Steel Fibre Reinforced Roller-Compacted Pavements

Steel Fibre Reinforced Roller-Compacted Pavements: Research and Practical Experience Kyriacos Neocleous (1); Kypros Pilakoutas (2); Angela Graeff (3); Kostas Koutselas (4) (1) Senior Research Fellow, Centre for Cement and Concrete, Department of Civil and Structural Engineering / The University of Sheffield, S1 3JD, UK. Tel +44-114-2225729, [email protected] (2) Professor, Centre for Cement and Concrete, Department of Civil and Structural Engineering / The University of Sheffield (3) Researcher, Centre for Cement and Concrete, Department of Civil and Structural Engineering / The University of Sheffield (4) Research Manager, Research and Development Department, Aggregate Industries UK

Abstract Steel fibre reinforced concrete has been used for many years for the construction of rigid pavements. However, in countries with relatively low labour costs, the high cost of steel fibre reinforcement can be prohibitive for use in concrete pavements and, hence, cheaper sources of steel fibre reinforcement are required; one possible source is steel tyre-cord wire, recycled from post-consumer tyres. To facilitate the use of this type of fibre reinforcement in concrete pavements, a European research project (called EcoLanes) investigated the behaviour of concrete pavements reinforced with recycled steel tyre-cord fibres; both wetconsistency and roller-compacted concrete were investigated. This three year interdisciplinary project comprised a range of research and technological activities, which were relevant to tyre recycling, concrete, transportation and environmental engineering; and the aim of this paper is to provide an outline of the main project findings. The concrete mix optimisation studies and the accelerated cyclic load testing of full-scale pavement sectors indicated that roller-compacted concrete, reinforced with recycled steel tyre-cord fibres, can be used for the construction of long-lasting rigid pavements. Environmental and cost life cycle studies, undertaken by the project, showed that the energy consumption of steel fibre reinforced roller-compacted concrete pavements can be up to 40% less than commonly used asphalt pavements and up to 12% cheaper. In addition, the construction of four demonstration concrete pavements in different European environments demonstrated the benefits of the proposed pavement type of steel fibre reinforcement. keyword: SFRC, roller-compacted concrete, demonstration pavements, recycled steel tyre-cord fibres

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1

Introduction

Steel fibres are often used to reinforce concrete pavements; the use of steel fibre reinforcement in these applications is cost effective as it can reduce the costs associated with the placement of conventional reinforcement in concrete, speed-up the construction process, reduce the concrete slab thickness as well as the number of lateral and longitudinal joints (AASHTO 2001). The first industrial applications of steel fibre reinforced concrete (SFRC) pavements were made over forty years ago; these were followed by other applications such as in airports and for repair/strengthening of existing pavements (SWAMY and LANKARD 1974, PACKARD and RAY 1984, AASHTO 2001). Steel fibres were also successfully used, in experimental investigations, to reinforce rollercompacted concrete (RCC), which is a dry consistency concrete mixture (NANNI 1989). Despite the improved mechanical characteristics of steel fibre-reinforced (SFR) RCC, up to now, very few SFR-RCC pavements have been constructed; this may be attributed to the practical problems associated with adding steel fibres in in-situ RCC as well as lack of design recommendations for SFR-RCC. In countries with relatively low labour costs, the high cost of primary steel fibre reinforcement can be a prohibitive factor for the extensive application of SFRC pavement construction and, hence, alternative sources of low-cost steel fibre reinforcement are required (NEOCLEOUS et al. 2011). One possible source of such reinforcement is recycled steel tyre-cord wire (Figure 1) produced from post-consumer tyres. Research carried out over the last decade (e.g. PILAKOUTAS and STRUBE 2001, PILAKOUTAS et al. 2004, TLEMAT et al. 2006, AEILLO et al. 2009) has indicated that concrete reinforced with recycled steel tyre-cord wire has similar mechanical behaviour as concrete reinforced with primary steel fibres. However, to optimise the use of the recycled steel tyre-cord wire as fibre reinforcement in concrete, it is necessary to remove the rubber particles from the steel, minimise the geometrical variability of the steel wire in order to arrive at the optimal lengths required to utilise the steel characteristics (PILAKOUTAS et al. 2004). The use of recycled steel tyre-cord wire as fibre reinforcement of concrete pavements was investigated by the EC FP6 STREP project “EcoLanes”, which aimed at developing economical and sustainable pavement infrastructure using roller-compaction techniques and SFRC (NEOCLEOUS et al. 2011). This paper presents an overview of the project output, including the four demonstration SFR-RCC pavements constructed by the consortium of EcoLanes towards the end of the project.


