Search

The current research reports the development of a green lightweight engineered cementitious composite (GLECC) using local industrial wastes. Three types of industrial waste materials, including stone sludge powder, electric arc furnace dust and silica fume, were utilised fully or partially to replace ordinary constituent materials of engineered cementitious composite. Moreover, polypropylene fibres were substituted for polyvinyl alcohol fibres. The influences of different dosages of polypropylene fibres and silica fume on the mechanical properties of GLECC were experimentally tested. Then, the response surface method was employed for developing mathematical models of predicting mechanical properties and executing optimisation to obtain optimum combinations of polypropylene fibres and silica fume. The results revealed that the fresh and hardened densities and compressive strength declined with an increment in polypropylene fibres, while both flexural strength and toughness improved due to incorporating polypropylene fibres up to 2%. Adding up to 10% silica fume not only enhanced the strength and toughness but also reduced the fresh and hardened density of GLECC. The mathematical models developed to predict the mechanical characteristics were significant and accurate, with the highest error of 10%. The optimum dosage of variables was 14.2% silica fume and 2% polypropylene fibres with 79% desirability. [ABSTRACT FROM AUTHOR]

In this paper, the flexural ductility of lap-spliced reinforced concrete (RC) beams is experimentally investigated. Twenty-four specimens were designed and manufactured for laboratory experiments. Concrete compressive strength, amount of transverse reinforcement over the splice length, and the diameter of longitudinal bars were selected as the main variables. The ductility of tested specimens is evaluated based on a previously defined ductility ratio. Results show that concrete strength and amount of transverse reinforcement over the splice have major effects on ductility. With an appropriate amount of transverse reinforcement, a satisfactory ductility response for different concrete strengths can be obtained. The CSA-A23.3-04 Standard provisions on bond strength and ductility of lap-spliced RC beams are evaluated and discussed. This study shows that the provisions in predicting the bond strength of lap-spliced concrete beams are adequate but may not achieve a satisfactory performance for ductility. An equation is proposed to achieve the appropriate ductility. Key words: bond, ductility, longitudinal tensile reinforcement, reinforced concrete beam, splice length, transverse reinforcement. Cet article presente une etude experimentale sur la ductilite en flexion de poutres en beton arme a recouvrement. Un total de 24 specimens a ete concu et fabrique pour des experiences en laboratoire. Les principales variables sont la resistance en compression du beton, la quantite d'armature transversale sur la longueur du recouvrement et le diametre des tiges longitudinales. La ductilite des echantillons testes est evaluee en se basant selon un rapport de ductilite predefini. Les resultats montrent que la resistance du beton et la quantite d'armature transversale du recouvrement ont un impact sur la ductilite. Avec une armature transversale adequate, nous obtenons une reponse en ductilite satisfaisante pour differentes resistances de beton. Les dispositions de la norme CSA A23.3-04 sur la resistance des liens et la ductilite des poutres en beton arme a recouvrement sont evaluees et discutees. La presente etude montre que les dispositions servant a predire la resistance du lien de poutres en beton arme a recouvrement sont adequates mais pourraient ne pas atteindre un niveau de rendement adequat en ductilite. Une equation est proposee afin d'atteindre la ductilite adequate. [Traduit par la Redaction] Mots-cles: lien, ductilite, armature en tension longitudinale, poutre en beton arme, longueur de recouvrement, armature transversal., Introduction Bond between concrete and the tensile reinforcement is a major problem in reinforced concrete (RC) structures, as far as strength and safety is concerned. The bond strength of spliced [...]

The size effect on flexural properties and fracture behavior of polypropylene fiber-reinforced engineered cementitious composite (PPFECC) containing local waste materials was investigated. Geometrically similar notched beams with dimensions of 190 x 70 x 70 mm (small), 380 x 70 x 140 mm (medium), and 760 x 70 x 280 mm (large) were tested using three-point bending to study the size effect on flexural properties, toughness, and fracture behavior in PPFECC and the influence of tensile ductility of PPFECC on the size effect parameter. Two PPFECC mixtures containing 1% (PPFECC1) and 2% (PPFECC2) volume fraction of polypropylene fibers were prepared. The results indicated clear size effect on ductility, flexural strength, normalized deflection, normalized toughness, and fracture energy for both PPFECCs. The flexural properties and fracture behavior in PPFECC1 were more sensitive to the size effect parameter due to its lower tensile ductility compared to PPFECC2. Moreover, according to Bažant's size effect curve, the behavior of notched beams in PPFECC2 with higher tensile ductility was closer to the strength criterion compared to PPFECC1. [ABSTRACT FROM AUTHOR]

