Characterization of joint sealants through an innovative test procedure

Joint sealants are indispensable components of Jointed Plain Concrete Pavements (JPCP), the standard construction method in Germany. The joint filling system is subjected to various loads during their service life, which in practice lead to a regular renewal of the sealing after about 7 -10 years. Nevertheless, it must be expected, that the joint sealing material shows an adequate durability, which is a crucial element for the life cycle costs of concrete pavements.

Against this background, a holistic test procedure was developed in a BASt funded research project, which uses scientific approaches to depict the decisive effect on the overall system “joint”, with cut concrete joint flanks, the primer and the joint sealant. This enables a reliable characterization of joint sealants. In addition to the horizontal and vertical stress (static / cyclic), in particular various aging influences in the joint system were included. For this purpose, the joint sealants were subjected to long-term aging (temperature conditioning) and the system specimens subjected to UV-conditioning and freeze-thaw-cycles. The determined residual tensile strength of the tensile-/shear tests with and without cyclic pre-stress showed the considerable influence of aging on the overall system “joint”. The additionally determined rheological properties of the joint sealants before and after aging by means of the dynamic shear rheometer also confirmed the material changes due to artificial aging. The artificial aging achieved in the laboratory was compared with in situ aged and extracted samples and a corresponding correlation was established.

Taking into account the systematic tests on laboratory and in-situ samples, an initial evaluation method was developed that enabled an evaluation of joint sealant compounds using scientifically based parameters and limits in their original reference state and in their artificially aged state. The characteristic parameter was established as expansion at 80% of maximum tension in the declining stress branch.

Through a holistic characterization of the joint system and the joint sealants, including significant aging effects, it should be possible to be able to carry out joints much more permanently in the future and thus make the JPCP overall more robust and economical.