Characterization and damage of brick masonry

Series : Building pathology and rehabilitation, ISSN 2194-9832, vol. 2Clay brick is among the oldest used masonry materials. Given the technological evolutions since the industrial revolutions, old brick are much dif-ferent from todays’ bricks. This chapter provides a review on the chemical, physi-cal and mechanical properties of mortar, brick and masonry. In addition, a discus-sion on the possible causes of damage and the usage of expert systems in building diagnostics is also given

Damage in porous media due to salt crystallization

We investigate the origins of salt damage in sandstones for the two most common salts: sodium chloride and sulfate. The results show that the observed difference in damage between the two salts is directly related to the kinetics of crystallization and the interfacial properties of the salt solutions and crystals with respect to the stone. We show that, for sodium sulfate, the existence of hydrated and anhydrous crystals and specifically their dissolution and crystallization kinetics are responsible for the damage. Using magnetic resonance imaging and optical microscopy we show that when water imbibes sodium sulfate contaminated sandstones, followed by drying at room temperature, large damage occurs in regions where pores are fully filled with salts. After partial dissolution, anhydrous sodium sulfate salt present in these regions gives rise to a very rapid growth of the hydrated phase of sulfate in the form of clusters that form on or close to the remaining anhydrous microcrystals. The rapid growth of these clusters generates stresses in excess of the tensile strength of the stone leading to the damage. Sodium chloride only forms anhydrous crystals that consequently do not cause damage in the experiments

Анализ способов и устройств для уплотнения мелкофракционных шихт

Выполнен анализ способов уплотнения мелкофракционных сыпучих материалов. Предложена схема уплотнения на основе валковых прессов с многоступенчатым уплотнением

Decay Patterns and Damage Processes of Historic Concrete: A Survey in the Netherlands

Historic concrete buildings (end of 19th century – 1960s), because of their “experimental” character, require a specific approach to both survey and conservation. Although they were built with empirical approaches, some buildings show a fair state of conservation and resilience –even though they have already exceeded the 100-year threshold– while others of comparable age are in severe need of restoration. As part of the European project CONSECH20, aimed at contributing to the conservation of cultural-heritage concrete buildings, this paper investigates what are the most common types of damage and hypothetical causes, and what direct and non-direct parameters can lead to a faster or slower deterioration of historic concrete in the Netherlands. The research is based on an initial screening study, which will be used as a basis for a larger research among the participant countries. The current research is divided in three phases. Firstly, a selection of 15 case studies from the Netherlands are investigated; the selection was based on criteria of age, state of conservation and type of ownership. Secondly, the history and materials of the buildings are examined. Thirdly, an on-site visual survey is performed per each building, with pre- design templates, to identify types of damage, extent and severity. The data is then analysed combining different factors with a calculated index of severity. Results are discussed and contrasted to provide further clarification of the degradation of historic concrete. A fourth phase, not discussed in this paper, will use this methodology in a broader context, with a larger number of case studies in different countries. The results indicate that the majority of types of damage are related to corrosion, being the hypothetical cause carbonation-induced corrosion. The outcomes of the investigation point out that the factors with a higher impact on the durability are the environment, the use and maintenance of the buildings, the existence of a sacrificial plaster in exposed elements, and the type of ownership. Considering the limited number of buildings, the conclusions presented in this paper will be further contrasted with a larger number of case studies

Recommendation of RILEM TC 271-ASC: New accelerated test procedure for the assessment of resistance of natural stone and fired-clay brick units against salt crystallization

This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests

Recommendation of RILEM TC 271-ASC: New accelerated test procedure for the assessment of resistance of natural stone and fired-clay brick units against salt crystallization

This recommendation is devoted to testing the resistance of natural stone and fired-clay brick units against salt crystallization. The procedure was developed by the RILEM TC 271-ASC to evaluate the durability of porous building materials against salt crystallization through a laboratory method that allows for accelerated testing without compromising the reliability of the results. The new procedure is designed to replicate salt damage caused by crystallization near the surface of materials as a result of capillary transport and evaporation. A new approach is proposed that considers the presence of two stages in the salt crystallization test. In the first, the accumulation stage, salts gradually accumulate on or near the surface of the material due to evaporation. In the second, the propagation stage, damage initiates and develops due to changes in moisture content and relative humidity that trigger salt dissolution and crystallization cycles. To achieve this, two types of salt were tested, namely sodium chloride and sodium sulphate, with each salt tested separately. A methodology for assessing the salt-induced damage is proposed, which includes visual and photographical observations and measurement of material loss. The procedure has been preliminarily validated in round robin tests

A new accelerated laboratory test for the assessment of the durability of materials with respect to salt crystallization

The RILEM Technical Committee 271-ASC was set up in 2016 with the aim ofdeveloping an improved procedure for the assessment of the durability of porous building materials, such as brick and natural stone, against salt crystallization, accelerating the deterioration process without significantly altering its mechanism.The test procedure developed by the TC 271-ASC proposes a new approach to salt crystallization tests. It starts from the consideration that it is necessary to accumulate a certain amount of salt to activate the damage. Thus salt damage can be seen as a process developing in two phases: accumulation and propagation. Based on this approach, a new salt crystallization test procedure has been defined, consisting of two phases: a first phase, in which salts are introduced in the material and accumulate close to the evaporation surface, followed by a second phase, in which damage propagates because of repeated dissolution and crystallization cycles induced by re-wetting with liquid water and by relative humidity (RH) changes.In this paper the procedure is described and the reasons for the choices made are elucidated. The procedure has been tested on two types of limestone and, at the moment of writing, is being validated in a round robin test carried out on 9 different substrates and involving 11 laboratories. Based on the results of the round robin test, the procedure will be fine-tuned.Heritage & Technolog

Keuze van steenreparatiemortels voor historische gebouwen: geen eenvoudige zaak

Steenreparatiemortels worden gebruikt voor het aanvullen van een ontbrekend deel van het originele materiaal. Dat laatste kan verloren zijn gegaan door een mechanische belasting of door bijvoorbeeld aantastingsprocessen waarbij vocht, vorst en of zouten een rol spelen. Het ontbrekende deel wordt dan aangevuld met een mortel met een passende kleur en textuur. De gebruikte mortel is als het ware ‘kneedbaar’, zodat aanpassing aan de gewenste vorm eenvoudig mogelijk is. Gewoonlijk gaat het om kleinschalige ingrepen, waarbij individuele stenen, details en delen van ornamenten of beelden worden behandeld. In de kleinschaligheid, de individuele benadering en de ‘boetseerbaarheid’ liggen de voornaamste verschillen met andere ingrepen waarbij mortel wordt toegepast, zoals hervoegwerk, vervangen van pleisterwerk en dergelijke