Use Of High Strength Concrete Research Articles

Experimental study on creep behavior of high-strength concrete filled steel tubular (HSCFST) columns

The use of High Strength Concrete Filled Steel Tube (HSCFST) members has become widespread, but there is limited research on their creep behavior. This study examines the creep and shrinkage characteristics of HSCFST columns subjected to axial loading by testing fifteen specimens with various steel ratios over a period of 365 days. The experimental data is then compared to the predictions made by the creep prediction models MC 90, ACI 209, and AFREM. The results indicate that the creep coefficients of HSCFST specimens are significantly lower than those of plain concrete specimens. By the end of 365 days, the creep coefficient of plain concrete is more than twice that of concrete in HSCFST. The steel ratio has a slight effect on the creep of CFST specimens, with the creep coefficient decreasing as the steel ratio increases. The comparison of the results shows that the MC 90 and ACI 209 models overestimate the creep of concrete, while the AFREM model underestimates it. Furthermore, the ACI 209 model is modified based on the experimental results by applying a correction factor of concrete strength, which significantly improves its accuracy and makes it suitable for predicting the creep of high strength plain concrete and HSCFST.

A Parametric Study on Fibre Reinforced Concrete

Abstract: The investigation is focused to study the effect of various types of fibres on compressive strength, split tensile strength and flexural strength of High strength concrete. The water to cementitious material ratio considered for the study of High strength concrete was 0.25. The content of silica fume and fly ash in every mix was 5% and 10% by the weight of cementitious material. Two types of fibres considered for the study include, Polypropylene Fibres (PF) and Flat Steel Fibres (FSF). Dosage of fibre was varied from 0.5% to 4% at an interval of 0.5% by weight of cementitious material. Type of cement, fine aggregate, coarse aggregate, type of Superplasticizer and its dosage are kept constant in every mix. The use of High Strength Concrete (HSC) is increased now a days. It is observed that HSC relatively brittle material. Fibres are added to improve its ductility. Experimental study is carried out to assess mechanical properties of high strength concrete (HSC) of grade M70.

Experimental investigation on axial local compressive behavior of square concrete-filled double tubular stub columns

This paper investigated local compressive behavior of square concrete-filled double tubular (CFDT) specimens. A total of twenty-nine specimens were tested under axial local compression to study the influence of the inner tube, bearing block shape, local compression area ratio, outer steel tube thickness, concrete strength, and steel strength on the local compressive bearing capacity of specimens. The working mechanism of CFDT under local compression was analyzed. The results show CFDT specimens exhibit superior bearing capacity and ductility, compared to conventional CFST specimens. The larger confinement effect coefficient ξ or local compression area ratio β can delay the appearance of the descending stage of N - Δ curve and improve the ductility of the specimen. The increasing degree of bearing capacity is related to β. When β = 2.25, the most effective measure is to increase the thickness of the outer tube, up to 36.8 %. When β = 9, the use of high-strength concrete is more conducive to improving the bearing capacity, up to 21.8 %. The shape of bearing block has little effect on the bearing capacity. In addition, finite element model was established and analyzed based on experimental results, reasonably agreement was obtained between numerical and measured results. An evaluation method for calculating the local bearing capacity were proposed, which showed good consistency with experimental results.

Serviceability behavior of High Strength Concrete I-beams reinforced with Carbon Fiber Reinforced Polymer bars

Fiber Reinforced Polymer (FRP) bars are anisotropic in nature and have high tensile strength in the fiber direction. The use of High-Strength Concrete (HSC) allows for better use of the high-strength properties of FRP bars. The mechanical properties of FRP bars can yield to large crack widths and deflections. As a result, the design of concrete elements reinforced with FRP materials is often governed by the Serviceability Limit States (SLS). This study investigates the short-term serviceability behavior of FRP RC I-beams. Eight RC I-beams reinforced with carbon-FRP (CFRP) and four steel RC I-beams, for comparison purposes, were tested under two-point loading. Deformations on the concrete and crack widths and spacing are measured and analyzed. A discussion on the main aspects of the SLS of FRP RC is introduced. The service load that fulfills the serviceability requirements, at a cross-section level, ranges between 0.27 and 0.38 times the ultimate load for sections dimensioned to fail in concrete crushing. The determinant criterion is the deflection limitation

