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As global urbanization flourishes, the adverse effects on the environment also incredibly increase. This urbanization leads to the evolution of construction and building materials. To meet the requirements of eco-balanced construction materials without compromising their original properties, many evolutions of concrete are in practice nowadays. One such evolution of concrete is geopolymer concrete. The objective of the current study is to produce high-strength geopolymer concrete using ground granulated blast furnace slag (GGBS), metakaolin (MK), and nano-silica (NS) in ambient-cured conditions. The influence of nano-silica in the geopolymer concrete is evaluated by workability, setting time, mechanical strength, durability properties, and microstructural analyses, which include scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and correlation analysis. In this research, the effect of nano-silica on formulating the equation for modulus of elasticity was determined. Nano-silica was replaced at a percentage of 1, 2, and 3% of the binder material. It is summarized that the molar ratios and properties of the precursor materials are the defining factors in altering the systems of geopolymer concrete. The highest strength of 89.4 MPa at 28 days of ambient-cured concrete with outstanding durability performance was achieved. [ABSTRACT FROM AUTHOR]

Objectives Development of compositions filled with binders based on recycled materials for monolithic high-strength concrete.Method The research methods adopted in the work are based on the theoretical principles and laws of designing and optimizing polydisperse multicomponent systems, the phase and structure formation of clinker minerals, the logic of mathematical calculations, the technological features of the structure formation of composite masses, the theoretical principles of controlling the rheological processes of mixes. All experimental data presented in the work were obtained according to the methods of current regulatory documents (GOST, recommendations, etc.).Result The paper provides an analysis of the experience of using recycled materials in the form of products of demolition of buildings and structures, the technology for producing secondary raw materials for concrete on their basis. Formulations filled with binders with an activity of 60-71 MPa with finely dispersed mineral fillers from concrete scrap and brick combat with a ratio of 70:30%, respectively, were developed and investigated.Conclusion The optimal formulations of highly mobile concrete mixtures were designed using local natural and technogenic raw materials with a grade of P5 cone sediment and persistence for more than 8 hours to obtain high-strength classes of compressive strength up to B60-B80 with unique operational properties.

Utilization of artificial aggregates and waste products are more prevalent nowadays. Many attempts and researches were made to justify the use of by products will be a viable solution than using natural resource in buildings. In the present study, aiming high performance concrete mix with ferro slag aggregates were replaced partially with coarse aggregate by 50% and 100% and its impact strength is evaluated systematically. The test results shows that replacement of ferro slag aggregate records a better value than normal aggregates. 100% replacement of aggregates shows comparatively higher value than control concrete mix. [ABSTRACT FROM AUTHOR]

The objective of this study is to focus on "low carbon binders," given the adverse environmental impacts resulting from the extensive emission of greenhouse gases. In the current context, the term "geopolymer concrete," often referred to as "low carbon binders," is gaining prominence as a means to develop an eco-friendly binding material. Furthermore, this study focuses on creating high-strength geopolymer binders using ambient curing conditions. Numerous factors are involved in determining the mix ratios for geopolymer concrete. Nonetheless, the reluctance to apply it in practical scenarios arises from an insufficient understanding of how to select the appropriate mix proportions based on these parameters. Therefore, utilizing Multi-Criteria Decision-Making presents the best choice for evaluating the geopolymer parameters. Among several MCDM methods, TOPSIS has been selected for this research. Geopolymer binders are produced using Ground Granulated Blast furnace Slag (GGBS), a by-product from the steel industry and metakaolin (MK), a product from the calcination of clay. A total of thirty-two combinations of geopolymer mortar mixes were created by varying the percentage of metakaolin, the ratio of alkaline activators (sodium silicate to sodium hydroxide, SS/SH), and the concentration of sodium hydroxide (NaOH). The assessment of these mixtures involves nine response factors, encompassing flow characteristics, initial and final setting time, compressive strength (7 and 28 days), initial drying shrinkage, energy consumption, CO 2 emission, and financial expenses. A study of the microstructure is carried out to explore the impact of MK presence on geopolymers using GGBS as a base precursor. Hence, techniques for optimizing multiple responses were employed to attain the desired attributes while maintaining all measurable factors within an acceptable range. This approach to optimization holds significant importance, particularly when dealing with geopolymer concrete, as it can enhance its utilization compared to traditional cement-based concrete. • This study focuses on optimizing low-carbon binders that meet all the experimental, environmental, and economic criteria. • TOPSIS is one of the multi-criteria decision-making tools with high computational efficiency adopted to optimize low-carbon binders. • To validate the result obtained through TOPSIS, microstructural analysis was performed. • Employing this method has mitigated the complexity that arises when multiple parameters for concrete are taken into account. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Engineering properties of FAGP and AAS concrete have been investigated. • The FAGP concrete has been produced by blending an alkaline activator with FA. • The AAS concrete has been produced by blending an alkaline activator with GGBFS. • The FAGP concrete has been produced using heat curing at 80 °C for 24 h. • The AAS has been produced at ambient curing condition. Abstract Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength. [ABSTRACT FROM AUTHOR]

