Fiber-reinforced Self-consolidating Concrete Research Articles

Predicting the compressive strength of fiber-reinforced self-consolidating concrete using a hybrid machine learning approach

Predicting the compressive strength of fiber-reinforced self-consolidating concrete using a hybrid machine learning approach

Investigating the applicability of deep learning and machine learning models in predicting the structural performance of V-shaped RC folded plates

Reinforced concrete folded plates (RC-FPs), which are a special class of shell structures, have recently become very popular in modern architectural and engineering applications because of the need for lightweight and aesthetic structures to cover large areas. However, it is known that studies on the structural performance of RC-FPs are insufficient. Therefore, this article presents a study on the development and comparison of different deep learning (DL) and machine learning (ML) models for the prediction of the structural performance of full-scale V-shaped RC-FPs produced from hybrid fiber-reinforced self-consolidating concrete (HFR-SCC) having different plate thicknesses (50, 60, 70, and 80 mm), fiber volumes (1.00% and 1.25%), and combinations (single, binary, and ternary). While vanilla long short-term memory (VLSTM) and bidirectional long short-term memory (BILSTM) are used as DL models, random forest (RF), extremely randomized trees (ERT), and adaptive boosting (AdaBoost) are preferred for ML models. To construct the models, the structural performance results of a total of 44 full-scale V-shaped RC-FPs subjected to four-point bending loading were adopted as the database. In addition to all these, the AdaBoost model is used to determine the relative feature importance of the input parameters. Based on the results, among the DL models, the BILSTM has the best ability to predict the structural performance values of V-shaped RC-FPs (such as R-squared values for maximum load-bearing capacity, cracking load, toughness, and deflection ductility are 0.934, 0.987, 0.972, and 0.812, respectively), while in ML models, this is valid for the ERT (such as R-square values are 0.917 for maximum load-bearing capacity, 0.936 for cracking load, 0.947 for toughness and 0.825 for deflection ductility). On the other hand, DL models predicted all other structural performance values better than ML models, except for deflection ductility. Besides, the most relative important input features for maximum load-bearing capacity and toughness values is plate thickness, whereas for cracking load and deflection ductility values compressive strength is important. In conclusion, it can be emphasized that the use of DL models can provide significant advantages in engineering applications, such as predicting the structural performance of V-shaped RC-FPs.

Use of hybrid fibers and shrinkage mitigating materials in SCC for repair applications

Self-consolidating concrete (SCC) is used to repair structural elements with congested reinforcement or restricted access to placement and consolidation. In addition to adequate flowability, passing ability, filling capacity, and stability, adequate bonding to the substrate and reinforcing bars, low shrinkage and cracking resistance are required for successful repair. This study employs various shrinkage mitigating materials, including expansive agent (EA), coupled use of EA with shrinkage reducing admixture (SRA), and EA with pre-saturated lightweight sand (LWS) to fulfill these requirements. The effect of these materials on the performance of SCC made with a hybrid synthetic (PP) fiber and a hybrid steel-synthetic (STPP) fiber is investigated. The investigation included key fresh and hardened concrete properties and flexural performance of composite beams repaired using these materials. Test results show that the investigated fiber-reinforced self-consolidating concrete (FRSCC) mixtures can secure adequate workability and mechanical properties and low shrinkage, limited to 600 µstrain after 224 days. High EA content (10% by mass of binder) can lead to excessive expansion at early ages resulting in microcracking and drop in mechanical properties. The FRSCC made with 5% EA and 0.5% SRA, by mass of binder (5EA0.5SRA mixture), had superior mechanical properties (50 MPa compressive strength and 36 GPa modulus of elasticity). The cracking potential due to restrained shrinkage of this mixture is very low. The 5EA0.5SRA mixture made with hybrid synthetic fibers is successfully used to repair reinforced concrete beams prepared with various reinforcement ratios in the tension zone. The results indicate a 48% increase in first crack load, 4% gain in peak load, and 33% increase in flexural toughness compared to the monolithic beam cast with the conventional concrete. A comparison between the cracking load and ultimate flexural capacity of the repaired beams with estimated values by ACI 544 reveals the estimated to experimental ratio of 0.36–0.70 for cracking load and 0.56–0.74 for the flexural capacity. This can stem from the promotion of FRSCC concrete by the effect of hybrid synthetic fibers and the development of internally induced stress in the presence of shrinkage mitigating materials and fibers that led to higher mechanical properties and enhanced performance of FRSCC for repair. Reinforced beams repaired using FRSCC made with 0.5% hybrid synthetic fibers and combination of EA-SRA can reduce the steel reinforcement ratio by 21% to 27%, depending on the primary steel reinforcement.

