Effects of including the gypsum component in reinforced beams

Abstract

Casting structural elements using concrete is a traditional technique that is still applied recently. It is characterized by its important strength and durability properties. However, several studies were conducted, that focus on finding new eco-friendly and fire-resistant mix designs, such as gypsum. Therefore, the main focus of this research was to perform a study on the mechanical properties of gypsum, when applied in the structural field. As a first step, two types of control specimens, consisting of small gypsum cubes (5 cm) having different retarder ratios, and cylinders (L=200 mm, D=100 mm) cast in two different procedures by half concrete and half gypsum mix, were performed. The initial time of setting results from the Vicat apparatus test, performed on the gypsum mixes of the cubes specimens, and the compressive strength test applied on the gypsum cubes have shown that 0.35% of the retarder-to-binder ratio is the most suitable for a gypsum mix. Also, the results of the splitting tensile strength test performed on the cylinders, during the 28 days, revealed extra-bonding properties between concrete and gypsum, depending on the casting method and the curing process. After that, two similarly large scale reinforced gypsum beams, supporting flexure and shear were cast, with one of them having a concrete infill. Tested on the 14th day, under two-point loading, and compared with a previously tested concrete beam, sharing the same reinforcement properties, the latter carried the highest load (118.7 KN) and the lowest deflection (20.2 mm). The other two beams supported almost equal maximum loads (110.4 KN and 110.2 KN, respectively). However, the full gypsum beam showed the highest deflection among the beams (29.5 mm), and the gypsum beam with concrete infill showed a deflection of 23.6 mm. Concerning the failure mode of the beams, cracks were developed diagonally from the bottom to the top and simultaneously along the beams.