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Cement Grout vs. Chemical Grout: Which One to Use, When, and Why
Used on a myriad of new and rehabilitation construction projects, cementitious and chemical grouts share a common category and name, but the distinct differences far outweigh the common qualities. Both grout types are used in civil applications ranging from sewer pipe rehabilitation to new tunnel or shaft construction, used to fill narrow cavities/cracks, rock fissures or to permeate soils for the control of groundwater, void filling or to increase structural support of the geology. Although cement and chemical grouts can differ in composition, application and cost, they are ultimately complementary products on the same projects. This paper will explore when and why to use the various types of grouts and the cost range of each product.
The practice of injecting grouts and the wide array of grout products available can make choosing the right grout for the project complicated. Because it’s difficult to summarize the complexity of the topic into a single paper, some specific topics within this paper have been generalized for simplicity. If a situation exists on your project where grout injection is required, a qualified grouting contractor and an experienced grouting consultant should be engaged to provide grouting and installation recommendations and a knowledgeable grout supplier, like Avanti International, should be consulted to assist with proper grout selection.
Grout Family and Subtypes
Grouts used in civil construction and rehabilitation projects can be generally categorized into either a cement or chemical grout. Within each grout family, there are primary grout subtypes: within the cement grout family, ordinary Portland cement and ultrafine cements define these subtypes. The chemical grout family includes sodium silicate, acrylic gels and polyurethane expansive foams. Although each parent grout type has primary grout spawns, this is where the commonalities end and the individual grout types split into their own unique characteristics.
Cement grouts are considered to be suspended solids grouts, because they have particulates that comprise their composition which is derived from grinding Portland cement clinker. The level of grinding effort applied to the clinker determines the average particulate size. Portland cement grout generally has particulate sizes on average of 15 microns. Microfine cements range from 6 to 10 microns while ultrafine cements can have average particulate sizes of 3 to 5 microns. US Grout in Malad, Idaho, can provide custom blended cementitious grouts meeting project specific requirements. A grout’s ability to penetrate a rock fissure largely depends on particulate size whereas its ability to permeate a soil is also dependent upon surface tension within the grout. A cement’s rheology, which is the grout’s ability to flow, is accomplished through the control of the water/cement ratio and almost always a superplasticizer is added to reduce viscosity. While additives can be added to slow the cure time, once mixed with water, cement grouts will begin to cure and create high compressive strength. Once injected, cements are considered long-term solutions for either water control or structural improvement having lifespans ranging between 100 to 200 years. Ordinary Portland cement costs (mixed) will typically range between 1 and 2 dollars a mixed gallon while microfine/ ultrafine cements costs (mixed) will typically range between 3 and 4 dollars per mixed gallon. These costs can further reduce when higher water/cement ratios are employed.
The primary types of chemical grouts (silicates, acrylics and polyurethanes) are each unique in composition. Although it’s truly a suspended solids grout, because the particulates are so small sodium silicates have a high degree of penetrability into soils and rock, very similar to the true solution grouts, which have no suspended solids. Sodium silicate is a two-component grout that typically has very low viscosity but will often expunge water after gelling by a process called syneresis. Sodium silicates can be sensitive, bordering on unstable, when injected into any groundwater condition. With relatively short gel times, a few minutes to a few hours, sodium silicates are commonly used as temporary solution for water control or structural support with an estimated life span of a few years. Longer life spans can be experienced with silicates depending on the chemistry of the soils. Sodium silicates typically range between 2 and 3 dollars per mixed gallon.
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