The Effects of Higher Strength and Associated Concrete Properties ...

1.2.1 Required Levels of PCC Properties and Material Characteristics
Table 1.2.1 lists the JPCP design requirements for concrete properties and material
characteristics for eight European countries in wet freeze (WF) and wet no freeze (WNF)
climate regions. In addition, requirements are given for pavement and base type. The
concrete requirements are shown for the 28-day compressive strength, 28-day flexural
strength, water/cement (w/c) ratio, cement content, aggregate gradations, cement types,
mix proportions, and air content. Not all eight countries have requirements for all
parameters. It should be noted that table 1.2.1 represents design requirements from the
early 1990’s and revisions may have occurred.
Table 1.2.1 shows that the European countries have similar requirements for compressive
strength with the exception of Norway which requires strength values from 45 to 75 MPa.
However, a wide spread is seen in the flexural strength requirements ranging from 4.3 to
as high as 7.0 MPa. The typical value is around 5.0 MPa. The requirements for w/c ratio
are between 0.40 and 0.50, while the cementitious contents range from 300 to 350 kg/m 3 .
Most of the countries allow for cementitious substitutions using slag and fly ash. In
Germany fly ash is usually not used due to its variability. The concrete must be freezethaw
resistant with air contents of 3 to 7 percent. Finally, Germany and France have
requirements for the aggregate gradations. It is noteworthy that the mix proportions are
typically based on trial mixes. Finally, it should be emphasized that only Norway allows
the use of granular bases, and that Germany only allows for bonded cement bases.
The German “autobahn” has for decades been considered to be the best European
highway, which has been a result of high quality control. For instance, the minimum
specified 28-day strength (as determined on 20-cm cubes) is 35 MPa. Normally, as in
most US pavements, the field strength substantially exceeds minimum requirements. In a
two-layer pavement the compressive strength is often 65 MPa in the top layer and 50
MPa for the bottom layer. Furthermore, the maximum w/c ratio is 0.42, the minimum
cement content is 349 kg/m 3 , and the air content is typically about 5 percent. A 5-m joint
spacing is used with variably spaced, plastic coated dowel bars. An important feature of
the German pavement cross section is the use of a 15-cm lean concrete (LCB) or cement
treated base (CTB). Special for the German design is that the CTB is bonded to the slab,
thereby achieving a thicker monolithic slab for several years after construction. To
prevent reflection cracking, the CTB is pre-notched to match the transverse joint in the
slab. To decrease edge stress the concrete pavement extends 0.5 m beyond the traffic
lane.
1.2.2 European Concrete Pavement Demonstration Project in Michigan
Based on the European design catalogs, an experimental higher strength rigid pavement
section was constructed in Detroit, Michigan, in 1993. The test road was designed as a
premium JPCP based on the German design guidelines for the local climate, soil, and
traffic conditions. The project used high quality concrete aggregate and higher than
normal concrete strengths combined with a nonerodible lean concrete base to limit slab
deflections (Larson et al., 1993, Till et al., 1994).
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