High Strength Concrete

This paper presents the development of simple semi-empirical formulae for the analysis of nominal flexural strength of high strength steel fiber reinforced concrete (HSFRC) beams. Such developed formulae were based on strain compatibility and equilibrium conditions for fully and partially HSFRC sections in joint with suitable idealized compression and tension stress blocks. The stress blocks were given by suitable empirical functions for the compressive and post-cracking strengths of HSFRC. The enhancement in compressive strength due to fibers inclusion is proposed as a function of concrete matrix strength and fiber reinforcing index. To account for the pullout resistance of fibers in tension, the post-cracking strength was evaluated as a function of fiber reinforcing index and bond strength. The fiber reinforcing index was considered as a function of volume content, aspect ratio, orientation and length efficiency factors of the fibers. In view of the degenerative nature of the pullout resistance of the fibers with the increase of crack width, a limit was placed on the useful tensile strain extent; depending on fiber length and crack spacing. It was found that there is a good agreement between the flexural strengths for HSFRC beams predicted by the proposed formulae and the experimental results reported in the literature, while the predicted flexural strengths as computed by ACI Committee (544) were very conservative. The parametric studies indicate that the nominal moment section capacity increases with the increase of fiber content and fiber aspect ratio.

The aim of this study is analyzing the self-healing capability of high strength concrete (M70) with nano silica and crystalline admixture in three types of environmental exposures i.e. water immersion, wet/dry cycles and water contact. The percentage replacements of cement with nano silica were 1%, 2%, 3% with addition of 1.1% crystalline admixture. The specimens were pre-cracked at 28 days in the range of 0.10-0.40mm and the time set for healing was 42 days. The result shows that all the mixes have considerable amount of closing ability and strength regaining capacity for all exposure conditions. The concrete with 2% nano silica and 1.1% crystalline admixture (CA) has complete crack closing ability and strength regaining capacity for water immersion and wet/dry cycle conditions.

In the present paper, a numerical and experimental study about creep and shrinkage behavior of a high strength self-compacting concrete is performed. Two new creep and shrinkage prediction models based on the comprehensive analysis on the available models of both conventional concrete and self-compacting concrete are proposed for high strength self-compacting concrete structures. In order to evaluate the predictability of the proposed models, an experimental program was carried out. A concrete which develops 60 MPa within 24 h was used to obtain experimental results. Several specimens were loaded: (i) at different ages and (ii) with different stress-to-strength ratios. Deformation in non-loaded specimens was also measured to assess shrinkage. All specimens were kept under constant stress during at least 600 days in a climatic chamber with temperature and relative humidity of 208C and 50%, respectively. Results showed that the new models were able to predict deformations with good ac...

This paper presents the results of a research work aimed to determine the efficiency of using different materials to increase the punching shear strength of slab-column connections. These materials are steel bars, and glass or carbon fiber reinforced polymers as shear reinforcement stirrups. Openings in reinforced concrete (RC) slabs are not commonly prescribed in design codes. Even when they are, they raise concerns regards to the size of the openings and the location of the applied loads. There are many developments in concrete technologies that have major impacts on structural systems. The main conclusions obtained from previous researches are also included in this paper.

Three types of concrete with compressive strengths of about 45, 80 and 100 MPa are exposed in a loaded state in a closed container and subjected to a sequence of wetting by salt fog and drying. For each concrete, the measurements of chloride content on three prismatic specimens allow us: 1/to study the profiles of chloride ingress into concrete, 2/to compare the different results obtained in relation to the loading state of each specimen, and 3/to calculate the apparent diffusion coefficient D a.

The urgency of carrying out research works on development of high-strength concrete for production of monolithic structures in the conditions of the North is shown. Results of researches on application of river sand from the Lena River flood plain as a filler for highquality high-strength concrete for concreting of monolithic reinforced concrete structures are presented.

Current concrete design Codes raise concerns about concrete spalling during fire particularly under compressive stresses and high heating rates. High strength concrete columns would be more prone for explosive spalling due to their low permeability and high brittleness. This paper represents an experimental program on the behavior of high strength concrete columns under fire. The research includes testing reinforced high strength concrete columns subjected to various loading levels and heating rates. Eighteen columns were tested under four loading levels and two heating rates. The paper represents the main results including the measured concrete and steel temperatures and axial displacements. The paper includes also the results of testing extra 12 high strength columns executed to enhance the experimental program and to verify more precisely the effect of loading level on the structural performance of high strength concrete columns in fire. Valuable conclusions on the effect of loads and heating on concrete explosive spalling are shown in the paper.

