Variation in Strength of Mortars made of Different Cements Due to Carbonation

Abstract

By carbonation strength is varied in the area of the concrete surface: in the case of portland cement strength is increased, on the other hand, it was suggested that with slag sulphate cement strength is reduced by carbonation. This has been confirmed by researches on structural concrete at an age of 4 to 10 years. Due to the considerable decrease in strength of concrete made of slag sulphate cement caused by absorption of atmospheric carbon dioxide which must be equalized with the known phenomenon of concrete corrosion, it should be considered whether this corrosion is confined to the slag sulphate cement only or whether it can be observed with other cements. Therefore, researches on the carbonation of mortar prisms made of six types of cements were carried out, namely on specimens of 1 portland cement, 1 slag sulphate cement, 2 blast fumace cements, 2 trass blast furnace cements. The specimens were cured after drying in an air current enriched by 9% CO2 and their strengths were compared with specimens cured at 20oc at a relative humidity of 65%. The influence of the absorption of carbon dioxide proved to be dependent on the type of cement, essentially on the content of portland cement clinker and thus on the content of Ca(OH)2 produced by hydration: at a content over 40% clinker strength increased by up to 70%, at a content below 40% of clinker it decreased by up to 50%. The variation in strength is accompanied by a variation in the modulus of elasticity and in weight. The variation in weight is linear to that in strength so that it is possible to estimate by the variation in weight whether carbonation will induce an increase or decrease in compressive strength. The inves- tigations will be continued. Introduction