Since 2009, the concrete industry has been actively engaged in developing guidelines and evaluating specifications at the agency level. This report documents the details of those efforts.
In 2009, industry decided to update the ACPA 1995 Relative Cost survey as the results were almost 15 years old at the time. One aspect of the updated report included a smoothness survey. The purpose of the smoothness survey was twofold:
1. To determine the cost, if any, to achieve various ranges of specified smoothness level
2. To determine what additional effort is needed to meet a given level of smoothness and what consists in that effort
To accomplish this, a smoothness level of 7 in./mi. on a 0.2” blanking band was selected as the “Control” roughness by which all improvements would be compared. At this time, most state agencies were using the profilograph profile index for smoothness acceptance. And at the time of this 2009 survey, real time smoothness and stringless paving were not mainstream.
In 2013 the ACPA smoothness task force developed smoothness guidelines to assist in specification development. In addition, there is also a separate ACPA specification for industrial facilities which is not discussed in this document. It should also be noted that the specification does not currently provide additional incentives for smoothness levels below and MRI of 40.
In 2014, the IGGA updated its smoothness specifications for diamond grinding. IGGA Diamond Grinding Specifications were developed for three categories of roadway:
1. Next Generation Concrete Surfaces
2. City Streets
3. Preservation Grinding—conducted on existing roadways and does not include bump grinding on new construction. As with the ACPA specifications, two roadway speeds are considered; above and below 45 mph
IGGA specification development involved reviewing existing specifications and contractor experience—actual pre- and post-grind data were not available for evaluation. Note that the preservation grinding specification is based upon a percent-improvement concept. Since existing roads can be very rough, the only way to get them smooth is by reducing thickness. The use of a percent improvement allows the roads to achieve a significant improvement without a significant reduction in the thickness to achieve an arbitrary new construction standard.
In 2016, spell out AASHTO established a concrete task force under the Transportation System Preservation Technical Services Program (TSP-2) umbrella. This task force was established to develop concrete preservation specifications for submission to the AASHTO TS5b for consideration as an AASHTO specification. The first spec considered for development was the diamond grinding specification. Although the IGGA preservation spec was the basis for much of the proposed specification, there was a need to acquire actual pre- and post-grind data from state projects, but it turned out to be more difficult than anticipated as actual construction profile data was difficult to retrieve.
Each of seven states eventually provided data for analysis. Two of the states had actual construction data, while five of the states provided PMS data. The difficulty with PMS data is that the before and after measurement times vary considerably from actual construction data and the sensors used for PMS data are sometimes not appropriate for diamond ground surfaces.
2018: For several years, industry and Caltrans has been working on improving smoothness specifications. The Southwest Concrete Pavement Association and its members have put together actual pre- and post-grind construction data to evaluate the percent improvement for five construction projects. They have also collected a small sample of new construction profile data. The IGGA/ACPA requested the raw data from this plot, with the new construction data flagged so that cumulative distribution plots could be developed.
The measurement of pavement smoothness has evolved from approximate profiling methods obtained at a walking speed to very accurate measurements obtained at highway speeds. It is now even possible to measure smoothness in real-time during paving, which has allowed more research and analysis into pavement roughness statistics.
In recent years, the highway community is moving to the International Roughness Index (IRI) with approximately one third of the states currently using it for construction acceptance. Virtually, all states are using IRI as their roughness measurement in their PMS systems, and this is one of the measurements that will be reported to the FHWA as part of the each state’s performance requirements. The SHRP II research effort has now moved from the research phase into the implementation/demonstration phase.
APPENDIX 1: Initial pavement smoothness has been of interest to pavement designers and the traveling public for over 100 years … since the early 1900‘s. No other pavement quality has as significant impact on the traveling public and perhaps pavement performance as roughness. The concept of pavement serviceability, by which all federal aid projects have been designed by over the past half century, is essentially based on initial pavement smoothness and how roughness changes over time. The new ME Design process also incorporates roughness as one of its design parameters.
Most DOT pavement management systems (PMS) trigger their rehabilitation and preservation activities based, at least, upon the current level of roughness and/or the rate of change in roughness. This essentially establishes when intervention will occur, impacting LCCA analysis and maintenance expenditures. Therefore, capital expenditures are directly related to pavement roughness.
With the introduction of IRI and the increased ability to accurately and efficiently measure smoothness, new construction specifications have seen a trend towards lower initial smoothness requirements and the use of the same specifications for both asphalt and concrete pavements. Additionally, a short interval roughness component somewhat analogous to the bump detection of old has been incorporated in current specifications. There is a need to conduct research into several primary areas.
To download the 13-page PDF, please click on image above, or go to: http://www.acpa.org/wp-content/uploads/2018/05/IndustryDevelopedSmoothnessSpecs-2018.pdf
Referenced in the documents: Larry Scofield, ISCP Corporate Member; and Southwest Concrete Pavement Association (California and Nevada)—an ISCP Corporate Member (ACPA)