Durability of concrete with supplementary cementitious materials

Maxime Ranger

Research output: Book/ReportPh.D. thesis

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Abstract

The concrete industry currently is currently in a major transition phase to lower its CO2 emissions. In this respect, using Supplementary Cementitious Materials (SCMs) is key to lower the amount of Portland cement in concrete. Traditional SCMs such as fly ash and blast furnace slag are industrial by-products which have been used for many years in concrete. However, the supply of these materials is expected to decline soon. This emphasises the need to find alternative SCMs and to adapt regulatory frameworks to allow their use in a safe and efficient way.

This PhD project intended to investigate the effect of SCMs on Alkali-Silica Reaction (ASR), one of the main issues that affect concrete durability. In particular, the main objective was to develop a generic procedure to qualify all types of SCMs with respect to ASR in the Danish concrete specifications. For this purpose, the experimental work was carried out on a selection of SCMs representing the diversity of sources.

The experiments focused on two main aspects. On the one hand, the influence of SCMs on the amount of alkalis in the pore solution was studied via cold water extraction (CWE). CWE is a simple method that can be performed with basic laboratory equipment, so it has the potential to be used at an industrial scale. On the other hand, several ASR expansion tests were carried out to evaluate the ability of SCMs to prevent the expansion induced by ASR. Field exposure cubes were cast to evaluate the validity of three accelerated laboratory tests: ASTM C1567, TI-B 51 and RILEM AAR-10.

The results showed a strong link between the SCM reactivity and their ability to reduce free alkalis in the pore solution. CWE allowed to determine the free alkali contribution from SCMs, which is a key value for calculating the alkali loading in concrete. The latter seemed to be linked with the ASR expansion via a threshold effect, i.e. no expansion occurred below a certain free alkali content around 2.4 kg/m3 Na2Oeq. This was only observed for AAR-10 and field cubes, which correlated well for all the mixes tested. Conversely, significant deviations occurred with ASTM C1567 and TI-B 51, which questions the suitability of these tests to assess the efficacy of SCMs.

A procedure was suggested to screen the suitability of SCMs with respect ASR. In addition, a proposal was formulated to update the Danish regulations regarding the qualification of SCMs.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages242
Publication statusPublished - 2023

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