Behavior Of High Strength Concrete Research Articles

Postpeak Stress–Strain Behavior of High-Strength Concrete under Different FRP Confinement Stiffness Ratios

Postpeak Stress–Strain Behavior of High-Strength Concrete under Different FRP Confinement Stiffness Ratios

Blast retrofit of shear-deficient high-strength concrete beams with ultra-high performance concrete

This research has investigated the ability of ultra-high performance concrete (UHPC) to improve the blast performance of high-strength concrete (HSC) beams. As part of the study 4 shear-deficient HSC beams built without stirrups and with dimensions of 125 mm × 250 mm × 2440 mm were retrofitted with a UHPC jacket and tested under simulated blast loads using a shock-tube. The retrofit involved replacing the existing cover with a cast in-situ UHPC jacket (with thickness of 20–40 mm). A companion set of beams was also tested under quasi-static four-point bending. The results from the blast and static tests are compared to a control set of HSC beams built without and with stirrups to examine the ability of UHPC to increase shear and flexural resistance, respectively. The effect of steel ratio (ρ = 1.6% or 2.4%), an important parameter which affects the behavior of HSC and UHPC beams, was also investigated in beams with 15M and 20M bars. Under static loading, the results show that the UHPC jacket was able to prevent shear failure, and improve flexural performance by increasing strength by 40–125%, stiffness by 80–100% and overall toughness by 56–144%, when compared to the companion HSC beams. Under blast loading, the UHPC increased shear capacity, prevented shear failure and improved blast performance by reducing displacements, increasing overall blast capacity and improving damage tolerance. For example, in the 20M set, the UHPC-retrofitted beam showed reductions of 26–63% in maximum displacements, and 88–100% in residual displacements under varying blast intensities. The steel ratio was found to play an important role on the failure mode of the retrofitted beams under static loading, with bar fracture observed in the beam with lower steel ratio of 1.6%. As part of the numerical study, the blast response of the UHPC retrofitted beams was predicted using 3D finite element (FE) modeling. The FE models were able to predict the failure modes and maximum displacements of the control and UHPC retrofitted beams, with an average numerical-to-experimental displacement ratio of 1.03 and an average error of 8%.

Chopped carbon fibre reinforcement in high-strength concrete: Flexural characteristics

In this study, the flexural behaviour of high-strength concrete was tested with chopped carbon fibres that were 30 mm long and added in amounts of 0.2%, 0.4%, 0.6%, 0.8%, and 1%. Thirty-six prisms were evaluated experimentally for flexural strength at 28 days using an ultrasonic pulse velocity test and a flexural testing machine. X-ray diffraction and linear regression analysis were carried out to characterise crystalline material and linear correlation amongst different mixes. Increasing the number of carbon fibres in high-strength concrete led to unexpected and innovative findings, such as lower pulse velocities and improved flexural characteristics up to an optimum dosage point. In SEM images of chopped carbon fibres, debonding was the most prevalent cause of failure.

Compressive Behavior of Concrete Subjected to High Rate of Loading Using SHPB

Concrete is the most widely used construction material for strategic structures which are subjected to high rate of loading (impact and blast loading). Hence, the study of the concrete material becomes essential day by day for the structural engineers for the analysis and design of the concrete structures for safety and security purposes. This paper focuses on investigating the dynamic compressive response of the standard concrete (M35) and high-strength concrete (M60) under impact loading by using the newly developed split Hopkinson pressure bar setup (SHPB) apparatus. First, the calibration of SHPB performed at a 4.90[Formula: see text]ms[Formula: see text] impact velocity generates almost similar incident and transmission trapezoidal profile waves with minor reflection showing accuracy. Second, the dynamic compression tests were performed on the standard concrete (SC) and high-strength concrete (HSC) specimens of 29.5[Formula: see text]mm in diameter and [Formula: see text][Formula: see text]mm in length with an aspect ratio of about 1([Formula: see text]) and a comparative study of strain rate effect and quasi-static compressive strength on the material properties has been investigated. The dynamic compression behavior of SC and HSC thus studied under varying strain rates has been presented in terms of the compressive strength, dynamic increase factor, stress–strain relationship, material failure, and fragmentation. Compressive strength increments of 114% and 41% were observed in SC and HSC as the loading condition changed from quasi-static to dynamic. In addition, the HSC described the [Formula: see text]% and [Formula: see text]% higher compressive strength corresponding to 290[Formula: see text]s[Formula: see text] and 131[Formula: see text]s[Formula: see text] strain rate as compared to SC describing that the HSC is more sensitive to the strain rate. The dynamic mechanical properties increased with an increase in the strain rate, and the DIFs were found to vary in the range of 1.42–2.14 and 1.07–1.41 for SC and HSC, respectively. The critical strain and ultimate strain were also found to be sensitive to strain rate and increased with increase in strain rate for both grades of concrete. Moreover, strain rates exert a noteworthy influence on fragmentation, leading to an increase in the percentage weight of fine fragments and a decrease in the percentage weight of large fragments as the strain rate increases. Additionally, there is an overall increase in the quantity of fragments for both SC and HSC specimens under these conditions. The flaky, elongated, angular, and irregular shape fragments were observed but their quantity and size varied significantly with strain rate.