Influence of thermal cycles and high-temperature exposures on the residual strength of hybrid steel/glass fiber-reinforced self-consolidating concrete

Although using steel fiber has been efficiently studied to mitigate the thermal damages of concrete samples exposed to high-temperature exposure, however reducing the workability is the primary concern of researchers. Accordingly, the present study aims to investigate the effect of glass and hybrid steel/glass fibers on compensating the workability and improving the thermal resistance of SCC mixtures, which was not precisely investigated by the literature. SCC specimens with various types of fibers, different packing factors (1.12 & 1.14), different sand-to-all aggregate ratios (0.50 & 0.57), and SCC grades (M40 & M80) were considered in the present study. Also, two thermal damages of thermal cycles at 200 °C (1, 3, 14, and 28 cycles) and high-temperature exposure (200 °C, 400 °C, and 600 °C) were selected. Concrete resistivity, ultrasonic pulse velocity (UPV), and concrete compressive strength are the tests considered in the present study. Results indicate that hybrid steel/glass fiber-reinforced SCC specimens have considerably higher thermal resistance as compared to single steel and glass fiber-reinforced ones. Accordingly, using glass fiber in combination with steel fiber in SCC can considerably compensate for the workability reduction along with reducing strength loss due to thermal cycles and high-temperature exposure.

Repair of Damaged Continuity Joints Using Ultra-High Performance, Fiber Reinforced Self-Consolidating, and Magnesium–Aluminum–Liquid–Phosphate Concretes

Bridge elements known to develop damage over time are individual continuity joints connecting girders. Replacing damaged joints is an expensive and invasive process and a need exists to design a less invasive repair method. This study focused on evaluating an encapsulation repair method for continuity joints that would not require extensive demolition of the bridge deck to implement and could potentially be constructed without bridge closure. Approximately half scale connected bridge girder specimens were constructed and purposely damaged to create similar crack patterns to those seen in bridges. Once damaged, a set of three specimens was repaired using the encapsulation method with three different high performance materials, ultra-high performance concrete (UHPC), fiber reinforced self-consolidating concrete (FRSCC), and magnesium–aluminum–liquid–phosphate (MALP) concrete. Of the three repaired specimens for each material, one was tested in positive moment bending and two in negative moment bending, similar to in situ conditions. The results appear to indicate that using each of the tested materials as an encapsulation repair for damaged continuity joints is viable to re-establish continuity and load capacity. However, the UHPC repairs’ resistance to cracking could indicate the best performance by further protecting the continuity joint reinforcing steel from water ingress.

Homogeneous flow performance of steel-fiber reinforced self-consolidating concrete for repair application: A biphasic approach

