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KLE/NFELOER �Bright People.Right Solutions. tight barrier. Tears and punctures in the membrane should be completely repaired prior to placement of concrete. Until recently, the local practice and ACI standard has been to place a 1- to 2-inch thick layer of relatively-dry, fine- to medium-grained "clean" sand over the membrane to promote uniform curing of concrete and to protect the membrane. ACI has now revised their standard, and this layer of sand is no longer recommended. To compensate, a lower water cement ratio and improved curing methods are suggested. If the design engineer still prefers to specify a sand cushion, we suggest that the moisture content of the sand not exceed 4 percent by dry weight. If the sand becomes overly wet, it should be removed and replaced with suitable sand. The capillary break should not replace in whole or in part the Subgrade Preparation recommendations discussed in Section 5.6.2. Over the past few years, problems with wet, curled, and loose floor coverings have become an issue. Accordingly, prior to placement of floor coverings, moisture emissions through the concrete and the pH and relative humidity of the concrete should meet the manufacturer's recommendations and requirements. A guide for preparing concrete floors that will receive moisture-sensitive floor covering is presented in ASTM F 710. Since Kleinfelder is not a floor moisture proofing consultant or expert, it is our professional opinion that these standards should be incorporated into the project design and construction unless otherwise revised by a qualified specialist with local knowledge of slab moisture protection systems, flooring design, and other potential components that may be influenced by moisture and/or moisture vapor. In warehouse, equipment storage, and other similar areas where the floor slabs are not covered with floor coverings or support moisture-sensitive equipment, it is common to replace the gravel and capillary break with at least 4 inches of Class 2 Aggregate Base (AB) that is compacted to at least 95 percent relative compaction. If the lime treatment option is selected for floor slab support this AB layer will likely already be present in order to help cure the underlying lime treated soil. The aggregate base also provides added support for concentrated and/or storage loads and less deflection at the slab joints caused by forklift or other equipment traffic. The moisture-proofing specialist and structural engineer should approve this slab support prior to final design and construction. 5.6.4 Additional Considerations The following modulus of subgrade reactions (for a 1 ft. by 1 ft. square plate) of 150 pci may be used for slab design for subgrade soils prepared as presented in Section 5.6.2. This modulus may need to be modified accordingly to reflect differences in slab size and shape. The project 20210067.001A/ST020R111447 Page 23 of 37 May 11, 2020 ©2020 Kleinfelder www.kleinfelder.com