Evaluation of brick resistance to freeze / thaw cycles according to indirect procedures

U radu je ispitana otpornost opeke direktnim postupkom te nekim indirektnim postupcima sukladno svjetskoj literaturi i propisima. Zahtjevi za indirektnu procjenu otpornosti opeke na cikluse smrzavanja/odmrzavanja postavljeni prema kanadskim i američkim normama su se pokazali neprimjenjivima kao i mogućnost ocjene na temelju strukture pora. Uočena je povezanost sposobnosti upijanja/otpuštanja vode i otpornosti opeke na cikluse smrzavanja/odmrzavanja.The brick resistance was tested in the paper by direct method, and according to some indirect procedures presented in international literature and regulations. Requirements for indirect estimation of brick resistance to freeze / thaw cycles set by Canadian and U.S. standards have proven to be inapplicable, and the same applies to estimation based on pore structure. A connection between absorption/ desorption of water and brick resistance to freeze/thaw cycles was observed

Evaluation of brick resistance to freeze / thaw cycles according to indirect procedures

U radu je ispitana otpornost opeke direktnim postupkom te nekim indirektnim postupcima sukladno svjetskoj literaturi i propisima. Zahtjevi za indirektnu procjenu otpornosti opeke na cikluse smrzavanja/odmrzavanja postavljeni prema kanadskim i američkim normama su se pokazali neprimjenjivima kao i mogućnost ocjene na temelju strukture pora. Uočena je povezanost sposobnosti upijanja/otpuštanja vode i otpornosti opeke na cikluse smrzavanja/odmrzavanja.The brick resistance was tested in the paper by direct method, and according to some indirect procedures presented in international literature and regulations. Requirements for indirect estimation of brick resistance to freeze / thaw cycles set by Canadian and U.S. standards have proven to be inapplicable, and the same applies to estimation based on pore structure. A connection between absorption/ desorption of water and brick resistance to freeze/thaw cycles was observed

