New Method for Breaking High Strength Prestress Cable, MLR-97-6, 1997

A new method was developed for breaking high strength prestressed cable. The old method used an aluminum oxide grit packed into a special gripping jaw. The new method uses aluminum shims wrapped around the cable and then is gripped with a V-grip. The new method gives nearly 100% "good breaks" on the cable compared to approximately 10% good breaks with the old method. In addition, the new cable breaking method gives higher ultimate tensile strengths, is more reproducible, is quicker, cleaner and easier on equipment.

New Method for Breaking High Strength Prestress Cable, MLR-97-6, 1997

A new method was developed for breaking high strength prestressed cable. The old method used an aluminum oxide grit packed into a special gripping jaw. The new method uses aluminum shims wrapped around the cable and then is gripped with a V-grip. The new method gives nearly 100% "good breaks" on the cable compared to approximately 10% good breaks with the old method. In addition, the new cable breaking method gives higher ultimate tensile strengths, is more reproducible, is quicker, cleaner and easier on equipment.

Bond Development in Concrete Overlays, August 1995

Data collection to determine the rate of bond strength development between concrete overlays and existing pavements and the evaluation of nondestructive testing methods for determining concrete strength were the objectives of this study. Maturity meters and pulse velocity meters were employed to determine the rate of flexural strength gain and determine the time for opening of newly constructed pavements to traffic. Maturity measurements appear to provide a less destructive method of testing. Pulse velocity measurements do require care in the preparation of the test wells and operator care in testing. Both devices functioned well under adverse weather and construction conditions and can reduce construction traffic delay decisions. Deflection testing and strain gaging indicate differences in the reaction of the overlay and existing pavement under grouting versus nongrouted sections. Grouting did enhance the rate of bond development with Type I11 cement out performing the Type I1 grout section. Type I11 and Type I1 cement grouts enhanced resistance to cracking in uniformly supported pavements where joints are prepared prior to overlays achieving target flexural strengths. Torsional and direct shear testing provide additional ways of measuring bond development at different cure times. Detailed data analysis will be utilized by TRANSTEC, Inc. to develop a bonded overlay construction guidelines report.

Development of a Rational Characterization Method for Iowa Fly Ash, HR-286, 1988

This research project was conducted in an attempt to determine the cause of paste strength variability in Iowa fly ashes and to develop test methods to more adequately reflect fly ash physical and chemical characteristics. An extensive three year sampling and testing program was developed and initiated which incorporated fly ash from several Iowa power plants. Power plant design and operating data were collected. The variability was directly linked to power plant maintenance schedules and to sodium carbonate coal pretreatment. Fly ash physical and chemical properties can change drastically immediately before and after a maintenance outage. The concentrations of sulfate bearing minerals in the fly ash increases sharply during shutdown. Chemical, mineralogical, and physical testing indicated that the sodium, sulfate bearing minerals, lime and tricalcium aluminate contents of the fly ashes play important roles in the development of hydration reaction products in fly ash pastes. The weak pastes always contained ettringite as the major reaction product. The strong pastes contained straetlingite and monosulfoaluminate as the major reaction products along with minor amounts of ettringite. Recommendations for testing procedure changes and suggested interim test methods are presented.

The Flexural Fatigue Strength of Prestressed Steel I-Beams, HR-73, 1962

The purpose of this investigation was to study the flexural fatigue strength of two prestressed steel I-beams which had previously been fabricated in connection with a jointly sponsored project under the auspices of the Iowa State Highway Commission. The beams were prestressed by deflecting them under the action of a concentrated load at the center of a simple span, then welding unstressed high strength steel plates to the top and bottom flanges to retain a predetermined amount of prestress. The beams were rolled sections of A36 steel and the plates were USS "T-1" steel. Each of the two test specimens were subjected to an identical repeated loading until a fatigue failure occurred. The loading was designed to produce stresses equivalent to those which would have occurred in a simulated bridge and amounted to 84 percent of a standard H-15 live load including impact. One of the beams sustained 2,469,100 repetitions of load to failure and the other sustained 2,756,100 cycles. Following the fatigue tests, an experimental study was made to determine the state of stress that had been retained in the prestressed steel beams. This information, upon which the calculated stresses of the test could be superimposed, provided a method of correlating the fatigue strength of the beams with the fatigue information available on the two steels involved.