Subject matter

Over the past few years, there has been a significant effort in the research, development and application of Fiber Reinforced Concrete (FRC). This has been facilitated by the work of the many research groups and technical committees (such as RILEM 162-TDF) and the introduction of FRC in major national or international codes of structural Concrete (ACI 318, MC 2010, EC2, among others).

However, the long-term behavior of FRC under sustained load is still a controversial topic in both scientific and in technical forums. A proof of this are the papers presented at the last RILEM BEFIB 2012 Conference in Guimaraes. Currently, more than 15 research groups in the world are working on the subject and interest has been very strong in the business field. The research focus is mainly on the influence of the type of fiber, of fiber-concrete bond and of environmental conditions such as temperature and humidity.

The study of the creep response of cracked FRC is essential to ensure the viability of structural applications of FRC and has important consequences on structural durability and safety. One of the main problems that has complicated the development of guidelines or models to consider this phenomenon lies in the absence of a standardized testing methodology to quantify creep in FRC, and the work conducted by different groups employs different procedures, leading to results and conclusions that are difficult to compare or to generalize. Consequently, to obtain comparable results and to achieve a sufficiently large database to propose models applicable in the structural design, it is of the outmost importance to unify the methods and the criteria for the assessment of creep in FRC.

In recent meetings, the FIB TG 8.3 discussed the possibility of working on the issue of creep in cracked FRC elements as a specific topic. The same concern was raised at the CEN TC 250/SC2/WG1/TG2. However no committee was formed with that intention given that it was considered that the ideal framework for such proposal would be RILEM.

The main objectives of the committee are:

(1) - To coordinate research efforts and compile the results of studies into mechanisms of creep behavior of FRC.

(2) - Evaluate the structural repercussions of the phenomenon, analyzing elements subjected to sustained load in which creep may represent a problem.

(3) - Propose unified test methods to determine the parameters characterizing creep behavior and to assess the feasibility of those test methods, clarifying the criteria to analyze the test results.

(4) - Analyze the variables that influence creep behavior of cracked sections of FRC (including composition and properties of concrete; dosage and fiber type, external conditions of work and stress level) 

(5) - Develop practical recommendations and design criteria for structural elements subjected to this phenomenon.

In summary, the aim is to collect all available information and knowledge, as well as to coordinate on-going research efforts to ultimately produce a state-of-the-art report and RILEM recommendations. The objectives of the TC should be achieved within 4 working years.

Terms of reference

The scope of the TC may be considered new since there is no active national, regional and international associations (fib, ACI, IABSE, etc) working on the topic. 

The members of the TC are recognized experts in the topic from several parts of the world. This way it will be possible to reach a consensus that takes into account the different practices and standards, as well as their respective spheres of influence, including ISO, EN and ASTM standards.

Detailed working programme

The work of the TC will initially focus on bringing together the expertise and knowledge of all participating members.

In this context, the TC will simultaneously address the following:

Activity. 1 - Organization of a RILEM workshop:

In the first year, the committee will focus on the organization of a RILEM Workshop. The tentative time for the workshop should be the end of 2015 or the beginning of 2016. The aim is to prepare a document / publication that collects updated observations and results on the topic. 

Activity. 2 - Compilation of State-of-the-Art Report:

An overview of FRC creep behavior will be compiled. The outcome of this work will be a state-of-the-art report including critical ideas or agreements, calculation criteria and recommendations for the practitioner. 

Activity 3.Definition of standard test methods.:

The decision on whether one or several proposals (depending on objectives or applications, for instance: tunneling, structural elements), to be assessed will be a result of Activity 3.

A series of round-robin tests is expected to be performed in order to compare different test methods or real applications.