Quarry dust is a by-product from the granite crushing process in quarrying activities. This paper presents the findings from experimental work undertaken to evaluate the suitability of quarry dust as a partial substitute for sand in high-strength concrete (HSC) containing rice husk ash (RHA). Two grades of HSC mixes, to achieve 60 MPa and 70 MPa at 28 days, were designed with and without the incorporation of RHA. Quarry dust was then used in the mixes containing RHA as a partial substitute for sand, in quantities ranging from 10 % to 40 %. The slump of the fresh concrete and the compressive strength development were monitored up to 28 days. Based on the results obtained, the mixes containing 20 % quarry dust were chosen as the optimum mix design for both grades of concrete, which would then undergo further evaluation of their strength and mechanical properties up to one year. The results obtained in the next stage suggest that even though the use of quarry dust as a partial substitute for sand results in some minor negative effects in the compressive strength and other mechanical properties of concrete, these outcomes can easily be compensated by a good mix design and by the incorporation of RHA. The findings of the research assert that quarry dust can be used as a viable replacement material to sand to produce high-strength RHA concrete.

The results of a test programme to study the use of recycled concrete aggregate (RCA) in high-strength, 50 N/mm 2 or greater, concrete are described. The effects of coarse RCA content on the ceiling strength, bulk engineering and durability properties of such concretes have been established. The results showed that up to 30% coarse RCA had no effect on concrete strength, but thereafter there was a gradual reduction as the RCA content increased. A method of accommodating the effects of high 1KCA content, involving simple adjustment to water/cement ratio of the mix is given. It is shown that high-strength RCA concrete will have equivalent engineering and durability performance to concrete made with natural aggregates, for corresponding 28-day design strengths. The practical implications of the study for concrete construction are discussed.

The effect of polypropylene and steel fibers on high strength lightweight aggregate concrete is investigated. Sintered fly ash aggregates were used in the lightweight concrete; the fines were partially replaced by fly ash. The effects on compressive strength, indirect tensile strength, modulus of rupture, modulus of elasticity, stress-strain relationship and compression toughness are reported. Compared to plain sintered fly ash lightweight aggregate concrete, polypropylene fiber addition at 0.56% by volume of the concrete, caused a 90% increase in the indirect tensile strength and a 20% increase in the modulus of rupture. Polypropylene fiber addition did not significantly affect the other mechanical properties that were investigated. Steel fibers at 1.7% by volume of the concrete caused an increase in the indirect tensile strength by about 118% and an increase in the modulus of rupture by about 80%. Steel fiber reinforcement also caused a small decrease in the modulus of elasticity and changed the shape of the stress-strain relationship to become more curvilinear. A large increase in the compression toughness was recorded. This indicated a significant gain in ductility when steel fiber reinforcement is used.

This paper describes a multi-national collaborative study that included both numerical and experimental efforts carried out on geometrically similar normal strength concrete (NSC) cylinders of different sizes subjected to axial impact. A parallel study on high strength concrete (HSC), that was carried out earlier, was described in a previous paper (International Journal of Impact Engineering, Elsevier Ltd. 2003; 28: 1001-1016. This study investigated the size effect phenomenon for NSC cylinders under short duration time-dependent compressive loads. Unlike the study on HSC that used soft impact only, this study on NSC used both soft and hard impact. Results from the tests and simulations showed the existence of a size effect in NSC cylinders under both, hard and soft, impact loading. This time-dependent size effect is different from the known static size effect. r

A mathematical model is presented for estimating compressive strength of high-strength concrete incorporating pozzolanic materials, based on the strength of a control ordinary Portland cement (OPC) concrete made with similar mixture characteristics and curing history. In this study, metakaolin (MK) and silica fume (SF) were used as cement replacement materials at 5%, 10%, and 15% by mass. Water/cementitious materials (w/cm) ratios varied from 0.27 to 0.33, and strength testing was conducted up to an age of 180 days. It was found that the strength of a pozzolanic mixture could be related to the strength of its equivalent control by a linear function. Key parameters involved in the model are the pozzolanic and dilution factors, which can be correlated to the pozzolan content in the mixture. The study concludes that the accuracy of the model increases with concrete age. At ages 28 days and above, 97% of the estimated strengths are within ±5% of the actual value.

