International Concrete Abstracts Portal

Every segment of the transportation industry is experiencing maintenance problems with rapidly deteriorating portland cement concrete structures. The Federal Highway Administration, aware of such problems, has sponsored research and development work to find a rapid-setting durable composite that can be used to repair deteriorated concrete and/or to effectively reduce chloride and moisture penetration into concrete.

Concrete polymer materials are a series of composite materials which have strength and durability characteristics far superior to those of portland cement concrete. In the USA, a number of hydrotechnical rehabilitation projects have used polymer impregnated concrete (PIC) in order to repair cavitated or eroded stilling basins. Examples of these projects are Dworshak Dam and Libby Dam. Although both of these projects used polymer-impregnated fiber-reinforced concrete, indi-cations are that the fibers do not increase the resistance of the concrete to normal erosion. It is reasonable to assume that the fibers may help to resist cavitation forces since fibers increase the tensile strength of the PIC. Epoxy resins have been used for many years and if applied correctly, results have been found to be excellent when used in the repair of hydraulic structures. In 1977, the Water and Power Resources Service (formerly the Bureau of Reclamation) used polymer concrete (PC) containing vinyl ester in test repairs on two concrete drop structures on the Madera Canal, Central Arizona Project, in California, where erosion dam-age resulting from abrasive sediments carried by flowing water was evident. In the USSR, much experimental work is being performed on new hydrotechnical structures; precast PC and PIC slabs are being used in high velocity water and sediment passages. With the help of the construction industry, new inexpen-sive techniques could be developed; and concrete polymers could become the construction material of the near future.

The U. S. Electric Power companies purchase over $500 million insulators per year for outdoor and indoor use. A variation of polymer concrete appears to have the necessary characteristics to replace a large proportion of the insulation presently in use. Over four years of development and testing by the Electric Power Research Institute (EPRI) and its counterpart in Mexico indicate the material is now suitable for commerciali-zation. A wide range and variety of applications are expected.

The feasibility of using the products of free-radical copolymerization of cyclic and linear organosiloxanes in the formation of polymer concrete (PC) composites for use in the completion of geothermal wells has been demonstrated. The PC contained a mixture of tetramethylvinylcyclotetrasiloxane and polydimethylsiloxane used in conjunction with aggregate materials such as silica flour and portland cement. The use of these compounds resulted in composites with high strength and with thermal and hydrolytic stability. Thermogravimetric analyses and compression strength tests at elevated temperatures have been used to determine the thermal stability of the composites. The results from these studies indicate that over the temperature range 25 to 350°C, the compressive strength is essentially constant at a value of -72 MPa and there is also a relatively low weight loss of polymer (-1.0 wt%). The hydrolytic stability of the composites was determined by using infrared spectroscopy on a variety of free and bonded OH functional groups before and after the samples were exposed to a 25% brine solution at 300°C. These results showed that the inclusi on of various additives such as Ca or Mg compound inorgan i c phase affects the hydrothermal stability. s in the Pumpability tests were also performed, and the results indicated that a PC slurry containing 35.5 wt% organosiloxane mixed with 64.5 wt% silica flour and cement as an aggregate did not change viscosity at temperatures of 150° to 165OC and a pressure of 36.5 MPa for at least 4.5 hr. Increasing the temperature to 205OC resulted in increased viscosity after 4 hr. The results from these studies indicated that this system can be used as a geothermal well-completion material.

The Air Force Engineering and Services Center (AFESC) at Tyndall AFB, Florida is currently engaged in a seven-year research and development effort to rapidly repair bomb damaged concrete runways. Polymer concrete because of rapid cure and high strength is one of the most promising methods of repair. The problems of moisture, temperature extremes and mechanization are all being studied for development of a rapid all-weather polymer concrete repair system. Research includes work at the University of Texas at Austin, AFESC, Battelle Columbus Labora-tories, Brookhaven National Laboratory, and the BDM Corporation. Polymers being considered include acrylics, epoxies, polyesters and furans.