Maximum Field Mix Grout Placement Time for a Single Lift

[thoughtofthis]

A contractor has decided to switch from ready-mix grout to field mix grout. No problem...except it took a whole day to pour one lift (<5') in a wall 30 ft long. I know that there is a maximum batch time of 90 minutes on a batch, but I could not find any guidance on a single lift. It seems like they would get multiple cold joints taking that long, especially within a bond beam. Any thoughts?

 

[yaschief]

Yes they would get a series of cold joints as the grout will have achieved a "set" within 30 min. They could have used a pencil vibrator (1" to 1 1/2" diameter head) but in truth they probably didn't.

My experience is they will have not only cold joints but voids at the junction with the mortar fins between the CMU.

Did they do grouting windows as per code or just dump it in and hope?

 

[thoughtofthis]

Are you referring to the clean-outs for high lift grouting? That would not apply to this situation. Initial set is not defined in ACI 530.1 that I could find and even then is only mentioned in this context:

Place grout within 1 1/2 hr from introducing water in the mixture and prior to initial set.

...which I interpret to mean before that batch sets, not adjacent grout placements. I agree with your conclusion, but cannot find a code provision to support it. What am I missing?

 

[yaschief]

Nothing you missed. My answer is based upon my experience with site mixed grout and also doing demo on a CMU wall that was constructed 2 years before demo and "inspected" during grouting.

Fully 1/3rd of the total voids were not filled completely, vertical void heights were 3 to 4 inches in some areas and 1/3rd the width of the void...caused by grout being poured when it was too thick to flow and HUGE mortar fins at the horizontal joints.

A pencil vibrator will help some but thick grout does not like to flow, it likes to sit there and set.

Same with the bond between lifts, the top of the grout lift should be 1/3rd below the top of the top CMU to allow the next lift to "key" into the CU and the created grout column.

BTW don't buy the "we vibrated the rebar so the grout flowed well" BS...it don't work that way.