AFRL cooperative agreement to research insulated concrete blast response Published Sept. 12, 2007 By Mindy Cooper AFRL Materials and Manufacturing Directorate TYNDALL AIR FORCE BASE, Fla. -- The Air Force Research Laboratory Materials and Manufacturing Directorate Airbase Technologies Division entered into a Cooperative Research and Development Agreement to research insulated concrete products to see how they respond to explosive blasts. Under this CRADA, the Portland Cement Association will provide AFRL with insulated concrete products to investigate material behavior and structural response to blast pressure loads. "This research will provide valuable information concerning each product's ability to withstand explosive blasts, and will help accurately predict behavior for threats often included in the design criteria for government facilities," program manager Robert Dinan said. "This CRADA is unique because the partner is an association that has the membership to provide ML (Materials and Manufacturing Directorate) with materials from several different trade associations and a wide range of product designs." "It is important that government facilities provide safe building structures for their personnel to work in. In order to do this, it is important that these building be manufactured with materials that provide a significant level of blast resistance," Dinan explained. "Some insulated concrete products have been excluded as construction options for government projects because they lack the required research data to demonstrate performance under blast generated loads." The Air Force Civil Engineering Support Agency approached the experts at ML's Force Protection Branch at Tyndall Air Force Base, Florida, with the idea of having ML research insulated concrete products in order to gauge their blast resistance. ML then entered into a CRADA with the Portland Cement Association. The association agreed to provide ML with different types of insulated concrete products. ML agreed to conduct the research and record the results and provide that data to the association and AFCESA. "As ML began Phase I of the agreement, we started investigating 13 mature products that are already widely used in the commercial market," Dinan said. Those product included two pre-cast, pre-stressed sandwich panel products, then four concrete masonry products, then two tilt-up products and lastly, five insulated, stay-in-place concrete forms. The engineers at AFRL constructed a three-story reaction structure to conduct full-scale explosive experiments to validate the engineering models developed to predict blast response for each insulated concrete product. Once validated the models are used to develop engineering tools like range-to-effect charts that can be used to determine if a product can provide protection for a specified blast threat. During Phase II of the agreement, insulated concrete products that are recent to the market will be researched using the same process of developing predictive models and conducting full-scale validation experiments. The process of validating predictive models with full-scale experiments is essential to valid force protection research Validity is primarily determined by measuring wall deflection and reflective pressures during the full-scale experiments. By measuring pressures the engineers are able to rerun the models using the actual pressures seen during the experiment and compare the model deflections to the measured deflections to see if they are accurate. "The goal is to have a 5-15 percent over-prediction of deflection by the models with a good timing match between model response and gauges measuring peak deflection during the experiments," Mr. Dinan explained. "This over-prediction then yields engineering tools with inherent factors of safety desirable in all structural design decisions." Once it is determined that the models are accurately predicting blast response, the engineers will begin Phase III of the CRADA. This phase will involve material testing in the lab combined with parametric studies using the Phase I & II computer models to identify material or design modifications that deliver improved blast protection. Once again the essential full-scale experiments will be conducted on products manufactured with the modifications to validate model predictions.