Excerpt from the February 2000 Concrete Construction Article by M.K. Hurd
Concrete form-release agents represent only a small fraction of the cost of a manufactured concrete item, but they have a big influence on the quality and success of the concrete surface.
Though no American Concrete Institute or ASTM standards define these products, common usage suggests that form release agents are materials containing proprietary reactive ingredients specifically formulated for use on concrete forms. ACI 301-96, “Standard Specification for Structural Concrete,” does, however, give performance-based requirements for release agents. Section 18.104.22.168 says to use “commercially manufactured form-release agents that will prevent formwork absorption of moisture, prevent bond with concrete, and not stain concrete surfaces.”
Today, precasters can choose from among hundreds of form-release products, and new ones are still being developed. Many changes have been introduced as manufacturers scramble to meet federal and state environmental regulations, particularly with respect to volatile organic compounds (VOCs).
With the myriad form-release products available, how do you select the best one for a particular application? Here are a few of the fundamental questions you should ask:
- On what form surfaces can it be used?
- Will it provide clean, easy release without damage to either the concrete or the form?
- Will it produce a stain- and blemish-free concrete surface?
- Is it compatible with admixtures in the fresh concrete and with surface coatings that may be applied later to the hardened concrete?
- Is it ready for use without site mixing, and is it appropriate for anticipated casting and curing temperatures?
- Is it user-friendly and compliant with environmental regulations?
The table on pages 61-68 answers some of these questions and summarizes manufacturers’ recommendations for many currently available form release products. How release agents work Release agents are classified by how they work rather than what they contain. Two basic categories are barrier agents and chemically active agents (also referred to as reactive agents). Some release agents are a combination of the two types. Barrier-type release agents create a barrier between the form surface and the fresh concrete, preventing the concrete from sticking to the form
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