Ultrahigh Performance of Concrete using Manufactured Sand

The resistance and durability of concrete structures can be improved by using ultra-high performance concrete (UHPC). A crucial component of energy conservation and concrete cost reduction is the use of locally available materials. In this study, the effects of a common type of locally accessible manufactured sand (MS) on the characteristics of UHPC were investigated from both a physical and chemical standpoint. The main objective of the current study is to use locally available materials to create a UHPC with a compressive strength of 100MPa. The impact of fine materials, binder type and content, mixer type, steel fibres, and curing regimes on the concrete’s compressive strength was examined in this study. The use of high strength concrete has various benefits, including a reduction in the size of beams and columns and an increase in the height of buildings with multiple stories. In recent years, high strength concrete has seen increased use in civil engineering. By minimising non-homogeneity, porosity, and micro-cracks in the concrete and its zone of transition, high strength is made achievable. Super plasticizers and additional cementing substances such granulated blast furnace slag, silica fume, and natural pozzolana can be used to achieve it. Concrete with a high modulus of elasticity is strong. On cement, fine aggregate, and coarse aggregate, preliminary studies have been conducted. In the current study, 920KK is employed as a chemical admixture and silica fume is used as a mineral admixture. For M100 concrete, the w/c ratio is taken to be 0.25. The mix proportion for M100 grade concrete can be calculated by following the design process suggested by the ACI Method as 1:0.454:1.527.

Behavior and design-oriented model for elliptical FRP-confined concrete under axial compression

Elliptical fiber-reinforced polymer (FRP)-confined concrete members have gained increasing attention due to their aesthetical characteristics and structural efficiency. This paper investigated the behavior of 24 elliptical FRP-confined concrete stub columns under axial compression. Effects of the amount of FRP confinement, the cross-sectional aspect ratio, and the use of high-strength concrete were discussed. The test results indicated that the stress and strain capacities of the confined concrete were enhanced with the increasing amount of FRP confinement. By contrast, the increasing sectional aspect ratio and the use of high-strength concrete had an adverse effect on the inner concrete’s axial behavior due to the increasingly non-uniform distribution of FRP confining pressure. In general, the typical stress–strain curves of elliptical FRP-confined concrete were categorized into four types. Furthermore, using the concept of equivalent diameter, the threshold for sufficient confinement of elliptical FRP-confined concrete was determined by the equivalent confinement stiffness ratio to ensure an overall ascending behavior. After addressing some key issues, a design-oriented model for elliptical FRP-confined concrete with a relatively wider range of concrete strength (from 32.6 to 72.4 MPa) was developed herein with more satisfactory accuracy than existing models. This model with a simple form could be naturally reduced to a widely accepted model for FRP-confined concrete with circular sections.

The Effect of Using White Sand As Material High Quality Concrete Mix

The use of concrete in Indonesia cannot be separated from skyscrapers, bridges with long spans, and underground buildings which generally have a larger load, so the use of high-strength concrete is necessary. This study aims to determine the value of compressive strength, split tensile strength, flexural strength, modulus of elasticity of concrete and determine the workability of fresh concrete with the addition of 0.8% superplaticizer. The test objects used in the form of cylinders with a diameter of 15 cm and a height of 30 cm as many as 15 pieces, and 3 pieces of blocks measuring 15 cm × 15 cm × 60 cm. From the results of the study, the compressive strength value was 43,007 MPa. The split tensile strength test is 3.584 MPa. The flexural strength test is 4,340 MPa. The elastic modulus test is 28447.956 MPa. From the slump test on fresh concrete with the addition of a superplaticizer, it is obtained by 10 cm.

Sensitivity of lateral impact response of RC columns reinforced with GFRP bars and stirrups to concrete strength and reinforcement ratio

This is the first study in the literature which experimentally and numerically investigates the impact behavior of concrete columns reinforced with fiber-reinforced polymer (FRP) reinforcements. The effect of concrete strength (50 MPa vs 100 MPa) and longitudinal FRP ratio on the lateral impact response of the columns was investigated. The experimental results showed that the longitudinal reinforcement ratio strongly affected the failure modes and impact-resistant capacity while the use of high strength concrete (HSC) did not effectively improve the performance of the columns, which on the contrary, might have caused spalling failure due to its brittleness. The peak impact force and displacement of the columns increased linearly with the impact velocity up to their maximum capacity. The longitudinal reinforcement ratio slightly affected the peak impact forces while the concrete strength showed marginal variation. The use of HSC did not effectively reduce the maximum displacement of the columns. The energy absorption of the columns and the impact velocity exhibited an approximately linear relationship regardless of the reinforcement ratio and concrete strength. Different from the static case, the numerical results show three critical sections, i.e. at the impact location and column ends, which need to be carefully designed.

