Automatic surveillance system for detection of alkali-silica reactions

Danish Technological Institute has developed an automatic surveillance system that potentially can detect ongoing alkali-silica reactions at an early state and thus reduce the damage caused by the chemical reaction. The surveillance system is currently being tested in a full-scale setup on a highway concrete bridge located in Vallensbæk, Denmark (Figure 1).

Figure 1. A surveillance system for detection of ongoing alkali-silica reactions in concrete structures is currently being tested on a Danish highway bridge (picture on the left). The installed datalogger is seen in the picture to the right.

Alkali-silica reaction is a reaction, which over time causes expansion of aggregates contained in concrete and subsequently can result in severe cracking of structures made of such concrete. A highly alkaline cement paste, reactive silica aggregates and sufficient moisture must be present in the concrete structure to trigger the chemical reaction. In Denmark as well as in other countries worldwide old existing bridges that are known to contain both alkaline cement paste and reactive aggregates exist. Such structures can be potentially threatened by the alkali-silica reaction. In worst case, the alkali-silica reaction can result in the demolition of the structure. 

In the developed surveillance system the chemical reaction is being detected by strain gages that are cast into bore holes made in the structure. The strain measurements together with local temperature and relative humidity measurements are collected by a data-logger that is based on an open source microcontroller Arduino Uno. The microcontroller has been extended with GSM capability that allows to wirelessly transfer the measured data from the bridge to a server for further post-processing and control. The data logger operates on batteries and allow for several years operation on single battery set. Thanks to the automatic surveillance system, any non-periodic long-term changes in deformation of the structure can registered and analysed allowing for early state detection of ongoing alkali-silica reaction.