Measurement of Shrinkage-Induced Stress in Polymer Concrete Overlays

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Title: Measurement of Shrinkage-Induced Stress in Polymer Concrete Overlays

Author(s): Jamal-Aldin H. Zalatimo and David W. Fowler

Publication: Special Publication

Volume: 166

Issue:

Appears on pages(s): 37-60

Keywords: deformation; epoxy resins; esters; polymer concrete; resurfacing; shrinkage; strains; stress relaxation; stresses; urethanes; Materials Research

Date: 12/1/1996

Abstract:
Shrinkage is a form of dimensional change which, if restrained, can produce stresses similar to those caused by the contraction of a material subjected to a temperature drop. However, a significant portion of total shrinkage takes place during the first few hours after mixing when the polymer concrete mix is still viscous. In addition, shrinkage is typically a one-time occurrence with effects extending over a long period of time. The significance of this difference is associated with a property known as stress relaxation. Research eventually led to the development of a test method for determining shrinkage-induced stresses in overlays. The basic idea behind this method is to accumulate shrinkage-induced stresses in a restrained polymer concrete overlay, to remove the restraint, and to measure the total released strain. To perform the proposed test, the middle region of a portland cement concrete beam is covered with several layers of plastic sheets that act as a bond breaker. Once overlay placement is complete, a DuPont device is positioned within the limits of the unbonded central region. Restraint provided by the substrate through the end regions is then removed by cutting the overlay transversely near one end of the unbonded central region. Test results indicated that shrinkage-induced stresses are not encountered with the use of slow curing systems, such as the epoxy concrete considered in this study. As for systems with high unrestrained shrinkage, it was observed that a residual amount of shrinkage-induced stress was sustained. The stress, however, was much lower than the level indicated by the unrestrained shrinkage results.