In this experimental research, the effects of polypropylene fibers on size effect and fracture properties of lightweight aggregate concrete were studied. Two methods, including size effect method and work of fracture method, were used to investigate and analyze the size effect and fracture properties on different sizes of notched beams. The polypropylene fiber contents were 0.5%, 0.75%, and 1% by volume fraction. The obtained results revealed that increasing the polypropylene fibers in lightweight aggregate concrete relatively decreased the dependence of strength on the size effect parameter, while the addition of polypropylene fibers exhibited significant influence on decreasing the size dependency of ductility and fracture energy in lightweight aggregate concrete. Moreover, the increase of polypropylene fibers improved the total fracture energy (GF), initial fracture energy (Gf), characteristic length (lch), length of fracture process zone (cf), and critical stress intensity factor (KIc) of lightweight aggregate concrete in both size effect method and work of fracture method. This increase was more significant in work of fracture method because of considering the post-peak behavior. The size effect method was suitable and accurate for plain lightweight aggregate concrete. The GF/Gf ratio increased from 2.88 in plain lightweight aggregate concrete to 12.26 in polypropylene fiber reinforced lightweight aggregate concrete. [ABSTRACT FROM AUTHOR]

This study presents a new method for strengthening the circular reinforced concrete (RC) column to foundation connections with shape memory alloy (SMA) bars and carbon fiber reinforced polymer (CFRP) sheets. In the experimental part of the study, three specimens of RC column-foundation connections were cast and tested. One specimen was used as the reference specimen without strengthening. Two other specimens were strengthened with longitudinal SMA bars and CFRP sheets. These specimens were under a constant axial compressive load and cyclic lateral displacements, simultaneously. Next, initial stiffness, energy dissipation capacity, lateral load capacity, ductility, and residual displacement of the specimens were investigated. Due to the superelastic behavior of SMA bars, the residual displacement of column-foundation connections was considerably less than that of the reference specimen. Compared to the reference specimen, the SMA-strengthened and SMA-CFRP-strengthened connections recovered 71.59% and 76.57% of the residual displacement. Therefore, SMA bars were able to recover residual displacements under cyclic loading. Also, the combination of the SMA bars with CFRP sheet was a promising solution for enhancing the amount of the energy dissipation, lateral load capacity, initial stiffness, and ductility parameters. Compared to the reference specimen, the energy dissipation, lateral load capacity, initial stiffness, and ductility ratio parameters of SMA-CFRP-strengthened connection increased about 43.45%, 76.20%, 81.69%, and 242.45%, respectively. In the numerical part of the study, a subroutine was applied for modeling the SMA materials. For the analysis, this subroutine was linked with ABAQUS software. The numerical results showed a close correlation with the experimental results. [ABSTRACT FROM AUTHOR]

Many primary behavioral properties of concrete, including flexural strength, fatigue resistance, impact, thermal shock and brittle fracture could be improved by using reinforcing fibers into the concrete. The present study deals with the physical and mechanical behavior of Self-Compacting Concrete (SCC) containing polypropylene fibers as well as the effect of polypropylene fibers on increasing the strength of SCC and increasing its impact resistance and thermal properties. To this aim, self-compacting concrete containing 0, 0.1 and 0.3 percent by volume of polypropylene fibers was used. In order to investigate the effect of heat on the fiber-reinforced concrete, experiments were carried out on the specimens with 28 days of age, which were exposed to 250°C temperature for 8 hours. In this research, 6 cylindrical compressive test specimens, 6 tensile test specimens and 15 rectangular beams are built. Results showed that tensile strength and impact resistance are improved by increasing the presence of fibers in SCC. It was found that by adding fibers, impact resistance has increased up to 140%. Concerning the effect of fibers on the heated concrete containing fibers, it was found that fibers reduce the negative effect of heat on compressive strength, tensile strength as well as on impact resistance. [ABSTRACT FROM AUTHOR]

This paper presents an equation to calculate the required development/ splice length of reinforcing bars. The equation is based on previous studies on bond between normal-strength concrete (NSC) and high-strength concrete (HSC) and reinforcing bars. The previous proposed equation to predict the bond strength has been modified to account for the effect of rib properties of reinforcing bars. Also, a new parameter to account for the effect of transverse reinforcement (TR) on bond strength has been introduced. The comparison between the results of 284 available tests in cases of NSC and HSC shows that the new proposed model correlates very well with the test results. Using the proposed equation for bond strength, an equation to calculate the development/splice length has been derived. The equation requires providing some amounts of TR along the development/splice length. By providing the calculated value of TR, the proposed development/splice length would result in adequate ductility for beams with spliced bars. The proposed procedure correlates well with the test results. [ABSTRACT FROM AUTHOR]

Comments on the results of the study "Punching Shear Strength of Reinforced Concrete Slabs Strengthened With Glass Fiber-Reinforced Polymer (GFRP) Laminates," by Cheng-Chih Chen and Chung-Yan Li. Information on the proposed method to predict the ultimate punching shear strength of reinforced concrete slabs strengthened with GFRP laminates; Comparison of test results with calculated values; Function of GFRP laminates as the tensile steel reinforcement.