Experimental investigation of structural behaviour and microstructural characteristics of steel fibre-reinforced concrete beams

Due to rapid development in urban area, use of high strength concrete in the construction industry is increasing rapidly. Mineral admixtures such as Ground Granulated Blast furnace Slag (GGBS), Metakaolin, Silica fume and Alccofine are become unavoidable in high strength concrete because of their effects in hardened concrete properties. Replacing the Ordinary Portland Cement (OPC) by mineral admixtures is retaining the natural resources for future generation. In present scenario, replacement of river sand with manufactured sand is almost mandatory due to scarcity of the river sand. Superplasticizers are used to improve the workability of concrete at low water-cement ratio and increase the compressive strength by reducing it. In urban infrastructure development, the high strength concrete is mandatory to reduce the size of structural member, and to increase the utility space to carry heavier load. In this study M100 grade concrete mix was designed with replacement of OPC by different types of mineral admixtures using river sand and manufactured sand along with Polycarboxylate Ether (PCE) based superplasticizer. The Compressive strength, flexural strength and split tensile strength at various curing periods such as 28 and 56 days. The durability properties such as Rapid Chloride Penetration test, Water penetration test and water absorption test were carried out on the specimens at 28 and 56 days. Also, the Drying shrinkage of the concrete was tested at 14 days. From the experimental test results it is observed that, all the mixes were achieved the target mean strength, among these the Alccofine with Manufactured sand combination has achieved 21% higher than the target strength at age of 56 days and other strength parameters such as split tensile and flexural strength also slightly increased in this combination comparatively. The durability tests (Rapid chloride penetration, water penetration and drying shrinkage) were conducted and the obtained values at the age of 56 days are within permissible limit as per the codal provisions and the concrete with manufactured sand shows slightly higher value than concrete with river sand.

The use of coconut fibre (CF) from agricultural waste offers a sustainable solution to environmental challenges by reusing residues from the coconut industry. This approach respects the principles of sustainability and environmental preservation by minimising waste and encouraging the use of renewable resources in construction. A study was carried out to assess the effectiveness of untreated (UT) and treated CFs as reinforcement in high‐strength concrete (HSC), targeting an average strength of 60 MPa. The study evaluated the mechanical and durability characteristics of HSC reinforced with raw and processed coconut fibres (CFR‐HSC). The CFs underwent physical treatment by boiling and chemical treatment using a 1% sodium hydroxide (NaOH) solution. Different fibre contents were examined, and analyses including scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS) were carried out on untreated and treated fibres. The results showed that additional fibre content reduced the workability of the concrete, its fresh density, and its air void content, but that the treated fibres had better workability than the UT fibres. While compressive strength was not significantly improved with CFR‐HSC compared to the HSC control mix after 28 days of curing, tensile and flexural strengths were improved with fibre content. Notably, the NaOH‐treated (NT) CF showed the greatest increase in tensile strength, while the boiling‐treated (BT) CF showed the greatest improvement in flexural strength. An increase in fibre content resulted in a reduction in crack width, and CFR‐HSC showed an increase in water absorption but better resistance to sulfuric acid, with NT CF producing the most promising results.

The widespread acceptance of concrete can be attributed to its unique characteristics, despite inherent drawbacks such as brittleness and weak tensile strength. The study was aimed at evaluating the optimal content and characterization of steel fibres required to impede crack propagation and enhance overall strength of concrete. The influence of critical factors like fibre content, length, diameter, and volume fraction on the performance of steel fibre reinforced concretes (SFRC) through statistical analysis of 209 experimental data. The influence of these factors on the compressive, flexural, and tensile strengths of concrete was analyzed as a function of the mean and coefficient of variation of the normalized strength values. The study found that steel fibres in concrete produced success rates of 67.9% (7.1% average strength improvement = ASI) in compressive strength, 78.5% (38.2% ASI) in flexural strength and 84.2% (23.8% ASI) in tensile strength. The study further separately examined the impact of steel fibres on both normal strength concretes (NSC) and high strength concretes (HSC). The findings indicated an overall success rate of 60% (6.97% ASI), 69.9% (38.36% ASI), and 75.6% (23.59% ASI) for compressive, flexural, and split tensile strength, respectively, in NSC. However, higher degree of strength enhancement of 74.0% (7.16% ASI), 84.8% (39.21% ASI), and 86.6% (23.51% ASI) were recorded for compressive, flexural, and split tensile strength, respectively in HSC. The research underscores the effectiveness of incorporating steel fibres as a reinforcement strategy in enhancing various strength aspects of concrete.

