Field Monitoring of Alkali-Silica Reaction
Dr. Ian Robertson secured a long duration (2014-2019) project from the Hawaii Department of Transportation (about $250,000) to compare lab and field results.
Alkali Silica Reaction (ASR) occurs in concrete when the alkali hydroxides (Na, K and OH) from the cement react with unstable silica, SiO2, in some types of aggregate. The resulting gel will expand when it absorbs water, potentially leading to cracking and overall expansion of the concrete. Concrete aggregates available in Hawaii have not demonstrated a history of ASR, however, results of accelerated laboratory tests using ASTM 1260 indicated a potential for ASR with some aggregates.
In order to assess the accuracy of the laboratory test results, a long-term field study of the potential for ASR in concretes made with Hawaiian aggregates was initiated in 2011. Forty concrete specimens were constructed of various concrete mixtures using aggregates from all Hawaiian aggregate sources, and some US mainland aggregates known to exhibit ASR expansion. The specimens are located in an open field site in Manoa valley on Oahu, exposed to relatively high humidity and frequent rainfall. The specimen dimensions are monitored on a regular basis to determine whether any expansion is occurring. A weather station at the site records the ambient conditions on a continual basis.
At the same time, a series of laboratory tests is being performed on aggregates from various suppliers around the Hawaiian Islands. The results of the laboratory tests will be compared with the long-term results of the field specimen observations to determine which of the laboratory tests is most reliable.
High Performance Geopolymer and Portland Cement Concrete Using Hawaiian Fly Ash
Dr. Lin Shen obtained a three year (2015-2018) project from the Hawaii Department of Transportation (about $200,000) to to develop high performance geopolymer concrete using locally generated Fly Ash.
Fly Ash, also called coal ash, is an industrial byproduct of coal-burning power plants. In the US, about 43% of Fly Ash is recycled to supplement Portland cement in concrete production. The other 57% unused ash, or 50M tons per year, is landfilled or put in storage ponds. Geopolymer is a type of aluminosilicate materials such as alkali-activated Fly Ash and slag. This new generation of geopolymer concrete looks like traditional concrete, and can be placed at ambient temperature with controlled setting time.
The ultimate goal is to formulate standard equipment mixed, single component activated, high performance geopolymer concrete with flexible working times. Using geopolymer concrete with Hawaii-sourced Fly Ash will generate more options to cut cost, improve material performance, benefit the local economy, support the future success of the State’s recycling program, reduce the waste stream going to landfills, and support Federal mandates on sustainability.
