2000•Roads & bridges/Roads & bridges (Des Plaines, Ill. Online)Requires access
TRY NOT TO FALL THROUGH THE CRACKS
Gary E. Crawford
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Abstract
A new draft guide specification titled Portland Cement Concrete (PCC) Resistant to Excessive Expansion Caused by Alkali-Silica has been prepared by the alklali-silica reactivity (ASR) Lead States team to assist highway agencies and contractors in protecting new PCC roads and bridges from the pervasive effects of ASR. ASR is the result of silica in some aggregates and alkalis in cement combining with water to form a gel-like substance in the aggregate. As the gel expands, it causes the aggregate and then the concrete to crack. The aggregate's composition is often a prime indicator of its susceptibility to ASR. The new guide specification contains measures that states can take to evaluate aggregate for ASR potential. The specification also offers some cement-related strategies for fighting ASR. These include using low-alkali cement and incorporating fly ash or lithium in the mix.