Study of Scalp-and-Replace Equation in: Compaction Specification for Soil with: High Gravel Content

Under AASHTO T224, AASHTO-1 and AASHTO-2 are adapted to AASHTO T180 Method A or B to obtain the adjusted maximum dry density of soil and soil aggregates. If AASHTO T180 Method C or D is followed, the adjusted density is obtained from the graphical method. However, if the amount of field test data is very large, the graphical method is not pragmatic. Within a study, compaction tests followed AASHTO T180-D and an equation, called the scalp-and-replace equation, was derived. This equation method is proposed to replace the graphical method, especially for the cases of large amounts of field-test data. In addition, the applicability of AASHTO-1, AASHTO-2, and ASTM-1 to AASHTO T180-D is examined. The study result reveals a positive effect because the difference between the graphical method and the scalp and- replace equation method is about ±0.3 percent. Results of the study also indicate that AASHTO-1 is more applicable than AASHTO-2 and ASTM-1 to obtaining the adjusted densities for coarse particles retained on the 19-mm sieve. Percentage differences among AASHTO-1, AASHTO-2, ASTM-1, and the scalp-and-replace equation method are high for coarse particles retained on the 4.75-mm sieve. This shows that AASHTO-1, AASHTO-2, and ASTM-1 are not applicable to AASHTO T180-D for calculating the adjusted densities. Finally, changing coefficient and correction factors propose two revised equations of AASHTO-1 and AASHTO-2. The study results show that smaller percentage differences are obtained. The proposed revised AASHTO equations are applicable to AASHTO T180-D for computing the adjusted densities for particles retained on the 4.75-mm sieve.