Ultra High Performance Fiber Concrete Research Articles

Preliminary findings from experimental study on blast performance of steel-concrete composite columns

Abstract The use of steel-concrete composites in blast resistance has gained importance in the recent years, since concrete is not able to resist higher explosive charges. The authors have designed an experimental device to test steel-concrete composite columns subjected simultaneously to axial and blast loading. The experimental device in a shape of a closed steel frame allows to test plain steel columns, composite steel-concrete columns and composite steel-using ultra-high performance fiber-concrete (UHPFRC) columns. The specimen is loaded with 800f of explosive charge while subjected to axial compressive loading. The response of the specimen is acquired using photonic-doppler velocimetry (PDV). The paper presents preliminary results from the first run of the experiment documenting the benefits of composite action on blast resistance of the tested columns. The use of UHPFRC also showed its beneficial effects. This paper presents preliminary findings from the experimental program.

Experimental investigation of heat-damaged reinforced concrete columns strengthened with different schemes

This paper experimentally investigates the efficacy of two jacketing techniques in the rehabilitation of square and circular reinforced concrete (RC) columns that were exposed to highly elevated temperatures. Twenty-four RC columns were tested under an axial compression load, which was divided into three groups. The first group consisted of the control specimens without applying any strengthening approach. Group 2 consisted of the columns with the strengthening configuration of near-surface-mounted (NSM) rebars and carbon fiber-reinforced polymer (CFRP) layers. Regarding the third group, columns were strengthened using two layers of welded-wire mesh (WWM) and ultra-high-performance fiber concrete (UHPFC) jacketing. Four columns from each group were subjected to an elevated temperature of 600 °C for a duration of 3 h, while the remaining half were subjected to room temperature. The results showed that after three hours at a temperature of 600 °C, both strengthening schemes successfully restored and exceeded the initial load-carrying capability of all columns. Utilizing WWM with UHPFC jacketing as new strengthening technique proved to be the most efficient method for reinstating the load-carrying capability of circular columns (+321.8 %) and square columns (+140.6 %) that were subjected to high temperatures. Additionally, an analytical model was proposed to estimate the ultimate load capacity of RC columns after rehabilitation.

Preliminary Study on the Use of Recycled Glass, Ceramics, and Granite as Fillers in Ultra-High Performance Fiber Concrete

Preliminary Study on the Use of Recycled Glass, Ceramics, and Granite as Fillers in Ultra-High Performance Fiber Concrete

Investigations on Blast Performance of Steel-Concrete Composite Structures

Blast performance of concrete and ultra-high performance fiber concrete (UHPFRC) has been subject to numerous publications in the past decades. The enhanced force-deflection diagram of fiber concrete and ultra-high performance fiber concrete provide massive increase on the protective function of these materials compared to regular concrete. Nevertheless, concrete spalling cannot be fully avoided even when using UHPFRC. The next step for harmful debris ejection prevention can be supplementing the concrete specimens with steel slabs. The steel slab will not just hold the debris, but can, if properly bonded with concrete, contribute to the load bearing capacity as steel-concrete composite structure. This paper presents an overview of recent experiments on blast resistance of steel-concrete composite slabs. In total 6 pairs of specimens (dimension 1.000/1.000/150mm) were prepared, 6 specimens using regular concrete and 6 specimens using UHPFRC. One pair of specimens was reinforced by a steel mesh at 30mm cover from the soffit, one pair was supplemented by a steel plate bonded with 4 studs in the corners, at the complementary specimen pair, the concrete was also covered with a steel plate at the side subjected to blast loading, in the case of the further pair of specimens, the steel plates were connected by steel bars arranged in a mesh 150/150mm. The final 2 pairs represented steel-concrete composite slabs, in the first case, the shear studs were supplemented with a steel mesh (according to provisions of the European standard for steel-concrete composite structures), in the last case, the shear studs were replaced by a shear plate. All specimens were subjected to the same contact blast loading. The paper presents the experimental arrangement, the achieved results and a brief discussion on the structural behavior.

