Thomaz Eduardo Teixeira Buttignol
Mackenzie Presbyterian University, Brazil
Biography
The prediction of transient creep involves a lot of uncertainties due to its complex mechanisms of activation. Transient creep is seated in the cement paste and occurs due to hygrothermal conditions: water evaporation and CSH dehydration. Above 400ºC, it is accelerated by the aggregates geomechanical properties decay. There is also a thermal mismatch between aggregate expansion and cement paste shrinkage after 150ºC, leading to concrete microcracking. As a result, due to concrete complex behavior and the coupling effects of the different strain components (viscous+elastic+plastic+thermal) at high temperature, it is a very difficult task to uncouple the viscous strain component (creep) from other thermomechanical strain sources. In practice, transient creep can be described accurately enough by the concept of LITS (Load Induced Thermal Strains), which is defined as the difference between the total strain, measured on a preloaded specimen, and the free thermal strain, measured on an unloaded specimen, subtracting the initial elastic deformation at 20°C. In order to investigate transiente creep phenomenon in plain and fiber reinforced concrete structures, a new LITS semi-empirical model is proposed, recognizing concrete as a heterogeneous biphasic material (aggregates + matrix) and assuming that LITS is the sum of thermomechanical and thermochemical strain contributions. The semi-empirical model is compared with experimental tests performed on steel fiber reinforced concrete samples with 11-years-old. Moreover, a mesoscopic analysis was carried out in Abaqus in order to uncouple LITS strain contributions and highlight the effects of the boundary conditions, aggregates decomposition and concrete dehydration.