Strength Enhancement Of Concrete Research Articles

Experimental investigation on axial compressive performance of rectangular multi-cell stocky concrete-filled steel tubes stiffened with PBL

An experimental investigation on the structural performance of rectangular multi-cell stocky concrete-filled steel tubes (CFSTs) stocky stiffened with perfobond leiste (PBL) under compression. Compression tests were conducted on 12 stocky CFSTs, varying concrete strengths, number of cells, and cross-section shapes. The tests discussed the failure process, load-deformation behaviours, section capacities, ductility factors, and core concrete enhancement factors of the specimens. It was found that all the 12 tested CFSTs experienced local bucking, and owing to the inclusion of PBL, the short sides of the steel tubes exhibited double-wave bulging, while the long sides showed multiple-wave bulging. With the enhancement of concrete strength from 29.4 to 65.1MPa, the section capacity exhibited a significant increase of 18–30%. As the cell number increased from 1 to 3, the section capacity increased by 1.35–1.59 times. When the cross-section of triple-cell CFSTs changed from the I-shape to the L-shape, the section capacity only increased by 3–9%. Moreover, the enhancement factor of the core concrete and the confinement factor showed a significant correlation. The comparison between test capacities and predicted capacities using the methods given in design codes ANSI/AISC 360-16, EN 1994-1-1, and GB 50936-2014, as well as proposed by Zhang, revealed that the capacity ratios of predicted values to experimental values ranged from 0.63 to 0.89, indicating an overly conservative prediction. Considering the confinement factor, a modified design method, based on Zhang’s method was proposed, to more accurately predict the section compressive capacity of rectangular multi-cell stocky CFSTs stiffened with PBL.

Concrete Strength Enhancement due to High‐Performance Fibre‐Reinforced Concrete Jacketing Solution

AbstractHigh‐Performance Fibre‐Reinforced Concrete (HPFRC) jacketing technique provides a sustainable solution to the constantly growing infrastructure degradation. This paper investigates the effect of HPFRC jacketing solution on strength enhancement of plain concrete. The experimental work included 23 samples, 15 of which were jacketed with HPFRC, and the remaining 8 were used to measure the unconfined strength. The key parameters were jacket thickness (25 mm, 35 mm, and 45 mm) and pre‐damage level (40% and 80%). The results show that jacketed columns exhibit a ductile behaviour. It is found that a 25 mm HPFRC jacket increases the compressive strength by 31%. Moreover, increasing the jacket thickness further enhances the compressive strength. However, the enhancement rate gradually decreases with increasing the jacket thickness. The results from sensor technology used on each concrete layer revealed that the lateral strain of jacketed concrete at a given axial strain was greater than that of unjacketed concrete, indicating an increased rate of dilation for the jacketed concrete. The results show that strengthening of existing columns at their mid‐service life (i.e., 40% pre‐damaged) is as effective as strengthening of new columns. The obtained knowledge suggests that HPFRC jacketing solution has a great potential to revolutionise infrastructure rehabilitation techniques.

Effect of waste glass powder and recycled fine aggregate in sustainable concrete

It is required to help improve concrete's efficiency through the use of waste while also preventing river sand and valuable area from becoming pollution dumpsites. Construction and demolition waste (CDW) has a wide range of possible uses in the construction sector and is quite ubiquitous. It is used as recycled aggregates (RA) in building supplies like mortar and concrete, however, is remaining relatively constrained. This is mostly because it lacks the strength and has more porosity and variability when compared to natural aggregates (NA). Countless research has been conducted with the goal of lowering CO2 emissions, reducing NA exploitation, and enhancing the qualities of these RAs. This research study undertakes a complete experimental assessment to evaluate the impact of adding glass powder and recycled fine aggregates on the creation of sustainable concrete. The study looks at varied proportions of glass powder and recycled fine aggregates, ranging from 0% to 20% with 5% intervals. At a constant temperature of 20°C, the concrete samples are treated to various curing conditions, including both wet and dry curing. Curing times of 3, 7, 14, and 28 days are evaluated. This particular mixture demonstrates a significant increase of 7.2% - 10.76% in strength, indicating that the combined use of 20% GP and 20% RFA results in the highest enhancement of concrete strength among the tested mixtures. This research experiment can be drawn that the inclusion of GP and RFA in concrete gives a tremendous influence in the implementation of mechanical properties and durability for a sustainable concrete.