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Figure 1 – Recycled steel tyre-cord wire produced from the mechanical treatment of post-consumer tyres

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Overview of EcoLanes Research Output

EcoLanes’ main objectives were to develop, test and validate SFRC pavements that will contribute towards the strategic objectives of European Union’s thematic priority area of Sustainable Surface Transport. Thus, EcoLanes aimed to use roller-compaction techniques (based on existing asphalt laying equipment) as well as recycled materials to reduce construction costs in the range of 10-20%, construction time by 15% and energy consumption by up to 40%. The three year project, which started in October 2006, comprised 9 work packages: 4 research-training-technological (RTD), 3 demonstration, 1 dissemination and 1 management. The project drew expertise from six European countries (Cyprus, France, Italy, Romania, Turkey and the United Kingdom) and its consortium comprised four universities, three industrial partners, a Recycling Association and three end-users (see http://ecolanes.shef.ac.uk). An outline of the main scientific and technological results of the project is presented in the following subsections, followed by the four demonstration SFR-RCC pavements, constructed in different European environments.

2.1

Fibre Processing

One of the main problems, encountered when mixing recycled steel tyre-cord fibres in fresh concrete, is the fibre tendency to agglomerate. Thus, recycled steel tyre-cord fibres, originating from various mechanical treatments of post-consumer tyres, were classified and the fibre balling mechanism was investigated in laboratory and field conditions. These activities assessed the level of treatment that recycled steel tyre-cord fibres required to arrive at the optimal fibre lengths and minimise fibre agglomeration. Following an investigation of a range of cleaning and sorting processes, the project developed and optimised hardware prototypes, which were capable of producing and 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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packaging sorted steel tyre-cord fibres to the project specification (Figure 2). During the three year period of the project, 105 tonnes of sorted recycled steel tyre-cord fibres were produced for EcoLanes’ scientific research as well as technological and demonstration activities. Formal specifications were also developed for the production and classification of recycled steel tyre-cord fibres (NEOCLEOUS et al. 2009). 100%

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Figure 2 - Steel tyre-cord fibres, recycled from the mechanical treatment of post-consumer tyres: (a) sorted to EcoLanes’ specification, (b) 25kg packaging

2.2

Fibre Reinforced Concrete

To attain the project objective of developing wet and dry consistency SFRC mixes (termed here wet SFRC and SFR-RCC, respectively), which have reduced energy requirements and are suitable for pavement construction, a comprehensive laboratory investigation was undertaken on the fresh and hardened properties as well as durability of wet and dry SFRC (ANGELAKOPOULOS 2011, GRAEFF 2011). The main differences in the wet and dry SFRC mixes were: a) in the cement content (dry mixes had ~20% less cement), b) aggregate type and gradation (crushed aggregates with continuous gradation were used for the dry mixes, whilst fluvial dragged aggregates were used for the wet mixes), and c) compaction procedure (wet mixes were compacted using an external vibrator, while the dry mixes were compacted using a hydraulic hammer attached to a specially developed steel frame, as elaborated by Neocleous et al, 2011). Initially, a pilot study was carried out to charactetise RCC mixes reinforced with industrially produced and recycled steel tyre-cord fibres. The pilot study indicated that, for the same fibre content, RCC with industrially-produced fibres is stronger than RCC with steel tyrecord fibres (Figure 3). However, it was shown that steel tyre-cord fibres have the potential to offer a viable alternative to the industrial fibres, if used in high amounts or blended with industrial fibres (ANGELAKOPOULOS, 2011). To optimise the SFR-RCC mixes, initially investigated by the pilot study, a parametric laboratory study was undertaken to assess the effect of key parameters on the fresh and hardened properties of dry SFRC (ANGELAKOPOULOS, 2011). These included the length, shape and tensile strength of industrially-produced steel fibres, content of recycled steel tyre-cord fibres, as well as content of recycled and natural aggregates. Experimental 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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results indicate that the flexural behaviour of SFR-RCC mixes, made with recycled concrete aggregates, is equivalent to the one obtained from SFR-RCC mixes made with natural aggregates (e.g. Figure 4). EcoLanes also collaborated with the Federal University of Rio Grande do Sul (GRAEFF et al., 2011) to investigate the fatigue flexural behaviour of selected wet SFRC and SFR-RCC mixes. Work was also undertaken (GRAEFF, 2011) to study the durability (corrosion and freeze-thaw resistance) of selected wet SFRC and SFR-RCC mixes; this work also included chloride ingression, permeability and porosity tests. Experimental results indicate that SFR-RCC mixes are more susceptible to corrosion and freeze-thaw than wet SFRC mixes. However, these results may be due to the boundary conditions used in the specific tests.