Ultra-high performance fiber concrete for architectural purposes

The aim of the research works is the development of ultra-high-performance fiber concrete (UHPFRC) for architectual purposes, such as facade panels and their accessories. Research is aimed at achieving high utility properties in the form of high flexural tensile strength, low absorption and very good durability of the developed UHPFRC. The research is also focused on the development of the production technology itself, by pouring and spraying fresh UHPFRC mixtures into molds. The development of cast UHPFRC is also focused on the design and optimization of the production technology, which will enable an automatic production process and reduce costs for the production of flat facade panels. The development of sprayed UHPFRC will make it possible to produce 3D elements with higher utility properties compared to currently produced products from ordinary fiberglass concrete (GFRC).

Studying the effect of embedded length strength of concrete and diameter of anchor on shear performance between old and new concrete

Abstract This article illustrates the specifications required to accurately design, specify, and install embedded anchor bolts between old and new concrete composite specimens for concrete repair or reinforcing of collapse concrete a research hotspot. The concrete slabs are facing a major challenge with deterioration, especially for reinforcement corrosion caused mainly by severe cycles of various chemical attacks. In this research, the impact of using contact plates between composite specimens was investigated by testing grouped specimens, thereby the models were divided into two groups, which tested under static load. The findings of a series of tests conducted to evaluate the structural behavior of shear connections (by pushout test) by including many parameters; the diameter (8, 12 and 16 mm), bounding between different compressive strength should be changed [normal concert (NC) mixes , ultra-high performance fiber concrete (UHPFC), and self-compacting mortar (SCM)]. Also, the embedded length of bolts was varied from 70, 130, to 190 mm. These parameters were studied individually in two groups. The first group was without contact plate and the second group was with contact plate. Experimental findings were obtained and reported, including the failure modes, maximum resistance, slippage capacity, and load–slip characteristic responses of the connections. Based on the obtained data, a relationship between the studied parameters was investigated. Experimental findings showed that the ultimate strength of rough surface specimens (without contact plate) was about 31% greater than that of smooth surface specimens (with contact plate), and obviously, all pushout specimens failed due to stud shank failure.

Punching Shear Behavior of Slabs Made from Different Types of Concrete Internally Reinforced with SHCC-Filled Steel Tubes

The punching shear failure of reinforced concrete (RC) flat slabs is an undesirable type of failure, as it is sudden and brittle. This paper presents an experimental and numerical study to explore the behavior of flat slabs made of different types of concrete under the influence of punching shear. Experimental tests were carried out on four groups of flat slabs, each group representing a different type of concrete: ordinary normal concrete (NC), high-strength concrete (HSC), strain-hardening cementitious composite concrete (SHCC), and ultra-high-performance fiber concrete (UHPFC). Each group consisted of six slabs, one representing an unreinforced control slab other than the reinforcement of the bottom mesh, and the others representing slabs internally reinforced with SHCC-filled steel tubes and high-strength bolts. An analytical equation was used to predict the punching shear capacity of slabs internally reinforced using steel assemblies. A numerical model was proposed using the ABAQUS program, and was validated by comparing its results with our experimental results. Finally, a case study was performed on large-scale slabs. The results showed that using steel assemblies inside NC slabs increased the slab's punching shear capacity but does not completely prevent punching shear failure. Internally unreinforced slabs made of UHPFC and SHCC were able to avoid punching shear failure and collapse in a ductile bending pattern due to the high compressive and tensile strength of these types of concrete. The proposed analytical method succeeded in predicting the collapse load of slabs reinforced with steel assemblies with a difference not exceeding 9%.

Strengthening of slab-column connections using ultra high-performance fiber concrete

This experimental work intends to assess the efficiency of employing ultra-high-performance fiber concrete (UHPFC) as a strengthening system for improving the punching shear capacity of slab-column connections (SCCs). Seven reinforced concrete SCCs were constructed and tested under axial load. One of them was retained as a control slab (un-strengthened), and the other six were strengthened with different strengthening schemes. The results revealed that the strengthening scheme is effective in improving the punching shear capacity of slab-column connections significantly. Strengthened slabs achieved increases in punching shear capacity, pre cracking stiffness, post-cracking stiffness, and toughness of up to 172.68 %, 235.70 %, 300 %, and 233.59 %, respectively. It turns out that it is important to use UHPFC with longitudinal reinforcement (R-UHPFC) to enhance the strength and toughness. Finally, the punching shear capacities of the tested specimens were compared to those predicted by the existing theoretical approach.

