Environmental and economical impact of SFRC pavement construction was estimated by a life cycle methodology. LCA is a cradle-to-grave analysis avoiding the environmental ‘problem shifting’ to another stage in a product's life cycle. LCA perspective can be applied in analysing the origins of issues, comparing variation for improvement purpose, designing new products, and choosing between comparable products [10].

Agency cost and user cost are the two components used for expressing the LCCA of the pavement. The first is associated with costs incurred directly by the agency over the life of the pavement and usually includes construction costs, maintenance costs and operation costs. Costs incurred by pavement users travelling and on the facility and those who cannot use the facility due to agency or self-imposed detour requirements are characterised as user cost. Generally, user cost is an aggregation of user delay costs (because of construction and maintenance work zones), vehicle operating costs and crash costs (risk of traffic accidents) [11].

According to a Life project titled “SUSCON”, LCA output of a flexible asphalt pavement construction in Cyprus indicates that the largest impact to the environmental score is the asphalt production and use as well as bitumen production [12]. The recycling of asphalt pavement is not considered an option as gas emissions increase with the recycling rate. In addition, the asphalt-laying operation is considered a nuisance because bitumen fumes can cause irritation to the mucous membranes of eyes and the respiratory track. Therefore, national regulations of mean exposure values have been set for road workers [13]. In order to assess a more preferable road design, comparison studies were implemented for diverse concrete pavements [14,15]. In the Netherlands, a study has illustrated that the value of concrete pavements is less or quite similar to asphalt pavements in terms of environmental impacts and costs criteria. Furthermore, SFRC was concluded to be more attractive than jointed plain concrete and continuously reinforced concrete pavements because of improved strength capacity and lower score, respectively [16]. However, more extended research is required to compare the environmental impact and cost of SFRC and asphalt pavements, and also to consider the use of post-consumer tyre products in the road industry. Landfill tax (introduced in many countries) increases the interest in decreasing the amount of solid waste deposited in landfills and investigating new alternatives to make use of by-products [17].

The overall methodology of the life cycle assessment (LCA) is summarised in Figure 1. After the Goal and Scope of work were set, an Inventory Analysis was undertaken to assemble environmental, energy and cost data from local and literature sources. Life Cycle Impact Assessment was implemented by loading all data gathered by the previous phase in the LCA and life cycle cost analysis (LCCA) software named Gabi and CUT model respectively [18].

The LCA and LCCA was initially undertaken for the “EcoLanes” demonstration pavement constructed in Cyprus, whose profile is illustrated in Figure 3, and this was followed by a parametric study carried out to assess the effects of design parameters on the LCA and LCCA outputs of the proposed pavement type. Life cycle results include, in addition to the parametric study output, a comparison of a steel fibre-reinforced roller-compacted concrete (SFR-RCC) pavement with four alternatives: one flexible asphalt pavement and three concrete rigid alternatives (see Figure 2). The design of the SFR-RCC was altered in the comparison study to apply in a global scale and not only to the local construction conditions (geological and meteorological variables) [18-20].

To demonstrate the research findings of “EcoLanes”, the Public Works Department in Cyprus constructed (in April 2009) an SFR-RCC pavement overlay on a problematic section of the old road leading to Galataria village (road F624)—at Pafos district, Cyprus—lying on a layer of bentonitic clay [9,21,22]. Figure 3 illustrates the road cross section as constructed by the Public Works Department [18-20].

The area is situated between the villages of Pentalia and Galataria (road F624) where the steep ground morphology and the continuous landslides and active land creep observed, render the existing ground an unsuitable foundation for supporting the transportation network of the area (see Figure 4) [18].

The objective of reconstructing a stretch of the F624 road was to minimise the problems of asphalt differential displacement and cracking (and subsequent infiltration of rainwater causing further instability and deterioration problems to the pavements), thus improving the safety and comfort of the area's transport infrastructure, and at the same time reducing the maintenance operations (and hence the costs incurred) regularly required to keep the road up to acceptable standards.

Due to the unstable geology, it was decided that the road improvement should be achieved by strengthening the existing road system without disturbing the sensitive ground and this meant that no preparation work could be carried out on the sub-grade and sub-base of the existing pavement. Consequently, a LLRP overlay, made with SFR-RCC (containing 2% by mass recycled RTC fibres) was constructed rather than a flexible one. The existing asphalt layer was ground up by using a milling machine to achieve a better bond between the existing pavement and the new SFR-RCC overlay [21,22].

The SFR-RCC was transported by insulated trucks (covered for the duration of the trip to avoid any moisture loss due to high temperatures and wind effects) and fed into an asphalt paver, which placed the material in a single 30 cm-thick layer along the whole transverse road width.

To avoid moisture loss from the concrete mix to the base, water was sprayed just before the laying of the SFR-RCC overlay started. To prevent moisture loss from the top surface, a curing membrane was applied immediately after rolling was completed.

The placed SFR-RCC was initially compacted from the surface by using the tamping, vibrating, and pressing compaction systems of the paver, achieving (directly out of the back of the paver) densities equal to or greater than 90% of a modified Proctor test. This resulted in a working width, 25 cm-paving depth, transverse road profile, surface accuracy, and surface texture of the highest possible quality achievable for roadway pavements.

