Abstract

Concrete is a multi-phase composite material and used widely in construction industry because of high compressive strength and low cost. Its limited tensile strength makes it prone to cracking. Important parameters like characteristic length, fracture energy Gf critical crack width WC are used to understand cracks in concrete. The crack width is estimated either as crack mouth opening displacement (CMOD/COD) or as crack tip opening displacement (CTOD). Several optical and non-optical methods can provide information about crack presence but do not provide information on crack opening and crack width which are important from considerations of durability. To this end we present our research results in three point bend tests on pre-notched concrete samples (M-20 composition) using (a) Intensity based plastic optic fiber (POF) using phase difference measurement method (b) Fiber Bragg grating (FBG) method. The CMOD estimation and relative sensitivity of these methods will be presented.

Keywords: Crack mouth opening displacement; Three point bend specimens; UTM; FBGs; Plastic optical fiber; Phase difference method; Prenotched concrete