Concrete Pavements on the German Autobahnen

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Title: Concrete Pavements on the German Autobahnen

Author(s): F.H. Jackson and Harold Allen

Publication: Journal Proceedings

Volume: 44

Issue: 6

Appears on pages(s): 933-976

Keywords: none

Date: 6/1/1948

Abstract:
The inspection upon which this paper is based was prompted by a desire to reconcile conflicting reports which have come out of Germany during the last 3 years regarding the performance of concrete pavements on the autobahnen as compared to the performance of similar pavements in this country. The survey was mede during the summer of 1947 and covered approximately 1,000 miles of four-lane dual pavement in the British and American zones of occupation. The present condition of the German pavements is discussed from the standpoint of both structural performance and quality of concrete per se. All of the structural defects which usually develop in concrete pavements in the United States were found. However, aside from transverse cracking, which was quite common, defects such as joint spalling, joint faulting, settlement, etc., were not serious except in the area immediately north and south of Frankfurt. It is believed that the comparative freedom of the German motor roads from structural defects is due primarily to two factors: The comparatively small amount of heavy truck traffic using these roads, now and in the past, and the comparatively mild climate. The soils of Germany vary from cohesionless sands to plastic, silty clays and clays. Most of the silty clays examined on the system were of such a nature as to require careful moisture control for adequate compaction. Such soils would be subject to frost heave under adverse drainage conditions. Pumping at joints would occur on these soils if free water entered expansion joint or cracks and if a sufficient number of granular material under the pavement was, no doubt, a contributing factor in the prevention of mud pumping in such cases. The concrete was, almost without exception, of excellent quality. Scaling was confined almost entirely to the sections between Munich and Salzburg. Disintegration was practically nonexistent. An outstanding surface characteristic was the absence of the heavy layer of surface mortar which is frequently found on pavements in the United States. It is believed that the exellent quality of the concrete is due to (1) the excellent quality of the aggregates, (2) the low water-cement ratio, (3) thorough consolidation by tamping and vibration of a very dry mixture with a maximum aggregate size of about 1 inch, (4) thorough curing, and (5) the comparatively mild climate. The effect of the cement is not clear. German cements were definitley inferior as judged by modern American standards. Whether they were actually inferior remains to be seen. As the result of their survey the authors recommend that steps be taken to initiate a comprehensive program of research on each of the flollowing subjects: 1. A program to study the possibility of insuring greater uniformity in concrete for pavements by reducing the maximum size of the coarse aggregate. 2. A program to develop more effectively methods of compacting concrete in pavements by mechanical means, such as vibration, tamping,etc. 3. A program to study the effects of variations in the chemical composition of cements and the methods of manufacturing cements on the properties of concrete.