Ultra-high-performance Fiber-reinforced Concrete Research Articles

Flexural performance of pre-damaged RC beams strengthened with different configurations of UHPFRC layer –experimental and analytical investigation

This paper reports a study comprising both experimental and analytical works to capture the flexural behavior of pre-damaged reinforced concrete (RC) beams strengthened with different configurations of ultra-high-performance fiber-reinforced concrete (UHPFRC) layers on the beam’s surface. Firstly, a selected mixture of normal concrete and steel reinforcing bars (both used for casting the RC beams) and a selected mixture of UHPFRC (used for strengthening the RC beams) were characterized, followed by preparing 14 RC beam specimens. While one RC beam was used as a control specimen, the other 13 beams were pre-damaged to three levels by applying flexural loads corresponding to 30, 75, and 90 % of the ultimate flexural load-bearing capacity of the control RC beam. The pre-damaged RC beams were strengthened by applying 30 mm-thick UHPFRC layer(s) to their surface(s) using three different strengthening configurations that included a tensile surface, two vertical surfaces, and three surfaces (tensile and two verticals). The strengthened beams were subjected to flexural loading, and the data pertaining to load versus deflection and strain in reinforcing bars were recorded until the failure. While no changing in the pattern of the strain development in reinforcing steel bars and the mode of failure of the strengthened beams were observed, their flexural performance was significantly affected by their degree of pre-damaging and the strengthening configuration. The strengthened RC beams pre-damaged by 30 % showed significantly higher enhancement in the load-bearing capacity than the strengthened RC beams pre-damaged by 75 and 90 % because of the fact that the steel reinforcement in strengthened RC beams with a pre-damage of 30 % did not yield before strengthening, contrary to the beams pre-damaged by 75 and 90 % in which the steel reinforcement bars yielded during the damaging process before strengthening and therefore the steel reinforcement had insignificant contribution in improving the flexural performance after strengthening. The three-sided, two-sided, and one-sided UHPFRC strengthened RC beams showed the highest to the lowest enhancement in the flexural performance. The analytical models were derived to predict the ultimate load-bearing capacities of the strengthened RC beams for all three UHPFRC jacketing configurations. Results obtained using the developed analytical models matched very well with the corresponding experimental results.

Confined ultrahigh-performance fibre-reinforced concrete in retrofitted beam–column joint: experimental study

The beam–column joint (BCJ) is a critical region in a framed structure because during such events as earthquakes it is susceptible to earlier failure than adjacent members, leading to shear failure, and will endanger building users if not designed properly. BCJs designed using preseismic code provisions follow the non-ductile approach and might not resist postelastic rotation without enduring greater damage. Retrofitting techniques offer great opportunities for strengthening damaged BCJs. In this study, the effectiveness of a novel retrofitting scheme based on carbon fibre reinforced polymer (CFRP) confined ultrahigh-performance fibre-reinforced concrete (UHPFRC) in rehabilitating initially damaged BCJ specimens was assessed. Three retrofitting schemes using UHPFRC with and without confinement are proposed: (1) in situ casting of 25 mm thick UHPFRC jackets; (2) in situ casting of steel wire mesh-confined UHPFRC and (3) in situ casting of CFRP-confined UHPFRC. The confining action was achieved by sandwiching wire or CFRP mesh between two layers of UHPFRC. The results of this study indicate that BCJ specimens retrofitted with confined UHPFRC had improved overall seismic response, compared with specimens retrofitted only with UHPFRC. Further, the wire mesh-based retrofitting scheme proved to be more efficient than the CFRP mesh-based scheme.

Steel rebar effect on tensile and cracking behavior of UHPFRC based on direct tensile tests and digital image correlation

