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While there is a permanent improvement of concrete pavement mixtures and pavement construction types over the last decades, the state-of-the-art joint sealing materials and joint constructions seem to stagnate on an antiquated empirical level. This status has been reaffirmed in the latest European standard. The consequences in the motorway network due to unsatisfying capability and durabilty of joint sealing systems are unacceptable. In addition, inadequate traffic performance (noise emissions, roll-over comfort) and traffic safety losses in the joint area of concrete pavements are existing challenges. These deficits and weaknesses reflect a demand for joint sealing materials and constructions whose approval requirements take functional aspects into account. Furthermore a sufficient analysis of decisive loads and a practice-oriented method to evaluate the requirements towards performance and durability is still missed. In this contribution decisive loads to German highways are analyzed. The design of test specimen for representative functional testing of joint sealing systems is discussed. The focus is on the geometry of the test specimens and the used concrete mixture. Finally, a new approach for a function-orientated test concept that considers representative load functions is presented. The potential of this approach to validate the durability and capability of various joint sealing systems is also presented using an example.
A new approach towards performance-related design and scientific evaluation of joint sealing systems
(2020)
While there is a permanent improvement of concrete pavement mixtures and pavement construction types over the last decades, the state-of-the-art joint sealing materials and joint constructions seem to stagnate on an antiquated empirical level. This status has been reaffirmed in the latest European standard.
The consequences in the motorway network due to unsatisfying capability and durability of joint sealing systems are unacceptable. In addition, inadequate traffic performance (noise emissions, roll-over comfort) and traffic safety losses in the joint area of concrete pavements are existing challenges. These deficits and weaknesses reflect a demand for joint sealing materials and constructions whose approval requirements take functional aspects into account. Furthermore a sufficient analysis of decisive loads and a practice-oriented method to evaluate the requirements towards performance and durability is still missed.
In this contribution decisive loads to German highways are analyzed. The design of test specimen for representative functional testing of joint sealing systems is discussed. The focus is on the geometry of the test specimens and the used concrete mixture. Finally, a new approach for a function-orientated test concept that considers representative load functions is presented. The potential of this approach to validate the durability and capability of various joint sealing systems is also presented using an example.
Ultra high performance concrete (UHPC) is known for its high compressive strength of more than 150 MPa and its high durability. Thermal treatment at 90°C can accelerate the strength development so that the 28-days-strength can be achieved immediately after the treatment and an additional increase up to 30 % in some cases. The reason for the strength development is an accelerated hydration of the clinker minerals and an intensified pozzolanic reaction leading to a denser microstructure.
In previous research inhomogeneities in form of a zonation after unprotected thermal treatment were observed and analysed in respect to changes in the microstructure. This zonation is defined by a different microstructure in the core compared to the outer zone in the matter of porosity, mineral phase composition and a significant change in the potassium and sulphur concentration of the zones is measurable.
To isolate different transport mechanisms responsible for these element distributions UHPC samples were thermally treated at 90 °C and the microstructure was investigated under dry conditions and after immersion in water to investigate the influence of dehydration during and rehydration after the thermal treatment on the microstructure. Through durability testing via water absorption, water vapour diffusion, permeability testing and sulfuric acid resistance transport mechanisms like diffusion, migration, capillary suction are under investigation in correlation with the microstructure analysis. For the microstructure analysis measurements with µXRF, mercury intrusion porosity, XRD and SEM were conducted.
Ultra high performance concrete (UHPC) is known for its high compressive strength of more than 150 MPa and its high durability. Thermal treatment at 90°C can accelerate the strength development so that the 28-days-strength can be achieved immediately after the treatment and an additional increase up to 30 % in some cases. The reason for the strength development is an accelerated hydration of the clinker minerals and an intensified pozzolanic reaction leading to a denser microstructure.
In previous research inhomogeneities in form of a zonation after unprotected thermal treatment were observed and analysed in respect to changes in the microstructure. This zonation is defined by a different microstructure in the core compared to the outer zone in the matter of porosity, mineral phase composition and a significant change in the potassium and sulphur concentration of the zones is measurable.
