The optimization of mix proportions based on the targeted fresh and hardened performances of self-compacting concrete (SCC) is a foundation for its transition from laboratory research to industrial production. In this paper, the mix proportions of various SCC mixtures were designed by the absolute volume method with changes in the content of river sand and manufactured sand, the content of fly ash and granulated ground blast furnace slag (GGBS) and the maximum particle sizes of coarse aggregates. This experimental study was carried out to verify the workability, density and cubic compressive strength of SCC. The results show that SCC demonstrated good performance with appropriate mix proportions of manufactured sand and river sand. A hybrid effect of fly ash and GGBS appeared on the fresh performance of SCC with a constant strength, and the coarse aggregate with a smaller maximum particle size was beneficial to the workability but detrimental to the compressive strength of SCC. Finally, the optimization of the mix proportion of SCC was evaluated by grey relational analysis, in which the weight of the indicators was determined by the entropy method to improve the evaluation credibility. As a result, the optimal mix proportions of SCC were selected.

For the structural application of high-performance Steel Fiber Reinforced Expanded-shale Lightweight Concrete (SFRELC), a reliable bond of ribbed steel bar should be ensured. In this paper, an experimental study was carried out on the bond properties of ribbed steel bar embedded in SFRELC by the direct pull-out test. The SFRELC was produced with a strength grade of 35 MPa and a volume fraction of steel fiber as 0%, 0.8%, 1.2%, 1.6% and 2.0%, respectively. Fifteen groups of specimens were made with a central placed steel bar with diameter of 14 mm, 20 mm and 28 mm, respectively. Complete bond stress-slip curves were determined for each group of specimens, and the characteristic values of bond-stress and slip at key points of the curves were ascertained. Results show that the bond strength, peak-slip and residual bond strength increased with the increase of the volume fraction of steel fiber. With the increase of steel bar diameter, bond strength decreased while the peak-slip increased, and the descending curves became sharp with a decreased residual bond strength. Formulas for calculating the bond strength and peak-slip were proposed. The relationships were determined for the splitting bond strength, residual bond strength with the bond strength, the splitting bond slip and residual bond slip with the peak-slip. Combined with rational fitting analyses of bond strength and slip, a constitutive model was selected for predicting the bond stress-slip of ribbed steel bar in SFRELC.

Considering the random orientation and distribution of steel fibers in concrete, the synergistic reinforcement of steel fibers on concrete is much complex than the bond of single fiber. It is meaningful to study the bond behavior of steel fiber during many actions. With the inclination angle of steel fiber to pullout direction and the fiber spacing as main factors, this paper carried out fifteen groups of pullout tests for hook-end steel fiber embedded in manufactured sand mortar. The inclination angle ranged from 0 to 60°, and the fiber spacing ranged from 3.5 mm to 21.2 mm. The characteristic pullout load-slip (PL-S) curve of steel fibers are given out after treating the original complete curves of each group test. The values of key points featured the debonding, peak and residual pullout loads and slips are determined from the characteristic PL-S curves. Based on a multi-index synthetical evaluation method, the nominal debonding strength, bond strength, residual bond strength and the debonding work, slipping work, and pullout work, as well as the debonding energy ratio, slipping energy ratio, and pullout energy ratio are analyzed. Results indicate that the bond performance represented by above indexes changes with the inclination angle and spacing of steel fibers. Except for the bond mechanism performing the same as aligned steel fibers by pullout test, the bond is dominated by the resistance of mortar to peeling off near pullout surface and scraping along pullout direction. When the inclination angle is over 15° or 30°, the bond performance is generally decreased, due to the peeling off of mortar on surface of transversal section with a certain depth. When the fiber spacing is over than 5 mm, the bond performance becomes worst due to the scraping out of mortar along with the slip of steel fibers.

The reliable bond of steel fibers to concrete matrix is fundamental to ensure they work together under internal and external actions throughout their service life. Due to the lack of research on the long-term bond property, this paper conducted an experimental study on the bond of hook-end steel fiber in the manufactured sand mortars with different water to binder ratios cured for different ages from 7 days to 360 days. The characteristic pull-out load-slip curves are measured, and bond performance indexes at different curing ages are analyzed by using the multi-index synthetical evaluation method. The results show that the bond strengths, the fiber strength use efficiency, the debonding work and the pull-out work increased with the increase in curing age up to to 90 days, which became stable with little variation with the follow-up curing age. The variations are closely associated with the development of mortar strength. Steel fibers embedded in high-strength mortar presented a higher debonding ductility and a lower slipping ductility. In addition, the prediction formulas of long-term debonding strength, bond strength and residual bond strength are proposed.

Composed of recycled small-particle coarse aggregates with virgin large-particle crushed stones, satisfactory composite-recycled aggregates are developed to overcome the shortcomings of large particle recycled coarse aggregate, making a new concrete with similar mechanical properties to conventional concrete. This brings a development of steel fiber reinforced satisfactory composite-recycled aggregate concrete (SFRSCAC) used for structural engineering. To identify the shear performance of longitudinally reinforced SFRSCAC beams without stirrups, ten test beams were fabricated and experimentally studied by four-point bending tests, incorporating ingot-mill steel fiber in volume fraction from 0 to 2.0%. Results show that steel fibers could delay shear cracking and effectively increase shear strength of test beams, but could not fundamentally change the shear failure with brittle characterization of bond cracking along the longitudinal reinforcement. The assessment using existing prediction formulas of reinforced steel fiber reinforced concrete (SFRC) beams demonstrates that the shear cracking resistance and shear strength of longitudinally reinforced SFRSCAC beams reach the level of reinforced SFRC beams. This provides a basis for broadening the application of SFRSCAC, just like conventional SFRC in structural engineering.