This paper investigates the maximum shear strength limits specified in the ACI Code and the combinations of shear span, concrete strength, and amount of shear reinforcement where this limit is very conservative. A series of new experiments are described and their results, along with those of 127 experiments from the literature, are compared to predictions from the ACI, AASHTO-LRFD, and CSA codes. It is shown that an upper shear stress limit of 0.225fc′ provides a good estimate of maximum shear capacity. The current ACI limit, on the other hand, seriously underestimates the shear strength of high-strength concrete members when they include large quantities of shear reinforcement or have short shear spans. [ABSTRACT FROM AUTHOR]

In the recent years, many research efforts have been carried out on the bond strength between normal strength concrete (NSC) and reinforcing bars spliced in tension zones in beams. Many codes gave a minimum splice length for tension and compression reinforcement as a factor of the bar diameter depending on many parameters such as concrete strength, steel yield stress, shape of bar end, shape of bar surface and also bar location. Also, codes gave another restriction about the percentage of total reinforcement to be spliced at the same time. Comparatively limited attention has been directed toward the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. HSC has high modulus of elasticity, high density and long-term durability. This research presents an experimental study on the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. It reports the influence of several parameters on bond in splices. The parameters covered are casting position, splice length as a factor of bar diameter, bar diameter and reinforcement ratio. The research involved tests on sixteen simply-supported beams of 1800 mm span, 200 mm width and 400 mm thickness made of HSC. In each beam, the total tensile steel bars were spliced in the constant moment zone. Crack pattern, crack propagation, cracking load, failure load and mi span deflection were recorded and analyzed to study the mentioned parameters effect.

Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1–8]. This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800 mm span and 200 × 400 mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.

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Integrating fiber-reinforced polymer (FRP) reinforcement into high-strength concrete (HSC) would effectively contribute to enhancing the stiffness of cracked concrete sections when the FRP bars are undergoing high strain and stress levels. Nonetheless, neither the concentric nor the eccentric behavior of HSC columns reinforced with FRP reinforcement has yet been investigated. This paper presents the results of an experimental investigation on the concentric and eccentric behavior of full-scale circular HSC columns reinforced with glass FRP (GFRP) bars and spirals. A total of 10 columns were tested under monotonic loading with different eccentricities. The test variables were the eccentricity-to-diameter ratio and the longitudinal-reinforcement ratio. Compression failure in the concrete controlled the ultimate capacity of specimens tested under small eccentric loading. A flexural-tension failure initiated in specimens tested under high eccentric loading, however, resulted from excessive axial and lateral deformations and cracks on the tension side until a secondary compression and stability failure occurred owing to the strain limitations in the concrete. The axial force-moment interaction diagrams were predicted based on the principles of strain compatibility and internal force equilibrium in accordance with the recommendations in the available design standards. [ABSTRACT FROM AUTHOR]

This paper reports experimental data on the behavior and strength of high-strength concrete slender beams reinforced with vertical shear reinforcement. Tests were conducted on ten reinforced concrete beams with stirrups in different positions using high-strength concrete (compressive strength about 85.0 MPa). The beams measured 2000 mm long, 100 mm wide and 200 mm deep, and were tested under two point loads. The test variables were position and amount of web reinforcement; conventional steel bars were used as longitudinal reinforcement in this investigation. The test results indicated that beams with shear reinforcement (vfy = 1.65 to 4.24MPa) within the shear span (G1) and along the beam length (G2), were failed in flexure, while beams with shear reinforcement (vfy = 1.65 to 4.24MPa) between two point loads (G3) and the beam without shear reinforcement (G4) were failed in shear. The optimum position of stirrups is the shear span for high strength concrete beams and for different amounts

Spalling of concrete in fire is due to dislodgement of small pieces of concrete. This phenomenon is one of the most detrimental effects causing damage or even failure of the concrete members during or after a fire by decreasing the residual mechanical properties and durability of the structure. In spite of many experimental and numerical studies, the real mechanism of spalling is still not well understood, which is mainly due to the erratic nature of this phenomenon and inhomogeneity of the concrete structures. To establish a more clear view of the achievements in this area and also the areas in need of more investigations, this paper critically reviews the latest findings on concrete performance during heating in general and specifically the fire spalling behaviour of concrete members and different views on governing factors that affect this phenomenon.

