TG4.1 - Fibre-reinforced concrete

Fibre concrete is more than 50 years old and the design rules have undergone developments over the years. TG4.1 will make theoretical and practical developments in the field of fibre-reinforced concrete materials technology, rheology and materials characterisation and modelling and to present these developments in code-type formulations.

The task group collects and validates information on the behaviour of fibre-reinforced concrete materials, subjected to various types of loading and environmental conditions.

TG4.1 is currently finalising a bulletin on the background to the design rules in MC2010.

Convener
Lucie Vandewalle

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TG4.2 - Ultra high-performance fibre-reinforced concrete

Task Group 4.2 (TG4.2) will make theoretical and practical developments for concretes with strength > 120 N/mm2 in the field of fibre-reinforced concrete materials technology, rheology and materials characterisation and modelling to present these developments in code-type formulations. Work is applicable to concrete with fibres of various types, such as steel, polymeric or combinations thereof.

The work of TG4.2 is coordinated with the work of fib TG4.1 (Fibre-reinforced concrete) that develops recommendations for conventional fibre-reinforced concrete.

Convener
Joost Walraven

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TG4.3 - Structural design with flowable concrete

Flowable concrete (highly flowable, self-compacting and/or self-levelling) has evolved from a special type to a commonly applied building material. fib Task Group 4.3 (TG4.3) considers three aspects of flowable concrete (FC) for structural design: material properties, production effects and structural boundary conditions. The flow of concrete (initiated by some vibration and/or the weight of concrete) can affect the structural characteristics of hardening or hardened concrete. The mixture composition has to be adjusted and optimised in order to obtain a high flowability. TG4.3 aims at promoting the application of flowable concrete, improving and adapting the concrete design and the production technology and its implementation in guidelines and codes.

Convener
Steffen Grünewald

Co-Convener
Liberato Ferrara

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TG4.4 - Aesthetics of concrete surfaces

The notion of exposed concrete is subjective and varies according to the viewer. The motivation of fib Task Group 4.4 (TG4.4) is to show possibilities how to categorise and evaluate visible concrete surfaces and how to point out technical factors of influence.

TG4.4 will formulate a state-of-the-art technical report on how exposed concrete is defined and built. The final aim is to create a generally accepted recommendation or guidelines for exposed concrete with a homogenous appearance. This generally accepted recommendation or guidelines will be characterised by classifying exposed concrete in different categories. The limit of its objective performance will be considered as well as the consequences on the effort on-site and the planning of structural framework.

Convener
Ludger Lohaus

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TG4.5 - Time-dependent Behavior of Concrete

The primary objective of the task group is to identify limiting aspects during the design of new or assessment of existing structures related to predicting the time-dependent (mechanical) behavior of “new” but also “traditional” concrete types. Based on the identified short-comings the task group will initiate literature reviews, compile/ update consistent databases and update existing model formulations. Where possible the TG will make use of the data already available in the scientific literature. Where this is not the case, the task group will strive to develop research strategies and coordinate research efforts by its members, supported by national or international research funds.

The task group plans to develop databases and calibrated prediction models for the time-dependent mechanical properties of cast concrete including:

• Maturity vs. time concepts, applicable to early age and multi-decade predictions
• Development of compressive and tensile strength as function of maturity/ time;
• Development of Young’s modulus as function of maturity/ time;
• Development of fracture energy as function of maturity/ time;
• Development of creep and shrinkage as function of maturity/ time;
• Empirical relationship between mechanical properties and compressive strength as function of maturity/ time;
• Development of stress-strain diagram as function of maturity/ time;
• Transport of liquids and gases;
• Guidance for the coupled hygro-thermal chemo-mechanical analysis of concrete with relevance to e.g. mass concrete or certain structural components prone to early-age cracking;
• Guidance for the time-dependent nonlinear (fracture mechanical) analysis of concrete including advanced constitutive models and strain rate effects;
• Time-dependent resistance of concrete subject to sustained load
• Time-dependent resistance of concrete subject to fatigue;

Convener
Roman Wan-Wendner

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TG4.6 - Constitutive laws for concretes with supplementary cementitious materials

The use of Supplementary Cementitious Materials (SCM) as binder in concrete is increasing, mainly driven by the need of the concrete industry to make concrete more environmentally friendly and in particular to meet official requirements for lower CO2 emissions. Here, it is to replace considerable amount of the high emitting Portland cement with low emitting SCM. The fib Model Code for Concrete Structures 2010 (MC2010) covers the use of SCM, but limits the materials and the amount of SCM. The overall motive of fib Task Group 4.6 (TG4.6) is to prepare the basis for an extension of the MC2010 that includes assessment of less known SCM as well as larger replacements.

TG4.6 aims to prepare a state-of-the-art report addressing the items in chapter 5.1 Materials – Concrete in the MC2010. The constitutive relations can be formulated as in, and assessed in relation to compliance with those given in MC2010.

Convener
Fragoulis Kanavaris

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TG4.7 - Structural Applications of Recycled Aggregate Concrete – Properties, Modeling, and Design

The main objective of the TG is to formulate design recommendations for the structural use of RAC. This will take the form of proposing new or adjusting existing expressions and models for mechanical and structural properties of reinforced and prestressed concrete structures.

To achieve this goal, the TG will first perform a comprehensive critical review of literature alongside a preparation of databases of experimental results regarding mechanical and structural properties of RAC. Where necessary and possible, identified gaps in existing results will be complemented by new studies of TG members within existing or new research projects. Based on this work, the TG will formulate expressions and models for the following:

• Physical properties of RAC – density, water absorption, permeability
• Mechanical properties – compressive strength, tensile strength, modulus of elasticity, stress–strain relationship, fracture energy, shrinkage, creep
• Durability-related properties – carbonation resistance, chloride ingress, freeze-thaw resistance, chemical attack
• Structural behavior – flexural strength, shear strength, axial strength, punching strength, seismic resistance, fire resistance, deformation, cracking, bond and anchorage
• Fire resistance of RAC and RAC structures – resistance under fire and residual resistance after exposure to elevated temperatures of RAC and reinforced and prestressed RAC members

Convener
Nikola Tošić

Co-Convener
Jean-Michel Torrenti

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TG4.8 - Low-carbon concrete structures

Decreasing the environmental impact of concrete structures is an objective put forward by almost all the actors involved in the domain of construction. Although cementitious materials intrinsically involve low embodied energy, their use in large volumes in worldwide construction lead to approximately 8% of global CO2 emissions. Portland cement is the main constituent responsible for the environmental impacts caused by the life cycle of concrete, as it generates on average more than 800 kg CO2/t of clinker.

The task group will have two main objectives:

1- Identify the different ways to obtain low-CO2 concretes among the different possible routes:

• Evaluate which ones are rapidly reachable and how far we are from an universal utilization of these concretes.
• Define the work to carry out to bring these concrete at an industrial level.
• Estimate the scientific, technical and economical obstacles and challenges that could retard the implementation and acceptances of such concretes.

2- Evaluate the consequences of these low-CO2 concretes on the design of concrete structures, in terms of:

• Durability, for instance the impact of these new concretes on carbonation and chloride ingress, the most widespread problems facing reinforced concrete worldwide.
• Structural design, with the verification of the applicability of the international codes (Eurocodes…). The part concerning creep and shrinkage will be developed in the new COM4/TG Time dependent behavior of concrete.

Convener
Martin Cyr

Co-Convener
Michael Haist

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