Pre-Project Evaluation & Planning
Before construction begins, a thorough assessment of the existing pavement and base is essential. Testing for material properties such as gradation, Atterberg limits, and moisture content helps determine the optimal cement dosage. Instead of relying on assumptions, laboratory testing should guide mix design to ensure the right balance of strength and durability. Drainage considerations should also be addressed to prevent future deterioration.
Determining Cement Content
Selecting the correct cement content is fundamental for achieving a durable and stable base. A cement series test should be conducted before construction to determine the optimal percentage. If no prior data is available, it is recommended to start with 3% cement by weight and increase in 0.5% increments until the target strength is achieved. This ensures the mix is neither under-stabilized (leading to inadequate strength) nor over-stabilized (resulting in excessive stiffness and cracking). Proper testing, including compressive strength evaluations, helps refine the mix design for long-term performance.
Cement Application & Mixing
Before cement application, initial pulverization may be necessary to achieve full-depth mixing, particularly when the material’s moisture content deviates by more than 3% from the optimum or when using a slurry application. Bulk spreaders or controlled slurry applications ensure even cement distribution. Once spread, reclaimer equipment should be used to thoroughly blend the cement with existing materials. Mixing must begin immediately after cement is applied and continue until a uniform mixture is achieved. Maintaining proper moisture content during mixing is essential for facilitating hydration and ensuring effective stabilization. The entire process, including cement application, mixing, spreading, compacting, and finishing, must be continuous and completed within 2 hours from the start of mixing.
Figure 1. Water truck and reclaimer working together during FDR with cement operations in an urban setting.
Figure 2. Grading of FDR with cement base using a motor grader.
Compaction & Curing
Achieving proper density through compaction is crucial for long-term performance. A combination of padfoot and smooth drum rollers should be used, with field density tests verifying compliance. Compaction should continue until a uniform and adequate density is achieved, reaching at least 98% of the maximum dry density. Equally important is proper curing. Applying a moisture-retaining method, such as water spraying or a bituminous curing seal, prevents premature drying and promotes strength development. If a curing material is used, it must be applied as soon as possible, but no later than 24 hours after finishing operations. The surface should remain continuously moist until the curing material is applied.
Figure 3. Initial compaction of FDR with cement base using a padfoot roller.
Figure 4. Compaction of FDR with cement base using a smooth drum roller.
Microcracking for Crack Prevention
Microcracking helps reduce shrinkage and reflective cracking in cement-stabilized bases by using a vibratory roller 24 to 48 hours after compaction to create fine cracks that dissipate stresses. This technique improves durability and minimizes long-term cracking. See Randy Bowers’ article this month for more details.
Quality Control & Performance Monitoring
On-site testing should be conducted throughout construction to confirm material consistency, strength gain, and density compliance. Monitoring the early-age strength helps determine the optimal time for traffic opening or final surfacing. Adjustments to the mix design or construction methods should be made as necessary based on test results and site conditions.
Figure 5. FDR with cement specimen during unconfined compressive strength testing.
By following these best practices, FDR with cement can provide a durable, resilient, and cost-efficient solution for rehabilitating aging pavements while minimizing long-term maintenance needs.