For the purpose of systematically ascertaining the influence of clay-contaminated microfines (CCM) on concrete properties and feasibility of utilizing waste microfines in concrete, the effects of CCM on fresh and hardened properties of C30 and C60 concrete were investigated by means of incorporating 10 % of microfines containing variable clay contents in two series of constant-slump concretes. The results show that inclusion of CCM significantly increases the amount of water or water reducer required to achieve constant slump and drying shrinkage, and the increases are positively correlated with methylene blue value (MBV) of CCM. For constant-slump concrete of variable water contents (variable water-to-cement ratio), CCM significantly decrease compressive strength and chloride-ion permeability with increasing MBV; however, for constant-slump concrete of variable water reducer amounts (constant water-to-cement ratio), CCM have no adverse effect on compressive strength and chloride-ion permeability of C30 concrete but deteriorate that properties of C60 concrete only when MBV exceeds 10 g/kg. The extent of influence of CCM on properties of C60 concrete is greater than that of CCM on properties of C30 concrete. Qualified concrete with satisfactory mechanical property and durability could be successfully prepared with 10 % incorporation of CCM under the help of water reducer and MBV to be controlled within 10 g/kg, which confirms it is applicable to utilize these waste microfines in concrete production. [ABSTRACT FROM AUTHOR]

In the recent years, many research efforts have been carried out on the bond strength between normal strength concrete (NSC) and reinforcing bars spliced in tension zones in beams. Many codes gave a minimum splice length for tension and compression reinforcement as a factor of the bar diameter depending on many parameters such as concrete strength, steel yield stress, shape of bar end, shape of bar surface and also bar location. Also, codes gave another restriction about the percentage of total reinforcement to be spliced at the same time. Comparatively limited attention has been directed toward the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. HSC has high modulus of elasticity, high density and long-term durability. This research presents an experimental study on the bond between high strength concrete (HSC) and reinforcing bars spliced in tension zones in beams. It reports the influence of several parameters on bond in splices. The parameters covered are casting position, splice length as a factor of bar diameter, bar diameter and reinforcement ratio. The research involved tests on sixteen simply-supported beams of 1800 mm span, 200 mm width and 400 mm thickness made of HSC. In each beam, the total tensile steel bars were spliced in the constant moment zone. Crack pattern, crack propagation, cracking load, failure load and mi span deflection were recorded and analyzed to study the mentioned parameters effect. [ABSTRACT FROM AUTHOR]

Abstract: Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1–8]. This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800mm span and 200×400mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers. [Copyright &y& Elsevier]

The paper shows the effect of curing condition on compressive strength in high strength concrete in three cases (Group A(moist curing in water for 7 days followed by air curing ) ,Group B(curing until the age test in water) and Group C(curing at high temperature 60ºC±2ºC for six days ) and two types of specimen of cubes (150 x150 and 100 x 100) used in the test age (7,28and 90 day) respectively in four mix proportion (Mix No.1(40 Mpa ,Mix No. 2(fcu 60 Mpa) ,Mix No. 3 (fcu 70 Mpa) and Mix No. 4 (fcu 80 Mpa) ). Results demonstrate that, in general, concrete specimens moist cured until testing ages (Group B) give compressive strength greater than specimens moist cured for 7 days in water then followed by air – drying (Group A). The percentage of increase in strength is (5 and12%) for mix No.3 and 6% for mix No.4, as compared with 3% for mix No.1 and (2 and4%) for mix No.2. When the curing temperature (group C ) increases, the compressive strength increases at different ratios ,the percentage of increase in compressive strength at 7,28 and 90 days for mix No.1 , mixes No.2 and 3 are (20,15 and 14% ), ( 7,11 and 5% ) and (13,12 and 5% ) respectively, while mix No4. shows an increase of 4 and 10% in compressive strength at 7 and 28 days where there is a reduction in the strength at 90 days by about 2%. Generally, as the size of specimen decreases, the effect of temperature curing (group C)on the compressive strength increases.

