Assessment of toughness of concrete subject to elevated temperatures from complete load-displacement curve - Part II: Experimental investigations

In Part I of this paper, six energy- and deformation-based toughness indexe s were summarized and derived for assessing the concrete toughness based on a two-portion complete load-displacement relationship compromising paramet ers such as load, characteristic displacements, and geometric coefficients, by considering the effect of self-weight of the beam specimen under three- point bending. In this paper, the effects of heating temperature, exposure time, and curing age on the fracture and toughness of concrete were experim entally investigated by conducting three-point bending tests on a total of 55 notched plain concrete beams that had been preheated at temperatures bet ween 100 and 600 C over varied exposure time up to 168 h and for four ages ranging from 7 to 90 days. The relationships of these parameters with heati ng scenarios and curing ages were established. Thus, six toughness indexes could be used to quantitatively assess the toughness of concrete in varied heating scenarios and curing ages. A higher heating temperature always led to a larger toughness. A longer exposure time also led to a larger toughnes s, but such an effect was more significant at the early exposure age under 12 h, and became weaker thereafter. A longer curing age only led to a lower toughness in the first 28 days and did not significantly affect concrete t oughness after 90 days.