In this study, researchers investigated the mechanical properties of high-strength steel fiber-reinforced concrete (HSFRC). The experimental study involved evaluating high strength concrete (HSC) using various steel fibre contents (ranging from 0.25% to 2.00%) and different water-cement ratios (WCR) (0.25, 0.30, 0.35, and 0.40). Adding 1.50% steel fibre to HSC led to an increase in compressive strength (CS). Specifically, the CS improved by 13.42% to 15.19% for WCR of 0.25, 0.30, 0.35, and 0.40. Including 1.50% steel fibre enhances split tensile strength (STS). The STS increased by 25.89% to 32.62% for the same WCR. High-strength concrete with 1.50% steel fiber exhibited improved flexural strength (FS). The FS rose 29.00% to 35.07% for the specified water-cement ratios. The study also considered the modulus of elasticity (ME) at 28 days. Interestingly, the strength of HSC decreased as the WCR increased. Lower WCR generally contributed to better mechanical properties. The experimental results were compared with linear regression analysis and existing empirical formulas. The regression analysis demonstrated good agreement with the experimental findings. Overall, the optimal steel fibre content was 1.50% across all WCR, significantly improving mechanical properties. The study provides valuable insights for designing HSC with enhanced performance.

The structural performance of deep beams is significantly influenced by the development and propagation of diagonal cracks, which compromise their shear capacity and overall stability. This study investigates the mechanical behavior of diagonal cracks in high-strength fibre-reinforced concrete (HSFRC) deep beams. Fibre reinforcement, known for its crack-bridging capacity and toughness enhancement, offers potential improvements in the ductility and shear resistance of deep beams, particularly under high-stress concentration zones. In this experimental investigation, deep beams with varying fibre contents and types were cast using high-strength concrete and tested under two-point loading conditions. The primary parameters studied include load-bearing capacity, crack initiation and propagation patterns, crack width, and post-cracking behavior. High-resolution digital image correlation techniques and mechanical strain gauges were employed to monitor strain distribution and crack evolution in real time. The results indicate that fibre incorporation significantly delays the onset of diagonal cracking and enhances the post-crack load-carrying capacity. Moreover, the addition of fibres contributes to a more distributed cracking pattern and increases energy absorption, thereby improving the ductility and overall structural resilience. Comparative analysis with control specimens revealed up to 30% enhancement in shear strength and a notable reduction in crack width and spacing. The study concludes that integrating fibres into high-strength concrete can effectively mitigate the adverse effects of diagonal cracking in deep beams, offering a practical solution for enhancing the performance of critical structural elements in modern construction. These findings provide a foundation for future research and development of design guidelines for HSFRC deep beams.

This research presents an experimental study to investigate the effect of coarse aggregate maximum size on the shear behavior of self-compacting concrete (SCC) and conventional concrete (CC) slender beams having the same compressive strength and make a comparison between the shear behavior of concrete beams. The experimental program included casting and testing eight beams with a constant size of 150mm height ×125mm width×1000mm length. Two coarse aggregate maximum sizes were used (10mm and 20mm) with SCC and CC in normal and high strength concrete. The results showed that increasing the coarse aggregate maximum size from 10mm to 20mm results in a slight increase in the diagonal cracking load and ultimate shear strength of SCC beams, while for CC beams the result was more significant. Also, it was found that the effect of increasing the coarse aggregate maximum size was more significant for normal strength as compared with high strength beams for both concrete types. Furthermore, the comparison between the shear behavior of SCC and CC beams having the same compressive strength and a concrete with the same coarse aggregate maximum size revealed that the SCC exhibited less diagonal cracking load and less ultimate strength compared with CC.  Â

Development of a sustainable high early strength concrete incorporated with pozzolans, calcium nitrate and triethanolamine: An experimental study