This paper reports experimental data on the behavior and strength of high-strength concrete deep beams reinforced with shear reinforcement. Tests were conducted on eight reinforced concrete deep beams with stirrups in different type and positions using high-strength concrete (compressive strength of about 85.0 MPa). The beams measured 1400 mm long, 100 mm wide and 300 mm deep, and were tested under two point loads. The test variables were type and position of web reinforcements [Shear stress of vertical stirrups (ρvfy), Shear stress of horizontal stirrups (ρhfy) and Shear stress of inclined stirrups (ραfy)] within shear span, within middle span(between two point loads) and along the beam. Conventional steel bars were used as longitudinal reinforcement in this investigation. The test results indicated that beams with vertical and inclined shear reinforcement within the shear span (B4) resisting the ultimate load of about 417.90kN. While beams with horizontal shear reinforcement (B3), shear reinforcement between two point loads (B7), and the beam without shear reinforcement (B8) resisting, 7..522, 762.18 and 7.25..kN respectively. All the beams failed in shear and the optimum position of stirrups is the shear span for high strength concrete deep beams and with combination of vertical and inclined stirrups. [ABSTRACT FROM AUTHOR]

Abstract: A numerical technique for the analysis of high-strength reinforced concrete slender columns subjected to end loadings is presented. The finite difference method is applied to calculate the load corresponding to a specified deflection, considering both material and geometric nonlinearities. In this way, the complete load–deflection curve was computed for X columns that were also tested experimentally. The analysis procedure is applicable for columns with hinged extremities, although only isolated columns are evaluated herein. [Copyright &y& Elsevier]

This paper evaluates the bond behavior of high strength (HS), steel reinforcing bars and highlights the effect of various key parameters believed to affect the bond characteristics. Nine reinforced concrete spliced beams were constructed and tested. The beams had different splice lengths and levels of confinements. The applicability of different hypotheses for development of conventional steel bars was examined for the HS bars. The study is extended to examine the behavior of the reinforcing bars as shear reinforcement for concrete beams by testing twelve concrete beams reinforced with HS steel stirrups under static loading conditions. The main variables in the study included steel type, concrete compressive strength, web reinforcement ratio and shear span-to-depth ratio. The applicability of various building codes and standards for concrete beams with HS shear reinforcement was also evaluated. [ABSTRACT FROM AUTHOR]

Critical crack tip opening displacement (CTODc) of concrete using experimental and analytical evaluation with seven different compressive strengths ranging from 30 up to 150 MPa was studied based on two types of fracture tests: three-point bending (TPB) and wedge splitting (WS). In the tests, the values of CTODc were experimentally recorded using a novel technique, in which fiber Bragg grating (FBG) sensors were used, and two traditional techniques, in which strain gauges and clip gauges were deployed. The values of CTODc of tested concrete were also predicted using two existing analytical formulae proposed by JENQ & SHAH and XU, respectively. It is found that the values of CTODc obtained by both experimental measurements and analytical formulae exhibit a negligible variation as the compressive strength of concrete increases, and the test geometry adopted has little impact on the value of CTODc. Regarding the experimental measurement of CTODc, the clip gauge method generally leads to a larger value of CTODc and shows a more significant scatter as compared with the other two methods, while the strain gauge method leads to a slightly lower CTODc as compared with the FBG sensor method. The analytical formula proposed by JENQ and SHAH is found to generally lead to an overestimation, while the analytical formula proposed by XU shows a good accuracy. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the behaviour of pin-ended axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element model was developed to analyse the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered that allowed the bond behaviour to be modeled and the different components to retain their profile during the deformation of the column. Furthermore, the initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against published experimental results. The main objective of the study was to understand the structural response and modes of failure of the columns and to assess the composite column strengths against current design codes. The study covered slender, non-slender, stub and long concrete encased steel composite columns. The concrete strengths varied from normal to high strength (20–110 MPa). The steel section yield stresses also varied from normal to high strength (275–690 MPa). Furthermore, the variables that influence the composite column behaviour and strength comprising different slenderness ratios, concrete strength and steel yield stress were investigated in a parametric study. It is shown that the increase in structural steel strength has a small effect on the composite column strength for the columns having higher relative slenderness ratios due to the flexural buckling failure mode. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American Institute for Steel Construction AISC and Eurocode 4 for composite columns. Generally, it is shown that the EC 4 accurately predicted the design strength for the concrete encased steel composite columns having a concrete cylinder strength of 30 MPa and structural steel yield stresses of 275 and 460 MPa, which are in the limits of the code, which otherwise, was generally conservative. The AISC predictions were quite conservative for all the concrete encased steel composite columns. [Copyright &y& Elsevier]

