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Project No. JB -314 24 March 2003 Page 13 b. Moisture -condition and compact the upper 12 inches of subgrade soil to a minimum relative compaction of 95 percent at a minimum moisture content of 2 percent above the optimum moisture content. All pavement subgrade should be stable with no "pumping" at the time the base rock is placed. c. Use only good quality materials of the type and minimum thickness specified. All base rock should meet the Standard Specifications of the State of California for Class 2 baserock and should be angular in shape. d. Compact the baserock uniformly to a minimum relative compaction of 95 percent. e. Place the asphalt concrete only during periods of fair weather when the free air temperature is within the prescribed limits as set forth by the Asphalt Concrete Institute. f. Compact all trench backfill under the pavement to minimize pavement damage resulting from settlement. Mechanical compaction is recommended because material placed by jetting or ponding will probably not attain satisfactory densities. g. Provide adequate drainage or V -ditch systems to prevent surface water from migrating into the subgrade pavement soil from behind curb -and - gutter sections. For areas where pavement abuts landscaping, we recommend extending the concrete curb a minimum of 3 inches below the bottom of the base rock layer to form a cut-off wall to prevent water from migrating into the base rock. h. The flexural strength of the rigid pavement (concrete pavement) should have a minimum modulus of rupture (MR) of 600 pounds per square inch (psi). The design concrete compressive strength should be specified in order to attain the recommended MR. Our experience is that a compressive strength of about 4,500 psi is required for a MR of 600 psi. I. The rigid pavement section should consist of aggregate interlock joints. j. Joint spacing for rigid pavement should be at a maximum of 15 feet square. k. The rigid pavement section should be designed according to the latest Portland Cement Association (PCA) recommendations (ref. PCA publication "Design and Control of Concrete Mixtures"). I. Concrete placement and curing operations should be according to the American Concrete Institute and PCA. Improper curing techniques and/or excessive slump could cause excessive shrinkage, cracking, and/or curling. Korbmacher Engineering, Inc.