Micro Surfacing Quality Trouble

The following are the most common problems with potential solutions. It may take an investigative approach to determine the actual problem. If you are experiencing a problem not addressed here, consult the ISSA Inspector’s Manual.

IF FINISH TEXTURE IS TOO ROUGH:

• Discuss with contractor to modify secondary strike off setting.
• Application rate may be too low for the aggregate gradation.
• Mixture being placed may be too dry or may be breaking too fast.
• If using Type III aggregate, it may not be possible to decrease the roughness.

IF FINISH TEXTURE IS TOO SMOOTH:

• Discuss with contractor to modify secondary strikeoff setting.
• Application rate may be too high for gradation.
• Excess liquids may be floating emulsion to the top.

IF DRAG MARKS APPEAR IN FINISH MAT:

• Aggregate may be oversized, improve stockpile quality control and screen aggregate if you are not already doing so.
• Material may be built up, scrape pugmill and spreader box more often. Clean pugmill and spreader box daily at a minimum, and more often as needed to provide a proper application.
• Mix may be breaking too quickly, use additive to slow down the break and set of the material.

IF EXCESS LIQUID IS COMING OUT OF THE SPREADER BOX:

• If a test strip was placed successfully, determine what condition changed since then.
• Decrease water content added to the mix.
• Verify paver is set to the proper ratios as specified in the Job Mix Formula (Mix Design).
• Decrease the amount of water used to fog the pavement.

IF MIX IS BREAKING TOO FAST, INCLUDING SETTING UP IN THE CORNERS OF THE SPREADER BOX:

• Verify paver is set to the proper ratios as specified in the Job Mix Formula.
• Understand how the mineral filler affects the mix, it varies with different Job Mix Formulas.
• Determine how the mix reacts at both the upper and lower end of the mineral filler range specified in the Job Mix Formula.
• Determine if the aggregate has been contaminated, particularly with soil.
• Verify the spreader box augers are not worn excessively, and are turning in the right direction.
• Verify the asphalt emulsion strainer is clean, to ensure sufficient flow to the pugmill.
• Fog the pavement ahead of the spreader box with water.
• Ensure that asphalt emulsion is formulated for current temperatures.
• Check the asphalt emulsion temperature to determine if it is too hot.
• Check the gradation and sand equivalence of the aggregate.
• Add retarder (additive) to the mix.
• Verify the pugmill water delivery system is not clogged in the strainer or pugmill spray hood.
• Add water to the mix, but ensure the consistency does not get too wet.
• Verify the pugmill is running at the proper speed, excessive speed can cause early breaking.
• Verify the surface is clean, as dust and dirt on the street can cause the emulsion to break.

IF MIX IS BREAKING TOO SLOW:

• Verify paver is set to the proper ratios as specified in the Job Mix Formula.
• Understand how the mineral filler affects the mix, it varies with different Job Mix Formulas.
• Determine how the mix reacts at both the upper and lower end of the mineral filler range specified in the Job Mix Formula.
• Reduce the retarder (additive) being added to the mix.
• Reduce the water being added to the mix.
• Ensure that the asphalt emulsion is formulated for current temperatures.

IF DRY AGGREGATE ON PAVEMENT:

• On a continuous paver, check the nurse truck/paver interface, ensure all aggregate is deposited in the front hopper.
• Check conveyor(s) seals, repair if necessary.
• Check pugmill/conveyor belt interface, ensure all aggregate is being deposited in pugmill.

IF THERE IS EXCESSIVE RAVELING:

• The aggregate may lack sufficient embedment in the matrix caused from insufficient asphalt quantity to hold the larger aggregate.
• Poor quality aggregates may de-bond from the matrix.
• The application rate may have been too thin to hold larger aggregates.
• The matrix may have a lack of fines to fill voids between larger aggregates.
• Cooler temperature may result in slowing of the cure necessary for traffic.
• The project may have been prematurely opened to traffic.
• The project may have been exposed to rain before final cure was achieved.

IF THERE ARE EXCESSIVE TIRE MARKS AND SURFACE ABRASION:

• The base asphalt may have been too soft.
• Rolling of low traffic areas will properly set the aggregate in the matrix.
• For subsequent projects, the Micro Surfacing could be placed during cooler weather, to allow a full cure before being exposed to traffic at elevated temperatures.
• Broadcast sand to help break the bond and friction between the micro surfacing and vehicle tires.