| Abstract | 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. |
| Abstract (english) | 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. |
