Experimental study of composite beams having a precast geopolymer concrete slab and deconstructable bolted shear connectors

Abstract

Traditional steel–concrete composite beams are known to exhibit excellent structural characteristics, in terms of their stiffness and strength, when compared with bare steel or reinforced concrete beams. However, within current paradigms of lowering carbon emissions and enhancing the possibly of material recycling, such traditional composite beams cannot be deconstructed easily and their elements are not recyclable because they rely on welded headed stud connectors that are encased within cast in situ concrete to achieve the necessary shear connection. This paper presents the detailed results of quasi-static tests conducted on full-scale composite beams as part of a novel deconstructable and sustainable structural system. For this system, precast concrete slabs are attached to a steel beam using tensioned high-strength friction-grip bolts in clearance holes as the elements to provide the shear connection. The precast slabs are made using geopolymer concrete in lieu of concrete made from ordinary Portland cement, whose manufacture is a major contributor to anthropogenic CO2 emissions worldwide, thereby enhancing the low-carbon attributes of the structural system. The test results demonstrate the very significant ductility of the beams, with substantial interface slips being developed and sustained at loads close to the ultimate strength limit state. The tension induced in the bolts provides sufficient frictional resistance between the precast slabs and steel beams to ensure that the composite system has full shear interaction throughout the range of service loading. It is also confirmed that composite beams with bolted shear connectors can be deconstructed easily at the end of their service life, with the slabs, steel beams and bolts being reusable in other structural applications.