For more information, look for Destry Kenning's article, "Dealing with the Reactivity of Aluminum Forms and Concrete" in the Summer 2018 edition of Concrete Facts magazine. It's part 1 of a 4-part series so stay tuned for more!
Are you seeing veins or worm-like trails on your concrete panels? There's a reason for that. The elemental aluminum present in the aluminum forms is very reactive with the cementitious materials in concrete. Chemical reactions are much stronger than physical reactions and the results are concrete buildup. Additionally, hydrogen gas creates bubbles on the concrete surfaces. As these bubbles migrate upward, they leave these unsightly trails on your panels.
There are ways to prevent these problems. You can try a resinous coating on the aluminum form surface, but there are pros and cons to a heavy coating and a thin coating. Another option is to react the aluminum with something in advance to prevent or minimize further reaction when it comes into contact with the concrete. This process is known as "seasoning". Read the article to see what Kenning has to say about various seasoning methods!
What is the Osmotic Effect?
"Osmotic effect” occurs when water migrates out of a tilt-up panel into the casting slab during the critical hydration process. Cement on the downside of the panel does not completely hydrate. Effects range from minor panel surface defects like dusting to more severe damage like complete skin pull-off.
Why does it Happen?
When wet concrete from a newly poured panel is cast against a casting slab with less water content, a gradient forms. Water draws out of the panel and into the casting slab through osmosis. The difference in moisture content between the panel and the casting slab affects the osmotic force, or pressure, necessary to reach equilibrium between the two.
Osmosis is further encouraged by the force of gravity naturally pulling water out of the panel and into the casting slab. Additionally, a temperature gradient often exists between cooler freshly poured concrete and the warmer casting slab. This can contribute to osmosis as water draws into the casting slab.
How can I Prevent the Osmotic Effect?
The most effective preventative measure against the “osmotic effect” is to eliminate the previously mentioned gradient differentials from the start. This is achievable by saturating the casting slab with water before placing the concrete panel. This increases the water concentration in the casting slab, eliminating the gradient, which in turn eliminates osmosis. Please note that removal of excess water from the casting slab immediately prior to panel placement is crucial. Otherwise, the reverse effect of too much water can cause surface dusting.
Another key step in preventing the osmotic effect is using a chemically active, breathable cure and bondbreaker. This will reduce water migration through the bondbreaker while allowing vapor transmission. Chemically active Silcoseal Select forms an amorphous gel which effectively seals concrete surface pores, restricting moisture exit or entry and retaining concrete mixing water to assist in proper hydration. Silcoseal Select resists osmosis by restricting water’s migration from freshly poured concrete through the bondbreaker into the less moist slab.
Additionally, a silicate based hardener, sealer and dustproofer such as Duro-Nox provides added resistance to the “osmotic effect”. I reacts with hydrated lime in the casting slab to densify, harden, and reduce the porosity of the slab surface, thereby reducing the opportunity for osmosis to occur.
Inform yourself of the dangers of working with muriatic acid and learn about the benefits of removing concrete buildup with an organic acid based product in Lisa Wells' article, "Safe Alternatives to Muriatic Acid" in the April/May 2018 issue of Concrete Contractor magazine.
Read the full article here on page 50!
Anyone in the concrete industry knows how difficult removing built-up concrete on tools and equipment can be. Many turn to muriatic acid to do the cleaning but this chemical is dangerous to those using it and anyone close enough to inhale its fumes. It's also highly corrosive and will damage many of your tools.
There are safer, organic-acid based alternatives that actually do a better job. Blast-Off, for example, is made from sugar beets and it turns caked-on concrete to mush that easily washes away. And Blast-Off is safe to use on all surfaces, even rubber, glass, metal, and electrical components.
Marty O’Mara joined Nox-Crete Products Group in April with over 20 years of sales and marketing experience in the construction market, focusing on commercial, industrial and transportation. Marty brings technical sales skills to the previously unfilled Decorative Market Segment Manager role as well as know-how in developing new distribution and expanding new markets. Through seminars, trade shows and hands-on training, Marty is well established in the architectural, engineering, and contracting community. Extensive training experience with decorative products, curing and sealing compounds, waterproofing, and cementitious repairs make Marty an especially great fit for this role. Welcome, Marty!
Look for our article, "Safe Alternatives to Muriatic Acid" in the coming-very-soon April/May issue of Concrete Contractor magazine (a brand of AC Business Media) to learn more about the benefits of using an organic acid based concrete remover.
Are you still using muriatic acid to remove concrete buildup from your tools, equipment and machinery? Did you know there's another way that's safer for you and the environment and is even more effective? An organic acid based concrete remover like Blast-Off is ideal for safe, effective concrete buildup and splatter removal.
Here are a few Highlights of the Differences between Muriatic and Organic Acid
Read the article in Concrete Contractor - coming soon! - for even more information!