66 Transportation Research Record 814 Long-term observations will be necessary to docu­ 2. Delay Task Force Study, Volume 1: Executive ment maintenance costs and possible design modifica­ Summary. Chicago O'Hare International Airport, tions to improve on the construction and performance Rept. FAA AGL-76-1-I, July 1976 (prepared of a prestressed overlay system. through the joint efforts of FAA, Chicago De­ ' It is strongly recommended that qualified, expe­ partment of Aviation, and the airlines that rienced personnel be employed in the design, con­ serve O'Hare). struction, and quality assurance of prestressed con­ 3. R. Heinen. Prestressed Concrete Airfield Pave­ crete pavements. ments. International Air Transportation Confer­ ence, New Orleans, LA, May 1979, Proc., Air REFERENCES Transport Division of ASCE, Vol. 2, 1979, pp. 220-233. 1. D.M. Arntzen, E.J. Barenberg, and R.J. Krause. Airfield Pavement Demonstration-Validation Study. Transportation Engineering Journal of ASCE, Vol. 106, No. TE6, Proc. paper 15813, Nov. Publication of this paper sponsored by Committee on Pavement Rehabilitation 1980, pp. 721-730. Design. Bonded Portland Cement Concrete Resurfacing JERRY V. BERGREN The experiences of the state of Iowa in developing and refining the process of Various types of PCC overlays, which include resurfacing concrete pavements by using portland cement concrete (PCC) are plain, nominally reinforced, and continuously rein­ described. The methods of evaluating the condition of the underlying pave­ forced overlays, have been demonstrated on concrete ment and determining the thickness of the resurfacing layer are discussed. pavements as well as a few cases on bituminous pave­ Several projects that used PCC resurfacing to satisfy different roadway needs ments. For example, since 1959, 13 different are described. Several methods of surface preparation, the methods of bond­ states, including Iowa (Greene County), have had ing, and the bond test results are included and discussed. It is concluded that .projects that used continuously reinforced concrete bonding a layer of PCC 50-75 mm (2-3 in) thick to an existing concrete pave­ overlays (!_). ment Is a viable alternative to bituminous resurfacing for the rehabilitation and restoration of concrete pavements. In 1973, a research project was conducted in Greene County that used 50- and 75-mm (2- and 3-in) thicknesses of fibrous reinforced concrete in Iowa has more than 12 000 miles of portland cement various conditions of bonding: unbonded (two layers concrete (PCC) primary and Interstate highways, sec­ of polyethylene), partially bonded (wet interface), ondary or county roads, and city streets. Approxi­ and bonded (dry cement broomed over wetted sur­ mately 15 percent of these streets and highways have face). Also, in the fall of 1954, PCC resurfacing been in service more than 40 years and have had lit­ was placed on US-34 in West Burlington, Iowa. This tle or no surface maintenance and no additional was reinforced by using steel mesh, and most of the wearing surface. Many, however (especially those project was bonded by using a nominal 6 mm (0.25 in) that carry high volumes of traffic), need surface of cement-sand grout (l,) • attention at this time. Tne serviceaoiJ.it:y 1riae­ Although there is a variety or aesigns ana con­ ability) is approaching, and in some cases has ar­ struction procedures available, the projects men­ rived at, the point at which surface restoration or tioned above demonstrated the practicability of con­ reconstruction is imminently needed. crete for resurfacing in rehabilitating old concrete Nationally and locally, the trend has shifted pavements. In previous attempts at full bonding of from building miles of new pavement to restoring and overlays, the information available indicates that rehabilitating the existing pavement. This has been complete bonding was not obtained. for the most part due to financial, environmental, A definite need existed for a high-strength, dur­ and ecological restrictions. able, skid-resistant, long-lasting, and economical Historically, the restoration process on PCC resurfacing course for PCC pavements. Such a re­ roads and streets has usually involved resurfacing surfacing course, completely bonded to the existing by using bituminous materials to provide an accept­ pavement, would provide additional support for the able riding surface. The bituminous-resurfacing ever-increasing traffic loads and volumes on our process has provided city, county, and state govern­ roads and streets. ment agencies with a viable method of extending the Iowa has had considerable success in the use of service life of PCC pavement at a considerably lower thin, bonded, dense concrete overlays used in the cost than that of reconstructing or replacing the repair of deteriorated bridge decks <1>· This pro­ facility. cess involves the removal of unsound concrete down Since 1976, this nation has been made aware that to and around the top layer of steel