AcrylateGrout_final_for-September-issue_2015-3Resins that are chemical grouts are the perfect example of science and engineering going hand in hand.

“Grouting” describes the art — and science — of injecting a grout into soils, fissures and concrete cracks for stabilizing soil, sealing leaks and repairing structures. Chemical grouts are chemicals, both organic and inorganic, that can undergo the phase transformation from liquid to solid accompanied by the enhancement of their physical and mechanical properties during the curing process.

What’s in a Name?


In current common usage, grout materials are typically distinguished into two broad categories — chemical grouts and cement grouts. From a chemistry standpoint, however, this is an artificial distinction: Both undergo a chemical reaction. The curing of most cementitious grout systems is driven by the pozzolanic activity, which is how cementitious materials go from a liquid to a solid. Chemical grouts can be organic or inorganic based on the raw materials that make up the primary reacting resins and transform through a reaction triggered with an activator, sometimes water.

That said, we will observe the common usage here of “chemical” grout as we explore the development of acrylate resinous grout systems.

Chemical grouts are currently used for a number of structural, geotechnical and environmental applications. Some of the most common applications include soil stabilization, void filling, sealing leaks and lifting slabs.

Selecting the Right Product


Several factors dictate the selection of a grout for the desired application. For instance, soil stabilization by grouting requires considering the type of soil and its properties such as density and porosity, as well as the soil area and depth to be stabilized, and the water table depth.

The field conditions and requirements go hand in hand with the resin selection. The field conditions have a pivotal role to play.

For example, since most of the chemical reactions enabling the phase transformations are exothermic in nature, a chemical grout that has a gelling time of five minutes at optimum conditions could be used in a hot tropical climate, though the set time may be marginally shortened as the field temperature might be higher than the optimum. That same grout may not be appropriate, however, when the conditions are below the optimum temperature because the set time may be increased due to low field temperatures, which could result in excessive seepage of the grout outside of the area to be treated. Similarly, if this same resin is thin and easily flowable, it may not be a good option when the soil strata to be stabilized is shallow since the area to be grouted is often not a confined space.

Research and Development


Given the technical limitations and toxicity issues of acrylamide grouts and the need for flexible grouts with a wide adjustable range of set times, research and development in exploring the capabilities of acrylate resinous grout systems is under way.

Extensive research by Prime Resins has resulted in the emergence of two innovative grout systems, AR 800 and AR 870, which are engineered for geotechnical and structural applications under varied environmental conditions.

The Chemistry


AR 800, an acrylate-based chemical grout, is a three-component aqueous grout system that is used primarily for geotechnical applications. Independent testing verifies that it meets NSF/ANSI Standard 61 for contact with potable water.

The phase transformation is driven by the free radical polymerization reaction of the acrylate monomers. The AR 800 system may be used as a two-component system by premixing AR 800 with Primeset TEA and premixing Primeset SP with water. These two premixes may then be mixed and injected at a ratio of 1:1 by volume.

The reaction begins with the activation of persulfate free radicals by combining the two premixes (premix 1: Prime Set TEA and AR 800 resin; premix 2: Primeset SP and water). These SP-based free radicals react with the acrylate monomers to form acrylate-based free radicals, which in turn react with unreacted monomers to form a long chained solid polymer during the propagation phase of the chemical reaction. When all the free radicals are used up, the reaction terminates itself, leading to a long-chained acrylate polymeric grout.

AR 870 is also a three-component chemical grout system based on acrylate monomers that can be used as a two-component system by premixing the components. AR 870 is designed for applications such as sealing fine concrete leaks; the swelling capabilities of acrylate-based polymeric systems have been perfectly tapped to enhance the sealing capabilities of the grout.

The highlights of the AR 870 grout system are its extreme adhesion to concrete and the swelling capabilities under moist environments. The swelling of AR 870 ensures complete sealing of the cracks and fissures that might be a potential opening for water to enter a structure.

AR 870 is also tailor-made to be used in different environmental conditions. As with AR 800, the set time and performance depend upon using the right amount of the activator and the catalyst (TEA and SP) that carry through the polymerization of the resin.

Adjusting Set Times


Figures 1 and 2 provide guides to adjusting the set times of AR 800 and AR 870 based on the amounts of activator and catalyst added at different material temperatures.

Recommended Uses


AR 800 is appropriate for geotechnical applications such as curtain grouting below-grade parking structures or foundations and stabilization of sandy, silty soils. Lab testing proves that it can cure in the presence of extremely hot water (180 F or 82 C), making it feasible for deep mining applications.

AR 870’s outstanding adhesion, ultra-low viscosity and swelling capabilities make it well suited for sealing cracks in concrete structures such as culverts, water and sewer pipes, and other below-grade structures.

Acrylate Resins as another Option


Contractors and engineers who need a flexible, elastomeric grout for wet environments and want a wide adjustable range of set times should consider acrylate chemical grouts, which are acrylamide-free. They provide an excellent alternative to acrylamides, which are not permitted in many instances due to their toxicity. The adaptability of acrylate grouts in varied environmental conditions along with their performance make them another tool available for infrastructure repair projects.
Shiva Sunder, Ph.D., EIT, is with Prime Resins Inc., Conyers, Ga.