Jizhe Zhang

Role of primer in rubber to nylon 6,6 bonding☆

Abstract Primers are often used in rubber to metal bonding to protect the bonded area against corrosion in service. Their role in rubber to nylon 6,6 bonding was studied by means of peel tests. Test-pieces in the form of bonded strips were prepared by vulcanising a natural rubber compound containing 60 parts per hundred rubber by weight (p.p.h.r.) high abrasion furnace carbon black in contact with nylon 6,6 substrates. Proprietary organic solvent-based or water-based primer and covercoat bonding agents were used for bonding the rubber. Peel tests were performed under constant load at an angle of 90° and at ambient temperature (∼23°C). When rubber was peeled, bond failure was cohesive in the primer and in the rubber as well as at the primer/nylon interface. Interestingly, when rubber was bonded to nylon using organic solvent-based or water-based covercoat and peeled under similar test condition, bond failure was cohesive in the rubber and the strength of the bond improved noticeably.

Moisture sensitivity examination of asphalt mixtures using thermodynamic, direct adhesion peel and compacted mixture mechanical tests

Moisture damage in asphalt mixtures is a complicated mode of pavement distress that results in the loss of stiffness and structural strength of the asphalt pavement layers. This paper evaluated the moisture sensitivity of different aggregate–bitumen combinations through three different approaches: surface energy, peel adhesion and the Saturation Ageing Tensile Stiffness (SATS) tests. In addition, the results obtained from these three tests were compared so as to characterise the relationship between the thermodynamic and the mechanical tests. The surface energy tests showed that the work of adhesion in dry conditions was bitumen type dependent, which is in agreement with the peel test. After moisture damage, all of these three tests found that the moisture sensitivity of aggregate–bitumen combinations were mainly aggregate type dependent. Based on the peel test, the moisture absorption and mineralogical compositions of aggregate were considered as two important factors to moisture sensitivity. This phenomenon suggests that in a susceptible asphalt mixture, the effect of aggregate may be more influential than the effect of bitumen. The SATS test and the peel test showed similar moisture sensitivity results demonstrating the good correlation between these two mechanical tests. However, the surface energy tests and the mechanical tests cannot correlate in terms of moisture sensitivity evaluation.

Moisture damage evaluation of aggregate–bitumen bonds with the respect of moisture absorption, tensile strength and failure surface

The moisture-induced deterioration of asphalt mixture is because of the loss of adhesion at the aggregate–bitumen interface and/or the loss of cohesion within the bitumen film. An experimental study was undertaken in this paper to characterise the effects of moisture on the direct tensile strength of aggregate–bitumen bonds. The aim of this paper was to evaluate the moisture sensitivity of aggregate–bitumen bonds in several different aspects, which included moisture absorption, tensile strength and failure surface examination. Moisture absorption and mineralogical compositions of aggregate were measured using gravimetric techniques and a Mineral Liberation Analyser (MLA), respectively, with the results being used to explain the moisture sensitivity of aggregate–bitumen bonds. Aggregate–bitumen bond strength was determined using a self-designed pull-off system with the capability of accurately controlling the bitumen film thickness. The photographs of the failure surface were quantitatively analysed using Image-J software. The results show that the magnitude of the aggregate–bitumen bonding strength in the dry condition is mainly controlled by bitumen. However, the retained tensile strength after moisture conditioning was found to be influenced by the mineralogical composition as well as the moisture diffusion properties of the aggregates. The linear relationship between retained tensile strength and the square root of moisture uptake suggests that the water absorption process controls the degradation of the aggregate–bitumen bond. The results also suggested that the deterioration of aggregate–bitumen bonds is linked to the decrease in cohesive failure percentage.

Experimental evaluation of crumb rubber and polyethylene integrated modified asphalt mixture upon related properties

Due to the dramatic increase in traffic volume, asphalt pavements deteriorate gradually with the high-temperature rutting and low-temperature thermal cracking as two main failure modes. This paper focuses on the integrated modification of bituminous binders and asphalt mixtures with the aspect of improving the performance of asphalt pavement at both high and low in-service temperatures. The recycled crumb rubber (CR) and polyethylene (PE) were chosen as polymer agents in order to modify the bitumen property. Analysis on the rheological performance of modified bitumen indicated the addition of CR decreased the bitumen creep stiffness at low-temperature which in turn reduced the brittleness and cracking risk. Meanwhile, the addition of PE increased the bitumen stiffness at high-temperature which resulted in improved rutting resistance. With respect to the integrated modified bitumen, the addition of CR and PE cooperatively improved the bitumen properties at both high and low temperatures. In terms of the asphalt mixture, PE contributes to the permanent deformation resistance at high in-service temperature while the CR enhanced the flexibility at low in-service temperature. The integrated modified mixture prepared with CR and PE obtained significantly enhanced performance at both high and low in-service temperatures. Consequently, utilisation of these two recycled materials is able to improve the pavement properties reached to or even better than those prepared with styrene-butadiene-styrene modified bitumen.

Experimental Study of Moisture Sensitivity of Aggregate-Bitumen Bonding Strength Using a New Pull-Off Test

Moisture damage in asphalt mixtures is a complicated mode of pavement distress that results from the loss of interfacial adhesion between the aggregate and bitumen and/or the loss of cohesion within the bitumen. Both adhesive and cohesive strength of aggregate-bitumen bonds can be determined in the tensile testing mode. This paper presents the development of suitable procedure consisting of an innovative sample preparation, controlled moisture conditioning and new pull-off test set-up to characterise moisture damage resistance of the bonding strength of aggregate-bitumen samples that is sensitive to the mineralogical and physicochemical properties of the aggregates as well as key bitumen physical properties. The test set-up consists of three main parts: a moisture conditioning step designed to ensure characteristic moisture diffusion into the aggregate-bitumen interface, accurate determination of bitumen film thickness using a modified dynamic shear rheometer and direct tension fixtures mounted on an Instron universal testing machine. The capability to vary loading rate, accurately control film thickness and ensure moisture diffusion to the aggregate-bitumen interface are an important improvement over most existing pull-off tests. The test was also found to be sensitive to moisture conditioning time, moisture uptake and the type of aggregate. All samples were subjected to the pull-off test to characterise their tensile strengths before and after moisture conditioning. The results show that the magnitude of the aggregate-bitumen bonding strength in the dry condition is mainly influenced by bitumen. However, the magnitude of the tensile strength after moisture conditioning was found to be influenced by mineralogical composition as well as the moisture diffusion properties of the aggregates. The new test was found to be repeatable with variability comparable to most advanced tensile testing systems for bitumen.