Betono šarminė korozija Lietuvos sąlygomis

Abstract

Atlikus ilgalaikius betoninių konstrukcijų šarminės korozijos stebėjimus ir tyrimus, ištyrus Lietuvos telkinių užpildų užterštumą reaguojančiomis su šarmais uolienomis nustatyta, kad šie užpildai užteršti opoka, titnagu ir kitomis reaktyviosiomis uolienomis, kurios reaguodamos su cemente esančiais šarmais, betone sukelia vidinius įtempimus, gėl ko betonas plečiasi, pleišėja, mažėja jo stiprumas ir pan. Kai naudojami Lietuvos telkinių užpildai, šarmų kiekis (ekv. Na2O) cemente neturi viršyti 0,8% cemento masės, o betone - 4 kg viename kubiniame metre. Kur galima, betono šarminės korozijos prevencijai turėtų būti naudojami smulkiadispersiai hidrauliniai priedai.

Rezults of long term observations and investigation of concrete alcaline corrosion under Lithuanian conditions, of contamination of Lithuanian deposits by reactive rocs as well as preventive measures to avoid concrete alkaline corrosion are presented. Exploitation conditions damaged constructions, character of breaks, composition and structure of ruined concrete, composition of corrosion products were given an integrate study. It was found that the main cause of concretedeterioration is the contamination of Lithuanian aggregate deposits rocks such as opoka, flint, silicatized limestone, etc., which in humide conditions react with the alcali present in cement, and the newly forming growths give rise to internal tensions and damage the concrete. The deterioration character and area depend on the nature of the reactive grains present in the aggregates (e.g., opoka is more dangerous than flint, their diameter and depth in concrete, as well as on the concrete structure. Reactive admixture are present in practically all Lithuanian aggregate deposits. The average fine aggregate contamination is 1.5-2.0%, while in coarse aggregates it reaches about 0.5%, calculated taking into account the granulometric composition. Investigation of Lithuanian aggregate deposit corrosion dependencies on alcali content in concrete according to special at present standardized methods showed that the content of alkali in concrete should not exeed 4 kg/m3. If larger amounts are presented, alcaline corrosion of concrete can occur under certain conditions.