Search Results (8)

Remote-pumped concrete for infrastructure construction is a key innovation of the mechanized and intelligent construction technology. This has brought steel-fiber-reinforced concrete (SFRC) into undergoing various developments, from conventional flowability to high pumpability with low-carbon features. In this regard, an experimental study on the mixing proportion design and the pumpability and mechanical properties of SFRC was conducted for remote pumping. Using the absolute volume method based on the steel-fiber-aggregate skeleton packing test, the water dosage and the sand ratio were adjusted with an experimental study on reference concrete with the premise of varying the volume fraction of steel fiber from 0.4% to 1.2%. The test results of the pumpability of fresh SFRC indicated that the pressure bleeding rate and the static segregation rate were not the controlling indices due to the fact that they were far below the limits of the specifications, and the slump flowability fitted for remote-pumping construction was verified by a lab pumping test. Although the rheological properties of the SFRC charactered by the yield stress and the plastic viscosity increased with the volume fraction of steel fiber, those of mortar used as a lubricating layer during the pumping was almost constant. The cubic compressive strength of the SFRC had a tendency to increase with the volume fraction of steel fiber. The reinforcement effect of steel fiber on the splitting tensile strength of the SFRC was similar to the specifications, while its effect on the flexural strength was higher than the specifications due to the special feature of steel fibers distributed along the longitudinal direction of the beam specimens. The SFRC had excellent impact resistance with an increased volume fraction of steel fiber and presented acceptable water impermeability. Full article

Steel-fiber-reinforced concrete (SFRC) is a composite material made by randomly distributing short steel fibers in normal concrete (NC). In this study, central pull-out tests of 32 specimens were performed to investigate the bond behavior between high-strength rebar and SFRC under the influence of the fraction of steel fiber by volume (V_f = 0%, 0.5%, 1.0% and 1.5%) and temperature (T = 20, 200, 400 and 600 °C). The results show that in NC specimens, splitting failure occurs below 400 °C, while split-pullout failure occurs above 600 °C. Split-pullout failure occurs in all SFRC specimens at each tested temperature. The bond strength between rebar and SFRC was found to decay significantly between 400 and 600 °C. The effect of V_f on the improvement in bond strength was more obvious between 400 and 600 °C than between 20 and 400 °C. The positive contribution of steel fibers to bond behavior is the construction of a rigid skeleton with coarse aggregates that can play a bridging role and effectively retard the expansion of concrete cracks. This improves the bond strength between rebar and SFRC at high temperatures. The bond–slip curve can be divided into five stages, namely the initial micro-slide phase, slip phase, splitting failure phase, stress drop phase and residual pull-out phase. A model of the bond–slip relationship between rebar and SFRC considering temperature and V_f was developed by modifying the existing model of the bond–slip relationship between rebar and NC. The model calculation results agree well with those of testing. Full article

The large production of cement is resulting in a high-carbon footprint, which is essential to minimize for sustainable concrete construction. Moreover, the large quantity of recycled coarse aggregate (RCA) from the demolition of old concrete structures is creating problems for landfill and disposal. The primary goal of this study is to investigate the seismic efficiency of innovative fiber-reinforced polymer (FRP)-recycled aggregate geopolymer concrete (RAGC) steel-tubed columns (FGSTCs) with an internal steel tube (STT), an external glass-FRP tube (GLT), and RAGC located between the two-tubed components to develop a serviceable structural element. To study their seismic functioning under axial load and lateral repeated load, five FGSTC specimens were manufactured and analyzed under quasi-static loads. The influence of three variables on the performance of FGSTC specimens, consisting of STT reinforcing ratio, compression ratio, and recycled coarse aggregate (RCA) replacement ratio, was investigated in this investigation. The produced specimens’ ductility, hysteretic loops, strain distribution, skeleton curves, stiffness functioning, energy capacity dissipation, damaging functioning, and strength loss were all assessed and discussed. The results of this investigation revealed that percentage substitution of RCA had a minor impact on the seismic functioning of FGSTCs; however, the compression-load ratio depicted a substantial impact. The energy loss of the FGSTCs was 24.5% higher than that of their natural aggregate equivalents. FGSTCs may have a 16.9% lower cumulative failure rate than their natural aggregate counterparts. Full article

In recent years, prepacked aggregate fibrous concrete (PAFC) is a new composite that has earned immense popularity and attracted researchers globally. The preparation procedure consists of two steps: the coarse aggregate is initially piled into a mold to create a natural skeleton and then filled with flowable grout. In this instance, the skeleton was completely filled with grout and bonded into an integrated body due to cement hydration, yielding a solid concrete material. In this research, experimental tests were performed to introduce five simple alterations to the ACI 544 drop weight impact test setup, intending to decrease result dispersion. The first alteration was replacing the steel ball with a steel bar to apply a line impact instead of a single point impact. The second and third introduced line and cross notched specimens at the specimen’s top surface and the load applied through a steel plate of cross knife-like or line load types. These modifications distributed impact load over a broader area and decrease dispersion of results. The fourth and fifth were bedding with sand and coarse aggregate as an alternate to the solid base plate. One-hundred-and-eight cylindrical specimens were prepared and tested in 12 groups to evaluate the suggested alteration methods. Steel and polypropylene fibers were utilized with a dosage of 2.4% to produce PAFC. The findings indicated that the line notched specimens and sand bedding significantly decreased the coefficient of variation (COV) of the test results suggesting some alterations. Using a cross-line notched specimen and line of impact with coarse bedding also effectively reduced COV for all mixtures. Full article

