Hard Choice: Emerytop 400

Let's say that you're out in the tool shop and you need to grind down a chunk of iron. You go to your emery grinding wheel, sparks fly and the iron disappears like butter. So, based on your own experience, which is harder, the iron or the emery?
Which one rusts?
Which is more resistant to abrasion?
Now, which one makes the tougher floor?

The daily grind:
Impact, weight, abrasion, chemical attack
Let's talk about the daily grind
It is rare that a concrete floor fails structurally. A key factor that determines the life expectancy of a concrete floor is its ability to withstand abrasion. It is true that as the compressive strength of concrete increases, resistance to abrasion increases, but only to a point. In those industrial applications that require resistance to high point loads and high abrasion, going to higher strength concrete is not just expensive; most of the time, it just won't work.

One of the earliest successful attempts to increase the abrasion resistance of an industrial concrete slab was to make a mortar consisting of portland cement and mild, cast iron borings and place this iron topping mortar over plastic or hardened concrete. This system has been used for years, and still is.

While significantly improving the wear resistance of the floor, iron topping mortars have a down side, too. Two adverse physical property characteristics exist with the use of these products: rusting and drying shrinkage.

It is true that the iron used in concrete is protected from rusting by the high pH of the cement paste. However, as the cement paste wears away the iron becomes exposed and is no longer protected. Also, in some installations regular or frequent exposure to moisture will cause oxidation and, as a result, limit the acceptable placement areas for iron topping mortars.

Iron topping mortars tend to have significant drying shrinkage properties and are, therefore, problematic when placed on a hardened concrete substrate. Delamination caused by drying shrinkage is a common problem with these toppings. A review of available product literature indicates that it is common for manufacturers to recommend concrete nails or pins be placed around the edges of the base concrete slab at regular intervals, with half the length left above the surface of the concrete. The reason for this is two-fold: first, to provide a mechanical bond between the topping and the concrete substrate, and second, to restrain delaminating forces caused by movement due to drying shrinkage.

In addition to the nails, a bonding agent must be used. If an epoxy resin bonding agent is used, the moisture content of the concrete substrate must be below a certain percent. Time and temperature are also factors which influence the successful use of an epoxy bonding agent. Epoxy bonding agents have a limited temperature range in which they can be applied and cause their own problems if the topping is applied after the "tack" time has passed.

Don't worry, it gets better
Today, there is a far better option to increase concrete abrasion resistance than iron topping mortars. L&M's top-of-the-line impact and abrasion resistant toppings rely on high-grade Emery Aggregates. Mineralogically, emery is a mixture of corundum and magnetite. Corundum is a natural form of aluminum oxide, which gives emery its toughness. Magnetite is known for its high iron oxide content, which provides additional durability and impact resistance.

L&M selects only high grade, emery aggregates to be used in its toppings. Using the industry standard measurements, our aggregates score close to 9 on the mohs hardness scale. (The mohs scale is an indicator of aggregate hardness. Each single digit increase on the scale indicates a ten-fold increase in hardness. Diamonds are rated highest at 10; quartz is 6; talc is rated as a one.)

How can emery be proven more abrasion-resistant than iron, let alone steel? It can be proven in two ways: 1) by looking a few years back into emery aggregate history and 2) the mohs hardness scale.

In the past emery was crushed into a powder and mixed with a binder of sodium silicate. In this form, it was then shaped into a bar or wheel and allowed to harden into a solid mass. The resultant product is well known as a way to sharpen steel and metal cutting tools. (Just as a point of reference, a knife blade on the mohs hardness scale is a 5.5, iron is a 4 to 5, and a hardened steel file is 7+. These numbers come from the American Federation of Mineralogical Societies.)

Emery aggregates are often generalized as "natural aggregate" or "mineral aggregate", but there is a world of difference between natural aggregates, which includes quartz and trap rock aggregates which are used frequently as shake-on floor hardeners, as well as a world of difference between emery aggregates themselves. Being a natural occurring aggregate, there are wide variations in mineral component percentages based on the location of these deposits throughout the world.

