Evaluating different geogrid products for modulus improvement with bender element sensor technology

Geogrids extend pavement lifespans by stiffening the unbound aggregate base/subbase through geogrid-aggregate interlocking and restraining of the lateral movements of aggregates. Different geogrids may provide different mechanisms of stabilization based on aggregate size and shape distributions, geogrid properties, and the stabilization mechanism. This study proposed the experimental results of evaluating five different geogrid products: three extruded, one woven, and one welded, with different physical properties tested using a dense graded crushed limestone base course aggregate material. The direct and quantitative stiffness measurements were performed using shear wave transducers (bender elements (BEs)). Small strain shear modulus was measured using three BE sensor pairs instrumented on 300 mm height and 150 mm diameter cylindrical specimens with geogrids installed at specimen midheight. The aggregate material was used based on its as-received gradation. Geogrid-stabilized and unstabilized control tests were conducted in repeated triaxial loading at the 15 stress states following the AASHTO T 307 resilient modulus test protocol. Although the resilient modulus tests could not differentiate the effects of geogrid stabilized specimens, local measurements of small strain shear modulus using the BE sensor pairs demonstrated certain increases in shear moduli owing to the incorporation geogrids. Thus, BE sensor technology was demonstrated as an effective tool for quantifying stiffening/stabilization of different geogrids through increased small strain shear modulus.