4specs.com    4specs.com Home Page

a split slab true to it's nature (ind... Log Out | Topics | Search
Moderators | Register | Edit Profile

4specs Discussion Forum » Archive - Specifications Discussions » a split slab true to it's nature (industrial application) « Previous Next »

Author Message
Doug Brinley
Senior Member
Username: dbrinley

Post Number: 6
Registered: 12-2002
Posted on Friday, May 28, 2004 - 04:35 pm:   Edit PostDelete PostPrint Post

What else should have been done with this slab?

Pacific Northwest location using Puget Sound area aggregates notorious for being 'funky'. Dry subgrade and low washdown water consumption operation, so the concrete stays remarkably dry for this application.

Industrial floor slab (the 'wear slab') in an enclosed solid waste transfer station begins coming apart in irregular chunky pieces, variable size, minimum dimension not known. 4 years after completion. These are bare concrete floors which receive refuse and have 20 ton 300 hp wheeled loaders moving back and forth every day. Buckets do not wear on the concrete - there are 8 inch thick rubber tire protection pads full width on buckets. There are no warps or breaks in the floor and the floor slopes to drain quite well.

Structural slab also begins showing signs of failure in areas where stress accumulates (around penetrations). Owner and architect cooperating to solve problems including permanent shoring in tunnel areas beneath the floor; project structural engineer (scapegoat?) banished for other reasons possibly including stupidity - partly because he 'forgot' to reinforce an 18 foot tall site retaining wall until after the first four feet were poured.

The assembly: Slab on grade, 8 inch reinforced structural slab, Class 4000 design, admixtures unknown to me, unable to find batch tickets or the mix design proposed by the batch plant.

Wear slab consisting of 6 inch, Class 6000 design, unidentified admixtures, conversation with the project architect leads me anticipate no reinforcing was placed in the wear slab ("...it's supposed to wear, right?"). Same lack of information on what actually got placed.

Semi-rural location with a distant batch plant lead me to anticipate the contractor probably added water and or manipulated the plasticizer based on local conditions just to get the stuff down. Very cost conscious owner and architect (at the time).

The project architect assumes no chemical bond was achieved (a bond promoter was specified) and it is unclear what the physical conditions of the structural pour were, particularly how the slab was struck.


I can surmise the obvious stuff - surely some stress fractures, shrinkage cracking potential, probable insufficient/missing steel reinforcing in the wear slab (which should not have been subject to much flexure if the structural slab was doing it's job).
Anonymous
 
Posted on Tuesday, June 01, 2004 - 02:07 pm:   Edit PostDelete PostPrint Post

Time for the Owner to hire a forensic investigator. WJE, PSI, etc. Don't try to wear that hat - you are exposing yourself to even more liability.
Anne Whitacre, CCS CSI
Senior Member
Username: awhitacre

Post Number: 90
Registered: 07-2002
Posted on Tuesday, June 01, 2004 - 04:08 pm:   Edit PostDelete PostPrint Post

I would have put a densifier/hardener in the topping slab as well that would hold up under both point loading and concentrated wheeled loads. this is clearly the structural engineer's concern, and I agree with "anonymous" regarding getting an investigator. However, there are numerous toppings for warehouse floors to help with both exposure and wear, and it sounds like at least one of those products should have been in there.
Anonymous
 
Posted on Tuesday, June 01, 2004 - 04:54 pm:   Edit PostDelete PostPrint Post

Surface applied concrete densifiers are merely for increased abrasion resistance at the surface (MAYBE an 1/8 inch), and do not make any appreciable contribution toward structural performance. I disagree with poster about this product holding up to point loading where the slab will not hold up....From the information given, no surface applied product would have had any impact on the slab failure.

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration