C. M. Grossi

Soiling of building stones in urban environments

Abstract This paper studies the black soiling rate of building granite, marble and limestones in two urban environments with different climates. Specimens were placed horizontally, sheltered and unsheltered from rainfall. Colour changes were monitored. Changes in L ∗ were utilised to determine the total darkening of the stones and their soiling rate and were compared by statistical analysis. Black soiling depended on the type of stone and exposure. Limestones, mainly, showed a soiling proportional to the square root of the time of exposure. In this case, soiling coefficients could indicate frequency of necessary cleaning. The rest of the selected stones did not show such an evident relationship. The soiling tendency of all sheltered limestones was quite similar and more severe than in marble and granite. Soiling was related to the stone colour, type of voids and surface characteristics. Soiling of unsheltered specimens also seemed to depend on the rainfall conditions (rain periods, intensity, amount, temperature, etc.), which could influence both particle deposition and removal from stone surfaces.

Airborne particulate matter around the Cathedral of Burgos (Castilla y León, Spain)

A methodology to collect and analyse atmospheric particulate matter has been developed at the Cathedral of Burgos (Spain). Particles were collected in a portable particle sampler on carbon layers and stone surfaces. The analyses were undertaken under SEM-EDX by means X-ray mapping and Featurescan (a program for the automated characterisation of particles). To determine their possible sources, particles collected in the sampler and on carbon layers were classified according to their composition, mainly by cluster analysis. Then, they were compared with those deposited on stone surfaces. This classification is useful when a plan of preventive conservation for monuments is to be undertaken. In general, no important differences are observed between the chemical composition of particles directly collected from the atmosphere and those deposited on different substrates. Fine particles present the highest sulphur contents (almost 100%), while calcium is the major element in the medium and coarse particles. Other abundant elements are silicon, chlorine and phosphorus. The number of iron-rich particles is small. The study of the material deposited on carbon layers and stone substrates has confirmed the presence of gypsum in all cases.

NON-DESTRUCTIVE ULTRASONIC PROCEDURE TO EVALUATE IN SITU THE RELATIVE DETERIORATION OF MONUMENTAL STONES: PRELIMINARY RESULTS

To evaluate in-situ the relative deterioration of monumental stones, a non-destructive ultrasonic procedure is under development: ultrasonic waves are introduced into the rock and after travelling through it are processed for evaluation of their Vp, amplitude, duration, energy and count number. The procedure was applied to two Spanish Monasteries, one built with a granodiorite (El Escorial, Madrid, which results are included here) and the other built with sandstone (Sta. Maria de Ripoll, Gerona). Laboratory ageing tests, involving monitoring of the above mentioned ultrasonic parameters, were performed as a basis for interpreting the in-situ measurements. The energy seems to be the most sensitive parameter as an indicator of the rock deterioration, so, the value obtained for a masonry block in the monument can be used to classify the rock into one of preset deterioration groups.

Mechanical Stresses Generated by Crystallization of Salts Inside Treated and Non-Treated Monumental Stones; Monitoring and Interpretation by Acoustic Emission / Microseismic Activity.

The crystallization of salts in building stones is one of the most common and severe deteriorating phenomencndeveloped on Historic Buildings. To evaluate their mechanical effects in treated and non-treated stones, experimental salt crystallization tests and the monitoring of the corresponding acoustic emission / microseismic activity, AE/MS, have been planned. Salt crystallization tests have therefore been performed on a high porosity (30%) limestone used in the building of the Cathedral of Murcia (Spain). Each test consisted of 11 and 20 cycles (for the non-treated and treated specimens, respectively) of immersion of specimens in salt solution (14% Na 2 SO 4 . 10H 2 O) for 4 h., drying in an oven at 60 °C for 14 h. and final cooling at room temperature for 6 h. The treated specimens were consolidated by total immersion in ethyl silicate -Tegovakon V- and protected with a water repellent, oligomeric polysiloxane -Tegosivin HL- 100-, (both from Th. Goldschmidt, FRG). The AE/MS, was monitored in the 100-300 KHz range. The preliminary results show a very different AE/MS behaviour between the non-treated and the treated specimens.

Reactivity of laser-cleaned stones to a SO 2 ageing test

Con el fin de estudiar la reactividad o susceptibilidad frente a un ambiente contaminado de piedras limpiadas con radiacion laser Nd:YAG, se ha sometido una serie de materiales rocosos cementados (calizas) y cristalinos (marmol, granito) a un ensayo de exposicion a atmosfera concentrada en dioxido de azufre. Los efectos producidos en las muestras ensayadas se han valorado en funcion de las variaciones en la morfologia superficial, en el peso y en el color. Se concluye que la aplicacion de radiacion laser a las muestras de piedra seleccionadas no influye, de manera significativa, en la reactividad de estas frente al dioxido de azufre.