Abstract: This paper presents a nonlinear 3-D finite element model for eccentrically loaded concrete encased steel composite columns. The columns were pin-ended subjected to an eccentric load acting along the major axis, with eccentricity varied from 0.125 to 0.375 of the overall depth (D) of the column sections. The model accounted for the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall geometric imperfection was carefully incorporated in the model. The finite element model has been validated against existing test results. The concrete strengths varied from normal to high strength (30–110MPa). The steel section yield stresses also varied from normal to high strength (275–690MPa). Furthermore, the variables that influence the eccentrically loaded composite column behaviour and strength comprising different eccentricities, different column dimensions, different structural steel sizes, different concrete strengths, and different structural steel yield stresses were investigated in a parametric study. Generally, it is shown that the effect on the composite column strength owing to the increase in structural steel yield stress is significant for eccentrically loaded columns with small eccentricity of 0.125D. On the other hand, for columns with higher eccentricity 0.375D, the effect on the composite column strength due to the increase in structural steel yield stress is significant for columns with concrete strengths lower than 70MPa. The strength of composite columns obtained from the finite element analysis were compared with the design strengths calculated using the Eurocode 4 for composite columns. Generally, it is shown that the EC4 accurately predicted the eccentrically loaded composite columns, while overestimated the moment. [Copyright &y& Elsevier]

The flexural and cracking behavior of hybrid strength concrete beams cast with two concrete compressive strengths of 20 and 70 MPa were compared with 20 MPa normal and 70 MPa high strength beams. The hybrid beams showed an improvement in the load carrying capacity at cracking, yielding and ultimate loading as compared to normal strength beams. The increase in load carrying capacity was (1.80–70.8%) higher than normal strength beams and only (3.3–9.8%) lower than corresponding high compressive strength beams. Also from experimental results the crack spacing of hybrid beams were between those of normal strength and high strength beams, but the crack width in the hybrid beams were narrower than both types of beams at all loading stages. At service and ultimate loading stages, the crack width in the hybrid beams were 19.5–26.0% narrower than those of corresponding normal strength beams, and 9.2–15.1% narrower than high strength beams. [ABSTRACT FROM AUTHOR]

Abstract: The effect of structural boundary conditions and explosive spalling on performance of concrete elements in fire is still an area of interest within the research community. This paper presents the results of experimental research executed on 30 high strength concrete columns. The parametric study investigated the high strength concrete columns under five loading levels (0.2, 0.3, 0.4, 0.5 and 0.6) subjected to two heating rates, with special attention directed towards explosive spalling. The second part of the paper represents a three-dimensional finite element (FE) model of the reinforced concrete columns, taking into account exposure to high temperatures. The effects of tension softening are included in the model and are based on the Hordjik, Cornelissen and Rienhardt curve. The concrete columns were modelled taking into account the embedded reinforcement and crack formation and propagation using the smeared cracks model, which allowed a nonlinear transient structural analysis to be conducted. The comparison of the results of the FE analysis and the tests performed showed a reasonable agreement and a divergence in some cases due to concrete spalling. An assessment of stresses generated in the high strength concrete columns under fire using the FE model is also presented in the paper. The evaluation shows that mechanical and thermal tensile stresses could reach up to 8.69 MPa, which is high enough to cause concrete spalling. [Copyright &y& Elsevier]

Abstract: Experimental investigation of concrete-filled stainless steel tubular X-joints fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members was conducted. High-strength stainless steel (duplex and high-strength austenitic) and normal-strength stainless steel (AISI 304) specimens filled with nominal concrete cylinder strength of 30MPa were tested. The concrete was filled in the chord member of the test specimens along the full chord length. A total of 25 X-joint tests was performed that consists of 9 test specimens with brace members and 16 test specimens with steel bearing plates. The axial compression force was applied to the brace members, which were welded at right angles to the opposing sides of the continuous chord member. Local buckling failure of brace was the main failure mode observed during the tests. Therefore, steel bearing plates were used to simulate the brace members, which avoid failure of the brace members. These specimens were failed by chord face failure and chord side wall failure as well as crushing of concrete. The test results were compared with the design strengths calculated using the CIDECT design rules for concrete-filled carbon steel tubular structures. It is shown that the design strengths calculated using the existing design equations are quite conservative for the test specimens. It is recommended that the influence of stainless steel tubes on the bearing capacity of concrete-filled stainless steel tubular X-joints should be considered in the design rules. [Copyright &y& Elsevier]

