High Concrete Compressive Strength Research Articles

Experimental study of bond-slip relationships in high-performance self-consolidating concrete with plain steel bars

Self-consolidating concrete is being used more frequently in structures with high density of reinforcement bars or prestressing strands therefore, it is important to carefully consider whether bond stress-slip relations defined for normal strength concrete can be safely applied to high-strength and self-consolidating concrete. This paper aims to investigate the bond behaviour between plain steel bars and high-performance self-consolidating concrete, with a focus on studying the effect of embedment length and concrete compressive strength on bonding performance. The main parameters that were tested are the active bonded length and the compressive strength of the concrete. The value of adhesive bond stress is discussed, as a factor in determining whether the bar slips against the adhering concrete. Based on the results, it can be observed that the maximum bond stress tends to increase with higher concrete compressive strength, while it decreases with longer embedment length of plain steel bar. Conversely, the adhesive bond tends to increase with longer embedment length and higher concrete compressive strength. The experimental investigations indicate that the bond strength increases proportionally to the square root of the compressive strength of concrete, regardless of the concrete compressive strength. Furthermore, a new bond stress-slip model has been analyzed, which takes into account the initial bond strength (adhesive bond) and the lower convex property to predict the post-peak branch. The model has been compared to the test results, and good agreement has been achieved.

High strength concrete compressive strength prediction using an evolutionary computational intelligence algorithm

High strength concrete compressive strength prediction using an evolutionary computational intelligence algorithm

Numerical investigation on dynamic response of air-backed RC slabs subjected to close-in underwater explosion

With the increase of global terrorism, the marine reinforced concrete (RC) structures (e.g. immersed tunnels, caisson wharfs and floating platforms, etc.) inevitably face the potential threat of underwater explosion during their services. However, there are few studies to date that have investigated the RC slabs subjected to underwater explosion and further studies on this subject are warranted. This study focuses on the dynamic response analysis and damage modes prediction of air-backed RC slabs under close-in underwater explosion. Firstly, two experiments and several empirical formulas were used to verify the correctness of the underwater explosion load and the RC material model, respectively, with error of less than 4% for most parameters. Secondly, a 3-Dimensional finite element model of air-backed RC slab was established in LS-DYNA. The different parameters analysis indicated that the dynamic response of RC slabs increases with the increase of charge weight or the decrease of standoff distance, both high reinforcement ratio and high concrete compressive strength can effectively improve the blast-resistance ability of RC slabs. After that, four damage modes of air-backed RC slabs were identified based on the support rotation angle, including slight (≤2°), medium (2°–6°), severe (6°–12°) and fail (>12°), which mainly manifested as flexural failure to flexural shear failure. Finally, three empirical formulas were proposed to predict the damage modes of air-backed RC slabs within 2 m standoff distance and 0.2 kg charge weight.

Cyclic performance of exterior R.C beam-column strengthened with different thicknesses of CFRP sheets

The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the numerical cyclic performance of connection strengthened with different thicknesses of CFRP need to be well investigated. This study assessed the performance of RC exterior beam column connection strengthened with CFRP sheets First, two grades of concrete are utilized to be control specimens, normal concrete compressive strength (C20) and high concrete compressive strength (C50) then, the specimens are retrofitted with different thicknesses (1.2, 2.4, 3.6mm) of CFRP sheets. The stresses and damage states showed the importance of connection retrofitting. The CFRP shift the plastic hinge zone away from the panel zone. Furthermore, the results demonstrated that by increase of CFRP thickness the connection resistance will be improved. The comparison between the hysteresis curves demonstrated that the yield and ultimate loading were enhanced for strengthened connection for both concrete grades and the incremental in thicknesses also increase them. The outputs also exhibited that the stiffness and ductility has increased for retrofitted specimens indicating that the CFRP comprehensively overcome the applied cyclic loading and the beam column connection is able to resist such type of loading.

