and Repeated Load

Continuous Deep Beams (CDBs) are highly exposed to repeated loads especially at the bridges during vehicle loads and adding rubber into it support the ductility to overcome concrete brittleness. Six Beams were designed in considering the strut tie method (STM) and tested under monotonic and repeated loads. Mathematical model for such problem has been investigated. It can be concluded that, the CDBs lose some of its ultimate capacity due to the dropping of concrete compressive strength after aggregate-rubber replacement, while an increment in the deflection could be seen due to the higher deformability of the rubcrete mix i.e., the concrete gained some flexibility after replacing. Also, the ultimate strength of the beams decreases when comparing with the static loads by 14%, 8% and 9% for conventional beam, gravel and sand replacement beams respectively. Fuzzy regression system offers a polynomial from the third degree to represent the Fuzzy data of the CDBs.

High early strength-high performance concrete produced with combination of ultra-fine slag and ultra-fine silica: Influence on fresh, mechanical, shrinkage and durability properties with microstructural investigation

This study relates to High early strength- High Performance concrete (HPC) produced with incorporation of Ultra-fine Slag (UFS) and Ultra-fine Silica (UFSi). Compressive Strength development was studied from an early period of 14–15 h of casting up to 180 days. The variations in workability and its retention levels after 60 min of mix preparation were recorded. Elastic modulus, compressive strain behaviour, flexural parameters, early age shrinkage and few durability properties were measured for resulting optimal concrete mixes. Modifications induced at microstructural level were assessed by Scanning Electron Microscopy (SEM) and Nanoindentation tests. Incorporation of UFS and UFSi resulted in reduction of fresh properties beyond certain addition percentages. Usage of UFS as part replacement to GGBS in HPC mixes showed considerable improvement with regards to mechanical and durability aspects. Incorporation of UFSi was evaluated to prominently improve early age strength of concrete in combination with UFS at optimal quantities, while moderately improving other mechanical properties. Early age shrinkage induced stress levels and the brittleness of concrete were observed to increase with use of selected admixtures under multiple blend system. Improvement in the microstructure was observed with denser hydrated matrix offering enhanced homogeneity and better bonding with aggregates. Increase in strength governing hydration phases was evidenced for optimal addition of UFS and UFSi. Durability behaviour was significantly enhanced for combination of UFS and UFSi owing to microstructural improvement through pore refinement.

Studies of nano-SiO2 and subsequent water curing on enhancing the frost resistance of autoclaved PHC pipe pile concrete

Autoclave curing will cause severe deterioration on the frost resistance of pre-stressed high-strength concrete (PHC) pipe pile. To clarify the frost resistance degradation mechanism of autoclaved PHC pipe pile concrete and obtain effective improvement measures, nano-SiO2 (NS) with cement replacement ratios of 0.5%, 1.0%, and 1.5% were adopted, and concrete specimens were fabricated and subjected to standard curing, autoclave curing, and autoclave curing + one week of subsequent water curing, respectively. Then, a rapid freeze-thaw cycle experiment was utilized to test their frost resistance. In addition, the micro-morphology and pore structure of different concrete were studied through scanning electron microscopy and nuclear magnetic resonance. The results indicate that the mechanisms of the degradation of autoclaved concrete in frost resistance are the increase of concrete porosity, harmful pore ratio, and concrete brittleness. Compared with standard curing, autoclave curing can result in 68.5% loss in the frost resistance of concrete. Through playing the filling and pozzolanic effects, NS can improve the compactness of autoclaved concrete and increase its frost resistance to a certain extent. Subsequent water curing can replenish water into concrete, promote the hydration of the residual unhydrated cementitious materials in concrete, enhance the compactness of concrete, and play a positive role in improving the frost resistance of concrete. The incorporation of 1.0% NS can enhance the frost resistance of autoclaved concrete by 66.6%, while the combination of 1.0% NS incorporation and one-week subsequent water curing can enhance the frost resistance by 89.2%. Exponential function can be used to simulate the frost resistance degradation of the autoclaved PHC pipe pile and predict its service life based on frost resistance.

