2008 Survey of European Composite Pavements (2010)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

1 Executive Summary Highway authorities are vitally interested in developing a consistent, systematic approach to highway renewal that makes it rapid and minimally disruptive and produces long-lasting facilities. Composite pavement systems have been identified as having potential to achieve these standards of highway renewal. Two systems of particular interest involve new portland cement concrete (PCC) pavement surfaced soon after placement and curing either with a new, relatively thin, high-quality asphalt concrete (AC) layer or with a relatively thin, high-quality PCC layer. Although these two systems show great promise for providing durable, rapidly renewable, and long-lasting pavements that require minimal maintenance, their structural performance and functional per- formance are not well understood or documented in the United States. Some states and urban areas have constructed new AC over PCC with success. There have been virtually no two-layer PCC pavements constructed in the United States in many years. However, recent high-visibility federal concrete pavement initiatives have mentioned composite concrete pavements and have led to the development of the experimental two-layer PCC sections com- pleted in Kansas on I-70 near Abilene in September 2008. These sections are the most recent U.S. research attempts to better understand two-layer PCC and its performance, economy, manner of construction, and ability to accommodate innovative designs and materials. Given the limited information provided by these new American studies into two-layer PCC and AC-over-PCC, members of the second Strategic Highway Research Program (SHRP 2) research team for Renewal Project R21 (Composite Pavement Systems) visited with pavement engineers and assessed field sections in the Netherlands, Germany, and Austria in May 2008. These three countries use com- posite pavements on a much larger scale than the United States. AC/PCC composite pavement was studied in both the Netherlands and Germany. The Netherlands has built porous AC over recently placed continuously reinforced concrete pavement (CRCP) on numerous major projects during the past 10 years. These projects are all performing well with low noise levels and no reflection cracking from the CRCP, despite their relatively thin AC layer of approximately 2 to 3 inches. Germany has built stone matrix asphalt (SMA) surfaces on jointed plain concrete pavements (JPCP) and most recently over CRCP. One SMA/JPCP section was 15 years old, under heavy traffic, with sawed and sealed joints that had performed very well. Two-layer PCC paving (wet-on-wet)—constructing two layers with different properties for structural, economic, environmental, or safety reasons—has been much more common in Europe than in the United States. Austria in particular has been active in regular two-layer PCC paving for concrete pavements; the standard concrete pavement in Austria is constructed according to the two-layer PCC specification. Two-layer PCC paving has been used in countries such as Switzerland, Belgium, the Netherlands, France, and Germany with regularity since the 1980s and even much earlier in some. Two-layer PCC is becoming more common as the techniques are refined further. European research related to two-layer PCC pavements includes construction techniques and the use of recycled materials, such as recycled concrete aggregates in the lower

2 layer. One particular strategy in texturing that is often paired with two-layer PCC in Europe is exposed aggregate concrete (EAC) texturing, which is a brushed concrete surface that exposes the aggregates at the surface. This creates a unique texture that is an improvement over textures produced by conventional texturing methods in terms of durability, safety, and noise reduction. This report describes projects visited in the Netherlands, Germany, and Austria. In reviewing these case studies and discussing the composite pavements with the host engineers and practi- tioners, the research team identified several benefits and potential challenges in implementing European techniques in the experimental sections to be constructed under the SHRP 2 Renewal Project R21. The first major benefit of the two-layer method is that it can reduce costs in circumstances where high-quality aggregates are costly and in short supply and where using low-quality materials throughout a single layer is not an option. The benefit is achieved through utilizing low-cost, more plentiful materials—including reclaimed concrete asphalt and other secondary materials—in the lower PCC layer and reserving materials of higher cost, scarcity, and quality for the upper layer. The lower-cost materials, which have no effect on the structural integrity of the roadway, make composite pavement an attractive option when aggregates are difficult to obtain. Furthermore, as sustainable practices such as recycling and reduced maintenance become more of a concern in the United States, American pavement engineers will need to look to technologies such as composite pavements to develop more efficient and economical recycling techniques. Austria in particular has a great deal of experience with recycling concrete pavements. In the late 1980s, Austria undertook the long process of recycling PCC pavements along the A1 motorway that were more than 30 years old into new two-layer PCC pavements (some of these are detailed in the case studies). This experience has led Austrian researchers to claim that the recycling con- cept is “an important innovation that is both economically and environmentally advantageous.” Another important performance benefit of composite pavements is the ability to use better materials and more specialized techniques in the pavement-wearing course. These efforts—which can include the use of durable, high-quality aggregates, porous grading, or EAC texturing—can lead to reduced pavement noise, improved friction numbers and skid resistance, and smoother pavements. This particular benefit of composite pavements is one that the road user will imme- diately appreciate in a smoother, quieter, and safer ride. Rapid renewal of the shorter-lived porous AC-over-PCC composite is one of its advantages, whereas the EAC-over-PCC composite has the advantage of more than double or triple the service life. The report also identifies potential challenges of composite pavements, particularly in the con- struction of PCC-over-PCC. Two-layer construction requires a consistent, quality effort. Con- struction techniques were one of two main areas emphasized in Germany and Austria (the other being the quality of the aggregate in the upper layer). The I-75 experiment near Detroit and a recent survey of two-layer PCC pavements have cited construction techniques as a major obstacle to the adoption of two-layer PCC pavements in the United States. To start, the use of multiple pavers in Europe for PCC-over-PCC is a technique that will be difficult to replicate in the United States. PCC-over-PCC used to be placed at once using a single slipform paver; however, countries such as Austria and Germany currently use multiple paving machines and are more comfortable with the “two-paver” system for two-layer PCC. The report discusses the use of multiple pavers and contrasts this with the single-paver option. Another challenge in PCC-over-PCC is the need for multiple batching plants, a drawback that has been previously cited by investigations into importing two-layer PCC into the United States. The report proposes means of overcoming this obstacle through proper planning and expanded batch plant capabilities. Another challenge will be the introduction of local techniques, such as exposed aggregate brushing, and local materials and mixes that are not commonly used in the United States. Overcoming these challenges will require careful planning, an awareness of materials used in the United States, and laboratory work in support of the full-scale experimental sections to account for these differences. In short, Dutch, German, and Austrian researchers claim that composite pavements, such as two-layer PCC pavement, provide a structural performance similar to equivalently thick single- layer pavement at the same price, with the additional benefits of a road surface with higher-quality

3 and longer-lasting friction and noise reduction resulting from the high-quality top layer. Further- more, composite pavements allow for the optimization of costs and materials throughout the pavement cross-section: 1. High-quality materials can be used in lesser quantities in the upper layer, where they will be most beneficial to the system; and 2. Cheaper, lower-quality materials can be used in greater quantities in the lower layer, where they will contribute structurally without detracting from the quality and performance of the overall pavement. Although there are several obstacles to the adoption of composite paving in the United States, it is clear from the Dutch, German, and Austrian experiences that overcoming these obstacles will result in quality, durable, and sustainable composite pavements. This European survey has provided ample information to help develop experimental sections for construction under SHRP 2 Renewal Project R21 at the MnROAD test site.