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

Richardson, Alan, Coventry, Kathryn, Lamb, Thomas and Mackenzie, David (2016) The addition of synthetic fibres to concrete to improve impact/ballistic toughness. Construction and Building Materials, 121. pp. 612-621. ISSN 0950-0618

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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 programme 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. Damage 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.

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