Ultra-high performance fiber-reinforced concrete (UHPFRC) is usually used as the reinforcement and protection layer for structural members, and adding steel rebars to UHPFRC to form reinforced UHPFRC (R-UHPFRC) is widely employed in engineering practice. This paper focuses on the differences in tensile and cracking behavior triggered by the addition of steel rebars in UHPFRC, which significantly impacts its strengthening effect and durability performance. Six UHPFRC and six R-UHPFRC specimens are tested by direct tensile tests; the mechanical responses and the full-filed and full-process cracking behaviors are characterized by the digital image correlation (DIC) system. The fiber number, dispersion, and orientation are quantitatively obtained and evaluated based on image recognition, while their variations initiated by the addition of rebars are determined. Moreover, the correlations between fiber distribution, tensile mechanical response, and cracking behavior are analyzed, and the interaction mechanism in the full tensile process between the steel rebars and UHPFRC component in R-UHPFRC is studied. Test results show that the UHPFRC component in R-UHPFRC has deteriorated fiber distribution quality and lower load-bearing capacity than UHPFRC. With the addition of steel rebars in UHPFRC, the cracking mode changed from chain-like to full-field development, leading to better multi-cracking behavior. Meanwhile, the employment of steel rebars significantly improved the capacity of UHPFRC to control the crack width and weakened its susceptibility to the non-uniformity of fiber distribution. During the cracking process of R-UHPFRC, a peculiar load redistribution exists between the UHPFRC component and steel rebars. The experimental and analytical results illustrate that the axial tensile yield and peak load of R-UHPFRC can be evaluated based on the superposition principle, while this method may overestimate the stiffness in the service limit state.

Quantitative analysis of steel fibers on UHPFRC uniaxial tensile behavior using X-CT and UTT

Steel fiber is usually used to improve ultra-high-performance fiber-reinforced concrete (UHPFRC) tensile properties and remedy its brittle failure. X-ray CT scanning (X-CT) was used to observe the orientation and distribution of steel fibers inside UHPFRC. It revealed that the steel fiber inside UHPFRC distribution angle is not equal probability, and the probability is higher along the pouring direction in uniaxial tensile specimen mold. The uniaxial tensile tests (UTT) of 19 UHPFRC specimens with different fiber volume fractions and aspect ratios were performed to analyze the steel fiber on the tensile response and tension failure patterns of UHPFRC. Test results indicated that with an increase in the volume fraction or aspect ratio of steel fiber, the first-cracking strength, tensile strength and peak tensile strain of UHPFRC increase; while they have different growth rates. In addition, with the increase of volume fraction and aspect ratio, the failure patterns of UHPFRC tension specimens gradually changed from brittle failure with single crack to ductile failure with multiple cracks. The stress superposition compositions of tensile strength were different under different failure patterns. Combining mechanical analysis and numerical statistical analysis, prediction equations of the tensile strength of strain softening UHPFRC and pseudo-strain hardening UHPFRC considering the effect steel fiber parameters were respectively proposed. Through the mesoscopic equivalent model analysis of UHPFRC uniaxial tensile specimens, the functional relationships between the effect of steel fiber parameters on the first-cracking strength and peak tensile strain were analyzed, and then their prediction equations were proposed, combined with numerical statistical analysis. The calculation accuracy of the series of prediction equations proposed in this paper were verified by the collected literature data. Meanwhile, comparing the prediction equations proposed in this paper with the existing equations in the literature, the equations proposed in this paper were better.

Enhancing shear behaviour of the exterior beam-column joint using sufficient reinforcement details or ultra-high-performance fiber-reinforced concrete

This study aims to improve the low shear strength of an exterior beam-column joint (BCJ) by using a different reinforcement pattern or ultra-high performance fiber-reinforced concrete (UHPFRC) in the beam-column joint. The main studied parameters were the transverse reinforcement ratio, anchorage of the longitudinal beam reinforcement, beam-column depth ratio, and utilizing UHPFRC. Five specimens with a one-third scale were experimentally tested under one-direction cyclic loading. All the samples were compared to the control sample in terms of crack pattern, mode of failure, hysteresis and envelope behavior, ductility factor, energy dissipation, normalized shear strength, percentage of beam flexural capacity, and stiffness degradation. Compared to the control specimen, the joint shear strength increases by 13%, 25%, 9%, and 38% for specimens that were made better by increasing the transverse reinforcement ratio, increasing the beam anchorage bar length in the joint, lowering the beam-column depth ratio to 0.80, and using UHPFRC instead of normal concrete in the beam-column joint. The UHPFRC in BCJ can be used instead of increasing the anchorage of the beam bars or the transverse reinforcement within the joint to get the same or better shear strength performance.