Urbanization and industrialization have dramatically increased the manufacture of cement causing substantial pollution of the environment. The primary global concern related to cement manufacture has been the management of the large carbon footprints. The usages of environmentally friendly cementitious materials in the construction of structures have proved to be a viable option to deal with this environmental concern. Therefore, it is necessary to further explore the usage of cementitious materials which can replace cement albeit partially. In this direction of research, two such cementitious materials, namely, natural zeolite and metakaolin have been investigated in this study. High‐strength concrete M60 with natural zeolite and metakaolin as the partial replacements for the cement has been prepared in this work. Polycarboxylic ether‐based superplasticizer solution has been used to enhance workability. The test specimen cast and cured for 3, 7, 28, 60, and 90 days at ambient room temperature has been tested for compressive strength, split tensile strength, and flexural strength as per the Indian standards. The optimum mix of high‐strength concrete thus manufactured has met the Indian standards, and the combination of cement +5% natural zeolite +10% metakaolin has exhibited the highest compressive, split tensile, and flexural strengths at 90 days of curing. Natural zeolite and metakaolin when used in smaller proportions have increased the concrete strength, and these materials are recommended for partial replacement of cement.

Increasing demand for high-rise buildings and massive structures has led to the production and use of high-strength concrete in large quantities, which in turn has led to higher environmental impacts. Self-curing concrete produced using polyethylene glycol and recycled fine aggregates (RFA) along with superplasticizers is found to be the most promising solution for attaining high-strength concrete with significantly lower environmental impacts. This work deals with the experimental and analytical evaluation of the mechanical properties of high-strength self-curing (HSSC) concrete using RFA. The replacement proportion of RFA considered are 0%, 10%, 20%, 30%, 40%, and 50% with respect to the weight of natural fine aggregates. Experimental investigations indicate that the optimum replacement proportion of RFA in this HSSC concrete is 30% when considering the strength characteristics. An empirical model based on regression analysis using Minitab software is developed for compressive strength, split tensile strength, and flexural strength to evaluate its correlation with the existing analytical models of international codes. Analytical evaluation indicates that the compressive strength and flexural strength of HSSC concrete correlates highly with American Concrete Institute (ACI) code. The split tensile strength of HSSC concrete is found to have a better correlation with Eurocode. RFA self-curing concrete can be effectively used to produce high-strength concrete.

The hybridization of Basalt Fibers (BF) and Polypropylene Fibers (PF) in High-Strength Concrete (HSC) has immense potential to improve its mechanical properties. This paper investigates the compressive strength, tensile splitting strength, and flexural strength of HSC reinforced with single BF, single PF, and hybrid fibers. Samples from thirteen mixes (i.e., one control, four BF, four PF, and four hybrid mixes) were prepared and tested at 7, 14, and 28 days. The BF content ranged from 0.1 to 0.7%, while that of PF ranged from 0.05 to 0.3%. The results indicate that at 0.3% BF dosage, the compressive strength increased from 60.66 MPa in the control mix to 62.70 MPa (a 3.36% increase). Similarly, at a 0.1% PF dosage, it increased to 61.42 MPa (a 1.25% increase). The tensile splitting strength increased from 3.97 MPa in the control mix to 4.61 MPa (a 16.12% increase) with optimal BF, and to 4.22 MPa (a 6.30% increase) with optimal PF. Similarly, the flexural strength increased from 6.22 MPa to 7.40 MPa (an 18.97% increase) with optimal BF, and to 6.70 MPa (a 7.72% increase) with optimal PF. The optimal hybrid combination consisted of 0.3% BF and 0.1% PF, which increased the compressive strength to 64.62 MPa (a 6.53% increase) at 28 days. The tensile splitting strength and flexural strength increased by 44.33% and 29.58%, respectively. It was therefore concluded that combining both fiber types in concrete produced a positive synergistic effect. Thus, using fibers in a hybrid form is more beneficial for producing high-strength fiber-reinforced concrete.