Seismic performance of low-rise building using graded concrete as flexural elements

Graded concrete is a material innovation in the field of civil engineering that aims to create environmentally friendly and economical construction materials. Previous research has shown that graded concrete increases material rigidity so that graded concrete can increase the level of serviceability of structures, indicated by the decreasing of deflection. Investigations on the performance of structures using graded concrete as building material need to be studied further with broader structural indicators. Further studies related to structural performance including base shear reactions, fundamental periods, storey stiffness, storey drift, and storey displacement, should also be discussed. In this study, a 3-storey residential building is modelled using ETABS in 3D approach. The effect of disparity in concrete strength on structural performance is examined. The buildings that employ graded concrete as a construction material can offer a better level of occupant comfort due to the lesser vibration period generated. The application of graded concrete in beam components can increase the value of the storey stiffness. It is because of the greater the modulus of elasticity, the greater the stiffness produced by the beam. It increases the confinement of the enclosed plate so that the stiffness of the building floor also increases. The use of high strength concrete in the beams will change the mode shape of the structure from flexure to shear type. In shear mode shape, the column will form a double curvature so that the mode shape of the structure tends to form a convex pattern. The benefit of the shear-type mode shape is the lesser value of storey displacement at the top level.

Experimental study on cracking behavior of steel fiber-reinforced concrete beams with BFRP bars under repeated loading

This study aimed to investigate the feasibility of using steel fibers to control crack spacing and width for concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars under repeated loading. Four-point bending tests were performed on 11 concrete beams reinforced with BFRP bars having various concrete strength grades, BFRP reinforcement ratios, steel fiber volume ratios, and steel fiber shapes. The flexural strength, cracking moment, crack propagation, crack spacing, and crack width of the beams were obtained from experiment, among which the cracking moment, crack spacing, and crack width were compared with their counterpart predicted from analytical models in various codes and literature. Compared with concrete beams reinforced with BFRP bars but without steel fibers, steel fiber-reinforced concrete (SFRC) beams with BFRP bars exhibited a higher cracking resistance, higher cracking moment and flexural strength, and smaller crack spacing and width. The use of high-strength concrete increased cracking moment and reduced crack width and spacing; however, the BFRP reinforcement ratio only affected crack width and spacing but does not affect cracking moment. The ACI 400.1R-15, CAS S806-12, and Chinese national standard GB 50608-2010 codes all underestimated the cracking moment of SFRC beams with BFRP bars but overestimated the crack width. Finally, a series of new analytical models based on the tensile constitutive law of SFRC were developed for the cracking moment, crack spacing, and crack width and validated by experimental results that they performed better than their counterparts in ACI 400.1R-15 and CAS S806-12 codes.

Reassessment of the flexural behavior of high-strength reinforced concrete beams under short-term loads

This work aims at describing the behavior of high-strength reinforced concrete (HSRC) beams under short-term ultimate loads with concrete compressive strengths higher than 50 MPa. A plastic approach besides a cross sectional analysis is employed to primarily trace the nonlinear response of nineteen HSRC simply supported beams for which experimental results are available. This proposed theoretical approach is able to acceptably match the experimental data with minor overestimation of flexural moments. Closed-form expressions to evaluate ductility indexes regarding deflections and curvatures as well as plastic rotation capacities are also proposed herein. Predictions of the National Brazilian Regulation for design of concrete structures NBR6118 in terms of ultimate flexural moments are also computed for comparison. A complete assessment of ductility in which plastic rotation capacities are computed for the studied beams is also given. It is found that the flexural ductility of a member could be increased with the use of high strength concrete. The use of a maximum tension steel ratio to guarantee a minimum flexural of ductility is highlighted.

Effect of steel tube thickness on the behaviour of CFST columns: Experimental tests and design assessment

In this paper, the results of experimental tests conducted on concrete-filled steel tubular (CFST) columns are presented. There is currently a deficit of data available that can be used to evaluate current guidance documents and provide assessment to improve their accuracy when considering the behaviour of CFST columns filled with high strength concrete. Thus, this paper aims to increase the volume of experimental data available with a series of groups of tests on stub CFST columns subject to axial compression. Among the specimens of the same group only one dimension changes, the steel tube thickness. The columns are filled with both normal and high strength concrete for comparison purposes. The use of high strength concrete in circular tubes increases the concrete contribution, but this effect does not fulfil in rectangular specimens where also the confinement is less effective than in circular CFST even when the former have thin steel tubes and high strength concrete. The specifications of four commonly used codes are discussed. Comparison of their predictions with the experimental data collected shows that AISC is conservative but EC4, DBJ and AS produce similar non-conservative predictions.