Experimental and numerical studies on shear stud connectors under combined shear and tension force

Shear stud connections have been widely used in steel–concrete composite bridges, while research on shear studs under combined shear and tension force is still lacking. In this research, 18 specimens, including sixteen push–out specimens under different tension force ratios and two pull–out specimens were tested to study the failure modes, load–slip curves and shear capacity of shear stud connectors under combined shear and tension force. The experimental results show that both the shear capacity and shear stiffness decrease remarkably as the tension force ratio rises. The maximum reduction in shear capacity and in shear stiffness are 37.0% and 68.9%, respectively, when tension force ratio rises from 0 to 0.6. Shear slip and necking are both demonstrated in the failure mode of shear stud connectors when shear and tension forces are coupled. Numerical models were established using ABAQUS and verified by the experimental data to investigate the influence of concrete strength, reinforcement ratio and stud diameter thoroughly via parametric analysis. The results indicate that the shear capacity of shear stud connectors increases as concrete strength and stud diameter rise. Higher concrete strength and closer reinforcement spacing offer better collaborative deformation ability between the studs and the surrounding concrete, and also develop the ratio of the shear capacity under combined shear and tension force to the shear capacity under uniaxial shear force ( Vu/ Vuu). Equations to give prediction of the shear capacity integrated with concrete strength enhancement factor and to describe the load–slip curves of shear stud connectors under combined shear and tension force were proposed and proved to be more accurate.

Transforming spent coffee grounds into a valuable resource for the enhancement of concrete strength

The decomposition of organic waste going to landfills produces methane gas, which is 21 times worse than CO2 in its global warming potential. Spent coffee grounds (SCG) are one type of organic waste that makes up a significant proportion of the organic waste going to landfills. Therefore, it becomes imperative to look for a recycling solution to transform this waste into a valuable resource. The concrete industry has the potential to contribute significantly to increasing the recycling rate of this waste material. However, due to its high organic content, it is unsuitable to be used directly in structural concrete. Therefore, this experimental project looks at pyrolysing this waste at different temperatures (350 and 500 °C) to identify its suitability in improving the physicochemical and mechanical properties of concrete. The raw and pyrolysed forms of SCG were used as a replacement of fine aggregates (FA; sand) at 5, 10, 15 and 20% volume replacement levels. X-ray fluorescence (XRF), Carbon, Hydrogen, Nitrogen, and Sulfur (CHNS) analysis, laser diffraction particle size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and compressive strength tests were undertaken to investigate the properties of the raw material and their performance in the blended concrete composites. The results show that the leaching of organic compounds from the SCG hinders the hydration reaction of cement particles, thereby significantly hampering the compressive strength of SCG-blended concrete. However, pyrolysing the SCG at 350 °C led to a significant improvement in its material properties, which resulted in a 29.3% enhancement in the compressive strength of the composite concrete blended with coffee biochar.

Hybrid effects of basalt and polyvinyl alcohol fibers on the mechanical properties and macro-microscopic analysis of low-heat portland cement concrete

In this study, the pattern of the effect of hybrid basalt fibers (BF) and polyvinyl alcohol fibers (PVAF) on low-heat Portland cement (LHPC) concrete was investigated through mechanical properties and microstructural tests. The compressive stress-strain relationship law for hybrid fiber-reinforced LHPC-C is also summarized by the test data. The test results showed that BF reduced the slump of LHPC-C more significantly than PVAF, and hybrid fibers were better than individual fibers for the strength enhancement of concrete. When the total fiber content was less than 0.4%, the two fibers showed a positive hybrid effect. The optimum hybrid fiber contents for 28 d compressive, splitting tensile, and flexural strength of concrete were 0.15% BF and 0.1% PVAF, 0.2% BF and 0.1% PVAF, and 0.15% BF and 0.3% PVAF, respectively. Compared with the control group, the three mechanical strengths were increased by 30.05%, 56.79%, and 43.51%, respectively. Meanwhile, the toughness of LHPC-C became more apparent as the fiber contents grew. Concrete with BF contents of 0.2% and PVAF of 0.3% had the highest toughness index. At the microscopic level, the components in LHPC-C were mainly SiO2, Ca(OH)2 and C–S–H gels. The surfaces of BF and PVAF were well-bonded to the hydrated cement matrix, and appropriate amounts of hybrid fibers can effectively reduce the porosity of LHPC-C.

