Carbonation resistance of high volume fly ash concrete estimated with accelerated and natural tests

The reuse of industrial residue streams such as fly ash (FA) can be beneficial both from economic and ecological points of view but the durability properties remain the key properties to ensure sustainable application of these materials. The paper presents the results of accelerated carbonation tests carried out under CO2 concentration of 1%, 2%, 4% and 16% on high volume fly ash concrete (HVFAC) with 200 kg/m3 of cement and the same amount of fly ash. Concrete samples were also exposed to natural conditions of 0.0471% CO2 in the laboratory and after 21 months carbonation depths were measured. The effect of CO2 concentration on the kinetics of the carbonation process was analyzed. The suitability of widely used Tuutti’s model for the prediction of carbonation depth was tested on designed HVFAC. Based on collected results, modified expression derived from this model was proposed in order to secure a more accurate and reliable prediction of carbonation depth of HVFAC under natural conditions

Carbonation resistance of high volume fly ash concrete estimated with accelerated and natural tests

The reuse of industrial residue streams such as fly ash (FA) can be beneficial both from economic and ecological points of view but the durability properties remain the key properties to ensure sustainable application of these materials. The paper presents the results of accelerated carbonation tests carried out under CO2 concentration of 1%, 2%, 4% and 16% on high volume fly ash concrete (HVFAC) with 200 kg/m3 of cement and the same amount of fly ash. Concrete samples were also exposed to natural conditions of 0.0471% CO2 in the laboratory and after 21 months carbonation depths were measured. The effect of CO2 concentration on the kinetics of the carbonation process was analyzed. The suitability of widely used Tuutti’s model for the prediction of carbonation depth was tested on designed HVFAC. Based on collected results, modified expression derived from this model was proposed in order to secure a more accurate and reliable prediction of carbonation depth of HVFAC under natural conditions

Uticaj prslina na trajnost armiranobetonskih konstrukcija

Pojava prslina dovodi do narušavanja strukture zaštitnog sloja betona i do ubrzanja transporta štetnih materija, čime utiču na trajnost armiranobetonskih (AB) konstrukcija. Kroz sveobuhvatni pregled literature, zaključeno je da deterioracija AB konstrukcija izazvana karbonatizacijom predstavlja jedan od glavnih problema trajnosti širom sveta. Za potrebe ispitivanja, u okviru doktorske disertacije, spravljeni su referentni beton, beton sa 50% letećeg pepela (LP) i beton sa 100% recikliranog agregata (RA). Analizirani su postojeći modeli predikcije dubine karbonatizacije i predložena je njihova modifikacija u slučaju betona sa RA i LP. Ustanovljena je veza između karbonatizacione otpornosti i čvrstoće pri pritisku na osnovu koje je izvršena analiza upotrebnog veka kroz definisanje debljine zaštitnog sloja različitih vrsta betona. Za potrebe ispitivanja uticaja prslina na upotrebni vek spravljeni su uzorci sa 5 različitih širina prslina (0.05, 0.10, 0.15, 0.20 i 0.30 mm) kao i referentni uzorci bez prslina. Na kraju, predloženo je ograničenje napona u armaturi čime se omogućava da celokupni upotrebni vek (period inicijacije i propagacije) AB konstrukcija zadovolji propisane zahteve trajnosti

Influence of cracks on the deterioration mechanisms and durability of reinforced concrete structures

