The present study concentrated on the possible use of the German Light Drop-Weight device for measuring the mechanical properties of the compacted layers of the pavement formation. The study found that compared with the conventional FWD moduli, LDW moduli (E (sub V1)) are of a smaller magnitude. In the same manner, the adjusted LDW moduli to a second cycle of loading (E (sub V2)) are also of a smaller magnitude compared with the conventional FWD moduli. Obviously, this discrepancy in moduli results requires the use of the most critical values in order to obtain the proper safety-level factor. Thus, if the German Code for a minimum static plate bearing modulus (second cycle of loading) is to be followed (45 MPa measured on the formation of the pavement) an 80 MPa FWD deformation modulus or a 35 MPa LDW deformation modulus of E (sub V1) should also be followed. These moduli requirements are more stringent than those suggested recently by the British TRL. Additionally, the present study revealed a substantial scatter in the in situ LDW moduli-density comparative results in some cases. In other words, in-situ density tests may be compared to in-situ modulus tests only when the material is uniform with respect to a single maximum Modified AASHTO density. The main conclusion of this study stemming from both (a) the transition to mechanistic-empirical pavement-design procedures and (b) the possible variation of the maximum Modified AASHTO density along any tested strip is the need to include stiffness along with density measurements in quality-control and assurance testing. The German LDW can serve as a cost-effectiveness testing device for quality control and assurance during subgrade and pavement-layer compaction. The use of the outputs of this device, however, for the purposes of structural design should be further studied. (a)
Abstract