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Betong på asfalt.: Svenska fältförsök 1993-1995
CBI - Cement- och betonginstitutet.
1995 (Swedish)Report (Refereed)
Abstract [sv]

Rutted asphalt roads may be repaired with either a thin, high strength concrete overlay (whitetopping) or an overlay of open asphalt filled with high strength mortar (Densiphalt). The thickness of the whitetopping does not need to exceed 70 mm, if the thickness of the remaining underlying asphalt is at least 150 mm. The old asphalt road must have a sufficient load carrying capacity before intervention. The concrete overlay ought to be sawn into square panels with a joint spacing not exceeding 1.5 m. A Densiphalt layer thickness of 30 to 40 mm seems to be appropriate. These promising results were obtained in field tests on a heavily trafficked asphalt road in the Stockholm area. _x000D_ _x000D_ Rutting on old, intensively trafficked asphalt roads is a problem for the Swedish road authorities. The rutting is caused by the frequent use of studded tyres during winters and by heavy vehicles during hot summer days when the asphalt pavement is soft. Several tests have shown that high strength concrete with a wear resistant aggregate has a high resistance against wear due to studded tyres. Additionally, concrete is not deformed by heavy vehicles, not even during hot summer days. In this study, it has been shown that also Densiphalt has a rather good wear resistance, at least initially. Consequently, both whitetoppings and Densiphalt overlays would be promising repair alternatives, if it can be shown that overlay cracking can be avoided. _x000D_ _x000D_ In current report, the overlay crack risk has been studied both analytically and through field tests. In a 70 mm thick, high strength whitetopping on 150 mm asphalt, computations show that the combined stresses due to traffic, temperature, and shrinkage are less than the available strength. A good bond between concrete and asphalt is necessary. Milling the asphalt surface and cleaning it carefully prior to overlay placement will create sufficient bond strength. Short joint spacings are more beneficial than long ones since both traffic, thermal, and shrinkage stresses decrease with decreasing joint spacing. In small overlay panels, the flexural tensile stresses under traffic load decrease whereas the (harmless) compressive stresses increase. _x000D_ _x000D_ On the old road between Stockholm and Uppsala, close to Märsta, in situ tests are carried out on four test sections. The test sections were constructed in 1993 and have a total length of 450 mm. Three test sections have concrete overlays, the fourth one has a Densiphalt overlay. A concrete compressive strength of 90 MPa was obtained after 28 days. The concrete overlay is 70 mm thick and is placed on a 150 mm milled asphalt layer. The concrete overlay was sawn into 3.5×3.75 m panels on one test section and into 1.25×1.25 m panels on two sections. Two test sections were cast with steel fibre reinforced concrete and one section (with 1.25×1.25 m panels) with plain concrete. The bond between concrete and asphalt was tested through coring and pull-off tests. The average failure stress was 0.25 to 0.30 MPa. Through computations, it has been shown to be sufficient for composite action. _x000D_ _x000D_ On the concrete test sections, damaged transverse joints and some tiny corner cracks exist. The joint edges were probably damaged already during the sawing procedure. No further deterioration has been observed. Consequently, the joint damages may be considered as harmless. The corner cracks are more annoying. In the worst case, the corner cracks will eventually lead to the deterioration of the pavement corners. No such tendency has, however, been observed. Furthermore, the corner cracks are concentrated to the test section with a joint spacing of 3.5 m. The test sections with smaller panels are uncracked. Consequently, future whitetoppings ought to be sawn into small panels with joint spacing preferably not exceeding 1.5 m. No performance difference has been observed between steel fibre reinforced and plain concrete overlays. Perhaps, the expensive steel fibres may be dispensed, especially since a better evenness was obtained on the plain concrete test section. The choice of sawing time is important in order to avoid damaged joint edges. Furthermore, the saw blade should be as thin as possible. _x000D_ _x000D_ The Densiphalt is 40 mm thick and is placed on 120 mm milled asphalt. Three tiny transverse cracks have been observed on the Densiphalt test section. No crack width increase has been observed. Consequently, the transverse cracks do not need to form a problem. Measured friction and evenness values have about the same magnitude as corresponding values on the concrete test sections. The conclusion is that Densiphalt seems to be a promising material. It must, however, be stated that the thin Densiphalt overlay cannot improve the load carrying capacity of an old asphalt road with insufficient capacity. The long longitudinal crack that occurred during the frost heave period testifies that. _x000D_ _x000D_ Future research ought to cover development of design procedures for thin whitetoppings with short joint spacings and for overlays of open asphalt filled with high strength mortar (e.g., Densiphalt). Support for the choice of right time for joint sawing and fast-track pavement considerations ought to be developed. _x000D_ _x000D_ It may be added that the technique of thin concrete overlays does not need to be limited to repair of rutted asphalt roads. This technique will also have an impact on the development of composite pavements for new construction._x000D_

Place, publisher, year, edition, pages
Cement och Betong Institutet , 1995. , 77 p.
Series
CBI rapport, ISSN 0346-8240 ; 1995:1
Keyword [sv]
Whitetoppings, Field tests, Design, Evaluation
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:ri:diva-3028OAI: oai:DiVA.org:ri-3028DiVA: diva2:960633
Note
282 Går att beställa: kontakta eva.lundgren@cbi.se "Whitetoppings. Swedish Field Tests 1993-1995"Available from: 2016-09-07 Created: 2016-09-07Bibliographically approved

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