Steel Fiber Reinforced Lightweight Aggregate Concrete Research Articles

Seismic performance of precast steel fiber reinforced lightweight aggregate concrete shear walls assembled with a socket horizontal joint

In the context of constructing a precast shear wall structure, the connection of precast units plays a crucial role in ensuring structural safety and facilitating efficient construction, while the use of conventional concrete for heavy precast units leads to low lifting efficiency. It promotes the study of this paper, which proposed a novel type of socket horizontal joint for precast shear walls made of steel fiber reinforced lightweight aggregate concrete (SFRLAC). Three specimens were tested using the low-cyclic loading test: two reinforced SFRLAC shear walls assembled with a socket horizontal joint and a cast-in-place reinforced SFRLAC shear wall as a reference. The failure patterns and process of the shear walls were observed, while the load-displacement curves were obtained. Additionally, finite element (FE) numerical models were built to conduct parametric analysis on different influencing factors. The bearing capacity, energy dissipation capability, deformation ability, and stiffness degradation of the shear walls were studied. Results indicate that when the precast shear walls failed in bending-shear, the socket horizontal joint remained intact. The three shear walls exhibited fewer differences in seismic behaviors with relatively full hysteretic curves. The seismic mechanisms of the shear walls assembled with a socket horizontal joint are elucidated by analyzing the numerical distribution of stress in both SFRLAC and steel bars at different stress levels. Meanwhile, the study assesses the mechanical properties of precast shear walls by analyzing the impact of the shear to span ratio and the axial compression ratio.

Experimental and numerical study on seismic behavior of precast shear walls assembled with a socket vertical joint

In the development of precast shear wall structures, reliable and efficient connections of precast units are crucial for their seismic behavior. Meanwhile, the heavy precast units using conventional concrete bring a low lifting efficiency. Considering these issues, the paper proposed a novel type of socket vertical joint for precast shear walls made of steel fiber reinforced lightweight aggregate concrete (SFRLAC). Sixteen socket connection specimens, with four socket depths (100 mm, 150 mm, 200 mm, and 250 mm) and two interface treatments (smooth and exposed aggregate), underwent interface bonding performance tests using uniaxial tensile testing and finite element (FE) numerical models to determine the appropriate socket depth. Three specimens were tested using the low-cyclic loading test, including two reinforced SFRLAC precast shear walls assembled with a socket vertical joint and a cast-in-place reinforced SFRLAC shear wall as a reference. The failure patterns and process of the shear walls were observed, while the load-displacement curves were obtained. Additionally, a parametric analysis of different influencing factors was conducted using finite element (FE) numerical models. This analysis studied the bearing capacity, energy dissipation capability, deformation ability, and stiffness degradation of the shear walls. Results indicate that when the precast shear walls were damaged, the socket vertical joint was integrity and failed in bending-shear. The three specimens exhibited fewer differences in seismic behavior with relatively full hysteretic curves. The seismic mechanisms of the shear wall assembled with a socket vertical joint were elucidated by analyzing the numerical distribution of stress in both SFRLAC and steel bars at different stress levels. Furthermore, an expansion analysis was conducted to assess the impact of axial load ratios and shear to span ratios on the seismic behavior of precast shear walls.

Serviceability performance of fiber-reinforced lightweight aggregate concrete beams with CFRP bars

Six lightweight aggregate concrete (LWC) beams reinforced with carbon fiber–reinforced polymer (CFRP) bars were tested under a four-point bending load with different steel fiber contents, reinforcement ratios, and clear span lengths to investigate their flexural behavior and serviceability performance. The test results showed that using steel fiber–reinforced lightweight aggregate concrete (SFLWC) and increasing the reinforcement ratio enhanced the serviceability performance of the beams. The incorporation of 0.6% by volume of steel fibers reduced the midspan deflection by 22.70%–36.87% at the same load level in service stage. At service load, all the CFRP-reinforced beams exhibited conservative deflections when compared to the deflection limits recommended by ACI 440.1 R and GB 50608, and satisfied the crack width limit of 0.7 mm. Comparing the measured maximum crack widths with the corresponding predictions revealed that the bond-dependent coefficient value of 1.4 specified in ACI 440.1 R was reasonable yet conservative. Moreover, an energy-based method was adopted to quantify the influence of the fibers on the beam stiffness. On this basis, a rational deflection model for SFLWC beams reinforced with CFRP bars was suggested.

