Does GGL determine concrete strength?
GGL does not evaluate the compressive strength of concrete. California DOT requires that sample concrete cylinders be collected to evaluate the conformance of concrete compressive strength to the strength requirement. Where data collected by GGL shows that a CIDH pile is uniform, the engineer can conclude that the entire pile has concrete of the same strength as the collected cylinder samples. Where significant drops in density occur, the concrete at that zone is anomalous and the concrete strength is usually compromised. How does California DOT interpret GGL data? California utilizes the statistical principles of mean and three standard deviations to analyze the homogeneity of a pile. For a homogeneous set of GGL readings, the data is normally distributed. As a result, it is improbable that data points will exceed three standard deviations. Therefore, when points are detected with a value less than three standard deviations, these values are associated with anomalies within the pile.
