Analysis of structural performance of rigid pavement concrete reinforced with recycled tyre steel fibres and blast furnace slags as aggregates

Abstract

Dumping of waste tyres on land represents a global major environmental problem. Their disposal concern is increasingly raising mostly in urban areas of Rwanda and other urbanized areas of African countries. These worn tyres contain potential resistant non-toxic materials termed tyre steel fibre (TSF) which if well extracted or recycled (RTSF), have proven effective to increase mechanically strength of concrete, especially for highways, parking and airports landing and runway pavement where impact resistance and flexural toughness is the governing criteria for pavement materials. In another hands, in nowadays the increasing amount of waste generated from metal industries have a major contribution to the environment pollutions. GBFS (Granulated Blast Furnace Slags) are successfully regenerated from the metal casting process, where after several times of usage is considered as waste. The disposal of these metal waste affects the land and cause it to be unfit for other use. Natural sand used in construction industry is a depleting material due to high demand and economically of high cost related to the labour charges and extraction method, and this is a major challenge faced by the construction industry. Researchers have been conducting different studies to find alternative materials that can replace natural sand. In this study, the combined structural performance effects of recycled tyre steel fibres (RTSF) and GBFS on concrete is investigated. Different sizes of slags (0.15mm to 2.36mm) have been used to partially replace normal sand by fraction of 10, 20, 30, 40, 50 and 60 % volume to investigate the effect of Blast furnace slags on concrete mechanical properties, with optimum value obtained at 50% replacement. The resulting concrete is named cement slags concrete. To study the influence of RTSF in concrete, different percentages of recycled tyre steel fibres with length of 20, 40 and 60% are incorporated in cement slags concrete by replacing 0.5, 1.0 and 1.5% of total mass of concrete. Different sets of mix have been casted and tested at 28 to assess the structural behaviour of concrete. The first set of CS0, CS10, CS20, CS30, CS40, CS50, 60 was casted to investigate the effect of different slags volume on concrete tensile and compressive strength. The second set of CS50-F0.5L60, CS50-F1.0L60, CS50-F1.5L60, CS50-F1.5L20, CS50-F1.5L was casted to assess the effect of RRSF contents incorporated in slags concrete. The last set of CS50F1.5L60, CS50-F1.5L20, CS50-F1.5L was used to study the influence of fibre aspect ratio on cement slags concrete performance. The results obtained showed that at 50% of slags content, Compressive, tensile and flexural strength increased by 8.05, 10.75, 2.76 % respectively, while Flexural toughness reduced by 2.33 % and Impact strength increased by 13.11% at 28 days.

vi The addition of RTSF volume up to 1.5% at the length of 40 mm, increased the compressive, tensile, impact energy and flexural toughness of Recycled tyre steel fibre reinforced cement slags concrete (RTSFRCSC) by 33.12, 16.37, 298.63, and 460.84 % respectively compared to plain concrete at 28 days. The results further indicated that, the increase in aspect ratio from 17.2 (20 mm long and 1.16 mm diameter) to 34.4 (40 mm long and 1.16 mm diameter) of RTSF resulted in increase of impact resistance, mechanical properties and flexural strength, while beyond 40 mm long, mechanical properties started to decrease, therefore limitation of RTSF length should be considered to avoid balling effect caused by higher value of aspect ratio. Therefore, fibres of 40 mm length were adopted as the maximum. The interesting results confirm the promising application of recycled tyre steel fibres and slags concrete in construction of rigid pavement roads.