Experimental Investigation on Physical Properties of Concrete Containing Polypropylene Fiber and Water-Borne Epoxy for Pavement

Cement concrete pavement accounts for a large proportion of the road network due to its excellent mechanical strength and durability. However, numerous microcracks are generated due to the high brittleness of concrete, which poses a threat to the service life of concrete pavement. Currently, simultaneous addition of fibers and polymers is a feasible approach to resolving the issues associated with the brittleness of concrete. This study explores the properties of concrete mixtures containing different levels of polypropylene fibers and water-borne epoxy. Additionally, fly ash is also introduced to concrete mixtures. The tests performed include slump, compressive strength, flexural strength, shrinkage, depth of water penetration, and abrasion. The results indicate that water-borne epoxy, at all levels, contributed to improving the weak interfacial bonding between polypropylene fibers and concrete. In addition, the combined incorporation of polypropylene fibers and water-borne epoxy could improve the mechanical and durability properties of concrete, with the combined utilization of 0.1% polypropylene fibers and 10% water-borne epoxy exhibiting the best performance. Moreover, with the incorporation of 10% fly ash into concrete, the mechanical strength and abrasion resistance experienced a slight reduction, while the workability, drying shrinkage resistance, and impermeability were improved. The current findings indicate that the combined utilization of polypropylene fibers and water-borne epoxy at appropriate levels is beneficial for application in pavement; however, in spite of superior drying shrinkage resistance and impermeability, the incorporation of fly ash into concrete pavement should be properly treated according to the actual engineering conditions.

Impact of crumb rubber particle size on the mechanical and microstructure properties of rubberized concrete

AbstractCrumb rubber (CR) concrete (CRC) characterized with high ductility and environment friendliness, has recently been studied widely in the field of green concrete. Generally, high volume fraction of CR in cementitious system leads to low strength. However, the effect of CR particle size has not been concluded yet. This paper focuses on the impact of CR size on the mechanical and microstructure properties of CRC. Two novel substitution approaches of CR for natural fine aggregate are adopted. In total, 10 groups are designed and experimentally tested for their workability in fresh state and mechanical properties in hardened state. Brittleness coefficient, fineness modulus, and micro‐morphology of CRC were analyzed and discussed. Results show that as size of CR decreases, workability improves significantly, apparent density and strength exhibit a firstly decrease and then increase trend, with the lowest value obtained around 1.18 mm CR size. The brittleness of concrete was significantly improved in the presence of CR, and the improvement was more significant for smaller‐sized CR. Weak ITZs between CR particles and interfacial porosity are the main reasons for the sharp strength deterioration. Crack arresting effect of CR makes the crack propagation path more tortuous, and smaller particle‐sized CR exhibits greater capability.

Hybrid Steel Fiber of Rigid Pavements: A 3D Finite Element and Parametric Analysis

Rigid pavements have high compressive strength and low flexural strength due to the brittleness of concrete. This leads to the formation of cracks easily under the applied loads of vehicles; therefore, the design of concrete pavements usually leads to an increase in the high thicknesses. Hybrid steel fibers are used in concrete to increase flexural strength and minimize crack formation. Using concrete with steel fibers in pavements reduces the required concrete thickness. In recent decades, the application of the finite element method to predict the behavior of rigid pavements has increased. This study investigates the influence of hybrid steel fiber on the behavior of rigid pavements; a finite element modeling approach is used to simulate the case study. Several parameters are entered and investigated in this study, including the proportion mix of hybrid fiber concrete (HFC), which contains 0.2% macro synthetic fibers and 0.68, 0.8, and 0.96% of steel fibers, compressive strengths of 25, 35, and 45 MPa, slab thicknesses of 150, 200, and 250 mm, and the load of the tandem axle at the edge of mid slab on the Winkler foundation. The ATENA software package is used to perform a nonlinear finite element analysis. Thirty-six rigid specimen pavements with dimensions of 3600 × 3600 mm were modeled in this investigation. The results showed that the addition ratio (0.68 + 0.2)% of hybrid fibers is more effective in improving the load bearing capacity with a slab thickness of 150 mm and 25 MPa compressive strength.

Optimization Based on Toughness and Splitting Tensile Strength of Steel-Fiber-Reinforced Concrete Incorporating Silica Fume Using Response Surface Method.

