Use of Microcracking to Reduce Shrinkage Cracking in Cement-Treated Bases

Abstract

Shrinkage cracking occurs in cement-treated bases because of desiccation and cement hydration; eventually these cracks start to reflect through the pavement surfacing. Although initially considered cosmetic, these cracks open the pavement to water infiltration and increase the likelihood of accelerated pavement distress. Numerous options exist for minimizing the amount of reflective cracks that appear; microcracking is a promising approach. The microcracking concept can be defined as the application of several vibratory roller passes to the cement-treated base at a short curing stage, typically after 1 to 3 days, to create a fine network of cracks. In addition to the microcracked test sites, the contractor constructed moist-cured, dry-cured, and asphalt membrane–cured sites for comparison. Researchers used falling weight deflectometer (FWD) tests to control the microcracking process, periodic crack surveys to monitor crack performance, and FWD tests through time to track base moduli. Microcracking proved quite effective at reducing shrinkage cracking problems in the base; applying the procedure with three passes of the roller after 2 to 3 days of curing resulted in the best performance. In addition, researchers observed that, without microcracking, excessively high cement contents resulted in problematic cracking in the base even if they were cured according to good construction practice. Microcracking did not result in pavement damage or diminished inservice modulus; thus, microcracking should be considered a viable and inexpensive option to incorporate shrinkage crack control into the construction of cement-treated bases.

QA/QC in Transport Infrastructures: Issues and Perspectives

“…D can also be estimated on the basis of the design report (in which it is usually specified). Empirical or rational design can be used after having estimated structural layer coefficients or moduli from resistance thresholds set out in the contract (Marshall Stability, MS, for surface course, base course and bituminous treated bases, California Bearing Ratio (CBR), for untreated bases or subbases, Unconfined Compressive Strength -7 day break (UCS) for cement treated bases, (Huang, 2003), see figures 9 to 13); by knowing thickness and traffic loading it is therefore possible to estimate D. Importantly, on the basis of the international literature (Van Til et al, 1972;Gaspard, 2000;Sebesta, 2005) and current practice, the modulus of cement treated bases which corresponds to a given laboratory resistance (Unconstrained Compressive Strength -7-day break) can vary to a great extent in relation to many factors (time from base construction, traffic, subgrade drainage, shrinkage cracks, etc). Figure 9 shows the relationship between resistances and structural layer coefficients according to (Van Til et al, 1972).…”

Strength and Deformation Characteristics of Cement-Treated Reclaimed Pavement with a Chip Seal

“…Proper design of CTB is a balance between achieving suitable strength and durability and minimizing the risks of shrinkage cracking. In the past, the mindset "stronger is better" often governed design, so cement contents around 6 to 8 percent were frequently used (14,17,18).…”

“…However, as previously discussed, these high cement contents can lead to excessive shrinkage cracking and poor pavement performance. Many researchers therefore recommend limiting the cement content or design strength to minimize shrinkage (12,14,17,19). To achieve a balance of strength and durability, the Portland Cement Association (PCA) recommends a moderatelystabilized CTB with a cement content yielding a 7-day unconfined compressive strength (UCS) between 300 and 400 psi (20).…”

“…In addition, the cement will continue to hydrate and "heal" the hairline cracks, restoring the CTB stiffness to near or above the pre-microcracked state within a few days. Researchers have found microcracking to be an effective means of reducing reflective cracking without compromising the integrity of the CTB (12,14,15,21). Other proposed construction techniques to reduce reflective cracking include jointing of the CTB (21), delayed HMA surfacing (12,15), and installation of a stress-relieving interlayer between the CTB and the HMA (12).…”

Kaolen Türü Killi Zeminlerin Dayanım Özelliklerinin Melamin Formaldehit Sıvı Polimeri Kullanarak İyileştirilmesi

“…Ayrıca, çimentomsu malzemelerle iyileştirilen zeminler daha gevrek hale gelmekte ve böylece dinamik yükler altında veya büzülme etkisinde çatlak oluşma ihtimali artmaktadır (Little 1992;Sebesta 2005;Li 2014). Bu çatlaklar zamanla yüzey kaplamalarına da yansımakta ve yollarda sorunlara neden olmaktadır.…”