The purpose of the research conducted was to determine if aggregate degradation takes place and to measure the possible degree of degradation after bituminous mixtures are heated inside the NCAT Asphalt Content Tester. A study was conducted which compared the original aggregate blend (control specimens) to the residual aggregate blend (experimental specimens) obtained after several bituminous mixtures were heated inside the NCAT Asphalt Content Tester. The control specimens and the experimental specimens used to produce the bituminous mixtures were the result of an aggregate sample which was split three times. Two methods of analysis were used to review the gradation results.

The Materials and Tests Division's Bituminous Section evaluated the ignition method as an alternative to the solvent method for determining asphalt content. Three ovens (the Gilson Asphalt Binder Ignition Furnace, Model HM 378; the NCAT Asphalt Content Tester; and the Troxler Asphalt Quality Analyzer) were evaluated for accuracy, precision, and performance. Ignition was proven to be an appropriate method of determining asphalt content. The test procedure resulting from this work is Tex-236-F, which is included in Appendix A.

In May 2000, the Colorado Department of Transportation (CDOT) requested a forensic study of a project located on I-24 north of Denver. The request was made because, within a year of the 1997 overlay, longitudinal cracking appeared in the surface. Transverse cracks were attributed to reflective cracking. However, the longitudinal cracks appeared to be surface initiated. In October 2000, a forensic team reviewed the project and established a sampling and testing plan to take cores from the roadway. Based on data analysis of the cores, the higher than expected in-place air voids, the low effective asphalt, and segregation within the mat, all contributed to the early cracking.

Summary of current research studies.

Corrosion of reinforced concrete structures has been a significant problem for many state and transportation agencies since the application of deicing salts was introduced. Much research has been conducted to develop corrosion protection systems that can prolong the life span of reinforced concrete structures. The Colorado Department of Transportation (CDOT) has several routine and experimental measures to prevent corrosion of the rebar including epoxy-coated rebar, calcium nitrite admixture, organic corrosion inhibitors, a thick cover of quality concrete, and a waterproofing membrane covered by an asphalt overlay. An extensive literature review was performed to collect information on various corrosion protection systems that have been used in the U.S. and around the world. Current CDOT practices in terms of corrosion protection measures were reviewed. A draft inspection plan for Colorado's bridge structures was proposed.