Ana Paula Ferreira Pinto

Polyethylene glycol oligomers as siloxane modificators in consolidation of carbonate stones

Abstract The overall performance of alkoxysilanes as stone consolidants is constrained by stone mineralogy (particularly in the carbonate varieties) and by their tendency to crack during drying. In an attempt to overcome these problems, polyethylene glycol “chains” with two carboxylic acid end-groups (PEG-CA) were introduced in siloxane sols obtained by sol-gel chemistry using tetraethoxysilane (TEOS) as precursor. Different pre-condensation degrees (by varying the stirring times of sol-gel reaction: 10 min, 2, and 24 h) and PEG-CA chains with different molecular weights were studied as variables affecting the initial efficacy of the consolidants when applied into a limestone. The sol containing siloxanes with the lowest pre-condensation degree (10 min stirring) was quite susceptible to the carbonate media and thus a poor consolidation was achieved. The sol with the highest pre-condensation degree (24 h stirring) together with the PEG-CA chains with intermediate molecular weight produced significant and uniform strength gains along the stone depth. The consolidation also showed to be highly dependent on the molecular weight of the PEG-CA chains, the PEG-CA with highest molecular weight produced a non-uniform strength increase with potential harmful side effects. The results confirmed the role of carboxylic acid end-groups as efficient sol-gel catalysts and their ability to be incorporated into the silica matrix in the presence of carbonate stone.

Reaction to Fire of Existing Timber Elements Protected With Fire Retardant Treatments: Experimental Assessment

Fire safety is an important issue of building safety, especially when the building’s fire load contents enhance the risks of fire deflagration. When existing timber structures are involved, the most usual way to improve its reaction to fire is to treat wood with fire retardants. This study focuses on the surface protection of existing timber roof structures against fire, through the use of fire retardant (FR) treatments applied on site. An experimental investigation was carried out to study the effect of FR treatments on timber reaction to fire, with a special emphasis on timber members with biological deterioration and previously treated with preservative products. The behaviour and effectiveness of intumescent and non-intumescent treatments was also investigated. The study showed that the application of FR treatments improved the reaction to fire of timber, even in the presence of previous preservative treatments. However, the choice of the specific FR treatment should take into account the substrate conditions. In addition, test results suggest that protection systems involving multi layers (intumescent and non-intumescent) with different functioning modes each are likely to have a good global performance on the protection of timber elements against fire.

In Situ Techniques for the Characterisation of Rendering Mortars

Compressive strength, porosity and two “in situ” techniques (ultrasonic velocity and rebound hardness test) are used for the characterisation of several aerial, hydraulic lime-based and cement-based mortars. Prismatic specimens and mortars applied as a brick render are used for the characterisation. A comparative analysis of the “in situ” test results and compressive strength is performed and the relationship between porosity and ultrasound velocity is analysed. A satisfactory relationship between the porosity and ultrasound velocity values is found and this indicates the possibility of estimating porosity from ultrasound velocity. The relationship between ultrasound velocity, rebound values and compressive strength emphasizes the potential of the “in situ” test methods for characterisation of mechanical properties of mortars.