Abstract: Lightweight aggregates have been manufactured by sintering fly ash and crushing the product into suitable sizes. These aggregates possess unique characteristics that make them suitable for high strength and high performance concrete. Concrete produced using these aggregates is around 22% lighter and at the same time 20% stronger than normal weight aggregate concrete. Drying shrinkage is around 33% less than that of normal weight concrete. Moreover, the aggregates possess high durability characteristics required in high performance structures. The importance of the new aggregates lies mostly in the fact that superior qualities are achieved without having to increase the cement content. Thus it is possible to reduce the amount of cement by as much as 20% without affecting the required strength. Weight reduction may reduce precast concrete transportation costs as well as provide slender and spacious construction. Utilising fly ash to produce quality aggregates should yield significant environmental benefits. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental research on high strength concrete columns subjected to compression and biaxial bending forces. The aims of the experimental program are, first, to provide experimental tests of high strength concrete columns under the loads described and, second, to contribute to the knowledge regarding the behaviour of this type of columns. The tests presented intend to put forward experimental results that will help in the validation of numerical models used to analyse slender columns subjected to compression and biaxial bending forces, as well as to fill the existing lack of experimental results subjected to this type of loading. The following parameters have been considered in this research: eccentricity, skew angle and slenderness of the test specimen, from which a total of 56 test columns resulted. The cross-sectional dimensions are 200×100 mm, the lengths of the columns are 1, 2 and 3 m, and the cubic average compression strength is 103 MPa. [Copyright &y& Elsevier]

An effective compliance matrix c͂ is proposed to model the behavior of concrete based on phenomenological evidence and physical insight. Three parameters α, β and γ are introduced in the effective compliance matrix c͂. α and β introduced to model the different behavior of concrete in tension and compression, while the third parameter γ is introduced to account for volumetric change. The predictive capability of the proposed elasto-damage model for uniaxial and multiaxial stress paths is investigated for uniaxial compression, biaxial compression, triaxial compression, uniaxial tension, and tension-compression-compression. The simulative capability of the model to capture the phenomenological behavior of concrete such as strain softening, stiffness degradation, biaxial strength envelope, volumetric dilatation, different behavior in tension and compression, and gain in strength under increasing confinement is reflected. The predicted results correlate well with the available experimental data. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an accurate nonlinear finite element model for the behaviour and design of axially loaded concrete-filled square hollow section (SHS) and rectangular hollow section (RHS) steel tube columns. The nonlinear material models for confined concrete and steel tubes were carefully modeled in the finite element analysis. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled SHS and RHS steel tube columns. The study was conducted over a wide range of concrete cube strengths ranged from 30 to 110MPa. The overall depth of the steel tube-to-plate thickness ratio ranged from 10 to 40 covering compact SHS and RHS steel tube sections. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results obtained from the parametric study, it is found that the design strengths calculated using the American Specifications and Australian Standards are conservative, while the design strengths calculated using the European Code are accurate, except for the concrete-filled RHS compact steel tube columns having the overall depth of the steel tube-to-plate thickness ratio of 40. [Copyright &y& Elsevier]

Abstract: This paper presents the behaviour and design of axially loaded concrete-filled steel tube circular stub columns. The study was conducted over a wide range of concrete cube strengths ranging from 30 to 110 MPa. The external diameter of the steel tube-to-plate thickness () ratio ranged from 15 to 80 covering compact steel tube sections. An accurate finite element model was developed to carry out the analysis. Accurate nonlinear material models for confined concrete and steel tubes were used. The column strengths and load–axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled compact steel tube circular stub columns. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results of the parametric study, it is found that the design strengths given by the American Specifications and Australian Standards are conservative, while those of the European Code are generally unconservative. Reliability analysis was performed to evaluate the current composite column design rules. [Copyright &y& Elsevier]

Abstract: This paper presents a nonlinear finite element model to investigate the behaviour and design of axially loaded concrete-filled cold-formed high strength stainless steel tube columns. The study was conducted over a wide range of concrete cylinder strengths from 20 to 100 MPa. The depth of flat portion-to-plate thickness ratio of the square and rectangular hollow sections ranged from 16 to 96, covering compact and slender sections. The columns had different lengths so that the length-to-depth ratio remained a constant of 3. Nonlinear material models for confined concrete and stainless steel tubes were used in the finite element model. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of cross-section geometry and concrete strength on the behaviour and strength of the columns. The column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards. A design equation was proposed for concrete-filled stainless steel tube columns. It is shown that the design strengths obtained using the proposed modified equation are more accurate compared to the American and Australian/New Zealand predictions. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental investigation of concrete-filled cold-formed high strength stainless steel tube columns. The high strength stainless steel tubes had a yield stress and tensile strength up to 536 and 961 MPa, respectively. The behaviour of the columns was investigated using different concrete cylinder strengths varied from 40 to 80 MPa. A series of tests was performed to investigate the effects of the shape of the stainless steel tube, plate thickness and concrete strength on the behaviour and strength of concrete-filled high strength stainless steel tube columns. The high strength stainless steel tubes were cold-rolled into square and rectangular hollow sections. The depth-to-plate thickness ratio of the tube sections varied from 25.7 for compact sections to 55.8 for relatively slender sections. The columns had different lengths so the length-to-depth ratio generally remained at a constant value of 3. The concrete-filled high strength stainless steel tube specimens were subjected to uniform axial compression. The column strengths, load–axial strain relationships and failure modes of the columns were presented. The test strengths were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards that consider the effect of local buckling using an effective width concept in the calculation of the stainless steel tube column strengths. Based on the test results, design recommendations were proposed for concrete-filled high strength stainless steel tube columns. [Copyright &y& Elsevier]