The current paper is a report on the preparation and testing of 10 reinforced concrete column specimens of (120x120) mm2 cross section and 1000 mm height, for the experimental clarification of the behavior of columns under the influence of pure axial loads. The research addresses the influences of some parameters and conditions on the mentioned behavior, including concrete type (normal strength, high strength or modified reactive powder concrete), the amount of reinforcement and the percentage of steel fibers. The effects of the above variables on the ultimate capacity, failure mode, stiffness, ductility and axial load-lateral displacement behavior were studied. It has been found that increasing the compressive strength and steel reinforcement ratio lead to increasing the ultimate capacity and stiffness of the tested columns. The effectiveness of increasing the steel fibers ratio is manifest in increasing the ultimate strength, ductility, and decreasing the stiffness and the ductility of the tested columns.

Behavior and failure mechanisms of circular HSC columns reinforced with CFRP bars and spirals under eccentric loads are presented. The performance of CFRP bars in compression is assessed. A detailed sectional analysis for predicting the axial force and bending moment at different load eccentricity is introduced. The P-M interaction diagrams encompassing different parameters are developed. a b s t r a c t So far, limited research has been conducted on high-strength concrete (HSC) columns reinforced with fiber-reinforced polymer (FRP) bars under axial and eccentric compressive loads. The behavior and failure modes of steel-reinforced HSC (steel-RHSC) columns are well known: they fail in compression by concrete crushing and/or in tension (steel yielding). The strength and failure mechanisms of HSC columns reinforced with carbon-FRP (CFRP) bars and spirals has not, however, been investigated yet. This paper presents test results from an experimental program conducted to study the failure mechanism and axial–moment capacity of 10 circular HSC columns reinforced with either CFRP or steel bars and tested under different levels of eccentricity. All the specimens measured 305 mm in diameter and 1500 mm in height. The test variables included different eccentricity-to-diameter ratios and two types of reinforcement (CFRP and steel). Laboratory recorded load–axial displacement, load displacement, failure mode, and reinforcement strain responses of the CFRP-RHSC columns were compared to the steel-RHSC columns. A further analytical study was then conducted based on the test results and plane section theory. Based on this study, the axial and flexural capacity of CFRP-RHSC columns can be accurately predicted using plane sectional analysis. Furthermore, a comprehensive parametric investigation was conducted to generate numerous axial force–flexural moment (P-M) interaction diagrams.

This paper reports results of a study conducted to evaluate the effect of four types of coarse aggregates, namely calcareous, dolomitic, quartzitic limestone, and steel slag, on the compressive and tensile strength, and elastic modulus of high strength concrete. The highest and lowest compressive strength was obtained in the concrete specimens prepared with steel slag and calcareous limestone aggregates, respectively. Similarly, the split tensile strength of steel slag aggregate concrete was the highest, followed by that of dolomitic and quartzitic limestone aggregate concretes. The lowest split tensile strength was noted in the calcareous limestone aggregate concrete. The type of coarse aggregate also influences the modulus of elasticity of concrete. Weaker aggregates tend to produce a more ductile concrete than stronger aggregates do.

Pervious concrete is a tailored-property concrete with high water permeability which allow the passage of water to flow through easily through the existing interconnected large pore structure. This paper reports the results of an experimental investigation into the development of pervious concrete with reduced cement content and recycled concrete aggregate for sustainable permeable pavement construction. High fineness ground granulated blast furnace slag was used to replace up to 70 % cement by weight. The properties of the pervious concrete were evaluated by determining the compressive strength at 7 and 28 days, void content and water permeability under falling head. The compressive strength of pervious concrete increased with a reduction in the maximum aggregate size from 20 to 13 mm. The relationship between 28-day compressive strength and porosity for pervious concrete was adversely affected by the use of recycled concrete aggregate instead of natural aggregate. However, the binder materials type, age, aggregate size and test specimen shape had marginal effect on the strength-porosity relationship. The results also showed that the water permeability of pervious concrete is primarily influenced by the porosity and not affected by the use of recycled concrete aggregate in place of natural aggregate. The empirical inter-relationships developed among porosity, compressive strength and water permeability could be used in the mix design of pervious concrete with either natural or recycled concrete aggregates to meet the specification requirements of compressive strength and water permeability.