Shear capacity estimation of core steel tube reinforced PCCC column-beam interior joint under quasi-static load

In this study, the quasi-static tests were conducted on 13 core steel tube (CST) reinforced PVC-CFRP confined concrete (PCCC) column-beam interior joints. Distinct shear failure occurred in all joint specimens. The load-displacement hysteresis curves appeared pinching phenomenon, and the shape of hysteresis loops gradually deformed from shuttle to arch and finally changed to reverse S shape. The overall shape of hysteresis curves were relatively full, demonstrating that the joints had favorable seismic performances and energy dissipation capacity. The strain development law of materials in the joint area in the process of stress was clarified. The increment of joint stirrup ratio ([Formula: see text]), axial compression ratio ([Formula: see text]), column reinforcement ratio ([Formula: see text]) or beam reinforcement ratio ([Formula: see text]) improved the calculated shear capacity of the joints. The calculated shear capacity increased first and then decreased slightly as the diameter-thickness ratio of CST ([Formula: see text]) increased. In comparison, spacing of CFRP strip had little impact on the calculated shear capacity. Additionally, the concrete strength enhancement coefficient ([Formula: see text]) and joint stirrup utilization coefficient ([Formula: see text]) were introduced respectively to modify the shear capacity of concrete and joint stirrups, and a simplified formula for predicting the shear capacity of CST reinforced PCCC column-beam interior joints under quasi-static load was proposed. The predicted results agreed well with the test data.

Behavior of hexagonal concrete-filled steel corner columns under eccentric compression

Irregular hexagonal concrete-filled steel tubes (HCFST) are suitable for corner columns in high-rise buildings. In this paper, thirteen slender HCFST columns were tested under axial or eccentric compression. The experimental parameters included the slenderness ratio and load eccentricity. A finite element model was then developed to simulate such HCFST columns under compression. After validating the finite element model against experimental results, a comprehensive parametric analysis was carried out to generate a numerical database for HCFST corner columns to cover a wide range of parameters. Concrete strength enhancement from confinement was observed before and after the peak load. In an HCFST column, the interaction between the hexagonal tube and core concrete is mainly developed near the corners of the steel tube. A stronger interaction is found at the right-angle corners than at other corners. Equations were then proposed to predict the load-carrying capacities of HCFST corner columns under eccentric compression. Compared with the test and numerical results, the predictions from the design equations are generally on the safe side.

Thermal Stress of Early-Age Concrete Made with Different Cement Compositions

A temperature stress testing machine (TSTM) was used to investigate effect of cement composition and temperature history on thermal stress of concrete. Results show that the benefit of higher amount of C3S on concrete strength enhancement was compromised by the relatively higher temperature rise at early age, leading to a lower temperature difference. However, by means of a delicate design of cooling history, the deficiency of concrete with higher amount of C3S can be compensated and the cracking sensitivity was closer to that of concrete with lower amount of C3S.

Mechanical strength analysis of fly-ash based concrete in presence of red mud

Sustainable construction practices require transformation in construction industry aiming at reduction of environmental pollution along with enhancement of performance and durability of cementitious structures. Application of pozzolanic materials have been proven promising in this concern as auxiliary cementitious materials for partially replacing cement in mortar and concrete with a positive impact on strength and microstructure of cement matrix. Use of industrial wastes with pozzolanic properties in this category is exceedingly required in order to abate the issue of environmental pollution. Fly ash (FA) and red mud (RM) are the two industrial wastes that pose an issue of safe disposal. Although, FA is already in use as a pozzolanic material, yet not much work is available on the use of RM in concrete. This study examines suitability of RM for use in presence of FA for strength enhancement of concrete. In this analysis, FA was utilized in a dosage of 0–24% by weight of cement while RM was varied from 0 to 24% in presence of 8% FA for partial replacement of cement in concrete. Mechanical strength analysis of concrete specimens was performed and compared with control specimen. The results show that optimized use of FA leads to strength enhancement and the effect is more pronounced in presence of optimized dosage of RM. Thus, RM in presence of FA can be used as a strength modifier and can decrease the cement demand leading to sustainable construction practices.

Strength enhancement of concrete using incinerated agricultural waste as supplementary cement materials

The potassium (K) and sodium (Na) elements in banana are needed for hydration reaction that can enhance the strength properties of concrete. This research aims (a) to determine the material engineering properties of banana skin ash (BSA) and concrete containing BSA, (b) to measure the strength enhancement of concrete due to BSA, and (c) to identify optimal application of BSA as supplementary cement materials (SCM) in concrete. The BSA characterization were assessed through X-ray fluorescence (XRF) and Blaine’s air permeability. The workability, compressive strength, and microstructures of concrete containing BSA were analysed using slump test, universal testing machine (UTM) and scanning electron microscope (SEM). A total of 15 oxides and 19 non-oxides elements were identified in BSA with K (43.1%) the highest and Na was not detected. At 20 g of mass, the BSA had a higher bulk density (198.43 ± 0.00 cm3) than ordinary Portland cement (OPC) (36.32 ± 0.00 cm3) indicating availability of large surface area for water absorption. The concrete workability was reduced with the presence of BSA (0% BSA: > 100 mm, 1% BSA: 19 ± 1.0 mm, 2%: 15 ± 0.0 mm, 3% BSA: 10 ± 0.0 mm). The compressive strength increased with the number of curing days. The concrete microstructures were improved; interfacial transition zones (ITZ) decreased with an increase of BSA. The optimal percentage of BSA obtained was at 1.25%. The established model showed significant model terms (Sum of Squares = 260.60, F value = 69.84) with probability of 0.01% for the F-value to occur due to noise. The established model is useful for application in construction industries.