Pull-out creep of hooked-end fibre embedded in ultra-high-performance concrete

If the beneficial effects of fibre reinforcement are to be considered in design of ultra-high performance fibre reinforced concrete (UHPC) structure, an understanding of the long-term creep behaviour is essential. The flexural/ tensile properties of UHPC depend on the individual contribution of discrete fibres that control the overall tensile properties. The creep of UHPC therefore depends on the pull-out creep of individual fibres under sustained load. Very little research has been conducted on single steel fibre pull-out creep. To address this lack of understanding, the impacts of fibre embedment length, fibre embedment angle and sustained load on pull-out creep are investigated in this research. The outcomes of the research show that for hooked-end fibres, a change of embedment length does not significantly influence pull-out creep. The inclination angle (angle between loading axis and fibre-embedded axis) had a significant role in concrete breakage at the loading end (embedded end at loading side) which generally occurred during the application of sustained load. Therefore, the pull-out creep was influenced by the fibre inclination angle for concrete breakage during application of sustained load. Finally, as expected with an increase in load, fibre pull-out creep increased.

Effect of mixture flowability on strength and fiber distribution of Ultra High-Performance Fiber Reinforced Concrete

The uniformity of distribution and the orientation factor of steel fibers are crucial parameters that determine the strength and uniformity of properties of Ultra High-Performance Fiber Reinforced Concrete (UHPFRC). The paper considers the influence of flowability and the method of casting the concrete mixture on the strength and fracture energy in bending of UHPFRC. The flowability was determined by the spread diameter of the mixture from the Hägermann cone, which was 270, 300, and 350 mm. It was found that the compressive strength of UHPFRC increases from 142 to 155 MPa with an increase in the mixture spread diameter. The strength and fracture energy in bending of UHPFRC near the ends of the mold are on average 14.5 and 17.7% less than in the central part. A relationship has been established between the flexural strength of UHPFRC and the fracture energy as a function of the relative area of the fiber in the cross-section. The optimal flowability range of UHPFRC (270…290 mm) was established analytically and experimentally, in which there is no critical decrease in strength properties and the ability of the mixture to self-leveling is maintained. Negative effects were established when changing flowability, outside the specified range.

Direct tension tests for determining the relationship between tensile stress and crack opening of ultra-high performance concrete

This study reports the test results of direct tension tests of ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHPFRC). The idealized model of tensile stress versus crack opening was described for the prediction of tensile behavior. The mixtures of UHPC and UHPFRC were designed to achieve a compressive strength of 200 MPa. The direct tension tests were conducted on the prisms of 40x40x80 mm with notches of 5x5 mm in the middle of the prisms. The test results indicated that UHPC prisms failed in a brittle manner with a sudden drop of load in the descending branch, while UHPFRC prisms failed in a ductile manner with a strain hardening stage after the cracking stress and with a softening stage after the ultimate stress. The crack opening of UHPFRC prisms was much higher than that of UHPC prisms. The values of cracking stress, ultimate stress, and crack opening were significantly improved by increasing the volume of steel fibers from 1% to 2%. The prisms with small dimensions were adopted for the direct tension tests in this study, thus leading to the feasibility of testing and reducing the cost.

Ultra-high performance recycled steel fiber reinforced concrete segments under the thrust force of TBM jacks and their environmental potentialities

Investigations have indicated that segmental tunnel linings are mainly affected during their installation phase, especially at the stage of applying thrust force. Although these concentrated thrust forces are applied temporarily, they can cause cracks and serious damage to segments. One of the main goals of this research is to evaluate the performance of ultra-high performance fiber reinforced concrete (UHPFRC) using recycled steel fibers (RSF) in tunnel lining segments. An experimental and numerical research program, including small-scaled segments (panel samples), was developed to achieve this goal. In this program, an axial load equivalent to the thrust force of a tunnel boring machine (TBM) is applied to 4 different types of samples. Three common states of defects in the support area have also been simulated to examine the more accurate and realistic performance of segment specimens. Another goal of this research is to present a hybrid design for tunnel segments using UHPFRC with RSF in order to significantly reduce the consumption of reinforcement rebar despite the significant increase in the performance of tunnel segments. Based on the results obtained, it was observed that UHPFRC segments with RSF have a good ability to reduce the opening and growth of cracks caused by the thrust forces. The new hybrid reinforced designs have shown significantly better performance compared to the conventional reinforced segments. Crack openings, the first crack starting force, and the environmental friendliness in the full-recycled fiber UHPFRC segments and two new hybrids reinforced samples were improved compared to the conventional reinforced design.