A review of tests on slab-column connections with advanced concrete materials

Advances in concrete technology during the last decades have resulted in the development of materials with enhanced mechanical properties, such as High Strength Concrete (HSC), Fibre Reinforced Concrete (FRC) and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The application of these materials in flat slabs, which are a popular structural solution in Reinforced Concrete (RC) buildings worldwide, has the potential of significantly reducing raw material consumption by enabling the design of slenderer and therefore lighter structures. However, flat slabs are susceptible to punching shear failure, which is a complex phenomenon that remains challenging, even though significant efforts have been made to experimentally study it. For advanced concrete materials (HSC, FRC and UHPFRC), the challenge is further accentuated by the continuous and rapid development of these materials. With the purpose of identifying and highlighting gaps in the published literature, a review of tests with HSC, FRC and UHPFRC slab-column connections in non-seismic and seismic loading applications is presented in this paper. It is shown that future research directions in this field include, among others, testing thicker slabs, HSC slabs with higher concrete compressive strength, HSC combined with FRC and several more cases related to seismic loading conditions.

Finite Element Modeling of High Strength Self-Compacting Concrete T-Beams under Flexural Load Reinforced by ARFP

A finite element models were constructed for comparison self-compacted concrete (SCC) T-beams to study a behavior change of these that reinforced with aramid fiber reinforced polymer (AFRP) and steel bars when compared with experimental data. Nine T-beam specimens reinforced with ARFP and three beams reinforced with steel bars were modeled and analyzed. The key variables were different high strength self-compacted concrete compressive strength, different ratios of AFRP and conventional steel bars for comparison. The comparison for output of flexural strain, load-deflection relationship and crack propagation are taken into consideration. The FE models by using (ANSYS) software show good agreement with the experimental data from previous study by (Yaseen, 2020). The numbers of cracks were reduced in all FE models while the final crack spacing was smaller than experimental samples by maintain the final deflection. Beams reinforced steel bars show better load capacity than those reinforced by AFRP. The FE models were stiffer than the experimental beams. The overall trend of analytical and experimental beam capacity vs reinforcement ratio, shows that the ANSYS response was conservative compared with experimental data of SCC AFRP reinforced beams.&nbsp

EFFECT OF SUBSTRATE PREPARATION ON THE LOAD-BEARING BEHAVIOR OF CFRP-CONFINED RC COLUMNS

The confinement of reinforced concrete (RC) columns with fiber reinforced polymer (FRP) jackets is an effective measure for the strengthening and retrofitting of existing structures. The jacket withstands the increasing lateral strains of the axially loaded column causing a three-dimensional stress state inside the concrete. In the result, a higher concrete compressive strength can be achieved. So far, extensive international research on FRP-confined concrete has been conducted, but there are still some open issues regarding the influence of different parameters on the load-bearing behavior. This paper is focusing on the effect of the substrate preparation on the maximum concrete strength and stress-strain behavior. Therefore, an experimental study of carbon fiber reinforced polymer (CFRP) confined concrete cylinders with various substrate conditions and preparation methods is presented. The results are compared with previous investigations and assessed accordingly. Furthermore, recommendations regarding the substrate preparation by current national codes and guidelines are specified and considered critically.

Behavior and new strength model of FRP square columns based on the FRP effective circumferential failure and the effective lateral confining pressure

This paper presents an experimental investigation of the effect of concrete compressive strength, strengthening ratio and corner radius on the behavior of small-scale square columns wrapped with carbon fiber-reinforced plastic (CFRP) materials. A total of 39 specimens (150 × 150 × 300 mm) wrapped with one, two, and three plies of CFRP wraps were tested. In addition to the FRP jacket thickness, the effect of three different concrete mixes and four cases of corner radius were examined. The effective circumferential CFRP failure strain and the effect of the effective lateral confining pressure were investigated. The obtained results show that the CFRP reinforced columns provide a significant increase in ultimate conditions (strength and ductility) compared to the case of the unconfined specimens. It can be seen that higher concrete compressive strength and lower strengthening ratio reduce the effect of confinement with CFRP material. The test results demonstrated that the corner radius ratio is in direct proportion to the increase in confined concrete strength. A new model is presented to predict the compressive axial strength and corresponding strain of CFRP-confined columns based on the effective lateral strain of FRP material.

