Case Study of the Structural Performance of Composite Slabs with Low Strength CRC Delivered by Concrete Truck

Concrete mixing in laboratory conditions has a high level of quality control enabling it to achieve the designed workability and strength by accurately controlling the material quantity, mixing sequence, and mixing time. However, concrete mixing in construction sites or plants can suffer from some unpredictable situations, especially when implementing a newly designed concrete mix with uncommon materials in large-scale projects. Crumb Rubber Concrete (CRC) is a class of concrete that is formed by replacing conventional concrete (CC) fine aggregate by crumb rubber made from scrap tyres. CRC is not a completely new concrete class, as it has been researched in the laboratory level for a while. However, mixing CRC in industrial concrete plants and pouring it on-site, has had very limited implementation in Australia. This paper presents a case study of low-strength truck-delivered CRC poured on large-scale composite slabs. The slabs were reinforced by 0.75 mm-thick BONDEK profiled steel sheets and were tested under 4-point bending load. The variables in this study were the concrete material (CC and CRC), compressive strength (10, 20, and 25 MPa), the use of crack inducers (with and without), and the length of shear span (long and short). The low-strength CRC slabs were tested and compared with CC and CRC slabs having satisfactory strength. The results showed that, 30 % reduction in concrete compressive strength did not affect the load carrying capacity of composite slabs under bending, and slabs with 66 % reduction in concrete strength achieved 75 % of the flexural performance of that in conventional concrete composite slabs. This indicated that the flexural behaviour of composite slabs does not depend only on concrete compressive strength, and that the substitution of low-strength CRC in composite slabs can achieve a satisfactory flexural performance.