An experimental investigation is carried out on Nine Slender HSC beams with constant size 125mm x 130mm and effective length 900mm by varying (i) The longitudinal reinforcement ratio and (ii) the web reinforcement ratio were casted and tested to understand the shear behavior of the beams with minimum web reinforcement as per IS CODE and ACI CODE and maximum web reinforcement. The load-deflection behavior and the failure pattern of the beams, ultimate shear strength are studied with varying longitudinal reinforcement and varying shear reinforcement. The experimental results obtained are compared with the theoretical values as per code. Based on these observations, it can be concluded that, there are many parameters influencing the shear behavior of RC beams such as shear span to depth ratio (a/d ratio>2), concrete grade, depth of the beam, the percentage of the longitudinal reinforcement and shear reinforcement. It can be concluded that, the shear failure is brittle, sudden and very explosive. As the spacing of shear reinforcement reduced (75mm) the load carrying capacity increased and as the spacing of shear reinforcement increased (225, 300mm) the load carrying capacity decreased. Shear failure is characterized by small deflection, lack of ductility and catastrophic failure.

An experimental investigation was conducted to evaluate the performance of metakaolin (MK) concrete at elevated temperatures up to 800°C. Eight normal and high strength concrete (HSC) mixes incorporating 0%, 5%, 10% and 20% MK were prepared. The residual compressive strength, chloride-ion penetration, porosity and average pore sizes were measured and compared with silica fume (SF), fly ash (FA) and pure ordinary Portland cement (OPC) concretes. It was found that after an increase in compressive strength at 200°C, the MK concrete suffered a more severe loss of compressive strength and permeability-related durability than the corresponding SF, FA and OPC concretes at higher temperatures. Explosive spalling was observed in both normal and high strength MK concretes and the frequency increased with higher MK contents.

High strength concrete (HSC) was produced using locally available materials. The effect of rice husk ash (RHA) passing #200 and #325 sieves as a lO-30% replacement of cement on the strength of HSC was also studied. The RHA was obtained by burning rice husk, an agro-waste material which is abundantly available in the developing countries. A total of 200 test specimens were cast and tested at 3,7,28 and 150 days. Compressive and split tensile strengths of the test specimens were determined. Cube strength over 70 MPa was obtained without any replacement of cement by RHA. Test results indicated that strength of HSC decreased when cement was partially replaced by RHA for maintaining same level of workability.

Rice husk is an abundantly available waste material in all rice producing countries. In certain regions, it is sometimes used as a fuel for parboiling paddy in the rice mills. The partially burnt rice husk in turn contributes to more environmental pollution. There have been efforts not only to overcome this but also to find value addition to these wastes using them as secondary source of materials. Rice husk contains nearly 20% silica, which is present in hydrated amorphous form. On thermal treatment, the silica converts to crystobalite, which is a crystalline form of silica. However, under controlled burning conditions, amorphous silica with high reactivity, ultra fine size and large surface area is produced. This micro silica can be a source for preparing advanced materials like SiC, Si3N4, elemental Si and Mg2Si. Due to the high pozzolanic activity, this rice husk silica also finds application in high strength concrete as a substitute for silica fume. Possibility of using this silica as filler in polymers is also studied. The present paper is an attempt to consolidate and critically analyse the research work carried out so far on the processing, properties and application of rice husk silica in various laboratories and also highlighting some results on the processing and characterization of RHA and reactive silica obtained from it in the authors' laboratory.

The interest in concrete having an early age strength is increased due to the possibility to limit the construction time. A rapid hardening concrete (RHC) can be applied in order to limit the interruption of heavy traffic ways, for the construction of infrastructures such as bridges, viaducts, etc.In this paper, a practical case of using RHC is presented. The deck

This paper presents the results of a series of experiments conducted to investigate the e ectiveness of ÿbre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel ÿbres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the ÿbre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size e ect on splitting strength, exural strength and toughness.

In the present paper, a numerical and experimental study about creep and shrinkage behavior of a high strength self-compacting concrete is performed. Two new creep and shrinkage prediction models based on the comprehensive analysis on the available models of both conventional concrete and self-compacting concrete are proposed for high strength self-compacting concrete structures. In order to evaluate the predictability of the proposed models, an experimental program was carried out. A concrete which develops 60 MPa within 24 h was used to obtain experimental results. Several specimens were loaded: (i) at different ages and (ii) with different stress-to-strength ratios. Deformation in non-loaded specimens was also measured to assess shrinkage. All specimens were kept under constant stress during at least 600 days in a climatic chamber with temperature and relative humidity of 208C and 50%, respectively. Results showed that the new models were able to predict deformations with good ac...

