Subject matter

Roller compacted concrete was used for gravity dams, but in the last decade it was increasingly applied for heavy duty pavements.  This zero slump cementitious material can by densified by roller compaction in the unhardened state by using asphalt paving equipment (Portland cement association 2013). It can be placed in a single lift with thickness up to 250 mm in a relatively high speed of construction (Harrington, 2010). RCC has lower water and cement paste content and can be placed without dowels or junctions. Typical cementitious binder contents range between 240 and 360 kg/m³, while the maintenance costs are relatively low. Multiple lifts appear to exhibit a sufficient interface bond (apart from the edges) to consider the material as a monolithic block (ACI Committee 325 1995:13-14). This is a relevant quality in the pavement construction field. Lower maximum aggregates size are generally used (< 20 mm) as conventional concrete, in order to get an adequate surface finish. Environmental studies (Dominique Mathieu, 2010) and SCM’s are also used to further lower the carbon footprint as seen for the aforementioned material characteristics. The compressive and the flexural strength are strongly dependent on the compaction, while the shrinkage and the cracking susceptibility appear to be low, because of the low cement content. The resistance to freeze/thaw is high due to the inherent strength and density of the structure, while the addition of SCM’s (C. Cao, 2000) and air bubbles seem to increase the durability (Material expert service Inc. 2004, Canada).

The RCC is used for container yards, manufacturing plants, local roads, bike trails and industrial projects. In the US an increase of RCC use is observed starting from 2005 (C. Zollinger, 2013). Many other paving applications are used where cyclic loading on large surfaces are present (B. Killingsworth, 2011). In other areas of the world, especially in Europe and Asia, the use of RCC is increasing and alternative wastes, SCM’s, recycled aggregates and/or fibres are added to the mixtures (K. Neocleous, 2011; G. Calis, 2019; M. Selvam, 2021; N. J. Delatte, 2014; Zar Phyu Tun, 2016; S. A. Yildizel, 2020; A. Kheirbek, 2022). Also reclaimed asphalt pavement aggregates may be added to the blends (C. Settari, 2015).

In spite of the existing application guides, such as the one produced by the Iowa State University National concrete pavement technology center in 2010, most of the knowledge is still strongly based on field experience without a systematic scientific approach. Moreover, a wide, constant and well structured sharing of the knowledge in the topic is missing. In this concern, the fresh state compaction techniques, the mechanical, physical, chemical and the durability properties, the mix designs as well as the influence of the addition of SCM’s, recycled material, wastes and fibres to the blends are still not clearly and widely investigated.

The main goal of the technical committee is to gather the worldwide experience gained so far in the field, in real applications, but also within the laboratories. A main task is to review the scientific publications and knowledge produced in the recent past concerning the pavement applications, to critically assess the results, and to evaluate the implementation potential of this material and the technique for a more widespread paving of urban roadways. Laboratory and field trials in the different countries sponsored by the public-private sectors would complete the TC tasks. These actions will allow to use a more rigid and durable pavement as compared to asphalt concrete pavements, to reduce the Albedo and the heat islands, to use a material with a higher recycling potential, to reduce the use of cement, the life cycle costs and the maintenance works as well as the frequent closure of road sections in heavily trafficked areas.

• Material:

The main components will be composed of local materials, although depending on the geographic region and production plants avalability. Concrete characteristic, aggregate granulometric curves, aggregate type, fillers, chemical additives, recycling cementitious materials (fine and coarse) and SCM’s to be added to the concrete blends, superplasticizer type and dosage, fibre type and dosage

• Structures:

Road pavements exposed to different classes of traffic and conditions, such as secondary roads, main roadways, highways, parking lots, bus stops, roundabouts, airport runways and various environmental exposures, such as continental climates, cold, hot, mild, humid and arid climas.

• Phenomena or specific aspect:

Part I: Literature review. Study of the mechanical (compressive and flexural strength, modulus of elasticity, fatigue performance, interface bond between the lifts) and durability (freeze/thaw resistance, carbonation, sulphate and chloride penetration consequences, shrinkage) properties in the fresh and in the hardened state of the concrete materials as well as characterization of the compaction techniques (compaction methods, paving, joints, curing) and the resulting performance of the pavements. Complete bibliography of the construction systems down to the unbinded levels to the soil (sub-base and sub-grade preparation). This first action will allow to consolidate the actual state of the art, the experience and the scientific knowledge present in the field.

Part II: Laboratory tests. This phase will allow to focus the investigations on implementation targets regarding the mix design and durability with a special attention to the reducing carbon footprint materials and recycled components. The experimental investigation and implementation of the pavement properties, in particular the durability, by adding recycled cementitious components, by using SCM’s, low carbon binders and by managing the superplasticizer type and dosage as well as the microstructure development during time and the modelling at the different micro-macro levels will be shared among the different TC members. This will keep under control the work load of the committee members and their institutions. The compaction techniques and the performance relation to the field will be essential. This is why the following part III would be necessary.

Part III. Real field tests on site by exposing especially chosen mix designs to specific trafficked condition and climas. In order to limit the costs, each member may try to get a field trial road section (10-500 meters length) or surface area, and the experimental tests partially funded by a public or a private institution. 

• Level of investigation:

Part I. Complete search of the actual knowledge based on a literature review and field experiences worldwide with a particular emphasis on the durability of the pavement systems.

Part II. Laboratory investigation in order to implement the long-term performance of the pavement with recycled, SCM’s as well as low carbon binder components.

