Question

1) What is the additional water content to be added to the mix, if the slump has to be maintained at 3 in. when the fresh concrete temperature changes from 60 oF to 80 oF?

2) Suppose the additional water content in question 3 was added to the mix to maintain the required slump of 3 in. while maintaining the same cement content.  What is the water-cement ratio of the mix at 80 oF?

Answer 1

Ans 1) According to ASTM C94 , a 10^o F rise in temperature of concrete require an additional gallon of water to maintain a same slump that the concrete had at lower temperature . Here rise in temperature is ,

T = 80 - 60

   T = 20 F

Water required to be added = (2 x 1) gallon

Water required = 2 gallon

Ans 2) Let the water cement ratio at temperature 60^o F = 0.50

Let initial mass of concrete = 100 lb

Mass of cement = 0.50 x 100

Mass of cement = 50 lb

Mass of water = 25 lb

Mass of water at 80^oF = 25 + 2

= 27 lb

Water cement ratio at 80^oF = 27 / 50

= 0.54