Accelerated aging of unidirectional hybrid composites under the long-term elevated temperature and moisture concentration

Analytical model to predict the lifetime of concrete members externally reinforced with FRP

“…In brittle materials there are three regimes of crack growth as K II varies from 0 to its critical value K IIC . Consequently, the relationship between da/dt and K II /K IIC exhibits three different trends [22,23,25,31,36,[44][45][46][47].…”

“…The literature [2,3,5,13,[21][22][23]26,28,43,47,49] also reveals that v c and N depend on humidity and temperature as well, but these dependences are not strong. Ultimately, for concrete members with a carbonation depth greater than the cover, K IIC is close to 1.0 MPa m 0.5 [31,36,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61], v c to 0.0015 m/s [22][23][24]31,36,41,[43][44][45][46], and N to 16 [18,24,41,43,59]. It is to note that N is the exponent and thus it is important to provide the model with a reliable value; however, N = 16 is simultaneously an accurate and preservative assumption.…”

“…[2,3,5,13,[21][22][23]26,28,43,47,49], brings out the fact that, in a carbonated concrete, the ranges of variation of K IIC , v c , and N are reasonably narrow. In fact, these parameters depend mainly on the depth of carbonation and the strength of concrete.…”

“…In order to plug into the model the actual values that K IIC , v c , and N assume in a specific concrete, instead of a priori values, tests have to be accomplished, either on-site or in laboratory [18,[22][23][24]29,31,36,39,41,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58]. On the contrary to K IIC , however, v c and N are not simple to be measured; thus, it is more convenient to use the aforementioned values borrowed from literature.…”

“…Unfortunately, practice often extends this property from the separate and standalone FRP-composite material to the entire FRP-strengthened system. However, durability of a RC member externally reinforced with FRP depends not only on durability of the individual materials, but also on the capacity of the concrete cover to sustain the bond stresses s b [22][23][24][25]. In fact, on one hand, the FRP-composite material keeps its original strength, elasticity, and toughness [5,13,15,16,[26][27][28]; on the other hand, however, the combination of s b and initial cracks (flaws) in the concrete cover may give rise to slow crack growth up to the critical length, and eventually to debonding of the external reinforcement [29][30][31][32][33][34][35][36].…”