Have you used Concrete Hardeners

[damorim]

My area of expertise is in bridges and other transportation structures, however I was recently tasked with the detailed design for a potable water pump station. I have never even heard of concrete hardeners before as they are not used in bridge construction as far as I am aware. The architect wants to spec a hardener for the floor slab of our pump station. Just wondering what your guys' experience is with concrete hardeners? Do you regularly use them? Do they really provide a benefit? Any specific products you would recommend?

Thanks

 

[dik]

I've used them on several projects and they come as two types, metallic and non-metallic. Both work, but most of the projects have used non-metallic. This is a cementitious material with a 'hard' stone product mixed with it, and it is broadcast on the plastic concrete surface and trowelled in for the first 1/4" or so. It works well for interior usage; I would not use it for exterior slabs in these environs (cold).

The applicator has to be skilled; there is a chance of messing up and ending up with a slab that delaminates from improper timing or over-trowelling.

Dik

 

[damorim]

Thanks Dik. I'm just curious (the architect has decided he wants it so I'll let him spec it). From my bridge experience, I feel that there is no substitution for an extended wet cure - however, I'm not even sure the building industry is regularly using wet curing? From some quick reading online (this was a great source:

http://www.concreteconstruction.net/how-to/construction/are-hardeners-effective_o),

it sounds as though there is a huge difference in opinion as to whether a hardener does anything. Every producer seems to supply a hardener that blows away the competition. But hearing from the people actually applying it and seeing the effects, I'm curious if there is an appreciable increase in wear resistance. How have you cured these slabs you have used hardeners on Dik? I realize that project schedules often don't have the time to allow for a proper wet cure.

 

[jayrod12]

In my experience, it's usually cheaper to go with a higher strength mix than it is to add the hardener. And if it's a post installed hardener, then 9 times out of 10 it's installed incorrectly. What's the reasoning behind the hardener (besides the architect wants it)? If it's improved durability, go to a thicker slab with more clear cover, and a higher strength mix.

 

[damorim]

I think its the classic "I've always done it that way" mentality. Aside from periodic maintenance crews, the slab won't really see regular heavy traffic. Once equipment is installed, there shouldn't be equipment dragged around or anything like that either. I'm already using a 35 MPa mix design and don't really need to go any higher. The isn't an adverse exposure and like I said, wear and tear would be expected to be minimal.

 

[JAE]

Sometimes a higher strength mix, with its added Portland Cement, adds to shrinkage and the resulting cracking. So be careful with that.

Besides the two types of hardeners dik mentioned (which generally are shake-on types) there is also a more moderate system referred to as a "liquid penetrating hardener" such as this one:

Link to SealHard



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[Ron]

As noted, there are various types of "hardeners" or surface treatments. For any of them, make sure the contractor knows what he is doing. For your application, the dry shake or broadcast hardeners (Euclid Euco Plate, Fosroc Nitoflor Hardtop and similar) will likely provide better serviceability. The liquid hardeners that are applied post curing work by filling the voids in the concrete with a reaction of constituents within the concrete. Most are calcium silicates or sodium silicates in some proprietary form. When you have moisture migration through the slab from below, some of these materials, particularly the sodium silicates, will produce a white powdery residue that does not look good.

You could also consider an epoxy coating on the floor.

 

[dik]

Ron reiterates that a skilled trade is required.

Jayrod: a properly placed hardened slab is much better than a kazillion MPa conc slab with the added shrinkage, noted by Ron.

Dik

 

[jayrod12]

Dik,

Although what you say is quite true. The fact that you had to specifically note properly placed is why I try to avoid it unless absolutely necessary. Especially given the description of intended final use. It seems an overall waste of money and effort.

 

[damorim]

I tend to agree with Jayrod, time and cost isn't worth it given the final intended use.

 

[dik]

I've never had a problem with one and I've been involved with dozens of them. A good slab contractor is not difficult to find... it was just a caution I put in my original response to the OP... and, depending on circumstances, I will not hesitate to use the next one, and, occasionally you really need a hardened slab.

Dik