Cinder Concrete Floor?

[justhumm]

A couple of weeks ago, I was inside a portion of a building constructed around 1927.

We were taking a core on an existing stairwell slab, which the GPR guy said was about 10" deep. The core cracked at about 2" down, at a material interface. And then cracked again at about another 2" down.

We didn't want to drill through the slab, so we called it there. Can anybody venture a guess as to what was below what we took out? Total thickness?

And other than rushing out and buying a textbook, can anyone recommend a good source of information for historical cinder concrete slab construction?

Thanks!

These were some interesting discussion of the topic:
[URL unfurl="true"]https://www.structuremag.org/?p=8405[/url]
[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=281173[/url]

And here are full-sized images:
[URL unfurl="true"]https://files.engineering.com/getfile.aspx?folder=d6b615a7-9872-42fa-8d6b-fe3aaaf137e1&file=Capture.PNG[/url]
[URL unfurl="true"]https://files.engineering.com/getfile.aspx?folder=19ce9640-9c25-4120-97ff-6dec217067da&file=20200214_170332.jpg[/url]
[ul]
[li]All floors, including XXXX or future fourth floor to have cinder concrete slabs, reinforced with wire fabric of approved XXXXX having a sectional area of 17/100 sq. in. per foot in width of fabric.[/li]
[li]Floor slabs to be 4" thick for spans XXXX 6'-6" C to C of I-beams.[/li]
[li]Floor slabs for spans mre than 6'-6" C to C of I-beams to be 4-1/2" thick.[/li]
[li]XXXX[/li]
[li]Slab for loft floor and XXXX of connecting corridors and pent house to be 4" thick.[/li]
[li]All slabs to have 17/100 sq. in. of reinforcement.[/li]
[li]Live load for all floor not otherwise indicated: 100 pounds per square foot.[/li]
[/ul]

 

[SlideRuleEra]

Don't buy a book... download one (or more) for free. Any USA publication 1924, or earlier, is in the public domain. Fortunately, cinder floor slab technology is also. Here is a listing of several sources.

This is an extract from the first one:

http://www.SlideRuleEra.net

 

[nmerr]

I did an evaluation of a building with a lightweight cinder concrete arched roof deck with a normal concrete topping. we had cores done and the separate sections break tested and were able to analyze the arches that way. IIRC the roof was more than adequate for 100 psf live load if they wanted to put a roof deck up there. The building was constructed around 1920.
Your case might have just been a cold joint in the pour causing an inherently weak concrete to be even weaker at that spot and break off.