The expert's opinion
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10/7/2025
Designing durable concrete with macro-synthetic fibers: a software-based method
A new software-based design method to fully leverage macro-synthetic fiber reinforced concrete, ensuring durability, sustainability, and compliance with European standards
The integration of macro-synthetic fibre-reinforced concrete (MSFRC) into structural applications is gaining momentum due to its advantages in durability, constructability and sustainability. Carles Cots introduces a design methodology supported by CivilMapei – a structural design software which enables engineers to incorporate MSFRC effectively, particularly in precast and industrial applications. CivilMapei facilitates compliance with Eurocode 2(1) and national standards by implementing advanced models for residual strength, crack control and early-age checks. Its use streamlines the design process, allowing for optimised reinforcement strategies and reliable structural performance.
Over the past decade, macro-synthetic fibres have emerged as a credible alternative to steel reinforcement in both structural and non-structural concrete elements. Their use addresses key durability concerns, particularly corrosion, and offers practical benefits such as reduced labour, improved safety and lower environmental impact. However, structural use of macro-synthetic fiber-reinforced concrete (MSFRC) requires rigorous design verification, especially at ultimate and serviceability limit states. This article presents a software-based approach that aids engineers in adopting MSFRC while ensuring code compliance and structural reliability.
Motivation for using macro-synthetic fibres
Steel corrosion remains a primary limitation to the longevity of reinforced concrete structures. Macro-synthetic fibres offer a corrosion-free reinforcement system with effective post-cracking behaviour, particularly beneficial in aggressive environments or where reduced maintenance is critical.
Benefits include:
- elimination of corrosion-related deterioration
- reduced embodied carbon compared with traditional steel
- simplified handling and placement.
Applications in precast elements further benefit from the consistent fibre distribution and the possibility of reducing or eliminating conventional bar reinforcement, particularly in serviceability-driven scenarios. Design using macro-synthetic fiber-reinforced concrete must address minimum ductility requirements and ensure sufficient post-crack tensile resistance, especially when load redistribution or accidental actions are expected. These requirements demand appropriate modelling tools to simulate residual tensile capacity under flexure and shear.
Software-based design framework
CivilMapei implements the design principles outlined in the fib Model Code(2) as well as in national Codes and Annexes, ensuring compliance with evolving international standards for fiber-reinforced concrete.
CivilMapei builds on over 25 years of validated modules originally created for bridge and civil infrastructure design. These modules have been extended to incorporate the contribution of macro-synthetic fibres in flexure, shear and crack control. The software is available under a free license to promote the adoption of advanced MSFRC solutions in structural applications.
CivilMapei supports design using MSFRC by automating key verifications required by international and national standards. It includes dedicated modules for:
- sectional analysis (eg, beams, walls, tanks)
- 2D plate analysis (eg, slabs, panels)
- industrial pavement design (per TR34(3)).
Supported Standards include:
- Eurocode 2 (EN 1992-1-1)
- fib Model Code 2010(4)
- TR34 (slabs-on-ground)
- National Annexes.
Users can define geometry, loads, support conditions and material properties, and then perform detailed ultimate limit state (ULS) and serviceability limit state (SLS) checks.
Extended joint spacing with Expancrete and fibers: example of extended saw-cut joint spacing achieved by combining shrinkage-compensated concrete with macro-synthetic fiber reinforced concrete.
Practical applications
The design tools have been applied to a range of structural elements. Key sectors where MSFRC provides substantial benefits include:
• Modular housing and architecture: precast walls, panels, stair flights and façade elements for modular building systems benefit from improved crack control and durability, enabling thinner sections and more efficient production cycles.
• Hydraulic, utility and energy infrastructure: precast pipes, inspection chambers, underground vaults, utility boxes and transformer cabins achieve high durability and resistance to aggressive environments. MSFRC is especially useful in sanitation, stormwater and energy distribution networks.
• Architectural urban elements: furniture, benches, planters and barrier elements can be produced with enhanced durability and aesthetic consistency using fibre-reinforced mixes.
• Industrial pavements.
• Internal floors: warehouses, logistics centres and production areas benefit from fibre-reinforced concrete due to reduced jointing, high fatigue resistance and improved crack control under repetitive loads.
• External slabs: loading docks, container yards and exterior storage platforms are exposed to varying weather conditions and mechanical loads, where MSFRC provides long-term durability and reduced maintenance.
• Linear infrastructure: roads, access routes, bicycle lanes, airport service areas, tramway slab tracks, port zones, container terminals and water channels are applications where MSFRC enables durable, joint-optimised solutions with lower reinforcement demand.
In addition, the use of MSFRC without conventional reinforcement opens the possibility for more creative and functional geometries. Elements can be designed with curved profiles, cellular cores, ribs and integrated voids, offering enhanced flexibility in both architectural and structural applications.
Concentrated loads from storage racks: internal industrial floor cast with MSFRC, designed to support concentrated point loads from high-density pallet racking systems.