Premium blend:
Most domestic emery aggregates have a low aluminum oxide and iron oxide content. While they provide good abrasion resistance, they are inadequate to resist impact conditions. The select emery aggregates used in L&M's Emerytop 400 topping have a high aluminum oxide content of 58% for hardness, and a minimum iron oxide content of 25% for malleability. During the formation of the emery aggregate, the iron oxide in the emery aggregate is fully oxidized. Therefore, rusting cannot occur.

But Emerytop 400 is much more than simply a mixture of portland cement and high quality emery aggregates:

  • Emerytop 400 is formulated to allow placement at a flowing consistency and, at the same time, has very low drying shrinkage. This property makes for good bonding to the substrate concrete.
  • Independent tests on Emerytop 400, according to ACI 544.2, demonstrate impact resistance that is equal to that of iron topping mortars.
  • Unique to Emerytop 400 is its very dense, hardened cement paste. This feature provides two long-term benefits. First, a harder paste insures a longer-lasting cement matrix paste to hold the high-grade emery aggregates in place for even wear. Secondly, when tested in accordance with ASTM C 1202, the penetration of chloride and other contaminants is found to be very low. This very important feature proves that Emerytop 400 offers unique protection from the penetration of common chemicals that deteriorate cement-based toppings from the inside, shortening their useful life.

Emerytop 400 is ready to handle the nasties.
Handling the nasties
The conditions that are found in solid waste transfer stations are identified as some of the worst imaginable for concrete floors. These concrete floors are constantly called to hold up to abuse from not only impact and abrasion, but also from common household chemical attack. Emerytop 400 can meet each of these challenges.

Emerytop 400's durability in these hostile conditions is being proven every day not only in solid waste transfer stations, but also in those floors that are required to be resistant to high impact loads, high abrasion and mild chemical attack. Typical installations for Emerytop 400 include heavy equipment maintenance areas, manufacturing plants, machine shops, track wheel vehicle areas, and waste container roll-off pads. In short, any floor surface that is subject to significant impact and abrasion can benefit from Emerytop 400.

Abrasion is the most significant challenge to a high strength topping mortar. Constant movement of large front-end loaders, moving trash across its surface 24 hours a day, 7 days a week, takes a major toll on this floor like no other. Independent tests prove that Emerytop 400 floors withstand twice the abrasive wear of iron toppings, and provide from 6 to 8 times the abrasion resistance of a standard 5,000-psi concrete floor. This factor provides economic rationale for investing, up-front, in an Emerytop 400 floor. The collective benefits of an Emerytop 400 floor over the long term provide the best investment in either new construction or rehabilitation of an existing facility.

But wait-There's more!
An Emerytop 400 floor costs less than its iron topping competitors. High strength toppings are normally placed in thicknesses of inch to 3 inches, depending upon anticipated wear. For many municipalities, initial placement cost becomes a major budget factor. All topping projects are specified by the thickness of the topping to be applied to the concrete substrate, but the topping mortar is packaged in a bag and sold by the pound. Having a much lower specific gravity than that of an iron aggregate gives the emery-based product a yield advantage over the iron product, simply because it can cover more per pound.

For example, for each one-inch depth of topping the material requirements per square foot are 14 pounds of Emerytop 400 compared with 18.7 pounds required of conventional iron topping mortars. That's 4.7 more pounds for the same inch! Therefore, inch for inch, using Emerytop 400 requires 25% fewer pounds than does using an iron topping. This results in significant material cost savings, even while the owner gets a more effective product.

In summary, with twice the life expectancy of iron topping, equal impact resistance, the non-rusting benefits, a significant initial 25% savings in material yield, Emerytop 400 is a bargain even before you factor in the rising price of iron aggregate.

Do I need to say more? It's no miracle, nor is it too good to be true. It's just good, sound material engineering coupled with the best raw materials available. That's what we offer every day at L&M.

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© 2005 L&M Construction Chemicals, Inc. | ConcreteNews Winter 2005.

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