Two pour foundation wall....

[jimtheengineer10]

I am working on a set of plans with a walkout basement. The owner would like to have the walkout wall constructed out of concrete. My questions is how is a 14' tall concrete wall (4' frost wall and 10' basement wall) typically constructed? Do they typically pour the frost wall and then pour the basement wall after? If so, do you just leave some rebar sticking up from the first pour so it can be tied into the second pour? Should the rebar be overlapped where the two pours meet? Thank you.

 

[dcarr82775]

If the wall is on spread footings, the footing is cast with dowels sticking up for the wall reinforcing which is lapped with the dowels. Then for something like you described the wall would be cast full height.

 

[Ironfrenzy]

The wall can be poured in separate pours provided that you allow for for adequate lap length of your vertical reinforcement. Also, a bonding agent should be used on non-monolithic pours to ensure that the concrete is adequately sealed at the construction joint(s).

 

[jimtheengineer10]

what type of bonding agent would you recommend?

what is an adequate lap length?

 

[Ironfrenzy]

I would recommend something similar to "Quikrete" or "Sika" products.

Lap length (aka. splice length), should be determined based on the size of your vertical reinforcement. These lengths can be found in the ACI concrete design manual as "development lengths". It is very important to ensure you have enough overlap of your reinforcement so that a hinge is not created at the join location, and so that bending moment can be adequately resisted through tension in the reinforcement.

 

[jimtheengineer10]

I just spoke with the Sika tech support and they said the 4' frost wall would have to sit for 28 days before the bonding agent and upper wall could be installed. Is there another product that doesn't require the 28 day wait? Also, is the bonding agent an absolute requirement or just a recommendation? Thank you.

 

[Ironfrenzy]

Bonding agent is preferred, but in this case, not a necessity. Just make sure that the splices are detailed properly for the vertical reinforcement.

 

[concretemasonry]

jim -

The Sika rep was somewhat in error and cited the "28 days" because that is a canned number to relate to concrete strength. It is not the product problem, but the rep problem.

For compression strength, even the traditional cement/water slurry can be adequate for most needs and your situation is not a critical one. For flexure and to develop the walls flexurally, the vertical rebar should be lapped and spliced an amount according to existing standards (ACI, CRSI, building codes).

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

jim,
Concretemasonry is correct. The Sika rep's advice is a good example of the old saying "a little knowledge is a dangerous thing". If we alway waited 28 days before casting subsequent building elements, nothing would get built.

Forget about the bonding agent. All that is required is a clean and slightly roughened surface. Bonding agents have their place, but they are often misused, and can act to debond if the timing is not right.

Your questions indicate that you have little experience with reinforced concrete design and construction practices. You can't learn it all on the internet, so you need a mentor.