Jürg Schlumpf, Civil Engineer B.Sc., Switzerland
It is a great challenge to improve sustainability of concrete. Strongest argument for concrete as the most important building material is its durability behavior over more than 100 years. As longer the service life as less maintenance as better the sustainability, nothing easier as that! But to improve energy efficiency and climate protection in such durable recipes the concrete mix has to adapt. Reduction and replacement of pure Portland cement and use of crushed aggregates are two of the key actions. By using these materials, concrete behavior change completely, very often water reduction is no longer an issues, but segregation and bleeding, slump retention of a required time period becomes to a major topic. Finally keeping the construction speed by achieving the needed compressive early strength is a challenging task.
For the implementation of durable and based on its components sustainable concrete new concrete technology instruments have to be in place. Design by volume paste instead of content of cement, newest concrete admixture technologies as special slump keepers and high performing concrete accelerator in combination with practical tool to measure the progress of sustainability are key actions to fulfill the request of sustainable durability.
Durability and WorkabilityDue to the great number of infrastructural installations everywhere around the world and the maintenance costs which have developed in the meantime for these structures, a pronounced consciousness has also developed for the quality of the construction materials which thereby extend to their durability. In local norms and in international recommendations these requirements are described, and by means of suitability tests are also being measured. There remains, of course, the difficulty of time acceleration, so that with a test of some few weeks a prognosis of durability over decades can be concluded. This difficulty holds true for concrete as well.
Figure 1: Schematics of the entire life cycle of construction products.
If the requirements for fresh concrete properties have been sensibly defined (appropriate to the construction material) and properly described in the testing plan, and then rigorously checked, then the second of the four relevant demands for durable concrete has been fulfilled. Alongside the sensible and goal-oriented fresh concrete properties the following is valid:
- Concrete installation & curing (expert treatment)
- Fresh concrete properties (constant adherence to specifications)
- Concrete mix design & manufacturing (according to requirements)
- Construction & dimensioning