Gomaco, together with ISU Research and Manatt’s, were on site checking and recording data with the help of Gomaco’s non-contact profile device, the “GSI” (Gomaco Smoothness Indicator). The GSI is a device that records the profile of each wheel trace simultaneously, displaying results on a computer monitor and then by print out at the end of each day. Each sensor takes measurements 40 times/sec and in Tama Co. the GSI traveled at approximately 17ft/min, which means it, would have taken an average of approximately 272 readings every 2”.

GSI Sensors Attached to Paver

Monitor on the paver displaying traces

For the first three days, four sonic sensors were placed directly on the paver behind the pan and at each wheel path for each lane and the other four sensors were on the GSI, which recorded data behind the cure texture machine.  This was very interesting and we were able to compare the traces behind the paver, before the V-screed and then the same path directly behind the texture machine.  There was some correlation between the traces but what was evident was the PI numbers were considerably higher behind the texture machine, as a result of the chips being pulled to the surface by dragging the astroturf which is required by spec for micro texturing. With the IDOT’s permission we did switch the astroturf for a burlap drag for two segments and as a result less chips were pulled to the surface, and better readings were achieved for those segments.

    After the first three days of paving, sonic sensors were shifted into various positions in the paving train to compare and correlate the affect of each operation behind the paver.  Results were compared directly behind the pave pan, behind the v-screed, behind the finishers, and then after the cure texture machine. This was able to give us an indication of how each operation contributed to the smoothness of the road. One of the many things tried, was once strength was achieved we ran a light blade and a mechanical broom over the surface removing any excess chips that would otherwise be counted in the trace and work against us. The QC team was able to push the California profilograph before and after the blade and sweeping operation, producing traces that indicated to us that the sweeping operation reduced our PI results by approximately 8 to 10 points, which in some segments would mean the difference of 0% incentive to 100% incentive.

    As you can imagine all this created a ton of traces to try and correlate and compare, and these are currently being done.  Although we can gain a lot from measuring smoothness with the aid of the latest technology such as the GSI, achieving a smooth road comes from the efforts of the string line crew, paving crew and finishers, wet batch trucks staying clear of the string line and a supply of a consistent concrete mix.  On the Tama County Project, I believe this was achieved, as we ended up with zero grinding on the project and a road with a smooth ride. Well done to Ponch’s crew and all those involved for their efforts on the Highway 30 Project in achieving a smooth road.

    Manatt’s would also like to thank the Gomaco Corporation and ISU research for their involvement and sharing their data collected on this project.