Tensile strength is approximately 10% of concrete’s compressive strength.
When you add new concrete to existing concrete the interface will result in a cold joint and vibration will not transfer across a cold joint. In this situation, special materials will need to be considered in order to bond with the existing concrete. A foundation or mass can be extended with Escoweld or Chockfast materials if the correct concrete preparation is done.
A foundation should be at least 6 inches wider than the base plate for motors up to 500 HP and should be 10 inches wider for 501 HP and up.
You need to consider the weight of the equipment, driver and base plate weight and make sure the soil is strong enough to support this weight (3 to 5 times mass) in both static and dynamic loads.
Grout is the effective conduit transferring unwanted vibrations form the equipment to the foundation. A good epoxy grout is a vital component for vibration transfer.
You can reduce vibration in the equipment by properly transferring the vibration out of the machine to a properly sized foundation. This should be done through use of epoxy grout material.
If multiple equipment is set on the same foundation, one piece of equipment can pollute the other piece of equipment causing a sympathetic vibration.
For rotating equipment, the foundation mass should be three times the mass of the equipment. For reciprocating equipment, the foundation mass should be five times the mass of the equipment.
Concrete needs to be completely hydrated which is typically 28 days with standard concrete. Concrete could be hydrated faster than 28 days but would need to be tested to verify full hydration.
Assuming the concrete is properly cured, grout can be poured after all concrete laitance is removed.
A concrete foundation should be prepared for grout by removing all laitance with a chipping hamper with a chisel bit.
A foundation should be between 65°F to 90°F to install grout. Having the right temperature is important to ensure proper flow, adhesion and cure of the grout material.
The depth of the foundation should be beep enough to properly embed the anchor bolts. This would vary based on the size of the equipment. First, consider the mass required for the foundation. Next, consider the 30 degree rule for a stable footprint.
All concrete should have a minimum compressive strength of 4000 psi at 28 days.
Remove all laitance with a chipping hammer.
Make sure the concrete is properly hydrated.
Be sure the concrete is free of any oil or contaminants.
Multiple concrete pours are not recommended as there will be a cold joint between pours and vibration will not transfer across a cold joint.
A cover may be necessary to protect a foundation from sun, wind and rain.
The foundation should be covered to keep the grout from being exposed to direct sunlight.
The foundation should be completely enclosed and provided with a heat source to raise the entire foundation and equipment to a temperature above 65°F for 48 hours prior to and after a grout pour.
It is unacceptable to sand blast a foundation in preparation for grout. Preparation will need to be done with chipping hammers. A chipping hammer will properly profile the foundation and remove the laitance layer.