Flowable Fill as trench backfill on highway pavement 3

[harmsgundam]

We are planning to use a flowable fill as alternative backfill (subgrade level) on our utility trenched located on major roads. My major concerns are the following:

1. How long would it take (hours?days?) for the flowable fill to sufficiently harden before we can place a cement treated base on top of it? Let's say the unconfined compressive strength is 0.7MPa at 28days was specified.

2. If there is a "rule of thumb" or usual practice for the duration in question from item 1 above, is there a basis for that I mean is there a standard test that can be done to prove the adequacy of the flowable fill subgrade before placing the cement treated base?

We are in need to open the roadway to traffic ASAP so that is the reason why I am asking for guidelines since I cannot find any on the net aligned to our situation.

 

[GeoEnvGuy]

I have only seen poured fill used in rural roads with detours or as slurry trenches blocking off a lane for an extended period of time.

If you want to know how long you need to wait then cast sample cylinders and break them at the 3,7,28 days and draw the strength gain curve. The other consideration is shrinkage I believe that weak concrete typically has significant shrinkage unless additives are used.

 

[harmsgundam]

@GeoEnvGuy, some articles are mentioning (no elaboration) that pavement can be placed within 3 to 5 hours after pouring. So I am thinking that you do not need to wait for the flowable fill to fully harden before applying any load.

 

[cvg]

there are multiple ways to check, none requiring cylinders
generally 24 hours is more than adequate

A. When a person of average weight and shoe size can walk on the surface of the CLSM without creating greater than 1/8-inch indents in the material, or

B. When the in-place CLSM has reached a strength of 30 psi, when tested in accordance with ASTM D4832

C. When a ball drop indentation of 3-inches or less is obtained, when tested in accordance with ASTM D6024

D. When a penetration resistance reading of 650 is achieved, when tested in accordance with ASTM C403.

Additionally, CLSM shall not be covered if proof rolling by pneumatic-tired or steel wheel vibratory roller results in the bringing of free water to the surface or results in surface undulation (pumping).