Fibre optical sensors for monitoring chemical attacks on concrete structures: Fid-Bau Portal

Fibre optical sensors for monitoring chemical attacks on concrete structures

Grahn, W. / Kowlasky, W. / Wichern, J. / Wiese, S.

Life cycle assessment of buildings via innovative monitoring is becoming increasingly important because of ageing, change in use, or improved safety standards. According to an integral quality concept the monitoring of structures has to be considered in the planning stage. lt is therefore necessary to provide non-destructive test procedures. Concrete is one of the most important building materials. lt is an inhomogeneous porous material with a ph-value normally in the range of 11 to 13. The high ph-value is caused by dissolution of calcium-hydroxide in the pore-liquid. In reinforced concrete, this basic environment protects the steel against corrosion by producing an inert surface. Damage of structures of reinforced concrete like bridges can be caused by environmental conditions. Exhaust fumes like CO2 and SO2, which are soluble in the pore-water, react to carbonic acid and sulfuric acid, respectively. This leads to a decrease in the ph-value during the lifetime of concrete structures. To judge the condition of a concrete structure it is therefore necessary to observe the moisture content and the ph-value in the material. Within the collaborative research centre Life Cycle Assessment of Structures via innovative Monitoring the authors have developed fibre optical moisture- and ph-sensors for an in-situ measurement system. Ease of use, trouble free behaviour, high resistance against chemical attack, low loss and low costs are the main advantages of a fibre optical system. Up to nine sensors can be connected to the in-situ measurement system for automated data analysis. First sensors have been attached to a concrete test structure, which is being exposed to acid to induce a faster ageing. The measurement is still in progress.