Geopolymer concrete (GPC) has been used increasingly in recent years and has been applied to various structural components. Considerable interest has been developed in using geopolymer in concrete to increase the load carrying capacity of the structural members in service. It has been used recently to increase the flexural capacity of concrete slabs by applying overlay layer of GPC onto an existing slab, a technique known as cement base bonded overlay. The objective of this research is the investigation of the flexural behavior of substrate cement reinforced concrete (RC) slabs with a GPC overlay. Seven RC slabs with 300 x 1700 x 100 mm, 33 MPa compressive strength after 28 days and reinforced with steel with a diameter of 8 mm. Because the performance of these composite slabs depends on the bonding between the substrate and overlay concrete, six different techniques were used for preparing the RC substrate surfaces including, (as smooth as cast (AS), carving 2mm width and 1 mm deep (Carv), dowels 8 mm Z section (DZ), painting with epoxy resin on the surface (ER), surface roughened by a stiff brush in both the transverse and longitudinal directions (T&L) D and surface roughened in the transverse directions by a stiff brush (TD). The evaluated properties were load-deflection relationship, strain distribution curves and the interface slip.
Based on the experimental tests, the ductile performance of the slab depends not only on adding GPC to the topping but mainly on the type of interface roughness. Moreover, the ductility ratio may be arranged in desponding order as (TD), (T&L) D, (ER), (Carv), (DZ) and (AS). The biggest slip happened for slab control at 0.25mm, signifying poor bonding strength at the interface. Slab (L&T) D, with zero mm of slippage, showed the best interface slip.