Abstract: An experimental programme on high-strength rectangular concrete-filled steel hollow section columns is reported. A total of 22 specimens were tested under concentric loading. The test variables include the material strengths ( MPa; and 89 MPa), cross-sectional aspect ratio (1.0–2.0) and volumetric steel-to-concrete ratio (0.13–0.17). Favourable ductility performance was observed for the specimens in the tests. The experimental results are employed to calibrate the specifications in the codes (EC4, ACI and AISC) for the design of high-strength composite columns. Comparison indicates that the specifications in ACI and AISC conservatively estimate the failure loads of the specimens by 9 and 11%, respectively. The EC4 method gives a close and conservative estimate of the ultimate capacities with a difference of 1%. [Copyright &y& Elsevier]

The behaviour of circular concrete-filled steel tubes (CFT) with various concrete strengths under axial load is presented. The effects of steel tube thickness, the bond strength between the concrete and the steel tube, and the confinement of concrete are examined. Measured column strengths are compared with the values predicted by Eurocode 4, Australian Standards and American Codes. 15 specimens were tested with 30, 60 and 100 N/mm2 concrete strength, with a D/t ratio from 22.9 to 30.5. All the columns were 114 mm in diameter and 300 mm in length. The effect due to concrete shrinkage is critical for high-strength concrete and negligible for normal strength concrete. All three codes predicted lower values than that measured during the experiments. Eurocode 4 gives the best estimation for both CFT with normal and high-strength concrete. [Copyright &y& Elsevier]

The effects of mineral admixtures on fluidity, mechanical and hydrational exothermic behavior were studied. The results show that, double-adding ways, i e, fly ash and slag were added at the same time, not only improves the fluidity of fresh concrete with low W/B and compensates the lower early compressive strength of harden concrete caused by high adding amount of fly ash, but also greatly reduces the highest temperature rise, exothermic rate and total heat liberation of 3 day of binder pastes in HLPC, and postponed the arrival time of the highest temperature rise. HLPC was prepared and applied to project practice successfully. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the water permeability and chloride penetrability of high-strength lightweight concrete (LWC) in comparison to that of high-strength normal-weight concrete (NWC) with or without silica fume. The results were also compared with those of the concrete at a normal-strength level of about 30–40 MPa. In order to compare the water permeability and chloride-ion penetrability, LWC and NWC had the same proportion by volume. The only difference between them was the coarse aggregate used. The results indicated that at the strength level of about 30–40 MPa, the water permeability of the LWC was lower than that of the corresponding NWC. However, the water permeability of the high-strength LWC and NWC was of the same order. The resistance of the LWC to the chloride penetration was similar to that of the corresponding NWC both in the normal-strength and high-strength levels. As the compressive strength of the LWC was lower than that of the corresponding NWC, the results indicated that for a given 28-day strength, the LWC would probably have high resistance to water and chloride-ion penetration than the NWC. The results indicated that the resistance to the chloride penetration does not seem to be correlated to the water permeability of the concrete. There appears to be, however, a direct relationship between the rapid chloride penetrability determined by ASTM C1202 and the observed chloride penetration depth determined by the immersion and salt ponding tests. [Copyright &y& Elsevier]