Trajnost betona definisana je njegovom otpornošću na dejstvo štetnih agenasa iz okolne sredine koji dovode do različitih vrsta oštećenja (mehanizmi deterioracije). U ovoj tezi, kroz pregled literature, izvršena je analiza postojećih rezultata istraživanja i znanja o glavnim mehanizmima deterioracije koji predstavljaju najveću opasnost za objekte u različitim klimatskim sredinama. Mehanizmi deterioracije mogu uticati na strukturu betona (mraz i soli za odmrzavanje) ili na pojavu korozije armature unutar betona (karbonatizacija i penetracija hlorida). Na deterioracione mehanizme i koroziju koja nastaje njihovim dejstvom u velikoj meri utiče prisustvo prslina. Prsline koje nastaju kao posledica savijanja presecaju armaturu i znatno olakšavaju prodor kiseonika i vode. Shodno tome, uloga prslina prouzrokovanih opterećenjem ne sme se zanemariti u sagledavanju upotrebnog veka armiranobetonskih (AB) konstrukcija. Korozija izazvana hloridima bila je predmet mnogih istraživanja proteklih godina. Za razliku od nje, u literaturi postoji vrlo malo podataka o uticaju prslina na koroziju armature izazvanu karbonatizacijom, pogotovo na razvoj korozije tokom vremena. Došlo se do zaključka da deterioracija AB konstrukcija usled korozije armature izazvane karbonatizacijom predstavlja jedan od glavnih problema trajnosti širom sveta, imajući u vidu da je veliki broj infrastrukturnih objekata izložen okruženju bogatom ugljen–dioksidom (CO2). Zbog toga je karbonatizacija postala važno pitanje u analizi trajnosti AB konstrukcija. Da bi se generisalo novo znanje i doprinelo poboljs anju postojećih standarda i inz enjerske prakse, razvijena je odgovarajuća eksperimentalna postavka kako bi se ispitao uticaj prslina na dubinu karbonatizacije i trajnost AB elemenata napravljenih od različitih vrsta betona...Durability of concrete is defined by its ability to resist harmful environmental agents that damage concrete (deterioration mechanisms). In this thesis an analysis of existing knowledge about most harmful deterioration mechanisms in different climates was made. These mechanisms affect inner concrete structure (freeze/thaw with de-icing salt) or induced reinforcement corrosion (carbonation and chloride penetration). The most important factor that affects concrete deterioration is the appearance of cracks on reinforced concrete (RC) structures. The presence of cracks that cross the reinforcement physically interrupts the passivation layer and induces the beginning of corrosion. Accordingly, the influence of cracks should not be neglected when the service life of RC structures is analysed. Chloride induced corrosion has been the subject of many studies in recent years, but there is a very little information about the influence of cracks on carbonation induced corrosion. Furthermore, deterioration of RC structures due to carbonation induced corrosion is one of the major durability issues worldwide, given that a large number of structures are exposed to a carbon dioxide (CO2) rich environment. Therefore, carbonation has become an important issue in RC structures durability analysis. In order to generate new knowledge and contribute to the improvement of existing standards and engineering practice, an appropriate experimental setup was developed to evaluate the influence of crack widths on the carbonation depth and durability of RC elements made from different concrete types..

Influence of Loading Cracks on the Carbonation Resistance of RC elements

In reinforced concrete (RC) structures, carbonation induced corrosion is one of the most significant durability issues. A very important factor that affects the carbonation process is the appearance of cracks in RC structures. According to the current state of the art, cracks have not yet been considered as a parameter in carbonation models which are used for defining the service life of concrete structures. The main objective of this research is to analyse the influence of cracked concrete cover as reinforcement protection. The analysis was carried out using own experimental results and the application of available standards and novel predictions regarding carbonation depth. For that purpose, prismatic RC samples without cracks and with different crack widths (0.05, 0.10, 0.15, 0.20 and 0.30 mm) were made and subjected to accelerated carbonation. The influence of carbonation depth on the corrosion of cracked and uncracked samples was analysed by observing the reduction of the reinforcement cross section. The compressive and tensile stress influence on carbonation resistance was also evaluated. The conducted analysis showed that even with low crack widths (0.05 mm) the maximum carbonation depth was significantly higher compared with uncracked samples. It was also shown that reduction in the reinforcing bar cross section after 28 days of exposure to 2% CO2 was between 0.05% and 0.13%, depending on the crack width. The results showed that compressive stress increase had no significant effect in the carbonation depth of samples

