Practical Applications

Internally cured concrete has been used for many concrete facilities, the majority of which have been bridge structures. However, as noted below, there have been a number of pavement applications, primarily in the Dallas-Fort Worth area. The pavements in the Dallas area used a relatively small substitution of intermediate aggregate sizes with lightweight aggregate. Some examples of the projects in Texas include:

• A 1,400-foot section of CRCP on the outer lane and shoulder of State Highway 121 north of Dallas in 2006. The remainder of this project was constructed with conventional concrete to enable a performance comparison. Follow-up surveys indicated that the initial crack pattern that developed in the internally cured section exhibited much longer spacing than is normal for CRCP, and the cracks are also much tighter. After several years, the crack spacing became similar to that of the conventional sections; however, the cracks remained much tighter.
• A high early-strength mixture in a section of an off ramp on I-635 for early opening to traffic in2012. The use of internal curing had no adverse effect on early strength and was able to reducing shrinkage cracking.
• A 360-acre Union Pacific intermodal terminal located 12 miles from downtown Dallas, within the city limits of Hutchins and Wilmer. Minor joint spalls and limited cracking have been observed. Performance has been similar to the conventional sections, with both in excellent condition.
• A residential subdivision in south Fort Worth, Windsor Park, constructed in 2006-2007. A survey after 8 years in service identified no significant longitudinal or transverse cracking, plastic shrinking cracking, spalling, or other defects. In general, the pavement was in excellent condition.
• A residential subdivision in north Fort Worth, Alexandria Meadows North, constructed in 2006-2007. This project contained streets both with and without internally cured concrete. Afield survey revealed both the internally cured concrete and conventional pavement sections were in excellent condition, with very limited cracking. No slab curl was identified.

The mixtures used in the aforementioned studies used intermediate size lightweight aggregate. Table 1 provides an example of one such mixture design that was used on the Union Pacific intermodal facility in Dallas-Fort Worth. This table provides the mixture proportions for both conventional and internally cured concrete mixtures.

The two key benefits determined for internally cured concrete in concrete pavement are structural longevity and durability. Structural longevity is improved with internally cured concrete due to its small reduction in unit weight, elastic modulus, and coefficient of expansion, and a small increase in strength. These small effects, when combined, amount to a significant positive impact on slab fatigue damage and associated slab cracking in jointed concrete pavements. Likewise, internally cured concrete leads to tighter crack openings and reduced punchout failures for CRCP. Several case studies were analyzed using the Pavement ME Design procedure, and the results indicated improved performance and longer lives for internally cured concrete sections. Life-cycle cost analyses for these projects showed generally lower costs for internally cured concrete as compared to conventional concrete.