Quantifying alkali-silica reaction in Pennsylvania

As drivers, we take for granted the aggregates that makes up roads and bridges.

To the majority of drivers hustling along roads and bridges, the possible occurrence of alkali-silica reaction – or ASR, as it is commonly known in the industry – on the concrete below them means little, if anything at all.

ASR is the chemical reaction between the alkali in the cement, the silica in the aggregate and the presence of water. When ASR occurs in a concentrated concrete product, issues such as cracking, deformation and weakening of joints have been found, thus putting into question the structural integrity and lifespan of roads and bridges.

It was long thought that Pennsylvania’s aggregates were highly reactive and subject to substantial mitigation before they could be used to make concrete. Otherwise, the deterioration of a concrete structure was thought to be inevitable.

Producing more sustainable roads

In the interest of public safety, time and money, the Pennsylvania Department of Transportation (PennDOT) and members from the aggregate and concrete industry conducted a study to measure the reactive levels of the rocks, minerals and sand in the state. Through the study of Pennsylvania’s geology, 374 aggregate sources were tested using a year-long test method known as ASTM C1293. It was discovered that the state does not have a lot of highly reactive aggregates, and that they are safe to use in the creation of concrete pavements and bridges.

While this is excellent news for the industry as a whole, it sets PennDOT apart from its peers as the lead state in quantifying ASR. ASR testing and research have not only advanced, but they now show companies how they must design, as well as the level of mitigation needed, before starting a project. The long-term benefits of enhanced testing will continue to make a difference in the lives of millions.

Thanks to PennDOT’s study and continued dedication to being the lead state in quantifying ASR on thousands of miles of roads and bridges in the commonwealth, the safety of not just Pennsylvanians, but the nation’s drivers, is greatly improved.

By working together, the aggregate and concrete industry and PennDOT can focus on designing for strength and durability. This will help not only benefit Pennsylvania residents but the state’s overall infrastructure.

Susan Armstrong is with Central Builders Supply Co. and Mark Moyer is with New Enterprise Stone & Lime Co. Armstrong is the immediate past chair of the Pennsylvania Aggregates & Concrete Association’s (PACA) Concrete Technical Community while Moyer is the current chair of the PACA Concrete Technical Community.