Experimental investigation of bond between glass textile reinforced mortar overlays and masonry: the effect of bond length

In this paper, an experimental program involving shear bond tests on double-lap/double-prism specimens is presented aiming to assess the bond characteristics of interfaces comprising uncoated alkali-resistant glass fiber textile reinforced cementitious mortars (TRM) applied as overlays on unreinforced masonry substrates. In total, 19 test results are presented with the bond length being the parameter under investigation. Bond lengths studied were equal to 50, 100, 125, 150, 200 and 250 mm, whereas at least two specimens per bond length were tested. According to the experimental findings, the effective bond length for the specific type of TRM overlay applied on this type of masonry substrate was found to be approximately equal to 130 mm. Failure of the bonded TRM strips was due to textile slippage within the mortar and simultaneous fiber rupture. Slippage of the entire TRM strip in relation to the masonry was practically zero as confirmed by application of a digital image correlation (DIC) method. The experimentally derived load-relative displacement curves can be approximated as bilinear up to the maximum load with a linear post-peak descending branch; a residual shear bond capacity was present only for bond lengths lower that the effective one. Finally, data on DIC-enabled crack detection and crack width evolution throughout the load response is also presented.