The addition of synthetic fibres to concrete to improve impact/ballistic toughness

Abstract

Concrete is relatively weak in tension and may require some form of reinforcement to cope with tensile forces. Steel reinforcing bar is often used to cater for tensile and compressive forces. However, current research shows that the use of steel reinforcing bar does not afford concrete protection against impact. Alternatively it has been shown that where fibres are added to concrete mixes protection is afforded through increased energy absorption. It would appear that the dispersion of fibres throughout a concrete mix affords a degree of toughness between the reinforcement bar spacing.This research investigates the use of Type 1 micro synthetic fibres, Type 2 macro synthetic fibres and steel fibres used as post crack reinforcement in concrete samples when subject to a variety of stress induced states and compares the performance of these fibre mixes to that of a plain concrete mix. The test program adopted, subjected cube specimens to compressive strength tests, beam samples to both three point flexural bending and single point impact loading, and concrete slab sections to shot gun fire. The parameters investigated under test were: compressive strength, flexural strength, load deflection analysis, energy absorption and impact performance/resistance. Modelling the impact of shot fire on the test specimens was carried out using Finite Element Analysis, to inform slab design. The results of this investigation are of particular significance to the resilience of concrete structures under terrorist attack.The results show that the adoption of Type 2 macro synthetic fibres as concrete post crack reinforcement provide the greatest toughness when compared with the other fibre types and offer the greatest protection from spalling of the back face of the concrete slab, being the main consideration with regard to the performance of the slab on testing with shotgun fire. 2Damage containment after ballistic testing was also noted where Type 2 fibres were used.The Finite Element Analysis models were successful at predicting the damage recorded to the concrete slabs, when subject to the shotgun fire performance test.

Ballistic Impact Resistance of UHPC Plates Made with Hybrid Fibers and Low Binder Content

“…According to Wang and Gao, a higher content of fibers can increase entrapped air voids (3.5-5.5%), hence impairing mechanical properties [42]. This performance was discussed in other publications [18][19][20][21][22][23][24][25][26][27]. It was stated that there was a direct relationship between the fiber volume ratio and the mechanical strength of concrete [28].…”

“…Fiber-reinforced concrete (FRC) has a pseudo-ductile behavior, with increased energy being necessary for failure of the tested element [25]. The addition of more than one type of fiber, whether by material or form, can result in gains in toughness and impact resistance [26].…”

“…A brittle matrix with fiber hybridization can behave differently from a composite with a mono-fiber type, which presents a simple crack when subjected to tensile stress [27]. As reported by Richardson et al [26], the hybridization of steel fiber (90%) with polymeric fiber (10%) with a total amount of 1.15% can yield a greater level of hardness, toughness, and spalling resistance when used to test UHPC plate elements of 0.76 m in thickness subjected to impact loading of up to 6500 J. Máca et al [28] evaluated the effect of fiber contents of 1%, 2%, and 3% by volume on the projectile impact behavior of UHPC with different chemical admixture and SCM contents. The authors concluded that the addition of 2% fiber presented the best performance for impact resistance.…”

Fiber bridging in polypropylene‐reinforced high‐strength concrete: An experimental and numerical survey

“…They also improve the dynamic toughness of mixtures, but to lower extent. 7 Polypropylene fiber-reinforced concrete is somehow a new construction material and its mechanical behavior under different conditions has been studied infrequently. Generally, the elastic modulus and peak strength of concrete are less affected due to the reinforcing effects of polypropylene fibers, whereas the post-peak performance is tremendously enhanced.…”

Investigation of High-Velocity Projectile Penetrating Concrete Blocks Reinforced by Layers of High Toughness and Energy Absorption Materials

“…Kamal and Eltehewy (2012) [16] investigated the penetration resistance of concrete blocks reinforced by different number of layers of woven wire steel mesh experimentally and numerically using a steel blunt-nose projectile with a diameter of 23 mm with striking velocity about 980 m/s, they found an overall reduction in penetration depth and damage of target when with using wire meshes as a reinforcement. Richardson et al (2016) [17] compared the impact performance of fiber concrete to plain concrete to predict the damage of concrete in both cases, they simulated concrete slabs with finite element model and tested the use of two types of fibers as a reinforcement in concrete samples. Rajput and Iqbal [18] studied experimentally and numerically the ballistic impact behavior of reinforced and prestressed concrete targets, the experiment was carried out with different projectile striking velocities for three types of concrete, and the numerical investigation was modelled in finite element code ABAQUS.…”