2. An aggregate sample is described as follows: 46.5 kg of fine aggregate is mix
ID: 1885074 • Letter: 2
Question
2. An aggregate sample is described as follows: 46.5 kg of fine aggregate is mixed with 72.3 kg of coarse aggregate. The fine aggregate has a moisture content of 2.0% and absorption of 3.4%. whereas the coarse aggregate has a moisture content of 1.3% and absorption of 3.8%. (a) What is the amount of water required to increase the moisture content of both fine and coarse aggregates to reach absorption? (b) W hy is it important to determine the amount of water required to increase the moisture content of aggregate to reach absorption? (Take concrete for example)Explanation / Answer
Fine Aggregate:
Mass of fine aggregate = 46.5 kg
Moisture Content = 2.0 %
Absorption = 3.4 %
Free moisture = Absorption - moisture content = 3.4 - 2.0 = 1.4 %
Coarse Aggregate:
Mass of coarse aggregate = 72.3 kg
Moisture Content = 1.3 %
Absorption = 3.8 %
Free moisture = Absorption - moisture content = 3.8 - 1.3 = 2.5 %
(a) Amount of water required to increase the moisture content of both fine and coarse aggregates to reach absorption:
Amount of water required = (mass of aggregate * free moisture of aggregate)coarse aggregate + (mass of aggregate * free moisture of aggregate)fine aggregate = (72.3 * 0.025) + (46.5 * 0.014) = 2.4585 kg
(b) By using the moisture content and absorption of the aggregates, you can adjust the batch weights of the mixture in concrete to account for the actual moisture condition.
If the moisture content is higher than the aggregate’s absorption value, the aggregates will contribute free water to the mix.
If the moisture content is below the absorption value, the aggregates will absorb a portion of the mix water.
In this problem, the moisture content of aggregates is below the absorption value of aggregates, hence it is important to determine the amount of water required in the mix to increase the moisture content of aggregate to reach absorption.
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