Subject matter

The proposed TC will address key questions related to the rate and mechanisms of chloride transport in alkali-activated binders and concretes, with a view toward drafting Recommendations for the appropriate selection and application of testing methods. This work will build from the initial work of TC 224-AAM in scoping and defining the character and durability of alkali-activated materials, and TC 247-DTA which has conducted a round-robin analysis of durability test methods developed for Portland cement-based concretes, aiming to assess their suitability to be used for alkali-activated concretes. From this work, it has been identified that there is a need to understand in more detail the factors which control the movement of chloride (driven either by concentration gradients or by electrical potential gradients) into alkali-activated concretes. This is essential if we are to appropriately link behaviour under testing conditions with performance under actual service conditions. Moreover, results from the round-robin testing program showed that existing testing protocols for Portland cement-based concrete are not suitable for alkali-activated concrete.

Importantly, the proposed TC will benefit of the outcomes of the Cooperative Research Centres for Low Carbon Living (CRC-LCL) project. The CRC-LCL (grant number RP1020) was funded from 2014 to 2017 by the Cooperative Research Centres program, an Australian Government initiative. The proposed TC chair, A/Professor Arnaud Castel, was one of the Project Leaders of RP1020 in charge of the durability. The main goal was to reduce barriers for commercial adaptation of alkali-activated concrete, major barriers being the lack of guidance, track record and exclusion from current standards. Performance-based specifications for alkali-activated concrete were developed. A handbook will be published in 2018 through Standards Australia. The handbook is currently being reviewed by industry partners. The most important standardised tests for chloride diffusion (ASTM C1556, ASTM C1202, NT BUILD 492) have been modified and performance-based requirements recalibrated to be used to assess alkali-activated concrete performance in chloride environments. However, this project involved a large but still limited number of concrete mix designs using almost exclusively Australian fly ash, GGBS and aggregates. The proposed TC will assess further the accuracy and reproducibility of the new testing protocols via a limited programme of new laboratory test work using materials sourced not only from Australian suppliers but from all around the world.

Additionally, the TC will also aim to compare the results to data obtained from analysis of samples placed in the field under service conditions, both during the test programme and also historically.

Another key point of focus will be the connection between chloride transport and other material characteristics which can more rapidly or inexpensively be measured: parameters such as porosity (determined through various means) or other microstructural characteristics, chloride binding through chemical and/or physical interactions with the paste (which can be measured for crushed paste samples), and basic mix design parameters. Any possible correlations with compressive strength will also be investigated; although it is beginning to be better understood in the scientific community that strength and durability characteristics are largely decoupled in alkali-activated concretes, strength remains a core aspect of almost all performance-based specification pathways and so cannot be neglected here.

Terms of reference

We plan that the work of the TC will be completed in a 5-year period. The TC will aim to meet in full twice per year for full and open discussion of outcomes and objectives, with the possibility of additional working group meetings (either in person or via teleconferencing) more regularly than this. The work plan is detailed under (4) below. We will conduct some laboratory research, using samples of designed chemistry and microstructure wherever possible. Many of the TC participants already hold stocks of single-source precursor materials for synthesis of alkali-activated binders obtained through the work of TC 247-DTA, and this will provide a starting point for some of the mix designs to be investigated. However, the key focus will be on each laboratory testing and understanding samples of chemistry and microstructure that are relevant to their own local precursors and conditions, with selective interchange of samples rather than a full round-robin test. Parameters measured in each participating lab for their own materials will be used to generate databases from which correlations and relationships can be drawn/inferred, and used as well to assess and improve the new testing protocols from the CRC-LCL.

It is expected that the TC will involve participants from Australasia, Asia, Eastern and Western Europe, and North and South America. Researchers with expertise in standards development for Portland-based cement systems (not specifically from a background in alkali-activation) will be invited to participate, so the TC will be able to utilise their skills and understanding in application to this newer class of materials. Research and development in the area of alkali-activated materials is active in academia, government laboratories and commercial environments worldwide, and it is expected that the TC will draw its membership from across this range of backgrounds.

Detailed working programme

The activities of the TC will be scheduled as follows:

Year 1 – Initiate collaborative networks, discuss new testing protocols from CRC-LCL and select additional testing methods to form the basis of further analysis based on outcomes from TC 247-DTA and CRC-LCL, and with reference to the applicable testing methods that are likely to be (or have been) incorporated into performance-based specifications in in key jurisdictions. Identify alkali-activated concrete samples that have been exposed to chloride under natural conditions in service, and negotiate with asset owners to gain access for sampling and analysis. Identify key results and ongoing studies in participating groups that can be dove-tailed to provide information of value.

Years 2-3 – Draw together results from testing programmes ongoing in different laboratories regarding the within-laboratory (and, where possible using identical samples, inter-laboratory) reproducibility of the selected test methods. Compare and contrast results obtained, for matching samples, from diffusion and migration test methods, to define whether this relationship follows established understanding which has been developed for Portland cement-based binders.

Year 4 – Correlate lab test results with analysis of field samples. Identify and select the microstructural and other material characteristics (strength, porosity, chloride binding characteristics, etc.) that are influential in controlling chloride ingress as measured by diffusion and migration tests, and in the field. Open symposium to be held either in Year 3 or early in Year 4, for participants to share and discuss preliminary results and to select targets for the remainder of the TC lifespan. Prepare and release document(s) outlining initial recommendations based on work in Years 1-3, for publication in Materials & Structures if appropriate.

Year 5 – Finalise results of all testing, compile all data, complete analysis and prepare final TC reports. Develop and release final recommendations document, specifying performance-based testing protocols suitable for the analysis of chloride transport across a wide range of alkali activated material formulations, correlating chloride transport rates and mechanisms with other measurable material parameters in a performance-based formulation of the key questions. Discussions will also be held with regard to planning for the establishment of a future TC to build from the work of the current TC if appropriate.