Alkali‐silica reaction (ASR) – Performancetesting

Abstract

Whether or not concrete prism tests developed for assessment of alkali‐silica reactivity of aggregates is suitable for general ASR performance testing of concrete has been evaluated. The work has been part of the Norwegian COIN program (2007‐2014), and has been performed in co‐operation with the "performance testing" task group of RILEM TC 219‐ACS. Thus, the RILEM aggregate concrete prism tests (CPTs) form the basis for the laboratory program.

As a foundation for the experimental work, an introductory study focused on the following:

• Summary and assessment of the main findings in the EU "PARTNER" project (2002–2006), in which the author participated actively.

• Summary and discussion of the experience gained from more than 15 years of performance testing in Norway.

• A comprehensive literature review, with the main objective to assess how various parameters might influence the laboratory/field correlation with respect to ASR performance testing.

Based on the introductory work, the experimental part of the study focused on the effect of specimen "pre‐treatment", "ASR exposure conditions" and prism size on:

• Porosity and internal moisture state of the concrete prisms.

• Concrete transport properties (with respect to mobility of water and ions).

• Alkali leaching (rate and amount) from the concrete prisms during the ASR exposure.

• Concrete prism expansion (rate and ultimate expansion).

Additionally, the effect of water‐to‐cementitious‐materials ratio (w/cm) and type of binder have been assessed.

The results clearly show that parameters of importance for the development of ASR are significantly influenced by the specimen "pre‐treatment", "ASR exposure conditions" and prism cross‐section. Most test conditions included are representative test procedures used in various "commercial" CPTs. The extent of the impact depends on the concrete quality, i.e. w/cm ratio and cement type. Consequently, the conclusion from a concrete performance test will differ depending on the test procedure used.

Generally, a high fraction of the in‐mixed alkalis was leached out of the concrete prisms during the ASR exposure. In fact, the rate of alkali leaching during the first weeks of exposure is the parameter found to have the highest impact on the development of ASR expansion. When exposed to 60°C, it completely controls the prisms expansion. However, a modified test procedure was developed (cotton cloth with added alkalis) in the study which might be a promising tool to mitigate alkali leaching during accelerated laboratory testing.

For less permeable concretes, with a high degree of self‐desiccation, the lower internal RH for the 38°C test series contributes together with the lower rate of diffusion to reduce the rate and extent of ASR.

The main part of the thesis is the papers enclosed. However, the summary gives an overview of the work and the main findings. Furthermore, some supplementary results are included together with an overview of a follow‐up project initiated based on the results of the PhD study. The thesis also gives some general recommendations for performance testing.