Stiffness-based stress–strain model of FRP-confined high-strength and ultra-high strength concrete column with various corner radii

This study introduces a unified design-oriented stress–strain model tailored for fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) with diverse cross-sectional shapes. The proposed stress–strain model incorporates more suitable mathematical forms, incorporating post-peak axial stiffnesses as crucial parameters, thereby enabling the model to accurately capture the three types of post-peak stress–strain behavior observed in FRP-confined HSC: strain-hardening, strain softening, and strain softening recovering to strain hardening. This variation in post-peak axial stiffness arises due to insufficient FRP confinement at the initial peak strength point, as well as changes in the confinement stiffness ratio stemming from the altered dilation behavior of FRP-confined HSC during the post-peak stage. To address the nonuniform effects of FRP confinement, the concept of effective confinement rigidity was defined, unifying the behavior of FRP-confined circular and square HSC. Additionally, the model incorporates the ultimate condition and the characteristic point on the post-peak branch, representing the change in FRP confinement stiffness, to establish the stress–strain model for FRP-confined HSC. The model parameters were evaluated using available experimental results, and the stress–strain curves derived from the proposed model were compared with existing models in the literature, revealing the proposed model's accuracy and rationality.

Experimental Behavior of High-Strength Concrete Reinforced with Aramid Fiber and Polyurethane Resin

Over the past few decades, research has been conducted to develop high-strength concrete (HSC) for high-rise structures and bridge decks. The research discussed in the study focuses on using polyurethane resin (PR) and aramid fibers (AF) to develop HSC, which enhances its strength, durability, and structural properties without increasing the cementitious content. This approach can lead to more sustainable and cost-effective construction practices by reducing the cementitious materials required. In the present investigation, M50-grade concrete mixes were designed in accordance with the guidelines mentioned in Indian Standard (IS) 10262 along with the addition of supplementary cementitious materials, such as fly ash and silica fume. Initially, varying percentages of AF (0% to 3%) and PR (0% to 6%) were added into the concrete mixes and detailed experimental investigations were completed on workability, strength, durability, and structural properties. It is concluded that the addition of AF and PR shows significant improvements in strength, durability, and structural properties compared to traditional HSC created with zero AF and PR content. As reinforced concrete (RC) elements serve as the final product for human construction projects, it is crucial to ensure that their structural properties are reliable. In order to validate the findings from experimental investigations, numerical simulations were conducted using the ANSYS commercial package software. Specifically, the structural properties of RC beams were analyzed using this software, allowing for further validation and verification of the experimental results. From the detailed investigation, it is concluded that 2.5% addition of AF and 4% addition of PR demonstrates better results and is considered the optimum ingredient dosage, which can be used as a reference for future studies and practical applications. These findings can result in the development of new and improved building materials and techniques that can potentially lead to safer, more durable, and sustainable structures.

Cracking failure behavior of high strength concrete containing nano-CaCO3 at early age

Nano-calcium carbonate (CaCO3) has been added to high strength concrete (HSC) to reduce cement usage, control greenhouse gas emissions, increase durability, and control excessive shrinkage of HSC. Many investigations on the mechanical properties and shrinkage of HSC containing nano-CaCO3 have conducted. However, the early-age cracking failure behavior of that considering temperature, shrinkage, restrained stress, and tensile creep simultaneously was rarely investigated. Temperature stress test machine, which could measure these factors simultaneously, was used to investigate the influence of nano-CaCO3 contents (0%, 1%, 2%, and 3% by weight of cement powder) on the early-age cracking failure behavior of HSC in the present investigation. Mechanical properties of HSC containing nano-CaCO3 were tested. The addition of nano-CaCO3 to HSC improved the mechanical properties, and reduced the tensile creep as well as autogenous shrinkage of that at early age. A simplified stress-strain failure criterion was proposed.

