Seamless construction joints on concrete floor

Question

By construction joints I mean the joints between a batch of concrete floor poured one day and the new work on a following day. What is the proper way to get the most seamless joints when making finished concrete floor in a large area?

Since I will be making small batches, it will be at least 10 days, so at least 10 joints to deal with, and if the joints are too visible it will look terrible.

I read many different opinions on this:

• Each joint should end in a 90°, preferably with a form.
• Chamfer the joint (more perpendicular or more shallow angle?), no need for forms.
• Before the start on the new batch, break the end of the previous one to ensure it is level, well adhered to the base and rough to receive the new batch (no need for forms as well)
• Use plastic strips for control joints as construction joints (how does this work exactly?)

I liked the idea of using the plastic control joints, but I'm not sure how I use it for construction joints. Any thoughts?

I tried the chamfer option and I didn't like it: too hard to make set the new batch. The break and 90° options seems to work, but I would rather not have to rely on forms or having the break part of the previous day's work.

Answer 1

I'd go for a square joint with a form. If you are using reinforcement (either as a part of the structural design for the slab or simply as an anti-crack measure), carry it through to stop any possible differential movement. That said, the concrete within two adjacent slabs poured within a relatively close period (approximately 3 days) will fuse as the cement hydrates and form a single "unit".