Civil Engineering has a very important role in practical life because it creates a safe foundation & provides facility for smooth conduction of life. So it's very important that the structure under which the people breathe should resist all worst conditions and provide them safety. For that purpose, for a maximum safety, to achieve good strength of components of building during its maximum life period, here we introduce a material Fiber Reinforced Polymer (FRP). A relatively new class of non-corrosive, high-strength, and lightweight materials, have, over the past 15 years or so, emerged as practical materials for a number of structural engineering applications. Fiber Reinforced Polymer has a very important role in construction work. We can get more strength from the components of building by using it. Also we can increase the load carrying capacity of the components of buildings. When an FRP specimen is tested in axial tension, the applied force per cross sectional area (stress)...

The use of high-strength concrete (HSC) has increased all over the world. Among the factors that justify this increased use is the strength increase for structural aspects and durability. The production of this material results in large consumption of natural sources and energy, as, in general, it is characterized by larger consumption of cement, when compared to the conventional concretes (compressive strength 6 50 MPa). In Brazil, little emphasis has been given to the HSC mix proportioning methods, for their use is not common practice in the construction industry yet, the production of HSCs being achieved through proportioning methods used for conventional strength concretes. The use of these methods, besides presenting technical difficulties, also generates high cement consumption, large consumption of energy and high consumption of raw materials in general. For the present study four proportioning methods were selected, one being for conventional concrete and three specifically for high strength. The resulting concretes are compared for compressive strength, cement consumption and economic viability. The results obtained indicate the advantage of using specific proportioning methods for HSC, as for the same compressive strength at 28 days, savings up to 50% in the consumption of cement were achieved, which represents a significant reduction of energy, raw material consumption and costs.

An experimental and analytical investigation was conducted in order to study the effect of axial compression forces on the shear behavior of high strength fiber reinforced concrete (HSFRC) beams. To the author's knowledge, the effect of applying axial compression forces, to the HSFRC beams, has not yet been studied. Nineteen simply supported HSFRC beams were subjected to axial compression forces and tested under two-point vertical loading for three values of shear span to depth ratio. The studied beams contained variable amount of fiber content, two types of fibers (corrugated shape and hooked-end), and variable amount of web reinforcement. It was found that the shear strength of beams subjected to axial compression stress level equals 0.1, is higher than that in the literature for beams tested without applying axial stress by a range of 22-98%. In addition, increasing the axial compression stress level to 0.2 led to an increase in the first crack load, ultimate load by 24% and 10%, a reduction in the deflection by (19-30%), compared with those subjected to axial compression stress level equals 0.1. A combination of web reinforcement and fibers resulted in a significant increase in the cracking and ultimate loads by 123% and 59%, respectively, over those of the reference beam. A new formula is proposed for predicting the shear strength of HSFRC beams subjected to axial compression. The results obtained by the proposed formula are in good agreement with the test results.

Comprehensive microstructural investigations were performed on normal-strength (33 MPa) and relatively high-strength concrete (43 MPa) as well as concrete specimens with and without restraint against drying shrinkage movement. The effects of different load and environmental damaging phenomena (cold and hot environment) on concrete microcrack system were detected. Fluorescent and environmental scanning electron microscopy (ESEM) techniques with image analysis methodologies were employed to quantify microcrack attributes on planar sections. Stereological aspects were used to derive information on spatial (3-D) microcrack systems in terms of planar (2-D) quantitative data generated on perpendicular sections. Statistical analysis of data was used to determine the differences in microcrack characteristics between normal-strength versus relatively high-strength and unrestrained versus restrained specimens.

The effect of post-fire-curing on the strength and durability recovery of fire-damaged concrete was investigated. Twenty normal-(NSC) and high-strength concrete (HSC) mixes incorporating different pozzolans were prepared and exposed to elevated temperatures till 800°C. After natural cooling, the specimens were subjected to post-fire-curing in water and in a controlled environment for a total duration of 56 days. Unstressed compressive strength, rapid chloride diffusion, and mercury intrusion porosimetry (MIP) tests were conducted to examine the changes in the macro-and microstructure of the concrete. The test results indicated that the post-fire-curing results in substantial strength and durability recovery and its extent depend upon the types of concrete, exposure temperature, method, and duration of recuring. In one case, the recovered strength was 93% of the original unfired strength. Scanning electron microscopy (SEM) investigations indicated that the recovery was due to a number of rehydration processes that regenerate the calcium-silicate-hydrate (C-S-H). The new rehydration products were smaller in size than the original hydration products and filled the internal cracks, honey combs, and capillaries created during the fire. The surface crack widths were also reduced during the recuring process, and in most cases, they were found within the maximum limits specified by the American Concrete Institute (ACI) building code. D

