WORK PLANS - Laserfiche WebLink

Home Browse Search

Geotechnical Engineering and Geological Hazard Study Lincoln Elementary School Modernization Project Manteca, California Page 14 minimum thickness of 15 mils, a permeance as tested before and after mandatory conditioning (ASTM E 1745, Section 7.1.2 — 7.1.5) of less than 0.01 perms [grains/(ft2 - hr - inHg)], and comply with the ASTM E 1745 Class A requirements. Vapor retarders having these properties are commonly referred to as "vapor barriers". The designer of record may omit the blotter at their discretion when a concrete with a water -cement ratio of 0.45 or less is specified. The vapor retarder should be constructed in accordance with ASTM E 1643 using material which meets ASTM E 1745. A licensed copy of ASTM E 1643 is included in Appendix D. Slab surfaces to receive moisture sensitive floor coverings should have considerations for maximum vapor emission levels. Most floor coverings require a 3 or 5 pound emission levels for a warranted installation. Emission levels may be controlled by the use of a sub -slab vapor barrier meeting ASTM E 1745 Class A, ASTM E 154 resistance to puncture of not less than 3000 grams and ASTM E 154 tensile strength after soaking of not less than 55.5 (MD/TD) average. Slabs should be cast using concrete with a maximum slump of 4 inches or less. Excessive water content is the major cause of concrete cracking. To reduce concrete shrinkage, a water reducing agent or plasticizer may be utilized in the concrete to increase slump while maintaining an appropriate water/cement ration. Hot reinforcing steel should be cooled prior to concrete placement to help prevent concrete shrinkage at the bar location. Where there is potential for moisture accumulation under the slab, special consideration should be given to allow gravity drainage of any water that could migrate into the subgrade of the slab or rock cushion. The following table provides our recommended interior slab -on -grade alternative. The final design interior floor slab thickness and reinforcement should be provided by the Project Structural Engineer. SLAB -ON -GRADE ALTERNATIVE Notes: a. PCC = Portland Cement Concrete with minimum compressive strength of 4,000 psi, and jointed and reinforced per structural design for shrinkage. b. All grading recommendations per Section 7.2 are to be followed. 9.2 EXTERIOR CONCRETE SLABS Exterior concrete slabs (i.e., sidewalks, building aprons, etc.) should be constructed over 4 inches of Class 2 Aggregate Base over 12 inches of native soil or import compacted to the requirements of engineered fill, and should be reinforced or jointed and scored to limit cracking from shrinkage. The final design exterior slab thickness and reinforcement should be provided by the Project Structural Engineer. 10.0 PAVEMENTS Based on our exploratory borings, the near -surface soils across the site are generally silty sands that have a moderate to high traffic support capacity when recompacted and used as pavement subgrade. A sample of the near -surface fill soil was collected from within the proposed west parking area for R -value testing. The test on the soil yielded an R -value of 72. t41