CALCULATION METHOD FOR CRACK WIDTH OF STEEL FIBER-REINFORCED LIGHTWEIGHT AGGREGATE CONCRETE BEAMS REINFORCED WITH FRP BARS CONSIDERING BOND-SLIP BEHAVIOR

Regarding the crack development of concrete beams reinforced with fiber-reinforced polymer (FRP) bars as a process wherein the FRP bars are pulled out from concrete on both sides, a differential equation of crack width of lightweight aggregate concrete beams reinforced with FRP bars considering bond-slip behavior was established. According to the crack width limits provided by the design codes, the upper limit of slip was reasonably determined and constitutive models for bond-slip relationship between FRP bars and steel fiber reinforced-lightweight aggregate concrete in ‘low slip’ stage which were suitable to the service stage of the beams were proposed and introduced. The maximum crack spacing, lmax, amplification factor of crack width, h2/h1, and residual stress of fiber reinforced-concrete in cracked sections, σfib, were specified. On this basis, a crack width model of steel fiber reinforced-lightweight aggregate concrete beams reinforced with FRP bars was proposed using iterative algorithm and its accuracy was evaluated based on measured data of maximum crack width in service stage. It is shown that within crack width limit of 0.5 mm, the proposed model generates accurate maximum crack width predictions for steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars.

Flexural cracks in steel fiber-reinforced lightweight aggregate concrete beams reinforced with FRP bars

Fourteen plain and steel fiber-reinforced lightweight aggregate concrete (LWC) beams with two types of fiber-reinforced polymer (FRP) reinforcing bars were tested under a four-point bending load with different reinforcement ratios, bar diameters and clear span lengths to evaluate their cracking behavior. The test results showed that using steel fiber-reinforced lightweight aggregate concrete (SFLWC) and increasing the clear span length mitigated the maximum crack width at low load levels, while increasing the reinforcement ratio tended to decrease the maximum crack width during the entire loading period. At service load, all CFRP-reinforced beams satisfied the crack width criteria of 0.7 mm, while more than half of the GFRP-reinforced specimens exhibited unconservative crack widths. Crack width prediction equations in the current design codes in the US, China, and Canada were compared based on the experimental results. The original average crack spacing equation recommended by GB 50608 was modified considering the effect of bar position. Furthermore, using the method of probability and statistics, the relationships between the maximum crack width and the average crack width for the tested beams were investigated. Accordingly, a rational alternative crack width model was proposed for CFRP- and GFRP-reinforced beams incorporating the effects of lightweight aggregates and steel fibers.

Flexural Capacity and Deflection of Fiber-Reinforced Lightweight Aggregate Concrete Beams Reinforced with GFRP Bars

Adding fibers is highly effective to enhance the deflection and ductility of fiber-reinforced polymer (FRP)-reinforced beams. In this study, the stress and strain conditions of FRP-reinforced lightweight aggregate concrete (LWC) beams with and without fibers at ultimate load level were specified. Based on the sectional analyses, alternative equations to predict the balanced reinforcement ratio and flexural capacity for beams failed by balanced failure and concrete crushing were established. A rational equation for estimating the short-term stiffness of FRP–LWC beams at service-load levels was suggested based on Zhu’s model. In addition, the contribution of the steel fibers on the short-term stiffness was quantified incorporating the effects of FRP reinforcement ratio. The proposed short-term stiffness model was validated with measured deflections from an experimental database for fiber-reinforced normal weight concrete (FNWC) beams reinforced with FRP bars. Furthermore, six glass fiber-reinforced polymer (GFRP)-reinforced LWC beams with and without steel fibers were tested under four-point bending. Based on the test results, the proposed models and procedures according to current design codes ACI 440.1R, ISIS-M03, GB 50608, and CSA S806 were linked together by comparing their predictions. The results showed that increasing the reinforcement ratio and adding steel fibers decreased the strain of the FRP bars. The flexural capacity of the LWC beams with and without steel fibers was generally underestimated by the design codes, while the proposed model provided accurate ultimate moment predictions. Moreover, the proposed short-term stiffness model yielded reasonable estimations of deflection for both steel fiber-reinforced lightweight aggregate concrete (SFLWC) and FNWC beams.

Flexural Behavior of Steel Fiber–Reinforced Lightweight Aggregate Concrete Beams Reinforced with Glass Fiber–Reinforced Polymer Bars

AbstractNine beams reinforced with glass fiber-reinforced polymer (GFRP) bars and one reinforced with steel rebars fabricated using high-strength lightweight aggregate concrete (HSLC) were tested u...

