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An investigation into the bonding capabilities of 0.6 in. (15.2 mm) prestressing strands cast in belitic calcium sulfoaluminate (BCSA) cement concrete beams was performed to determine if the current ACI development length requirements for prestressing strands are applicable to BCSA cement. Portland cement and BCSA cement concrete beam specimens of one mixture design were cast, with varying concrete ages at prestress release. Transfer lengths were determinedfor 28 days after casting using surface strain measurements and strand end slip. Prestress losses were measured using vibrating wire strain gauges and were compared to the AASHTO andPCI/Zia et al. methods. Flexural tests were performed to determine if adequate flexural bond performance was achieved with the specified development length. The BCSA prestressed concrete beams performed at least as well as the portland cement control specimens with regards to transfer length, development length, and flexural performance even when prestress release was performed at 2 hours after casting. Measured prestress losses for BCSA cement concrete beams were significantly less than predicted using the currently available methods. More work is needed to extend these findings to other mixture designs and water-cement ratios (w/c). Keywords:belitic calcium sulfoaluminate (BCSA) cement; bond; development length; prestressed concrete; rapid setting concrete; transfer length.

A persistent rise in the costs of construction materials has led to the need to address this problem in line with the Sustainable Development Goals. This research employed vegetal soft and rigid fibers in a screed mortar to produce a sustainable fabric-cement matrix. Four different vegetal-dried fibers (hemp, flax, miscanthus, and bamboo) with dosages of 0.4, 0.6, 0.8, 1.2, 2, and 4 kg/m[sup.3] were used. Laboratory investigations were slump test, bulk density, air occluded, shrinkage, and mechanical strength. Scanning Electron Microscope (SEM) assessments were performed and analyzed on the natural fibers and the screed formulation. The results highlight that fiber dosages significantly influence the above-mentioned properties.

Ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHP-FRC) were introduced in the mid 1990s. Special treatment, such as heat curing, pressure and/or extensive vibration, is often required in order to achieve compressive strengths in excess of 150 MPa (22 ksi). This study focuses on the development of UHP-FRCs without any special treatment and utilizing materials that are commercially available on the US market. Enhanced performance was accomplished by optimizing the packing density of the cementitious matrix, using very high strength steel fibers, tailoring the geometry of the fibers and optimizing the matrix-fiber interface properties. It is shown that addition of 1.5% deformed fibers by volume results in a direct tensile strength of 13 MPa, which is 60% higher than comparable UHP-FRC with smooth steel fibers, and a tensile strain at peak stress of 0.6%, which is about three times that for UHP-FRC with smooth fibers. Compressive strength up to 292 MPa (42 ksi), tensile strength up to 37 MPa (5.4 ksi) and strain at peak stress up to 1.1% were also attained 28 days after casting by using up to 8% volume fraction of high strength steel fibers and infiltrating them with the UHPC matrix.

This paper presents the experimental results concerning the mix design and fresh properties of a high-performance fibre-reinforced fine-aggregate concrete for printing concrete. This concrete has been designed to be extruded through a nozzle to build layer-by-layer structural components. The printing process is a novel digitally controlled additive manufacturing method which can build architectural and structural components without formwork, unlike conventional concrete construction methods. The most critical fresh properties are shown to be extrudability and buildability, which have mutual relationships with workability and open time. These properties are significantly influenced by the mix proportions and the presence of superplasticiser, retarder, accelerator and polypropylene fibres. An optimum mix is identified and validated by the full-scale manufacture of a bench component.

