NDT-control of injection of an appropriate grout mixture for the consolidation of the columns foundations of Our Lady’s Basilica at Tongeren (B).

With a grant of the Flemish government (IWT) and the support of a group of Belgian companies involved in restoration activities, a research project started in 2005, trying to control grout injections in masonry in a more reliable way. The study of appropriate grout mixtures and the application of geo-electrical measurements for restoration purposes are both parts of this research project. This paper discusses the analysis of the data, obtained during an on site measuring campaign, carried out to evaluate the injections of the columns’ masonry foundations of Our Lady’s Basilica at Tongeren (Belgium). The development of an appropriate grout for the injection is also briefly discussed in this paper. The selections of the grout composition, as well as the design of an effective injection procedure are based on laboratory and on site tests. It is demonstrated that a grout containing a specific mixture of slaked lime and hydraulic cement performed excellently within the preset boundary conditions. 554 Structural Analysis of Historical Constructions • Integration of non-destructive techniques Secondly the integration of non-destructive techniques in the field of grout injections will be studied, not only for the evaluation of the quality of the deteriorated or injected massif (masonry or concrete) before and after injection. The aim is to develop the NDT-technology that hopefully makes it possible for on-line surveying of grout injections. The benefit is the possibility to alter the injection parameters during the injection itself so that the desired injection result can be obtained. Geo-electrical survey of masonry already proved to be a reliable non-destructive tool for this purpose (Janssens 1993, Keersmaekers 2003, Keersmaekers et al. 2004, Venderickx 2000, Van Rickstal et al. 2003) • Test programme The last objective of the project, indispensable as a support for the first goal, is a thorough investigation of the physical, physical-chemical, chemical and mechanical properties of different grout compositions and the correlation between the different parameters responsible for these properties. Special attention is hereby given to the bending strength of mineral grout mixtures. 2 CASE STUDY: OUR LADY’S BASILICA AT TONGEREN (B)