×
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

Cracks in concrete
2

Cracks in concrete

Cracks in concrete

(OP)
I have some crack issue on site. The concrete was poured between June and September 2009. The concrete used was 40 MPa concrete, the slump measured was 40mm and 50mm at the time of pour. The concrete cylinders strength results were ranging between 35 to 60 MPa. The slab poured at 45 angle for channels. The cracks were noticed in slab in July 2010 (see attached photo). I am just wondering what causes slab to cracks so quickly. The slab was poured on granular base.   

RE: Cracks in concrete

Those are shrinkage cracks.  They were likely there long before becoming obvious.  They are also going to/from penetration features in the slab, which have caused restraint to the slab (thus the shrinkage cracks).  If you do cores through the cracks you might also find thickness anomalies.
 

RE: Cracks in concrete

gosai,

About 70% of the shrinkage occurs in the first 12 months after pouring the concrete. As your time period is about 9-10 months, you would be expecting shrinkage cracks by July.

RE: Cracks in concrete

(OP)
Are the slump and the temperature of concrete (25 C) at the time of pour contributes to shrinkage cracks?

RE: Cracks in concrete

gosai...both can contribute; however, 25C is a good temperature for concrete placement.  You have to look at temperature differentials at the time of placement.  For instance if your concrete temperature is 30C and the air temperature is 15C at time of placement, this can cause immediate shrinkage during the initial setting of the concrete.

If you have a high slump that was caused by a high water-cement ratio, then you will have a lot of shrinkage.  If your high slump was a result of admixtures, shrinkage is not usually an issue from the slump indication. A 40-50mm slump is not much, so I wouldn't consider that to be a contributing factor.  It is more likely just drying and autogenous shrinkage, coupled with some physical restrain conditions from the pipe and variable thickness.

RE: Cracks in concrete

40 to 50 slump and 25C are both good.  I would think the cracking is more likely related to curing or lack thereof.  The panels look small in plan, but also thin.  You said it was cast on a granular base.  Plastic under the slab?  Weather conditions?  Method and time of curing?

RE: Cracks in concrete

Is that Milton, Brisbane, AUS?

RE: Cracks in concrete

(OP)
Hokie66,

There is no plastic placed between granular base and concrete. As per sub contractor wet curing was carried out for 7 days by placing wet burlap on top.

Kikflip,
It is not Milton, Brisbane, Aus this one is in America

Thanks for all your help
 

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