Subject matter

The introduction of Superabsorbent Polymers (SAP) as a new component for the production of concrete materials makes available a number of new possibilities with respect to water control and, as a result, to the control over the rheological properties of fresh concrete, in addition to purposeful water absorption and/or delayed water release in either fresh or hardened concrete. As examples of this, inducing of an abrupt change in rheological behavior during shotcreting and the internal curing(IC) of High-Performance Concrete (HPC) might be given here, respectively, but the potential for innovation is far wider, e.g.for creating in concrete of appropriately size-designed pore systems which could improve its durability, especially in terms of freeze-thaw resistance. Pore systems built up as a result of SAP addition seem to remain stable regardless of the consistency ofthe concrete, the addition of superplasticizer, or the method of placement and compacting. Further applications have been proposed, some as vague ideas as well as some supported by preliminary investigations. An example of such suggestions is the utilization of SAP as micro-reservoirs for chemical substances which would be released under specific conditions such as temperature, changes of the chemical composition of pore solutions, passage of time, etc., to improve the durability and overall performance of concrete. Also, the use of SAP as a multifunctional additive has been recently demonstrated.

The increasing interest in the use of SAP as a concrete additive and the need for intensive scientific exchange among research groups led in 2007 to the initiation of the RILEM Technical Committee 225-SAP “Application of Superabsorbent Polymers in Concrete Construction”. The committee’s objective was to coordinate research efforts and compile the results of studies with respect to the effects of SAP addition on the properties of concrete in its fresh and hardened states. The main product of the committee’s work was a State-of-the-Art Report which summarized the available information and knowledge in the area and provided as well a solid basis and a good reference for further research. Also, it served as starting point for further activity of RILEM TC 225-SAP, including two round-robin tests. The first round-robin test was performed by 13 international research groups. All found a considerable decrease in autogenous shrinkage of HPC attributable to internal curing with SAP. This demonstrates that internal curing using SAP is a robust approach, working independently of some variations in the concretes’raw materials, production process, or measuring techniques. Furthermore, effects of internal curing on other properties ofconcrete in its fresh and hardened states were investigated. The second round-robin test run at 14 international laboratories has focused on the durability aspects, specifically on the freeze-thaw resistance with and without de-icing salt. The results of the tests are being evaluated currently and an article for Materials and Structures is in preparation. Furthermore, RILEM TC 225-SAP organised an International RILEM Conference on “Use of Superabsorbent Polymers and Other New Additives in Concrete”, Lyngby, Denmark, 15-18 August 2010. Another conference on this topic is being organised by the TC in Dresden,Germany, 14-17 September 2014. The proceedings of these conferences provide additional references to that constituted by the State-of-the-Art Report.

Terms of reference

Researchers and practitioners in different countries around the world are presently investigating possibilities and limits of using SAP for solving various problems encountered by practitioners in the field. There are also first promising pilot applications which encourage companies and scientists to move forward the use of this new additives in concrete construction.However, the step from the research lab into the practice of construction requires considerable efforts. At the first place, the practitioners need clear recommendations in which cases and how SAP can or should be used, how to consider addition of SAPand possibly IC water in concrete mix design, how to estimate the effect of SAP addition on various properties of concrete infresh and hardened state.

The main objectives of the committee are (1) to collect and analyze information on applications of SAP in concrete, (2) toinitiate necessary research activities for clarifying open questions related with practical use of SAP, and (3) to develop practical recommendations for utilizing SAP in concrete construction. These recommendations will mainly address technological procedures (e.g. storing of SAP, mixing procedure, pumping, spraying, curing), concrete mix design (e.g.optimization of the type, dosage and properties of SAP, the amount of additional water) and testing methods for specific material properties which may be affected by the use of SAP, as well as the specification of SAP for practical applications. In doing so, numerous interacting phenomena such as shrinkage, creep, thermal effects, cracking, and interface quality should beinvestigated and taken into account.

In summary, the aim is to produce recommendations on the use of SAP as a practical guide to assist material technologists, design engineers and researchers. The conclusions of the TC are expected within 4 to 5 working years.

The members to be recruited for the TC will be recognized experts in the domain. In order to take into account the different practices and standards in Europe, Japan and North America as well as their respective spheres of influence, including ISO, EN and ASTM standards, the TC will include representatives from the aforementioned world regions.

Since the main goal of the new TC is the elaboration/generation of recommendations for engineers and practitioners, their participation is necessary. Actions are expected in the different geographical areas covered by the members of the TC to initiate local (national or multi-national) groups involving practitioners. These groups will work complimentarily to the TC.The close information exchange between the TC and the practitioners groups will enable recognizing the most relevant and current practical problems on one hand, and implementation of the recent findings and recommendations of the TC in practice on the other hand.

Detailed working programme

The work of the TC will focus on bringing together the expertise and knowledge of all participating members. The first synthesis of expertise will be done at the inaugural TC meeting.

On this base, the TC will simultaneously address the following items:

- Recommendations for testing of SAP (methods, characteristic parameters, description of properties, etc.)

- Recommendations for material design and manufacturing of concrete with addition of SAP for various purposes

- Recommendation on considering effects of SAP addition on workability (incl. pumping and spraying), setting time and early age properties of concrete

- Round-robin test for the effect of SAP addition on plastic shrinkage and recommendations on curing of SAP concrete in early age

- Recommendations on considering effects of SAP on concrete properties in the hardened state.

Activities of the committee will include organizing an international RILEM conference on Application of Super Absorbent Polymers in Concrete Construction.