Subject matter

Alkali-activated concrete is considered as an environment-friendly construction material with a great potential for construction. In the last decade within concrete research, alkali-activated concrete is reported to be the ‘hot topic’. Many research projects are being carried out world-wide on aspects like reaction and chemistry of alkali-acted materials, mechanical properties and durability. RILEM has been active within the field of alkali-activated materials, by the organisation of RILEM Technical Committees (Committee TC- 224-AAM on Alkali-activated materials chaired by Prof. Jannie van Deventer, Committee TC-247-DTA on Durability testing of alkali-activated materials chaired by Prof. John Provis, Committee TC-283-CAM on Chloride transport in alkali-activated materials chaired by Prof. Arnaud Castel).

The RILEM Committee TC 247-DTA on durability testing of alkali-activated materials is finalising its work. Within this Technical Committee, the durability testing methods of alkali-activated concrete are focused on. A few papers on this subject are being prepared for publication in journal of Materials and Structure. Following up the TC-DTA, committee TC-CAM is focused on the chloride transport in alkali-activated materials, activity starting from 2018. Although the general materials behaviour was reported in TC- 224-AAM on Alkali-activated materials, the durability testing methods are reported in TC 247-DTA and chloride transport will be reported by TC-CAM, some important issues concerning alkali-activated concrete will still remain. One main topic in this respect is related to the mechanical properties of alkali-activated concrete.

It is at this moment not fully clear whether existing design codes for structural concrete can be fully applied in case of alkali activated concrete. As the chemical composition of alkali-activated concrete differs from that of conventional concrete, and also differs substantially from one mixture to another because of different precursors and alkaline solutions used, the bond behavior, the strength gain and time dependent properties in conventional concrete and alkali-activated concrete are not the same. Although short term behaviour (28 days) might be similar, this might not be the case for the long-term behaviour and simply applying existing codes for conventional concrete to design alkali-activated concrete structures could be problematic. As a consequence, can we still apply the traditional constitutive law as we do for traditional concrete? These are the main matters the TC will be focused on.

Another key point of focus will be the creep and shrinkage of alkali-activated concrete. When dealing with shrinkage, it is sometimes mentioned that alkali-activated concrete made of blast furnace slag as precursor is showing an increased risk on early age cracking due to a possibly increased shrinkage. However, it is also clear that early age mechanical properties of alkali-activated concrete might be developing much faster than for conventional concrete. What is the net effect on early age cracking risk due to shrinkage effects? How do we prevent early age cracking in restrained alkali-activated concrete? Can we still apply traditional creep and shrinkage laws, or do we have to include new parameters? It would be very interesting to collect the available data in this area, and with some detailed analysis and practical conclusions.

The proposed new RILEM Technical Committee on Mechanical properties of alkali-activated concrete will have to gather the available information related to mechanical properties and mechanical behaviour of alkali-activated concrete. Due attention should be given to the fact that the composition of alkali-activated concrete might be significantly different in different regions, and the mechanical properties of alkali-activated concrete are affected by the curing condition.

All relevant mechanical properties of alkali-activated concrete will be considered, like compressive strength and softening behaviour, tensile strength, flexural strength, elastic modulus, bond behaviour, shear strength, tension stiffening, creep, drying shrinkage, autogeneous shrinkage, restrained-shrinkage and early age cracking.

Terms of reference

The committee will comprise a selected membership of those organisations and research centres world-wide that have been active in searching for a basic understanding and modelling of mechanical properties of alkali-activated concrete. It will include universities, research institutes, material suppliers, contractors, building owners, public agencies, etc... The members will also be recruited from participants in international symposiums and workshops on the topic of alkali-activated concrete, and from earlier RILEM TC’s dealing with alkali-activated concrete.

The state-of-the-art-report on Mechanical properties of alkali-activated concrete will be based on the following input:

• Previous state-of-the-art reports related to alkali-activated concrete (like ‘Alkali-activated materials AAM’ and ‘Durability testing methods of alkali-activated materials’)
• The proceedings of international symposiums on alkali-activated materials
• Collection of data from relevant work, as published in international scientific journals
• The committee will represent a majority of ongoing research projects in this field. The committee will gather, as far as possible, the results of relevant parts of these projects

Estimated duration of the work is 4 years. The new committee could start its activities in the begin of 2020.

Detailed working programme

The committee will meet twice a year. The main activities of the TC will be scheduled as follows:

Year 1:

• Establishing of consensus on strategy and limitation of work
• Collection and discussion of published data
• Identification of on-going projects regarding mechanical properties of alkali-activated concrete
• Defining a table of contents of the STAR on mechanical properties of alkali-activated concrete, and identifying authors

Year 2 - 3:

• First draft of the different chapters of STAR, by different authors
• Discussion of the first draft
• Planning of symposium

Year 4:

• Second draft of the STAR
• Final version of STAR, in ready to print format
• Symposium