Mechanical characteristics of self-compacting concrete with and without fibres

Fibre-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fibre addition. Considering these properties, the application ranges of both FRSCC and SCC can be covered. A test program is carried out to develop information about the mechanical properties of FRSCC. For this purpose, four SCC mixes - plain SCC, steel, polypropylene and hybrid FRSCC - Are considered in the test program. The properties include compressive and splitting tensile strengths, modulus of elasticity, modulus of rupture, and compressive stress-strain curve. These properties are tested at 3, 7, 14, 28, 56 and 91 days. Relationships are established to predict the compressive and splitting tensile strengths, modulus of elasticity, modulus of rupture, and compressive stress-strain curve. The models provide predictions matching the measurements

Evaluation and Comparison of Analytical Models to Determine the Bond Characteristics of Steel Fibre Reinforced Self-Compacting Concrete

Steel fibre reinforced self-compacting concrete (SFRSCC) can be placed and compacted under its self weight with little or no mechanical vibration. It is at the same time cohesive enough to be casted without segregation or bleeding. Steel fibres improve many of the properties of self-compacting concrete (SCC) elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibres on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fibre and SCC. This by comparison of the five analytical models including (i.e. Naaman et al. (1991a,b), Dubey (1999), Cunha (2007), Soranakom (2008) and Lee et al. (2010)) with the experimental results from the four recently conducted single fibre pull-out tests. The influence of the fibre end hook, embedded length, fibre orientation angle, on the bond characteristic between fibre and SCC are determined and discussed. The accuracy of each analytical model also has been examined

A Comparison of the Bond Characteristics in Conventional and Self-Compacting Concrete, Part I: Experimental Results

Self-compacting concrete (SCC) is a very flowing material that can flow through the reinforcement and fill the formworks without any need of vibration during the concrete placement process. The material properties of SCC including bond characteristics must be well understood in order to use this type of high performance concrete in structural members broadly. This paper presents a comparison of the experimental results from the nine recent investigations on the bond strength of SCC and conventional concrete (CC). The comparison is based on the measured bond between reinforcing steel and concrete by utilizing the pullout test on the embedded bars at various heights in mock-up structural elements to assess the top-bar effect and on single bars in small prismatic specimens and conducting the beam tests. The investigated affecting parameters on bond strength are: the steel bar diameter, concrete compressive strength, types of bar (plain or deformed), embedded length of the bar, concrete type, concrete cover, curing age of concrete, casting direction of concrete and height of the embedded bar along the formwork

A Comparison of the Bond Characteristics in Conventional and Self-Compacting Concrete, Part II: Code Provisions and Empirical Equations

Self-compacting concrete (SCC) is a highly workable concrete that flows through complex structural elements under its own weight. It is cohesive enough to fill the spaces of almost any size and shape without segregation or bleeding. This makes SCC become more practical wherever concrete placing is difficult, such as in heavily-reinforced concrete members or in complicated formworks. Bond behaviour between concrete and reinforcement is a primary factor in design of reinforced concrete structures. This study presents a comparison between code provisions and empirical equations with the experimental results from the recent studies on the bond strength of SCC and conventional concrete (CC). The comparison is based on the measured bond between reinforcing steel and concrete by utilizing the pullout test on the embedded bars at various heights in mock-up structural elements to assess the top-bar effect and on single bars in small prismatic specimens; and conducting the beam tests. The investigated varying parameters on bond strength are: the steel bar diameter, concrete compressive strength, concrete type, curing age of concrete and height of the embedded bar along the formwork

Comparison of Creep Prediction Models for Self-Compacting and Conventional Concrete

Realistic prediction of concrete creep is of crucial importance for durability and long-term serviceability of concrete structures. To date, research about the behaviour of self-compacting concrete (SCC) members, especially concerning the long-term performance, is rather limited. Hence, the realistic SCC creep strain prediction is an important requirement of the design process of this type of concrete structures. SCC is quite different from conventional concrete (CC) in mixture proportions and applied materials, particularly in the presence of aggregate which is limited. This paper reviews the accuracy of the creep prediction models proposed by six international codes of practice, including: CEB-FIP 1990, ACI 209R (1992), Eurocode 2 (2001), AASHTO (2004), AASHTO (2007) and AS 3600 (2009). The predicted creep strains are compared with actual measured creep strains in 60 mixtures of SCC and 17 mixtures of CC. The affecting parameters on the creep of SCC including: the water to binder ratio, binder to aggregate ratio, sand ratio, and curing age are investigated and discussed

Bond characteristics of steel fiber and deformed reinforcing steel bar embedded in steel fiber reinforced self-compacting concrete (SFRSCC)

© Versita sp. z o.o. Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of the self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fiber and SCC firstly. Based on the available experimental results, the current analytical steel fiber pullout model (Dubey 1999) is modified by considering the different SCC properties and different fiber types (smooth, hooked) and inclination. In order to take into account the effect of fiber inclination in the pullout model, apparent shear strengths (τ(app)) and slip coefficient (β) are incorporated to express the variation of pullout peak load and the augmentation of peak slip as the inclined angle increases. These variables are expressed as functions of the inclined angle (φ). Furthurmore, steel-concrete composite floors, reinforced concrete floors supported by columns or walls and floors on an elastic foundations belong to the category of structural elements in which the conventional steel reinforcement can be partially replaced by the use of steel fibers. When discussing deformation capacity of structural elements or civil engineering structures manufactured using SFRSCC, one must be able to describe thoroughly both the behavior of the concrete matrix reinforced with steel fibers and the interaction between this composite matrix and discrete steel reinforcement of the conventional type. However, even though the knowledge on bond behavior is essential for evaluating the overall behavior of structural components containing reinforcement and steel fibers, information is hardly available in this area. In this study, bond characteristics of deformed reinforcing steel bars embedded in SFRSCC is investigated secondly