Investigating The Mechanical Behavior of High-Strength Concrete Reinforced with Hooked Steel Fibers

The engineering properties of high-strength concrete are significantly different from those of ordinary concrete, and as a result, this concrete has become popular in a variety of applications, including the construction industry, particularly for tall buildings, bridges with long spans, and precast members. Reinforcing high-strength concrete using fibers is a common method for increasing ductility without losing strength. In this study, steel fibers were employed to replace 1, 1.5, 2, and 2.5 percent of the total volume of concrete, and a total of 5 mixed designs were conceived and constructed. The findings showed that the addition of steel fibers up to 2% by volume boosted the compressive strength and decreased at 2.5% by volume. The incorporation of steel fibers has diminished the mixes' durability.

Mechanical response of recycled carbon fiber reinforced polymer fibers in high-strength concrete

The present paper studied the mechanical behavior of High Strength Concrete by incorporating recycled CFRP (Carbon Fiber Reinforced Polymer) fibers. The hardened properties of high-strength concrete were assessed using fiber volume fractions of 0.2 %, 0.4 %, 0.6 %, 0.8 %, and 1 % with a 30 mm average size of recycled chopped carbon fibers. The hardened properties of concrete test samples were evaluated using UPVT (Ultrasonic Pulse Velocity Test) and compressive strength test. Thirty-six specimens were tested at 28 days compressive strength to characterize mechanical properties. X-ray Diffraction analysis was carried out on a nominal mix test sample and a sample having an optimum dosage of fibers to characterize crystalline materials and understand the mineralogical properties of the concrete matrix. Analytical analysis was carried out using linear regression analysis for high-strength concrete's mechanical properties, considering different volume fractions or dosages of recycled chopped carbon fibers. The results showed that the increase in recycled chopped carbon fibers volume fractions or dosages enhances the compressive strength and increases the porosity of concrete samples up to the optimum dosage of recycled chopped carbon fibers.

Effect of temperature rise inhibitor on early-age behavior and cracking resistance of high strength concrete under uniaxial restrained condition

Temperature rise inhibitor (TRI) is used to modify the cement hydration and reduce the heat release of high strength concrete (HSC). Many investigations on the mechanical properties, temperature process, and autogenous shrinkage of cement-based materials with TRI have been conducted. However, the evaluation of the early-age behavior and cracking resistance of HSC with TRI under uniaxial restrained condition considering the effects of temperature, shrinkage, restrained stress, and tensile creep simultaneously was rarely conducted. Temperature stress test machine, which could measure these factors simultaneously, was used to investigate the effect of TRI contents on the early-age behavior and cracking resistance of HSC in this research. The peak temperature, temperature rising rate, autogenous shrinkage, and tensile creep decreased with increasing TRI contents. The addition of TRI improved the early-age cracking resistance of HSC. A modified stress-strain failure criterion and a prediction model for autogenous shrinkage of HSC with TRI were proposed.

Meso-scale numerical simulation of the effect of aggregate strength on damage and fracture of high-strength concrete under dynamic tensile loading

The dynamic mechanical behavior of high-strength concrete is sensitive to aggregate properties, thus an accurate description of the effect of aggregate strength on the dynamic tensile mechanical properties of high-strength concrete is essential to evaluate the structural stability of concrete. In this paper, a concrete meso-scale modeling framework was proposed based on discrete element method (DEM). The meso-scale model considered the three-dimensional meso-structure of concrete (coarse aggregate, mortar and interfacial transition zone), and the crushable aggregate model with realistic morphological characteristics was generated by the “clump-cluster” method. Based on this, the effects of aggregate strength on dynamic tensile properties and damage behavior of high strength concrete were quantitatively studied by splitting tensile test. The simulation results reveal the influence of aggregate strength and strain rate on the tensile properties of concrete at both macroscopic and mesoscopic levels, including dynamic deformation behavior, microcracks propagation mode and the proportion of different kinds of microcracks at different loading stages. The results show that the aggregate strength plays an important role in the dynamic tensile properties of concrete. The failure behavior of concrete and the damage degree of different components under dynamic tensile loading are influenced by the ratio of aggregate strength to mortar strength.