Experimental and numerical investigation of one-way reinforced concrete slabs using various strengthening systems

This paper presents different effective strengthening techniques to enhance the flexural strength of one-way reinforced concrete (RC) slabs. To assess the effectiveness of utilizing the suggested strengthening techniques, an experimental and numerical study was conducted. The experimental program included seven one-way RC slabs with dimensions of (2000 mm × 1000 mm x 150 mm). The first specimen was considered a control slab without providing any strengthening technique, and the remaining six specimens were strengthened with various systems. Ultra-High Performance Fiber Concrete (UHPFC) was used to strengthen the second specimen (S1-UHPFC), where a layer of UHPFC with a thickness of 50 mm was placed in the tension side of the slab within the specified slab depth. The third specimen (S2-HSC) is the same as the second specimen, but it is strengthened with High-Strength Concrete (HSC). The fourth specimen (S3-R.B) was strengthened from the bottom of the slab by bonding steel skewer bars with square cross sections (12 mm × 12 mm) by near-surface mount (NSM) technique. The fifth specimen (S4-C.B) is the same as the fourth specimen (S3-R.B) but the square skewer bars have been replaced by circular ones with a diameter of 12 mm. The sixth specimen (S5-S.P) was strengthened from the bottom of the slab by bonding stainless steel strips with a width of 50 mm and a thickness of 1 mm. The last specimen (S6-A.P) is similar to the sixth specimen (S5-S.P), but the stainless steel strips were replaced with aluminum ones. The results show that the failure loads of specimens S3-R.B and S4-C.B are greater than the control specimens S0-C.S by about 62 % and 41 %, respectively. In addition to specimen strengthening, using stainless steel strips or aluminum strips was less effective than the previous strengthening methods. However, this type is distinguished by its resistance to corrosion. To verify the outcomes of the experimental tests, a finite-element model using ABAQUS program was performed. Finally, An excellent agreement between the experimental and numerical results was obtained.

Behavior of Precast Segmental Beams Made of High-strength Concrete and Ultra-high Performance Fiber Concrete Connected by Shear Keys Technique

The segments of the precast concrete beams can be assembled by joints have interlaced shear keys. This paper presents an experimental and numerical study of ten samples, six of them were tested under the influence of direct shear; these samples represent reinforced and non-reinforced shear keyed joints made of high-strength concrete (HSC) and ultra-high performance fiber concrete (UHPFC) under the influence of different levels of confining stress. In addition, four beams were tested under the influence of bending, two of them are unconnected control beams made of HSC and UHPFC, and the other two beams are precast segmented and were assembled using reinforced shear keyed joints of the same joints tested under direct shear. All the details of the shear keyed joints are fixed in all samples and they are dry non-epoxy joints, the external prestressing technique was used. Also, Abaqus program was used for numerical modeling of all samples that were tested in the experimental program using the 3D solid element model. The success of the modeling process was verified by comparing the experimental and numerical results as the results of the relationship between load and displacement and also the failure pattern. From the experimental and numerical study, it was found that by reinforcing the shear keys and/or by increasing the confining stress of the joints made of HSC and UHPFC, the shear capacity of the joints is increased. If the value of the used confining stress is constant at a value of 3 N/mm2 and by reinforcing the shear keys with reinforcement, the maximum load increases by 18% and 48%, respectively, than its non-reinforced counterparts joints. It was also found that by increasing the confining stress of the reinforced shear keyed joints from 3 N/mm2 to 6 N/mm2, the maximum load value is increased by 18% and 16%, for HSC and UHPFC shear keyed joints, respectively.

