International Concrete Abstracts Portal

Problems such as raised edges, "blow-ups" or even cracking have been observed in concrete overlays cast on precast concrete elements. These failures are due to the shrinkage, creep and thermal effects in the new concrete. To improve the perfor-mance of concrete in such slabs the tensile and shear strain ca-pacity of concrete has to be improved. This report gives the results of different tests made to study the effect of polymer modification on the properties of concrete. Both the strength and deformation characteristics of concrete under different kinds of loading were significantly improved by polymers. With its higher tensile and shear strength, and lower shrinkage, polymer-modified concrete should be a viable and attractive alter-native for concrete overlays and similar constructions.

Epoxide resin concrete produced by vacuum impregnation of a prepacked aggregate has handling properties and stiffness (40 GN/m 5 reatly improved at 70 C) when compared with conventionally mixed and placed epoxide resin concrete. This material has been developed for superconducting turbogenerators, but with its improved qualities coupled with high strength (150 MN/m ), resistance to aggressive environments, impervious nature, low shrinkage and electrical resistance a wide range of applications is forecast.

The objective of this study was to find an appropriate method of evaluating mold-releasability ofmold-releasingagents for polyester resin concrete. A tension or shearing test involving resin concrete cast in thin frames on steel plates coated with mold-releasing agents was selected as an appropriate method. BY apply- ing this method, 17 commercially available mold-releasing agents were tested and evaluated for mold-releasability. The effect of vibrating compaction on the mold-releasability was also examined. It is concluded from the results that the mold-releasability of silicone and fluorine-containing agents is excellent, and that generally it is considerably affected by vibrating compaction.

Polymer impregnated concrete (PIC) was overlaid with a low slump dense concrete (LSDC) or a latex modified concrete (LMC). Flexure strength, compressive strength, and freeze-thaw durability data were obtained on the composite specimens. Flexural data indicated a strong bond was established between LSDC, LMC, and PIC. Compressive strength data indicated the bond was weaker for the LMC than the LSDC. Freeze-thaw data showed that a durable bond was established between the PIC and the LSDC whereas the bond failed between the PIC and the LMC.

An epoxy resin system has been developed for modificat-ion of concrete providing handling and performance advantages over other polymer types. Description of two applications are pro-vided. Estimated costs of applied epoxy modified concrete are presented.

Polymer concrete has been successfully developed for use as an electrical insulating material. Work done at the Instituto de Investigaciones Electricas in Mexico has resulted in formulations using native materials and manufacturing techniques which promise to replace electrical porcelain in many instances. The technology and materials are especially suited to Mexico's requirements for electrical system expansion.

Latex modified overlays have been in service for over 20 years. This report summarizes the significant events during the development of this system and highlights data that have recently been generated by State Highway Departments and the FHWA in their continuing studies of field performance. Fifteen reports, covering 184 bridge decks, aged two months to 13 years, are reviewed. Specific comments regarding test methods, such as chloride pen-etration and half-cell potential, to measure performance, are included. Life expectancy, based on the testing done to date, as well as the actual life in the field, is projected to be a minimum of 15-20 years.

Potential solutions for improving the strength of poly-mer concrete made with wet aggregate have been investigated in re-search performed for the U.S. Air Force to develop rapid repair methods. Chemical additives, aggregate treatment, and addition of fibers have been evaluated." Moisture contents used in the re-search ranged up to 7 percent, with the maximum values usually 4 to 5 percent. No chemical additives for monomer were identified which provide significant strength increases. Aggregate treatments con-sisted of coated aggregate and moisture absorptive additives for wet aggregate. Aggregates coated with a silane coupling agent pro-vided very good strength even when the moisture content was in ex-cess of 4 percent. Several types of fibers were investigated; hooked steel fibers were found to provide the greatest strength. It was found that the addition of approximately 5 weight percent steel fibers provided good strength increases and ductility.

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.

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.