Test Methods for Alkali-Aggregate Reactions in Norwegian Aggregates: Petrographic Examination and the South African NBRI Mortar-Bar Test

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Title: Test Methods for Alkali-Aggregate Reactions in Norwegian Aggregates: Petrographic Examination and the South African NBRI Mortar-Bar Test

Author(s): B. J. Wigum and J. Lingard

Publication: Special Publication

Volume: 145

Issue:

Appears on pages(s): 781-796

Keywords: accelerated tests; aggregates; alkali-aggregate reactions; concretes; expansion; mortar bar test; petrography; rocks; Materials Research

Date: 5/1/1994

Abstract:
Petrographic examination and the South African mortar bar test have been performed at SINTEF--Structures and Concrete during the last 2 to 3 years to evaluate the reactivity of Norwegian aggregates to be used in concrete structures. Paper presents the relationships between these two test methods. The purpose of the petrographic examination is to identify, quantify, and group different rock types in an aggregate. These groups are: reactive (with known reactive field performance), potentially reactive, and innocuous aggregates. In Norway, further testing by the mortar bar test is recommended when petrographic examination indicates 20 percent of reactive or potentially reactive rock types in the aggregates. The mortar bar expansion after 14 days of exposure is used for the evaluation of potential expansivity of the aggregates. One main conclusion from the investigation is that mortar bar expansion increases to an upper level with increasing content of reactive rocks in the aggregates. Beyond a "marginal" amount of reactive rocks in aggregates, the mortar bar expansion increases no further. A significant difference in mortar bar expansion between different reactive rock types has not been found. The established limit of 20 percent of reactive rocks in aggregates appears, in most cases, sufficient for classifying aggregates as innocuous; however, no verification of the limit has been made.