For years, accepted engineering practice has called for sealing contraction joints in concrete pavements to keep out water and incompressible materials. The prevailing theory has been that if water enters the joints, it will erode the subbase and weaken the subgrade.
The Wisconsin Department of Transportation (DOT) began questioning this theory in the 1950s when they noticed that two sections of a concrete highway built in the same manner at the same time were performing differently in a most unexpected way. Joints in both sections of the highway were originally filled with an asphalt-based sealant, but only the joints in one section of pavement were routinely refilled with sealant. Joints in the other section were never refilled. Despite this, the pavement sections in which joints weren't refilled showed less faulting, less cracking and less spalling.
The Wisconsin DOT set out to answer the question once and for all with a ten-year study. Eleven unique test sections were built. Four sections with unsealed joints varied only in joint spacing. The other seven test sections resulted from different combinations of joint sealants and joint spacings.
A meaningful evaluation of joint sealing must be based on total pavement performance, not just on the performance of the joint or joint sealant. Based on such an analysis, this ten-year study produced four major conclusions:
- The pavements with unsealed joints performed better than the pavements with sealed joints.
- The pavements with shorter joint spacings performed better than the pavements with longer joint spacings.
- Some sealants can keep joints effectively sealed for ten years, if the joints are properly designed.
- Joint sealing costs are not justified.