Effect of synthetic fibre addition on heat and ballistic resistance of steel fibre-reinforced RPC

Reactive powder concrete (RPC) with dense microstructure are found to perform poorly at elevated temperatures due to a build-up of pore pressure that causes explosive spalling. This paper presents the results of an experimental investigation of the behaviour of six RPC mixes containing hybrid steel and polyvinyl alcohol (PVA) fibres, following exposure to high temperatures up to 700 °C. Residual compressive strength, static elastic modulus and ultrasonic pulse velocity measurements were carried out for all the RPC mixes. A mix containing hybrid steel–PVA fibre is proposed as suitable for high-temperature applications based on these results. Further tests were conducted for the mix at a hot state using a specially designed furnace–loading frame assembly. The hot-state elastic modulus, free thermal strains (FTS) and transitional thermal creep (TTC) were measured at the hot state. Residual compressive strength results for all the mixes indicated an initial increase in strength up to 300 °C, followed by a drastic drop. No apparent changes in elastic modulus and ultrasonic pulse measurements were observed till 300 °C, after which both dropped sharply. RPC containing only either steel fibres or only PVA fibres showed some form of instability, which was explosive in some cases. RPC with no fibres was also susceptible to explosive behaviour; however, the addition of hybrid fibres seemed to have beneficial effects. A mix containing equal volumes of steel and PVA fibres occupying a total fraction of 2 % by volume was found to give the best results. The FTS of that mix was similar to that of siliceous aggregate concretes, and the TTC was significant above 250 °C.

This study compares the interface bonding properties of Polyvinyl Alcohol (PVA) fibers and Polypropylene (PP) fibers with a Reactive Powder Concrete (RPC) matrix. The chemical composition and microstructure of the reaction were characterized using Scanning Electron Microscopy (SEM) to understand the influence of PVA and PP fibers on their surrounding matrix. The Interfacial Transition Zone (ITZ) between the fibers and the RPC matrix was examined in detail. The hydrophilic and hydrophobic behavior of PVA and PP fibers affected the tensile strain capacity and flexural strength properties of the concrete mixes. Two strength grades of RPC mixes were used (30 MPa and 60 MPa, both with 1% fiber content of PVA or PP). The PVA fibers showed superior bonding with the RPC matrix compared to the PP fibers. The 60 MPa PVA mix achieved the highest strain capacity of 13.8%. The 30 MPa PVA mix had a maximum flexural strength enhancement of 4.3%, while the 60 MPa PVA mix demonstrated a 23% increase. Such enhancement can broaden the use of RPC with PVA fibers in structural members subjected to tensile and flexural stresses, while its significant strain capacity lessens the likelihood of microcrack formation.

Reactive Powder Concrete (RPC) is a special type of ultra high strength, superplasticized, silica fume concrete, often fibre-reinforced, with improved homogeneity because the traditional coarse and fine aggregate are replaced by fine sand with particle sizes in the range of 100–400 μm [4–16 thousandths of an inch]. RPC properties are attractive because compressive strengths up to 800 MPa [116 ksi] have been recorded, but more typically in excess of 200 MPa [29 ksi]. Flexural strengths up to 141 MPa [20.4 ksi] and fracture energy of 40 kJ/m2[kJ/in.2] have been reported—the latter achieved when steel or stainless steel fibres were included in the mix (Bache (1998) Proceedings of the 2nd international conference on superplasticizers in concrete, Ottawa, pp 35–41; Coppola et al. L’Industria Ital Cemento 707:112–125 (1996); Blais and Couture PCI J 44(5):60–71 (1999); Richard and Cheyrezy (1994) Proceedings of V. Mohan Malhotra symposium on concrete technology: past, present, and future (SP 144). American Concrete Institute, Detroit, pp 507–518; Richard and Cheyrezy Cement Concrete Res 25(7):1501–1511 (1995)). Ductal®, a commercial RPC, has a compressive strength of approximately 150 MPa [22 ksi] with metallic or organic fibres. All tests described here were performed on 40 × 40 × 160 mm [1.6 × 1.6 × 6.3 in.] (Width (b) × Depth (d) × length (L)) prisms with Poly Vinyl Alcohol (PVA) fibres. Ductal® is a family of RPC and micro-defect-free concretes containing micro silica, silica fume, cement, Quartz sand, superplasticizer, and PVA fibres. Mechanical and fracture parameters were investigated using four point bending. Low and high cyclic fatigue tests were conducted in three stages, starting from low to high strain cycles. Cracks generated by cyclic fatigue tests were monitored periodically in order to evaluate the rate of crack propagation. Cracks were also investigated using a high magnification microscope. Three pairs of specimens were tested, notched and un-notched to evaluate fracture parameters. Four point bending was used again because determination of the J-Integral (J IC ) requires the application of pure bending over a portion of the beam. Load was applied at the third points over a span (S) of 120 mm [4.7 in.], providing a span to depth ratio (S/d) of 3.0. Specimens were notched using a 1 mm [0.04 in.] thick diamond saw. The crack tip generated was circular and the crack length (s) was approximately 10 mm [0.4 in.]. Tests on the notched specimens included measurement of the crack mouth opening displacement (CMOD). Closed-loop testing was developed using a feed back signal from the (CMOD) clip gauge attached to the notched specimens and from strain gauges attached to the un-notched specimens. The weight (w) of each specimen was obtained prior to testing. Fracture parameters were calculated from the load–deflection curves obtained from the notched and un-notched specimens.

