Durable concrete road pavements taking into account current ecological and economic aspects

Project duration: 01.11.2012 - 30.04.2015

Portland cement (CEM I) is traditionally used for the production of concrete road pavements, since experience has shown that concrete road pavements with high freeze-thaw resistance can be reliably produced without increased need for curing when CEM I is used. From an ecological and economic point of view, the use of cements containing granulated blastfurnace slag would also make sense, but there are concerns as to whether sufficiently high freeze-thaw resistance can be reliably achieved in concrete pavements when using such cements. This applies in particular to cements with blastfurnace slag contents > 30%. In addition to the ecological aspects, concretes with Portland cement are also to be classified as comparatively unfavorable with regard to a concrete-damaging alkali-silica reaction (ASR). When using potentially alkali-sensitive aggregates, a concrete-damaging ASR can be avoided or at least strongly delayed by cements with a blastfurnace slag content of approx. > 30 % [1] or by adding fly ash [2]. The positive influence of cements containing blastfurnace slag in terms of ASR prevention results from a denser microstructure of the concrete, which can significantly reduce moisture and mass transport. Furthermore, cement chemical influences such as a lower portlandite content, a reduced OH ion concentration and a lowering of the CaO/SiO2 ratio in the C-S-H phases also have a positive effect on the resistance to ASR. In the project presented here, the approach was to use cements with a high granulated blastfurnace slag content exclusively in the bottom concrete of a concrete pavement, while the top concrete, which is subject to higher stresses, is produced with CEM I or CEM II/A-S. The cements with a high granulated blastfurnace slag content are used in the bottom concrete of a concrete pavement. At present, however, TL Beton-StB 07 stipulates that in the case of two-layer paving, the top and bottom concrete must be produced with cement of the same type and strength class. In addition to cements containing blastfurnace slag, partial cement replacement with fly ash can also contribute to ecological optimization of the concrete pavement and, in parallel, also increase resistance to ASR. However, there are also concerns regarding the freeze-thaw resistance of the concrete pavement. Accordingly, the use of additives is restricted in TL Beton-StB 07, so that fly ash can be added, but it cannot be counted towards either the cement content or the w/c ratio in order to ensure the high freeze-thaw resistance.