Strength Assessment of Concrete using Rice Husk Ash, Polyvinyl Alcohol Fiber and Recycled Concrete Aggregate: A Critical Review

In this review study, the effect of three different materials such as rice husk ash, recycled concrete aggregate and Polyvinyl Alcohol fibre was reviewed in detail. Several past studies related to these material usage in strength enhancement of concrete was studied in detail. Rice husk ash is the ash which is mainly derived after burning the waste derived from the rice industry after the processing of rice. Recycled concrete aggregate is mainly the aggregate derived from the constructional waste. Polyvinyl Alcohol fibre is a special type of high strength fibre that is mainly used to improve the flexural strength and internal bonding of the concrete. Numerous studies were discussed in detail and depending upon the studies certain conclusion are drawn which are discussed further. Several studies related to the usage of rice husk ash conclude that the most optimum usage percentage of rice husk ash as partial replacement of ordinary Portland cement was at 10 percent usage. After 10 percent usage strength tends to decline. Results related o usage as partial replacement of natural fine aggregate that is sand showed that it can be used as partial replacement of natural coarse aggregate up to 20 percent and beyond that usage the strength was declining. The studies related to the usage of recycled concrete aggregate conclude that the most optimum percentage of usage of recycled concrete aggregate as partial replacement of natural coarse aggregate was 50 percent replacement and beyond this percentage the strength starts declining so therefore should not be used beyond that limit. Studies related to the usage of Polyvinyl Alcohol fibre revealed that the most optimum percentage of Polyvinyl Alcohol fibre was 1.5 percent and beyond this percentage both the compressive strength of concrete and flexural strength of concrete was declining. Test results concluded that Polyvinyl Alcohol fibre should be used up to 1.5 percent only.

Compressive Strength of Concrete Containing Laterite Stone and Palm Oil Clinker as Fine Aggregate Replacement

The high dependency of construction industry on supply of river sand has initiated research to find other alternative materials that can be used as partial sand replacement in concrete production. Two types of material, that is palm oil clinker (POC) which continuously produced waste from local palm oil industry and freely available laterite aggregate on earth surface have been investigated its potential to be used as partial sand replacement in concrete. The present research was carried out to determine the workability and compressive strength of concrete containing laterite aggregate and crushed palm oil clinker as partial fine aggregates replacement. Concrete mixes have been prepared by integrating various proportions of laterite aggregate and palm oil clinker by weight of river sand. The compressive strength test was conducted on the continuously water cured specimens at 7, 14 and 28 days. The results showed a perfect combination of fine laterite and fine palm oil clinker on S1 (25% of FL + 25% of FPOC) as partial fine aggregate replacement contributed towards enhancement of concrete strength.

Experimental and finite element analysis of mechanical behavior of concrete damaged by Alkali Aggregate Reaction (AAR) and repaired with CFRP Layers

Concrete structures is affected by a deleterious reaction, which is known as Alkali Aggregate Reaction (AAR). AAR can be defined as a chemical reaction between the alkali content in the pore water solution of the cement paste and reactive forms of silica hold in the aggregate. This internal reaction produces expansion and cracking in concrete, which can lead to loss of strength and stiffness. Carbon fiber-reinforced polymer (CFRP) is one of the methods used to suppress further AAR expansion and rehabilitate and support damaged concrete structures. In this research, thirty-six cylindrical specimens were fabricated from non-reactive and reactive concrete, which contained fused silica as 7.5%. In addition, twelve concrete prisms were fabricated from non-reactive and reactive concrete in which three different percentages of fused silica are used, 5%, 7.5% and 10% of the total aggregate. This paper investigates the impact of AAR expansion on the physical and mechanical properties of concrete. It also reports the effective use of one and two CFRP layers on wrapping concrete cylinders. The experimental results show that CFRP is effective in confining damaged concrete by AAR and results in concrete strength enhancement of up to 560%. A comparison of finite element (FE) analysis using ATENA 3D software and the experimental results indicated that FE analysis is capable of modelling the behavior of AAR-damaged concrete repaired with CFRP.

