19 KB122 KB18 KB200020242007Jozić, DražanRadovanović, IvanaZelić, Jelicaštevilka:24 straniletnik:41str. 91-94ISSN:1580-2949COBISSID:603818URN:URN:NBN:SI:doc-YFX9M6EQenInštitut za kovinske materiale in tehnologijeMateriali in tehnologijedodatkikorozijamaltemodul elastičnostitrajnostThe effect of silica fume additions on the durability of portland cement mortars exposed to magnesium sulfate attack| Vpliv dodatka silica fume na trajnost cementnih malt Portland, izpostavljenih delovanju magnezijevega sulfata|The deterioration of concrete structures due to the presence of sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended cements incorporating materials such as natural pozzolans, fly ash or silica fume have an important role in the long-term durability of concrete exposed to sulfate attack. In this work, the partial replacement (mass fractions 2-15 %) of commercially blended Portland cement (Type CEM IIA-S 42.5N) with silica fume (SF) was investigated in terms of the resistance of SF mortars to a magnesium sulfate (MgSOsub{4}) solution (w(SOsub{4})sup{2-}=2.5 %; exposure time up to 6 months at 20 °C). The changes in the length of the mortars due to expansion, as well as the changes in the elasticity modulusand mechanical strength loss as a function of silica fume replacement were determined. Structural changes in the mortars due to magnesium sulfate attack were also evaluated by differential thermal analysis (DTA) and by X-ray diffraction (XRD) analysis. The results show that the replacement of SF in most cases has a positive effect on the magnesium sulfate resistance. Mortars containing more than 8 % of mass fraction of SF replacement are characterized by a good sulfate resistance and show lower expansion than the control mortar on the basis of the sulfate-resisting Portland cement, due to the absence of the gypsum and ettringite, detected by the XRD analysis. It is also shown that the elastic modulus is proportional to the compressive strength, but higher compressive strength does not necessary correlate with a better resistance to sulfate attackPropadanje strukture betona v okolju sulfata (tla, podzemne vode in morska voda) je znan pojav. Uporaba mešanih cementov z dodatki, kot so naravni pucolani, leteči pepel ali "silica fume" (SF), ima pomembno vlogo pri dolgotrajni trdnosti betona, izpostavljenega sulfatni koroziji. V tem delu je preučevan vpliv SF (masni delež 2-15 %) kot nadomestni dodatek industrijskemu portlandskemu cementu (CEM IIA-S 42.5N) na odpornost cementne malte proti delovanju raztopin magnezijevega sulfata (w(SOspodaj{4})zgoraj{2-}=2.5 %; čas izpostavljanja do 6 mesecev pri 20 °C). Merili smo naslednje parametre v odvisnosti od deleža SF: sprememba dolžine malt zaradi ekspanzije, spremembe modulov elastičnosti in izguba mehanične čvrstosti. Strukturne spremembe v maltah, izpostavljenih vplivu sulfatne korozije, smo spremljali z diferencialno termično analizo (DTA) in rentgensko difrakcijsko analizo (XRD). Rezultati kažejo, da nadomestni dodatek SF v večini primerov povečuje odpornost malt proti vplivu magnezijevega sulfata. Malte z masnim deležem dodatka SF, večjim od 8 %, so okarakterizirane kot dobro sulfatno odporne in kažejo manjšo ekspanzijo kot kontrolna malta na osnovi sulfatno odpornega portlandskega cementa, ker nimajo gipsa in etringita, kar je potrjeno z analizo XRD. Opaženo je tudi, da je modul elastičnosti proporcionalen kompresijski čvrstosti, toda večje kompresijske čvrstosti niso nujno povezane z večjo odpornostjo malt proti korozijskemu delovanju sulfataTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaInštitut za kovinske materiale in tehnologije