Effects of binder paste-to-aggregate ratio and polypropylene fiber content on the performance of high-flowability steel fiber-reinforced concrete for slab/deck overlays

Abstract

Abstract In many infrastructural engineering techniques, a common challenge is how to control the continuous damage caused by the cracks of concrete slab/decks overlay under environmental impaction or vehicle load. It drives the development of a high-flowability hybrid polypropylene and steel fiber-reinforced concrete (HPSFC), which has peculiarities for the overlay construction. In this aspect, an experimental study of HPSFC was carried out considering the factors, the volume ratio of binder paste to aggregates (P/A ratio) varied from 0.48 to 0.60, and the polypropylene (PP) fiber content changed from 0.45 to 1.35 kg/m3 with a hybrid steel fiber at 0.8% volume fraction. The workability of fresh mixes was evaluated by the indices of slump flowability and static segregation rate with an explanation of the rheological properties, and it was verified by a pumping test. The peculiarity of HPSFC applied for slab/decks overlay was determined using the tests including the early cracking resistance, the water penetration resistance, the bond strength to existing concrete, and the impact resistance. Meanwhile, the basic mechanical properties including cubic compression strength, flexural strength, and toughness were also measured. Results indicate that the fresh mixes met the requirement of high-flowing without segregation, although the indices varied with the influence of P/A ratio and PP fiber content. The resistances to early cracking and water penetration obviously improved by increasing the PP fiber content. The bond strength to existing concrete could be improved by increasing the PP-fiber content. The impact resistance enhanced with the increase of the P/A ratio and the PP-fiber content. The compressive strength and flexural strength presented an increased tendency with the P/A ratio, while the flexural toughness reached a peak at certain values of P/A ratio and PP fiber content. Comprehensively, for the high-flowability HPSFC designed with a water-to-binder ratio of 0.36, a fly-ash content of 30%, and a sand ratio of 52%, the optimal P/A ratio is 0.54 and the PP-fiber content is 0.90 kg/m3.