ACPA Concrete Pavement Progress (CPP)

Volume 43, Number 2
February 21, 2007

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In This Issue... Special Report on the TRB 86th Annual Meeting

ACPA Staff Reports on Transportation Research Board Meeting
............• Evaluating Alternative Dowel Bars Concrete Pavement Construction
............• Roller-Compacted Concrete Shoulder Construction on an Interstate Highway
............• Fracture Mechanics Analysis for Saw Cutting Requirements of Concrete Pavements
............• Strength Profiling by Resonance Search Technique
............• A Novel Self-Consolidating Concrete for Slip-Form Application
............• Recycled Concrete Aggregate as Unbound Base
............• Need for Improved Specs on Dowel Bar Placement Tolerance
............• Determining Air Void Characteristics of Fresh Concrete Using the Air Void Analyzer

	ACPA Staff Reports on Transportation Research Board Meeting

...	Each year, ACPA's technical staff participates in the National Academies' Transportation Research Board meeting in Washington, D.C. The objective is to be front and-center in both presenting and learning about the latest in transportation research, technology transfer, and technology implementation. Of particular interest to ACPA staff are the topics of greatest interest and value to the concrete pavement industry, as well as the agencies we serve. Working our way through what is arguably the world's top research and tech-transfer venue involves participation in standing committees and task force meetings, as well as presentations. Covering the sheer volume of a meeting this size is a daunting task, so the following articles are presented simply as a representative sampling—in capsule summary format—of some of the many topics ACPA staff members considered to be among the best and most relevant to concrete paving industry. When reviewing the synopses below, it should be noted that photos are for illustrative purposes only; they neither reflect the authors' views nor should be construed as relating to problem statements or findings presented in the papers. Also, please note that some of the titles of the papers have been edited for brevity; actual titles of the papers may be different than indicated.	...

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	Evaluating Alternative Dowel Bars Concrete Pavement Construction

...	The many benefits of using dowel bars as load transfer devices are well known. Traditionally, such devices have been steel bars with a circular cross section. In an effort to optimize design, however, this report shows results from a study that investigated both materials and geometries of dowel bars. Included in the research were steel, epoxy-coated steel, stainless steel, and glass fiber reinforced polymer. The report also investigated geometric (round vs. elliptical) variations.	...
	None of the six dowels studied failed before ACI 325 allowable stresses were achieved, proving adequate for highway use. The elliptically-shaped dowel bars were found to reduce bearing stresses at the concrete/dowel interface. The deflections for the elliptically-shaped dowel bars, however, were greater than the round steel dowels, although not large enough to cause discomfort to road users.

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	Roller-Compacted Concrete Shoulder Construction on an Interstate Highway

...	In 2004, the Georgia Department ofTransportation(GDOT) became the first state to construct roller compacted concrete (RCC) shoulders on a portion of the Interstate Highway System. This report presents the mix design used and a thorough discussion on the properties of the fresh/hardened mix and the construction procedures used to place it. The increase in average density due to compaction resulted in a disproportionately large increase in average compressive strength. Although this anomaly wasn't as accurately represented by field specimens as it was by cores, it was recommended that field specimens still be taken as a quality control measure. A high density paver with an attached tapered-edge maker made for quick construction, with minimal impact on the traveling public.	...

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	Fracture Mechanics Analysis for Saw Cutting Requirements
...		...
	In an attempt to control the inevitable cracking in jointed plain concrete pavements, joints are sawed at predetermined locations soon after placing the pavement. Traditionally, the contractor is responsible for sawing all joints at the proper depth and in time to prevent random cracking and, if they fail, they are responsible for the outcome. This report presents a novel means of predicting the proper sawing depth/time based on the early age fracture properties. The fracture parameter, which is heavily dependent on concrete mixture proportions and constituents, can be derived from the wedge splitting test. The results of this study showed that increasing the cement content and the aggregate size increased the saw cut depth requirements and that a dramatic increase in the required saw depth was observed in all specimens after approximately 10 hours. It also showed that more rigid, thicker pavements are less sensitive to saw cut depth/timing than thinner pavements.