The maximum post-cracking tensile strength ([[sigma].sub.pc]) recorded in numerous investigations of ultra-high-performance fiberreinforced concrete (UHP-FRC) remains mostly below 15 MPa, and the corresponding strain ([[epsilon].sub.pc]) below 4/1000. Both values are significantly reduced when the specimen size increases, as is needed for real structural applications. Test data on [[sigma].sub.pc] and [[epsilon].sub.pc] from close to 100 series of direct tensile tests carried out in more than 20 investigations are analyzed. Factors influencing the strain capacity are identified. However, independently of the numerous parameters encountered, two observations emerged beyond all others: 1) the higher the post-cracking tensile strength (whichever way it is achieved), the higher the corresponding tensile strain; and 2) fibers mechanically deformed and/or with slip-hardening bond characteristics lead to an increase in strain capacity. A rational explanation for these observations is provided. The authors believe that achieving a large strain ([[epsilon].sub.pc]) at maximum stress is paramount for the successful applications of ultra-high-performance concrete in concrete structures not only for strength but, more critically, for ductility and energy absorption capacity improvements. Keywords: slurry-infltrated fiber concrete (SIFCON); slurry-infltrated mat concrete (SIMCON); steel fiber; strain capacity in tension; strainhardening; tensile strength; ultra-high-performance concrete (UHPC); ultra-high-performance fiber-reinforced concrete (UHP-FRC).

Impact resistance of Portland cement concrete (PCC) is an essential property in various applications of PCC, such as industrial floors, hydraulic structures, and explosion-proof structures. Steel-fiber-fortified high-strength concrete testing was completed using a drop-weight impact assessment for impact strength. One mix was used to manufacture 320 concrete disc specimens cured in both humid and dry conditions. In addition, 30 cubic and 30 cylindrical specimens were used to evaluate the compressive and indirect tensile strengths. Steel fibers with hooked ends of lengths of 20, 30, and 50 mm were used in the concrete mixtures. Data on material strength were collected from impact testing, including the number of post-first-crack blows (INPBs), first-crack strength, and failure strength. Findings from the results concluded that all the steel fibers improved the mechanical properties of concrete. However, hooked steel fibers were more effective than crimped steel fibers in increasing impact strength, even with a smaller length-to-diameter ratio. Concrete samples containing hybrid fibers (hooked + crimped) also had lower compressive strength than the other fibers. Comparisons and analogies drawn between the test results and the static analyses (Kolmogorov–Smirnov and Kruskal–Wallis) show that the p-value of the analyses indicates a more normal distribution for curing in a humid environment. A significant difference was also observed between the energy absorptions of the reinforced mixtures into steel fibers.

Efficient supplementary materials flourish the structural performance and sustainability of reinforced concrete structures. Steel fiber is one of these materials that have significant influence on enhancing tensile and flexural strengths and ductility of high strength reinforced concrete columns. This paper presents a review study on the structural performance of steel fiber reinforced concrete columns. The studied case was related to the columns that subjected to concentric or eccentric compression loads or combined compression loads and cyclic lateral loads. The current survey is divided into two branches; the first is related to fibreless HSC columns, while the other is specialized by SFRHSC ones. In addition to the prime actuator (steel fiber content), the investigated parameters were included concrete strength, transverse reinforcement properties, and axial load ratio. The results of this investigation showed that the positive influence of adding steel fiber on improving the flexural strength, fatigue life and resistance, delaying spalling failure of the exterior concrete shell and outward buckling of the longitudinal steel reinforcing bars. The optimum volume fraction of steel fiber used is 0.5% to 2% (by weight) and when 2% of steel fibers are introduced into the concrete mix, the columns’ cover didn’t spall away.

This study was conducted to investigate the effects of key structural parameters on the shear behavior of non-prestressed ultra-high-performance concrete (UHPC) beams passively reinforced with high-strength steel bars. The parameters studied were shear span to effective depth ratio a/d; volume fraction of steel fibers [V.sub.f]; longitudinal reinforcement ratio [rho]; and stirrups spacing s. Ten beam specimens with cross-section dimension (width x depth) 5.91 x 8.86 in. (150 x 225 mm) were quasi-statically loaded to failure on a simple span length of 68.9 in. (1.75 m), under a four-point loading configuration. The statistical analysis of the experimental data indicated that a/d, [V.sub.f] and s have significant effects on the shear capacity of UHPC beams, while the effects of [rho] are quite insignificant. A mechanistic model for estimating the shear capacity of reinforced UHPC beams was developed, validated, and shown to be reasonably accurate. Keywords: concrete beam; cracking pattern; high-strength steel; mechanistic model; shear capacity; ultra-high-performance concrete (UHPC); ultra-high-performance fiber-reinforced concrete (UHPFRC).