A CONTRIBUTION TO DURABILITY OF MASONRY STRUCTURES

Rad se bavi problemom otpornosti materijala zidanih konstrukcija te ziđa na cikluse smrzavanja i odmrzavanja. Istražen je utjecaj režima pečenja opeka na njihovu otpornost na cikluse smrzavanja i odmrzavanja te je zaključeno kako duži period zadržavanja opeka u peći na najvišoj postignutoj temperaturi rezultira boljom otpornošću opeka na cikluse smrzavanja i odmrzavanja te kako način izrade opeke i režim njezina pečenja utječu na sustav pora koji će se razviti u opeci tako da sličan sustav pora razvijaju opeke izrađene na isti način. Na 16 serija opeka su određeni sljedeći parametri: tlačne čvrstoće opeka prije i nakon izlaganja ciklusima smrzavanja i odmrzavanja te njihovi omjeri, koeficijent zasićenja, specifična površina BET metodom, udio pora pojedine veličine te ukupni udio pora, ukupni volumen pora i srednji radijus pora pomoću živinog porozimetra, ukupni udio pora hidrostatskim vaganjem, Maage koeficijent, koeficijent početnoga upijanja, vodoupojnost te je praćeno upijanje i otpuštanje vode kod opeka u vremenu od 24 h. Temeljem niza pobrojanih parametara matematičkim putem provjerena je mogućnost ovih parametara da klasificiraju opeku na otpornu i neotpornu na cikluse smrzavanja i odmrzavanja te potražen matematički model koji opisuje omjer tlačnih čvrstoća opeka nakon i prije izlaganja ciklusima smrzavanja i odmrzavanja. Zaključeno je da su vodoupojnost i koeficijent otpuštanja vode iz opeke u vremenu 180-360 minuta izvrsni klasifikatori za klasifikaciju opeke na otporne i neotporne. Za odabrane opeke provedena je nanotomografija kojom se dobio uvid u udio otvorenih i zatvorenih pora u opeci te je uočeno kako opeke s većim udjelom otvorenih pora u ukupnom udjelu pora imaju veći omjer tlačnih čvrstoća nakon i prije smrzavanja, a time i bolju otpornost na cikluse smrzavanja i odmrzavanja. Ovo u nastavku znači da osim distribucije pora bitnu ulogu kod otpornosti opeke na cikluse smrzavanja i odmrzavanja ima i vrsta pora. U nastavku je istražen utjecaj ciklusa smrzavanja i odmrzavanja na mortove različitih sastava; vapnene, produžne, cementne i cementne s dodatkom aeranta u kojima su volumno varirani omjeri komponenata unutar pojedine skupine. Najbolju otpornost u kontekstu omjera čvrstoća nakon i prije ciklusa smrzavanja i odmrzavanja pokazali su cementni mortovi sa aerantom, potom cementni mortovi dok su se uzorci vapnenog i produžnog morta raspali prilikom izlaganja ciklusima smrzavanja i odmrzavanja te im nije bilo moguće odrediti otpornost. Odabranom cementnom mortu te dvjema serijama opeka određena su toplinska svojstva prije i nakon izlaganja ciklusima smrzavanja i odmrzavanja te je uočeno da ciklusi smrzavanja i odmrzavanja negativno utječu na toplinsku provodljivost te da ona raste nakon izlaganja uzoraka tom djelovanju što znači da materijali nakon ciklusa smrzavanja i odmrzavanja osim na mehaničkim svojstvima gube i na svojstvu toplinske izolacije. Napravljeno je ziđe od odabranih opeka i odabranoga morta kojem je ispitivanjem određena početna posmična čvrstoća prije i nakon smrzavanja te računski određen koeficijent prolaska topline prije i nakon smrzavanja te isti stavljeni u omjer. Zaključeno je da ciklusi smrzavanja i odmrzavanja slabe kako mehanička tako i toplinska svojstva ziđa što u nastavku znači veću potrošnju energije i veće troškove grijanja u objektima te veću godišnju emisiju CO2. Ovo ukazuje na potrebu za bržom i cijenom pristupačnijom metodom za ocjenu otpornosti opeke, kao većinskoga dijela zidanih građevina, na cikluse smrzavanja i odmrzavanja te se temeljem u radu provedenog istraživanja kao odabrana metoda preporučuje ispitivanje vodoupojnosti. Ispitivanje vodoupojnosti je jednostavna metoda kojom bi i sami proizvođači opečnih zidnih elemenata mogli provjeriti otpornost opeke na cikluse smrzavanja i odmrzavanja u okviru kontrole tvorničke proizvodnje.The paper deals with durability of materials in wall structures and masonry with respect to freeze and thaw cycles. It also examines the effect of the selected brick firing regime on the resistance of bricks to freeze and thaw cycles. Results of the examination lead to the conclusion that the longer a brick is fired in the kiln at a maximum achieved temperature, the better is its resistance to freeze and thaw cycles. Another conclusion is that the brickmaking method and its firing regime also affect the pore system developed and that the pore system will be more similar in bricks made using the same method. The following parameters were determined based on 16 batches of bricks: compressive strength of bricks before and after exposure to freeze and thaw cycles and ratios of measured values; saturation coefficient; specific surface area determined by applying the BET method; portion of pores of particular sizes and total portion of pores; total pore volume and average pore radius measured by a mercury porosimeter; total portion of pores measured based on hydrostatic weighing; Maage’s index; initial absorption coefficient and water absorption. In addition, water absorption and desorption of bricks was monitored through a 24-hour period. Based on said parameters, the possibility of their use for the purposes of classifying bricks as resistant or non-resistant to freeze and thaw cycles was mathematically calculated. In addition, a mathematical model describing the ratio of compressive strength values of bricks, measured before and after exposure to freeze and thaw cycles, was also sought. It was concluded that water absorption and the water desorption coefficient of bricks, measured for a period of 180-360 minutes, are excellent classifiers for classification of bricks as resistant or non-resistant. Nanotomography was performed on selected bricks to gain an insight into the portion of open and closed pores in bricks. It was determined that bricks with a higher portion of open pores relative to the total portion of pores have a higher ratio of compressive strength values measured after and before the freezing cycle and are, therefore, more resistant to freeze and thaw cycles. What that indicates is that, in addition to pore distribution, the type of pore also plays a significant role in the resistance of bricks to freeze and thaw cycles. Furthermore, the paper examined the effect of freeze and thaw cycles on different types of mortars: lime; lime-based; cementitious; and cementitious mortar with added air-entraining agent. Ratio of the volume of components in said types of mortars was varied for each individual group. The highest resistance, in terms of compressive strength ratio of values measured before and after the freeze and thaw cycle, was measured in cementitious mortars with added air-entraining agent. They were followed by cementitious mortars, while the lime and lime-based mortar samples decomposed during exposure to freeze and thaw cycles, thus making their resistance impossible to determine. Thermal characteristics of the selected cementitious mortar and of two batches of bricks were determined before and after exposure to freeze and thaw cycles. It was observed that freeze and thaw cycles have a negative effect on thermal conductivity and that it increases after the samples are exposed to such processes. This means that both the mechanical and thermal insulation characteristics decrease after the materials are exposed to freeze and thaw cycles. Masonry was constructed by using selected bricks and mortar and, through tests, its initial shear strength was measured before and after exposure to the freeze cycle. In addition, the heat transfer coefficient was calculated before and after the freeze cycle, after which a comparison of these two values was made and their mutual ratio determined. The conclusion was that freeze and thaw cycles diminish both the mechanical and thermal characteristics of masonry, which, in turn, leads to greater energy consumption and higher heating costs in buildings, as well as higher annual CO2 emissions. This points to the need for a faster and more economical method of evaluating the resistance of bricks to freeze and thaw cycles, because masonry structures are, for the most part, constructed from bricks. Based on the research conducted for the purpose of this paper, the recommended method is water absorption testing. Water absorption testing is a simple method which could be used by manufacturers of clay masonry units within their production quality control in the factory to verify the resistance of bricks to freeze and thaw cycles