The greatest weakness of concrete as a construction material is its brittleness and low fracture energy absorption capacity until failure occurs. In order to improve concrete strength and durability, silica fume SF is introduced into the mixture, which at the same time leads to an increase in the brittleness of concrete. To improve the ductility and toughness of concrete, short steel fibers have been incorporated into concrete. Steel fibers and silica fume are jointly preferred for concrete design in order to obtain concrete with high strength and ductility. It is well-known that silica fume content and fiber properties, such as aspect ratio and volume ratio, directly affect the properties of SFRCs. The mixture design of steel-fiber-reinforced concrete (SFRC) with SF addition is a very important issue in terms of economy and performance. In this study, an experimental design was used to study the toughness and splitting tensile strength of SFRC with the response surface method (RSM). The models established by the RSM were used to optimize the design of SFRC in terms of the usage of optimal silica fume content, and optimal steel fiber volume and aspect ratio. Optimum silica fume content and fiber volume ratio values were determined using the D-optimal design method so that the steel fiber volume ratio was at the minimum and the bending toughness and splitting tensile strength were at the maximum. The amount of silica fume used as a cement replacement, aspect ratio, and volume fraction of steel fiber were chosen as independent variables in the experiment. Experimentally obtained mechanical properties of SFRC such as compression, bending, splitting, modulus of elasticity, toughness, and the toughness index were the dependent variables. A good correlation was observed between the dependent and independent variables included in the model. As a result of the optimization, optimum steel fiber volume was determined as 0.70% and silica fume content was determined as 15% for both aspect ratios.

Dynamic analysis of the COMPASS-U tokamak for the design of foundation

The COMPASS-U tokamak is currently at the final design stage. In order to design safe and reliable foundation slab for the machine, a dynamic analysis of the deformations and stresses during the most severe plasma disruptions was necessary. A global FEM model has been built including simplified geometry of the entire tokamak as well as the foundation slab and its supporting concrete pillars and the surrounding soil. Vertical forces from the worst-case axisymmetric plasma disruption scenarios were applied to the vacuum vessel and the coil system (CS, PF, TF), causing vibration of the entire tokamak. The deformations and stresses transmitted to the anchors in the reinforced concrete slab were computed. Based on the presented model, the initial thickness of the concrete slab of 1 m was decreased by 20% - to 0.8 m for the final design. Maximum tensile stress of 1.71 MPa was found in the brittle concrete, indicating that no cracking will occur during the worst-case axisymmetric disruptions. Motion of the vacuum vessel due to vertical forces was analyzed, showing maximum deformations below 1.13 mm over the course of the worst disruption. Velocities below 0.29 m/s and accelerations below 287 m/s2. The computational cost was analyzed in details, providing estimates for the computational time, RAM requirements of 25.8 GB/MDOF (77.4 GB/Mnode) and hard disc requirements for the results file of 0.5 GB/MDOF (1.5 GB/Mnode) for each transient time step.

Experimental and 3D mesoscopic investigation of uniaxial compression performance on basic magnesium sulfate cement-coral aggregate concrete (BMSC-CAC)

The constitutive relationship of basic magnesium sulfate cement-coral aggregate concrete (BMSC-CAC) under uniaxial compression was investigated using cylindrical specimens. The equal strain monotonic loading method was applied to obtain the stress-strain curves. Mechanical parameters such as elastic modulus ( E c ) and Poisson's ratio( μ ) were calculated. A 3D random aggregate mesoscopic model was used to simulate the failure process and crack propagation . The results show that when the strain approximated to maximum value, BMSC-CAC was rapidly destroyed in the shape of splitting. Compared with ordinary cement, the brittleness of concrete can be effectively improved due to the high toughness of basic magnesium sulfate cement (BMSC). The segmented constitutive equation of BMSC-CAC was given, which could express all of the compression test characteristics. The relative error of the peak stress and strain between the experiments and simulations were small. Analysis of the failure process reveals that damage first appears in the mortar and ITZ of the concrete, with micro-cracks converging into huge oblique cracks through the aggregate.

