Evaluation of the Durability of Hydrophobic Treatments on Concrete Architectural Heritage
Abstract The protection of historical concrete structures is a challenge for the coming years. Hydrophobic treatment may reduce the deterioration process while providing protection against water penetration. Existing commercial products - mainly silane or siloxane in either water or solvent based formulations - were submitted to different ageing processes including UV radiation, dry-wet cycles, thermal shocks, freeze-thaw cycles, carbonation and their effectiveness has been evaluated on the basis of contact angle, vapour and chloride permeability and, capillarity water absorption. The results obtained clearly show that hydrophobic treatments display a good behaviour under the main ageing conditions.
EXPERIMENTAL CHARACTERISATION OF INJECTION GROUTS
13 The present paper put forward a new hydrophobic silica fume and assesses their contribution 14 on the performance improvement of grouts for stone masonry consolidation. The experiments 15 were conducted using different dosages of hydrophobic silica fume with natural hydraulic 16 lime grouts in the presence of a polycarboxylate-based high range water reducer. Results 17 revealed that the effects of hydrophobic silica fume on properties of natural hydraulic lime 18 grouts optimise the use of ordinary silica fume. Remarkable rheological performance was 19 obtained in the presence of hydrophobic silica fume: the plastic viscosity and yield stress were 20 reduced compared with the ordinary silica fume. On mechanical strength aspects it was found 21 that hydrophobic silica fume slightly affect the flexural and compressive strength; however 22 the values obtained are suitable for the old stone masonry consolidation purposed. It was also 23 observed that water capillarity was substantially reduced, namely due to the water repellent 24 behaviour of hardened grouts. This study suggests that the promising effectiveness of this new 25 silica fume on injection grouts open the way to be used in many other applications. 26
Investigation methods utilising combined NDT techniques
This paper presents a two-stage method of approach for selecting repair methods for concrete structures suffering from various common problems. It is pointless to begin the repair process unless the deterioration processes have been identified correctly. The first stage is based on a rapid-scan visual assessment, often including limited sampling in areas of obvious damage, from which several areas can be chosen for more detailed investigation. The second stage is a detailed diagnostic survey, relying heavily on non-destructive testing (NDT) techniques. By combining at least two NDT techniques, the reliability of the information obtained can be maximised. Based on the authors' experience, guidance is given about the techniques that are most suitable for use in particular situations and in combined tests. This guidance is summarised in a table, recommending combinations of methods for various civil engineering applications, for the following materials: (1) testing concrete; (2) screeds and toppings; (3) walls and roofs; (4) buried objects; and (5) machinery. Only when the survey data have been processed is it possible to establish any variations in the behaviour of the structure on different elevations, levels, and elements. It is then possible to develop a prognosis, and plan effective repair strategies.