Influence of cracks on concrete carbonation resistance

In reinforced concrete (RC) structures carbonation induced corrosion is one of the biggest durability issue. There are many factors that affect carbonation process (CO2 concentration, relative humidity, temperature, curing conditions and concrete porosity). Probably, the most important factor that affects carbonation process is the appearance of cracks on RC structures. With relatively low concrete tensile strength, cracks are almost inevitable. According to the current state of the art, the cracks have not yet been considered as a parameter in carbonation depth prediction model which is used for defining the service life of concrete structures. The main objective of this research is to analyse the influence of cracks on concrete carbonation resistance using own experimental results and the application of available prediction models regarding carbonation depth. For that purpose, prismatic RC samples without cracks and with different crack width (0.05 mm, 0.10 mm, 0.15 mm, 0.20 mm and 0.30 mm) were made and subjected to accelerated carbonation. The accelerated carbonation tests were performed during 28 days at a CO2 concentration of 2%, relative humidity (RH) of 65±5% and a temperature of 20±2°C. The conducted analysis showed that even with low crack widths (0.05 mm) the maximum carbonation depth was significantly higher compared with the uncracked samples. In all cases, the cracks behaved as an additional exposed surface through which the CO2 molecules were diffused perpendicularly to the crack wall. The crack impact area was approximately the same regardless of the crack width. Further than 10 mm, the carbonation depths remained constant. Also, with decreasing the length at which the average value of the carbonation depth was calculated (averaging length), the mean carbonation depth increased. Finaly, the ratio between the calculated carbonation depths (according to fib-Model Code 2010) of cracked and uncracked samples was up to three times

Modeliranje nelinearnog ponašanja zidane ispune u AB skeletnim konstrukcijama

Zidovi ispune unutar AB skeletnih konstrukcija obično se posmatraju kao nekonstruktivni elementi i zbog toga se njihov doprinos zanemaruje pri proračunu konstrukcija. Istraživanja u novije vreme pokazala su da zidana ispuna može značajno izmeniti ponašanje konstrukcije. U ovom radu sprovedena je analiza ponašanja AB ramovske konstrukcije sa ispunom pri dejstvu zemljotresnog opterećenja. Ispuna je modelirana prema preporukama FEMA koristeći softverski paket SAP 2000. Za definisanje histerezisnog ponašanja ispune izabran je Pivot model. Rezultati proračuna upoređivani su sa rezultatima proračuna korišćenjem Kinematic modela na osnovu čega su usvojeni zaključci koji su prikazani u radu. Infill walls within frame buildings have been considered as non-structural elements and thus have been typically neglected in the construction design process. Research in recent years has shown that masonry infill can significantly alter the behavior of the structure. In the present paper an analysis has been made to study the behavior of RC frames with infill when subjected to dynamic earthquake load. Infill has been modelled according to FEMA using software package SAP 2000. Hysteresis behavior of infill was defined with Pivot model. The results of the calculations are compared with the results made using Kinematic model, based on this conclusions are presented

Ispitivanje otpornosti betona sa prirodnim i recikliranim agregatom ubrzanim karbonatizacionim testovima

Reinforcement corrosion due to carbonation is one of the main deterioration mechanisms of reinforced concrete structures. The key parameter in the model of carbonation applied in service life design methodology is the carbonation resistance of concrete. This property of the material is tested on accelerated tests, which consider exposure to relatively high concentration of CO2, measurement of the carbonation depth and it’s correlation with the designed concrete cover. The paper presents the results of accelerated carbonates tests conducted in conditions of CO2 concentration of 1%, 2% and 4%, on the concrete samples made with natural and recycled aggregates. Test results show the effect of CO2 concentration change on the kinetics of the carbonation process.Korozija armature usled karbonatizacije je jedan od osnovnih mehanizama oštećenja armiranobetonskih konstrukcija. U aktuelnim proračunskim modelima karbonatizacije, na kojima je zasnovana metodologija projektovanja prema upotrebnom veku konstrukcije, ključni parametar je karbonatizaciona otpornost betona. Ovo svojstvo materijala ispituje se ubrzanim testovima koji podrazumevaju izloženost relativno visokim koncentracijeama CO2, a zatim se dubina tako karbonatizovane zone dovodi u vezu sa projektovanom dubinom u uslovima realne izloženosti. U radu su prikazani rezultati ubrzanih karbonatizocionih testova sprovedenih u uslovima koncentracije CO2 od 1%, 2% i 4% na betonima spravljenim sa prirodnim i recikliranim agregatom. Rezultati ispitivanja ukazuju na efekte promene koncentracije CO2 na kinetiku procesa karbonatizacije