Numerical and theoretical analysis of beam-to-column connections with ECC ring beams subjected to local compression loading

Engineered cementitious composite (ECC) is a kind of high performance cement-based composite materials with strain hardening and multiple cracking behaviour. Replacing concrete with ECC in the beam-to-column connection with ring beam may effectively improve the load-carrying capacity and ductility, as well as prevent cracks and solve durability problems caused by the brittleness of concrete. In this paper, the failure mechanism of beam-to-column connection with ECC ring beam subjected to local compression loading was investigated with the nonlinear finite element (FE) method. The results indicated that continuous lateral pressure was provided by the ECC ring beam, which improved the local compression performance of the ring beam connection. Extensive parametric studies on the local compression behavior of connections with ECC ring beams were also conducted. According to the simulation results, the peak strength of ECC connections was 13.0%–24.2% higher than that of concrete specimens. Increasing the ECC compression strength or ring beam width can effectively increase the load-carrying capacity of the connection, but the ECC tensile strain can only affect the ductility of the connection when the ultimate tensile strain was lower than 1.5%. Based on the FE analysis, an effective restraint width of the ECC ring beam was proposed, and theoretical models were established to predict the axial compressive bearing capacity of the beam-to-column connection with ECC ring beam.

Enhancing the Impact Strength of Prepacked Aggregate Fibrous Concrete Using Asphalt-Coated Aggregates.

The brittleness of plain concrete represents a significant issue to the integrity of concrete structures when subjected to impact loading. Recent rapid industrialization has attracted researchers to find a solution for concrete brittleness and enhance its ductility. In light of this, the prepacked aggregate fibrous concrete (PAFC) with single and double precoated coarse aggregates using asphalt is proposed and examined. Nine different mixtures were designed using polypropylene and steel fibre of 3% dosage with single and double asphalt-coated aggregates. Specimens were prepared with natural aggregate and 100% C-graded asphalt-coated aggregate to evaluate their impact strength. The ACI Committee 544 drop-weight impact standard was followed in the testing of all specimens. Results indicated that using asphalt-coated aggregate can improve the impact energies of concrete. The impact energy at cracking and failure of the single asphalt-coated aggregate specimen was 1.55 and 2.11 times higher, while the double-coated aggregate specimens exhibited 1.73 and 2.56 times greater than the natural aggregate specimen, respectively. The contribution of fibres in enhancing the impact resistance is remarkable compared to the single- and double-coated aggregates used in PAFC.

Damage Management of Concrete Structures with Engineered Cementitious Materials and Natural Fibers: A Review of Potential Uses

The importance of the safety and sustainability of structures has attracted more attention to the development of smart materials. The presence of small cracks (&lt;300 µm in width) in concrete is approximately inevitable. These cracks surely damage the functionality of structures, increase their degradation, and decrease their sustainability and service life. Self-sensing cement-based materials have been widely assessed in recent decades. Engineers can apply piezoresistivity for structural health monitoring that provides timely monitoring of structures, such as damage detection and reliability analysis, which consequently guarantees the service life with low maintenance costs. However, concrete piezoresistivity is limited to compressive stress sensing due to the brittleness of concrete. In contrast, engineered cementitious composites (ECC) present excellent tensile ductility and deformation capabilities, making them able to sense tensile stress/strain. Therefore, in this paper, first, the ability of ECC to partly replace transverse reinforcements and enhance the joint shear resistance, the energy absorption capacity, and the cracking response of concrete structures in seismic areas is reviewed. Then, the potential use of natural fibers and cellulose nanofibers in cementitious materials is investigated. Moreover, steel and carbon fibers and carbon black, carbon nanotubes, and graphene, all added as conductive fillers, are also presented. Finally, among the conductive carbonaceous materials, biochar, the solid residue of biomass waste pyrolysis, was recently investigated to improve the mechanical properties, internal curing, and CO2 capture of concrete and for the preparation of self-sensing ECC.

Brittleness of Concrete under Different Curing Conditions.

