Combadura y dilatación de paneles de piedra natural: ensayo y evaluación de mármol y caliza

Natural stone has been used as a building material for centuries. In the past, load bearing members were made of entirely of stone, but in the last 50 years new processing techniques have made the production and use of thin facade cladding a profitable venture. Unfortunately however, marble facades on buildings in Europe and elsewhere have undergone severe deterioration. The EC-financed TEAM project (2000-2005) studied the bowing observed on marble facades in both cold and warm climates. TEAM’s main objectives were to understand and explain the expansion, bowing, and strength loss mechanisms governing the decay of marble- and limestone-clad facades, and to draft new European standards to prevent the use of marble and limestone poorly suited to outdoor cladding. A survey of some 200 buildings afforded a clear picture of the geographical, geological and climatic scope of the problem. Detailed case studies of six buildings resulted in a facade assessment methodology that included a monitoring system and risk assessment. Both laboratory and field research was conducted on almost 100 different types of stone from different countries and in place in different climates. The outcome was the determination of the decay mechanisms and critical factors. Two test methods and respective precision statements, one for bowing and the other for irreversible thermal expansion in high humidity conditions, were prepared for submission to CEN TC 246.La piedra natural se ha empleado como material de construcción durante siglos. En el pasado, se solía utilizar en elementos de carga, pero en los últimos 50 años las nuevas técnicas de procesamiento han permitido que sea comercialmente rentable producir y utilizar revestimientos para fachadas de espesor reducido. Desafortunadamente, numerosas fachadas de mármol de edificios tanto en Europa como fuera de ella han sufrido graves problemas derivados del deterioro de la piedra. El proyecto TEAM (2000-2005), financiado por la CE, ha tratado el problema de la combadura de determinados tipos de mármol observado en fachadas situadas tanto en climas cálidos como en climas fríos. Los principales objetivos del proyecto TEAM eran los de conocer y explicar los mecanismos de la dilatación, la combadura y la pérdida de resistencia que provocaban la degradación de las fachadas revestidas de mármol y caliza, así como prevenir el uso de mármol y caliza inadecuados mediante la presentación de borradores de nuevas normas europeas. La inspección de aproximadamente 200 edificios ofreció una idea clara del alcance del problema en términos geográficos, geológicos y climáticos. El estudio detallado de 6 edificios dio como resultado una metodología para la evaluación de fachadas que incluía un sistema de seguimiento y la evaluación de riesgos. Se investigaron tanto en el laboratorio como sobre el terreno casi 100 tipos distintos de piedra procedentes de diferentes países y utilizados en distintos climas, lo que permitió explicar los mecanismos de degradación y los factores que más influyen en ella. Se prepararon dos métodos de ensayo con sus correspondientes declaraciones de precisión parra enviar al CEN TC 246: uno sobre la combadura y otro sobre la dilatación térmica irreversible en condiciones húmedas

Time-Dependent Influence of ASR and Cracking on the Physical and Mechanical Properties of Laboratory-Accelerated Reinforced Slabs with Distinct Exposure Conditions

The impact of alkali-silica reaction (ASR) on the physical, mechanical, and structural behaviour of ASR-damaged structures in service is time-dependent. While destructive examinations of ASR-damaged structures in service offer a valuable snapshot of the structure’s condition at a particular point in the ASR deterioration process, they cannot provide a complete understanding of how the propagation of ASR cracking affects the physical, mechanical, and structural behaviour of the structure over time. To better understand the influence of ASR on structures affected by this deleterious reaction, it is essential to conduct laboratory experiments that simulate the progress over time. These experiments can provide insights into the impact of ASR cracking on the physical and mechanical behaviour of reinforced slabs. To assess ASR-affected bridge slabs in Denmark, it is crucial to consider the time-dependent impact of external alkali supply in the assessment methodology. While the equivalent Na2O content in older Danish bridge slabs is believed to be below the threshold value for initiating ASR, it is essential to recognize that external alkali sources, such as de-icing salts, may be critical for initiating ASR damages in reinforced bridge slabs in service. To address this gap, this study aims to improve understanding of the time-dependent influence of ASR on the physical and mechanical properties of reinforced slabs through accelerated laboratory exposure. Seven reinforced slabs were cast and stored under accelerated conditions, with three exposed to saturated NaCl solution from the top surface to simulate external alkali supply, two with initial high alkali content boosted by NaOH, and two as control slabs. Internal and surface expansion measurements were periodically taken, and cores were drilled and tested in compression. Fluorescent epoxy was impregnated into the cores to evaluate ASR crack extent and orientation.</div