Optimization of Different Properties of Ultra- High Performance Concrete Mixes for Strengthening Purposes

The current research’s purpose is to examine how Ultra-High Performance Fiber Concrete (UHPFC) holds up in terms of strength and durability for strengthening purposes. For this reason, the experimental and the theoretical studies in this research attempted to assess different fresh and hardened properties of a variety of ultra-high performance combinations. Steel fibers were utilized to differentiate all of the program's combinations at percentages of 0.25 %, 0.5 %, 0.75 %, 1%, and 1.25 % by volume. Mini flow slump, compressive and flexural strength, ultrasonic pulse velocity, water absorption, and porosity tests were all used to examine the performance of the strength and durability of the material. The findings of this study's trials showed that steel fibers increased the strength of UHPFC. The steel fiber ratio of 1% gave the maximum compressive strength, whereas 1.25 percent yielded the highest flexural strength. Because the fibers function as a bridge, preventing internal breaking, the tensile test results were improved as the proportion of steel fiber rises. Through the use of the multi-objective optimization approach, the optimal ratio of fibers was chosen at the end of the laboratory work since it has the best durability and strength characteristics. Statistical software (Minitab 2018) was used to find the optimal combination of UHPFC that meets all of the requirements. The theoretical selected optimum ratio of 0.77% of fibers obtained from the optimization was evaluated and validated experimentally. The optimized mix provided 90.28 MPa, 14.6 MPa, and 20.2 MPa for compressive, splitting tensile and flexural tests respectively with better durability performance compared to other mixes prepared in this investigation.

Flexural behavior of GFRP bar-reinforced concrete beams with U-shaped UHPC stay-in-place formworks

Poor durability of reinforced concrete structures in harsh marine environments is an intractable issue. Replacing steel bars with fiber-reinforced polymer (FRP) bars and utilizing ultrahigh-performance fiber concrete (UHPC) for the concrete cover can greatly increase the durability of such structures. A new hybrid GFRP bar reinforced concrete beam with a prefabricated U-shaped UHPC stay-in-place formwork was tested. Herein, nine beams—one reference beam and eight hybrid beams with prefabricated U-shaped UHPC stay-in-place formworks—were subjected to four-point bending tests. The test parameters included the existence of a U-shaped UHPC stay-in-place formwork, the GRFP bar reinforcement ratio, the core concrete strength, and the bottom longitudinal reinforcement type. Experimental results showed that the hybrid beams had approximately 93.8–228.2% higher cracking loads and the hybrid beams (except beams U2 and U5) had approximately 5.9–19.0% higher ultimate loads than the reference beam. Increasing the GFRP reinforcement ratio improved the cracking load and bearing capacity of the hybrid beams, and the ultimate load increased with increasing core concrete strength. Premature failures in some hybrid beams due to partial debonding occurred between the U-shaped UHPC stay-in-place formwork and core concrete. Thence, the partial debonding should be avoided in further studies by proposing a more effective interfacial bonding method for the hybrid beam.

The construction process for pre-stressed ultra high performance concrete communication tower.

Towers are important structures for installing radio equipment to emit electromagnetic waves that allow radio, television and/or mobile communications to function. Feasibility, cost, and speed of the construction are considered in the design process as well as providing stability and functionality for the communication tower. This study proposes the new design for construction of segmental tubular section communication tower with ultra-high-performance fibre concrete (UHPFC) material and prestress tendon to gain durability, ductility, and strength. The proposed mix design for UHPFC in this study which used for construction of communication tower is consisted of densified Silica Fume, Silica fine and coarse Sand and hooked-ends Steel Fiber. The prestressed tendon is used in the tower body to provide sufficient strength against the lateral load. The proposed design allows the tower to be built with three precast segments that are connected using bolts and nuts. This paper presents a novel method of construction and installation of the communication tower. The advantages of proposed design and construction process include rapid casting of the precast segment for the tower and efficient installation of segments in the project. The use of UHPFC material with high strength and prestress tendon can reduce the size and thickness of the tower as well as the cost of construction. Notably, this material can also facilitate the construction and installation procedure.

Physico-mechanical and microstructural characterization of concretes ultra-high performance matrix fiber

This work will be devoted on the one hand to the formulation of an ultra-high performance fiber concrete based on local materials (cement and fine sand) and on the other hand to the study of the effect of the fibers on the physico-mechanical behavior of the concrete. The formulation will be obtained by the search for the optimum percentage of the fibers and by adopting as criterion the workability of the concrete. For the optimal fiber retention, the influence of the fibers on the mechanical behavior of the concrete (compression strength, tensile strength and ductility) will be studied. The results of this study will highlight the impact of the microstructure on the improvement of the physico-mechanical characteristics of concrete.

