Cement slurry as bonding agent
Cement slurry as bonding agent
(OP)
The contractor wants to use a cement slurry as a bonding agent, to bond a new concrete where the top concrete has been removed to repair corrosion to top slab and beam bars, rather than using a proprietary bonding agent.
I have done this very successfully about 10 years ago and it gave good bond strengths when tested by the CSA bond pull test. I think at that time that I had the contractor proportion the slurry for a w/c = 0.40 and work it in to the concrete surface with a stiff bristled broom. But now I am not sure how to proportion the cement and water to get a w/c=0.40 becasue I am not sure if there is a "bulking" factor for the cement that has to be included in the calculation.
The contractor want to mix the slurry in 5 U.S. gallon pail. I figure that equals 0.67 cubic feet. If portland cement weighs 100 pounds per cubic foot, then to get w/c=0.40, my calculation is as follows:
w / c = 0.40
c/100 + w/62.4 = 0.67
where w = weight of water, pounds
c = weight of cement, pounds
Solving these 2 equations gives w = 2.75 pounds and c = 6.87 pounds.
But is that right? Is there a cement bulking factor to be included, and if so how do I include it?
I have done this very successfully about 10 years ago and it gave good bond strengths when tested by the CSA bond pull test. I think at that time that I had the contractor proportion the slurry for a w/c = 0.40 and work it in to the concrete surface with a stiff bristled broom. But now I am not sure how to proportion the cement and water to get a w/c=0.40 becasue I am not sure if there is a "bulking" factor for the cement that has to be included in the calculation.
The contractor want to mix the slurry in 5 U.S. gallon pail. I figure that equals 0.67 cubic feet. If portland cement weighs 100 pounds per cubic foot, then to get w/c=0.40, my calculation is as follows:
w / c = 0.40
c/100 + w/62.4 = 0.67
where w = weight of water, pounds
c = weight of cement, pounds
Solving these 2 equations gives w = 2.75 pounds and c = 6.87 pounds.
But is that right? Is there a cement bulking factor to be included, and if so how do I include it?






RE: Cement slurry as bonding agent
A w/c of 0.40 is probably too high for such a bonding paste. Remember...it needs to be a paste, not a slurry.
I would do a trial batch by consistency, not by w/c. Wet it a little extra if needed to keep if from drying out.
You are exactly right about the application procedure.
RE: Cement slurry as bonding agent
RE: Cement slurry as bonding agent
Back to the sand cement slurry. CSA A23.1 clause 7.6.4.2.2 provides an accepted procedure for sand cement slurries. Summarized as follows:
- proper surface prep
- prewet surface for at least 1 hour (remove any standing water for SSD)
- 1:1 sand:cement ratio with enough water for a flowable consistency
- w/c ratio similar to that of concrete being placed but in no case more than 0.45. I agree with Ron that consistency is key, I liken it to a thick cream.
- there are additional recommendations on maximum coarseness of sand and a definition of flowable consistency linked to a CSA test method.
In my experience, timing of the application is important, as well as scrubbing it into the surface. I preferred it when the slurry was scrubbed into the surface with a boat brush.