In this study, fiber-reinforced self-consolidating concrete (FR-SCC) was considered as a diphasic suspension of fiber and coarse aggregate (F-A ≥ 5 mm) skeleton in mortar suspension with solid particles finer than 5 mm. The coupled effect of the volumetric content of fibers, coarse aggregate particle-size distribution, and rheological properties of the mortar on the passing ability and dynamic stability of various FR-SCC mixtures was investigated. Nine high-strength and 10 conventional-strength FR-SCC mixtures for repair application were proportioned with water-to-binder ratios (W/B) of 0.35 and 0.42, respectively, and macro steel fibers of 0.1%–0.5% volumetric contents. The dosages of high-range water-reducer (HRWR) admixture were optimized to achieve a targeted slump flow of 680 ± 20 mm. The yield stress and plastic viscosity of the mortar mixtures varied between 4.6-17.7 Pa and 2.8–8.2 Pa s, respectively. Flow performance of the investigated mixtures were evaluated in terms of flowability (slump-flow test), passing ability (J-Ring and L-Box set-ups), and dynamic stability (T-Box test). According to the established correlations, the main influencing parameters on homogeneous performance of FR-SCC include W/B, paste volume, volumetric content-to-packing density of F-A (φ/φmax), HRWR dosage, fiber content, mortar rheology, and volume of excess mortar. The robustness analyses results revealed that homogeneous flow performance of FR-SCC is more sensitive due to variations of the φ/φmax and paste volume rather than mortar rheology, W/B, and HRWR dosage. The characteristics of the mixture constituents for FR-SCC mixtures with different strength levels were finally recommended to ensure acceptable homogeneous performance under restricted flow conditions of repair application.

Homogenous flow performance of steel fiber-reinforced self-consolidating concrete for repair applications: developing a new empirical set-up

Homogenous flow performance of steel fiber-reinforced self-consolidating concrete for repair applications: developing a new empirical set-up

Effect of type and content of expansive agent on performance of fiber-reinforced concrete with adapted rheology

A performance-based mixture design approach was utilized to optimize the binder content and composition for fiber-reinforced super workable concrete (FR-SWC) and fiber-reinforced self-consolidating concrete (FR-SCC). The test parameters included the replacement ratio of the cement by a Class C fly ash (FA), type and content of expansive agent (EA), and total binder content. Hooked-end steel fibers measuring 30 mm in length were used at 0.5% by volume. The investigated concrete was tested for slump flow, modified J-ring, sieve stability, bleeding, visual stability index, air content, unit weight, as well as compressive and splitting tensile strengths. The elastic modulus, autogenous, drying shrinkage, and restrained shrinkage were determined for optimized mixtures. The optimized binder content for the FR-SCC mixtures was 475 kg/m3 with 30% FA replacement, by mass of total binder. For the FR-SWC mixtures, the binder content was 380 kg/m3 binders with 30% FA, by mass. In both mixture types, a Type-G EA was incorporated at 4% by binder mass.Test results indicated that a sharp loss in filling ability was obtained in mixtures made with a Type-K EA compared to those made with a Type-G or no EA. The coupled used of fibers and EA resulted in a slight increase in compressive strength for the FR-SCC but considerable improvement in compressive strength (up to a 50%) in the case of FR-SWC. The FR-SCC and FR-SWC mixtures exhibited up to 55% and 80% greater splitting tensile strength, respectively, compared to the non-fibrous concrete. The combination of steel fiber and EA significantly reduced shrinkage, up to 65% lower shrinkage after one year for the FR-SCC and FR-SWC mixtures. An increase in restrained shrinkage resistance was observed when the EA or fiber was used in proportioning the FR-SCC. Combined use of fibers and 4% Type-G EA led to the highest reduction in cracking potential that decreased from relatively high to low level with the time-to-cracking increasing from 12.5 to 36.5 days.

Punching Shear Behavior of Synthetic Fiber–Reinforced Self-Consolidating Concrete Flat Slabs with GFRP Bars

Abstract Glass fiber–reinforced polymer (GFRP)-reinforced flat slabs offer a convenient construction option that is both simple to build and highly resistant to corrosion. The relatively low thickn...