4-point bending test

Figure 3 - Bending test results of dry SFRC prisms (150x150x550 mm) tested during EcoLanes’ pilot study (ANGELAKOPOULOS, 2011) R-300LECr-28d-RTC4-24-R6-(30r-70na) R-300LECr-28d-RTC4-24-R6-(70r-30na) R-300LECr-28d-RTC4-24-R6-(100r-0na) R-300LECr-28d-R0-(30r-70na) R-300LECr-28d-R0-(70r-30na) R-300LECr-28d-R0-(100r-0na) R-LEcr300-R0-28d-na R-LECr300-RTC1-15-R6-28d-na

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Figure 4 - WP2 experimental work: Flexural behaviour of dry-consistency SFRC mixes made with recycled concrete aggregates (ANGELAKOPOULOS, 2011)


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2.3

Pavement Testing, Analysis and Design

The parameters considered in the design and construction of existing plain concrete and SFRC pavements were also examined to develop the concept of long lasting rigid pavements (LLRP) made with low-energy SFRC. Various options for the construction materials and pavement layers were proposed and the developed LLRP concept was validated by undertaking accelerated cyclic load tests of selected wet SFRC and SFRRCC sectors (COSOSCHI et al., 2009). The wet SFRC sectors were made with natural river aggregates, CEM Type I (360 kg/m3), and a water to cement (w/c) ratio of 0.44; whilst the SFR-RCC sectors were made with natural crushed aggregates, CEM Type I (300 kg/m3), and a w/c ratio in the range of 0.50-0.57 depending on the recycled fibre content. The cyclic tests were carried out at the ALT LIRA facility in Romania (Figure 5) and 1.5 million load cycles were undertaken. Analysis of the results and visual examination of the tested wet SFRC and SFR-RCC sectors indicated that there was no failure in any them, showing that (over a design life of 30 years) the proposed wet SFRC and SFR-RCC roads would survive at least 20.5 million-single-axles of traffic (ESAL 115 kN). Numerical analyses and parametric studies were also undertaken to develop design algorithms and software for LLRPs made with wet SFRC and SFR-RCC (TARANU et al., 2009). (a)

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Figure 5 – (a and b) Construction of the trial SFRC sectors, (c)ALT LIRA facility in operation during the accelerated cyclic load testing of the SFRC sectors

2.4

Environmental studies and site processes

EcoLanes also carried out life cycle assessment (LCA) of the environmental impact and cost of LLRPs made with wet SFRC and SFR-RCC mixes in order to attain its aim in terms of reducing costs and energy consumption (Achilleos et al. 2011). The LCA considered all phases of the pavement’s life, including construction, use, maintenance and demolition. Comprehensive data was collected for the LCA of the demonstration pavements, constructed with SFR-RRC in Cyprus, Romania, Turkey, and the United Kingdom. For comparison purposes, LCA was also undertaken for four alternative pavements (asphalt and three made with wet concrete). In addition, a parametric study was undertaken to examine the effect of key parameters on the LCA of pavements made with wet SFRC and SFR-RCC. LCA results indicated that the energy consumption of SFR-RCC pavements can be up to 40% less than that of the commonly constructed asphalt pavements. The environmental impact of SFRC pavements improves by using local as well as recycled material (such as recycled concrete aggregates). It was also evaluated that the life cycle cost of SFR-RCC pavements can be lower (up to 12%) than that of wet SFRC and asphalt pavements. It was also evaluated that the environmental and cost impact of dry SFRC 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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pavements improves as the fibre content increases (due to the reduction in the pavement depth required to support the traffic loading). The industrial dispersion of fibres in concrete was also examined as well as the processes and equipment currently used for RCC. Trials of SFR-RCC pavement construction were carried out in the United Kingdom, Romania, Turkey, and Cyprus in order to assess these equipment and processes. The results of these trials showed that existing equipment, such as those used in ready mix concrete plants as well as asphalt pavers and rollers, can be used successfully for the construction of SFR-RCC pavements. Based on the findings of these trials, guidelines were prepared for the production of pavements made with SFRRCC (KOUTSELAS et al. 2010).

