Crack Sealants Research Articles

Analysis of Bituminous Crack Sealants by Physicochemical Methods: Relationship to Field Performance

Bituminous crack sealants were analyzed by viscometry, fluorescence microscopy, infrared spectroscopy, thermogravimetry, modulated differential scanning calorimetry, and low-temperature tensile testing. The results indicate that sealants are blends of bitumen, oil, copolymer, and filler. Upon blending, these components produce a three-phase system that consists of a polymer-modified bitumen (PMB) matrix, a filler, and a filler-PMB interface. Spectroscopy and microscopy indicate that the PMB phase is rich in styrene-butadiene copolymer, that the filler is recycled rubber, sometimes mixed with calcium carbonate, and that the interface depends on the filler and the oil content in the sealant. The physicochemical methods were used to predict the short- and medium-term performance of sealant mixtures. The short-term performance predicted from viscometry and microscopy correlated well with the 1-year field performance of the sealants. Sealants showed two glass transition temperatures ( Tg’s), and a reasonable correlation was also found between low Tg and medium-term performance in a wet-freeze climate. However, because Tg measurements do not account for stress relaxation and aging effects, correlation was not perfect.

Performance of pavement crack sealants in cold urban conditions

Twelve bituminous hot-pour crack sealants were evaluated over four years in temperatures ranging from -40°C to +40°C. Each sealant was evaluated over 900 linear meters of transverse and longitudinal routs of 12 × 12 mm2, 19 × 19 mm2, and 40 × 10 mm2 (width × depth). Results show that sealant source, rout size, and rout orientation affected sealant performance, i.e., debonding and pull-out levels. Debonding levels were 0-50% and pull-out levels 0-30%. Sealant failure was proportional to rout width; it was lowest in 12 mm wide routs and highest in 40 mm wide routs. This result is attributed to the proportional exposure of sealants to slow moving traffic. The increase of sealant failure over time was also found to be nonlinear. Three stages were identified in the failure-time plot. In stage 1, failure is rapid; in stage 2, it plateaus; and in stage 3, it increases again. Failure in stage 1 is thought to be related mainly to a weak sealant - asphalt concrete interface, whereas that in stage 3 is thought to be related to sealant weathering and stiffening. It was also found that standard test results correlate poorly with field performance.Key words: pavement, crack sealing, sealant, performance, cold weather, failure.

Effect of Hot-Air Lance on Crack Sealant Adhesion

The hot-air lance (HAL) is widely used in crack-sealing work based on the premise that it improves sealant adhesion. However, the effectiveness of the HAL in promoting adhesion is uncertain. The authors' goal was to measure the adhesion strength of bituminous crack sealant to dry asphalt concrete (AC) and assess the effect of the HAL on adhesion. To this end, they monitored the use of the HAL in the field and reproduced its effect on asphalt binders and AC pavements by using an automated HAL in a series of laboratory experiments. In those experiments, we looked at the effect of heat treatment on binder oxidation and embrittlement by means of infrared spectroscopy, thin-layer chromatography, and goniometry. They also compared the adhesion strength of three sealants applied to unheated, heated, and overheated AC substrates prepared with quartz or limestone aggregates. The results show that sealant adhesion and failure mechanisms are governed by the sealant source, the type of aggregate in the AC mix, and the heat treatment on the rout prior to pouring the sealant. The HAL does not oxidize the binder, but it may cause embrittlement by raising the asphaltenes content of the binder. Normal heat treatment has little effect on sealant adhesion to dry AC, but overheating can cause a 50% reduction in adhesion strength and lead to premature sealant failure. To retain the possible benefits of the HAL in sealing damp cracks and to prevent overheating, the HAL should be operated at reduced temperatures.

Development of a Laboratory Screening Test for Asphalt Pavement Crack Sealants

Premature failure of crack sealants and fillers in the field calls into question the effectiveness of these materials as a treatment for cracked asphalt concrete (AC) pavements. Although standard sealant test methods ensure the consistency of the product, they fail to account for the ability of the sealant material to bond to AC, especially at cold temperatures after the material has aged. In an attempt to evaluate this behavior, a study was undertaken at Michigan Technological University, through sponsorship by the Michigan Department of Transportation. This study’s objective was to develop a laboratory testing protocol to evaluate crack sealants and fillers in an attempt to obtain better predictions of field performance. The developed protocol tests sealed AC blocks at a low temperature before and after accelerated laboratory aging to assess stiffening and failure characteristics in tension of the sealant and filler materials. To date, four laboratory phases have been completed to verify the repeatability of the testing, and preliminary correlation has been made with limited field data. The results indicate that the developed protocol is able to measure relative sealant performance in various configurations, but it is not possible to establish definitive relationships between laboratory testing and field performance at this time. Additional testing of materials, with an emphasis on field correlation, will be necessary to calibrate the test procedure.

Performance of pavement crack sealants in cold urban conditions

Performance of pavement crack sealants in cold urban conditions

Sealant Degradation during Crack Sealing of Pavements

Application practices of bituminous hot-poured crack sealants, typically used to effect repairs on pavements, were monitored in the field and heating conditions were reproduced in the laboratory. From viscometry, thermogravimetry, and tensile testing measurements, it was found that sealants degrade upon heating at recommended installation temperatures. Consequently, given the level of product degradation observed from laboratory evaluations, it is not expected that a consistent low temperature sealant performance could be obtained in the field. These conclusions help explain the number of premature sealant failures that exist despite the fact that these materials may be in accordance with the requirements in ASTM D 3405.

Low temperature stress growth and relaxation in crack sealing materials

Stress relaxation after a nonsteady uniaxial extension with finite strain of crack sealants is studied at low temperatures. The integral constitutive model is used and the first normal stress difference, obtained experimentally, is modelled. It was found that the stretched exponential relaxation occurs in the tested materials. The stress growth and the stress relaxation in the tested materials are very well described by the discussed model which contains only a small number of parameters.

Oxidation protection of carbon-carbon composites using chemical vapour deposition and glaze technology

Low pressure chemical vapour deposition (LPCVD) has been used to apply silicon carbide coatings to a carbon-carbon (C/C) composite using methyl-trichloro-silane as the precursor. When cooled from the deposition temperature, the SiC coatings develop cracks due to thermal expansion mismatches between the coating and substrate. The cracks require sealing at temperatures between 600 and 1100°C to prevent oxidation of the underlying carbon. Two compositions of a borosilicate glass have been tested as crack sealants, being applied either as an outer glaze or between two layers of the CVD SiC. Compositional variations near the surface of the glass have been investigated using laser microprobe mass spectroscopy. Devitrification of the silica-rich surface of the glass has been studied using X-ray diffraction and scanning electron microscopy.