International Concrete Abstracts Portal

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.

A new family of latexes has been developed for use in portland cement that has a minimum film-formation temperature (MFFT) well above working temperature, eliminating the two major drawbacks of latex-modified mixtures: formation of a crust on the surface and difficulty in cleaning tools. Instead of coalescing to form a film, as do the typical latex modifiers for portland cement, these latex particles maintain their shape as spheres. Of the several formulations studied, two are reported here: a styrene polymer and a methyl methacrylate polymer, both carboxylated. In addition to extensive laboratory testing of both polymers, two field trials with the styrene latex formulation were conducted. These laboratory and field studies demonstrated that film formation is not necessary for latexes to contribute to the performance of portland cement mixes. The data from these studies are encouraging, but also revealed that much more work needs to be done to fully understand the capabilities and limitations of this family of latexes.

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."

Recycled polyethylene terephthalate (PET) plastic wastes could be used in the production of unsaturated polyester resins. If specially formulated, these unsaturated polyester resins could, in turn, be mixed with inorganic aggregates to produce polymer concrete (PC). The results of an extensive research confirm that PC materials using resins based on recycled PET are comparable in strength to conventional PC materials. Resins based on recycled PET could also easily be altered to achieve a relatively wide range in the strength and flexibility properties of the PC, depending on the intended use of the material. PC using resins based on recycled PET may be utilized in the repair and overlay of portland cement concrete structures or in the production of various precast products, such as utility, transportation, and building components. The recycling of PET in PC would help decrease the cost of PC products, save energy, and alleviate an environmental problem posed by plastic wastes.