A heavy duty dual drum vibrating roller compacted the SFR-RCC pavement overlay by passing over it until the pavement overlay met the density requirements as mentioned above (design density was achieved) (see Figure 5). The edges of the pavement overlay were compacted in a similar way by a lighter vibrating roller.

Figure 6 illustrates a flow chart of the work carried out to collect relevant information. Energy consumption data of materials were collected from the following industries: (i) a local ready mixed concrete plant; (ii) a local cement works and quarries company; (iii) a local asphalt plant; (iv) a local lime quarry and (v) a local aggregates quarries company. Material costs for construction and maintenance works were obtained from the Public Works Department. Maintenance strategies were designed based on the Public Works Department feedback. The cost and energy consumption cost for the recycled steel tyre-cord fibres were provided by the “EcoLanes” partner Adriatica Rciclaggio e Ambiente s.r.l. (ADRIA).

Emissions data could only be obtained from published literature as no constant air monitoring strategies were implemented by the industry or the government of Cyprus and therefore no available air quality data are available. The following list of emissions references is held in the LCI database.

As discussed in section 1, concrete is normally reinforced with industrially-produced steel fibres, mainly to improve its post-cracking mechanical behaviour; however, the high cost of these steel fibres can restrict the extensive use of SFRC in pavement construction. Thus, as discussed above, one of the objectives of “EcoLanes” was to develop and use a cheaper alternative to industrially-produced steel fibres, such as RTC fibres, produced by the mechanical treatment of post-consumer tyres [6].

These RTC fibres have variable geometrical characteristics and contain rubber particles on their surface. If the fibres are added in the concrete mix without removing the rubber or minimising their geometrical variability, fibre agglomeration will form in the concrete, affecting the concrete's mechanical properties. Thus, in order to avoid fibre agglomeration in SFRC pavements, “EcoLanes” developed optimised processes and a hardware prototype that cleans and minimises the geometrical variability of RTC fibres [6].

By the end of the project, 105 tonnes of processed RTC fibres were supplied for the project's research and demonstration activities, including the development of wet- and dry-consistency SFRC mixes, development of the concept of LLRP made with wet- and dry-consistency SFRC as well as the construction of the four demonstration pavements, including the one in Cyprus (examined in the current study).

To facilitate the use of RTC fibres in concrete pavements for surface transport, wet- and dry-consistency SFRC mixes were developed and optimised by EcoLanes. This included experimental investigation of the fresh (e.g., workability) and hardened properties (compressive and flexural) and durability (corrosion, freeze-thaw and flexural fatigue) of these SFRC mixes, For comparison purposes, the behaviour of SFRC mixes with industrially-produced steel fibres was also assessed [27,28].

The experimental results confirmed that the mechanical behaviour of wet- and dry-consistency concrete (especially flexural strength and toughness) is improved by the addition of steel fibres. The results indicated that industrially-produced steel fibres are more efficient at reinforcing concrete than RTC fibres (Figure 7). However, it was shown that RTC fibres have the potential to offer a viable alternative to the industrially-produced steel fibres, if used in high amounts (e.g., 6% by mass of concrete) or blended with industrially-produced steel fibres. In addition, it was indicated that the flexural behaviour of dry-consistency SFRC mixes (i.e., SFR-RCC), made with recycled concrete aggregates, is equivalent to the one obtained from SFR-RCC mixes made with natural aggregates [6,27].

Results of fatigue bending tests of SFRC prisms, carried out for both wet- and dry-consistency SFRC mixes, showed that dry-consistency SFRC containing 2% (by mass) RTC fibres has better fatigue performance than plain dry-concrete (especially at stress levels below 0.7 as shown in Figure 8) [28,29].

In addition, work carried out to assess the durability of the developed SFRC mixes showed that mechanical behaviour is barely affected by corrosive environments; it was observed that wet and dry SFRC containing 6% (by mass of concrete) RTC fibres demonstrates better freeze-thaw resistance than concrete mixes reinforced with industrially produced steel fibres. In addition, the results obtained for corrosion resistance indicate that the mechanical behaviour of wet and dry SFRC is not affected by corrosion, despite the rusty appearance of concrete [28].

Concrete pavements normally last longer than asphalt pavements [30], and to arrive at economical and sustainable designs for SFRC pavements (reinforced with RTC fibres), the concept of long-lasting rigid pavements made with “low energy” SFRC was developed by “EcoLanes” [31]. This concept was validated at the Technical University of Iasi by undertaking accelerated cyclic load tests of trial SFRC sectors [32]. By the end of the project, 1.5 million load cycles were accomplished and the experimental results indicated that there was no failure in any of the sectors, showing that (over a design life of 30 years) the proposed concrete roads would survive at least 20.5 million-single-axis of traffic. Extensive analytical and numerical (elastic and inelastic finite element) analyses of plain-concrete and SFRC pavements were also undertaken, with the aim of developing appropriate design tools and failure criteria for wet- and dry-consistency SFRC pavements. Existing design methods for concrete pavements were also examined, and a design framework and software were developed for LLRP made with wet- and dry-consistency SFRC [33].