Verification of the shear resistance of UHPFRC beams – Design method for the German DAfStb Guideline and database evaluation

This contribution focuses on the verification of the shear resistance of Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) beams. A verification method following Eurocode2 and the German DAfStbGuideline „Steel Fibre Reinforced Concrete“ is presented, which superimposes the shear resistance of a member without shear reinforcement, the shear resistance provided by stirrups, and the contribution of the fibers activated in the shear crack. With regard to the contribution of the fibers, the verification method differentiates between members with I-shaped and approximately rectangular solid cross section. This provides a more favorable design of members with I-shaped cross section. Reliability of the design approach is statistically evaluated by means of a total of 208 shear tests on UHPC and UHPFRC beams with different configuration. For 133 tests on beams with I-shaped cross section the ratio between ultimate shear force from experiment Vexp and theoretical shear resistance Vcal shows a mean value of X̅=1.48 and a 5 % quantile of Q0,05 = 0.94. For 75 tests on beams with approximately rectangular solid cross section the results are X̅=1.59 and Q0,05 = 0.94. For all 208 tests included in the database X̅=1.52 and Q0,05 = 0.94 are obtained. Based on the statistical parameters it is concluded that the prediction model is sufficiently reliable for being considered with the forthcoming German DAfStbGuideline on Ultra-High Performance Concrete.

Numerical Modelling of an Exterior RC Beam Column Joint Subjected to Cyclic Loading Strengthened Using UHPFRC and CFRP

A poorly detailed reinforced concrete (RC) beam-column joint (BCJ) is highly susceptible to damage under seismic forces due to the generation of shear stresses. Shear stresses are generated due to the continuous change in the direction of the compression and tension forces acting on the beam-column joint. As a result, the strength, stiffness and the energy dissipation of the whole structure is affected. It needs to be addressed beforehand by improving its shear, tensile and energy dissipation capacities so that the damage is minimised. So a structure needs to be strengthened prior to any major damage. In the present study the seismic performance assessment of a BCJ strengthened by a combination of ultra-high performance fibre reinforced concrete (UHPFRC) and carbon fibre reinforced polymer (CFRP) has been done analytically in ABAQUS. The seismic parameters observed are the hysteresis response, strength, stiffness, ductility and energy dissipation of the specimens strengthened both by UHPFRC and CFRP. From the results it is clear that the combination of the two strengthening schemes is very efficient in increasing the peak load 2.62 times and the ductility by almost 6% of the specimens as compared to the specimens strengthened using only one scheme. Also the energy dissipation shows an increase of 7.3% in case of using the combination strengthening strategy. The rate of degradation of the strength is also reduced substantially.

Modeling the behavior of shear‐dominated walls retrofitted with ultra high‐performance fiber‐reinforced concrete jackets

AbstractLarge‐scale tests of shear‐dominated walls with ultra high‐performance fiber‐reinforced concrete (UHPFRC) jackets have shown the high effectiveness of this retrofitting solution. The jackets can suppress brittle shear failures and result in a ductile response governed by yielding of the flexural reinforcement. In addition, due to the low porosity of UHPFRC and the crack control provided by the fibers, the jackets can also provide an effective corrosion protection. However, while this retrofitting solution is very promising, there is a lack of mechanical models that can predict the effect of UHPFRC jackets. This paper proposes such a model based on a three‐parameter kinematic theory (3PKT) for reinforced concrete walls. The 3PKT is extended by modeling three important effects associated with the UHPFRC jackets: tension in the fibers across the critical diagonal cracks, increased compression resistance of the critical loading zones, and enhanced crack control. The results show that the proposed approach can be used to design the properties of UHPFRC jackets in order to achieve a desired structural response in terms of strength, ductility, and crack control.

Fatigue behavior of ultrahigh-performance fiber-reinforced concrete as an alternative for flexible pavement rehabilitation

The fatigue behavior of ultrahigh-performance fiber-reinforced concrete for use as an overlay in the typical rehabilitation of a flexible pavement structure was analyzed in this study. Compression and four-point bending tests were carried out to characterize the concrete mechanical properties. Fatigue tests were performed using the four-point method, and test beams were evaluated without precracking. The specimens were subjected to constant-amplitude sinusoidal loading with a loading frequency of 10 Hz. The magnitude of each stress level was calculated as a percentage of the initial crack stress. The following results were obtained for the concrete: a compressive strength of 127.1 MPa, bending yield strength of 6.23 MPa, maximum bending stress of 9.89 MPa, Young's modulus of 38.1 GPa, and dynamic modulus of 28.6 GPa. The stress and strain at one million cycles were 6.0 MPa and 166 μm/m, respectively. The fatigue test results indicated superior properties of the ultrahigh-performance concrete to those of similar materials.