Creep and Shrinkage Self-Compacting Concrete (SCC) Analytical Models

Abstract: In the structures whose long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Creep and shrinkage, vary with the constituent and mixtures proportions, and depend on the curing conditions and work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including creep and shrinkage of the SCC. Hence, the realistic prediction creep and shrinkage strains of SCC are an important requirement of the design process of this type of concrete structures. In this study, three proposed creep models and four shrinkage models available in the literature are compared with the measured results of 52 mixtures for creep and 165 mixtures for shrinkage of SCC. The influence of various parameters, such as mixture design, cement content, filler content, aggregate content, and water cement ratio (w/c) on the creep and shrinkage of SCC are also compared and discussed

Epidemiology of Shigella-Associated diarrhea in Gorgan, north of Iran

Objective : Shigella is an important etiological agent for diarrhea and especially dysentery. Shigellosis is an intestinal infection that is a major public health problem in many developing countries. The aim of this study was to evaluate the prevalence of Shigella and its various species in diarrheal samples in Gorgan located in the north of Iran. Materials and Methods: Between January-December 2005, the epidemiology of Shigella- associated diarrhea was studied among 634 patients in Gorgan. The diarrheal samples accompanied with a questionnaire, which contained the demographic and main symptoms of the patients, were transported to the laboratory and inoculated in different culture media. Colonies suspected to be of Shigella were detected using differential biochemical tests and subsequently, the serotype of Shigella was defined using antisera. Results : Shigella was isolated from 56/634 diarrheal samples) (8.8%) of which S. sonnei was the predominant species (55%). Occurrence of Schigella was highest in the 2-5 years′ age group (70.9%) and highest in summer (73.2%) with the most frequent clinical manifestation being abdominal pain (67.8%). The prevalence of Shigella in males and females was 8 and 9.8% respectively, but this difference was not statistically significant. Conclusion: It has been shown that Shigella sonnei is the most common Shigella serogroup among 2-5 year-old children in Gorgan. It is therefore suggested that hygienic training be given to childcare attendants and the children themselves

Nano-to-Submicron Hydroxyapatite Coatings for Magnesium-based Bioresorbable Implants - Deposition, Characterization, Degradation, Mechanical Properties, and Cytocompatibility.

Magnesium (Mg) and its alloys have shown attractive biocompatibility and mechanical strength for medical applications, but low corrosion resistance of Mg in physiological environment limits its broad clinical translation. Hydroxyapatite (HA) nanoparticles (nHA) are promising coating materials for decreasing degradation rates and prolonging mechanical strength of Mg-based implants while enhancing bone healing due to their osteoconductivity and osteoinductivity. Conformal HA coatings with nano-to-submicron structures, namely nHA and mHA coatings, were deposited successfully on Mg plates and rods using a transonic particle acceleration (TPA) process under two different conditions, characterized, and investigated for their effects on Mg degradation in vitro. The nHA and mHA coatings enhanced corrosion resistance of Mg and retained 86-90% of ultimate compressive strength after in vitro immersion in rSBF for 6 weeks, much greater than non-coated Mg that only retained 66% of strength. Mg-based rods with or without coatings showed slower degradation than the respective Mg-based plates in rSBF after 6 weeks, likely because of the greater surface-to-volume ratio of Mg plates than Mg rods. This indicates that Mg-based plate and screw devices may undergo different degradation even when they have the same coatings and are implanted at the same or similar anatomical locations. Therefore, in addition to locations of implantation, the geometry, dimension, surface area, volume, and mass of Mg-based implants and devices should be carefully considered in their design and processing to ensure that they not only provide adequate structural and mechanical stability for bone fixation, but also support the functions of bone cells, as clinically required for craniomaxillofacial (CMF) and orthopedic implants. When the nHA and mHA coated Mg and non-coated Mg plates were cultured with bone marrow derived mesenchymal stem cells (BMSCs) using the in vitro direct culture method, greater cell adhesion densities were observed under indirect contact conditions than that under direct contact conditions for the nHA and mHA coated Mg. In comparison with non-coated Mg, the nHA and mHA coated Mg reduced BMSC adhesion densities directly on the surface, but increased the average BMSC adhesion densities under indirect contact. Further long-term studies in vitro and in vivo are necessary to elucidate the effects of nHA and mHA coatings on cell functions and tissue healing

Multiple Object Tracking in Urban Traffic Scenes with a Multiclass Object Detector

Multiple object tracking (MOT) in urban traffic aims to produce the trajectories of the different road users that move across the field of view with different directions and speeds and that can have varying appearances and sizes. Occlusions and interactions among the different objects are expected and common due to the nature of urban road traffic. In this work, a tracking framework employing classification label information from a deep learning detection approach is used for associating the different objects, in addition to object position and appearances. We want to investigate the performance of a modern multiclass object detector for the MOT task in traffic scenes. Results show that the object labels improve tracking performance, but that the output of object detectors are not always reliable.Comment: 13th International Symposium on Visual Computing (ISVC