January 27 - January 31, 2014
Is there a definitive relationship between mechanical properties of coatings (such as elongation and tensile strength) and crack-bridging capability?
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William slama of International Paint/Ceilcote Products on
February 10, 2014:
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For a single-layer, unreinforced coating (read “coating, lining, or flooring”), crack bridging capability can be determined by finite element analysis. And the value will be primarily affected by the coating's modulus of elasticity and maximum elongation capability.
However, at the surface, just over the crack, the coating theoretically encounters infinite elongation. Then, the toughness of the coating determines how much or little movement can occur before the coating tears through to the top of the coating.
Further complicating this is that there will be some local surface fracturing of the concrete adjacent to the crack that will, in effect, give the coating some “stretching length” that will help it to “bridge” the crack.
With the exception of very tough elastomers, the crack bridging of unreinforced systems is virtually negligible, probably only 1-3 thousandths of an inch of movement.. The “tough elastomers” that are known to bridge cracks are in the range of 400-600% elongation and 3,000-6,000 psi tensile strength. Use of these systems is limited because of theie lower cross link density, leading to lesser chemical resistance and greater permeability.
What several developers/manufacturers of chemical-resistant coatings, linings, and flooring have done is to develop reinforced multi-layer systems to provide significant crack bridging capability. This is accomplished by first applying a base layer of very flexible material, then applying a fiberglass- reinforced layer and finally a chemical-resistant top layer. That system's crack bridging is somewhat predictable by engineering calculations, and actual lab simulation tests have given “reasonable” correlation to calculated behaviour.
Those systems typically accomplish crack bridging capability of 0.020-0.050 inches (20-50 mils) of crack movement (opening) capability.
Reference: "Physical and Mathematical Representations for the Determination of Crack-Bridging Ability of Lining Systems," Proceedings from the SSPC 1994 Seminars (SSPC 94-19).
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