Experimental analysis of micro-cracks on the change of moisture transport properties of AAC

In this paper, series of experiment measurements is carried out in order to study effect of freeze/thaw loading on the change of moisture transport properties of autoclaved aerated concrete. The samples were subjected to 15, 30 and 45 freeze/thaw cycles and subsequently basic physical properties, pore size distribution and water vapor and liquid water transport properties were investigated. The results showed significant changes in material properties of the material. The results of this research can be further implemented into computational models in order to bring the simulation results closer to the reality

Assessment of Cumulative Damage of Selected Building Envelopes Exposed to Various Environmental Effects

Hygrothermal performance of building envelopes based on three different building materials (solid brick, high performance concrete, aerated autoclaved concrete) is assessed under climatic conditions of Prague and Atlantic City. Main objective of the paper is to evaluate the influence of cumulative damage, which was induced by means of natural weathering in 2012- 2015 period, on the long-term performance. The performance is assessed using various measures, namely time-of-wetness function, number of freeze/thaw cycles, and annual amount of energy transmitted through the envelope. The results show that thermal performance of the envelopes gets mostly better after weathering as the annual amount of energy is decreased by ~3.5% in average. On the other hand, time-of-wetness function and number of freeze/thaw cycles increase by ~24.1% and ~22.0%, respectively. Based on the results summary it can be concluded, that cumulative damage of materials has an indisputable influence on the hygrothermal performance of building envelopes which might be either negative or positive. A detailed computational assessment is therefore necessary, incorporating not only reference, but also weather-affected material properties

Equivalent thermal diffusivity of natural and recycled aggregate concrete at temperature up to 350 ⁰C

The paper presents the evolution of equivalent thermal diffusivity with temperature of concretes with natural coarse aggregates and recycled concrete aggregates. Thermal diffusivity was evaluated based on the temperature measurements made on cylindrical samples using so-called "inverse technique". Thermal diffusivity parameter was estimated for concretes manufactured with different replacement ratios of natural by recycled coarse aggregate (0, 50 and 100 %) produced by crushing the worn-out concrete pavement that was dismounted after exploitation period. The diffusivity of concrete was tested up to 350 ◦C. The progressive decrease of thermal diffusivity was observed, and the lowest D values were obtained for higher recycled concrete aggregates content. The results were presented against the background of other authors results and referred to the D values proposed in EUROCODE 2

Service Life Assessment of Historical Building Envelopes Constructed Using Different Types of Sandstone: A Computational Analysis Based on Experimental Input Data

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure

Salt Damage and Rising Damp Treatment in Building Structures

Salt damage can affect the service life of numerous building structures, both historical and contemporary, in a significant way. In this review, various damage mechanisms to porous building materials induced by salt action are analyzed. The importance of pretreatment investigations is discussed as well; in combination with the knowledge of salt and moisture transport mechanisms they can give useful indications regarding treatment options. The methods of salt damage treatment are assessed then, including both passive techniques based on environmental control, reduction of water transport, or conversion to less soluble salts and active procedures resulting in the removal of salts from deterioration zones. It is concluded that cellulose can still be considered as the favorite material presently used in desalination poultices but hydrophilic mineral wool can serve as its prospective alternative in future applications. Another important cause of building pathologies is the rising damp and, in this phenomenon, it is particularly severe considering the presence of salts in water. The treatment of rising damp in historic building walls is a very complex procedure and at Laboratory of Building Physics (LFC-FEUP) a wall base hygroregulated ventilation system was developed and patented

Comparison of drug prescribing before and during the COVID‐19 pandemic : a cross‐national European study

