Recent ODOT Specification Changes Provide For Longer Lasting Asphalt Pavements

Some of our industry's public sector customers have expressed a concern about a decrease in the length of time an asphalt pavement will last before it needs resurfaced again. Although we are not aware of any scientific studies that have been undertaken to document this, the general feeling expressed was that pavements were not lasting as long as they used to.

Desiring to provide the highest quality in HMA mixes FPI, through its strategic planning process, has made addressing this issue one of its top priorities.

About this same time FPI was developing its strategic plan, the Ohio Department of Transportation undertook a serious effort to also tackle this issue. Implementation of both industry suggested and ODOT initiated changes have come a long way in improving the life of asphalt pavements. A chronological listing of these changes follows:

1992

1. Starting in 1992, ODOT required all asphalt content dials in computerized plants to be set at the JMF. Even though contractors are allowed + 0.5% variance in asphalt content to account for testing accuracy. This increased asphalt content by 0.2% in many of the mixes.

2. ODOT specified that all asphalt samples must be cured for one hour before running asphalt content test. This allowed some of the asphalt to be absorbed into the stone. Depending on stone, the amount of asphalt needed for the mix increased from 0. I% to 0.3%.

3. Also this year ODOT limited RAP materials to those taken only from ODOT or Turnpike projects and instituted new processing requirements.

4. The use of the nuclear content gauge was introduced which all but eliminated test discrepancies between contractor tests and ODOT monitoring tests.

1993

1. A cooperative effort between FPI and ODOT lead to a new type 1-H specification which was introduced for heavy traffic pavements. This specification incorporated a set ratio between the #50 sieve and the #30 sieve to ensure a uniform gradation of the fine aggregate. The gradation of the coarse aggregate was changed to eliminate segregation. The percentage of crushed material for the coarse aggregate was increased as well as requiring 50% of the fine aggregate to be manufactured sand to increase its angularity. The fines to asphalt ratio was also changed to increase durability.

1995

1. An FPI task Force recommended to ODOT that the design air voids for medium traffic mixes be changed from 4% to 3.5%. ODOT implemented this suggestion which increased asphalt content from 0.2% to 0.3% in these mixes.

2. The FPI Task Force also recommended that for medium traffic mixes the amount of aggregate passing the #4 sieve be limited to 57% and the #50 sieve to #30 sieve ratio be implemented as was done in the I -H mix. ODOT added both of these to the specification which in effect made the mixes more coarse, reducing aggregate surface area thus increasing effective asphalt film thickness on the remaining aggregate.

3. ODOT instituted AASHTO T283 and methylene blue testing for gravel mixes to clean up dirty aggregate sources. This enabled a clean surface for the asphalt to stick to, which will provide greater durability.

4. Recognizing a deterioration of longitudinal joints, FPI asked ODOT to require the use of a three-wheeled roller to provide better joint compaction. ODOT accepted this recommendation and required a three-wheeled breakdown roller as part of the specification.

5. ODOT changed the amount of RAP that could be applied to the mix from 30% to 20%

for the surface course and from 50% to 30% for the intermediate course.

6. ODOT also instituted use of the loaded wheel tester on mix designs it felt may have questionable field performance even though they may technically meet specification.

1996

1. This year ODOT will be implementing additional aggregate quality requirements to reduce popouts and durability problems in siltstone type gravel.

2. Several SUPERPAVE products will come on-line this year. SUPERPAVE specifications require an increase in sample cure time to 4 hours. ODOT will be looking at this plus a 2 hour cure time. This should increase asphalt content another 0. 1% to 0.3%.

1997

1. This will see the use of PG binders starting on January 1st. While many improvements to-date have addressed the quantity of asphalt cement in the mixes, this will address the quality of the asphalt cement used.

All of these items in combination provide a significant improvement in today's asphalt pavements. Asphalt contents are up 0.4% to 0.6% over what they were 3 or 4 years ago. Aggregate quality is now improving through new testing requirements. Combining this with the improved quality of the PG binders is making asphalt pavements an even better buy for Ohio's transportation system..

From FPI Newsletter, Vol. 5 No. 1, March 12, 1996