Concrete encased composite column design provisions of the American Concrete Institute Code (ACI 318), AISC-LRFD Specification, and the AISC Seismic Provisions are reviewed and evaluated based on fiber section analyses that account for the inelastic behavior of steel and concrete, including the effects of strength and confinement on the concrete's stress-strain properties. Trial column designs are analyzed to evaluate their strength and ductility as a function of the ratio of structural steel to gross column area, the nominal compression strength of concrete, and confinement of concrete by seismic hoop reinforcing. The analyses highlight known differences in the calculated nominal strength requirements between the ACI 318 and AISC-LRFD provisions and suggest a review of criteria used to establish the limits of the provisions. Compared to columns with lowto medium-strength concrete, columns with high-strength concrete = 110 MPa) are shown to rely to a greater ( f Ј c degree on hoop reinforcement to provide the necessary ductility for seismic design.

Heavyweight high strength concrete can be used when particular properties, such as combined high strength and good radiation shielding, are required. Such concrete, using magnetite aggregates, can have a density in the range 3.2 to 4 t/m 3 , significantly higher than the density of concretes made with normal aggregate. The high strength can be achieved with low water/cement ratios with superplasticiser and the incorporation of silicafume. In the present work, from 41 trial mixes, 12 were selected to achieve a slump above 100mm and strength up to 140 MPa at 180 days. To achieve this a 0.24 water/cement ratio and 3.5% superplasticiser were used. The investigation used three levels of silicafume (0, 10%, 20% by weight of cement), two coarse aggregate proportions of total aggregate (0.48, 0.65 by volume) and both magnetite and natural sand fine aggregate were used. The investigation provided information on compressive strength, and shielding properties and indicated clear benefits from the use of silicafume as a mineral admixture and from using magnetite as fine as well as coarse aggregate.

Parts of the bridges in Sweden and other countries have shown to have a too low resistance with
respect to deterioration. This leads to costly repair interventions that disturbs the traffic and results in high Life
Cycle Costs (LCC) for the bridges. This investigation primarily focuses on the mechanical behavior, durability
and rheological properties and application of UHPFRC to develop more robust bridge deck slabs. UHPFRC
shows better performance at post-cracking due to the strain hardening behavior with distributed micro-cracks,
enhancing the service life of bridge deck slabs. The main idea is to use Ultra-High Performance Fiber
Reinforced Concrete (UHPFRC) to “harden” those zones of the structure that are exposed to severe
environment and high mechanical loading. This conceptual idea combines efficiently protection and resistance
properties of UHPFRC and significantly improves the structural performance of the rehabilitated concrete
structure in terms of durability and life-cycle costs. The concept is validated by means of four applications
demonstrating that the technology of UHPFRC is mature for cast in-situ and prefabrication using standard
equipment for concrete manufacturing. Moreover an inventory of two bridges in Sweden has been used as case
study to investigate the possibility of use of UHPFRC for rehabilitation.

In this paper, high strength concretes (HSC) containing manufactured sand (or maybe called crushed sand) as fine aggregate in the presence of fly ash (FA), silica fume (SF) were made. The HSC mixtures were designed to achieve 28-day compressive strength beyond 55 MPa. Compressive strength, drying shrinkage, water-tightness and sulfate attack tests were conducted to evaluate the feasibility on the production of HSC having crushed sand, FA and SF. The test results indicated that the compressive strength of all HSC mixtures exceeded 55 MPa at 28 days. There was an improvement in the compressive strength following the addition of SF in HSC. Introducing crushed sand to HSC as fine aggregate led to a reduction in compressive strength. The usage of crushed sand most effectively decreased the length change of HSC, compared with HSC containing natural sand. HSC mixtures can be classified into > B12 water-tightness class. Furthermore, weight loss of HSC was in a range of 0.040.29%.

The conventional ACI rectangular stress block is developed on the basis of normal-strength concrete column tests and it is still being used for the design of high-strength concrete members. Many research papers found in the literature indicate that the nominal strength of high-strength concrete members appears to be over-predicted by the ACI rectangular stress block. This is especially true for HSC columns. The general shape of the stress-strain curve of high-strength concrete becomes more likely as a triangle. A triangular stress block is, therefore, introduced in this paper. The proposed stress block is verified using a database which consists of 52 tested singly reinforced high-strength concrete beams having concrete strength above 55 MPa (8,000 psi). In addition, the proposed model is compared with models of various design codes and proposals of researchers found in the literature. The nominal flexural strengths computed using the proposed stress block are in a good agreement with the tested data as well as with that obtained from design codes models and proposals of researchers.