reinforcement. petroleum and products derived from petroleum are The entire remaining area of the bridge-deck surface becoming more and more expensive. Further, and more is removed to a nominal depth of 6 mm. This removal important, is the forecast that this nation's supply is most generally accomplished by using scarifying of crude oil is quite limited and may be exhausted equipment. before the turn of the century. Thus, there is a The existing surface is scarified to remove road stong emphasis on the search for substitute fuels, oils, linseed oil, etc., as well as the surface con­ products, and methods that are not dependent on pe­ crete that has the highest concentration of chloride troleum. ions from the interface. The entire surface is Transportation Research Record 814 67 vigorously sandblasted and then air-blasted prior to cannot be placed by using existing conventional the concrete-placement operation. The blasting is slipform paving equipment. The superplasticizing required to provide a clean dry surface to which a admixtures made possible the design of a concrete thin layer approximately 50 mm thick of dense, low­ mixture that had a workability similar to concrete slump PCC is bonded. The bond is obtained by mixtures used in concrete paving but still main­ brushing on a grout of creamy consistency that con­ tained the very low water/cement ratios of tradi­ sists of equal parts by weight of cement and sand tional bridge-deck repair mixtures (the design immediately before the concrete placement. water/cement ratio is 0.328 water to cement by By applying the same principles and methods weight). learned from bridge-deck repair and resurfacing This project clearly established that concrete since 1965, it was felt that this system could pro­ that had a low water/cement ratio could be increased vide a viable alternative to the bituminous resur­ to conventional paving workabilities to allow its facing that has traditionally been used in the res­ placement by using conventional slipform equipment toration and rehabilitation process on PCC pavements. in a thickness range of a nominal 50 mm. Also, it From the successful experience with bridge-deck was demonstrated that mixtures of this type could be repair and resurfacing in Iowa, it was expected that proportioned, mixed, and transported by means of dense PCC could be placed and bonded to an existing transit mix trucks and that the inherent problems concrete pavement. However, it was recognized that with the high slump loss that accompanies the use of higher production, different equipment, and higher­ superplasticizers could be and were overcome. slump concrete would have to be used to provide an With the successful completion of the first economically viable process for large-volume proj­ demonstration project, an application that had a ects. different requirement was investigated. This was a A typical one-day bridge-deck resurfacing place­ case of a relatively new concrete pavement 150 mm (6 ment is 15-183 m (50-600 ft) long and 4-7 m (14-22 in) thick that, because of changing traffic condi­ ft) wide and uses 19-mm (0.75-in) slump concrete on tions after the road had been completed, was now a prepared (ground or scarified) surface. This con­ considerably underdesigned. crete is mixed in a small paddle mixer or a Concret­ After the road had been constructed in 1968, a mobile (a self-contained unit that produces concrete commercial development that consisted of a grain by using volumetric proportioning). terminal resulted in very heavy truck traffic on a Obviously this rate of production would not be road designed for normal secondary-road traffic. economical if a project 11-16 km (7-10 miles) long Thus the desire to increase the load-carrying capa­ were to be resurfaced. Also, conventional paving city by bonding on a layer of concrete was the moti­ equipment would require a higher-slump concrete for vation for the second project. production and workability. In 1977, a 2.6-km (1.6 mile) research project was constructed in Clayton County, Iowa (_~). An ob­ EVALUATION OF PAVEMENT FOR RESURFACING jective of this project was to determine the feasi­ bility of proportioning and mixing a dense concrete In choosing a project location for the first attempt mixture by using superplasticizing admixtures in a at thin bonded PCC resurfacing, the Iowa Department conventional central-mix batch plant. A second ob­ of Transportation (IOOT) looked for a project that jective was to determine whether a conventional would be considered typical and for which the tradi­ (without superplasticizers) paving mixture of con­ tional bituminous resurfacing would be the obvious ventional water/cement ratios, still in the nominal corrective measure to take. In 1976, a section of 50-mm thickness, would achieve an adequate bond and concrete pavement of US-20 in Black Hawk County would adequately strengthen the section for the (northeast Iowa) was chosen for the first attempt at existing and anticipated traffic.