Mechanical properties of fiber-reinforced concrete with adapted rheology

This paper aims to assess and enhance the prediction of mechanical properties of fiber-reinforced self-consolidating concrete (FR-SCC) and fiber-reinforced superworkable concrete (FR-SWC) that can be used for infrastructure construction and rehabilitation. The mechanical properties included compressive strength (f'cf), splitting tensile strength (f'spf), flexural strength (frf), and elastic modulus (Ecf) and their increase with curing time. A total of 69 FR-SCC and FR-SWC mixtures were used in this investigation that involved the consideration of test results of 1467 cylindrical and 106 prismatic specimens tested at 3–365 days of age. The mixture parameters included fiber type (five types), fiber volume (0.25%–0.75%), material characteristics, mixture proportioning, admixture type and combination, as well as consolidation energy in the case of FR-SWC, and curing. The measured mechanical properties were compared to values estimated from 35 different models that take into consideration the fiber characteristics.Test results indicate that the mean experimental-to-theoretical ratio (mean exp/theo) and corresponding coefficients of variation (COV) obtained with the original models that yielded the best prediction (one model for each mechanical property) were 0.98–1.06 and 11%–18%, respectively. The best original models were then modified and new proposed models were developed, leading to mean exp/theo values of 1.00–1.02 and COV values of 8%–11%.

Effects of hybrid fibers on workability, mechanical, and time-dependent properties of high strength fiber-reinforced self-consolidating concrete

This paper aims to systematically investigate the impacts of hybrid fibers on properties of high strength fiber-reinforced self-consolidating concrete (FRSCC). In total, nine mixtures with different fiber types (Polyvinyl Alcohol/PVA, and hybrid fibers) and fiber factors (λ = 0 ~ 70) were fabricated with same basic mix proportioning. Workability tests include slump flow, T50 time, and J-ring tests were carried out to quantify the effects of fiber factor. The compressive strength, four-point bending tests, drying shrinkage, and compressive creep tests were performed on hardened concrete to reveal the intrinsic effects of single/hybrid fibers. Finally, a hyperbolic drying shrinkage prediction model with fiber factor was proposed. Experiment results indicated that single PVA fibers displayed identical influences on slump flow as steel fiber with similar fiber factor, however, can result in higher viscosity. Meanwhile, PVA fibers reduced the compressive strength and displayed limited restraining effects on the specific creep. However, the positive synergetic effects of hybrid fibers can reverse the reductions in compressive strength caused by the PVA fiber and increase flexural performances with multi-scale bridge effects. Moreover, hybrid fibers are more effective in inhibiting the time-dependent strains of FRSCC, followed by steel fiber and synthetic PVA fiber. The proposed hyperbolic drying shrinkage model is capable of predicting the drying shrinkage of FRSCC with a suitable shrinkage halftime.

Validation of Predicted Stress in Polypropylene Fiber-Reinforced Self-Consolidating Concrete Under Restrained Shrinkage Conditions

Validation of Predicted Stress in Polypropylene Fiber-Reinforced Self-Consolidating Concrete Under Restrained Shrinkage Conditions

Hybrid steel/glass fiber-reinforced self-consolidating concrete considering packing factor: Mechanical and durability characteristics

This study intends to determine the effect of fiber type and aggregate content on hardened and durability properties of self-consolidating concrete. Steel, glass, and steel/glass hybrid fibers are tested in the present experimental program. Additionally, the effect of aggregate content is considered by using different packing factors and sand-to-all aggregate ratios. Moreover, normal and high strength concrete grades are prepared. Compressive, splitting tensile, flexural, and impact tests are conducted for measuring hardened properties of concrete mixtures. Absorption, desorption, acid attack, resistivity, potential, and chloride diffusion are also durability tests carried out in the present study. Results show that 1.0% and 0.05% are the optimal dosage of steel and glass fibers respectively. Results show that packing factor plays a major role in mechanical characteristics of fiber-reinforced self-consolidating concretes so that an optimal value of 1.12 and 1.14 is obtained for mechanical properties. Also, experimental results reveal that for 1.12 packing factor, the sand-to-all aggregate ratio needs to be equal to the value of 0.50, while 0.57 is achieved as an optimum value for packing factor of 1.14. Overall, results show that hybrid-reinforced self-consolidating concrete is promising for mechanical and durability performance as compared to other mixtures.

