Publication

The role of aluminium from supplementary cementitious materials in controlling alkali-silica reaction

Theodor Alexandre Emmanuele Chappex
2012
Theses

Abstract

Alkali silica reaction (ASR) is a long-term reaction between certain aggregates containing amorphous silicate phases and the alkalis from the cement paste. These silicates react with the alkalis present in the pore solution of the cement paste and form an expansive gel in the presence of water, resulting in the macroscopic expansion and cracking of concrete. Supplementary cementitious materials (SCM), replacing a part of the Portland cement (PC) in blended pastes, are known to reduce or even stop expansion due to ASR. Studies indicate that the main reason for this is the decrease in alkalinity of the pore solution of the cement paste, which in turn is attributed to the change in composition of the C-S-H, the main cement hydrate. However, knowledge on the effect of SCMs on ASR control is incomplete, especially the role of aluminium. The first part of this work focuses on the effect of aluminium and silicon incorporation in C-S-H, provided by SCMs, on the composition of the pore solution of blended pastes. It was found that, contrary to the common idea, the incorporation of aluminium in C-S-H does not increase its alkali fixation capacity, suggesting that the greater effectiveness of SCMs containing alumina is due to other reasons. In a second part, it is proposed that the additional aluminium acts directly on the reactive phases of the aggregates. Marine chemistry and geology theories about the dissolution mechanisms of amorphous silicates were applied to cementitious systems. Aluminium species, provided by certain SCMs and present in the pore solution, are incorporated in the silica surface and limit the dissolution of amorphous silica of the aggregates, limiting ASR. The effect of aluminium was shown through a study of reactive aggregates in simulated pore solutions. The mechanism was explained through a more fundamental study with pure amorphous silica plates put in simulated pore solutions. Finally, the impact of various alkali cations on ASR was studied to better understand the reactions inducing gel formation.

Official source

https://infoscience.epfl.ch/entities/publication/5eab1081-61af-47a4-b514-722677828300

Theodor Alexandre Emmanuele Chappex
2012
Theses

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/5eab1081-61af-47a4-b514-722677828300

Related concepts (23)

Alkali–silica reaction

The alkali–silica reaction (ASR), more commonly known as concrete cancer, is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (i.e., non-crystalline) silica found in many common aggregates, given sufficient moisture. This deleterious chemical reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium silicate (Na2SiO3, also noted Na2H2SiO4, or N-S-H (sodium silicate hydrate), depending on the adopted convention).

Silicon dioxide

Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and most abundant families of materials, existing as a compound of several minerals and as a synthetic product. Notable examples include fused quartz, fumed silica, silica gel, opal and aerogels. It is used in structural materials, microelectronics (as an electrical insulator), and as components in the food and pharmaceutical industries.

Cement

A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.

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