Purpose: The COVID-19 pandemic had an impact on health care, with disruption to routine clinical care. Our aim was to describe changes in prescription drugs dispensing in the primary and outpatient sectors during the first year of the pandemic across Europe. Methods: We used routine administrative data on dispensed medicines in eight European countries (five whole countries, three represented by one region each) from January 2017 to March 2021 to compare the first year of the COVID-19 pandemic with the preceding 3 years. Results: In the 10 therapeutic subgroups with the highest dispensed volumes across all countries/regions the relative changes between the COVID-19 period and the year before were mostly of a magnitude similar to changes between previous periods. However, for drugs for obstructive airway diseases the changes in the COVID-19 period were stronger in several countries/regions. In all countries/regions a decrease in dispensed DDDs of antibiotics for systemic use (from −39.4% in Romagna to −14.2% in Scotland) and nasal preparations (from −34.4% in Lithuania to −5.7% in Sweden) was observed. We observed a stockpiling effect in the total market in March 2020 in six countries/regions. In Czechia the observed increase was not significant and in Slovenia volumes increased only after the end of the first lockdown. We found an increase in average therapeutic quantity per pack dispensed, which, however, exceeded 5% only in Slovenia, Germany, and Czechia. Conclusions: The findings from this first European cross-national comparison show a substantial decrease in dispensed volumes of antibiotics for systemic use in all countries/regions. The results also indicate that the provision of medicines for common chronic conditions was mostly resilient to challenges faced during the pandemic. However, there were notable differences between the countries/regions for some therapeutic areas

Numerical and experimental analysis of building envelopes based on autoclaved aerated concrete

Disertační práce se zabývá problematikou pórobetonových konstrukcí. V jejím úvodu je nejprve obecně pojednáno o pórobetonu, o jeho složení, výrobě a o jeho historii až po popis současného postavení na trhu. Vlastnosti pórobetonu jsou srovnány s ostatními stavebními materiály. V další části disertační práce jsou popsány experimentální metody, kterými jsou získány jednotlivé materiálové parametry. Jedná se o tepelné transportní a akumulační parametry a o transportní a akumulační parametry vody a vodní páry. Naměřená data poté figurují jako jeden ze vstupních parametrů pro navazující numerické simulace.Numerická analýza je provedena v širokém rozsahu a je stěžejní částí této práce. Nejprve se zaměřuje na tepelně vlhkostní analýzu několika variant pórobetonového obvodového pláště (bez vnější úpravy, s klasickou omítkovou úpravou, se speciální omítkovou úpravou, s vnější tepelnou izolací) za účelem detekce výskytu mrazových cyklů, které mají výrazný podíl na snižování životnosti. Dále je porovnáno tepelně vlhkostní chování pórobetonových obvodových plášťů s běžně dostupnými tepelně izolačními materiály. Na základě těchto výsledků je pak proveden počítačový návrh skladby s vnějším i vnitřním tepelně izolačním systémem za účelem zlepšení životnosti a jsou doporučeny optimální vlhkostní parametry tepelné izolace a dalších vrstev. Na závěr numerické analýzy je pak stanovena energetická bilance jednotlivých variant obvodového pláště a výsledky jsou porovnány s normovým postupem.Presented dissertation thesis aims at problems of autoclaved aerated concrete (AAC) constructions. In the beginning, general information about AAC, such its history, properties, production and current situation on building market are stated. Also comparison with other traditional building materials is presented.In the next part of dissertation thesis, the experimental methods for measuring heat, water and water vapor transport and accumulation parameters are described. Measured data are then used in subsequent numerical analysis.The numerical analysis is performed very widely and is the main part of this thesis. The hygrothermal analysis of several variations of AAC-based building envelope (simple building envelope, building envelope with traditional and special external finish, building envelope provided with external thermal insulation system) is performed in the first step in order to detect presence of freezing cycles during reference year, which can significantly decrease the service life of whole building envelope. In the next step, comparison of hygrothermal performance of AAC-based building envelope provided with several common thermal insulating materials is performed. Based on these results, computer aided design of external and internal thermal insulating systems follows. Main objective of the design is to optimize the service life and recommend the proper hygric properties of thermal insulating material and other layers. Finally, energy balance of several types of AAC-based building envelope is assessed and the results are compared with standard procedures.katedra materiálového inženýrství a chemi