Influence of Nano Particles in the Flexural Behavior of High-Strength Reinforced Concrete Beams

High strength concrete (HSC) characterized by high compressive strength but lower ductility compared to normal strength concrete. This low ductility limits the benefit of using HSC in building safe structures. Nanomaterials have gained increased attention because of their improvement of mechanical properties of concrete. In this paper we present an experimental study of the flexural behavior of reinforced beams composed of high-strength concrete and nanomaterials. Eight simply supported rectangular beams were fabricated with identical geometries and reinforcements, and then tested under two third-point loads. The study investigated the concrete compressive strength (50 and 75 N/mm2) as a function of the type of nanomaterial (nanosilica, nanotitanium and nanosilica/nanotitanium hybrid) and the nanomaterial concentration (0%, 0.5% and 1.0%). The experimental results showed that nano particles can be very effective in improving compressive and tensile strength of HSC, nanotitanium is more effective than nanosilica in compressive strength. Also, binary usage of hybrid mixture (nanosilica + nanotitanium) had a remarkable improvement appearing in compressive and tensile strength than using the same percentage of single type of nanomaterials used separately. The reduction in flexural ductility due to the use of higher strength concrete can be compensated by adding nanomaterials. The percentage of concentration, concrete grade and the type of nanomaterials, could predominantly affect the flexural behavior of HSRC beams.

Modified high-strength concrete with the addition of CONPLAST SP430

In most high-strength concrete technologies, high-quality Portland cements are used, which is not always achievable in conditions of a shortage of such binders. The research’s purpose is to obtain high-strength concrete based on ordinary Portland cement of the M400 brand. To achieve this goal, the possibility of using the superplasticizer Conplast SP430 was studied. The research was carried out using standard methods, like using mathematical planning and result’s analytical processing. The implementation of the experiment allowed us to determine the optimal values of the basic composition of concrete: the consumption of superplasticizer-1.0 % of the mass of cement; the consumption of cement-485 kg/m3, the ratio of sand/crushed stone-0.36. At the optimal value of the parameters, the achieved maximum compressive strength was 58.8 MPa. The novelty is the justification of the possibility of obtaining high-strength concretes using Portland cement with an activity not exceeding 40 MPa based on the use of a new generation superplasticizer and the development of the basics of the method for selecting the composition of concrete. The significance of the result is due to the expansion of the possibility of using ordinary Portland cement for the production of products and structures with the use of high-strength concrete.

Rational Use of High-Strength Concrete in Flat Slab- Column Connections under Seismic Loading

Rational Use of High-Strength Concrete in Flat Slab- Column Connections under Seismic Loading

Compressive behavior of FRP-confined steel-reinforced high strength concrete columns

Few studies have prospectively examined the axial compressive behavior of FRP-confined steel-reinforced concrete (FCSRC) columns employing high strength concrete (HSC) with a compressive cylinder strength up to 120 MPa. In FCSRC columns, the encased steel sections would ensure a ductile response under the large axial deformation and provide additionally axial and shear load-carrying capacities. Therefore, the FCSRC column with HSC is a promising type of hybrid structural element that enables effective utilization of both HSC and high-performance FRP. In this study, a comprehensive experimental study has been conducted to evaluate the compressive performance of FCSRC columns with HSC, considering the effects of steel section shape and thickness of FRP tube. For comparison purpose, the compressive behaviors of FCSRC columns using normal strength concrete (NSC), concrete-filled FRP tubes (CFFTs), and steel-reinforced concrete (SRC) columns were also investigated. The load and deformation capacities, dilation behaviors, failure modes and failure mechanism, composite effect between constituent materials, and enhancement effect of FRP confinement on SRC columns were discussed in this paper. This study revealed that the use of HSC produced higher axial stiffness as well as higher axial compressive capacity for the FCSRC columns, although the deformation capacity was reduced as compared to the use of NSC.

Modified strip model for punching-shear strength of FRP-reinforced concrete edge–column slab connections

The use of fiber-reinforced polymer (FRP) bars as internal reinforcement for concrete structures in aggressive environments has emerged as an innovative solution to eliminate corrosion problems. Glass FRP (GFRP) reinforcing bars have recently gained wide acceptance as a viable construction material for sustainable new constructions due to their costing less than other FRP types. This paper reports the test results for full-sized edge–column slab connections (ECS –connections) reinforced with sand coated GFRP bars. These connections were cast using normal-strength concrete (NSC) and high strength concrete (HSC). The effect of concrete strength (NSC and HSC) and moment-to-shear force ratio (M/V) (300 mm, 600 mm) on the performance of the tested connections were examined. In addition, a new mechanical model, called Modified Strip Model, is presented for punching-shear strength predictions of FRP reinforced concrete (RC) ECS –connections. The test results reveal that the use of HSC directly augmented the punching-shear strength and improved the load–deflection response of the tested connections, However, Increasing the M/V ratio produced significant shear stresses, thus decreasing the punching-shear strength for the NSC and HSC connections, respectively. The mechanical model presented herein takes into account all possible mechanisms of loads transfer in FRP-RC ECS-connections. Hence, a complete shear–moment (V-M) interaction diagram can be plotted to predict the punching strength of such connections. Moreover, the model revealed higher accuracy and narrower scatter for punching-shear strength predictions compared to other available equations in FRP design codes and guides. The EN 1992–1-1–05 punching-shear equation was also examined for FRP-RC ECS–connections and adapted to consider the tensile properties of the FRP bars instead of steel.

