Question

A mixture of 1080g of gravel with effective absorption of 0.9% and 720g of sand with surface moisture of 2.51% was added to concrete mix. Determine the adjustments that must be made to the added water to maintain a constant water cement ratio.

Answer 1

the amount of water required to be added to concrete should reduced by 8.352gm

Step-by-step explanation:

Given that;

amount of gravel = 1080 gm

absorption in gravel = 0.90 %

Now

Amount of water absorbed by gravel

= (0.90 / 100) x 1080 gm = 9.72 gm

we were also told that the amount of sand = 720 gm

and surface moisture = 2.51%

This means , sand will provide some water due to its moisture, therefore adding some water in concrete .Hence, we need to apply correction to maintain constant water cement ratio .

Since, sand is providing water, correction is negative

Amount of water provided by sand = - (2.51/100) x 720 = - 18.072 gm

Overall correction = 9.72 gm - 18.072 gm = - 8.352 gm

Negative sign indicate that the amount of water required to be added to concrete should reduced by 8.352gm