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IDENTIFYING TYPE OF CONCRETE

Correctly identifying the material being cut is probably the single most important factor in choosing a blade. It directly affects the cutting speed and life of the blade. Many other variables influence blade performance. Changing any one variable alters the performance of the blade.

As a general rule determine the material, which will be cut most often, or the material for which top blade performance is most important. Though they often look similar concrete slabs may vary greatly. Before choosing a blade many factors must be considered.

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Diamond Blades

Green or Cured Concrete
The drying or curing time of concrete greatly affects how the material will interact with a diamond blade. Green concrete is freshly poured concrete that has set up but is not yet fully cured. It is softer and more abrasive than cured concrete. A harder bonded blade with undercut protectors is appropriate to cut green concrete. A softer bonded blade is needed to cut the same concrete in a cured state.

The definition of green concrete can vary widely. Weather, temperature, moisture in the aggregate, time of year and the amount of water in the mix all influence curing time. Also, much of the concrete made today has additives, which can either shorten or extend curing time. Consult your mix design to find the relative curing time for each job. As soon as wet concrete sets up and does not spall or ravel, green cutting can begin.

Types of Sand
Sand is the part of the aggregate mix that generally determines the abrasiveness of concrete. Crushed sand and bank sand are sharp (abrasive) and river sand is usually round (non-abrasive).

Green concrete has more loose sand and as a result is more abrasive than cured concrete. When concrete is not fully cured sand can easily be scraped off the surface being cut. More loose sand means more abrasiveness.

Amount of Steel Rebar Reinforcing
Heavy steel reinforcing tends to make a blade cut slower. Less reinforcing tends to make a blade cut faster. Light to heavy rebar is a very subjective term. The following is a guideline of some types of reinforcing.

STEEL REBAR REINFORCING

Light

Wire mesh, single mat

Medium

#4 rebar every 12" on center
each way, single mat

Wire mesh, multi mat

Heavy

#5 rebar 12" on center each
way, single mat

#4 rebar 12" on center each
way, double mat

Rebar will rate heavier or lighter depending upon the grade of steel. Typical rebar is grade 40 steel and is assumed in the chart above. If grade 60 steel is used the #4 rebar in the medium category would be rated as a heavy rebar. Rebar gauges are measured in eighths of an inch -#4 rebar is 1/2" diameter, #5 is 5/8", etc. Where rebar specifications do not exist; pull a core sample of the concrete before buying a blade.

Compressive Strength
Compressive strength is measured in pounds per square inch (PSI). While most roads are 4-6,000 PSl, typical patios or sidewalks are about 3,000 PSI.

Concrete Hardness	PSI
Critically Hard	8,000 or more
Hard	6-8,000
Medium	4-6,000
Soft	3,000 or less

Hardness of Aggregate
When cutting hard aggregates the diamond grit dulls quickly so segment bonds generally need to be soft. This allows the segment to wear normally and bring new, sharp diamond grit to the surface. Softer aggregates will not dull diamond grit as quickly, so harder segment bonds are needed to hold the diamonds in place long enough to use their full potential.

Many different types of rocks are used as aggregates in concrete. The Moh's Scale of Hardness is often used to rate rocks on a scale of one to ten. For general geographic information on aggregate hardness in the U.S. refer to the aggregate map.

Size of Aggregate
The size of the aggregate also affects diamond blade performance. Large aggregates tend to make a blade cut slower while smaller aggregates tend to make a blade cut faster. The most common aggregates fall into three sizes: pea gravel; 3/4" or 1-1/2". Pea gravel is usually 3/8" or less in diameter.

Bon Tool Co. has made a serious effort to provide exact and current information, but does not guarantee the accuracy of the data. Bon Tool Co. cannot assume responsibility for the application of information nor guarantee results.