Alternate materials in the research of high strength concrete (HSC) have become a prominent practice all over the world in the past decades to enrich the long-term strength, high workability, better durability, economy and environmental factors. This study presents the mechanical characteristics of high strength concrete (HSC) with the influence of low calcium silicate alccofine (Alccofine 1203). The enhanced workability at the given low water cement ratio and improved pore filling capability was observed by indulging alccofine in the HSC. It is also observed that due to the presence of alccofine particles, the concrete gains high strength much early. The presence of optimum dosage of alccofine in the regular HSC is anticipated to progress the strength of concrete at early age and deliver superior durability characteristics such as resistance against accelerated corrosion attack, sea water attack and chloride attack. This work has its core on the investigational examination on mechanical properties such as flexural strength, split tensile strength and compressive strength on HSC by replacing cement with alccofine, which varied from 0 to 20% at 5% increments for 7, 14 and 28 days and concluded with the determination of optimum dosage of alccofine as the replacement of cement.KeywordsHigh strength concreteAlccofine 1203FlexuralSplit tensileCompressive strength

The world of building materials is constantly and rapidly developing. New technologies are needed to reduce the cost of producing these materials and to ensure better efficiency when the materials are used in various engineering projects. One of these materials is high-strength concrete. This paper investigates the production of low-cost, high-strength concrete by partially replacing fine aggregates (FA) with waste glass sand (WGS). Four concrete mixes were considered in this study with varying percentages of WGS (0%, 25%, 50%, and 75%). For each mix, cubic, cylindrical, and beam specimens were cast to study the workability and different mechanical properties of concrete-like density, elasticity modulus, compressive strength, ultrasonic pulse velocity (UPV), split tensile strength, and flexural strength. In addition, the cost of each mix was calculated to evaluate the cost reduction efficiency of concrete with WGS compared to normal concrete. Results showed that the workability of concrete enhanced as the percentage of WGS increased. In terms of concrete mechanical properties, it was shown that the elasticity modulus, compressive strength, split tensile strength, and flexure strength for a concrete mix with 50% WGS as FA replacement was increased by 7%, 27%, 9%, and 50%, respectively. Also, it was concluded that the presence of WGS in concrete mixes reduced the production cost by up to 30% for a 75% replacement level. The authors recommended the usage of 50% WGS as the optimum replacement percentage for low-cost, high-strength concrete.

Use of steel fibers as transverse reinforcement in diagonally reinforced coupling beams with normal- and high-strength concrete

This research work investigates the effect of rice husk ash (RHA) and grounds granulated blast furnace slag (GGBFS) on the mechanical properties of high-strength concrete (HSC). The HSC with different proportions of RHA and GGBFS have tested the compressive strength at 7, 14, and 28 days, split tensile strength, and flexural strength at 28 days. The ordinary Portland cement was partially replaced by a weight ratio of RHA (10%, 15%, 20%), and GGBFS (10%, 20%, 40%). Experimental work was completed to restore at 20°C and 65 percent relative humidity. A total of 90 cubes, 30 cylinders, and 30 beams were cast for different mixes for compressive strength, split tensile strength, and flexural strength of concrete. The test results reported that of RHA the compressive strength increases by 6.62 percent compared to the conventional mix at 28 days split tensile strength and flexural strength increases by 6.23 and 5.21 percent. Also, the optimum percent of GGBFS compressive strength increases by 6.81 percent, and split tensile strength and flexural strength increase by 6.89 and 5.61 percent. The RHA and GGBFS-based concrete are emerging construction materials with carbon dioxide (CO2) emissions compared to conventional cementitious materials. This research studied to investigate the mechanical strength characteristics of blended with RHA and GGBFS. It was observed that the addition of 30 percent GGBFS in concrete increases the compressive strength by 23 percent compared to the control mix. The experimental results showed the inclusion of GGBFS with RHA to attain compressive strength. It was accomplished that the GGBFS and RHA mixture did tend to form stable concrete.

High strength concrete is defined as concrete with characteristic cube strength above 40 MPa. The applications of high strength concrete are bridges, aqueducts, dams, high rise buildings etc. This work involves the comparative study of various mineral admixtures such as alccofine and metakaolin on high strength concrete. Alccofine is a new generation micro fine concrete material which is beneficial with respect to workability as well asstrength. The desirable properties of Metakaolin make it mostly preferred additives in high strength concrete. In thisstudy,cementispartiallyreplacedwithalccofine,metakaolinat5,10and15%. The mechanical properties like compressive strength, flexural strength and split tensile strength are evaluated and compared. The strength properties are maximum for the concrete mix with alccofine.