3D non-linear finite element analysis of concentrically loaded high strength reinforced concrete column with GFRP bar

The use of High Strength Concrete (HSC) material in Reinforced Concrete (RC) column has become widely used. HSC was found to be durable, strong in compression, but it has low ductility. This low ductility of HSC can be improved by providing confinement. However, for HSC with concrete strength higher than 70 MPa, additional clause for confinement in ACI 318-19 generates denser arrangement of transverse bars and eventually creates weak planes between the concrete core and the cover. These weak planes can trigger early cover spalling. To reduce the utilization of confining bars, high-strength Glass Fiber Reinforce Polymer (GFRP) bar can be used. However, the performance of GFRP bar varies significantly from their uniaxial behavior in tension or compression to the real performance when it is used as the main reinforcement. For that reason, this paper tries to investigate the behavior of HSC RC column with bars made of conventional steel rebar and with GFRP bars. Due to limited data on the strain gauge reading on the GFRP bars from the available test result, an inverse analysis is carried out to determine the best stress-strain curve for GFRP bars used as the main reinforcement. For that purpose, an inhouse finite element package called 3D-NLFEA is used. From the comparisons, it was found out that the peak load, softening behavior, and the concrete core enhancement prediction agrees well with the test result. From the inverse analysis, only 25% and 45% of the GFRP bar yield strength can be deployed when loaded under compression and tension, respectively.

Corrosion protection of reinforcing steel reinforced concrete structures of transport structures

The influence of reinforcing steel corrosion on the durability of reinforced concrete structures of transport structures and the degree of knowledge of this problem is considered. It is specified that the protection of reinforcing steel from corrosion is not able to completely replace the correct design and use of high-strength concrete. But it is able to extend the life of reinforced concrete structures. It is noted that corrosion of the reinforcement leads to a decrease in the structural strength due to wear and tear and by a third of the period of operation of reinforced concrete structures, as a result of which transport structures collapse. As an example of the detrimental effect of corrosion of reinforcing steel on the durability of transport structures, examples of accidents of bridges and overpasses caused by this type of corrosion are given. As a result, a conclusion is drawn on the advisability of ensuring a sufficient level of corrosion protection of reinforcing steel to achieve the required durability of reinforced concrete structures of transport structures. The types and causes of corrosion processes in reinforcing steel reinforced concrete structures are described. The compositions and technologies of anticorrosive protection are examined and analyzed. Comparison of the compositions of anticorrosive protection of reinforced concrete structures is carried out according to the following criteria: consumption, density, viability, curing temperature and the number of components of the composition. A comparison of anti-corrosion protection technologies is carried out on the basis of the following indicators: line dimensions, productivity and consumption of energy resources. A comparison is also made of the cost of using various anti-corrosion protection technologies. Based on the data obtained, the advantages and disadvantages of the considered compositions and technologies of corrosion protection are determined. As a result, the most effective and technologically advanced method of corrosion protection of steel reinforcement of reinforced concrete structures of transport structures is selected.

Minimizing environmental impact from optimized sizing of reinforced concrete elements

The construction field must always explore sustainable ways of using its raw materials. Studying the environmental impact generated by reinforced concrete raw materials during their production and transportation can contribute to reducing this impact. This paper initially presents the carbon dioxide emissions from reinforced concrete raw materials, quantified per kilo of raw material and per cubic meter of concrete with different characteristic strengths, for southern Brazil. Subsequently, reinforced concrete elements were optimized to minimize their environmental impact and cost. It was observed that lower values of carbon dioxide emissions and cost savings are generated for less resistant concrete when the structural element is a beam, and that reductions in the cross section dimensions of the beams, sized based on the use of higher strength concrete, may not compensate for the increased environmental impact and costs. For the columns, the behavior differed, presenting lower values of carbon dioxide emissions and costs for higher concrete strengths. The proposed methodology, as well as the results obtained, can be used to support structural projects that have less impact on the environment.