What:  Diamond grinding  uses closely-spaced diamond saw blades to remove a thin layer at the surface of hardened Portland

cement Concrete Pavements.  The blade assembly is run at a predetermined level (typically 3/16 to 1/4 “) across the pavement surface, producing saw cut grooves.  The uncut concrete between each saw cut breaks off, leaving a macroscopically level surface with longitudinal texture.  The new riding surface is level, smooth and quieter.  The closely spaced grooves give the riding surface excellent texture and frictional properties, reducing the potential for hydroplaning.  Diamond grinding is also often done in conjunction with other concrete repair methods to smooth the surface over and around repair sites.

While diamond grinding is sometimes used on asphalt pavements, it should not be confused with milling or scarifying.  Milling is an impact process that chips small pieces from the pavement surface.  Diamond grinding is an abrasive process.

Where:  Diamond grinding is appropriate on pavements with faulting, curling, warping, loss of friction and/or ruts caused by studded tires.  It is also used in conjunction with other concrete repair methods.

Why (advantages):  Provides a smooth riding surface that is often as good or better than a new pavement, removes faulting at joints and cracks, removes construction curling and moisture-gradient warping of the slabs, and removes other construction or environmental related roughness.  Diamond grinding enhances the surface texture and friction, and it reduces road noise and improves safety.  The improved macrotexture and the removal of ruts caused by studded tires reduce hydroplaning and accidents in wet weather.  Diamond grinding may be done in isolated areas as needed and during off-peak hours.  By providing a smooth surface, diamond grinding limits the dynamic loading, therefore extending the useful pavement life.  One of the lowest cost and quickest concrete treatments, diamond grinding is a cost-effective pavement preservation treatment.

Why not (disadvantages):  If the load transfer is deficient, faulting of the pavement joints will most likely recur.  If load transfer is not restored by other concrete pavement restoration techniques, such as dowel bar (load transfer) retrofit or undersealing, faulting will persist.  Diamond grinding does not correct any structural problems such as slab cracking or material problems such as reactive aggregates.  While removing more thickness than necessary to address the surface problems is not recommended, studies have shown that diamond grinding does not negatively affect fatigue performance when properly applied.  Diamond grinding does not significantly increase material durability.

When:  Diamond grinding may be done at any time when the distresses occur.  The earlier the problems are addressed, the fewer problems will be encountered in the future.  Diamond grinding can also be used to correct initial roughness due to construction problems and provide uniform skid resistance and appearance on new pavements.

Estimated life extension:  8-17 years.

For more information, see the Checklist for Diamond Grinding put together by FHWA and the Foundation for Pavement Preservation.

Micro Surfacing

What:  Micro surfacing is a high performance enhanced slurry seal composed of a mixture of polymer modified emulsified asphalt,

dense-graded crushed fine aggregate, mineral filler, break control additives and water.  The emulsifiers and additives allow micro surfacing to be placed at thicknesses up to 1.5 inches and the surface to cure in less than an hour. (Slurry seals are applied at the thickness of the largest aggregate, and can take up to 8 hours to cure sufficiently for traffic return.)  Micro surfacing requires a special machine with an attached spreader box with a double strike-off blade design.  The micro surfacing unit can be truck-mounted or self-propelled.  A special rut box is used for filling ruts over ½”.  Micro surfacing is used to fill non-working ruts, to restore skid resistance and as a preventive maintenance treatment for both flexible (asphalt) and rigid (Portland Cement Concrete) pavements.  It is available in two types, determined by the maximum aggregate size.  Type II, with slightly smaller average aggregate size, is used to fill surface voids, address surface distresses, seal, and provide a durable wearing surface on airports and city streets.  Type III, with a larger average aggregate size, provides maximum skid resistance and an improved wearing surface, and is used for heavily traveled highway, collectors and interstates pavements, for rut filling, or for placement on highly textured surfaces requiring larger size aggregate to fill voids.

Where:  Flexible or rigid pavements in good structural condition with loss of friction, non-working ruts, and/or low to medium severity surface distresses such as cracking and raveling.  Any cracks greater than ¼ inch should be sealed prior to micro surfacing.  Micro surfacing is an effective pavement preservation treatment for very high volume roadways where quick traffic return is important.  It has been successfully used on all types of pavements including airports, parking lots, residential streets, city streets and interstates.

Why (advantages):  High quality materials, strict specifications and performance-based design procedures yield a high performance surface that corrects minor surface profile irregularities, fills ruts, cures quickly for traffic return in less than an hour, lasts longer than some other surface treatments such as slurry seals, and can be constructed at night (or cooler temperatures).  It protects the pavement structure from moisture and the surface from further deterioration.  Micro surfacing is a cost-effective alternative to hot mix asphalt overlays for pavement preservation of concrete pavements as well as asphalt pavements.

Why not (disadvantages):  Micro surfacing requires special equipment that is heavier than a slurry machine.  The cost is higher than a slurry or chip seal treatment.

When:  Micro Surfacing should be applied when the pavement structure is in good condition, but there are minor to moderate surface distresses.

Estimated life extension: 6-8 years over pavements in good condition; 5-7 years on pavements in fair condition; 2-5 years for pavements in poor condition.

For more information on successful micro surfacing, consult the Micro Surfacing Checklist put together by the Foundation and FHWA