Blast Resistance of Slurry Infiltrated Fibre Concrete with Waste Steel Fibres from Tires

The utilization of waste steel fibres (coming from the recycling process of the old tires) in production of blast resistant cement based panels was assessed. Waste fibres were incorporated in slurry infiltrated fibre concrete (SIFCON), which is a special type of ultra-highperformance fibre reinforced concrete with high fibre content. The technological feasibility (i.e. suitability of the waste fibres for SIFCON technology) was assessed using homogeneity test. Test specimens were prepared with three volume fractions (5; 7.5 and 10 % by vol.) of waste unclassified fibres. SIFCON with industrial steel fibres (10% by vol.) and ultra-highperformance fibre concrete with industrial fibres were also cast and tested for comparison purposes. Quasi-static mechanical properties were determined. Real blast tests were performed on the slab specimens (500x500x40 mm) according to the modified methodology M-T0-VTU0 10/09. Damage of the slab, the change of the ultrasound wave velocity propagation in the slab specimen before and after the blast load in certain measurement points, the weight of fragments and their damage potential were evaluated and compared. Realized tests confirmed the possibility of using the waste fibres for SIFCON technology. The obtained results indicate, that the usage of waste fibres does not significantly reduce the values of SIFCON flexural and compressive strength at quasi-static load - the values were comparable to the specimens with industrially produced fibres. With increasing fibre content, the mechanical parameters are increasing as well. Using of the waste fibres reduces fragmentation of SIFCON at blast load due to the fibre size parameters. Using of low diameter fibres means more fibres in the matrix and thus better homogeneity of the whole composite with less unreinforced areas. Regarding the blast tests, the specimen with waste steel fibres showed the best resistance and outperformed also the specimen with commercial fibres. Using of waste fibres in SIFCON technology can reduce the price of this composite by 70 % by keeping the original SIFCON extraordinary properties, which makes it very competitive material in the concrete area.

Blast Resistance of Slurry Infiltrated Fibre Concrete with Waste Steel Fibres from Tires

The utilization of waste steel fibres (coming from the recycling process of the old tires) in production of blast resistant cement based panels was assessed. Waste fibres were incorporated in slurry infiltrated fibre concrete (SIFCON), which is a special type of ultra-highperformance fibre reinforced concrete with high fibre content. The technological feasibility (i.e. suitability of the waste fibres for SIFCON technology) was assessed using homogeneity test. Test specimens were prepared with three volume fractions (5; 7.5 and 10 % by vol.) of waste unclassified fibres. SIFCON with industrial steel fibres (10% by vol.) and ultra-highperformance fibre concrete with industrial fibres were also cast and tested for comparison purposes. Quasi-static mechanical properties were determined. Real blast tests were performed on the slab specimens (500x500x40 mm) according to the modified methodology M-T0-VTU0 10/09. Damage of the slab, the change of the ultrasound wave velocity propagation in the slab specimen before and after the blast load in certain measurement points, the weight of fragments and their damage potential were evaluated and compared. Realized tests confirmed the possibility of using the waste fibres for SIFCON technology. The obtained results indicate, that the usage of waste fibres does not significantly reduce the values of SIFCON flexural and compressive strength at quasi-static load - the values were comparable to the specimens with industrially produced fibres. With increasing fibre content, the mechanical parameters are increasing as well. Using of the waste fibres reduces fragmentation of SIFCON at blast load due to the fibre size parameters. Using of low diameter fibres means more fibres in the matrix and thus better homogeneity of the whole composite with less unreinforced areas. Regarding the blast tests, the specimen with waste steel fibres showed the best resistance and outperformed also the specimen with commercial fibres. Using of waste fibres in SIFCON technology can reduce the price of this composite by 70 % by keeping the original SIFCON extraordinary properties, which makes it very competitive material in the concrete area.

