Band 23, Heft 1 -

This study deals with the effect of using different silicic acid ethyl esters (SAE) on diverse sandstones and to estimate their influence on the properties of the treated stones. Prismatic samples of Baumberger Sandstone (BST), Sander Sandstone (SST) and Nievelsteiner Sandstone (NST) with the dimensions 50 mm×50 mm×100 mm were treated with three different consolidating agents based on silicic acid ethyl ester (KSE 100, KSE 300, KSE 510) in three different procedures (vacuum, 1- and 5- time impregnation). The aim of this study is to demonstrate that differences in application, for instance varying stone consolidation agents, other treatment procedures as well as using sandstone samples with different binders (BST: calcareous, SST: clayey, NST: quartzitic), cause in each case different results concerning the strengthening effect and the success of a consolidation action. Laboratory measurements were performed on treated and untreated material in order to estimate the effectiveness of stone consolidation actions. To detect the influence of subsequent treatment procedures, water vapour diffusion resistance (WVDR) and capillary water absorption (CWA) measurements were carried out. Furthermore, the effectiveness of a stone consolidation was analysed by measuring ultrasound velocity, compressive strength, flexural strength, bond strength by pull-off and the porosity of the stone samples. Due to varying treatment procedures the investigated sandstones showed different petrophysical and mechanical properties (no strengthening effect up to “over-treating”). Different treatment procedures lead to increasing amounts of strengthening agent in the pore space of the investigated stones and as a result to higher values in WVDR (except BST and NST samples), ultrasound velocity and to an improvement in mechanical strength (except compressive strength of NST). This applies in particular to 1-time, 5-time and vacuum impregnated SST and 5-time treated NST and BST, regardless of the used stone strengthener. On the other hand, these different treatment procedures lead often to a decreased CWA and to a reduction in total porosity. The performed measurements indicate a development in strength in case of 5-time and vacuum treatment, but also an increase of the possibility of sealing the pores, especially for SST samples.

Pigeon droppings are implicated in spoiling and decay of buildings. Several studies have examined the effects and chemistry of accumulations of pigeon droppings under highly localised pigeon roosts. Scant information exists on the impact caused by individual pigeon droppings at perch sites, even though these constitute the majority of bird use in urban areas. This study experimentally examined the processes that affect masonry immediately after pigeon excreta have been voided from the body and what effects discrete, fresh pigeon droppings have on different kinds of sandstone. The experiments demonstrated the susceptibility of freshly deposited excreta to environmental conditions (relative humidity and precipitation). In real-life situations, with pigeon excreta deposited on window ledges, cornices and parapets, the majority of damage would occur within the first two weeks of deposition. After that, the majority of individual droppings would have either dissolved or desiccated to such a degree that they would have rolled off. Much of the observed staining is superficial. While individual bird droppings make a building look dirty, even for months at a time, the effect on the building material is not substantial unless other factors come into play such as colonisation of the excreta by mould or leaching of salts from the excreta.

In 2010 burnt lime blocks were accidentally mixed with limestone concrete aggregates at a Belgian limestone and lime production plant. The contaminated limestone aggregates were used in precast concrete factories. The concrete elements used in several constructions quickly showed pop-outs, caused by swelling of lime nodules. The appearance of pop-outs in suspected constructions was recorded. An extensive experimental program as well as on site observations have been made, to monitor the evolution of the pop-out phenomenon with time. The pop-out evolution in outside exposure conditions is compared to the evolution of pop-outs under inside climatic conditions. Outside, the phenomenon becomes marginal after about 2 years. In inside exposure conditions, the phenomenon still continues after 7 years, be it at a low rate.