One of the most challenging concrete structures is concrete flooring.
It is the place where all the limits of concrete are highlighted and if the concrete flooring is not properly designed, will lead to customer dissatisfaction, complaints, and economical damages.
In order to avoid all of this, out of several experiences on the field (good and bad) I have written an agile booklet that you can download for free after being enrolled as a member of the P-Concrete forum. It is called “Concrete flooring tips and tricks”. It´s filled with interesting photos, suggestions and ideas.
These are the topics you will find:
The substrate
The separating layer
Visual checks before the casting
Slab´s thickness
Steel reinforcement
Bar joints
Concrete choice
Concrete shrinkage as a cause of cracks
Casting
Curing
The joints
One special case: flooring onto existing flooring
Alkali-silica reaction (pop-up)
Delamination of the use surface
Links and conclusion
For all of you that prefer just a glimpse into this specific field of use of the concrete I have here summarized some points.
THE SUBSTRATE
Each concrete floor sits on a substrate which basically represents its real foundation. The substrate must be free of surfacing water, clean (free of light elements that could come up to the surface) and free of clayey elements (read my post “Concrete & cleaning”).
THE SEPARATING LAYER
The purpose of the separating layer is twofold: minimize friction during the expansion and/or contraction of the floor and limit rising humidity from below.
VISUAL CHECKS BEFORE THE CASTING
These are the main controls:
1. Checking of the state of the ballast (see chapter dedicated to the substrate);
2. Absence of lights elements;
3. Checks on the pipelines which should be completely buried (if not buried, the thickness of the slab is reduced locally);
4. Correct filling of the trenches;
5. Insulation of the rising elevations;
6. Insulation of the walls;
7. Positioning of reinforcement irons in the corners.
SLAB´S THICKNESS
Slab´s thickness must be designed and calculated on the basis of the expected static and dynamic loads; it must not be the inevitable consequence deriving from the thickness of the ballast for slabs of limited thickness are much more subject to shrinkage phenomena of all sorts (read my posts “Concrete shrinkage part 1” and “Concrete shrinkage part 2”).
It is also necessary to avoid large differences in thickness. The differences in thickness are at risk of differentiated shrinkages and therefore at the risk of cracks.
STEEL REINFORCEMENT
The positioning of the reinforcement mesh is essential to allow it to adequately perform its function, that is, to limit the width and depth of the shrinkage and/or real cracks. To this end, the reinforcement must be positioned as much as possible (compatibly with the depth of the contraction joint) near the extrados of the floor itself where the contractions due to shrinkage are greater. Normally this distance is evaluated with h/3 where h is the thickness of the industrial floor slab.
In order to limit the cracks and increase the ductility of the concrete used, it is also possible to use metallic and/or synthetic structural fibers which, in suitable dosages and with an adequate aspect ratio, can even replace the reinforcement mesh (read my post “Fiber-reinforced concrete”).
THE JOINTS
The joints have the purpose of absorbing the tensions on the floor by reducing the formation of surface cracks. If no joints were designed beforehand, the risk would be to get completely random cracks originating from the tensile stresses to which the concrete is subjected both due to the loss of humidity and external forces.
There are 4 different kind of joints:
Construction joints
Contraction joints
Expansion joints
Structure´s insulating joints