Effect of Loading Rate on Tensile and Failure Behavior of Concrete.

Three-point bending experiments of concrete beams were conducted under the strain rate range of 10−6 s−1 and 1.5 × 10−3 s−1. A novel 3D laser scanner, Handy SCAN, was employed to detect the areas of interface, mortar and aggregate on the crack surface after the experiment. In this paper, the inhomogeneity of materials and the inertial effect were considered as the main factors in the strength enhancement of concrete together with a proposed dynamic model. With the obtained experimental results, the initial elastic modulus and tensile strength of concrete showed obvious rate sensitivity. Moreover, an empirical relationship of dynamic increase factor and strain rate was established for the strain rate range of 10−6 s−1 and 1.5 × 10−3 s−1. The contributions of aggregate and inertia effect to the dynamic enhancement of concrete strength were quantified with respect to the loading rate. The rate effect of concrete obtained by the experiments was verified by the finite element analysis on the mesoscopic scale with the model built by the three-dimensional random aggregate software.

Behavior of FRP-confined sea-sand concrete columns with a prefabricated concrete-filled FRP-steel core

Adopting fiber-reinforced polymer (FRP) composites as a confining device and a protective skin not only allows usage of sea-sand concrete which is generally forbidden in conventional steel reinforced concrete structures, but also leads to enhancement of concrete strength and deformation capacity. This paper presents a pilot study on axial compression tests on hybrid FRP-confined sea-sand concrete columns with a prefabricated concrete-filled FRP-steel tube core (simply referred to as FRP-Confined Sea-sand Concrete-Prefabricated Core Columns or FCSC-PCCs). The prefabricated concrete-filled glass FRP (GFRP)-steel core, serving as reinforcing core in FRP-confined concrete columns, is expected to enhance the FRP-confined concrete columns and enable to make use of sea-sand in the concrete between the two tubes. Effects of the steel tube diameter, the GFRP tube thickness and the thickness of the external Carbon FRP (CFRP) tube are carefully investigated. The axial load–axial strain curve of FCSC-PCCs as well as the confined concrete in FCSC-PCCs generally exhibit a monotonically ascending behavior owning to the confinement from the external CFRP tube and the internal FRP-steel composite tube. A new model for average ultimate axial stress and axial strain of confined concrete in FCSC-PCCs is established and the comparisons demonstrate that the proposed model is of satisfactory accuracy.

Comparative Study on Strength Enhancement of Concrete using Magnetic and Normal Water

Comparative Study on Strength Enhancement of Concrete using Magnetic and Normal Water

Compressive strength enhancement of concrete using fly ash as a partial replacement of fine aggregate and model development

The aim of the study is to observe the strength increment of concrete by using fly ash as a partial replacement of fine aggregate. For that, three mix ratios – 1:1.25:2.5, 1:1.5:3 and 1:2:3 (weight-based) have been considered. For each ratio, fly ash was used as 0%, 10%, 20% and 30% of the fine aggregate. The curing period and the water-cement ratio (W/C) were 28 days and 0.5, respectively. It was revealed that the compressive strength of the concrete was increased with the addition of fly ash. And it was the maximum at 10% of fly ash content. A nonlinear relationship has been proposed where compressive strength has been used as the function of the weight of cement, fine aggregate, coarse aggregate and fly ash.

Compressive strength enhancement of concrete using fly ash as a partial replacement of fine aggregate and model development

Compressive strength enhancement of concrete using fly ash as a partial replacement of fine aggregate and model development

Mechanical Properties of Fly Ash Based Concrete Aided With Recycled Aggregates and Manufactured Sand

Enhancement of concrete strength to shoot the need, demand and to make sustainable is being studied by bountiful researchers across the globe. Utilization of industrial waste and construction waste is an area being explored in the recent days properties of construction demolition waste is unique in nature and result of one research will not maintain with other due to heterogeneous nature of demolition waste. In this work a special type of demolition waste is obtained from building is utilized in concrete in tandem with fly ash instead of sand cost effective and sustainable mixed sand is used in this study in varying proportions. Four different mixes (M1 M2 M3 M4) is prepared using standard sampling procedures and tested for strength and durability. It is found that M2 shows considerable strength in with increasing curing period and it can be selected as optimum mixture. Graded mixed sand used in this study shows considerable increase in strength in coordination with recycled coarse aggregates.