Subgrade

Separation. In this function, the geotextile serves to separate two dissimilar materials (Fig. 3), eg, two different soils, landfill material and the native soil, stone material and subgrade sod, old and new pavement, foundation sods and various types of wads, or one of many other similar situations. In some instances, it is difficult to distinguish between the separation and stabilization functions because in both situations the geotextde is serving as a separator. However, in stabilization some additional phenomena occur. 

Two subgrades of SMR 5 are SMR 5RSS and SMR 5ADS, which are prepared by direct baling of ribbed smoked sheet and air-dried sheet (ADS), respectively. 

The amount of cement used can be varied to produce high-bearing capacities thereby making the waste/concrete material a good subgrade and subfoundation material. 

California bearing ratio tests are used to evaluate subgrades for pavements. These tests may be carried out in the field or in the laboratory. Such tests determine the resistance to penetration of a subgrade soil relative to that of a standard crushed-rock base. 

Plate bearing tests are field tests that are also used to evaluate subgrades for pavements. 

Thermal property is another critical property for furnace slag. Because of their more porous structure, blast furnace slag aggregates have lower thermal conductivities than conventional aggregates. Their insulating value is of particular advantage in applications such as frost tapers (transition treatments in pavement subgrades between frost-susceptible and nonfrost-susceptible soils) or pavement base courses over frost-susceptible soils. 

Asphalt concrete is primarily used as a structural pavement surface constructed over a subgrade and a subbase. It is designed to support the traffic load and distribute the load over the roadbed. Asphalt concrete pavements can be constructed using hot mix or cold mix asphalt. Hot mix asphalt is a mixture of tine and coarse aggregate with asphalt cement binder that is mixed, placed, and compacted in a heated condition. Cold mix asphalt is a mixture of emulsified asphalt and aggregate, produced, placed, and compacted at ambient air temperature. Cold mix asphalt pavement usually requires an overlay of hot mix asphalt or surface treatment to resist traffic action. 

Proper preparation of the subgrade and grade is extremely important for tanks that are to rest directly on grade. Precautions should be taken to prevent ground freezing under refrigerated tanks, as this can... 

More than 2 billion tires are disposed of annually in the USA. Before being recycled and/or reused, scrap tires or crumb rubber are first processed to remove any loose steel and fibers and then finely ground. Research has been conducted on the use of crumb rubber in highway construction such as in lightweight fill, subgrade insulation, and channel slope protection, as well as an additive to Portland cement concrete pavement [66,67,259,260]. 

Humphrey DN, Eaton RA (1993) Tire chips as a subgrade insulation - field trial. Symposium proceedings Recovery and Effective Reuse of Discarded Materials and Byproducts for Construction of Highway Facilities. Federal Highway Administration, FHA, 11... 

The entire construction was accomplished without incident the conventional equipment and techniques worked as well as with Sulphlex binders as with asphalt. After 2.5 years service, at a traffic volume of 1000 ADT (10 percent trucks), distress is evident in a number of sections. In general, the distress has been primarily attributed to poor subgrade drainage placement of certain sections with mix at extremely low temperature (below 65C (150F)) ravelling of dry mixtures and lateral shifting of lifts due to the absence of adequate tack between them. None of the distress is uniquely related to the use of Sulphlex binders in lieu of asphalt cement in the pavement. 

Fig. 3. Separation of subbase from subgrade soil by a geotextile.

The subgrade used in the analysis was assumed to be a clay material (A-6 classification) with a moisture content of about 23% and an elastic modulus of 15,000 psi. The base course used in the analysis was assumed to be a dense graded crushed aggregate with an elastic modulus of 60,000 psi. These two materials were assumed to be elastic and are typical of those used in construction of many pavements throughout the U.S. 

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