Experimental investigation of flexural and shear strengthening of RC beams using fiber-reinforced self-consolidating concrete jackets

The present study aims to investigate the efficiency of application of steel fiber-reinforced self-consolidating concrete (SFR-SCC) jackets for strengthening RC beams in flexure and shear. Accordingly, 10 beam specimens were constructed and categorized under two main groups. In the first group, the specimens were designed in a way that shear failure was dominant so that the effectiveness of SFR-SCC jacketing in shear strengthening could be evaluated. In contrast, specimens of the second group, designed with high amount of shear reinforcement, were strengthened with SFR-SCC jackets containing 2 GFRP rebars for the purpose of flexural strengthening. Parameters studied in this paper include the use of different steel fiber dosages, the effect of presence of shear reinforcement, utilization of GFRP rebars in the jackets, and behavior of specimens with different longitudinal reinforcement ratios. In the second group, failure mode of the strengthened specimens changed to flexure, while in the strengthened specimens reinforced with GFRP rebars, mode of failure changed to a combination of shear and compression.

Core confinement and cover spalling in square and rectangular SCC and SFRC columns

To ensure adequate strength and deformability, modern concrete codes require the use of closely-spaced confinement reinforcement in columns. In ductile columns, these requirements result in congested columns which are difficult to construct; the use of self-consolidating concrete (SCC) and steel fiber reinforced concrete (SFRC) can facilitate the construction of such columns. However, limited research exists on the axial behaviour of SCC columns. Moreover, further research is needed to understand the influence of fibers on core confinement in SCC columns. This research aims at better understanding the influence of transverse reinforcement and fibers on core confinement in SCC columns. To achieve this objective, this paper presents the results from thirteen columns built with SCC, steel fibers and varied amounts of transverse reinforcement. The columns, which had square (250 mm × 250 mm) and rectangular (350 mm × 175 mm) cross sections, were built without cover in order to examine the competing influence of transverse reinforcement and fibers on core confinement. The results confirm that an increase in transverse steel-ratio improves the axial strength and ductility of SCC columns. The findings also show that fibers improve core behaviour in SCC columns, with a more significant effect in columns with low transverse steel-ratios compared to well-confined columns. The results also point to a relative loss in confinement and fiber efficiency when the sectional shape changes from square to rectangular. The influence of fibers on the cover contribution was also studied using the results from companion columns containing identical reinforcing cages but constructed with cover. The results show that fibers transform the cover spalling mechanism from sudden to gradual, allowing the cover to contribute significantly to column capacity and ductility. However, bar buckling plays an important role in the SFRC cover spalling mechanism, particularly in columns with large tie spacing. The paper also presents an analytical study which predicts the axial response of the columns using different confinement models. The results show that the Cusson-Paultre and Aoude models can predict the axial response of plain and fiber-reinforced SCC columns, however recalibration of the models is recommended for columns having rectangular cross sections.

