<p><p><h2>Preferred QC/QA Procedures</h2>This technology lacks formal QC/QA procedures. Several QC/QA procedures are applied corresponding to different chemical stabilization methods at various stages of construction. It is essential to ensure that soil properties will be achieved that provide a reliable working platform and pavement section as a result of the construction process. The thickness of the stabilized layer, moisture content, stabilizer content, compaction effort and delay, gradation of mixture, shear strength, and elastic properties are all parameters that can be assessed as part of QC/QA program.</p><p>Construction quality is achieved by meeting established requirements, as detailed in project plans and specifications, including applicable codes and standards. Quality Control (QC) and Quality Assurance (QA) are terms applied to the procedures, measurements, and observations used to ensure that construction satisfies the requirements in the project plans and specifications. QC and QA are often misunderstood and used interchangeably. Herein, Quality Control refers to procedures, measurements, and observations used by the contractor to monitor and control the construction quality such that all applicable requirements are satisfied. Quality Assurance refers to measurements and observations by the owner or the owner's engineer to provide assurance to the owner that the facility has been constructed in accordance with the plans and specifications.</p><p>The components of QC/QA monitoring programs for Chemical Stabilization of Subgrades and Base Courses are listed in Tables 1, 2, and 3. The entries in the tables are a list of typical items, not a list of all methods that could be used for QC/QA. Some QC procedures and measurement items may also serve as QA procedures and measurement items.<br><h3>TABLE 1. TYPICAL EXISTING QC/QA PROCEDURES AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1931'><thead><th><center>QC or QA</th><th><center>Material or Process</th><th><center>Items</th></thead><tbody><tr><td ><center>QC</td><td ><center>Material Related</td><td >•Gradation, unit weight, moisture content, Plasticity; percent additive; strength, chemical identifier
</td></tr><tr><td ><center>QC</td><td ><center>Process Control</td><td >•Percent additive, mixing rate, additive uniformity measurements, curing time</td></tr><tr><td ><center>QA</td><td ><center>Material Related</td><td >•Mix design records; Sampling and testing of treated layers for unit weight, moisture content, density and strength
</td></tr><tr><td ><center>QA</td><td ><center>Process Control</td><td >•Document stabilizing agent type and rate of application, mixing adequacy and depth, compactive effort, moisture reasonableness and compaction compliance results (for stabilization/modification layers or treatments)</td></tr></tbody></table><br><h3>TABLE 2. PERFORMANCE CRITERIA USE IN QC/QA MONITORING PROGRAMS</h3><table class='tablepress' id='tablepress-1932'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Parameters</td><td >•Unconfined strength with time, resilient modulus on stabilized samples, volume change
</td></tr><tr><td ><center>System Behavior</td><td >•Proof rolling, FWD, Clegg Impact Hammer, DCP</td></tr></tbody></table><br><h3>TABLE 3. EMERGING QC/QA PROCEDURES AND MEASUREMENT ITEMS</h3><table class='tablepress' id='tablepress-1933'><thead><th><center>Topics</th><th><center>Items</th></thead><tbody><tr><td ><center>Material Related</td><td >•Resilient modulus on stabilized samples</td></tr><tr><td ><center>Process Control</td><td >•Machine integrated construction monitoring for compaction, moisture condition and mixing Review of intelligent process equipment records; geophysics for evaluating spatial variability of mix and effective depth</td></tr></tbody></table></p></p>
<p><p><h2>QC/QA Guidelines</h2><ul> <li style="list-style-type: none;"><ol> <li> Prior to stabilizer application<br>Sampling of loose processed materials is used to check gradation of the materials and ensure the oversize materials are limited to the specification target value. For controlling pulverization in cement stabilization, a sieve analysis is typically performed using a No. 4 sieve. For lime stabilization, the 1-inch and No. 4 sieves are designated for controlling pulverization. Gradation requirements for fly ash and bitumen-stabilized soil are detailed in Army and Air Force (1994).</li> <li> During stabilizer application:<br>Stabilizer additive content tests are performed transversely across the pavement and at various depths within the stabilized layer to assess the mixing effectiveness. Chemical analysis, phenolphthalein test, and visual inspection are used to estimate the stabilizer content. Chemical analysis can be expensive and slow, however. According to TRB (1987), a phenolphthalein test on a face cut in the stabilized layer is used as a “quick” test to determine the presence of lime or cement instead of the exact content of the stabilizer. A reddish-pink color develops if lime is present in the soil, for example.Trenches are dug and a visual inspection is made to assure uniformity of the mixture. Uniformity is checked throughout the depth and across the width of the pavement. The phenolphthalein test can also be used to check the uniformity of the mixture in the field.Moisture content measurements are obtained at various stages of construction. Moisture content is commonly determined by either oven-dry or nuclear gauge methods. The hand‑squeeze test is not frequently mentioned, but often used to estimate suitable moisture content. Although the hand-squeeze test cannot replace the standard moisture content test, it assists with improved process control. The control of moisture content is important in achieving required pulverization and hydration for lime, cement, and fly ash stabilization. Bitumen stabilization has specified requirements for moisture content.<br>Field personnel should be aware of the depth of the stabilized layers both before and after compaction. Depth of mixing can be checked as the same time as uniformity, and should be checked routinely during mixing operations.</li> <li> In-situ verification<br>Nuclear gauge testing is common for checking if the required dry density is obtained after compaction. Clegg impact hammer and dynamic cone penetrometer (DCP) tests are two methods to measure the stability of the stabilized subgrade at various times upon completion of stabilization. In addition, undisturbed samples following a laboratory curing process can be used to determined unconfined compressive strength and resilient modulus in the laboratory.</li></ol></li></ul> </p></p>
<p><p><h2>References</h2>Army and Air Force (1994). <em>Soil Stabilization for Pavements</em>. Joint Departments of the Army, the Navy and Air Force, Washington, DC.</p><p>Austroads (1998). <em>Guide to Stabilisation in Roadworks</em>. National Association of Australian State Road Authorities, Australia.</p><p>Little, D. N. (1995). <em>Handbook for Stabilization of Pavement Subgrades and Base Courses with Lime.</em> Kendall / Hunt Publishing Company, Dubuque, IA.</p><p>Portland Cement Association (1995). <em>Soil-Cement Construction Handbook</em>, Skokie, IL.</p><p>Qubain, B.S., Seksinsky, E.J, and Li, J. (2000). “Incorporating subgrade lime stabilization into pavement design.” <em>Transportation Research Record</em>, 1721, 3-8.</p><p>Qubain, B.S., Heirendt, K.M., and Li, J. (2006) “Quality Assurance and Quality Control</p><p>Requirements for Lime and Cement Subgrade Stabilization.” <em>GSP-154: Pavement Mechanics and Performance</em>, Shanghai, China, 229-238.</p><p>Transportation Research Board (1987). <em>Lime Stabilization</em><em>: </em><em>Reactions, Properties, Design and Construction</em><em>. </em>State of the Art Report 5, Report prepared by TRB Committee on Lime and Lime-Fly Ash Stabilization, Washington, DC.</p><p>Vennapusa, P.K. and White, D.J., (2009). “Comparison of Light Weight Deflectometer Measurements for Pavement Foundation Materials.” <em>Geotechnical Testing Journal,</em> Vol. 32(3), West Conshohocken, PA, 239-251.</p><p>White, D. J., Harrington, D., and Thomas, Z. (2005). <em>Final Report-Fly Ash Soil Stabilization for Non-Uniform Subgrade Soils</em>, Vol I: Engineering Properties and Construction Guidelines, Iowa State University, IA.</p></p>