Estimations of Soil Conservation Service Curve Numbers for Concrete and Asphalt

Abstract

The purpose of this study was to collect data to estimate curve number (CN) values for concrete and asphalt surfaces and to determine how these values are affected by rainfall intensity and duration, and pavement slope. Two concrete and two asphalt pavements of size 15.24m×3.05m at respective slopes of 2.2 and 4.6% and 2.4 and 5% were constructed to conduct field experiments. A water distribution system was specially designed and constructed to simulate rainfall at variable intensities. A total of 64 experiments were conducted. Rainfall intensities ranged from 0.635 to 36.29cm∕h(0.25to14.28in.∕h), and rainfall durations ranged from 0.25 to 4h. The CN for concrete was 100 for all conditions. The CN values for asphalt ranged from 97 to 100 with an average of 99. Statistical tests indicated that the average CN values for concrete and asphalt were not equal. As expected, there was a direct relationship between curve number and rainfall intensity and an inverse relationship between curve number; and rainfall duration. The slope did not affect the CN value for concrete but there was an inverse relationship between curve number and slope for asphalt. It is possible that this inverse relationship was due to construction or other defects in the 5% asphalt pavement. The presence of minor cracks in the concrete pavement lowered the CN value to 99 in some cases. The presence of an enhanced “porous” area in the 5% asphalt pavement, less than 1% of the total slab area, reduced the CN values by as much as 10% for relatively low-intensity events. It is likely that the presence of cracks due to construction defects or weathering, construction joints, or other construction defects can significantly reduced the CN value.