Full-scale experimental testing of the blast resistance of HPFRC and UHPFRC bridge decks

Because of the current geopolitical situation, research on improving the resistance of the civil and transport infrastructure to blast or impact loads has gained considerable attention in recent years. This paper presents the results of full-scale blast experiments designed to characterize the resistance of steel-fiber-reinforced concrete full-scale bridge decks subjected to near-field blast loading, and its dependence on the material properties of the concrete. The blast performance of reinforced concrete specimens increases with added high-performance steel fibers. An increase in fiber content and in compressive strength up to ultrahigh-performance fiber concrete (UHPFRC) further enhances its blast performance. An attempt was made to further increase the blast resistance of a concrete structure with the use of a basalt mesh. The UHPFRC specimen with a basalt mesh experienced a greater extent of internal damage than a regular UHPFRC specimen. However, the basalt mesh inserted into the concrete cover at the soffit of the UHPFRC specimen improved its blast performance, as expressed by the area of spalling and the volume of debris. This phenomenon was studied numerically, and it was proved that it is caused by the internal rebound of the shock wave, which causes a local increase in the stresses inside the specimen. The heterogeneity of the specimens, which is increased by an internal reinforcement or by a basalt mesh, converts the blast damage due to internal rebounds into layer delamination. The delamination of the concrete specimen can be very effective in dissipating the energy of the blast wave.

Strengthening of reinforced concrete beams subjected to torsion with UHPFC composites

The proposed techniques to repair concrete members such as steel plates, fiber-reinforced polymers or concrete have important deficiencies in adherence and durability. The use of ultra high performance fiber concrete (UHPFC) can overtake effectively these problems. In this paper, the possibility of using UHPFC to strengthen reinforced concrete beams under torsion is investigated. Seven specimens of concrete beams reinforced with longitudinal and transverse reinforcements. One of these beams consider as control specimen while the others was strengthened by UHPFC on four, three, and two sides. This study includes experimental results of all beams with different types of configurations and thickness of UHPFC. As well as, finite element analysis was conducted in tandem with experimental test. Results reveal the effectiveness of the proposed technique at cracking and ultimate torque for different beam strengthening configurations, torque - twist graphs and crack patterns. The UHPFC can generally be used as an effective external torsional reinforcement for RC beams. It was noted that the behavior of the beams strengthen with UHPFC are better than the control beams. This increase was proportional to the retrofitted beam sides. The use of UHPFC had effect in delaying the growth of crack formation. The finite element analysis is reasonably agreement with the experimental data.

Effects of Thickness of Ultra High-Performance Fiber Concrete Wrapping on the Torsional Strength of Reinforced Concrete Beam

Abstract: Two groups of rectangular beams, comprising of six specimens, the first group (L) were provided with four longitudinal bars, one at each corner while the second groups of beams (S) were fully reinforced with longitudinal bars and transverse reinforcement. Each group consisted of three beams. Two beams have been strengthened with ultra high performance fiber concrete (UHPFC) on four sides having a thickness of (15mm - 25mm) and one control beam. The variables considered in the experimental study include the transverse reinforcement ratios and the effect of thickness of UHPFC wrap. Experimental results show the effectiveness of the proposed technique at ultimate torque for strengthening beams and behavioral curves. Strengthened RC beams fully wrapped with a thin layer of UHPFC exhibit an enhanced torsional strength when compared to control beam. Results reveal that the transverse reinforcement ratios by 0.66%, increases the UHPFC contribution to torsional strength of strengthened beams with a 15 thick UHPFC; and by up to 7% for strengthened beams with a 25 thick UHPFC, respectively when compared to same strengthened beams without stirrup. It is found that the ultimate torque of beams with a 25 mm thin layer UHPFC is greater than beams with 15 mm by (28% and 28.3%) for the groups L and S, respectively.

Finite element analysis of longitudinal reinforcement beams with UHPFC under torsion

The proposed techniques to strengthen concrete members such as steel plates, polymers or concrete have important deficiencies in adherence and durability. The use of UHPFC plates can overtake effectively these problems. In this paper, the possibility of using UHPFC to strengthen RC beams under torsion is investigated. Four specimens of concrete beams reinforced with longitudinal bars only were tested under pure torsion. One of the beams was considered as the baseline specimen, while the others were strengthened by ultra-high-performance fiber concrete (UHPFC) on two, three, and four sides. Finite element analysis was conducted in tandem with experimental work. Results showed that UHPFC enhances the strength, ductility, and toughness of concrete beams under torsional load, and that finite element analysis is in good agreement with the experimental data.