High strength thin-walled rectangular concrete-filled steel tubular (CFST) slender beamcolumns under eccentric loading may undergo local and overall buckling. The modeling of the interaction between local and overall buckling is highly complicated. There is relatively little numerical study on the interaction buckling of high strength thin-walled rectangular CFST slender beam-columns. This paper presents a new numerical model for simulating the nonlinear inelastic behavior of uniaxially loaded high strength thin-walled rectangular CFST slender beam-columns with local buckling effects. The cross-section strengths of CFST beamcolumns are modeled using the fiber element method. The progressive local and post-local buckling of thin steel tube walls under stress gradients is simulated by gradually redistributing normal stresses within the steel tube walls. New efficient Müller's method algorithms are developed to iterate the neutral axis depth in the cross-sectional analysis and to adjust the curvature at the columns ends in the axial load-moment interaction strength analysis of a slender beam-column to satisfy equilibrium conditions. Analysis procedures for determining the load-deflection and axial load-moment interaction curves for high strength thin-walled strength thin-walled rectangular concrete-filled steel tubular slender beam-columns, Part I: Modeling", Journal of Constructional Steel Research, 2012, 70, 377-384. 2 rectangular CFST slender beam-columns incorporating progressive local bucking and initial geometric imperfections are presented. The new numerical model developed is shown to be efficient for predicting axial load-deflection and axial load-moment interaction curves for high strength thin-walled rectangular CFST slender beam-columns. The verification of the numerical model and parametric studies are given in a companion paper.

In this paper we investigate the influence of the shape and of the size of the specimens on the compressive strength of high-strength concrete. We use cylinders and cubes of different sizes for performing stable stress–strain tests. The tests were performed at a single axial strain rate, 10− 6 s− 1. This value was kept constant throughout the experimental program. Our results show that the post-peak behavior of the cubes is milder than that of the cylinders, which results in a strong energy consumption after the peak. This is consistent with the observation of the crack pattern: The extent of cracking throughout the specimen is denser in the cubes than in the cylinders. Indeed, a main inclined fracture surface is nucleated in cylinders, whereas in cubes we find that lateral sides get spalled leading to the so-called hour-glass failure mode. The remaining cube core gets fragmented due to crushing, in some cases exhibiting a dense columnar cracking in the bulk of the specimen. Finally, we investigate the relationship between the compressive strength given by both types of specimen for several specimen sizes.

Improvement of economy, durability and strength of the built environment has been a constant quest for engineers. During recent decades, the use of high-strength has been implemented in bridge members and other structures. Typically, highstrength concrete has uniaxial compressive strengths in excess of 8 000 psi, and its recognized as a more brittle material than the typical concretes with compressive strengths in the range of 4 000 to 6 000 psi.

In this research work, the investigation of shear behavior of corbel beams strengthened with Carbon Fibers Reinforced Polymer (CFRP) is carried out. The research objective was to study the effectiveness of wrapping of D-Regions of Corbel beams with CFRP, in increasing the shear strength of Corbel beams. To achieve these objectives, twelve corbel beams were tested which were divided into 4 groups. The beam samples were first designed by Strut and Tie Method. The theoretical values of strut and tie forces obtained during the design of corbel beams were compared with the strut and tie forces obtained on the basis of load at 1st shear crack and failure loads. It was concluded that loading capacity as well as energy absorption of corbel beams can be increased by using CFRP wrapping techniques. [Ahmad S, Elahi A, Kundi, S, Haq, WU. Investigation of Shear Behavior of Corbel Beams Strengthened with CFRP. Life Sci J 2013;10(12s):961-965] (ISSN:1097-8135). http://www.lifesciencesite.com. 156

The beam-column joint is one of the important structural elements of reinforced concrete structures. It has been the subject of intensive research for the past four decades. To date, most of the design procedures of joints have been devoted to ordinary-strength concrete as implemented in the current international design codes. The use of high-strength concrete has become useful because of the advantages of member size limitation and higher structural capacity. However, its applicability is still limited because its behaviour, especially under combined stresses and shear, differs from ordinary-strength concrete in the presence of axial loading on the column. Consequently, the existing design guidelines are not completely applicable. In order to establish the salient features of the behaviour, namely modes of failure, deformational characteristics, strength parameters and strain development, an experimental programme was performed on beam-column joints under quasi-static monotonic loading. The influence of axial compression, along with other actions imposed on the joint including shear and bending moment, was taken into consideration. The practical aspects of using a composite structure-that is, ordinary-strength concrete of different grades at floor level and high-strength concrete along the rest of the column-were considered. The effects of different permutations of longitudinal as well as transverse reinforcement and various configurations of stirrups were also investigated.

