Volume 21, Issue 1 -

The Italian standards, formerly NORMAL, define Extraordinary Maintenance as those where a major intervention on the building is carried out, usually referred to as a conservation intervention. These receive much attention from the media thus prompting the interest of NGO and for non-profit organizations which take an interest in funding such projects. Conservation interventions are critical for the preservation of our architectural heritage;however, the trigger for their undertaking, as well as their timing, is mainly determined by political interests. Because of the lack of ordinary maintenance, conservation interventions have to address heightened material deterioration problems thus increasing the complexity and invasiveness of the required operations, as well as an overall higher cost. The most worrisome issue is that once the intervention is completed, the building or monument is considered as being in a stable condition and not requiring any further action. Only in few cases is the most ordinary maintenance regularly carried out but what is neglected is the monitoring, the early identification of those “symptoms” revealing that a problem is present and should be addressed before more damage occurs. The paper uses various examples to illustrate the above points.

Precipitation of calcium carbonate minerals by bacteria, the so-called bacterial carbonatogenesis, is a promising method for the consolidation of decayed stone. Despite extensive laboratory testing that has demonstrated the efficacy of this method, little is, however, known regarding the medium- and/or long-term performance of this bacterial conservation treatment once applied in situ , on stone buildings. Here, we report on the evaluation of the performance of bacterial consolidation treatments applied in three different historical buildings placed in an urban environment and built using a highly porous, easily decayed calcarenite stone. Peeling tape tests show a significant long-lasting (up to four years) strength improvement following treatment with either a Myxococcus xanthus bacterial culture or a sterile nutritional solution that selectively activates the carbonatogenic bacteria inhabiting the stone. Total color changes, measured before and after treatment using a spectrophotometer, are systematically below the acceptable value of Δ E ≤ 5. Culture-dependent analysis of the microbiota shows that 100% of the culturable bacteria collected before and after treatment is carbonatogenic, and the total count of fungi spores remains constant or diminishes, while the population of acid-producing bacteria decreases over time after treatment application. Culture-independent microbial analyses show that no deleterious microbiota develops after treatment, being carbonate-producing Proteobacteria, Firmicutes and Actinobacteria the most abundant phyla both before and after treatment. Overall these results show that the in situ application of the bacterial consolidation method shows no detrimental side effects and is highly effective in the medium- and long-term.

Colors are frequently defined by three points on the L * a * b * coordinates of the CIELAB color space, and the distance between two colors can be expressed as the total color difference Δ E . In particular with respect to reproducibility of print media color differences are an important parameter, as well as for car finishes and textile dyes. Color changes are also the result of ageing and weathering which is an issue for art objects and in the building and restoration sector. However, the subjective perceptibility of color differences depends on numerous factors and general thresholds are difficult to define. This study aimed therefore on defining tolerance levels for color changes in dependence of color tones and color tone combinations as well as their resolution. In total 30 test persons evaluated samples, which had been painted with acrylic artist colors with defined color differences (Δ E = 0–7). The test subjects realized color differences already at Δ E = 1–4 for the highest resolution. Threshold values have been identified for different tones as well as the effect of interdependencies between tones and the level of color heterogeneity between adjacent areas.

Abstract: Mass consolidation of stone and brick masonry is considered, with exclusion of pure crack repair. Damage and specific failure mechanisms in multiple leaf masonry are presented. The aims of consolidation are explained, and the inherent advantages and disadvantages of distinct strengthening and consolidation techniques are given. An historical overview of consolidation methods and of development of consolidation grout materials is given, which explains how technology evolved to the actual procedures.

Development of mineral grouts for consolidation and strengthening of historical masonry was discussed in Ref. [1]. The properties of the injection grout must counteract the elements that initiate the failure mechanism of multiple leaf historical masonry and lead to its collapse. This paper presents a macro-approach to model the structural behavior of three-leaf masonry. A global approach is used, based on the properties and the behavior of the external leafs, in combination with the properties and behavior of the central core of the three-leaf wall. Evaluation of the models is made by comparison with experimental data.