Shrinkage of high-performance fiber-reinforced concrete with adapted rheology

The results of shrinkage (εsh) of fiber-reinforced self-consolidating mortar (FR-SCM), fiber-reinforced superworkable concrete (FR-SWC), and fiber-reinforced self-consolidating concrete (FR-SCC) are compared to results determined from different models. In total, four FR-SCM, five FR-SWC, and 10 FR-SCC, mixtures representing a wide range of mixture proportioning were studied. Five types of fibers, including steel, synthetic, and hybrid fibers having various properties were employed. The fiber volume varied from 0.25% to 0.75% for the FR-SCC mixtures and from 1.4% and 1.6% in the case of FR-SCM mixtures. The εsh results were evaluated for 13 months. Test results indicated that the εsh of FR-SWC/FR-SCC was lower than that of SCC. The drying shrinkage (εdr), which is part of the total shrinkage, εsh, was found to be mainly affected by the total porosity and volume of pores smaller than 50 nm. The εsh results were compared to values predicted from different models, including the AASHTO LFRD (2017), ACI 209 (2008), Bažant B4 (2015), B4s (2015), CEB-FIP (2010), Eurocode 2 (2004), Gardner and Lockman (2000), and JSCE (2007) models that were developed for conventional, non-fibrous concrete. The Aslani and Maia (2013), Khayat and Long (2010), and Poppe and De Schutter (2005) models proposed for self-consolidating concrete and FR-SCC were also considered. The εsh models of the fibrous mixtures were modified to better fit the experimental results. The modified εsh models were shown to yield accurate prediction of εsh of FR-SCM and FR-SWC/FR-SCC. The modified JSCE model provided the best overall prediction for εsh for the FR-SCM and FR-SWC/FR-SCC mixtures.

Effect of fiber characteristics on fresh properties of fiber-reinforced concrete with adapted rheology

The influence of fiber type and volume on fresh properties of fiber-reinforced self-consolidating concrete (FR-SCC) and fiber-reinforced super-workable concrete (FR-SWC) was investigated. These mixtures were developed for infrastructure construction and repair, respectively, and the fibers were incorporated to reduce cracking and enhance service life of concrete structures. The fibrous mixtures were proportioned with a Type-G expansive agent (EA) to reduce shrinkage and mitigate the risk of cracking. The selected fibers included a propylene synthetic fiber, five different steel fibers, and a hybrid fiber containing steel and polypropylene multifilament fibers. The fiber volume was fixed at 0.5% for the FR-SCC mixtures and varied between 0.5% and 0.75% for the FR-SWC. The investigated FR-SCC and FR-SWC mixtures had initial slump flow of 660–700 mm and 505–570 mm, respectively, and exhibited excellent passing ability and adequate stability. The investigated FR-SCC and FR-SWC mixtures with passing ability index greater than or equal to 12 and 11, respectively, evaluated using the modified J-Ring test exhibited good flowability without blockage and segregation. The passing ability index was inversely proportional to plastic viscosity for mixtures of a given coarse aggregate content and maximum nominal size of aggregate. Good relationships between slump flow and yield stress and T50 and plastic viscosity were established for the fibrous mixtures.

Crack Growth Monitoring in Fiber-Reinforced Self-Consolidating Concrete via Acoustic Emission

Crack Growth Monitoring in Fiber-Reinforced Self-Consolidating Concrete via Acoustic Emission

Early-Age Cracking Resistance of Fiber-Reinforced Expansive Self-Consolidating Concrete

Early-Age Cracking Resistance of Fiber-Reinforced Expansive Self-Consolidating Concrete

Analysis of material size and shape effects for steel fiber reinforcement self-consolidating concrete

An experimental program is conducted in this study to evaluate the specimen shape and size effects on the compressive strength of steel fiber reinforced self-consolidating concrete (SFRSCC). The results of fresh and hardened concrete properties are first examined through casting cubic specimens in five different sizes and three sizes of cylindrical specimens with a height-to-diameter ratio of 2. The shape-effect model is then evaluated and the coefficients are obtained. Furthermore, relations between cubic and cylindrical specimens are presented and suggestions for the practical cases are offered. Subsequently, the size effect models SEL, MSEL, MFSL, USEL, and the model proposed by Sim et al. are discussed and the coefficients for self-consolidating concrete (SCC) and SFRSCC are updated. Moreover, cubic and cylindrical specimens are compared regarding crack pattern. The results clearly express that with the increase of steel fibers, the size effect is decreased and the structure becomes more ductile. The size effect in cubes is more pronounced than that of the cylinder. By adding and increasing the steel fiber content, the size effect decreased owing to crack bridging and the reduction of crack growth. Also, failure moves towards the strength criteria region in the SEL and towards the Euclidian regime in the MFSL.