Exploitable results
The most important future user needs and expectations identified by the analysis carried out in the 1st phase of the NR2C project are:
- A more human city. All discussions with stakeholders highlight the importance to focus on 'human' aspects when working on cities evolution, as well as streets and transport infrastructure evolutions. This means to develop co-design with highest participation of users and residents, to encourage global approach of problems with multidisciplinary competences.
- A more mobile 'city'. Citizens' mobility demand will continue to increase, accompanied by the necessity of accessibility for all, possibility of choice, etc. This means to increase and diversify the various forms of mobilities by means of adaptability of the street, intermodality, new form of mobility (example car sharing).
- A city without harmful effects (e.g. reduction of pollution, reduction of disturbance during works and operation, etc.).
Innovations developed or studied in the 2nd phase of the NR2C project provide possible answers to these issues and have been arranged into two topics:
- Design-models for multimodal streets, which produced documents focussing on expectations and needs for innovation in urban roadway system, specifications and concepts for the integration of public transit platforms in urban settings (explaining what a model design is, how it can be used for the designing of streets and how new design models can be built), specifications and preliminary concepts for the design of multi-modal streets. 20 design models have been developed, accompanied by the methodology of use, which has been successfully implemented in Wattrelos city, near Lille in France (phase 3).
- Ecotechnic Road System (ERS) programme, which is a concept of an integrated infrastructure, based on the most innovative technologies in order to minimise globally pollution and disturbance due to traffic (noise, vibrations, air and water pollution). ERS are composed by 3 subsystems: pavements subsystem (i.e. resilient, resonant and reservoir pavements); barriers subsystem (i.e. anti noise, air depollutant, safety and green barriers); auxiliary subsystem (i.e. air cleaning unit, ventilation unit, ground catalyser, photocatalytic material and TiO2 coating). In particular, this program includes a particularly original work regarding mitigation of air pollution in tunnels first, in roads and streets secondly, and includes the verification of the use of titane dioxyde as air purifier on upper layer of pavement or building surfaces in order to reduce air pollution due to traffic. Under these topics a number of documents have been produced: multi-functional infrastructure feasibility studies and air cleaning model; a preliminary design of multi-functional infrastructure (phase 2); a detailed design and pilot study of multi-functional infrastructure (phase 3).
The NR2C project defined and published the 'Vision 2040' (available on www.fehrl.org/nr2c), whose original contribution consists in that it considers widely users and stakeholders, and delves deeply into the urban and peri-urban issues, attaching a lot of importance to the 'human' aspect.
Comparing the future with the present situation, the vision has identified research areas (directions of solutions) to face the future for four key concepts representing the dominant characteristics of the society's expectations for the road of the future.
1. Reliable infrastructure
- 'Lifetime engineering'. Lifetime engineering takes into account all transport-related costs by decision-making. The initial costs of structures will no longer be the only dominant factor; maintenance costs including the economic loss of traffic jams due to maintenance work will also play a role. Durable or long life infrastructure with low maintenance is the key to reliable infrastructure in the future. Because of the limitations of current construction materials to bear the increasing traffic loads, new materials and products will have to be developed.
- 'Fast, hindrance-free maintenance'. Even the most durable infrastructure cannot escape maintenance from time to time. To minimise the impact on the availability of the infrastructure, fast, hindrance-free maintenance techniques must be developed. In fact the foundation of these solutions is laid at the design stage of structures by remembering that maintenance will be necessary one day.
- 'Balancing demand and capacity'. Balancing demand and capacity to optimise the use of the existing infrastructure primarily requires good traffic management. In finding and achieving the right balance between demand and capacity, road-engineering activities are regarded more as an aid or support rather than dominant.
- 'Asset management tools'. The more traffic on the roads, the higher the sensitivity of the road systems to disruption in the traffic flows resulting from accidents and maintenance work. Good asset management tools must be developed to support decision-making by road authorities with respect to maintenance strategies and reserving funds for conservation of the road networks. Monitoring systems to quickly establish the condition of the infrastructure, performance models for structures, materials and maintenance techniques to forecast maintenance and in this context determine hard and smart intervention levels for maintenance from the safety point of view become the basic requirements of modern network management.
2. Green infrastructure
- 'Saving natural resources'. As a major consumer of building materials, an important contribution of road engineering to the green infrastructure concept involves the saving of natural resources. Road construction annexes land or scarce public space to urban areas and affects the landscape elsewhere for the supply of first class building materials. Furthermore, maintenance and reconstruction works generate a huge amount of building rubble that is transported to landfills, which also affect the landscape. The complete recycling and reuse of this building rubble will be the first challenge facing road engineers in the near future.
