Based on the stress history of saturated cohesive soils, they are considered to be either underconsolidated, normally consolidated, or overconsolidated. The overconsolidation ratio (OCR) is used to describe the stress history of cohesive soil, and it is defined as: OCR  vm / vo, where: vm or p  maximum past pressure ( vm), also known as the preconsolidation pressure ( p ), which is equal to the highest previous vertical effective stress that the cohesive soil was subjected to and consolidated under, and vo or v  existing vertical effective stress. In terms of the stress history of a cohesive soil, there are three possible conditions: 1. Underconsolidated (OCR  1). A saturated cohesive soil is considered underconsolidated if the soil is not fully consolidated under the existing overburden pressure and excess pore water pressures (ue) exist within the soil. Underconsolidation occurs in areas where a cohesive soil is being deposited very rapidly and not enough time has elapsed for the soil to consolidate under its own weight. 2. Normally Consolidated (OCR  1). A saturated cohesive soil is considered normally consolidated if it has never been subjected to an effective stress greater than the existing overburden pressure and if the deposit is completely consolidated under the existing overburden pressure. 3. Overconsolidated or Preconsolidated (OCR  1): A saturated cohesive soil is considered overconsolidated if it has been subjected in the past to a vertical FIGURE 6.22 Example of a consolidation curve. The Casagrande construction technique for determining the maximum past pressure is also shown on this figure. effective stress greater than the existing vertical effective stress. An example of a situation that creates an overconsolidated soil is where a thick overburden layer of soil has been removed by erosion over time. Other mechanisms, such as changes in groundwater elevation and changes in soil structure, can create an overconsolidated soil. For structures constructed on top of saturated cohesive soil, determining the overconsolidation ratio of the soil is very important in the settlement analysis. For example, if the cohesive soil is underconsolidated, then considerable settlement due to continued consolidation owing to the soils own weight as well as the applied structural load would be expected. On the other hand, if the cohesive soil is highly overconsolidated, then a load can often be applied to the cohesive soil without significant settlement. The oedometer apparatus is used to determine the consolidation properties of saturated cohesive soil. The typical testing procedure consists of placing an undisturbed specimen within the apparatus, applying a vertical seating pressure to the laterally confined specimen, and then submerging the specimen in distilled water. The specimen is then subjected to an incremental increase in vertical stress, with each pressure remaining on the specimen for a period of 24 hr. Plotting the vertical stress versus void ratio of the soil often yields a plot similar to Fig. 6.22. The plot is known as the consolidation curve and consists of two important segments, the recompression curve (defined by the recompression index Cr) and the virgin consolidation curve (defined by the compression index Cc). Figure 6.22 also illustrates the Casagrande construction technique, which can be used to determine the maximum

A vapor retarder placed in an appropriate location, however, can control such condensation. For many years NRCA has maintained that vapor retarders should be considered when both of the following conditions occur: the outside average January temperature is below 40
F (4
C), and the expected indoor winter relative humidity is 45% or greater. However, these are very simple guidelines. Both the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) and the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) have developed recognized practices for determining the need for a vapor retarder in a roof system. These methods differ, and designers should choose the methodology which they deem most applicable for a given project. Situations more likely to require the inclusion of a vapor retarder are those where interior conditions of high humidity exist, such as in textile mills, laundries, canning factories, creameries, breweries, and indoor pools. Perm Ratings. The effectiveness of a vapor retarder is measured by its perm rating, which is a measure of porosity of material to passage of water vapor. Perm ratings are established by ASTM procedures. To be classified as a vapor retarder, the material should have a perm rating between 0.00 and 0.50 perms. A perm rating for a material is the number of grains of water vapor (7000 grains equal 1 lb) that will pass through 1 ft2 of the material in 1 hr when the vaporpressure differential between the two sides of the material equals 1 in of mercury

Unless the exposed surface of cork floors is maintained with sealers and protective coatings, permanent stains from spillage and excessive soiling by heavy traffic will result. Cork tiles are particularly suitable for areas where quiet and comfort are of paramount importance. See also Art. 11.36. Flooring of this type is unbacked. For a discussion of backed vinyl, see below. It is intended for use on rigid subfloors, such as smooth-finished or screeded concrete supported above grade, or structurally sound plywood or hardboard floors. Vinyl floors are not recommended for use below grade. They must be applied with an alkaline, moisture-resistant adhesive when used at grade. Vinyl mats or runners may be laid without adhesive over relatively smooth surfaces. Large mats generally are installed in a recess in the concrete floor at building entrances. The mats are ribbed or perforated for drainage. Vinyl flooring consists predominantly of polyvinyl chloride resin as a binder, plasticizers, stabilizers, extenders, inert fillers, and coloring pigments. Because of its unlimited color possibilities and opaqueness to transparent effects, it is widely used. Common thicknesses are 0.080, 3/32, and 1/8 in. Since vinyl resins are tough synthetic polymers, vinyl flooring can withstand heavy loads without indentation, and yet is resilient and comfortable under foot. It is practically unaffected by grease, fat, oils, household cleaners, or solvents. But unless given a protective finish, it is easily scratched and scuffed. See also Art. 11.36. Backed Vinyl. The family of backed-vinyl flooring comprises vinyl wearing surfaces from 0.02 to 0.050 in thick, laminated to many different backing materials. In some products, the vinyl surfaces are unfilled transparent films placed over a design on paper, cork, or degraded vinyl. Filled vinyl surfaces with a 34% vinyl resin binder are placed over plastic composition backing or asphalt-saturated or resin-impregnated felt. The asphalt-felt type may be used in moist areas. Foamed rubber or plastic is incorporated in some of these materials to increase comfort and decrease impact noise. Asphalt-felt-backed vinyl materials may be applied with a moisture-resistant adhesive on concrete at or below grade. See also Art. 11.36. Rubber flooring is intended for use on rigid subfloors, such as smooth-finished or screeded concrete supported above grade, or on structurally sound plywood or hardwood subfloors. Rubber is not recommended for use below grade. When used at grade, it must be applied with an alkaline, moisture-resistant adhesive. Rubber mats or runners may be laid without adhesive over relatively smooth surfaces. Large mats generally are installed in a recess in the concrete floor at building entrances. The mats are ribbed or perforated for drainage. Most rubber flooring is produced from styrene-butadiene rubber. Reclaimed rubber is added to some floorings. The flooring also contains mineral pigments and mineral fillers, such as zinc oxide, magnesium oxide, and various clays. Another synthetic-rubber flooring, chlorosulfonated polyethylene (Hypalon), also is available. Rubber floorings can be obtained in thicknesses of 3/32, 1/8, or 3/16 in. They have excellent resistance to permanent deformation under load. Yet they are resilient and