Restoration of Buildings and Monuments

The articles presented in this issue deal with different aspects of restoration of historic monuments at urban, building and materials level through three case studies, and a review work on bioconsolidation of stone masonry. In the restoration of historic monuments one of the main challenges of the architect is to give a new function and identity to the monument, which needs to be appreciated and well perceived by the society. The first article “Revitalisation of the ruin.s of the Abbey-Tower at SintTruiden” reports a case study on the restoration of a tower conceived to be a key element between the town and the abbey site in Sint-Truiden in Belgium. The authors, D. Van Gemert and K. Brosens as the engineers and H. van Meer as the architect of this restoration project, reflect how societal sense can change the perception and appreciation of restoration decisions, and how a right reconciliation between monument, society and urban texture can lead to a successful restoration for the city by making the monument accessible and visible to the public. This can only be done with the active involvement of all parties of local society, local authorities, historians, technicians, architects and engineers in the restoration project. The presented case study represents a nice example on how a monument can be integrated successfully in the built and social environment so that it will contribute to the urban identity and its sustainable development. Another crucial item, which must be taken into consideration in the restoration of historic monuments, is the structural interaction between building and foundation. The second article presented by Van Gemert et al. reports structural deformations induced by the earlier foundation interventions that were performed inappropriately as part of an earlier restoration project in 1949–1950 as well as by non-balanced forces from the vaults of St Martin church at Meise in Belgium. A concrete footing placed in this earlier restoration under the total length of the south wall of the nave of the church was discovered as a result of archaeological excavations performed preceding the planned foundation works. Besides inappropriate execution of refilling of masonry joints with cement mortar has been identified as one of the main reasons for the observed cracks and deformations. Based on these findings, the authors have adapted a global restoration concept that was strongly simplified to consolidate the foundation, masonry and vaults. In the third article, another case study is reported on the materials level. Tarek Nazel has investigated the characteristics and damage problems of main construction materials of limestone, brick and mortar used in the construction of Sharaf Al-Din Mosque. This historic monument, dating back to the 14 century, represents an important example of Cairo’s Islamic historic architecture composed of polychrome technique with alternating courses of different building materials. However, the current state of material damages indicates that the Mosque is in need of intervention. The materials suffer from salt efflorescence and sub-florescence. Halite originates from the limestone as a natural impurity. Gypsum was found in the mortar while ettringite precipitated on brick boundaries due to building additions using Portland cement concrete. This clearly demonstrates incompability of cement with historic materials and the damage it is causing to them. The author suggests some intervention actions as a part of preventive conservation for the historic monument. Calcium carbonate precipitation by biological factors or carbonation through biomineralization, which occur in nature in many biological processes, have inspired many researchers to mimic this process in the conservation of carbonate stone monuments and historic building materials. The review paper “Bioconsolidation of Stone Monuments” by Tarek Nazel presents the main aspects of carbonation process through biomineralization known as Microbial Induced Calcium Carbonate Precipitation (MICCP) as well as a critical look to the current state of research and future challenges in the field.