Selected Answers

From Darell Chamberlain of C. Darell & Assoc. Inc. on April 6, 2015:
I agree with a previous submission; this is a ques ...read more I agree with a previous submission; this is a question with a lot of possible scenarios, thus variables. So, I am going to keep it relatively simple and make the following assumptions: we are talking about a horizontal slab on grade or a suspended slab in a parking structure, etc. Let's also assume the surface integrity and the concrete in question are otherwise structurally sound; the only two problems requiring solutions are the cracks and the permeability of the slab.

On the face of it, no pun intended, this is a relatively simple fix: The following system was developed in conjunction with the engineers of the British Columbia Ministry of Transportation and Highways and implemented and used on over 3 million square feet of concrete bridge decks, all on 4-lane freeways, new and old, from 1997 up to the present. These decks are tested and inspected with a "snooper truck" every years and still look like new!

First, insure the concrete is properly prepared. Usually, all that is required is insuring the surface of the concrete and the cracks themselves are clean and permeable, with any and all contaminants and dirt removed, and both the surface and cracks pressure-washed. Allow the surface and the cracks to dry to the damp (SSD) stage.

Using a Hudson can type (heavy) sprayer, apply a heavy, soaking of a deep-penetrating, water-based, sodium silicate penetrant. This heavy soaking is required as you only have about 15 to 20 seconds before the sodium silicate penetrant forms gels in the voids, and you must get enough penetrant down in 15 to 20 seconds for there to be enough there to "suck in" and penetrate up to half an inch.

Apply until the material stops absorbing into the surface and stays wet. Treat the cracks as thoroughly. This type of sodium silicate penetrant will form gels in the internal voids when it reacts with the alkali salts in these voids. These gels will hydrate into silicate "glass" crystals in about 72 hours. When it has done so, the treated surfaces of the slab and the cracks are now permanently waterproof, 98% vapor-proof, and 2 to 3 times as hard!

This meets the first requirement (sealing) and provides the perfect surface for adhering the product for meeting the second requirement, sealing the cracks. The material we found worked best for this was a two-part epoxy, the type which never really gets hard, but flexes a bit with deflection. The cracks will be of various width and depths. The epoxy alone will fill narrow cracks, but on larger cracks it will be necessary to insert backing rod to stop the epoxy from running out the bottom of the crack. Insert the backing rod at least an inch below the surface. Fill the crack with epoxy. The second requirement has been met.

From Warren Brand of Chicago Corrosion Group on April 1, 2015:
I think this question is too broad. Sealing concr ...read more I think this question is too broad. Sealing concrete is fundamentally different than filling gaps. In either case, for all material specifications, one needs to consider the following, in no particularly order: What is the desired appearance? What are the performance characteristics desired? Are there application or logistical limitations, in terms of time, temperature, location, accessibility, odor and/or VOC tolerance? What is the cure time of the material - goes back to logistics. Consider application issues: what contractor or workforce will be doing the installations? Some materials are very difficult to work with and require specialized equipment and/or experience.