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	Strength Profiling of Concrete Pavements by Resonance Search Technique
...		...
	This paper presents a new nondestructive method of estimating both thickness and strength (not just average strength of the section, but also a strength profile through depth) by measuring the shear-wave velocity profile of a pavement. Unlike alternative methods based on compression waves, the resonance search (RS) technique is not susceptible to sampling errors from mode conversion, confinement effects, dimension ratio effects, and moisture content of the concrete. The RS test provides improved accuracy, with the average errors being 3.3% and 3.6% for thickness and shear-wave velocity, respectively, a substantial improvement over the average error range of 5.2% to 7.0% for the impact-echo method.

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	A Novel Self-Consolidating Concrete for Slip-Form Application
...		...
	Self-consolidating concrete (SCC) is a relatively new class of concrete in which consolidation of the concrete is provided through mix design techniques rather than external energy (i.e. mechanical vibrator). A SCC used for slip-form paving must be sufficiently workable for self-consolidation but stiff enough to hold the proper shape, all while preventing segregation. Although the thin line between these conflicting objectives might seem difficult to walk, the potential benefits of a more workable, smoother, and durable concrete pavement with a highe rate of production make further investigation into SCC for slip-form applications justifiable. This paper presents a summary of SCC mix design and characterization and much discussion on its potential applicability to concrete pavements of the future.

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	Need for Improved Specifics on Dowel Bar Placement Tolerance
...		...
	Until the development of the MIT Scan-2, it was very difficult and costly to determine the misalignment of dowel bars in existing concrete pavements. With this non-destructive testing device, however, the measurement of misalignment of each individual dowel at each individual joint is now a trivial and relatively quick process. This paper presents several all the questions that arise from such a progressive technology, such as "Should evaluation be on a joint-by-joint basis?", "Should a certain number of joints be allowed to lock?", and "What are reasonable dowel placement tolerances?". Also included in this paper are suggested achievable dowel placement tolerances, based on extensive field observations.

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Determining Air Void Characteristics of
Fresh Concrete Using the Air Void Analyzer

...

It is well understood that sufficient air content and an adequate air void system are key elements for long-term durability of concrete pavements.

Traditionally, the total air was measured in the fresh state using a variety of field methods and the air void system was characterized by the spacing factor of a hardened specimen. Gaining quick acceptance by 14 State DOT's, the air void analyzer promises to measure the spacing factor and specific surface of the air voids of a fresh sample, allowing air characteristics to now become a quality control measure.

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ACPA Concrete Pavement Progress is published 12 times per year and covers current practices and case histories in the concrete pavement industry. ACPA Concrete Pavement Progress is distributed free of charge to public officials, ACPA members, executive committee, board of directors, and affiliated chapter/state paving associations. All rights reserved. Copyright 2007 by the American Concrete Pavement Association. No portion of this publication may be reproduced mechanically or electronically without the expressed written permission of the American Concrete Pavement Association.
American Concrete Pavement Association 5420 Old Orchard Road, Suite A100 Skokie, IL 60077 Phone: 847-966-2272. Fax: 847-966-9970 (Washington) 500 New Jersey Ave., NW 7th Floor Washington, DC 20001 Phone: 202-638-ACPA (202-638-2272) Fax:202-638-2688 (Mesa, AZ) 807 W. Keating Ave. Mesa, AZ 85210 Phone: 480-775-0908 Visit our website at http://www.pavement.com/		2007 Chairman, ACPA Board of Directors Pat Nolan, Interstate Highway Const., Inc. (IHC) 2007 Vice-Chairman, ACPA Board of Directors Kari Saragusa, Lehigh Cement Co. ACPA President/CEO - Gerald F. Voigt, P.E. Editor - Bill Davenport Managing Editor - Erin McKnight