Mesoscopic study on axial compressive damage of steel fiber reinforced lightweight aggregate concrete

The main purpose of this study was to reveal the failure mechanism and fiber reinforcing mechanism of steel fiber reinforced lightweight aggregate concrete (SFLWC) under uniaxial compression loading. The variation of acoustic emission (AE) parameters from the initial damage to final failure was analyzed. The statistical analysis methods of AE data were used for determining micro- and macro-cracking, as well as identifying the cracking modes (tensile cracking and shear cracking). The results showed that AE signals were positively correlated with the variation of stress. Micro-steel fiber could significantly reduce the density and intensity of AE signals. The frequency bands of SFLWCs were mainly distributed in four ranges: 15–45 kHz, 85–105 kHz, 235–255 kHz and 285–320 kHz, which corresponded to the compression of pre-existing cracks or pores in concrete, the fracture failure of aggregate/paste interface reinforcement layer, the penetration fracture of aggregate and the cracking of mortar, respectively. With the increase of micro-steel fiber dosage, the three-dimensional distribution of AE signal source became more dispersed, which indicated that the addition of steel fiber could disperse the internal damage of lightweight aggregate concrete (LWC) and prevent the local brittle fracture caused by stress concentration.

BOND PERFORMANCE OF DEFORMED REBAR IN STEEL FIBER REINFORCED LIGHTWEIGHT-AGGREGATE CONCRETE AFFECTED BY MULTI-FACTORS

For the innovation of building materials, a new high-performance Steel Fiber Reinforced Lightweight-Aggregate Concrete (SFRLAC) made of 100% fine and coarse expanded shales has been developed. In view of the importance of reliable bond properties between deformed rebar and this new SFRLAC, the experimental study of 39 specimens was conducted by using the modified pull-out test method with the evaluation of different slips at loading-end and free-end. In which the influencing factors were considered as the volume fraction of steel fiber, the water-cement ratio, the rebar diameter, the bond length of rebar, the strength of coarse expanded shales and the fine expanded shale replaced by manufactured sand. The complete bond stress-slip curves were measured, the bond failure modes of specimens were observed. Based on the bond mechanism of adhesion, friction and bearing action of deformed rebar in SFRLAC, the bond performance characterized by the bond strength and peak-slip, the differential of bond slip between loading-end and free-end, the bond sustainability in descending portion and the bond failure mode observed are analyzed. The recommendations are proposed for the design of SFRLAC structures related to the bond performance.

Comparison of flexural property between high performance polypropylene fiber reinforced lightweight aggregate concrete and steel fiber reinforced lightweight aggregate concrete

The main purpose of this study was to investigate the flexural property of high performance polypropylene fiber reinforced lightweight aggregate concrete (HPPLWC) and steel fiber reinforced lightweight aggregate concrete (SFLWC). Firstly, two widely used standards (ASTM C1609 and JSCE SF-4) were used to evaluate their flexural toughness. Meanwhile, the advantages and disadvantages of these two methods in evaluating the flexural toughness of HPPFLWC and SFLWC were analyzed. Then, a new toughness evaluating method specified in JG/T 472-2015 was used. In addition, the optimal fiber content was proposed according to the flexural toughness of fiber reinforced lightweight aggregate concrete. The results showed that the optimal high performance polypropylene fiber (HPPF) content and steel fiber (SF) content were 1.1vol% and 2.0vol% respectively. SFs performed better on improving the equivalent initial flexural strength and equivalent residual flexural strength than HPPFs. HPPFs’ effectiveness on post-peak behavior was higher than its effectiveness on pre-peak behavior. However, SFs performed better on pre-peak behavior than its effect on post-peak behavior.

Investigation on flexural toughness evaluation method of steel fiber reinforced lightweight aggregate concrete

The main purpose of this paper was to investigate the influence of steel fiber (SF) content on the flexural properties of steel fiber reinforced lightweight aggregate concrete (SFLWC) and propose a suitable method for evaluating flexural toughness. At the first step, the effects of SF content on the basic properties, including workability, density and compressive strength were investigated. Additionally, the microstructure of SFLWC was also observed by using scanning electron microscope (SEM). A slight change was made for Deng’s proposed toughness index which could reflect the degree to which the fiber improves the post-cracking toughness of plain concrete. A simple and practical method for evaluating the flexural toughness of fiber reinforced concrete was recommended by JG/T 472-2015 standard, which solved many problems in the existing methods. This method makes full use of pre-peak and post-peak information which can reflect the influence of fiber on the pre-peak and post-peak behaviors. The results revealed that SF had a negative impact on the workability and density of lightweight aggregate concrete (LWC). However, the addition of SF could improve the compressive strength of LWC to some extent. The optimal SF content of 2.0% was proposed based on the degree to which the fiber improved the toughness of plain LWC. SF addition could significantly enhance the equivalent initial flexural strength and the equivalent residual flexural strength of LWC. The effectiveness of SF on pre-peak behavior was superior to that on the post-peak behavior. The interfacial transition zone between aggregates and paste was not the weakest link in SFLWC.

