Elastic characterization of plywood used and reused in forms through impulse excitation

ABSTRACT The wood forms are the responsible elements in giving the desired shape to the fresh concrete and to provide protection against impacts and temperature variations in its curing process. Plywood sheets are the elements most used in building for this process. The reuse of the plates is common during the work - not exceeding 10 times. However, the material may have variation in its mechanical properties. The primary goal of this work was to experimentally determine the modulus of elasticity as a function of the amount of reuse of the plywood. The test used was a three-point bending, in which the modulus of elasticity was determined. During a work, the sending of samples for laboratory analysis requires time. Nevertheless, the construction company cannot wait such time to continue the execution of the construction. If the characteristics of the plywood could be determined quickly and practically, the service could have been done safely and quickly. The second goal was to present a non-destructive technique which fits this context, that is, the impulse excitation. The experimental design took three treatments and seven replicates per each treatment. The same samples for the impulse excitation test and the destructive trials were used. The results show that the moisture has little influence on the reuse of the forms, since the density has enough variation due to the loss of material during reuse. The modulus of elasticity has a decrease of 48% after the fifth reuse. The non-destructive test using impulse excitation is suitable for estimating the modulus of elasticity of concrete forms.