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Demonstration SFR-RCC Pavements

The EcoLanes’ research and technological findings were applied in four demonstration pavement projects in the UK, Romania, Cyprus and Turkey to reflect different climates and economies; the pavements were semi-rigid (were all overlaid with a thin asphalt layer). The SFR-RCC mixes, used for the demonstration pavements, were reinforced with “EcoLanes Class B” recycled steel tyre-cord fibres (NEOCLEOUS et al. 2009). The mixing was undertaken successfully in pan mixers of conventional ready mix concrete plants. Some fibre balling was observed during mixing and, to eliminate fibre balling, the consortium recommended that recycled steel tyre-cord fibres should be detangled (possibly through vibration) prior to dispersing in them in the RCC mix. The SFR-RCC pavements were placed and compacted successfully by using existing asphalt laying and compaction equipment. The behaviour of the pavements is periodically monitored by undertaking testing of insitu samples as well as visual observations. Current results (two years after construction) show that the pavements did not encounter any structural problems or durability problems.

3.1

Pavement in the UK

The UK demonstration pavement (Figure 6) was constructed in London and comprised a series of access channels (surface area 300 m 2), subjected to controlled heavy goods traffic (KOUTSELAS, 2009). The pavement was constructed in April 2009 and comprised three layers: foundation (150 mm deep of cement bound granular material), SFR-RRC base (170 mm deep) containing 5% (by mass) recycled steel tyre-cord fibres (cement content: 300 kg/m3 CEM I), and asphalt overlay (70 mm deep).

Figure 6 - Demonstration SFR-RCC pavement constructed by EcoLanes in the United Kingdom


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3.2

Pavement in Romania

The Romanian demonstration pavement (Figure 7) was constructed between Campulung Moldovenesc and Gura Humorului and comprised full rehabilitation of an existing heavilytrafficked national road (DN17). The pavement was constructed in May 2009 and comprised three layers: foundation, concrete base, and asphalt overlay (BULAU et al. 2009). The foundation was made with ballast material (300 mm deep), whilst the concrete base comprised three sectors (180, 230 and 280 mm deep); the depth of the asphalt overlay was 100 mm. The demonstration pavement (150 m long and 9.5 m wide) comprised two lanes: one made with plain RCC and one made with SFR-RCC, which contained 3% (by mass) recycled steel tyre-cord fibres (cement content: 300 kg/m3 CEM I). The concrete bases were jointed in both lanes (variable joint spacing was trialled: 4, 6, and 8 metres). A recent investigation of this pavement (March 2011) indicated that the pavement has not experience any freeze-thaw damage due to the low temperatures experienced in that region during the winter months.

Figure 7 - Demonstration pavement constructed in Romania

3.3

Pavement in Cyprus

The pavement in Cyprus (40 m long, 6 m wide) was constructed in April 2009 at a rural environment (old road leading to Galataria village in Pafos district at Troodos mountain) and comprised rehabilitation of the existing road, subjected to ground movements (NEOFYTOU 2009). The demonstration pavement (Figure 8) was placed over the existing asphalt pavement (to maintain the geotechnical equilibrium); however the asphalt 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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pavement was slightly milled to provide better bond. The demonstration pavement comprised two layers: an SFR-RCC base containing 2% (by mass) recycled steel tyre-cord fibres (cement content: 300 kg/ m3 CEM II with limestone) and an asphalt overlay (100 mm deep). The latest monitoring of this demonstration SFR-RCC pavement was undertaken in January 2011, and no damage (due to ground movements) was detected, while an adjacent asphalt pavement (rehabilitated at the same time) had experience deformations due to ground movements.

