Impact, Cause, and Remedies for Excessive Cracking in CRC Pavement

In the 1990's, the South Dakota Department of Transportation began a concerted effort to rebuild its aging Interstate highway network. Through analysis of performance and life-cycle cost, continuously reinforced concrete pavement (CRCP) was identified as an alternative of choice for interstate reconstruction in South Dakota. From 1995 to the present, the South Dakota Department of Transportation (SDDOT) has constructed over 250 2-lane miles of continuously reinforced concrete (CRC) interstate highway at an approximate investment approaching $300 million. CRC pavement is designed with substantial reinforcing steel to eliminate the need for transverse joints, which are the primary point of failure on jointed concrete pavement. Instead of joints, CRC exhibits hairline transverse cracks, which normally are spaced at intervals of two to four feet and which are thin enough to resist faulting, spalling, and intrusion of foreign material. However, some recently constructed CRC pavements exhibit cracking that is irregular, with spacing varying from as little as one foot to as much as 10 feet. Some of the cracks appear to be significantly wider than normal, which could allow intrusion of water, chemicals, and other foreign material. Some cracks have begun to deteriorate and spall. Finally, isolated punch-outs--usually located within a single lane and less than 20 feet in length--have appeared on some projects. Several factors could potentially contribute to these problems, including: (a) concrete mix design and composition (b) aggregate type and gradation (c) aggregate thermal expansion coefficients (d) ambient temperature during pour and cure (e) material temperatures at pour (f) reinforcing steel percentage and size (g) reinforcing steel location and lapping (h) slab thickness (i) underlying cushion or pavement layers (j) subgrade or drainage problems (k) paving equipment or operation (l) concrete vibration (m) attack from deicing chemicals (n) grade and paving direction The effect of the cracking and distress on long-term pavement life and serviceability is unknown. It is not yet clear whether the problems represent a major structural problem or a relatively minor, cosmetic problem. Whether the cracking and distress will significantly accelerate long-term failure mechanisms, such as steel fatigue, corrosion, or freeze-thaw damage is presently unknown. Research is needed to determine the extent of these problems, assess their impact on pavement performance, investigate their causes, identify ways to preserve existing pavements, and identify how to avoid similar problems in the future. The objectives of this research project are to: 1) Determine the character, extent, and severity of cracking and other distress in CRC pavements constructed in South Dakota since 1995. 2) Identify factors and interactions among factors that contribute to observed distress. 3) Assess the impact of observed distress on long-term pavement life and performance. 4) Recommend changes to design, specifications, and construction practice to substantially reduce the incidence and severity of distress in CRC pavements. 5) Recommend cost-effective maintenance and rehabilitation strategies for CRC pavements exhibiting unexpected levels of distress. Research tasks are as follows: (1) Meet with the project's technical panel to review project scope and work plan. (2) Review literature pertaining to CRC design, construction, and performance, with particular emphasis on cracking and distress. (3) Through direct contact with other states--such as North Dakota, Illinois, Texas, Michigan, and Oregon--that have recently built CRC pavements, as well as states that have decided to stop building CRC, evaluate their experience regarding the incidence and causation of unexpected distress. (4) Assemble and review available design and construction records for CRC pavements constructed in South Dakota. (5) Through observation of active CRC projects built in South Dakota during 2004 and early 2005, describe routine and exceptional construction processes that may contribute to unexpected levels of distress. (6) Through observations and measurements of in-service CRC pavements, describe the character, extent, and severity of cracking and distress in CRC pavements constructed since 1995 and compare these observations to concrete constructed prior to 1995 and to desirable CRC characteristics. (7) Submit an interim report summarizing the results of preceding tasks and offering interim recommendations. (8) Estimate the impact of observed levels of cracking and distress on long-term performance, serviceability, maintenance costs, and pavement life. (9) Identify factors that potentially contribute to unexpected levels of cracking and distress and, through analysis of design and construction records and observations and measurements of in-service pavements, evaluate their contribution. Include interactions among factors in the analysis. (10) Submit a second interim report summarizing the results of preceding tasks and offering interim recommendations. (11) In light of factors contributing to unexpected cracking and distress, recommend changes to design and construction specifications and procedures to minimize their occurrence and severity. (12) Recommend cost-effective maintenance and rehabilitation strategies to maintain and extend the life of in-service CRC pavements exhibiting unexpected levels of cracking and distress. (13) Recommend a strategy for monitoring the condition of in-service CRC pavements to better discern their condition and remaining life. (14) Prepare a final report and executive summary of the research methodology, findings, conclusions, and recommendations. (15) Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.