WG1 –TESTING OF CEMENT BASED MATERIALS AND RRT+

 

The testing of CBM performance during lifetime is an extremely complex and challenging task. During the service life of CBM structures, several phenomena occur simultaneously: hydration, heat release and transfer, drying, shrinkage, creep and relaxation, and development of mechanical properties. Particularly in the early age period, the physical, chemical and mechanical properties of CBM undergo rapid changes, resulting in significant influence on the final quality and durability of the hardened CBM. Thus, a good knowledge of the microstructure evolution during the successive phases of the hydration process is of great importance. The tasks undertaken within WG1 will focus on testing of CBM, ranging from the microscopic level, where the microstructure formation of CBM is observed up to the development of a set of parameters measured directly on concrete in addition to those measured on paste and mortar by using the most recently developed techniques, particularly those allowing continuous monitoring. This task will allow building a material database that is especially useful for the simulation models targeted in WG2 to predict the service life performance.

The cooperation of several groups with a very strong expertise in continuous monitoring at all necessary scales (particles, paste, mortar and concrete) will be a unique opportunity to integrate efforts, and provide robust validation of recent innovative experimental techniques in continuous monitoring of CBM at early ages. In addition, this will provide a better understanding and description of the development of CBM properties during the service life.

New testing equipments and experimental protocols that are used or designed recently are considered in this task. They must be able to describe properly the CBM properties during the setting time and throughout the service life, thus allowing new insights particularly at the initial (crucial) period that is not hitherto well understood by most conventional tests. In this WG, particular attention will be given to:

  • Fresh properties and setting: rheology and setting time;
  • Chemical and microstructural characterization: porosity, TGA, SEM, XRD;
  • Transport properties and boundary effects: thermal conductivity, specific heat, density and diffusion, sorption isotherms, permeability, convection coefficient, solar radiation, night cooling, evaporative cooling, electrical properties;
  • Mechanical properties: compressive, bending and tensile strength, Young's modulus and Poisson’s ratio, creep and relaxation;
  • Volume stability: thermal dilation associated with hydration heat; autogenous and drying shrinkage;
  • Fracture properties and cracking due to applied mechanical loads and/or restraint deformations.

For such purposes, Round-Robin Test (RRT) series will be conducted, based on a set of materials to be shared amongst all Action members within the first year of the Action, comprising a minimum of two concretes: a normal strength (NSC), a high performance (HPC) concrete. For complementarity, the corresponding mortars and cement pastes will be concurrently analysed, as well as associated eco-concrete mixes incorporating a selection of by-products and waste materials. Strong emphasis will be given to supporting the development and validation of new techniques for characterization of CBM properties from early ages, focusing on emerging techniques such as those based on piezoelectric elements and wave propagation, operational modal analysis, acoustic emission, and nanotechnology. The RRT will be discussed and launched during the first year of the Action, with a special session dedicated to its description and agreed strategy during the first workshop (Month 12). At all stages, additional members from other COST countries and even from non-COST countries will be invited (whenever relevant) to widen the representativeness of the study. The launch of the RRT program will provide definite information on several aspects such as: (i) the origin of the materials to be tested (which should be all the same during the entire Action); (ii) the transportation scheduling and pricing for each member; (iii) the mix proportions and reference properties of the CBM (according to preliminary tests using existing standards); (iv) the curing conditions to be studied (apart from 20ºC at full sealed conditions, other curing situations both in terms of temperature and humidity will be envisaged, in laboratories with such installed capacity) (iv) the mixing procedure; (v) the set of normalized testing that each laboratory needs to conduct in order to verify the compliance of each mix with the original mix; (vi) the website reserved area for this RRT programme and the way in which information will be managed (e.g. templates for uploading information). Even though virtual interactions will occur throughout the course of the entire Action, specific sessions will be held during all workshops/conferences planned for the Action for presentation and discussion of results, with possible re-routings of the programme and repetition of tests according to the main findings. Yearly reports will also be issued, documenting the progress of the programme. Once again, the importance of STSM’s is stressed in view of the possibility of exchanging knowledge on custom-built experimental methods and allow inter-laboratory testing of newly devised techniques. From a metrological standpoint, this will be a significant added value to the RRT programme and to the possible transfer of its main findings towards new draft regulations.