Unlike normal portland cement concrete, acrylic concrete contains no water and no portland cement. Aggregate is held together instead by an acrylic polymer. On the jobsite, during curing, acrylic molecules called monomers join together with other molecules of the same type to form long-chain acrylic polymers. Polymers are hard, tough solids; monomers from which polymers are made are generally thin to thick liquids. Acrylic concrete is normally made from either of two monomers: methyl methacrylate (also called MMA), or high molecular weight methacrylate (HMWM).
USES AND ADVANTAGES
Because it develops compressive strengths of 5,000 to 10,000 psi in 1 to 2 hours, acrylic concrete has been used to repair pavements, bridge decks, parking decks, and warehouse and factory floors that cannot be closed to traffic for several hours or days. Acrylics also naturally resist wetting by water. And because no water is used to make acrylic concrete, the concrete has few voids, making it dense and impermeable. Because of this, it resists intrusion of water, chlorides and most other corrosive chemicals, including bases, oils, detergents and fats. Unlike portland cement concrete, acrylic concrete resists strong acids.
MMA OR HMWM?
While both methyl methacrylate (MMA) and high molecular weight methacrylate (HMWM) gain strength in a matter of hours, they are different in a few important ways. MMA has a low flash point, produces a nontoxic but disagreeable odor, and has a short pot life. HMWM, on the other hand, has a high flash point and its odor is not strong. Less volatile than MMA, it will not evaporate as quickly. Because of its lower volatility, HMWM also can be formulated with a longer pot life than MMA.
MAKING ACRYLIC CONCRETE
When an acrylic monomer is shipped from the manufacturer, it normally contains an inhibitor to prevent the monomer from polymerizing spontaneously. At the jobsite, an initiator is added to activate the polymerization process and a promoter is added to speed up the process. For MMA and HMWM, benzoyl peroxide is a commonly used initiator, and dimethyl paratoluidine (DMPT) and dimethyl aniline (DMA) are widely used promoters.