Grout is a fluid-consistency cement mortar used to fill voids and joints in masonry and to repair cracks. Grouting is the process of injecting liquids, mixed suspensions, or semi-solid mixtures under pressure to achieve one or more desired end results in terms of engineering properties.
Grout differs from mortar since it is poured rather than spread into place with a trowel. Cement, fine or coarse sand, water and a small amount (if any) of grouting admixture are the main ingredients of grout mixture.
Uses of Grouting
- Grout is used to fill the spaces between tunnel walls and the surrounding earth in order to distribute earth stresses evenly across the structures.
- Grout is widely used in dams to fill cracks that form after the concrete hardens and sets.
- Grout is also used to inject soil to increase its bearing capacity.
- Grouting can be used to improve the mechanical properties of soil or rock foundation materials used to support structures or excavations.
- Grout is also used to fill hollow concrete blocks in order to develop a bond between the steel reinforcement and the concrete.
Applications of Grouting
- The main application is the control of ground movement during tunneling operations.
- Used to regulate the control of groundwater flow.
- It is also applied for strengthening of soil to reduce the need for lateral support.
- Control of volume change in expansive soil via pressure injection of lime slurry.
- Soil strengthening for piles to increase their lateral and vertical resistance.
- To avoid excessive settlement, voids must be filled by grouting.
- For stabilizing loose sand to prevent liquefication.
- Underpinning of foundation.
Types of Grout Materials
Grouting is also caterogized according to the material used in mix. Some of the grout materials are mentioned below.
- Asphalt Grouts
- Cementitious Grouts
- Chemical Grouts
- Epoxy Grouts
Asphalt Grout
In certain instances, asphalt grouts or hot bitumen are applied to stop quickly moving water.
At room temperature, asphalt is a solid, and it must be heated to above 275°F to become a flowable, viscous liquid. The hot bitumen is pushed into moving water, where it quickly cools and thickens, generating a weak clog.
Cementitious grouts are typically used after the running water has been stopped or slowed to increase the application’s permanence.
Cementitious Grout
Cementitious grouts are the most often used grouting materials, and they are classified according to their mobility. In order for a grout programme to be cost-effective, the grout must have enough mobility to fill the discontinuities intended for treatment while not flowing too far outside the treatment zone.
Cement grout can be applied at temperatures ranging from 32°F to 110°F, with no particular precautions needed to assure appropriate application.
General Properties of Cement Grout :
| Compressive Strength | 20-7 N/ mm2 |
| Tensile Strength | 1.5-3.5 N/ mm2 |
| Flexral Strength | 2-5 N/ mm2 |
| Elastic Modulus | 20-30 GPa ( IGPa=103 N/mm2 ) |
| Water Absorption | 5-12 % |
| Strength Development | 7-28 days |
| Linear Coefficient | (7-12) × 10-6/ C |
Chemical Grout
Often referred to as “chemical grouts,” these grouts are more accurately referred to as chemical solution or solution grouts. Solution grouts that are commonly used include sodium silicate, urethane, acrylate, and acrylamide.
Because of their capacity to set practically instantly within varying, but manageable time periods, these materials are particularly useful for water control. However, there are drawbacks, such as shrinking and swelling during wetting and drying cycles, as well as certain real and imagined environmental consequences.
Epoxy Grout
Epoxy grout differs greatly from the more common cement grout. Epoxy grout is made of epoxy resins combined with a filler powder and hardener, making it extremely strong and long-lasting. This makes it waterproof and nearly stain-resistant.
Because of its durability, it is an excellent choice for counter tops, outdoor patios, pool decks, splashbacks, and water line pool tile. It is also significantly more expensive than traditional grout.
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Types of Grouting Methods
Different grouting methods are used for different purpose. Major grout methods used in the construction industry are mentioned below.
- Jet Grouting
- Hydro-fracture Grouting
- Premeation Grouting
- Compaction Grouting
Jet Grouting
Jet grouting is a grout technique for forming soilcrete shapes in situ (grouted soil). Jet grouting entails injecting grout under high pressure (sometimes assisted by air and/or water jetting) to mix in-situ soil with cement to make “soilcrete”.
Jet grouting can be done in three different ways:
- Single Tube
- Double Tube
- Triple Tube
Jet grouting results can range from modest mixing to practically total replacement of in-situ soils with grout, depending on the jet grouting technology chosen and the withdrawal rate. Jet grouting can be used on any type of soil.
Hydrofracture/ Frac Grouting
The basic idea behind hydrofracture grouting or frac grout, is to inject grout under pressure into the soil, causing tensile failure and the injection of grout lenses into the soil.
It is typically employed to compact and harden the earth or to gain access to voids that are otherwise unreachable.
Permeation Grouting
The process of filling joints or fractures in rock or pore spaces in soil with grout without affecting the formation is known as permeation grouting.
Permeation grouting of soil is limited to soils that can be permeated reasonably quickly due to cost constraints.
Compaction Grouting
Compaction grouting is a grout technique that uses staged injections of low-slump, low mobility aggregate grout to displace and densify loose granular soils, reinforce fine grained soils, and stabilise subsurface voids or sinkholes.
Compaction grout is the preferred method for repairing settlement damage and minimising future damage by reducing future settlement through densification.
Admixtures in Grouting
Admixtures are widely used in grout mixtures for various purpose. Accelerators, retarders, gas forming and workability agents are some of common types of admixtures used.
In circumstances where a plugging effect is required, accelerators such as calcium chloride or triethanolamine are added to decrease the setting time.
The retarders or gas forming agents, such as lime sugar, mucic acid or gypsum are used when the grout is to be pumped.
As water-reducing admixtures, workability agents such as flyash, bentonite clay, diatomaceous earth and others are used.