Foundation, Concrete and Earthquake Engineering

How to Solve Alkali-Silica Reaction in Concrete Having Glass Sand Aggregates?

Now-a-days engineers are concerned with number of chemical reactions that produce effect on concrete. Of these most common is alkali silica reaction which defines chemical reaction between reactive silica in aggregates and alkalis present in cement. Here we would like to include why is this reaction harmful for understanding our present topic about application of glass as aggregate?

Under this reaction a gel of alkali-silicate product is formed which can take place in following locations:

Scanning under electron microscope of concrete section: Cracks due to ASR
a. Within weak planes

b. Pores in aggregates

c. Over the surface of aggregates.

The gel have swelling property and when found water, results an increase in volume thus producing expansion resulting cracks and we have learnt how much deterioration can take place under cracks in concrete.

So our topic was about replacing natural aggregates with glass. Glasses are inspecting for applying in concrete as replacement of fine aggregates, coarse aggregates and as cement replacement for many years. But most of the experiments produced unsatisfactory yields due to alkali-silica reaction as discussed above.

Now some researchers are introducing some suppressors of alkali silica reaction (ASR) to mitigate such problem and achieved some satisfactory results. An interesting fact is that remedial measure lies in glass itself i.e. if we ground glass to certain fineness it shows pozzolanic characteristics.

Glass are inspected for both coarse aggregates and fine aggregates. In case of coarse aggregates, workability of concrete is impaired badly; we have discussed this in our previous post. This is also worth mentioning that glass means waste glass as a recycled product.

Cracks in concrete pavement due to alkali-silica reaction

Matakaolin for alkali-silica reaction suppressor for glass concrete
Dear reader while we are discussing about solving deleterious expansion of alkali silica reaction, we have to know ASR suppressor that can be use to control such reaction; here we are listing some of these but as a general ASR suppression not considering ASR related to Glass application:

a. Fine siliceous materials

b. Application of pozzolana

c. Silica fume

d. Ground granulated blast furnace slag (GGBS)

e. Lithium salts like lithium nitrate

f. Matakaolin

Of these finely divided siliceous material, replacing cement with GGBS, fly ash, silica fume or by adding steel fibres and lithium carbonate and lithium chloride are examined. In these experiments the constituents percentage are altered to have best results. The glass aggregate that produce ASR also produce ASR suppression when ground in fine size enough to behave like pozzolana.

When glass sand (as fine aggregate) has size within (1.18 - 2.36) mm, exhibits severe alkali-silica reaction results maximum ASR expansion consequently. Here we like to include that the reaction is occurred when alkali-silica of reactive from come into contact. Now if we reduce silica content in concrete mix ASR can be controlled, at the same time if we control alkali sources ASR can also be reduced.
Crushing glass for producing fine aggregate for concrete
Glass aggregate that derived from silica-soda-lime sources produce ASR reaction from both sources i.e.

-Reactive silica

- A potential source of alkali source

Glass as a very finely divided from can also be used as cement replacement, but suitable when substitution fraction is low. There have also interesting behavior of glass that performance of glass also depends on its color, say flint and green color glass show better performance than amber glass.

Most of glass waste collected from United States are of soda-lime type; as discussed above these glasses are more susceptible to ASR reaction. In case of such application fly ash is applied to replace cement together with replacement of natural sand with crushed glass. Sometimes full replacement of sand is also tried.

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