Silicates, acrylics, and polyurethanes. Portland cement and ultrafine cements. Gels and foams. There are just two categories of grout for stopping leaks, stabilizing soil, and controlling water in sewer and water pipelines: cement and chemical. But thanks to various subtypes, formulations, and application methods — all of which impact price — specifiers face a bewildering array of options when choosing the product that will provide the best long-term value.
Cement: the go-to grout for new construction
Ninety-five percent of all grouting projects use cement grouts for new construction projects ranging from dams and tunnels to subway construction. This product family comprises three cement subtypes: ordinary portland, microfine (from foreign slag), and ultrafine (from domestic pumice).
All are “suspended-solids” grouts because the cement contains particulates that vary in average size:
- Portland cement – 50 to 100 microns
- Microfine – 6 to 10 microns
- Ultrafine – 3 to 5 microns
Particulate size is important because it can affect the ability of a cement grout to permeate soils or penetrate rock cracks. The smaller the particulate, the finer the soil it can permeate or the smaller the crack it can penetrate.
It is predominantly used in new construction to strengthen soils or to stabilize rock and control groundwater flow for dams, tunnels, and subways. For rehabilitation projects, it can be used to lift structures back into alignment, e.g., sagging pipeline.
Benefits: high strength, longevity, readily available
Lifespan: 100 to 200 years
Cost: $1 to $4 per gallon
Chemical grouts: strengthen soils, permanently control groundwater
Each of the three subtypes of chemical grouts (silicates, acrylics, and polyurethanes) is unique in composition.
Sodium silicates are suspended-solids grouts; instead of cement, the particulates are made of fine glass. Sodium silicate is a two-component grout requiring the sodium silicate and a hardener. When mixed, the injectable silicate typically has very low viscosity but will often expunge water after gelling through a process called syneresis, which can reduce its overall effectiveness to strengthen soil or control groundwater.
They temporarily strengthens soils and controls groundwater in soils.
Benefits: cost-effective and readily available
Lifespan: one to two years
Cost: $2 to $3 per gallon
Acrylamides and acrylates are “true solution grouts” because they lack suspended solids and have extremely low viscosity - similar to water. Also two-component grouts, they have a base resin that is mixed with a catalyst to create a gel or gel/soil matrix within a controllable time. The gel time for acrylamides is from a few seconds to 10 hours, while acrylates have limited gel times (one minute to one hour). Acrylamides generally form a better quality gel than acrylates.
Acrylamides are used to control groundwater infiltration in rehabilitating sanitary sewer pipelines. Both acrylamides and acrylates are used in new construction projects such as tunnels, subways, and deep excavations.
Acrylamide: three seconds to 10 hours
Lifespan: 300+ years
Cost: $6 to $8 per gallon
Acrylate: one minute to one hour
Lifespan: 50 to 60 years
Cost: $8 to $10 per gallon
Polyurethane foams and gels
Two types of grout are derived from polyurethane, which forms a foam or gel when mixed with water and is mostly used to control water through cracks in concrete such as manholes or underground vaults. Most manufacturers carry polyurethanes that have NSF or UL certifications approving their use in potable water applications.
Hydrophilic grouts are typically single-component systems; they begin to cure when they come into contact with water. They cure to an expansive flexible foam or nonexpansive gel requiring a moist environment to be functional long term, which is why they’re commonly used to control active water inflows. Hydrophilic foams expand four to six times their original volume.
Hydrophobic expansive foams are also typically single-component systems, but they require less water (4%) to react and can easily withstand wet/dry cycles. Hydrophobic foams cure to either a flexible or rigid state and expand up to 20 times original volume.
Highly expansive hydrophobic foams are suited for filling voids behind below-grade structures like manholes, vaults, and pipes. There are specially formulated foams used to lift concrete slabs to provide structural support, a process called slab-jacking. Because the foam weighs about 4 pounds per cubic foot, it’s a lightweight solution that won’t promote additional slab settlement like heavier mud-jacking material such as concrete.
Lifespan: 75 to 100 years
Cost: $60 to $90 per gallon
Fitting the product to the project
Be prepared to switch gears swiftly during new construction. Once a project’s under way, grouting may suddenly be required to control water or stabilize soil. Figuring out the right product can be a trial-and-error process.
It’s easier to determine which grout to use for rehabilitation because conditions usually are well known in advance.
In either situation, consult a grout consultant, qualified grout contractor, or a qualified grout supplier for advice.
—Britt N. Babcock, PE (firstname.lastname@example.org) is director of the Geotechnical Division for Avanti International, Webster, Texas. Visit www.avantigrout.com.