In order to shorten construction periods, concrete is often cured using steam and is loaded at an early age. This changes the performance and even the durability of the concrete compared to concrete that has been cured under normal conditions. Thus, the pattern and the mechanism of concrete performance change under different curing conditions, and loading ages are of great significance. The development of brittleness under different curing conditions and loading ages was studied. The evaluation methods that were used to determine concrete brittleness were expounded. Steam, standard, and natural curing conditions were carried out on single-side notched concrete beams as well as on a concrete prism and cubic blocks. The compressive strength and splitting tensile strength of the concrete blocks along with the fracture performance of the concrete beams were tested after 3, 7, 28, and 90 days. The steam curing condition significantly improved the strength of concrete before 28 days had passed, and the standard curing condition improved the strength of concrete after 28 days. Based on the experimental fracture parameters, a two-parameter fracture model was applied to study the development of fracture toughness , critical crack tip opening displacement , and critical strain energy release rate with hydration age under different curing conditions. With respect to long-term performance, the standard curing condition was better at resisting concrete crack propagations than the steam curing condition was. The characteristic length and the material length under the three curing conditions and the long-term development of brittleness in the concrete indicated that steam curing increased the concrete brittleness. Considering the effects of the curing condition and the loading age, a time-dependent concrete fracture toughness model was established, and the predicted value of the model was verified against the measured value. The results indicated that the model was able to accurately predict the fracture toughness with an error rate of less than 16%.

Strength and flexural toughness of hybrid fibre reinforced fly ash based concrete

To overcome concrete brittleness and to provide toughness, fibre reinforcement is commonly utilized. Fibre reinforcement to concrete in the form of hybrid fibre is a new concept to achieve individual fibre benefits. In this paper, the effect of polypropylene fibre (PF) and steel fibre (SF) either individually or with different combinations at 1% fibre volume fraction on the strength, flexural toughness, and Ultrasonic pulse velocity (UPV) value of FIBRE-reinforced fly ash (FA) based concrete has been presented. For this purpose, one control mix having 25% FA and 0% fibre and five mixes with different hybrid fibre combinations of 1%PF-0%SF, 0.75%PF-0.25%SF%, 0.50%PF-0.50%SF, 0.25%PF-0.75%SF, and 0%PF-1%SF were cast. ASTM C 1609 method was utilized to evaluate the flexural toughness. Experimental results have shown an improvement in all the above-said properties (expect UPV) by the addition of fibre, but improvement is more significant in mixes with a higher percentage of SF when compared with mixes at a higher percentage of PF. Mix with a hybrid fibre combination of 0.25% PF and 0.75% SF gave the best result among all the fibre-reinforced fly ash-based mixes.

Behavior of ECC columns confined using steel wire mesh under axial loading

Engineered Cementitious Composite (ECC) is a high-efficiency composite material that possesses work-hardening behavior in addition to its multiple-cracking specifications. It overcomes toughness and cracking problems caused by concrete brittleness due to the tight crack width it has. This paper studies experimentally the behavior of axially loaded reinforced ECC columns, with additional internal confinement using Steel Wire Mesh (SWM), to enhance ultimate capacity, durability, the crack pattern, and reduce the brittleness of traditional columns. Sixteen circular columns, one Normal Concrete (NC) specimen, and fifteen ECC specimens were subjected to axial compression up to failure. The main parameters of the study were the volume fraction of the polypropylene fibers (1%, 1.5%, and 2%), SWM arrangements, and number of SWM layers. Experimental findings demonstrated that ECC specimens exhibited better performance compared to NC specimen concerning crack control efficiency, load capacity, and ductility. As the ECC specimens presented very thin cracks and higher ultimate load in the range of 65.57%–107.39%, with greater ductility in the range of 0.87%–17.39% compared to the NC specimen. Additionally, ECC columns with 1.5% of polypropylene fiber, showed the highest compressive strength, superior durability, and maximum failure load. Moreover, the SWM contributed enhancing the capacity of ECC columns due to its confinement effectiveness. Besides, the full confinement scheme of SWM around the core of ECC columns, regardless of the fiber ratio, exhibited the maximum strength while maintaining appropriate flexibility. Moreover, the ultimate load increased by 16.82%, 13.22%, and 12.86% for fully confined ECC specimens containing PP fibers ratio of 1%, 1.5%, and 2%, respectively compared to their control specimens.