Cement vs. Epoxy vs. Polyester

What does precision grout do?

After being placed and hardened in the space between the machine or equipment base and the foundation, the grout is expected to perform one of the following functions:

1. Permanently maintain the initial level and level of machinery or equipment and transfer all loads to the foundation when removing shims and other temporary positioning devices.
2. Provide lateral support or corrosion protection for shims designed to transfer all loads to the foundation. Some grouts are also required to provide sound deadening and a mechanism to reduce vibration. This can often be achieved by a composite system consisting of elastomeric bearings and a structural adhesive.

The most important requirement of the grout that is intended to transfer the load to the foundation is to have volume change characteristics that lead to complete and permanent filling of the space. Simple grout, consisting of cement, aggregate and water, does not have those characteristics. Several other properties of grout such as consistency, strength, chemical resistance and compatibility with the operating environment are also important.

What factors determine which type of grout you need?

1. The size of the base plate

The size of the base plate determines the usage method:

• Little: Pouring is usually good
• big: It needs pumping
• Lack of access to pour: It needs pumping

2. Loading

dynamic:

This can be impact force such as hammer press, reciprocating machinery or repetitive forces such as crane rails or rail systems. Dynamic forces can cause cracks or fatigue in cementitious grouts. In these cases, use resin-based grout.

static:

T-hose that creates less stress (such as gaps under columns, footings, holes, cavities, general filling operations). These items require cement based grout.

3. Dimensional stability

Grouts must not be collected:

• Cement based grouts must be non-shrinking in the short term (plastic shrinkage) or long term (drying shrinkage).
• Resin-based grouts should not clump during curing.
• Grouts should also have thermal movement properties that are compatible with their surroundings.

4. Resistance to chemicals

The slurry should not react with metal as most bearings and plates are metal. Some slurries may react with the metal and produce corrosion or gases that affect the bond and can cause failure.

Grouts must be resistant to oils, greases and certain solvent chemicals as well as salts when used in marine environments.

5. Durability

Grouts must be resistant to creep (deformation over time) to allow intimate contact between bearing and foundation and effective stress transfer.

Precision grout should last at least 10 years – most resin grouts last longer than cement grouts, especially under dynamic loading conditions. They have a higher upfront cost, but their long life and the fact that they don’t need to be replaced regularly makes them much more cost-effective in the long run.

6. Effective bearing area

6. منطقه تحمل موثر

• Effective bearing area (EBA) is the proportion of slurry in close contact with the bottom surface of the bearing plate.
• The grout should provide at least 90% EBA.
• EBA is affected by poor grout flow, air voids, entrainment of air in the grout, and poor injection operation design.

7. Return to service

Engineers calculate the necessary resistance against initial stresses in the bearing application. Many grouts set quickly, allowing for an earlier return to service, but these grouts often generate heat, which can reduce work time and affect grout integrity, especially in thicker sections.

8. Gap size

A grout must fill the gap under a bearing plate, which may vary due to unevenness of the foundation.

Thin gaps (less than 5 mm) should be avoided because most grouts make it difficult to transfer load on this wafer-thin section.

Some epoxy grouts and structural adhesives are designed for thin sections but require additional considerations.

Most gaps between 15 and 50 mm can be easily grouted by pouring or pumping.

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