Modeling NSM FRP strengthened RC beams under fatigue due to IC-debonding

This paper presents an analytical model proposed to predict the flexural fatigue behavior and fatigue life of reinforced concrete (RC) beams strengthened with near-surface mounted (NSM) fiber reinforced polymer (FRP) reinforcements subject to intermediate crack-induced debonding failure. In deriving this model, a trilinear behavior is assumed for the bond-slip relationship of FRP-concrete interface. Based on a model previously developed for strengthened beams under monotonic loading, the proposed fatigue model considers the fatigue bond heterogeneity by imposing a degradation law for the peak interfacial shear stress. Theoretical solutions to the flexural behavior throughout the fatigue life are obtained by imposing appropriate boundary conditions. The predicted fatigue life under debonding failure mode and flexural behavior (e.g., tensile strain of the NSM reinforcement) are further verified by comparisons with existing experimental data, where good agreement is reached. The subsequent parametric study shows that higher concrete compressive strength and bond strength of NSM improves the flexural behavior under fatigue and elongates the fatigue life. The diameter and Young’s modulus of the NSM reinforcement have insignificant effect on the fatigue flexural behavior.

A discrete micromechanical model for predicting HSC compressive strength based on a yield design approach

This paper presents a discrete micromechanical model for predicting high strength concrete compressive strength. A numerical model is proposed based on a Voronoï tessellation which represents concrete as a set of aggregates interacting within a cement matrix. A static yield design approach is conducted at the mesoscopic scale to determine the maximum bearable compressive stress. Then, an analytical model is derived based on the numerical results. The geometric and mechanical effects are decoupled enabling a micromechanical explanation of the maximum paste thickness and the aggregates’ size distribution effects on concrete compressive strength. Finally, the analytical model is calibrated and validated on experimental results taken from literature.

Mechanical Properties of HPC and Numerical Simulation of Mine Shaft under 3D Load

The mechanical properties of high-strength concrete was studied in the laboratory, and obtained a high strength concrete uniaxial compressive strength changes with curing period, found that low temperature curing C100 Poisson's ratio of concrete is 0.24, and elastic modulus reached about 52.5GPa. The test results are applied to the numerical calculation, established a separate type reinforced concrete wall, and the multiaxial loading the stress state is simulated, the research shows that it is applied to C100 reinforced concrete shaft lining under its own gravity and the surrounding soil earth pressure, the maximum effective stress are respectively 25MPa , and effective strain is 4E-4mm, structure of shaft wall failure caused by shear wall structure. Under the three state of compression, the strength of concrete is improved.

Performance of HSC columns under severe cyclic loading

Experimental and analytical results of seismic investigation of high strength reinforced concrete columns performance is summarized in this paper. Twelve cantilever columns with different sizes and concrete compressive strengths were tested. The column sizes were \(325\times 325\) mm, \(520\times 520\) mm and \(650\times 650\) mm for the small, medium and large scale specimens, respectively. Concrete compressive strength was 80, 130 and 180 MPa. All specimens were designed in accordance with the Japanese design guidelines. It was noticed that spalling of cover concrete was very brittle for specimens made of 180 MPa followed by a significant decrease in strength independently of the column size. It was also observed that, while concrete compressive strength increases, the drift corresponding to the peak load decreases as well as the ductility of the specimen. Curvature was much important for the small size than for the medium size columns. Specimens with high concrete compressive strength showed a higher equivalent viscous damping at all drift angles. An equation was proposed for predicting the moment-drift envelope curves for the medium and large scale columns knowing that of the small scale columns. Experimental moment-drift and axial strain-drift histories were well predicted using a fiber model developed by the authors.