Material characterisation and input
Accurate modelling of MSFRC relies on proper mechanical characterisation. The software integrates test data based on EN 14651(5), converting results from CMOD-based residual strengths (fR1–fR4) into tensile constitutive models. Available modelling options include:
- rigid-plastic: suitable for conservative ULS design
- multi-linear: suited for serviceability checks, including crack width and deflection.
The software also supports input of full CMOD curves, enabling detailed analysis when advanced lab data is available. Cloud-based libraries allow firms to catalogue validatedfiber-reinforced concrete formulations, promoting standardisation across projects.
Definition of precast panel geometry with voids and specification of structural macro-synthetic fibre concrete in CivilMapei, including selection of constitutive model and automatic characteristic length for ULS checks.
Characterisation of fiber-reinforced concrete for precast under EN Standards
The use of fibre-reinforced concrete (FRC), especially with macro-synthetic fibres, in precast concrete elements is growing due to its benefits in durability, ductility and design flexibility. The Eurocode system and related EN Standards provide a clear framework for the mechanical characterisation and specification of FRC in structural applications.
Standard tests for FRC characterisation:
- EN 14651: Flexural tensile strength on notched beams (150 × 150 × 550mm), providing fLOP and residual strengths fR1 to fR4.
- EN 14889-2(6): Specifies synthetic fibre properties (tensile strength, geometry, anchorage, durability).
Criteria for FRC design based on standard tests
Designing structural elements in fibre-reinforced concrete requires the definition of constitutive models based on residual flexural strengths obtained from standard tests such as EN 14651. These models allow translation of material behaviour into simplified mechanical laws suitable for numerical analysis.
Types of constitutive models:
- Rigid-plastic (simplified) model:
- used for ULS design
- assumes constant post-crack strength: fFtu = (1/3) · fR,3
- moment resistance: MRd = (fFtu · b · h²) / 6
- no iteration required; suitable for ductility classes a–c
- • Multi-linear (bilinear) model:
- used for refined ULS and SLS verification
- two linear branches derived from:
- fFt,1 = κ · 0.37 · fR,1k
- fFt,2 = κ · (0.57 · fR,3k – 0.26 · fR,1k)
- strains computed from CMOD and geometry
- requires iterative solution for internal equilibrium and moment–curvature response.
Definition of imposed actions in CivilMapei, illustrating application of surface, line and point loads with their limit-state combination factors.
Structural validation and performance analysis
The CivilMapei design engine performs both ultimate and serviceability verifications, including:
- flexural resistance (MRd vs MEd)
- shear strength including fibre contribution (VRf)
- crack width checks per Eurocode 2
- moment–curvature analysis to evaluate ductility.
The 2D plate module in CivilMapei models support conditions, voids, openings and irregular load cases. Outputs include shear and bending moment maps, crack patterns and required reinforcement contours. For pavements, load cases from racks, forklifts and trucks are addressed and fibre dosage is calibrated accordingly.
Precast cabin panel
A practical case involved the optimisation of a precast concrete cabin using MSFRC. The fibre-reinforced mix allowed for a significant reduction in conventional steel fabric, improving production efficiency and reducing labour. Finite-element analysis performed using CivilMapei verified the post-cracking stress capacity and supported early demoulding, critical in precast workflows. Additional design modules were used to evaluate thermal effects and simulate handling stresses during transport and installation. The design process ensured compliance with structural performance and durability requirements.
Concluding remarks
Macro-synthetic fibre-reinforced concrete offers a robust and sustainable alternative to traditional steel reinforcement. It allows for innovative and efficient solutions across a range of applications, from modular construction and infrastructure to precast utilities and industrial pavements.
The integration of CivilMapei, an advanced structural design software, enables engineers to exploit the full potential of MSFRC by simulating post-cracking behaviour, validating residual strengths and streamlining structural verification. By aligning with Eurocode and fib Model Code Standards, the software supports consistent and safe implementation of FRC systems.
As standardisation and field data increase, the broader adoption of MSFRC in structural design is expected to grow, contributing to a more resilient and low-carbon construction sector.
Supplementary reinforcement in X direction with conventional steel, added to the macro FRC base reinforcement. Units: cm²/m.
References
- BRITISH STANDARDS INSTITUTION, BS EN 1992-1-1. Eurocode 2. Design of concrete structures - General rules and rules for buildings, bridges and civil engineering structures. BSI, London, 2023.
- FÉDÉRATION INTERNATIONALE DU BÉTON. The fib Model Code for Concrete Structures (2020). fib, Lausanne, Switzerland, 2024.
- CONCRETE SOCIETY. Concrete industrial ground floors. A guide to design and construction. Technical Report 34, Fourth Edition, Camberley, January 2018.
- FÉDÉRATION INTERNATIONALE DU BÉTON. fib Model Code for Concrete Structures 2010. fib, Lausanne, Switzerland, 2013.
- BRITISH STANDARDS INSTITUTION, BS EN 14651. Test method for metallic fibre concrete. Measuring the flexural tensile strength (limit of proportionality (LOP), residual). BSI, London, 2005+A1:2007.
- BRITISH STANDARDS INSTITUTION, BS EN 14889. Fibres for concrete. Part 2 – Polymer fibres. Definitions, specifications and conformity. BSI, London, 2006.