Experimental Study on Autogenous and Drying Shrinkage of Steel Fiber Reinforced Lightweight-Aggregate Concrete

Steel fiber reinforced lightweight-aggregate concrete (SFRLAC) has many advantages applied in structural engineering. In this paper, the autogenous shrinkage and drying shrinkage of SFRLAC for up to 270 days were measured, considering the effects of types of coarse and fine aggregates with the changes of water-to-binder ratio and volume fraction of steel fiber, respectively. The properties of mix workability, apparent density, and compressive strength of SFRLAC were also reported and discussed in relation to above factors. Test results show that the development of autogenous and drying shrinkage of SFRLAC was fast within 28 days and tended to be steady after 90 days. The development of autogenous shrinkage of SFRLAC reduced with the increasing water-to-binder ratio and by using the expanded shale with higher soundness and good water absorption, especially at early age within 28 days; the later drying shrinkage was reduced and the development of drying shrinkage was slowed down with the increasing volume fraction of steel fiber obviously; manufactured sand led to less autogenous shrinkage but greater drying shrinkage than fine lightweight aggregate in SFRLAC. The regularities of autogenous shrinkage and drying shrinkage of SFRLAC expressed as the series of hyperbola are analyzed.

Research of Punching Performance of Reinforced SFRLAC Superposed Two-Way Slabs

This paper introduces the test results of eight steel fiber reinforced lightweight aggregate concrete (SFRLAC) superposed two-way slabs under punching load. The tensile and compressive zones of the slabs were cast with the SFRLAC and the ordinary concrete respectively. The slab was simply supported along the four edges under central concentrated load on the short column. The main parameter of SFRLAC was the fraction of steel fiber by volume of 0.8%, 1.2% and 1.6%. The measurements were made such as the deflection, the strains of steel bar and concrete, the crack distribution, the loads corresponding to the yielding of steel bar and the ultimate state. It proved that the punching resistance of SFRLAC superposed two-way slab increased about 51%~78% with the increasing fraction of steel fiber by volume, the ability to resist punching deformation was enhanced remarkably, many fine cracks distributed on the tensile surface, and the ductility at failure state increased to a certain degree.

Experimental Study on the Flexural Tensile Properties of Fiber Reinforced Light-Weight Aggregate Concrete

In order to investigate the effect of fiber reinforced light-weight aggregate concrete on flexural tension properties, five groups of steel fiber reinforced light-weight aggregate concrete (SFLWAC) specimens with different steel fiber volumes including 0.5%,1.0%,1.5%,2.0%,2.5% and another five groups of plastics-steel fiber reinforced light-weight aggregate concrete (PSFLWAC) specimens with different plastics-steel fiber volumes including 0.5%,0.7%,0.9%,1.1%,1.3% were tested. The test results show that fiber can greatly improve ductility, and there are good interfacial bonding properties between fiber and light-weight aggregate concrete. The test results also show that it is not obvious to the upgrade of the flexural strength of light-weight aggregate concrete of LC30 with plastics-steel fiber. But the addition of steel fiber can gradually improve the breaking strength owing to the increase of steel fiber volumes.

Mechanical Properties of Steel Fiber Reinforced Lightweight Aggregate Concrete

Experiments were conducted to study the basic properties of steel fiber reinforced lightweight aggregate concrete (SFLAC) mixed with machine-made sand and expanded-shale. The effects of sand ratio and cement content on the cubic and axial compressive strengths, splitting and axial tensile strengths, flexural tensile strength as well as compressive and tensile elastic modulus of SFLAC are analyzed comparing with those of LAC in the same conditions. Data from the experiments shows that, the steel fiber has advantages to every mechanical properties of LAC especially to the tensile strengths, and also modifies the abruptness failure states of LAC into multi-cracked characteristics of SFLAC. The optimum mix proportion is suggested for getting better properties of SFLAC.