efflorescence

A Destructive Marriage: All You Need to Know About ASR

By G. Terry Harris Sr., FACI

Figure 1. Severe ASR-induced cracking viewed on the end face of a 20-year-old reinforced (portland cement only) precast concrete bridge beam. The reactive aggregate component was a river gravel containing a reactive chertii (flint) and quartzite component. Photo by Dr. Ted Sibbick, W. R. Grace & Co., www.grace.comBefore addressing alkali-silica reaction (ASR) in concrete, let’s start with what you already know. Concrete is essentially a mixture of two components: aggregates (stone, gravel and sand) and cement paste (water, cementitious materials, air and admixtures). The paste contains interconnected microscopic pores through which water can migrate. This pore water in concrete is a highly alkaline solution.

Alkali metal hydroxides in the pore solution chemically react with certain aggregates that contain silica. It is easier for these alkali metal hydroxides to combine with silica (quartz), which is in a more disordered, or reactive, form.

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Uninvited Mystery Guest: Efflorescence

By understanding the contributing factors, efflorescence can be minimized.

By Sue McCraven

Efflorescence as a chemical phenomenon presents its bright side in many venues. At night, the eerie greenish efflorescent glow of ocean  phytoplankton is almost magical. In another realm, botanical efflorescence thrills avid gardeners as blossoms reach their peak of floral beauty. Intellectually, efflorescence can mean the zenith of artistic or mathematical genius. In our natural world, the surprising bloom of efflorescence is a welcome event.

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