Based on its characteristics of early strength, good toughness, and excellent mechanical and impact resistance, steel fiber-reinforced fast-hardening reactive powder concrete (RPC) is expected to become an alternative material used in the rapid repair of marine concrete structures. However, the steel fibers have also caused corrosion problems in coastal environments. To make doped fiber fast-hardening RPC more adaptable for use in ocean engineering, this study prepares fast-hardening RPC mixed with straw and studied the effects of straw content and curing age on its slump flow, setting time, and mechanical performance (flexural strength, compressive strength, and flexural toughness). The effects of straw addition on the compactness and hydration products of fast-hardening RPC were studied through macro- (ultrasonic analysis) and micro-scopic analysis (electron microscopy scanning and X-ray diffraction patterns). The straw content mentioned in this paper refers to the percentage of straw in relation to RPC volume. The results showed that straw reduced the fluidity of RPC slurry by 10.5-11.5% compared to concrete without straw, and it accelerated the initial setting of RPC slurry. When the straw content accounted for 1% of RPC volume, the setting rate was the fastest, with a increasing rate being 6-18%. Compared to concrete without straw, the flexural and compressive strength of fast-hardening RPC was enhanced by 3.7-30.5%. When the content was either 3% or 4%, the mechanical properties improved. Moreover, when the straw content accounted for 4% of RPC volume, the flexural toughness was the highest, with the increase rate being 21.4% compared to concrete without straw. Straw reduces the compactness of fast-hardening RPC.

Reactive powder concrete (RPC) is a type of ultra-high strength cement-based material with a dense microstructure, which is made of ultra-fine powders. RPC demonstrate a very brittle behavior, thus adding fibers improves its mechanical properties. In this study, it was attempted to investigate the effect of using steel and polyvinyl alcohol (PVA) fibers as well as their combination on the properties of RPC. In this regard, hooked-end crimped steel fibers together with short PVA fibers were utilized. Steel and PVA fibers were used with the maximum volume fraction of 3% and 0.75%, respectively, and also different combinations of these fibers were used with the maximum volume fraction of 1% in the concrete mixes. In total, 107 concrete specimens were prepared, and the effect of fiber type and volume fraction on the physico-mechanical properties of RPC including compressive strength, tensile strength, modulus of elasticity, density, and failure mode was explored. In addition, the effect of the curing type on the properties of compressive strength, modulus of elasticity, and density of RPC was evaluated. Finally, coefficients for conversion of cubic compressive strength to cylindrical one for the RPC specimens were obtained under the two curing regimes of heat treatment and standard water curing.

