Evaluating the condition of solid structures

Information about the composition of solid structures as a whole or of individual structural elements as well as about the properties of the construction materials used are essential prerequisites not only for standard safety considerations, but also in terms of estimating remaining service life and determining repair requirements.

Older waterway constructions in particular were built under conditions and constraints with which we are no longer familiar. Not enough construction materials of identical quality were always available throughout some building projects and construction procedures also exercised much greater influence on the quality of building work (picture 1). However, because such influences are not usually documented in the engineering documentation, if such documentation exists at all, the condition of a structure can only be reliably assessed by performing a comprehensive building evaluation using core extractions and subsequently examining the material characteristics in the laboratory. In the case of structural elements such as lock-chamber walls, vertical holes are drilled through the entire structure to determine its fundamental composition and to detect any areas which may have different material properties (picture 2). This information is particularly important when considering a structure's static features. Short horizontal or vertical holes, on the other hand, are made to investigate the composition of the structure near its edges and, in particular, to obtain material samples from close to the surface of structural components; the material's durability characteristics can then be used to assess the structure's service life and need for repair (picture 3).

In some structural elements made with less than top quality concrete the stress caused by the drilling procedure itself can be enough to lead to changes in, or the destruction of, the drill core. In these cases the drill holes may also need to be examined using an endoscope (picture 4). When taking core samples the BAW Code of Practice 'Core Extractions for Examinations of Constructions' should be observed. If the intention is to inject the structural element in order to reduce water penetration, it may be appropriate to carry out hydraulic pressure tests in the drill holes in preparation for the planning and performance of such measures.

As well as determining the concrete characteristics, such as frost resistance or residual alcali-silica reactivity, the concrete covering and the carbonation depth of reinforced structual elements (when assessing the corrosion protection of the reinforcement) and the chloride distribution in structural elements which are suspected of being contaminated with chloride as result of de-icing salt or sea water must also be determined and compared.