Material properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 29

the resin has passed the liquid state, bending or alteration of the FRP
bar is not possible due to the inability of the fibers to reorient within the
resin matrix.
2.4.1 Gel time and peak exothermic temperature
To set the rate of the manufacturing process, the gel time and the peak
exothermic temperature of the thermoset resin have to be evaluated. The
gel time is the time from the initial mixing of the reactants of a thermo-
set plastic composition to the time when solidification commences, under
conditions approximating the conditions of use. The peak exothermic
temperature is the maximum temperature reached by a reacting thermo-
set plastic composition during the curing process. Errors in estimating a
correct rate may cause internal defects in the cured material, which would
ultimately induce lower durability and mechanical properties of the cured
material. Figure 2.4 shows an example of thermocracking due to under-
curing of the resin. Gel time and peak exothermic temperature are mea-
sured according to the ASTM D 2471, “Standard Test Method for Gel
Time and Peak Exothermic Temperature of Reacting of Thermosetting
Resins.” For this test method, the typical test setup and a sample test out-
put are shown in Figures 2.5(a) and 2.5(b). The bath simulates the oven
environment and the resin samples are used to investigate the behavior of
the resin in the oven.
ermo-crack
Figure 2.4 Thermocracking due to undercuring of the resin.