Quality Assurance and Quality Control in the Installation of Lightweight Cellular Concrete

Lightweight Cellular Concrete (LCC) offers significant advantages as a lightweight alternative to traditional backfill materials for engineered fill applications. The application of LCC, as compared to more expensive soil remediation techniques, has accelerated project schedules and reduced costs for projects across the country. LCC installation and quality testing methods, both field and laboratory, require different testing procedures and standards from traditional backfill or other aggregate materials. Quality installation of LCC is achieved through real-time testing of the LCC materials as they are being produced, mixed, as well as installed, and then verified through laboratory compressive strength testing. As compaction is not required for this flowable material, in-place density testing to verify relative compaction is not required. Given the relatively large air content of LCC, as compared to traditional concrete, conventional testing of air content is not appropriate. Testing of the density of the material at the point of placement has been identified as the acceptable means to measure the air content by targeting a density identified in project-specific mix designs. Confirming adequate density of the different components of LCC such as foam, water-cement grout, and the combined LCC mixture, is critical to achieving desired engineering properties. Quality processes incorporated into field work at the time of construction are verified through unconfined compression testing of cast LCC cylinders following ASTM C495 Standard Test Method for Compressive Strength of Lightweight Insulating Concrete. Improper collection and casting of the cylinders in the field may cause over-densified samples or inclusions producing materials that are not representative of that actually placed. Post casting, proper handling, protection, and curing of the samples is critical to producing samples representative of as-placed conditions. Compressive strength results are sensitive to the sample seating, end preparation, curing, rate of strain, and selection of a load cell sized appropriately for the anticipated compressive strength. Comparative testing data between curing and capping methods demonstrates the importance and effectiveness of QC procedures. Various non-destructive test methods have been researched for use with LCC, such as Geo-phone array, falling weight penetrometer, sounding hammer, and spring penetrometer test methods each have their benefits and limitations. Field and laboratory testing techniques, lessons learned, and best practices based on case studies are discussed to support proper quality control methods in LCC construction.