Title:
Laboratory Evaluation of Alkali-Silica Reaction in Concrete
from Saunders Generating Station
Author(s):
P. E. Grattan-Bellew
Publication:
Materials Journal
Volume:
92
Issue:
2
Appears on pages(s):
126-134
Keywords:
alkali content; alkali-silica reactions; concretes; dams; expan-sion;
mortars (material); prisms.
DOI:
10.14359/9763
Date:
3/1/1995
Abstract:
Concrete cracking, characteristic of alkali-aggregate reaction, was observed in Saunders Generating Station. This investigation was designed to confirm that alkali-aggregate reaction was the primary cause of the observed concrete deterioration, evaluate the extent of concrete deterioration, determine the remaining expansion potential of the concrete, and decide whether suflcient alkali remained in the concrete to sustain the reaction. The extent of the concrete deterioration was investigated by comparing the damage rating index (DI) of cores taken from various parts of the structure. The damage rating index is determined by measuring the number of defects observed on polished cores, under a stereobinocular microscope. Silica gel, a characteristic alkali-silica reaction product, was observed in concrete from various parts of the generating station, conjirming that alkali-silica reaction had occurred. The expansion potential of the concrete was evaluated by monitoring the expansion of cores stored under various accelerating conditions. The expansivity of the aggregate in the concrete was conJirmed by extracting aggregate from cores and testing it in the Canadian Standard concrete prism test. The aggregate was found to be marginally reactive. The concrete cores showed almost the same expansion as the prisms made with the aggregate reclaimed from concrete cores from the structure. The measured alkali contents of the concrete in cores were found to be higher than the original values; this is thought to be due to alkali derived from the aggregates. Experiments showed that a considerable amount of the alkalies in the aggregate could be extracted by cation exchange in pastes of calcium hydroxide. This supports the hypothesis that excess alkalies found in the concrete are derived from impure limestone aggregates.