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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 investigation aims to predict and optimize self-consolidating concrete (SCC) characteristics containing fly ash (FA), silica fume (SF), and limestone powder (LP) as part of the cement by mass in the total powder content. Total powder content (P), proportion of FA, proportion of SF, proportion of LP, water-powder ratio (w/p), and proportion of high-range water-reducing admixture (HRWRA) were the input parameters of the mixtures, and the desirable responses were slump flow, 7- and 56-day compressive strength, and flexural strength. A total of 90 concrete mixtures were designed using the central composite design (CCD) concept in Minitab 18 statistical software under response surface methodology (RSM) to simulate and optimize the variables and responses of models. Results showed that high relation can be developed between the responses and the constituent materials in predicting characteristics of SCC, removing the drudgery of repetitive laboratory testing and enabling rapid decision-making for building applications. The slump flow increased with the increase in total powder content, FA content, w/p, and HRWRA dosage and decrease in SF content, while LP has insignificant effect on slump flow results. The increase in partial replacement of cement by FA decreased the compressive strength of mixtures at early ages. The higher values of compressive strength were observed when SF incorporated in higher levels, and flexural strength also enhanced with the increase in SF content. Keywords: central composite design (CCD); compressive strength; flex-ural strength; optimization; response surface methodology (RSM); self-consolidating concrete (SCC).

This study investigated the serviceability behavior and strength of polypropylene fiber (PF)-reinforced self-consolidating concrete (PFSCC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five full-scale concrete beams measuring 3100 mm long x 200 mm wide x 300 mm deep (122.1 x 7.9 x 11.8 in.) were fabricated and tested up to failure under four-point bending cyclic loading. Test parameters included the longitudinal reinforcement ratio (0.78, 1.18, and 1.66%) and PF volume (0, 0.5, and 0.75% by concrete volume). The effect of these parameters on serviceability behavior and strength of the test specimens is analyzed and discussed herein. All the beams were evaluated for cracking behavior, deflection, crack width, strength, failure mode, stiffness degradation, and deformability factor. The test results revealed that increasing the reinforcement ratio and PF volume enhanced the serviceability and flexural performance of the beams by effectively restraining crack widths, reducing deflections at the service and ultimate limit states, and decreasing residual deformation. The stiffness exhibited a fast-to-slow degradation trend until failure for all beams, at which point the beams with a higher reinforcement ratio and fiber volume evidenced higher residual stiffness. The cracking moment, flexural capacities, and crack width of the tested beams were predicted according to the North American codes and design guidelines and compared with the experimental ones. Lastly, the deformability for all beams was quantified with the J-factor approach according to CSA S6-19. Moreover, the tested beams demonstrated adequate deformability as per the calculated deformability factors. Keywords: crack width; cyclic loading; deflection; deformability; flexural behavior; glass fiber-reinforced polymer (GFRP) bar; polypropylene fiber (PF); reinforced concrete beams; self-consolidating concrete (SCC); serviceability; strength.

Mixed recycled aggregate (MRA) is considered a sustainable construction material, and its use in precast concrete is currently banned due to its poor engineering performance. This paper aims to evaluate the feasibility of partial replacement of natural coarse aggregate with MRA in self-consolidating concrete (SCC) for manufacturing architectural precast concrete sandwich wall panels. To this end, five MRAs from recycling plants were characterized, out of which two were selected to develop SCC. SCC mixtures with three replacement levels and three water compensation degrees were produced, and their physical, mechanical, durability, and aesthetic properties were examined. The results showed that the incorporation of MRA dominated the mechanical properties of SCC, while the water compensation degree primarily affected the flowability and carbonation resistance. The presence of MRA had no considerable effect on the aesthetic characteristics. Up to 10% MRA in weight of total aggregates could be used in precast SCC. Keywords: aesthetic characteristics; architectural precast concrete; mechanical property; mixed recycled aggregate (MRA); natural carbonation; resilience; self-consolidating concrete (SCC); surface electrical resistivity; sustainability.

This systematic review and meta-analysis per PRISMA 2020 addresses the use of recycled concrete aggregates as a replacement for aggregates in self-consolidating concrete for structural and non-structural use. It provides a comprehensive evaluation of the available research and offers a synthesised overview of the potential use of recycled concrete aggregate in self-consolidating concrete beyond standardised replacement levels. A total of 256 research papers were obtained from different databases, and after a detailed content review, only 24 unique experimental research studies fulfilled the review criteria. Data were extracted on recycled concrete aggregate source, pre-treatment, replacement ratio, mix proportions, fresh properties, strength, stiffness, and durability. It was observed across all studies that the recycled concrete aggregates originated from precast concrete rejected elements with a low water-to-cement ratio, producing an equal or stronger concrete than the reference concrete in the studies; however, none of the studies included in this research resulted in a higher modulus of elasticity than the corresponding reference concrete. Additionally, moderate aggregate replacement (20–50%) preserved the workability, whereas high replacements (75–100%) affected fresh concrete properties as well as increased shrinkage and creep. The inclusion of fine recycled concrete aggregate in addition to coarse recycled concrete aggregate has a larger effect on lowering compressive strength and stiffness in the concrete. Overall, high-quality coarse recycled concrete aggregate (precast rejects or screened demolition waste)—an aggregate replacement level of around 50%—facilitates the production of sustainable self-consolidating concrete, whereas full replacement requires aggregate pre-treatment and a carefully optimised mix design.