- 'Emission control'. With respect to silent pavements, progress can be made by means of fine-tuning the mix design and application techniques. Prefabrication of thin noise absorbing surface layers on the roll under controlled circumstances will promote this development. Materials capable of absorbing noise and possibly air polluting components must be developed to reduce the impact of emissions under legal standards. To prevent exhaust (blacks) and non-exhaust (brake wear, tyre wear, etc.) particulate matter emissions blown up by wind and passing traffic, cleaning systems must be designed to remove these pollutions from urban and suburban areas. In the case of extreme polluting situations and where it is impossible to abandon polluting cars, covered roads in combination with air-cleaning systems are an option.
3. Safe and smart infrastructure
- 'Safe design'. The basic requirements of safe and smart infrastructure are naturally the quality of the hardware or the physical infrastructure. It is for the road engineers to design and construct infrastructure that inspires confidence in all road users with respect to safety under normal conditions, day and night.
- 'Smart design'. System optimisation demands smart design of the road networks involved. Here smart design stands for creating a 'playground' with enough free space and sufficient freedom of action to solve congestion caused by high traffic demand or incidents. System optimisation means being able to choose alternatives. Besides expanding the road network, creating temporary capacity inside and/or outside the network is the most obvious solution.
- 'Smart communication'. An essential element of smart design is smart communication: the way of communicating relevant information to the road users. Communication between the smart road systems and the cars will be crucial to the success of system optimisation. A realistic estimation concludes that automatic vehicle guidance will be achieved by the year 2040. In the meantime, communication will focus on dashboard displays and warning signals in cars and a range of traffic signs and information panels above and alongside the road. Research is required to develop real 'Dynamic road information panels' with the ability to integrate common traffic signs, static and realtime information so that the right information can be shown at the right time. This reduces the number of signs and other information panels alongside the road and focuses the attention of the road users on one spot.
- 'Smart monitoring'. Over the past few years, many applications of 'intelligent traffic systems' (ITS) have been developed and tested on a modest scale in local areas. These first generation systems rely on indicators that are used to manage traffic flows. Most studies and research point out that the weakness of such applications is the poor quantity and quality of real time data available for input. Easy and cheap data acquisition will be the critical success factor of ITS which requires the development of smart monitoring devices. In-vehicle and in-situ measurements will together provide the data needed to achieve 'system optimum' and enable road authorities/operators to maintain the networks to the high levels of comfort and safety expected by the road users.
4. Human infrastructure
- 'Public security'. Providing public security in public spaces will probably be most instrumental in persuading citizens and other potential road users to use the available infrastructure facilities. Special attention and care must be paid to the most vulnerable users of roads and public spaces: pedestrians, cyclists, people with disabilities, people with reduced mobility, old people and children. In general, well-designed and recognisable configurations of public spaces will inspire confidence in public security. Besides separating the vulnerable road users from motorists, a clear and open design will promote a sense of well-being.
- 'Multi-functional use'. Citizens want their streets back to upgrade their social activities in their living surroundings. They are tired of their living space being invaded by polluting cars and trucks speeding by. On the other hand, they expect facilities and services to meet their daily needs. All these needs must be satisfied by one and the same area of public space, which will be nearly impossible to attain without relinquishing some demands. Designing a configuration for public space that allows a multi-functional use of the available area at different times of the day could be an option. For example, the use of public transport (tram and bus) lanes for transporting and delivering goods in the late evening or even modelling parking areas so that they can be used as a children's play area during the day or at weekends. Moving the noisy and polluting traffic transport facilities and parking areas underground will create new empty spaces at ground level for the enjoyment of the citizens.
- 'Human design'. Higher buildings and wider roads create urban sprawl spreading across the countryside. Perpetuating this approach will ultimately lead to situations where citizens lose themselves in the built environment and road users in the plains of asphalt pavements. This lack of creativity and pursuit of quick wins will produce an environment that no longer reflects the needs of human beings. Society's demand for liveable surroundings requires a new design concept: human design, the harmonisation of the dimensions of the built environment and infrastructure with human dimensions.
