The Influence of Sand Grading on the Air Void System

Paper by CORPORAAL JURRIAANS from ISCR 12th 2014 Prague Czech Republic

In this research the influence of sand grading on the air void system in mortar is determined. Three sand grading types are defined: sand “low”, sand “mean” and sand “high”. The difference is the amount of fines, < 250 ?m, (low, mean and high amount of fines) in the sand. The sand grading does have a significant influence on the air void system in the mortar and with sand mean the most small air bubbles (<300 ?m), a lower spacing factor, a higher specific surface of the air voids and a higher total air content can be realized. This will lead to a better freeze thaw resistance and workability. Sand low is creating more large air bubbles. In opposite of what is mentioned in most literature, more and less fines in the sand, without water corrections, results in a lower total air content. Sand mean with the highest void content after vibration has the opportunity to create the highest amount of total air. If water corrections are made in the mortar to create comparable flow conditions for the three sand types, sand low is improving on the amount of small air voids and sand high is not. The conclusion is still the same: "Sand mean is producing the most small air bubbles in mortar". It is assumed that the air void grading in mortar tell something about the void sizes in the used sand. It looks like air bubbles are filling the gaps between the ideal mix grading and the used mix grading. An interesting aspect for concrete pavements and Frost-Thaw resistance.

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