Behavior of Reinforced Ultra-High Performance Concrete Slabs Under Impact Loading After Exposure to Elevated Temperatures

Steel fiber-reinforced ultra-high performance concrete (UHPC) material is prone to explosive spalling under elevated temperatures. With the addition of polypropylene (PP) fiber, thermal spalling of UHPC can be mitigated and its fire resistance can be improved. This research investigates the impact resistance of steel and PP fiber-reinforced UHPC slabs after exposure to elevated temperatures, and the structural behavior and damage were compared against normal strength concrete (NSC) slabs. Karagozian & Case concrete (KCC) model was adopted to simulate both NSC and UHPC materials. With consideration of thermal hazards, the material damage, equation of state and strain rate sensitivity were adapted. The validity of this numerical model was evaluated against available experimental results. The numerical model was used to investigate the impact resistance of the reinforced UHPC slabs after exposure to fire hazards. The effect of fire exposure time, impact velocity and impact mass on the resistance of the reinforced NSC and UHPC slabs were analyzed. The simulation results revealed that punching shear failure areas in the NSC slabs were 2.5 times, 3.4 times, 3.0 times and 1.2 times larger than the UHPC slabs after exposure to international standardization ISO-834 standard fire for 1[Formula: see text]h, 2[Formula: see text]h, 3[Formula: see text]h and 4[Formula: see text]h, respectively. After exposure to the standard fire ISO-834 for 2 h, the punching shear failure on the bottom side of NSC increased 90.9% with the increase in falling height from 1[Formula: see text]m to 7[Formula: see text]m, while for the UHPC slabs, the increment was around 67.9%. After exposure to the standard fire ISO-834 for 2[Formula: see text]h, the punching shear damage of the NSC slabs increased by 72.9% with the punch weight increased from 100[Formula: see text]kg to 700[Formula: see text]kg, whereas the damage in the UHPC slabs increased by 53.8%.

An overview of progressive advancement in ultra-high performance concrete with steel fibers

A progressive advance in the construction sector is attained by employing ultra-high performance concrete (UHPC) technology. Rigorous efforts have been made in this research domain to have remarkable quality levels with 150 MPa or more strength and significant durability, which was impossible previously. Steel fiber incorporation in UHPC is vital in improving its mechanical characteristics. This review on the incorporation of steel fibers in UHPC evaluates, identifies, and synthesizes research outcomes for creating a summary of current evidence that can contribute to evidence-based practice. This study summarized a review of the literature on steel fibers’ effect on UHPC, intending to explore its essential aspects. The aim is to summarize the literature in this research domain and provide guidance for future research. Moreover, the basic requirements and materials, mixing and casting, mechanical properties, modern applications, advantages and disadvantages, and future perspectives associated with steel fibers reinforced UHPC in the construction sector are discussed. It is revealed from the conducted analysis that the most widely applied keyword is “steel fibers.” Due to the graphical illustration of the contributing studies, the current work may benefit academic scholars in sharing novel techniques and ideas and establishing collaborative efforts. Furthermore, the present work reveals that steel fibers have the potential to enhance the mechanical properties of UHPC; however, the large-scale production and applications of steel fiber-reinforced UHPC are controlled by parameters like fiber content and geometry.

Strategies to Incorporate Ground-Granulated Blast-Furnace Slag and Copper Slag into Ultrahigh-Performance Fiber-Reinforced Concrete

Strategies to Incorporate Ground-Granulated Blast-Furnace Slag and Copper Slag into Ultrahigh-Performance Fiber-Reinforced Concrete

Physically explicable mathematical model for strength prediction of UHPFRC

This paper presents a quantitative analysis of the mechanical performance of ultra-high performance fiber-reinforced concrete (UHPFRC). UHPFRC shows great potential in the construction of the cities of tomorrow. However, establishing empirical formulas by incorporating existing data for the practical engineering design of UHPFRC remains a problem. To advance the understanding of UHPFRC, this paper qualitatively and quantitatively studied UHPFRC with an emphasis on its strength. Utilizing abundant data consisting of 111 different UHPFRC mixtures in literature, the key factors governing the strength of UHPFRC, e.g., the volumetric ratios and types of paste, aggregate, fibers and filler, were identified. Based on the key factors, a robust mathematical model for the strength prediction of UHPFRC was established. In addition, an artificial neural network model was constructed. This study shall provide useful guidelines for the mix design of sustainable and resilient UHPFRC.