Laboratory Curing Protocols to Replicate Thermomechanical Behavior of High-Strength Concrete in Mass Placements

Laboratory Curing Protocols to Replicate Thermomechanical Behavior of High-Strength Concrete in Mass Placements

Influence of Treatment Methods of Recycled Concrete Aggregate on Behavior of High Strength Concrete

Worldwide the concrete industry has started embracing the utilization of recycled concrete aggregates (RCAs) resulting from demolition and construction waste as full or partial substituents in the production of high-strength concrete (HSC) due to their economic and environmental benefits. Several parameters were experimentally investigated in this study. The first parameter analyzed the effect of replacing varying percentages of coarse aggregate with recycled aggregate. The second parameter examined the influence of two aggregate sizes (10 and 20 mm). The third parameter was intended for investigating the influence of three different RCA treatment methods utilizing sodium silicate immersion, cement slurry, and the Los Angeles (LA) abrasion simulation. The test results generally indicated degradation in the engineering properties of concrete produced using untreated RCA compared to the control. The degree of reduction increased as the replacement percentage was increased regardless of the aggregate size. The reduction in compressive strength appeared to have a more pronounced effect in comparison to the splitting tensile strength. The use of treated RCA improved concrete slump by 15–35%. This also caused enhancement in the engineering properties, especially for the LA abrasion mechanical treatment, which was very promising for both aggregate sizes. In comparison with the untreated RCA, the relative enhancement in water absorption was up to 76%, whereas splitting tensile and compressive strengths increased by 3–50% and 5–60%, respectively.

Impact Assessment of Pozzolanic Material Coupled with River Bed Aggregate on Expansive Behavior of High Strength Concrete

High strength concrete is widely used in engineering structures. Present work is an effort for suitability assessment of river bed aggregates in high strength concrete to be used at structural units of Dam (Spillway & Powerhouse) and the vulnerability of placed concrete expansion. Multiple sizes of coarse aggregate (5-20mm, 20-40mm, and 40-80mm) from Beor river bed material have been tested for physical (water absorption, crushing index, soundness, shape, and bulk density), and mineralogical characterization. Concrete Mix Design (CMD) for Spillway has been optimized using Fly ash and river aggregate that achieved the Unconfined Compressional Strength (UCS) up to 32.5 MPa. The accelerated mortar bar test (AMBT) has been introduced to gauge the reactive aggregates used in CMD.. Expansive properties of concrete were observed at the age of 7 days and 28 days that demonstrate more expansion of the specimen with slag rather than the Fly ash. Results of AMBT suggest that a minimum proportion of GGBS (40%) is needed to limit the AMBT expansion to less than 0.1% for crushed river bed aggregate and sand from the Beor source. The petrographical characterization of coarse aggregate shows the presence of deformed quartz in the coarse aggregate, which directly relates to water absorption (Wa), suggesting its suceseptility to Alkali-Silica Reaction (ASR). Modifications in Pozzolanic additives in CMD indicates that 30% mixing of Fly ash can reduce the expansion rate of concrete up to 96.15%.

Influence of Moisture Content and Wet Environment on the Fatigue Behaviour of High-Strength Concrete.

The influence of a wet environment on the fatigue behaviour of high-strength concrete has become more important in recent years with the expansion of offshore wind energy systems. According to the few investigations documented in the literature, the fatigue resistance of specimens submerged in water is significantly lower compared to that of specimens in dry conditions. However, it is still not clear how the wet environment and the moisture content in concrete influence its fatigue behaviour and which damage mechanisms are involved in the deterioration process. Here the results of a joint project are reported, in which the impact of moisture content in concrete on fatigue deterioration are investigated experimentally and numerically. Aside from the number of cycles to failure, the development of stiffness and acoustic emission (AE) hits are analysed as damage inductors and discussed along with results of microstructural investigations to provide insights into the degradation mechanisms. Subsequently, an efficient numeric modelling approach to water-induced fatigue damage is presented. The results of the fatigue tests show an accelerated degradation behaviour with increasing moisture content of the concrete. Further, it was found that the AE hits of specimens submerged in water occur exclusively close to the minimum stress level in contrast to specimens subjected to dry conditions, which means that additional damage mechanisms are acting with increasing moisture content in the concrete.

Experimental Shear Study on Reinforced High Strength Concrete Beams Made Using Blended Cement

With the increased application of High Strength Concrete (HSC) inconstruction and lack of proper guidelines for structural design in India,behavioral study of high strength concrete is an important aspect ofresearch. Research on the behavior of HSC reinforced beams with concretestrength more than 60 MPa has been carried out in the past and is stillcontinuing to understand the structural behavior of HSC beams. Along withthe many benefits of the high strength concrete, the more brittle behavior isof concern which leads to sudden failure. This paper presents the behaviorof reinforced HSC beams in shear with considering the effects of variousfactors like shear reinforcement ratio, longitudinal reinforcement ratio, l/dratio (length to depth ratio), etc. Ten numbers Reinforced Concrete Beamsof various sizes using concrete mix with three different w/c ratios (0.46, 0.26and 0.21) were cast for shear strength assessment. The beams were tested insimply supported condition over two fixed steel pedestals with load rate of0.2 mm/minute in displacement control. Mid-point deflection was measuredusing LVDT. A comparative analysis of theoretical approaches of Eurocode, extension of current IS code up to M90 and the experimental datawas done to understand the behavior of beams. Shear capacities of beamswithout any factors of safety were used to assess the actual capacities andthen was compared with the experimental capacity obtained. Results ofthis study can be used in the design of high strength concrete and will bemore reliable in Indian continent as the regional materials and exposureconditions were considered.