BETON MUTU TINGGI TANPA PROSES PEMADATAN MANUAL

The need of the advanced infrastructure facilities, such as long-span concrete bridges , high-rise concrete buildings should be considered as the new concrete development. Improving the quality of concrete can be done with a material change or replacement of some materials with steel slag. The recent time many industry take a part in using waste material from Cilegon steel. In Indonesia, high quality concrete compressive strength can be achieved a maximum strength about 60 MPa. Concrete properties will decrease as a result of the added material strength of cement, aggregates, and the presence of pores. Water cement ratio reduction (w/r) and the addition of admixture as silicafume often used to modify the composition of the concrete and reduce pores. W/r reductions result in reduced porosity and the pores of the concrete, but workability concrete also be difficult to do. In order to make concrete workable the used superplastisizer is the best solution to do. Small water cement ratio 0.2 and superplasticizer intramix kind High Range water reduction at a dose of 1.8% can produce high-performance concrete. In the cement composition 1217kg, 243kg of water, sand 446kg, 545kg steel slag, superplasticizer silicafume 24l 85kg and obtained high quality concrete with compressive strength of 588.53 kg/cm2 in slump flow with the weight of 2230kg/m3 64mm. Principles of compaction without using a vibrator to use a substance without reducing the quality of the concrete risers. Small factors of w/r requires careful stirring using a saturated aggregate surface is helpful meaning in manufacture high quality concrete.
 
 Keyword : High Strength concrete, superplasticizer, steel slag, water cement ratio, slumpflow.

고로슬래그와 플라이애시 대체율이 80MPa 3성분계 고강도콘크리트의 재료물성에 미치는 영향

보통포틀랜드시멘트(OPC)와 고로슬래그 및 플라이애시 만으로 설계기준압축강도 80MPa의 3성분계 고강도콘크리트(이하 고강도콘크리트)를 개발하기 위하여, 고로슬래그와 플라이애시의 대체율이 고강도콘크리트의 경화전 후 재료물성 변화에 미치는 영향을 평가하였다. 고강도콘크리트의 경화전후 재료물성 평가결과, 고로슬래그와 플라이애시 대체율이 최대 30%까지 증가할수록 유동성과 장기강도가 우수한 것으로 나타났다. 또한 OPC만으로 제작된 시험체와 비교하여 길이변화 특성이 우수하며, 혼화재 사용에 따른 탄산화는 없는 것으로 나타났다. 고강도콘크리트 재료물성 평가결과, 고로슬래그 대체율 25%, 플라이애시 대체율 15%일 경우, 경화전 후 재료물성이 가장 우수한 것으로 나타났다. 이 연구결과는 향후 고가의 실리카퓸을 대체할 수 있는 고강도콘크리트의 개발에 유용하게 활용될 수 있을 것으로 기대된다. To develop 80MPa-high strength concrete with ternary cement used in OPC, blast-furnance slag, and fly ash, mixing ratio of blast-furnace slag and fly ash was evaluated in material characteristics before and after hardening of the high strength concrete. According to the evaluated results of material characteristics before and after hardening of the high strength concrete, the flowability and long-term compressive strength increase up to 30% mixing ratio of blast-furnace slag and fly ash. Also, it is superior to characteristics of length change and neutralization due to the use of mineral admixture when compared in test sample mixed with OPC. The evaluated results show that material characteristics of the high strength concrete was the most outstanding performance at blast-furnace slag of 25% and fly ash of 15%. The result of this study will be useful for the development of high strength concrete as a substitute of costly silica fume in the near future.