The state-of-the art review carried out in the 1st phase of the NR2C project has clearly showed that the typical trends of innovative road construction, rehabilitation and maintenance are:
- the use of very high quality (premium) basic materials eventually with their special treatment;
- the establishment of sophisticated construction, rehabilitation and maintenance techniques utilising up-to-date scientific achievements;
- the development of special measures for enhancing traffic safety even in extreme conditions;
- decreasing the whole life (life cycle) costs of road pavements by constructing long-life variants with infrequent maintenance and rehabilitation need, and, consequently, minimal traffic disturbance;
- wider use of industrial by-products in road engineering without reducing pavement performance;
- wider use of recycling (eventually-re-use) of bound pavement structural layers in order to reduce the need for primary basic materials without jeopardising the performance of pavements;
- giving priority to low-energy pavement structural variants reacting to the ever increasing energy prices and the limited availability of crude oil supplies;
- there are some innovations which use some new scientific results coming from science areas far away from highway engineering.
In this field the NR2C project developed five innovation concepts (phase 2), which mainly address issues relating to preservation of rare resources via recycling and use of industrial by-products:
- Innovation 2.1A - Design of high performance underlayers with low cost materials and high percentage of re-use. The objective was to evaluate if the growing share of recycled aggregate used in asphalt high stiffness base courses influences the asphalt mechanical properties. This study led to the conclusion that no negative effect has been found by using a high percentage of reclaimed asphalt. However key parameters as for instance the mix design and RA properties require special attention.
- Innovation 2.1B - Crack free semi-rigid pavement incorporating industrial waste. The objective was to evaluate if the natural cement concrete shrinkage can be compensated by adding industrial by-products (steel slag, fly ash) with swelling ability to the mixture (The main idea was to minimise, or even to stop, the cracking of hydraulically bound layers and so, to avoid the reflection cracking in the asphalt layers built on them). A promising prototype has been designed and tested but it still needs improvements which could not have been done in the duration of the project to really check the feasibility of the proposed concept.
- Innovation 2.2 - Use of the infra-red characteristics of materials to improve drivers' visibility. The objective was to enhance the traffic safety by improving the drivers' visibility among unfavourable conditions (darkness, fog etc.). Numerical simulation tools developed have permitted to evaluate the size of cooperative elements of infrastructure required to be perceptible on infrared images by taking account the characteristics of on-board infrared vision system used. Nevertheless, experiments have also permitted to verify that improving contrast on infrared images by generating a thermal excitation on infrastructure typical elements can reduce their emissivity in foggy night conditions and so improve the visibility. Finally recovering energy from road could be a sustainable solution to generate active thermal elements for on board infrared vision system.
- Innovation 2.3 - New maintenance technique aiming at enlarging the overall conditions of application of mixtures for pavements. The objective was to evaluate whether asphalt laying activities can be performed without detrimental consequences under extreme weather conditions (too low or too high temperature, rain etc.). The proposed innovative techniques were supposed to ensure the required asphalt quality and not to increase the construction costs considerably. The benefit of such an innovation is to reduce the impact of the weather conditions on the quality of placing of pavement mixtures, and consequently on the mechanical properties and behaviour of the road structure. Another benefit is the reduction of the impact of road closure due to maintenance on the road users, as it would be more likely to carry out pavement maintenance at more opportune times or periods throughout the year. The solutions provided for enlarging the overall conditions of application for bituminous bounding materials have been founded only for the following climatic parameters: cold, rain, wind, heat, and loading. Some consequences of climatic parameters such as water on support and film of water on tack-coat have not been solved with original solutions (in case of storm or snow the best way is to wait better weather conditions). As to hydraulic bounding materials no original solutions have been provided for enlarging the overall conditions of application due to the fact that there is no means to smooth influence of cold, rain or wind.
- Innovation 2.4 - Improving the mechanical properties of a low noise section. The objective was to evaluate (and eventually to improve) the functional and the mechanical properties (durability) of low-noise poro-elastic layers built on cement concrete blocks. Laboratory and site tests have been performed for the evaluation of these properties. All together the pavement where concrete blocks with poro-elastic cover were placed into a cementitious screed layer has shown considerably better performance under applied conditions, compared to the sand bedding layer pavement. Considering these results it is advisable to continue with further experiments on this pavement. The research should be oriented to the field tests focusing on stability and suction forces under the typical traffic conditions.
The activities started with a complete review of state of the art on bridge innovations (phase 1 of the NR2C project), which included:
- main needs and problems on civil engineering structures;
- general view of new materials applications (high performance steel, ultra high performance fibre concrete, fibre reinforced polymers, other materials);
- owners and designers' expectations (this section was mainly based on interviews of specialists, designers, architects, owners, etc);
- evolution of civil engineering structures, with a particularly interesting analysis of the evolutions made in the past which highlight that rare disruptions are linked to new materials;
- vision on new bridges for the future.