Compressive Fatigue Behaviour of High-Strength Concrete and Mortar: Experimental Investigations and Computational Modelling.

A high-strength concrete and mortar subjected to compressive fatigue loading were comparatively investigated using experimental and computational techniques. The focus of the investigations was on the influence of the coarse aggregate in high-strength concrete. Accordingly, the fatigue behaviour was analysed experimentally using the macroscopic damage indicators strain, stiffness and acoustic emission hits. The results clearly show differences in the fatigue behaviour between the concrete and the mortar, especially at the lower stress level investigated. The basalt coarse aggregate here improves the fatigue behaviour of the concrete. Indication of a negative effect can be seen at the higher stress level. A finite element approach with a gradient-enhanced equivalent strain-based damage model combined with a fatigue model was used for the computational simulation of the fatigue behaviour. The damage model includes a differentiation between tension and compression. The fatigue model follows the assumption of the reduction in the material strength based on the accumulated gradient-enhanced equivalent strains. A random distribution of spherically shaped basalt aggregates following a given particle size distribution curve is used for the simulation of concrete. The comparison of the experimentally and computationally determined strain developments of the concrete and mortar shows very good agreement.

A comparative assessment of strength and fracture performance of alccofine and fly ash blended high performance concrete

The present study compares fracture behavior of high strength concrete (HSC) developed with high calcium fly ash (FC) and Alccofine (AL) as mineral admixtures. For the HSC mixes developed, proportion of mineral admixtures is maintained at 20% of ordinary Portland cement (OPC) whereas the water binder ratio is maintained at 0.26. The dosage of chemical admixture at 2% is adopted to achieve flow values in the range of 150–200 mm. The compressive strength at 7 and 28 days for blended mixes of FC (i.e., FC-HSC) and AL (i.e., AL-HSC) is compared with the control specimen strength. The observed results suggest comparable compressive strength for AL-HSC and FC-HSC. The control specimen strength is lower and was not further explored for fracture studies. The fracture behavior of the blended HSC mixes is then studied by comparing load-CMOD response of FC-HSC and AL-HSC specimens at 28 days. The fracture behavior of AL- HSC exhibits higher peak load and initial stiffness while FC-HSC exhibits higher post-peak ductility. The observed response is further analyzed to evaluate fracture parameters namely stress intensity factor (KIC), fracture energy (GF) and critical crack length (acr). The results indicate higher elastic modulus and KIC for AL-HSC while GF and acr is higher for FC-HSC.

Influence of industrial wastes on the mechanical and durability characteristics of high strength concrete

In this paper, the possibility of using granite powder and bottom ash in high strength concrete mix is evaluated. Phase composition and microstructure of the aggregate are reported using X-ray diffraction and scanning electron microscopy, respectively. The laboratory investigation focuses on addressing the impact of different combinations of wastes (0% to 40%) on fresh and hardened state behaviour of high strength concrete at different ages and exposure conditions. Even though the inclusion of these wastes individually in concrete showed detrimental effects on strength properties, the waste in combination did not show significant influence on mechanical and durability parameters.

Empirical equation and experimental validation of shear parameters for high strength concrete (HSC)

With many benefits of the high strength concrete (HSC) the more brittle behaviour that leads to sudden failure makes it important for proper understanding of its behaviour and safe and efficient estimation of capacities. Research on the behaviour of HSC has been extensively carried out since last decade. HSC has higher tensile strength hence a higher cracking shear can be expected. This paper analyzes the different international standards available for estimating concrete’s component of shear strength for reinforced cement concrete (RCC) beam. Different important factors mainly strength in compression, steel reinforcement (dowel action), ratio of shear span and depth, size effect i.e. depth along with the aggregate type (density of concrete) contributing to shear stress (Tc) of concrete has been also analyzed and thereafter, an equation has been proposed to compute or predict Tc value for concrete of both normal and higher grade or strength. The proposed equation has been validated by experimental results wherein 12 RCC beams (with and without reinforcement for shear) were cast and tested to fail in shear. The experimental results validated the proposed equation with considerable factor of safety keeping in view the sudden and brittle nature of failure in concrete in case of shear.