Husqvarna PG820, PG680 manuel dutilisation Determining the hardness of concrete

Diamond selection

Determining the hardness of concrete

All concrete may feel hard (particularly if you fall over on it), so what do we mean when we talk about hard, medium and soft concrete?

All concretes are measured by their compressive strength and depending on which part of the world you are from, different compressive strength indices (e.g. PSi & MPa). Generally speaking, the higher the com- pressive strength rating, the harder the concrete and therefore, the harder it will be to grind.

However, other factors beside compressive strength ratings determine how hard the floor will be, and therefore, the correct diamond selection. Since grind- ing normally only deals with the surface of the concrete (top 5mm or 1/4 inch), often the way the concrete floor has been finished or the condition of the surface will have a greater bearing on what type of diamond to select, rather than the compressive strength rating of the concrete.

SURFACE FACTORS TO CONSIDER WHEN MAK-

ING A DIAMOND SELECTION

Generally speaking, if a concrete surface is very smooth (i.e. Most likely it has been heavily trowelled/ helicoptered), the concrete will behave as if it has a high compressive strength and therefore, require a soft bond segment.

Accordingly, if a concrete surface is coarse/aggressive (e.g. rain-damaged, shot blasted, scarified, exposed aggregate e.t.c.), the concrete will behave as if it has a low compressive strength and therefore, require a hard bond segment.

Surface coatings/contaminants (e.g. Epoxy coatings, ceramic tile adhesives, levelling compounds/screeds) will often have a larger bearing on what diamond to se- lect, than will the compressive strength of the concrete.

As a general rule, when grinding a concrete slab for the first time and you are unsure about its hardness, always begin with harder bond diamonds under the machine. This will ensure the least amount of wear on the diamond segments. If a hard diamond segment is not suited to the application, all it has cost is a little amount of time without wearing out the diamonds.

If performed the other way around (i.e. a soft segment is used to begin with) and the concrete is soft or pos- sesses an abrasive surface or surface contaminant, it is quite possible to wear-out a considerable amount of diamond in very short period of time.

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