To isolate different transport mechanisms responsible for these element distributions UHPC samples were thermally treated at 90 °C and the microstructure was investigated under dry conditions and after immersion in water to investigate the influence of dehydration during and rehydration after the thermal treatment on the microstructure. Through durability testing via water absorption, water vapour diffusion, permeability testing and sulfuric acid resistance transport mechanisms like diffusion, migration, capillary suction are under investigation in correlation with the microstructure analysis. For the microstructure analysis measurements with µXRF, mercury intrusion porosity, XRD and SEM were conducted.
Wood protection technology in the marine environment has changed over the last decades and will continue to do so. New active ingredients, newer formulations, and novel wood-based materials including physically- and chemically-modified wood, together with increasing concerns over environmental impacts of wood preservatives, urgently demand a major revision of EN 275 “Wood preservatives – Determination of the Protective Effectiveness against Marine Borers”, dated from 1992. This IRG document reports on the technical work in CEN TC 38 regarding the revision of this standard. A Task Group within WG 24 of CEN TC 38 was formed consisting of experts from different field of competence (e.g. wood preservatives industry, wood scientists, marine biologists, archaeologists and cultural heritage conservators). Starting by e-mail correspondence in 2014, and continuing with four physical meetings (Berlin 2x, Florence, Venice) with experts from Germany, Italy, Sweden, and UK were held so far. Significant items for revision in EN 275 were identified as: number of replicates, duration of the test, dimension of specimens, number of test sites, number of reference species, reference material including reference preservative, re-immersion of specimens after non-destructive periodical evaluation for longer periods of time vs higher number of replicates for successive destructive examinations without re-immersion, utilization of X- ray apparatus and specific software to ease evaluation, etc.
Furthermore, the task group is working on a standardized lab test for time-saving evaluation of different wood qualities for their potential to resist attack by limnorids. The suitability of this lab test will be determined by round robin tests as soon as safe face-to-face collaboration permits. The outcome will be published as a CEN TR (Technical Report) document, with a view to eventual adoption within the revised standard.
Ultra high performance concrete (UHPC) is characterised by its high compressive strength of more than 120 MPa and its high durability. With thermal treatment at 90°C, hydration is accelerated and a strength comparable to the 28-day strength can be achieved immediately after the treatment. In applying Optimum process conditions, the strength can be even further increased by up to 30%. Previous Research showed that thermal treatment can lead to inhomogeneities in form of a visible zonation within the cross-section, if the UHPC is not protected sufficiently from desiccation. This led to the question, to what extent the related changes in mechanical properties, microstructure and phase composition are of relevance for the performance of the UHPC. First investigations of small specimens thermally treated without protection exhibited a decrease of compressive strength, indicating that the zonation aspect requires further research.
In this study the zonation of UHPC treated thermally at 90°C is investigated after applying four different procedures of treatment and curing in comparison. The samples are characterized with respect to their chemistry, mineral composition and microstructure to allow an assessment on durability and strength development, with focus on potential depth dependent changes associated with the zonation.
The measurements reveal the formation of a visible zonation in case of unprotected treatment, if followed by immersion in water. The compressive strength is not significantly impaired, but a decrease in bending strength gives reason for concern. Further results allow clear correlation with changes in pore structure, whereas the interpretation of relationships with phase distribution, degree of hydration, microchemistry is more complex and therefore, provides only partial clarification.
Scientific publications addressing the durability of the flame retardance of cables during their long-term application are rare and our understanding lacks. Three commercial flame retardants, aluminum hydroxide, aluminum diethyl phosphinate (AlPi-Et), and intumescent flame retardant based on ammonium polyphosphate, applied in ethylene-vinyl acetate copolymer (EVA) model cables, are investigated. Different artificial aging scenarios were applied: accelerated weathering (UV-irradiation/temperature/rain phases), humidity exposure (elevated temperature/humidity), and salt spray exposure. The deterioration of cables’ surface and flame retardancy were monitored through imaging, color measurements, attenuated total reflectance Fourier transform infrared spectroscopy, and cone calorimeter investigations. Significant degradation of the materials’ surface occurred. The flame retardant EVA cables are most sensitive to humidity exposure; the cable with AlPi-Et is the most sensitive to the artificial aging scenarios. Nevertheless, substantial flame retardance persisted after being subjected for 2000 h, which indicates that the equivalent influence of natural exposure is limited for several years, but less so for long-term use.