Durability of Concrete: Assessing the Performance Achieved in the Laboratory and on the Construction Site

To achieve a performance-based durability design for concrete, the corresponding materials’ properties must first be quantified. These properties, together with the expected environmental loads, are used as model inputs to assess the durability of the concrete structure. The quantification of these properties is carried out using mainly standardised concrete test specimens, cast and cured under optimal laboratory conditions. However, the real structure is built under different conditions and using different methods. This naturally leads to a difference between the concrete properties achieved at the construction site and those determined in the laboratory. This difference is currently being assessed in the context of an ongoing German research project. For this, samples of fresh concrete used at different construction sites were taken and used to cast separate, standardised test specimens, as well as a 2 m × 2 m, 25 cm thick dummy wall, which was built by the construction workers with the available tools and methods on site. The separate standardised test specimens were cured in the laboratory in accordance with current German standards. The wall was cured in the form for a determined number of days; in most cases 7 days. Core-drill samples were later taken from it and used to prepare test specimens for comparison against the laboratory specimens. Tests were carried out to determine the compressive strength, the carbonation rate and the chloride migration coefficient of the used concrete. The core-drill samples performed worse than the laboratory-cured samples, suggesting that the performance achieved in the construction may be lower than that of laboratory specimens.