The axial behavior of self-consolidating concrete (SCC) columns confined with engineered cementitious composite (ECC) was investigated through experimental and analytical investigations. Both square and cylindrical-shaped columns were considered in the study. The other variables of the study were the presence or absence of longitudinal reinforcement, the thickness of ECC confinement, and the loading types. The behavior of the columns was evaluated in terms of the axial load-deflection response, strain characteristics, ultimate load-carrying capacity, ductility, energy absorption capacity, and modes of failure. It was found that the ECC confinement significantly increased the ultimate axial load capacity and energy absorption of the SCC columns. The confined columns also exhibited enhanced ductile behavior compared to the corresponding core column under axial loading. The confined concrete strengths predicted by existing analytical models were found to be in satisfactory agreement with the experimentally obtained values. Keywords: axial behavior; confined column; ductility; energy absorption capacity; engineered cementitious composite (ECC); load-deflection response; self-consolidating concrete (SCC); ultimate load capacity.

The effect of the length of main and side chains of high-range water-reducing admixture (HRWRA) on some fresh and hardened properties of self-consolidating concretes (SCCs) was researched. For this purpose, three polycarboxylate ether-based HRWRA admixtures with different side and main chain lengths were synthesized. For a given SCC slump-flow value, the admixture requirement was the least when the admixture having a medium side chain length (2400 g/mol) was used. Moreover, decreasing the main chain length of the admixture improved the fresh properties' retention of SCC. The fact was attributed to the increase in free polymer in the mixture by increasing the side chain length of the admixture. The main and side chain lengths of the HRWRA admixture were significantly influential on the early compressive strength of SCC mixtures but had a negligible effect on their 7- and 28-day compressive strength and 28-day water absorption.

The aim of this paper is to investigate the mechanical properties of self-consolidating concrete (SCC) incorporating ground copper slag (GCS) as cement replacement. Herein, SCC has been produced using GCS as cement replacement by weight ratios of 5, 10, 15, 20, 25, and 30%. The mechanical and durability properties of self-consolidating ground copper slag concrete (SCGCSC) have been investigated in related tests as compressive, flexural, and splitting strengths; unit weight; water absorption; free drying shrinkage; water penetration; and alkali-silica reaction (ASR). Self-consolidating ability tests such as V-funnel, J-ring, slump flow, and L-box were also conducted to ensure the SCCs fulfilled the requirements for self-consolidating. The experimental results indicate that the compressive, flexural, and split tensile strengths of the SCC containing 5% GCS are the highest among the mixtures. However, up to a replacement level of 15%, hardened strengths and unit weights are almost equal to or slightly better than the control mixture. Keywords: cementitious material; copper slag; hardened properties; self-consolidating concrete (SCC).

In this paper, a fluid-solid coupling method is used to simulate the aggregate settling in mortar, and the accuracy of this method is verified by comparing the simulation results with experimental results. To evaluate the effects of aggregate shape characteristics and mortar rheological properties on aggregate settling, the authors simulate the settling processes of different aggregates in various mortars. The results show that the shape and orientation of aggregates have a greater influence than aggregate surface properties on settling. The effect of the mortar yield stress is greater than that of mortar plastic viscosity on the aggregate stable state. Considering the interactions between aggregates, the self-consolidating concrete (SCC) segregation process is simulated to observe the motion and distribution of aggregates and analyze the mechanical mechanisms between aggregates. Keywords: aggregate settling; aggregate shape characteristics; fluid-solid coupling method; mortar rheological properties; self-consolidating concrete (SCC) segregation.

Palm oil fuel ash (POFA) was used as a supplementary cementitious material to investigate its effects on the major mechanical properties and microstructure of self-consolidating high-strength concrete (SCHSC). Different SCHSC mixtures were prepared based on the water-binder ratios (w/b) of 0.25 to 0.40 and using the POFA contents of 10 to 30% by weight of cement. The hardened concrete specimens were tested at the ages of 28 and 56 days to determine the key mechanical properties, such as compressive strength, splitting tensile strength, flexural strength, and static and dynamic moduli of elasticity. The compressive strength was also determined at the ages of 3, 7, 14, and 91 days. The effects of the w/b and POFA content on the aforementioned mechanical properties were observed. The microstructures of the 56-day-old concretes were also analyzed based on their scanning electron micrographs (SEMs) in the cases of 0 and 20% POFA contents, considering all the w/b. Test results revealed that the compressive strength, splitting tensile strength, flexural strength, and static and dynamic moduli of elasticity increased with lower w/b and up to 20% POFA contents owing to a greater amount of calcium silicate hydrate (CSH) obtained from cement hydration and pozzolanic reaction. The SEMs of the concretes revealed that 20% POFA contributes to producing a denser microstructure with additional CSH, which enhanced the mechanical properties of the SCHSC with POFA. However, a POFA content substantially higher than 20% (for example, 30%) has a diminishing effect on the tested mechanical properties of the SCHSC, mainly because of reduced cement content and deficient pozzolanic reaction, leading to a lower amount of CSH. The overall research results revealed that the optimum POFA content and the best w/b are 20% and 0.35, respectively. Keywords: high-strength concrete (HSC); mechanical properties; micro-structure; palm oil fuel ash (POFA); self-consolidating concrete (SCC); water-binder ratio (w/b).