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Abstract
Great durability problems are being found in concrete structures related to the penetrability of aggressive agents through the concrete (ie. chloride penetration, sulphate attack, carbonation, freezing and thawing, and so on). Air permeability coefficient is used as an effective tool to estimate the potential durability of concrete structures due to its direct relation with the microstructure and the moisture content. This paper discusses the effect of the aggregate grading and water/cement ratio on the air permeability coefficient. An aggregate grading with more sand than coarse aggregates has resulted more beneficial from the point of view of concrete air permeability. This fact can be attributed to a denser skeleton formed by the finer aggregates. With fine aggregates, the higher water/cement ratio, the lower air permeability. However, the contrary was found with coarse aggregates. Overall, a temperature increase from 20 °C to 60 °C during preconditioning led to a D air increase of 40–80%.
Highlights
Long-time performance of concrete is consi dered currently as an important topic which has promoted an increasing study of the parameters related to its durability and the testing methods for its determination as in the case of air permeability
The calculated air permeability coefficient, Dcalc, is obtained from the slope of these straight lines (Figure 5) in which a good correlation has been found in all the cases (r2>0.99)
The results indicated that as the proportion of larger size aggregate increases in the mix, the air permeability increases
Summary
Long-time performance of concrete is consi dered currently as an important topic which has promoted an increasing study of the parameters related to its durability and the testing methods for its determination as in the case of air permeability. Compressive strength has been considered for long as the only indicator of durability. Volume of pores in aggregates is normally about 10% than that of the cement paste. The size and gradation of aggregates in the concrete can have an important effect in its air permeability [3]. The permeability of concrete is normally about 100 times greater than the permeability of cement paste [6]. It has been reported that air entrainment increases air permeability [7]
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