High-calcium fly ashes (ASTM Class C) are being widely used as a replacement of cement in normal and high strength concrete. In Greece such fly ashes represent the majority of the industrial by-products that possess pozzolanic properties. Even thought the contribution of factors, such as fineness and water/binder ratio, on the performance of fly ash/cement (FC) systems has been a common research topic, little work has been done on examining whether and to what extent reactive silica of fly ashes affects the mechanisms occurring during their hydration.

This paper concerns the incorporation of steel fibres in singly reinforced high strength concrete beams without stirrups failing under the combined effect of flexure and shear. An analytical model was developed and published for predicting the relative flexural capacity of steel fibre high strength concrete beams (Mu/M~) i.e. the ratio of moment with shear interaction to pure flexural moment. This paper investigates the significant role of steel fibres in increasing the beam strength up to its full flexural capacity. An equation is derived for the critical shear span-to-depth ratio (a/d)c at which there is a maximum reduction of the flexural strength due to shear influence. An analytical approach is developed to determine the domain of shear effect, by which it becomes possible to predict whether shear compression, diagonal tension, or flexural failure will occur for a given beam. The interaction between steel fibres and longitudinal reinforcement bars is studied, and a nonlinear expression is derived for the optimum percentage of fibres by which a singly reinforced beam without stirrups reaches its full flexural capacity and does not fail in shear regardless of shear span-to-depth ratio (a/d). © 1997 Elsevier Science Ltd.

Reinforced lightweight aggregate high-strength concrete slabs that incorporated fly ash were exposed to 2% chloride solution for over 15 months. Chloride ion ingress, corrosion potentials, corrosion current density and electrical resistivity were determined. These slabs were compared with slabs from normal weight concrete of medium and high-strength. The results indicated that lightweight high-strength concrete slabs with fly ash in the concrete mixture showed the least amount of chloride concentration. Values of corrosion current density were very low and values of electrical resistivity were very high and indicative of extremely low corrosion current. The dense matrix of the lightweight high-strength concrete is believed to restrict continuous pores that may carry chloride ions. The effect of fly ash in lowering the chloride diffusivity further contributed to reduce harmful chloride ions. In addition, the porous sintered fly ash aggregates are believed to have acted as buffer reservoirs for the chloride laden solution and thus prevented the chloride ions from reaching the steel surface.

The use of high-strength concrete (HSC) has increased
significantly in recent years due to its improved performance
characteristics when compared with normal-strength
concrete (NSC). Current design codes, however, are
predominantly based on data derived from tests on NSC.
Furthermore, the extrapolation of NSC design rules to HSC is
not always conservative and can lead to unsafe designs.
Extensions to the NSC provisions of current codes to
encompass HSC have been published, but their advice is
often ignored by engineers, because either their
recommendations are not mandatory, or the codes do not
give clear direction on their limitations.
This paper compares the behaviour of HSC with NSC and
highlights the brittle nature of HSC under axial loading.
Specific design and detailing requirements for achieving
adequate ductility in HSC columns are reviewed and
discussed. The paper describes how sufficient ductility can be
achieved by using an appropriate confining pressure
provided by the column links. A typical design example and
RC details are included to illustrate how an appropriate level
of ductility can be achieved.

High strength concrete (HSC), is being increasingly used in a number of building applications, where structural fire safety is one of the major design considerations. Many research studies clearly indicate that the fire performance of HSC is different from that of normal strength concrete (NSC) and that HSC may not exhibit same level of performance (as NSC) in fire. This paper discusses the material, structural and fire characteristics that influence the performance of HSC under fire conditions. Data from earlier experimental and numerical studies is used to illustrate the impact the concrete (material) mix design and structural detailing (design) has on fire performance of HSC systems. An understanding of various factors influencing fire performance will aid in developing appropriate solutions for mitigating spalling and enhancing fire resistance of HSC members. r