Influence of Type of Cement and Curing on Carbonation Progress and Pore Structure of Hydrated Cement Pastes
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INFLUENCE OF TYPE OF CEMENT AND CURING ON CARBONATION PROGRESS AND PORE STRUCTURE OF HYDRATED CEMENT PASTES
Th.A. BIER UniversitAt Karlsruhe, Institut fur Massivbau und Baustofftechnologie, Abteilung Baustofftechnologie, Kaiserstr. 12, D-7500 Karlsruhe, F.R.G.
ABSTRACT Different series of cement paste specimens were prepared with ordinary portland cement, with portland, blast furnace slag cements having slag contents of 30, 50 and 75% by mass, with commercial fly ash cement and with portland cement containing fly ash additions of 10, 20, 30 and 50% by mass. Moist curing of the specimens varied between 3 and 28 days before the pore size distribution and characteristics of the phase composition were analyzed. Subsequent to curing, the specimens were subjected to drying in air of 65% RH with a controlled CO2 content of 0, 0.03 and 2% CO2 by volume. Depth of carbonation, pore size distribution of the carbonated paste, and the phase composition were investigated after 28 days and 6 months of drying, respectively. The results show that carbonation alters the preImportant parameters are the vailing pore structure of the hydrated paste. type of cement used and the duration of curing.
INTRODUCTION The resistance of concrete surfaces to the attack of aggressive gases or fluids is strongly influenced by the pore structure of the cement paste matrix. Coarse pore structures with high permeabilities allow rapid penetration of gases such as carbon dioxide, resulting in high carbonation depths. This investigation was carried out to reveal the relations between the pore structure of the cement paste matrix and the type of cement used as Furthermore, the influence well as the subsequent curing of the concrete. of these parameters on the depths of carbonation and the pore structure of carbonated samples will be demonstrated.
EXPERIMENTAL Materials Different series of 20 x 20 x 80 mm cement paste prisms were made at a In addiwater-solid ratio of 0.50 using the materials listed in Table I. tion, portland cement pastes with water-cement ratios of 0.40 and 0.65 were investigated.
Treatment of the Specimens After casting, the cement paste samples were rotated in the molds for 24 hours and then demolded. Subsequently, the prisms were moist cured for 3, 7 and 28 days. At the end of the curing period the specimens were sealed so that carbonation and drying could only take place on two opposite faces. The partially sealed specimens were conditioned in atmospheres of 0, 0.03 In all cases and 2% CO2 by volume for 28 days and 6 months, respectively. the relative humidity of the ambient air was 65% at 20°C.
Mat. Res. Soc. SyMp. Proc. Vol. 85. 01987 Materials Research Soclety
124 TABLE I Cements and additives used to prepare cement paste prisms
portland cement (Type I) portland, blast furnace slag cement (slag content 30%) portland, blast furnace slag cement (slag content 50%) portland, blast furnace slag cement (slag content 75%) portland, fly ash cement (fly ash content 22.5%) portland cement (Type I) with additions of a low calcium fly
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