International Concrete Abstracts Portal

SP-166 This volume contains 11 symposium papers that were presented at the 10th and 11th symposia that were held in Minneapolis, MN and Tarpon Springs, FL in 1993 and 1994 respectively. There were a total of four sessions, the first titled "Polymer Concrete Overlays," the second "Recent Innovations in Polymer Concrete Technology", the third and fourth "Structural Properties of Polymer Concrete, Part I and II."

Epoxy asphalt concrete is a polymer concrete with a 25-year history of application as a bridge deck surfacing. Since 1967, over 100 million pounds (50,000 tons) have been installed on 22 bridge decks totaling 6.5 million square feet. Most installations have exhibited excellent performance. The epoxy asphalt binder is a two-phase, thermoset chemical system in which the continuous phase is an acid cured epoxy and the discontinuous phase is a mixture of asphalts. The aggregates and gradation are similar to those used in asphalt concrete. The epoxy asphalt binder components are premixed before being combined with the heated aggregate in a conventional asphalt batch plant and applied through conventional asphalt paving equipment. Epoxy asphalt concrete has found use as a pavement for new orthotropic steel bridge decks and as an overlay for existing concrete bridge decks. Epoxy asphalt has also been applied as a chip-seal. On one project, the epoxy asphalt concrete was shop applied to steel plates that were later installed as a bridge deck. Several installations have not performed as expected. Successful installations require close temperature control of aggregates and careful attention to early compaction. This paper also provides a history of the commercial use of epoxy asphalt in the United States and Canada.

An analytical procedure was developed by which thermally-induced stresses in polymer concrete overlays can be quantified. The distribution and the magnitude of thermally-induced stresses can be determined using the proposed procedure. The main variables which influence the thermal stress development are found to be the thickness ratio and the modular ratio of the polymer concrete to the portland cement concrete, the difference in the coefficients of thermal expansion, and the temperature change. The relationships between the variables and the thermal stresses are determined and presented. Analyses reveal that thermally-induced interface stresses decrease as the elastic modulus and the thickness of the overlay decrease for the thin polymer concrete overlays. The analyses assumed isothermal conditions.

Flexural behavior of a polyester polymer concrete was investigated by varying the polymer and fiber contents. The polymer content was varied up to 18 percent of the total weight of polymer concrete (PC). The chopped glass fibers were 13 mm long and the fiber content varied up to six percent (by weight of PC). The fine aggregates were well graded, with particle size varying from 0.1 to 5.0 mm and were mainly quartz. The fine aggregates and glass fibers were also pretreated with a coupling agent ( -MPS) to improve flexural and fracture properties of PC. In general, addition of fibers increased the flexural strength, failure strain (strain at peak stress), and fracture properties, but the flexural modulus of PC remained almost unchanged. Addition of six percent fiber content and silane treatment of aggregates and fibers increased the flexural strength of 18 percent PC to 41.6 MPa (6,040 psi), almost doubling the strength of unreinforced 18 percent PC system. Crack resistance curves based on stress intensity factor (K R-curve) have been developed for the fiber reinforced PC systems. A two- parameter relationship was used to predict the complete flexural stress- strain data. There is good agreement between the predicted and measured stress-strain relationships.

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.