Experimental investigations of precast concrete column with spliced connections based on ultrahigh‐performance fiber‐reinforced concrete

AbstractWhen compared with normal concrete, ultrahigh‐performance fiber‐reinforced concrete (UHPFRC) could signally enhance the bond with reinforcing bars. Accordingly, incorporating UHPFRC to connect precast concrete columns allows smaller bar splice lengths and provides ease of construction. In this article, a two‐stage research program was presented. First, the behavior of double‐row spliced rebars in UHPFRC was tested under direct tension, and the bars adopted internal strain measurement to characterize the bond stress distribution along the splice length. The failure of specimens was governed by UHPFRC splitting, and the bond stress of spliced rebars in UHPFRC presented a two‐local peaks profile. Second, the hysteretic performance of precast concrete columns with spliced connections based on UHPFRC was determined by full‐scaled cyclic tests and numerical simulations. Precast columns with UHPFRC connections at the column base exhibited similar ductility, energy dissipation capacity, and higher bearing capacity to the monolithic concrete columns. Finally, some practical considerations and recommendations were proposed.

Ultra high performance concrete and C-FRP tension Re-bars: A unique combinations of materials for slabs subjected to low-velocity drop impact loading

In this research work, different combinations of normal strength concrete (NSC), ultra-high-performance concrete (UHPC), and steel fiber-reinforced UHPC (SFR-UHPC) concrete with re-bars of conventional steel and of carbon fiber-reinforced polymer (C-FRP) are used in a two-way square slab of size 1000mm x 1000mm x 75mm subjected to 2500 mm free-fall impact loading. Experimental arrangement consisting of 105 kg dropping weight with the circular flat impacting face of 40 mm diameter used for carrying out impact test is modeled using a high-fidelity physics-based finite element computer code, ABAQUS/Explicit-v.6.15. After validating the experimental results of the NSC slab with steel bars, analyses are extended by replacing NSC and steel bars with UHPC/SFR-UHPC and C-FRP bars, respectively, under the same dropping weight. Only the remote face (tension face) of the slabs is provided with the re-bars. Widely employed and available with the ABAQUS, the Concrete Damage Plasticity model with strain-rate effects has been entrusted for simulating the concrete plastic response. Re-bars of steel are idealized with the Johnson-Cook plasticity damage model. C-FRP re-bars are defined with the classical plasticity model following the elastic-plastic constitutive laws. The impact responses of the slabs consisting of NSC/UHPC/SFR-UHPC concrete with re-bars of steel, and C-FRP combinations considered are discussed and compared. Slabs made of UHPC/SFR-UHPC concrete with the C-FRP re-bars are found to offer a promising combination of materials to withstand low-velocity impact load with little damage and extraordinary impact performance.

Rheological characterization of ultra-high performance concrete for 3D printing

The authors recently developed a 3D-printable ultra-high performance fiber-reinforced concrete (3DP-UHPFRC) for additive construction of structural members with significantly reduced reliance on steel bars. This study investigates the rheological behavior of the developed 3DP-UHPFRC. The effects of two major factors affecting the performance of 3DP-UHPFRC, namely steel fiber volume (0, 1%, and 2%) and nano-clay (NC) content (0, 0.1%, and 0.2% by binder mass) on workability, static yield stress, dynamic yield stress, and apparent viscosity were determined. Test results showed that the inclusion of steel fibers and NC reduced the workability and led to a significant increase in the static yield stress, dynamic yield stress, and apparent viscosity. However, the effect of NC content on the rheological properties became negligible in the mixtures made with 2% fiber content. Similarly, the effect of steel fiber volume became negligible in the mixtures made with 0.2% NC. In addition, the influence of changes in rheology due to the addition of steel fiber and NC on the extrudability and buildability of the mixtures were investigated by 3D-printing of 500 mm high hollow columns with three different print speeds. The results showed all mixtures exhibited satisfactory extrudability (i.e., no blockage of extruder or tearing of filaments was observed). In addition, the buildability of the mixtures increased as the steel fiber and NC contents increased.