Effectiveness of hybrid-fibers in improving the impact resistance of RC slabs

• Studied impact resistance of hybrid-fiber reinforced concrete (HFRC).
• HFRC was produced using steel, polypropylene and Kevlar fibers.
• A generalized model is proposed for predicting penetration depth and ballistic limit.
• Effect of fibers is incorporated in the model using a generalized reinforcing index.
• Prediction matches well with the test results available in literature.

In the present study, the work presented in our earlier work [Int J Impact Eng 2013; 58:17–30] is further extended to increase the confidence on hybrid-fibers in improving the impact resistance of RC slabs/plates. For this purpose, 27 new hybrid-fiber reinforced concrete slab specimens were cast using different proportions of hooked-end steel, polypropylene and Kevlar fibers. These slab specimens were tested against the normal impact of hemi-spherical nose steel projectiles and the relative importance of different quantities of the fibers on the improvement of impact resistance of hybrid-fiber reinforced slab specimens was studied. The importance of geometrical properties of fibers on improving the impact resistance of slabs was highlighted. The earlier proposed expressions for the penetration depth and the ballistic limit were generalized to incorporate the effect of hybrid-fibers made up of n-types of fibers. The generalized equations were developed using a larger set of data containing present as well as earlier test data. The prediction was compared with the current and other test data available in the literature covering a wide range of fibers and their combinations in different proportions. A good match was observed between the generalized prediction and the test results.