Subject matter

• Active Control of Concrete Properties is a recently identified subfield within concrete technology. A first (p)review paper was published in 2018 in Materials and Structures [https://link.springer.com/article/10.1617/s11527-018-1256-
  2?utm_source=CitationAlert&utm_medium=email&utm_campaign=CitationAlert_%20%20SPRINGER]. Concrete properties to a large extent depend on mix design and processing, leaving only limited options to actively modify concrete properties after mixing or during casting. The new concept of Active Control of concrete properties is based on the application of external signals to trigger an intended response in the material. Some current practices in concrete industry could be considered as active control, e.g. mechanical vibration, steam curing, cooling of mass concrete… More advanced active control mechanisms can be inspired on methodologies in other fields, e.g. based on hydrogels and other functional polymers. A specific approach recently studied in more detail focuses on active rheology control [https://www.taylorfrancis.com/books/oa-edit/10.1201/9781003289463/active-rheology-control-cementitious-materials-geert-de-schutter-karel-lesage]. Active rheology control of cementitious materials can be based on magneto-responsive mineral particles, and/or triggerable functional polymers. However, several challenges remain, like the stability and functioning of the responsive material in a cementitious environment, the applicability of the control signal in a cementitious material, and the cost, logistics and safety of a control system on a construction site or in precast industry. Finding solutions to these challenges will lead to marvelous opportunities in general, and for concrete 3D printing more particularly.
• The main purpose of this new TC is to create a State-of-the-art report on Active Control of Properties of Cementitious Materials, not only focussing on rheology but also on other properties in fresh state and during hardening. The committee work will not focus on active control in hardened state, but major hardened material characteristics will be referred to as potentially influenced by active control in fresh and hardening state. The following topics are intended to be included:
• General introduction, including discussion on the potential use of different kinds of trigger signals (magnetic, electric, redox, UV, temperature, light, mechanical…) in combination with different kinds of responsive components (nanoparticles, macroparticles, polymers…)
• Short overview of traditional methodologies to actively modify concrete properties
  
  • In fresh state: e.g. vibration as active control to achieve compaction, shear-induced behaviour…
  • Very early age: e.g. stiffening control by microwave, by electric current (Joule effect) …
  • During hardening: e.g. moist and heat curing, cooling …
  •  …
• Active control based on responsive particles
  • Magneto-responsive particles
    • General principles and mechanisms
    • Magnetic nanoparticles for rheology and stiffening control
    • Steel fibres for control of orientation, mechanical properties
  • Non-magnetic particles, e.g. thermos-responsive (Shape memory alloys, Phase change materials), Moisture-responsive particles, Electro-responsive particles
  •  …
• Active control based on responsive polymers
  • General principles and mechanisms
  • Responsive admixtures for rheology control
  • Responsive admixtures for internal curing
  •  …
• Case studies and potential applications of innovate active control techniques
  • Active control during pumping
  • Active control during formwork casting, including formwork leaking
  • Active control during 3D printing
  • Active control at early age (setting)
  • Active control during curing
  • ...
• Potential benefits of active control for concrete practice, remaining challenges, and recommendations to industry, including aspects of raw materials (production, storage, transport, quality control…)
• Summary and overview

While pumping, active rheology control could help reducing the pumping pressures for a given discharge rate, by controlling the bulk rheology and/or the properties of the lubrication layer. In case of 3D concrete printing, active stiffening control could help improving the buildability, turning the material from more flowable (pumpable) to more stiff while passing through the nozzle. RILEM TC ACP will study the control options, without entirely reviewing pumping and 3D concrete printing (as this is the topic of RILEM TCs working in parallel).

Terms of reference

• The TC is anticipated to start at the RILEM Annual Week in 2023 and is intended to take three to four years.
• Membership: The number of groups working on active control features applied to cementitious materials is growing fast. A key group initiating the field of ‘Active Control’ is Ghent University. They initially mainly focussed on rheology and stiffening control, but more recently also started studying other control applications. This work was partly inspired by preliminary studies by Nair and Ferron. Other groups have recently also started work regarding active control of cementitious materials, including Sobolev, Sanjayan, Aggelis…. Potential members are thus located worldwide. The main composition of the group will be academic, but efforts will be conducted to include potential industries such as polymer producers, pump producers, material suppliers, contractors and companies producing testing equipment.
• The target of the TC is to perform bibliographical research. No new research will be initiated within the committee itself, although joint research could result from the TC activities in a later stage.
• A document with recommendations or best practices can also be envisioned, depending on the progress rate of the TC.
• As ‘Active Control’ is a rather new field with Concrete Technology, the number of available publications is currently not very extensive. Nevertheless, several groups have initiated activities during the last years, resulting in a sufficient number of publications to motivate committee work. One of the objectives of the committee is also to clearly define and describe basic methodologies and vocabulary, so that the subfield has a sound basis for further actions, reports and publications.

Detailed working programme

The main goal of the committee is the STAR report, for which a first draft is anticipated to be ready in 2026. Based on the STAR, the recommendations could be created in 2026 or 2027.
The publication of the STAR report could coincide with the RILEM convention to be organized in Ghent in March 2026, on the occasion of the 100th anniversary of the Magnel-Vandepitte Laboratory