Reactive powder concrete (RPC), a composite that is cured to have ultra-high compressive strength, high durability and high toughness, has been developed in recent years. In this study, the penetration model as shaped charge jet (SCJ) into RPC targets was investigated. The penetration resistance and the anti-impact performance of RPC targets were analyzed. Restlts showed that depth of penetration (DOP) experiments had a good agreement with the calculations. The DOPs of RPC targets created by shaped charge jets are more sensitive to the compressive strength than cavity diameters. In addition, the effect of the jet velocity on penetration resistance was significantly greater than concrete strength do. The higher the jet velocity was, the smaller the compressive strength affected the penetration resistance. With the increase of the RPC compressive strength, the increase of the penetration resistance showed a gradual downtrend. The incrementary ratio of the penetration resistance with the increasing RPC compressive strength was smaller when the jet velocity range was 5.0~10.0km/s compared with that when 1.0~5.0km/s. Moreover, the impact crater depth is affected more by compressive strength of concrete than that by steel fiber volume fraction. The area of the impact crater is no longer reduced as the volume fraction of steel fiber is more than 2% (compressive strength is more than 180MPa), while the depth and volume of impact crater are still decreasing.

Two kinds of innovative re-entrant and hexagonal cell honeycomb sandwich structures filled with reactive powder concrete were proposed, and the ballistic resistance and energy absorption of the sandwich structures were investigated by numerical simulations. The deformation and failure modes of the different structures were analyzed and evaluated in detail. The honeycomb sandwich structures filled with reactive powder concrete prisms improved the capacity of ballistic resistance and energy absorption significantly, compared to the normal reactive powder concrete plates and sandwich structures without reactive powder concrete prisms. The analysis shows that the auxetic re-entrant cell honeycomb sandwich structures have a better ballistic performance than the hexagonal cell honeycomb sandwich structures. The sandwich structures were subjected to impact by three kinds of projectiles: flat, hemispherical and conical nosed. The ballistic limit of the flat nosed projectile is the highest, while the impact performance of the conical and hemispherical nosed projectiles is obviously different from the flat nosed projectile, especially in a relative high velocity range. The sharper nose leads to a higher value of exit velocity and mass loss. In addition, effects of different design parameters on ballistic resistance were also studied by changing the thickness of honeycomb cell and face plates. Results indicate that the thickness of honeycomb walls and face plates have significant effect on the ballistic resistance and energy absorption in a relative low velocity range, while there are no big differences when the initial impact velocity exceeds 400 m/s.

Reactive powder concrete (RPC) is used in structures such as radioactive storage plants, tall buildings and power plants. The performance of RPC after high-temperature exposure is therefore important. RPC (110 MPa) was prepared with different fibres (polypropylene fibres (PPF), polyester fibres (PEF) and their combination) at an optimum fibre dosage of 0.5% by weight of cement. The fibre-reinforced RPCs were exposed to temperatures of 200–800°C for different durations (30–120 min). Physical characteristics like colour change, fracture formation, weight loss, water absorption and residual compressive strength were evaluated. Ultrasonic pulse velocity tests were conducted. Scanning electron microscopy was used to observe the microstructure and assess the deterioration of hydrated substances after exposure to extreme temperatures for different durations. An increase in compressive strength was found for all fibre-reinforced RPCs after heating to 200°C for up to 120 min. The strength increased for 30-min exposure to 400°C. The strength of the fibre-reinforced RPCs decreased for all durations of 600°C and 800°C exposure. At these temperatures, the PEF-reinforced RPC had 10–15% greater residual strength than the RPCs. The PPF-reinforced RPC absorbed 6–12% more water than the RPCs made with PEF fibres after 120 min exposure to 800°C.

Explicit finite element code was applied to simulate the steel fiber reinforced concrete (SFRC) and reactive powder concrete (RPC) target penetrated by kinetic energy projectile. Crater formation, spall of concrete target in penetration process was simulated very well. The numerical results of penetration depths are in good agreement with recent experimental results obtained from ballistic gun with 57mm caliber. The factors effecting on anti-penetration property of SFRC and RPC are analyzed. The results show that: the compressive strength and toughness of the target body have greater impact on anti-penetration performance in the range of projectile velocity 300m/s-600m/s. Anti-penetration capability of RPC concrete is stronger than that of ordinary steel fiber at the higher speeds.