Influence of the size and type of pores on brick resistance to freeze-thaw cycles

This paper estimates the frost resistance of bricks using the ratio of compressive strength before freezing to compressive strength after freezing to describe the damage degree of bricks being exposed to freeze-thaw cycles. In an effort to find the ratio that clearly distinguishes resistant bricks from non-resistant bricks, the authors attempted to establish the correlation between the ratio and Maage factor as a recognized model for assessing brick resistance. To clarify the degree of damage of individual bricks, the pore size distribution has been investigated by means of mercury porosimetry. Additionally, micro computed X-ray tomography (micro-CT) has been employed to define the influence of the type of pores (open or closed) and their connectivity on the frost resistance of bricks. According to the results, it can be concluded that there is a good correlation between the Maage factor and the ratio of pre- to post-freeze-thaw cycle compressive strengths, and that the latter ratio strongly correlates with the percentage of large pores (≥3 mm) in the brick. If such a correlation could be confirmed in a larger sample, then the ratio of pre- to post-freeze-thaw cycle compressive strengths could be used as a new method for assessing brick resistance to freeze-thaw cycles and it would be possible to determine the minimum percentage of large pores required to ensure the overall resistance of brick to freeze-thaw conditions. The complexity of the problem is, however, evidenced by the fact that no clear connection between the type (open versus closed) or connectivity of pores and the frost resistance of bricks could be revealed by micro-CT

Influence of Freeze/Thaw Cycles on Mechanical and Thermal Properties of Masonry Wall and Masonry Wall Materials

In this study, the influence of freeze/thaw cycles on the mechanical and thermal properties of bricks and mortar as building parts of masonry walls, as well as the influence on the masonry wall itself is investigated. At the material level, the influence of freeze and thaw cycles on the mechanical and thermal properties of masonry components (bricks and mortar) was investigated; at the construction level, the influence of freeze and thaw cycles on the mechanical and thermal properties of a masonry wall was studied. To study the influence of freezing on the energy demand characteristics of masonry buildings, in terms of energy conservation and greenhouse gas emission, a case study was investigated on a typical structure of a historical building located in Croatia, that had undergone a process of energy certification. The applied freeze/thaw regime negatively influenced the compressive strength and the thermal properties of bricks and mortar, as well as the mechanical and thermal properties of the wall. Considering the thermal properties of the material before and after its exposure to freeze/thaw cycles, we concluded that the annual energy consumption, the heating costs, and the CO2 emission of a family house could increase up to 3.7% after frost action in the studied case

Pore Structure as a Response to the Freeze/Thaw Resistance of Mortars

In this paper, the resistance to the freeze/thaw cycles for four groups of mortars (lime—LM, lime based—LBM, cement—CM, and aerated cement—ACM mortars) with different amount of mortar components within each group is quantified via a ratio of flexural/compressive strength after and before exposure to freeze/thaw cycles. Using a pore system obtained by three different methods (mercury intrusion porosimetry, X-ray micro-computed tomography analysis, and SEM (Scanning Electron Microscopy) analysis), an attempt was made to explain why some mortars achieved better resistance to freeze/thaw cycles than others. The mortars with lime as a binder in the composition (LM and LBM groups) did not survive the freezing and thawing regime, while no visible damage was recorded in samples of the CM and ACM group. It is concluded that the low initial value of the mechanical properties of the LM and LBM mortars, as well as the higher proportion of harmful pores (pores greater than 0.064 μm) compared to CM and ACM mortars are responsible for their poor durability. According the results of nanotomography, it is concluded that the most important factor influencing freeze/thaw resistance is pore connectivity—the higher the connectivity of the macropores, the higher the freeze/thaw resistance of the mortar. SEM analysis proved to be a very useful method for aerated cement mortars as it revealed the pore sizes that were not covered by mercury porosimetry and nanotomography