Part III. Real field tests on site. Road intervals 10-500 m long or surfaces to be paved with RCC.

It is a review and updating and an implementing of an existing system, which is scarcely investigated in the applied research field. Rolled compacted concrete was used for dams and more recently in the paving sector. It is mainly used in the US. Nonetheless, the knowledge and the application of such material in combination with recycled cementitious components, SCM’s and low carbon binders in partial substitution of ordinary Portland cements as well as the interaction with superplasticizers to reduce the binder component and the microstructural development is widely unknown. Especially in Europe and in other countries worldwide the lack of experience is clear. The UK and Turkey are slowly increasing the use of such pavement technique and material. This new TC would create a worldwide state-of- the-art and would allow to implement this road building techniques by reducing the use of the less durable and flexible bituminous binders, in particular within urban areas, where roads are particularly subjected to horizontal shear stresses. Generally, there is a need to improve the durability of bituminous pavements and reduce cracking as well as deformation. A higher stiffness and a lower tendency to wide cracking is required. Two characteristics that may be more easily attained with RCC. Furthermore, a reduction of the heat island within urban areas may be easily implemented by replacing the black-colored bituminous pavements with white-grey RCC.

The review, the experimental and the applied part on site of this work will set a new starting point and implement this technique. Nonetheless, the work in manly focused on the material characteristics and compaction. The possible evolution of the paving techniques is not a goal of the TC, although the sharing of the knowledge within the TC among material scientist, academic institutions, concrete producers and paving companies, may trigger these latter to improve the technical and scientific changes on the paving equipments.

The reduced content of cementitious binder within the rolled compacted concrete, the use of recycled cementitious components as well as SCM’s and the reduced use of energy-rich bituminous binders that derives from the oil distillation, all significantly contribute to the reduction of the environmental impact of such rolled compacted concrete material, especially if we think on the millions of chilometers of roadways present in the urban areas of the world.

Terms of reference

The different part of the work (I, II, III) will be gradually achieved by means of regular meeting (presence / online) and by sharing the task to be reached within the part I, II, III of the work. After completing the part I, the discussions should led to the implementing factors to be tested with laboratory mix-design and durability tests. Each institution, in particular academic, but also industry, will get a precise blend range to investigate. This will share the work load among all TC members. Subsequently, after deep discussion and sharing of the results of part II, chosen mixes with a limited extended surface will be applied on site. In order to limit the costs, the road segments will not be longer than 500 meters and the participants will be required to assume the costs, especially the concrete producers, the paving companies or the public institutions, in collaboration with the Universities.

• Give an estimation of time necessary, provisional timetable

Part I: Start in September 2023, end June 2025

Part II: Start June 2025, end January 2027

Part III: Start January 2027, end July 2029 with the possibility of a continuous monitoring of the test surfaces on site.

• Membership:

The members of the new TC cover a broad range of countries, from Europe to Asia, Australia, Africa and South America. In addition, a member of the RCC technical council of USA is included in the TC, since the latest development of the RCC knowledge is occurring overseas. Academic, industry and in particular Ph D students are strongly welcome within the TC.

• Will the work imply bibliographical research?

The work will imply a wide state of the art bibliographical research, laboratory experimental investigation and on site tests. This latter action will improve the relationship between laboratory tests and field performance.

• Clarify in which respect the work of the TC will have direct industrial relevance.

The increase in the use of rolled compacted concrete as a paving material, especially in urban areas, will partially reduce the use of bituminous material and promote the use of a mineral binders. The additional use of recycled cementitious components, low carbon binders and a low cement concrete will trigger further development in these related fields and lower the environmental impact. Furthermore, the recycling of the old RCC pavement material will be more easy to accomplish as compared to the reclaimed asphalt pavement RAP recycling within bituminous pavements. A longer life cycle and a higher durability will be achieved and this is a key factor for the environment. The bituminous paving industry will continue to lead the pavement sector, since the paving devices remains the same, if not similar as for the bituminous pavement application and might take advantage of possible technical improvement of the equipments by applying the RCC. A single layer pavement stratigraphy as for the RCC will speed up the paving application, save costs and reduce the closing time of heavily trafficked roadways.

Detailed working programme

Part I: Start in September 2023, end June 2025

• Start meeting September 2023– definition of the tasks (Part I, II, III)
• Literature review: sharing of the topics to be analized.
• September 2023 - April 2024 RCC material characteristics, RCC mechanical properties, RCC durability aspects,
• April 2024-December 2024 RCC special additives / recycled materials / SCM’s additions,
• December 2024-June 2025 RCC compaction and application techniques

Part II: Start June 2025, end January 2027

Laboratory Experimental investigations

• June 2025-January 2026 definition of the best blend types to be prepared according to the main mix design parameters retrieved from the literature with respect to the mechanical and durability properties.
• January 2026-June 2026 Preparation and implementation of the RCC mixes with the addition of recycled, SCM’s materials and fibres.
• June 2026 - January 2027Mechanical and durability tests of the blends according to national / international norms.

Part III: Start January 2027, end July 2029

Field tests.

• January 2027-December 2027 Application of test surfaces of RCC along real trafficked structures: roadways, parking lots, bus stops, roundabouts.
• December 2027 - July 2029 continuous monitoring of the test surfaces on site, including regular sampling of RCC cores specimens (every 5 months) for the microstructural, mechanical characterization.