Shear stress distribution of flat-plate using Finite Element Analysis

ABSTRACT The development of a linear numerical model of flat-plate to predict shear stress distribution around slab column connection is presented in this paper. An attempt is made to model the slab, flexural reinforcement and shear reinforcement using three dimensional solid elements. The proposed finite element model has been proved to be capable of simulating the shear behavior of slab-column connection and to be suitable for analysis of structural performance of flat plate structures. Numerical results obtained from this model have good agreement with the available results of other researcher’s numerical model with one dimensional rebar element. Keywords: Flat plate, ABAQUS, shear reinforcement, slab-column connection. 1. Introduction Flat-plate slab system is widely adopted by engineers as it provides many advantages such as reduction of floor height, more spatial planning due to no beams present. These advantages further results in reduction in material cost. In the flat plate slab-column connection is always subjected to combination of high bending moments and shear stresses, which develop a punching, shear failure. This failure is undesirable as it occurs without warning and may lead to progressive collapse of slab. Due to large tensile stresses, the potential diagonal crack in the form of truncated cone or pyramid is formed around the column. The failure surface extends from bottom of the slab at the support, diagonally upward up to the top surface. The angle of inclination with the horizontal depends on slab reinforcement. Hence, designing of flat-plate requires a special attention for both strength and ductility when punching shear being consider. The punching shear capacity of the slab-column connection is affected by the size of the column, the depth of slab, flexural reinforcement and compressive strength of slab etc. The punching shear capacity can be increased by using a larger column diameter, larger effective depth, more flexural reinforcement, higher concrete compressive strength or by shear reinforcement. Among these methods, the most effective way to enhance the slab-column connection is to use shear reinforcement at the punching shear zone (ACI 421 R-99), which is permitted by most of the building codes. The provision of punching shear reinforcement in various forms help in increasing the shear and ductility of the concrete. The various forms of shear reinforcements include stirrups, shear studs, bend up bars, shear heads (placed above the column), etc. According to ACI 318-05, the shear strength is a function of compressive strength of concrete and geometrical condition. The provision given in EC2 also includes the size effect and the effect of the flexural reinforcement ratio. Allowable shear strength of concrete with shear reinforcement is calculated as 0.125 √f

Effects of Ratio of CFRP Plate Length to Shear Span and End Anchorage on Flexural Behavior of SCC RC Beams

The aim of this experimental investigation is to study the effect of the ratio of carbon fiber-reinforced polymer (CFRP) precured laminate length to shear span and different end plate anchorage systems on the flexural behavior of reinforced concrete (RC) beams cast with self-consolidating concrete (SCC). SCC with a grade of 54 MPa has been used throughout this research to ensure consistent high quality and high concrete compressive strength in all beams and to eliminate the need of any compaction. Ten RC beams strengthened with CFRP plate lengths to shear span ratio of 0, 25, 70, and 85% with and without end anchorages, were tested under monotonic loading. In particular, a single layer of U-wrap sheet and two layers of U-wrap sheets with one layer in the longitudinal direction and the other in the transverse direction were used as end anchorages (double wrap). The results were compared with each other and with those of the same test conducted on an unstrengthened control beam specimen. The load-deflection...

The structure behavior of reinforced concrete wing–wall under earthquake

Lately, the applications to structural and mechanical systems are extensively reported using new approaches such as fuzzy, neural network, genetic algorism, etc. Under the earthquake hazard, many retrofitting ways of construction were contributed to the study. This study was done to investigate the characteristics of wing-wall to be used on retrofitting some damaged buildings during the earthquake. It included two main parts: Firstly, one specimen was made with a single column, according to ACI-code with 20 × 20 cm section, 135 cm in length, 8 - 4# main bars and #3 size hoops, which are the main observation parts. In another, one set added wings to each side of the main column with a 10 cm thickness and width as 10, 20, 30 and 40 cm specimens, while another set with a 15 cm thickness and width as 10 and 20 cm specimens were made to find out how the thickness and width of these wings were influenced. Two higher concrete compressive strength specimens were made to find out how the concrete strength influences the specimen. In another, two specimens with higher steel ratio (ρ) were made to see the influence of the steel ratio on the specimen. Secondly, the characteristics of materials theoretically analyzed were used reasonably in finding the test results that simulated the construction elements under the attack of earthquake. The model characteristic of wing-wall, the effective height factor (K) of wing-wall, the relationship between the width of wing-wall and the width of column are found in this study. Finally, good agreements were obtained from these test results and the theoretical analysis. This shows that the study is reliable. Consequently, the wing-wall to be used on retrofit damage constructions is accommodation. Key words: Wing-wall, retrofit, effective factor, fuzzy, neural network, genetic algorism.