Structures located in seismic zones require significant ductility. It is necessary to examine the bond slip characteristics of high strength concrete under cyclic loading. The cyclic bond of high strength concrete is investigated under different parameters, including load history, confining reinforcement, bar diameter, concrete strength, and the rate of pull out. The bond strength, cracking, and deformation are highly dependent on the bond slip behavior between the rebar and the concrete under cyclic loading. The results of cyclic testing indicate that an increase in cyclic displacement will lead to more severe bond damage. The slope of the bond stress – displacement curve can describe the influence of the rate of loading on the bond strength in a cyclic test. Specimens with steel confinement sustained a greater number of cycles than the specimens without steel confinement. It has been found that the maximum bond strength increases with an increase in concrete strength. Cyclic loading does not affect the bond strength of high strength concrete as long as the cyclic slip is less than the maximum slip for monotonic loading. The behavior of high strength concrete under a cyclic load is slightly different from that of normal strength concrete.Key words: bond, high strength, cyclic loading, bar spacing, loading rate, failure mechanism.Les structures localisées dans des zones sismiques requièrent une ductilité significative. Il est nécessaire d'examiner les caractéristiques de glissement de liens du béton à haute résistance sous une charge cyclique. Le lien cyclique du béton à haute performance est étudié sous différents paramètres, incluant l'historique de la charge, le renfort par confinement, le diamètre des barres, la résistance du béton, et le taux d'arrachement. La résistance, le craquement et la déformation du lien dépendent grandement du comportement du glissement du lien entre la barre avec crêtes et le béton sous une charge cyclique. Les résultats des tests cycliques indiquent qu'une augmentation dans le déplacement cyclique résulte en des dommages au liens plus sérieux. La pente de la courbe de déplacement en contrainte du lien peut décrire l'influence du taux de charge sur la résistance du lien dans un test cyclique. Les spécimens avec un confinement en acier ont supporté un plus grand nombre de cycles que les spécimens sans confinement en acier. Il a été trouvé que la résistance du lien maximale s'accroît avec l'augmentation de la résistance du béton. La charge cyclique n'affecte pas la résistance du lien de béton à haute résistance en autant que le glissement cyclique est moindre que le glissement maximal pour une charge monotonique. Le comportement du béton à haute résistance sous une charge cyclique est légèrement différent de celui d'un béton de résistance normale.Mots clés : lien, haute résistance, charge cyclique, espacement entre les barres, taux de chargement, mécanisme de rupture.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Tests were conducted to evaluate the effect of increased cement contents, decreased slumps, and use of water-reducing admixtures on the strength of air-entrained concrete made with air-cooled, blast-furnace slag aggregate. Results obtained show that both increased cement content and decreased slump (compared to mixes ordinarily used) result in large increases in flexural strength of paving concretes and in compressive strength of structural concretes. An admixture of the hydroxy-carboxylic acid type was effective in increasing strengths of the slag mixes and appeared to have the greatest influence on compressive strength and in the richer mixes. Data on drying shrinkage, tensile splitting strengths, and moduli of elasticity were obtained for part of the tests and limited studies of the effects of aggregate size and type of aggregate were included. [ABSTRACT FROM AUTHOR]

Massive high-strength concrete structures tend to have a high risk of cracking. Ground slag powder (GSP), a sustainable and green industrial waste, is suitable for high-strength concrete. We carried out an experimental study of the effects of GSP with a specific surface area of 659 m2/kg on the hydration, pore structure, compressive strength and chloride ion penetrability resistance of high-strength concrete. Results show that adding 25% GSP increases the adiabatic temperature rise of high-strength concrete, whereas adding 45% GSP decreases the initial temperature rise. Incorporating GSP refines the pore structure to the greatest extent and improves the compressive strength and chloride ion penetrability resistance of high-strength concrete, which is more obvious under early temperature-matching curing conditions. Increasing curing temperature has a more obvious impact on the pozzolanic reaction of GSP than cement hydration. From a comprehensive perspective, GSP has potential applications in the cleaner production of green high-strength concrete. [ABSTRACT FROM AUTHOR]

• Effective microorganism and fly ash included modified concrete was produced. • Achieved concretes showed strong resistance against sulfuric acid and sulphate attack. • The modified concrete revealed enhanced durability and high strength. Environmentally sustainable construction materials with reduced carbon footprint have ever-growing demand worldwide. Based on this factor, some modified cement concrete mixtures incorporated with optimum ratio of fly ash (FA) and effective microorganism (EM) were produced. The strength performance, water absorption, resistance to aggressive environments (sulfuric acid and sulphate) and microstructures of the proposed concretes was evaluated. Four different ratios of FA replacing ordinary Portland cement (OPC) were used to select the optimum composition. The water content was replaced with the EM solution of 5, 10, 15, and 20%. The FA and EM incorporating OPC in the concrete matrix were found to enhance the mechanical and durability characteristics of the modified concretes. The early compressive strength of proposed concrete was enhanced over 30% and the durability was improved against the harsh environment due to the incorporation of OPC with 10% of FA and EM. The optimum concrete obtained with the FA and EM of 10% was asserted to be environmentally beneficial towards less global warming. [ABSTRACT FROM AUTHOR]