To ensure the quality of concrete construction, the workability of fresh mix measured by rational test methods is critical to be controlled. With the presence of steel fibers, whether the test methods and evaluation indices of fresh self-compacting concrete (SCC) are adaptable for self-compacting steel fiber reinforced concrete (SFRC) needs to be systematically verified. In this paper, seven groups of self-compacting SFRC, referenced with one group SCC, were prepared by using the mix proportion design method based on the steel fiber-aggregates skeleton packing test. The main factors included the volume fraction and the length of hooked-end steel fiber. Tests for filling ability, passing ability, and stability of fresh self-compacting SFRC and SCC were carried out. Results indicate that the adaptability was well for the slump-flow test with indices of slump flow and flow time T₅₀₀ to evaluate the filling ability, the J-ring flow test with an index of PA level to evaluate the passing ability, and the static segregation test with an index of static segregation resistance to evaluate the stability of fresh self-compacting SFRC. By the repeated tests and measurements, the slump cone should be vertically lifted off to a height of 300 mm within 3 s at a constant speed, the spacing of the rebar in the J-ring test should be adjusted to be two times the fiber length. If the table jumping test is used, the dynamic segregation percent should be increased to 35% to fit the result of the static segregation test. Good workability of the self-compacting SFRC prepared in this study is presented with the general evaluation of test results. Full article

Due to the mechanical properties related closely to the distribution of steel fibers in concrete matrix, the assessment of tensile strength of self-compacting steel fiber reinforced concrete (SFRC) is significant for the engineering application. In this paper, seven groups of self-compacting SFRC were produced with the mix proportion designed by using the steel fiber-aggregates skeleton packing test method. The hooked-end steel fibers with length of 25.1 mm, 29.8 mm and 34.8 mm were used, and the volume fraction varied from 0.4% to 1.4%. The axial tensile test of notched sectional prism specimen and the splitting tensile test of cube specimen were carried out. Results show that the axial tensile strength was higher than the splitting tensile strength for the same self-compacting SFRC, the axial tensile work and toughness was not related to the length of steel fiber. Finally, the equations for the prediction of tensile strength of self-compacting SFRC are proposed considering the fiber distribution and fiber factor, and the adaptability of splitting tensile test for self-compacting SFRC is discussed. Full article

A scientific and concise mix design method is an impending problem in the engineering application of self-compacting steel-fiber-reinforced concrete (SFRC). This paper focuses on the mix proportion of self-compacting SFRC, which is influenced by the steel fibers, along with its effects on the packing properties of the steel fiber aggregate skeleton. In total, 252 groups of packing tests were carried out for several main factors, including with various maximum particle sizes for the coarse aggregates, manufactured sand ratios ranging from 50% to 62%, and with different types of hooked-end steel fibers and crimped steel fibers, with volume fractions ranging from 0% to 2.0%. The results indicated that the void content and rational sand ratio of the steel fiber aggregate skeleton increased linearly with the fiber factor. These results provided a basis for the calculation of the binder content and rational sand ratio of the self-compacting SFRC. Combined with the absolute volume design method and the calculation formula for the water-to-binder ratio, a systematical procedure was proposed for the mix proportion design of the self-compacting SFRC. Based on the design method, eight groups of mixtures were cast and tested to verify the adaptability and practicability of the workability, air content, density, cubic compressive strength, and splitting tensile strength of the self-compacting SFRC. Meanwhile, the outcomes of this study confirmed the applicability of using manufactured sand as a complete replacement for natural sand for the self-compacting SFRC. Full article

This study explores highly eco-efficient preplaced aggregate concrete mixtures having superior tensile characteristics and impact resistance developed for pavement and infrastructure applications. A fully recycled granular skeleton consisting of recycled concrete aggregate and recycled tire rubber granules, and steel wire fibers from scrap tires are first placed in the formwork, then injected with a flowable grout. Considering its very high recycled content and limited mixing and placement energy (only the grout is mixed, and no mechanical vibration is needed), this material has exceptional sustainability features and offers superior time and cost savings. Moreover, typical problems of rapid loss of workability due to the high-water absorption of recycled aggregates and the floating of lightweight tire rubber granules are prevented since the aggregates are preplaced in the formwork. The much higher granular content and its denser skeleton reduce the cementitious dosage substantially and provide high volume stability against shrinkage and thermal strains. The behavior under impact loading of this sustainable preplaced recycled aggregate concrete, incorporating randomly dispersed steel wire fibers retrieved from scrap tires, was investigated using a drop weight impact test. The results show that recycled tire steel wire fibers significantly enhanced the tensile and impact properties. A two-parameter Weibull distribution provided an accurate prediction of the impact failure strength of the preplaced recycled aggregate concrete mixtures, allowing to avert additional costly laboratory experiments. Full article