Cylinder or Cube: Strength Testing of 80 to 200 MPa (11.6 to 29 ksi) Ultra-High-Performance Fiber-Reinforced Concrete

Due to the need for cylinder end preparation and large testing machine capacity requirements, accurate very high strength concrete compressive strength determination is currently a difficult proposition. To determine whether ultra-high-performance fiber-reinforce concrete (UHPFRC) compressive strength in the 80 to 200 MPa (11.6 to 29 ksi) strength range can be reliably determined through use of alternate specimen types, an experimental program was conducted. Alongside 51, 70.7, and 100 mm (2, 2.78, and 4 in.) cube specimens, 51, 76, and 102 mm (2, 3, and 4 in.) cylinders were tested. Acceptable alternatives to the standard 102 mm (4 in.) cylinder specimen were found in the 70.7 and 102 mm (2.78 and 4 in.) cubes and the 76 mm (3 in.) cylinder. In situations where there is concern about machine capacity and/or cylinder end preparation, the 70.7 mm (2.78 in.) cube specimen is recommended.

Bond Properties of High-Strength Carbon Fiber-Reinforced Polymer Strands

Forty-eight pullout tests were conducted to examine the bond properties of high-strength carbon fiber-reinforced polymer (CFRP) strands in different bonding agents, including normal concrete, high-performance concrete, epoxy resin, and grout. The bond properties were examined through measurements of slippages and corresponding bond stresses for CFRP strands as well as steel strands for comparison purposes. Studies show that bond stresses reach a maximum when the slippages of high-strength CFRP strands range from 0.012 to 0.016 in. (0.3 to 0.4 mm), and for steel strands, the slippages are approximately 0.787 in. (20 mm). Bar diameters 0.492 to 0.598 in. (12.5 to 15.2 mm) of CFRP strands have a moderate influence on allowable bond strength. The higher concrete compressive strength develops higher bond strength. The allowable bond strength (determined at 0.03937 in. [1.0 mm] slippage) of CFRP strands is 1.3 to 1.4 times that of steel strands, whereas the maximum bond stresses of steel strands are 30 to 50% higher than that of CFRP strands. Although the maximum bond stresses in steel strands are higher than those in CFRP strands, they occur at large slips, which explains why the allowable bond stresses are lower. In addition, on the basis of experimental tests, bond stress versus slip models for high-strength CFRP strands and steel strands are proposed.

Influence of section depth on the structural behaviour of reinforced concrete continuous deep beams

Although the depth of reinforced concrete deep beams is much higher than that of slender beams, extensive existing tests on deep beams have focused on simply supported beams with a scaled depth below 600 mm. In the present paper, test results of 12 two-span reinforced concrete deep beams are reported. The main parameters investigated were the beam depth, which is varied from 400 mm to 720 mm, concrete compressive strength and shear span-to-overall depth ratio. All beams had the same longitudinal top and bottom reinforcement and no web reinforcement to assess the effect of changing the beam depth on the shear strength of such beams. All beams tested failed owing to a significant diagonal crack connecting the edges of the load and intermediate support plates. The influence of beam depth on shear strength was more pronounced on continuous deep beams than simple ones and on beams having higher concrete compressive strength. A numerical technique based on the upper bound analysis of the plasticity theory was developed to assess the load capacity of continuous deep beams. The influence of the beam depth was covered by the effectiveness factor of concrete in compression to cater for size effect. Comparisons between the total capacity from the proposed technique and that experimentally measured in the current investigation and elsewhere show good agreement, even though the section depth of beams is varied.