×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

When to Reject Concrete

When to Reject Concrete

When to Reject Concrete

(OP)
Hi All,

Is there a recommended limit for rejecting plastic concrete based on temperature? I've heard many times that concrete begins to set at 90 degrees and obviously any placement which occurs above that temperature will affect the 28 day strength. The average air temperature during the day where I am located is generally between 80 and 90 degrees.

Thanks.

RE: When to Reject Concrete

Why do you think these slightly warmer temperatures will affect the curing concrete? Is it wetted properly?

Did it have the proper slump when poured?

RE: When to Reject Concrete

95 degrees is when we employ warm weather curing methods but, overall, as long as the final concrete hits it's strength, slump, and air entertainment, and you have no issues with the final product when you strip the forms, there really isn't any reason to reject concrete poured at a higher temperature. Obviously this assumes that you properly wetted the concrete and shielded it from direct sunlight.

Maine Professional and Structural Engineer
American Concrete Industries
www.americanconcrete.com

RE: When to Reject Concrete

(OP)
I'm looking for some established guideline for rejecting concrete that sits on the site too long. I'm aware of the 90min (batch to placement) guideline set by ACI but for concrete batched with retarders, the 90min rule may not be a practical guideline for rejection. Rejecting concrete based on slump alone also has its challenges. Any other thoughts?

RE: When to Reject Concrete

Get the mix design and the mill certificate on the cement. If the time exceeds initial set on the cement, reject it. 90 minutes is a reasonable arbitrary point of rejection (ASTM C94). There are many variables that can decrease or increase this time. Initial set doesn't lie though. It is a tested parameter of the cement and if you place concrete beyond this point, you risk a variety of issues.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources