How to Prevent ASR from Cracking and Deteriorating Concrete
How to Prevent ASR from Cracking and Deteriorating Concrete
Concrete can be found in almost any type of construction around the world. But how is it made?
During manufacturing, once in contact with water, concrete’s main ingredient, cement, binds to any aggregates present and goes through a number of complex chemical reactions. That eventually turns it into concrete, a material that is very durable and easy to work with. Despite this reliable durability, concrete can go through a number of internal processes that can lead to serious structural concerns. One of these is alkali-silica reaction (ASR), which can cause cracks in concrete and even put structures in danger of collapse over time.
ASR is usually related to the presence of silica in aggregates such as opal, chalcedony, cristobalite, tridymite, quartz and certain types of natural (volcanic) and artificial glass. It’s due to how highly they react to alkali. When these two components come into contact with each other inside concrete, they form silica gel, which absorbs any water present in the material. This causes the concrete to swell and consequently, expand, triggering cracks in the concrete and reducing its structural integrity. The entire process can take only a few years and can cause serious fractures that can expose the reinforcing rebar within the concrete to any nearby water and salts. That in turn can lead to corrosion and the acceleration of a concrete structure’s deterioration.
Due to the structural damage that can cause, building professionals all over have developed a number of strategies throughout the years to mitigate ASR. And a big part of that has been to look at the key elements that produce the reaction. As covered in this article by Kryton International Inc., there are three essential elements that cause ASR: alkalis, reactive aggregates and water. Efforts to prevent or mitigate these are almost always focused on measures to reduce or eliminate the first two elements. Using low-alkali cements; partially replacing them with pozzolins, such as fly ash and pulverized slag; and avoiding the use of reactive aggregates are all ways to avoid ASR. Nonetheless, it has been found that these methods only delay the problem instead of avoiding it completely.
Eliminating water from the equation has not often been considered a valid alternative, possibly because concrete is naturally porous and absorbs moisture. However, there are some ways to reduce or prevent excessive water penetration in concrete, increasing protection against ASR’s harmful expansive forces. One particularly appealing solution is to incorporate Krystol Internal Membrane™ (KIM®) into a concrete mix. As a hydrophilic crystalline admixture, it is used to create permanently waterproof concrete by reducing concrete permeability. It’s often considered a solution for replacing traditional surface-applied waterproofing membranes.
According to Kryton: “When added to concrete, KIM’s Krystol® technology chemically reacts with water and unhydrated cement particles to form insoluble needle-shaped crystals that fill capillary pores and micro-cracks in the concrete to block the pathways for water and waterborne contaminants. Any moisture introduced over the life span of the concrete will initiate crystallization, ensuring permanent waterproofing protection.”
In addition, the product reduces contractions and cracks, increasing the quality and longevity of concrete during plastic and curing stages, as well as attenuating the effect of expansion and contraction when concrete freezes and defrosts. It is also environmentally friendly, remains safe for potable water (certified to NSF/ANSI 61) and is non-toxic.
Learn more about this product in our catalog.
