THE USE OF FOSSILS AND MINERAL SPECIFICITY IN FORENSIC CONCRETE PETROGRAPHY

Several species of marine microfossils found in crushed limestone coarse aggregates of Portland cement concretes have been used in solving several disputes and litigation cases concerning the producers of the concrete mix. The use of specific fossils unique to certain limestone deposits have proven worthy where the source of concrete aggregates is needed beyond doubt. Case studies in which mineral specificity has been used in providing comparative identification of physical evidence in civil court cases are discussed. Examples of where mineral and fossil evidence from crime scene investigations have demonstrated merit in civil as well as criminal forensic applications are described. Discussion of several case studies where fossil and mineral specificity were used in solving “ownership” of concrete supplied to construction projects was a major issue. Litigation cases are described where the concern was for determining who sabotaged living coral reefs by improperly dumping concrete rubble in protected marine sanctuaries. The physical evidence hinged on the petrography of concrete and respective sources.

Forensic petrography has also helped solve investigations concerning the loss of airfreight shipments from around the world. The shipped goods and items such as computers taken from cargo containers were intercepted and replaced with rocks or various materials such as concrete, aggregates, or fabricated items such as brick pavers or concrete masonry units (CMU). Several cases have been solved using index fossils and specific mineral types to identify likely locations where the goods were stolen. The aggregates used in these replacement items were identified as being from specific local sources using the fossils in the limestone aggregates and associated mineral species unique to that area. Mineral specificity and fossils provide a good means to identify the source of concretes that have short-term performance problems such as alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). In addition, the petrography of sands used in historical mortars for preservation of historical courthouses, US Post Offices and other federal buildings have proven helpful in identifying likely sources for the original masonry sands or native stones used on the building.