United States Department of Transportation
i
Minimizing Shrinkage Cracking in Cement-Stabilized Bases through Micro-Cracking
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2018-10-01
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[PDF-4.76 MB]
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Edition:Final Report, 11/2012 to 10/2017
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Abstract:Cement stabilized soil base (so-called soil cement base) has been used in flexible pavement in Louisiana for more than 50 years. Soil cement has an excellent load carrying capacity and durability but is also well-known for developing shrinkage cracks, which can reflect through asphalt concrete surfaces and accelerate the deterioration of asphalt pavements. Micro-cracking is a special reflective cracking mitigation technique used in a cement-stabilized base construction. The objectives of the study were to determine if the micro-cracking technique is suitable for implementing on soil cement pavements in Louisiana and to evaluate the effectiveness of the micro-cracking on reducing the shrinkage/reflective cracking on soil cement pavements. To achieve the objectives, micro-cracked base sections were constructed on three selected pavement sites. Specifically, one pavement site was chosen at the Louisiana Pavement Research Facility (PRF), where six unsurfaced soil cement or cement treated base test sections were constructed including four of them micro-cracked. The PRF sections were used to investigate the shrinkage cracking performance considering various micro-cracking levels and cement contents. Two other pavement sites were selected on field pavement rehabilitation projects of LA 1003 and LA 599 through the support of Louisiana Department of Transportation and Development (DOTD) project engineers, in which nine 1000-ft. long test sections were constructed including four micro-cracked soil cement base test sections. In general, two types of DOTD’s soil cement base course design-cement stabilized design (CSD) and cement treated design (CTD) were considered in this study. In-situ non-destructive tests (NDT) and cracking surveys were performed periodically on PRF test sections after construction. Substantial amounts of hairline-type shrinkage cracks were first observed on all test sections during the early curing periods, but the surface cracks all disappeared in approximately six months thereafter. Not a single, wide and deep shrinkage crack could be found after three and half years of monitoring on those PRF sections. Saw-cutting beams also indicated that no underneath severe shrinkage cracks had been developed at the end of monitoring. The measured base stiffness, however, did show an increasing trend over time on all sections tested. Similarly, in-situ NDT tests and cracking surveys were performed on the testing sites of LA 1003 and LA 599. Based on the test results, it was found that a micro-cracked, 8.5-in. soil cement pavement (i.e., the CSD base design) generally showed a similar early performance (approximately three years of service) as compared to a non-micro-cracked soil cement pavement in terms of the overall cracking performance as well as pavement performance of rutting and pavement smoothness. However, due to very few reflection cracks having been developed so far on both the control and micro-cracked sections, whether or not the micro-cracking technique is effective in mitigation of reflection cracks on an 8.5-in. soil cement pavements in Louisiana may be still too early to be drawn. On the other hand, the two 12-in. cement treated soil base pavements (i.e., the CTD base design) did not show better early performance than non-micro-cracked control sections, especially in the cracking performance. After three years of trafficking, more cracks were found on the micro-cracked test sections than the control ones indicating that the micro-cracking technique may be not effective when applied on a 12-in. cement treated soil base in Louisiana.
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