In this research, the application of ultrasonic pulse velocity (UPV) test as a nondestructive method for estimating some of the mechanical and dynamic properties of reactive powder concrete (RPC) containing steel and polyvinyl alcohol (PVA) fibers, as well as their combination was explored. In doing so, ten different mix designs were prepared in 19 experimental groups of specimens containing three different volume contents of steel fibers (i.e., 1, 2, and 3%) and PVA fibers (i.e., 0.25, 0.5, and 0.75%), as well as hybrid fibers (i.e., 0.25-0.75, 0.5-0.5, and 0.75-0.25%). The specimens in these groups were prepared under the two curing regimes of normal and heat treatment. Moreover, the UPV test results were employed to estimate the compressive strength, dynamic modulus, shear modulus, and Poisson\'s ratio of the RPC concrete and to investigate the quality level of the used concrete. At the end, the effect of the specimen shape and in fact the measuring distance length on the UPV results was explored. The results of this research suggest that the steel fiber-containing RPC specimens demonstrate the highest level of ultrasonic pulse velocity as well as the highest values of the mechanical and dynamic properties. Moreover, heat treatment has a positive effect on the density, UPV, dynamic modulus, Poisson\'s ratio, and compressive strength of the RPC specimens, whereas it leads to a negligible increase or decrease in the shear modulus and static modulus of elasticity. Furthermore, the specimen shape affects the UPV of fiber-lacking specimens while negligibly affecting that of fiber-reinforced specimens.

Research on the self-sensing and mechanical properties of aligned stainless steel fiber-reinforced reactive powder concrete

Mechanical properties of steel fiber-reinforced reactive powder concrete at high temperature and after cooling

The brittle nature of reactive powder concrete (RPC) and existence of inertial stress (at high strain rates) made it suffer tensile failure and seriously affected the safety of concrete structure. Graphene with low density and small size easily dispersed in concrete matrix, while its high stiffness and diameter-to-thickness ratio could effectively offset the inertia stress, contributing to improve the energy absorption of the concrete. In this paper, the RPC was nano-modified by combining the characteristics of graphene and concrete. The mechanical behaviors of RPC under different strain rates were systematically studied, and the effects of graphene on mechanical performance of RPC were analyzed. Finally, the reinforcing mechanisms of graphene on RPC were understood, and the dynamic compression constitutive of RPC was established, which provided a theoretical basis for understanding the dynamic mechanical properties and behaviors of this concrete material for the first time. Experimental results showed that under quasi-static loads, the incorporation of graphene significantly enhanced the compressive toughness of RPC. Under the high rate dynamic loads (strain rate of 200–800/s), the dynamic compressive strength, peak strain and ultimate strain of graphene-reinforced RPC were increased by 59.1 MPa/63.9%, 4300 μe/66.0% and 12150 μe/32.7%, respectively. Additionally, the impact toughness of RPC was increased by 117%. The reinforcing mechanisms of graphene on RPC were mainly attributed to their nucleation and bridging effect. Furthermore, the interlaminar slip and structural fracture of graphene further absorbed strain energy released by cracking and therefore improved the mechanical properties of the RPC.

Due to extremely dense microstructure, reactive powder concrete (RPC) shows poor performance at elevated temperatures owing to the development of high pore pressure that causes the deterioration of the material. By using fiber reinforcement, elevated temperature performance of RPC can be improved, as noted by many researchers. To this end, 3% volume fraction of four combinations of steel fiber (SF) and glass fiber (GF) [(3%, 0%), (2%, 1%), (1%, 2%), and (0%, 3%)] was used in RPC to study the change in residual mechanical properties of RPC after exposure to elevated temperatures. Three main mechanical properties, i.e., compressive strength, splitting tensile strength, and flexural strength properties, were studied. Experimental results showed that using 3% volume fraction of fibers (regardless of combination), explosive spalling of RPC was completely prevented. Hybrid fiber RPC with 2%SF–1%GF showed the maximum best mechanical performance at both elevated and normal temperatures. Single 3%SF–RPC performed significantly better than single 3%GF–RPC at both normal and elevated temperatures. A strong correlation existed between the normal temperature strength, residual strength, and exposure temperature.

Performance evaluation of fiber-reinforced reactive powder concrete exposed to high temperature combining nondestructive test