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PERMIT CO-031-81 <br />S32 GRAVEL AND CRUSHED ROCK ROADS-STABILIZED ROADS <br />Where no underlying source of capillary moisture is present, long dry periods <br />without rainfall result in deterioration of untreated surfaces. When the moisture <br />film around the clay particles disappears, the binding power of the clay also disap- <br />pears, and the surface disintegrates under traffic. <br />Materials (or Untreated Road Surfaces <br />The usual specifications for materials for untreated road surfaces include the <br />important properties prescribed here. They also contain statements to control tfie <br />grading of the material, the plasticity of its fines, and the strength of the aggregate <br />particles. <br />Lradings recommended by AASHO for wrface and bases are shown in Table <br />i5-1. It is to be noted that, although a wide variety of materials are acceptable, <br />the limits assure a fairly uniform distribution of particle size from coarse to (ine. <br />The AASHO specifications include an added general requirement with a like pur- <br />pose: It is that the fraction passingthe No. 200 sieve shall not be greater than two- <br />thirds of the fraction passing the No. 40 sieve. A further stipulation for surface <br />courses is that all materials pass a 1 in. sieve. Larger materials are troublesome in <br />that they lodge under the blade of the motor grader used for maintenance and tear <br />up the surface as the grader passes over them. <br />TABLE 15-1. Grading requirements for soil-aggregate materials (MSHO designation <br />M747-651. <br /> Percentage by weight passing square mesh sieves <br /> Grading Grading Grading Grading Grading Grading <br />Sieve designation A B C D E F <br />2 in.(50 mm) 100 100 - - - .- <br />1 in. 125 mm) - 75-95 100 100 100 100 <br />3/e in. (9.5 mm) 30~i5 40-75 50-85 60.100 - - <br />No. 4 (4.75 mml 25-55 300 35-65 50-85 ~ 55-100 70-100 <br />No. 10 (2.00 mm) 15-40 205 25-50 40-70 40-100 55-100 <br />No. 40 (0.425 mm) 8-20 15-30 15-30 25-45 20-50 3U-70 <br />No. 200 10.075 mm) 2-8 5-20 5-15 - 6-20 8-25 <br /> sutra a or surface courses <br /> Suitable for bases and subbases <br />As indicated already, some clay binder otcontrolled quality is desirable in un- <br />treated surface courses. The AASHO specifications call for a maximum liquid <br />limit of 35, a plasticity index range from 4 m 9, and a minimum of 89E passing the <br />No. 200 sieve if the surface course is to be maintained for several years without <br />bituminous-surface treatment or other impervious surfacing. <br />Regarding strength and soundness of aggregates,'the AASHO specifications <br />read in pan as follows: <br />~ 4ct.~,,,,..,f <br />v '~-'9'~ <br />,r <br />