Then following activities focused on defining new material properties and modelling rules, providing to engineers and design consultants the necessary information for the design and calculation of bridges using ultra-high performance fibre-reinforced concrete or fibre-reinforced polymers.
NR2C has focused on short span bridges and in particular small industrial light structures easy to assemble on site, and likely to be used alone for smallest spans or themselves supported by structural elements, when used transversally, for most important spans.
The main idea of the design was to combine new materials, using the best performances of each material, including possible use of wood as a renewable building material.
Consequently, three main solutions families have been investigated (phase 2):
- Element of sandwich slab, combining UHPFC and FRP, filled with lightweight concrete. The sandwich construction consists of three layers: a glass fiber-reinforced polymer composite (GFRP) sheet with Tupstands for the tensile skin, lightweight concrete (LC) for the core and a thin layer of ultra-high performance fiber-reinforced concrete (UHPFRC) as a compression skin. Mechanical tests on long and short-span hybrid beams were performed using two types of LC with different fracture mechanics properties and two types of FRP-LC interface: unbonded (only mechanical interlocking of LC between T-upstands) and bonded with an epoxy adhesive. The experiments showed that ultimate load is determined by the shear strength of the LC core. A fracture mechanics-based shear strength prediction method was therefore developed. The experimental results and modeling highlighted the importance of considering not only static strength, but also fracture mechanics properties such as the LC characteristic length. Moreover, a design concept was developed demonstrating the feasibility of the suggested hybrid bridge deck and allowing the definition of the required LC material properties according to the transverse bridge.
- Solutions based on UHPFRC. The objective of the study was to develop future-oriented solutions for the construction of bridges using new materials to their best advantage in terms of durability and sustainable development. This study has explored solutions for 10 m and 25 m span bridge decks consisting of prestressed UHPFRC girders or mixed UHPFRC/composite and UHPFRC/steel girders. It showed that the most advantageous solutions in terms of materials savings are fully prestressed UHPFRC decks. For 10-metre span structures, these solutions lead to financially viable structures under current economic conditions. Mixed UHPFRC/glassfibre solutions are penalised by the poor ratio of the Young's modulus to the connection strength of the two materials which means that they have to be overdimensioned in order to respect the deflection requirements of the decks. For 10-metre span bridges, notched web girders and steel footings are interesting alternatives to fully prestressed solutions. Similarly, for 25-metre span bridges, the combination of UHPFRC and a composite can become advantageous in the case of partially prestressed UHPFRC prefabricated lattice beams. As a follow-up to this study, reflection can be pursued on the design of assemblies that will optimise the general design and building of the bridges. This reflection could include: the design of UHPFRC slab component assemblies in order to guarantee local stress transfer and water tightness of the slab; the design of UHPFRC and composite assemblies which could develop the adhesive bonding of systems that ensure the dispersion of concentrated stresses.
- Element of structure combining wood beams, slab UHPFRC, and FRP at the bottom of wood. The detailed design and large-scale validation of a prototype 10 m-span composite UHPFRC - carbon fibres - timber bridge helped drawing conclusions concerning the feasibility of the sandwich concept developed, the critical issues to be considered in practical realisation, and also the validity of the preliminary design hypotheses and detailing assumptions. These conclusions are:
- Material properties and design rules of UHPFRC and composites tend to get satisfactory mature understanding for design. On the contrary, the behaviour of the lightweight material (wood in the present sandwich concept) used for shear transmission, even though critical in the design, seems to be less controlled. Possible defects may significantly change the safety margin. Timber properties should thus deserve increased research and control efforts.
- Connection of UHPFRC pre-cast elements one against the other should deserve special attention, especially for thin elements. Stress concentrations and premature cracking may be caused by geometrical uncertainties and imperfect joint (or gluing) execution.
- Adhesive connection seems promising and ensures composite behaviour in the serviceability domain, which provides easily understandable linear behaviour and helps sound calculations. However, failure of this connection, which may be controlled by hardly detectable execution flaws, may result in very brittle structural failure. This implies an additional connecting system only for safety purpose, which may result in significant additional expense.
- Due to the orthotropic behaviour of wood, parallel reinforcement using (also orthotropic) composites does not prevent brittleness versus cracks propagating in-between the fibres. A kind of shear reinforcement (transversely to wood fibres) might be of interest for ensuring the desired non-brittleness.
- Simplified execution and material savings were searched in the tested multi-beam solution. However the beams redundancy did not result in high enough ductility, in the sense that the bearing capacity at first failure was hardly recovered when further loading the remaining beams. Possible advantage of cross-beams towards this end might be questioned.
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