Figure 8 - Demonstration pavement constructed in Cyprus

3.4

Pavement in Turkey

The Turkish demonstration SFR-RCC pavement (150 m long and 8.6 m wide) was constructed in Antalya (in April 2009) and comprised full rehabilitation of an existing urban road (Necip Fazıl Kısakürek Street), (BUDAK 2009). This required removal of the existing asphalt road and foundation. The demonstration pavement (Figure 9) comprised four layers: foundation (ballast, 200 mm deep), base course (broken stone, 100 mm), concrete base (190 mm deep), and asphalt overlay (40 mm deep). The concrete base (cement content: 300 kg/m3 CEMIIA) was constructed in four joint-less sectors: sector A (70 m long, 5.1 m wide) was made with SFR-RCC containing 3% (by mass) recycled steel tyre-cord fibres, sector B (40 m long, 5.1 m wide) was made with SFR-RCC containing 2% (by mass) industrially-produced steel fibres, sector C (40 m long, 5.1 m wide) was made with plain RCC, and sector D (150 m long, 3.5 m wide) was made with SFR-RCC containing 3% (by mass) recycled steel tyre-cord fibres. 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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Following the experienced gained from the construction and operation of this demonstration pavement, the local authority in Turkey decided to adopt SFR-RCC (reinforced with recycled steel tyre-cord fibres) for the construction of surface transport pavements. In March 2010, a city centre road in Antalya was fully rehabilitated using SFRRCC (Figure 10), while the construction of a 7 km rural SFR-RCC rural road is under planning by the local authorities.

Figure 9 - Demonstration pavement constructed in Turkey

Figure 10 - Rehabilitation of a city centre road using SFR-RCC (March 2010 - Antalya Turkey)

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Discussion and Conclusions

The research and technological findings discussed in this paper demonstrate the potential benefits of adopting roller-compacted concrete, reinforced with recycled steel tyre-cord fibres, for both the rehabilitation of existing roads and the construction of new pavements. The developed fibre reinforced concrete mixes were technically validated by undertaking accelerated cyclic load tests of trial pavement sectors. The results indicate that, over a design life of 30 years, the proposed pavement type would survive at least 20.5 millionsingle-axles of traffic. In addition, periodical monitoring of the four demonstration pavements, constructed as part of this research, indicates that no damage was detected on the pavements during the first two years of operation (since Spring 2009). Furthermore, the LCA results of this study show that the proposed method opens the way for the construction of long lasting rigid pavements, which are more economic (up to 12% cost savings) and environmentally friendly (40% less energy consumption). 53º CONGRESSO BRASILEIRO DO CONCRETO - CBC2011

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The proposed pavement construction method is expected to provide a sustainable market for steel tyre-cord fibres recycled from post-consumer tyres and, this will encourage the material recovery of large amounts of tyres.

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Acknowledgements

This research has been financially supported by the 6 th Framework Programme of the European Community within the framework of specific research and technological development programme “Integrating and strengthening the European Research Area”, under contract number 031530.

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References

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as fatigue reinforcement for concrete pavements. Second international conference on Best Practices for Concrete Pavements, November 2011. KOUTSELAS, K.. Feedback on the design, construction and service of the new road. Assessment of the cost, environmental and energy benefits of the project. Aggregate Industries UK, EU FP6 STREP project, Report of Deliverable 5.4, 2009. KOUTSELAS, K.; NEOCLEOUS, K.; ANGELAKOPOULOS, H.; PILAKOUTAS, K.. Specifications for the construction of steel fibre-reinforced roller compacted concrete roads. 11th International conference on Concrete Roads – The answer to New Challenges, Seville Spain, 13-15 October 2010. NANNI, A.. Properties and design of fibres reinforced roller compacted concrete. Transportation Research Record, No. 1226, 1989. NEOCLEOUS, K.; PILAKOUTAS, K.; WALDRON, P.; GOULDING, J.. Specification for classifying steel tyre-cord fibres. WP1 (Fibre Sorting) Deliverable Report 1.4d, FP6 EU STREP Project EcoLanes (031530), Ref. ECO/D1.4d, September 2009. NEOCLEOUS, K.; ANGELAKOPOULOS, H.; PILAKOUTAS, K.; GUADAGNINI, M.. Fibre reinforced roller compacted concrete transport pavements., ICE Transport, Vol 164 (TR2), 2011. NEOFYTOU, P.. Feedback on the design, construction and service of the new road.

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