Cement Treated Base Shrinkage

[Hennen]

I have a contractor who is claiming to have put 320 CY of CTB in an area that called for 240 CY. I have his haul tickets to verify the amount of CTB he placed and a representative onsite that verified that little to none of the material was wasted. I have a topo of the area's subgrade and though the subgrade was not perfect, it does not account for that large of an overrun. Am I missing something ? Can CTB shrink by 25% when compacted to a density of 98 % at 1 foot in depth ? I can not seem to come up with a reasonable explanation of how this is possible.

 

[Ron]

Bulking can certainly be a factor, particularly if the material was mixed in a pugmill and contains a high sand percentage. I doubt that it would explain all the difference, but combine that with a few subgrade glitches and a slight width and length overrun and you're probably there.

Do you have confidence that his haul tickets are accurate? Have you done a rough measurement of the truck volume to validate?

 

[cvg]

drying shrinkage is minimal.
you are only verifying tons, not cubic yards (check your density calculation) and not elevations of either subgrade or finished grade (check your surveys)

 

[Drumchaser]

This is why some DOT's pay by the SY in place at a required thickness.

Is your subgrade low PI sand?

Were the haul trucks bobtail (3 axle)?

Generally speaking, if the haul truck volume calc.s check out, and they were not showing the top of the material to be at water level full.....

I think he is trying to take you to school.

 

[jrm73]

Shrinkage and poor measuring are typically not problems. This is very simple. You bring the material to the site in a loose state which means a low density. The material is placed and compacted which means a high density. It is all a matter of comparing the loose versus compact density.

 

[Ron]

jrm73...it isn't that simple. Run your numbers. Loose condition and compacted condition for a CTB would only account for about 1/2 the noted difference.

Agree with drumchaser that the contractor is probably trying to school someone.