Sub-base

Lubrication is typically provided by two separate oil pumps—a direct shaft-driven pump on the gear case and an auxiliary electric motor-driven oil pump that is usually mounted on a lube skid or similar sub-base. Oil filters, oil coolers, and oil heaters complete tlie lubrication system, which has many (if not all) feamres in coimuon with traditional auxiliary systems. A typical schematic is shown in Figure 4-42. 

Sub-base selected imported granular material to form a stable level surface on which to construct the slab. Where lean-mix concrete is not used the surface is normally blinded with sharp sand ... 

Slip membrane serves to reduce friction between the slab and sub-base to minimize subsequent slab cracking. This is normally a polyethylene sheet. It may also serve as a damp-proof membrane ... 

Concrete slab ip membrane Sand/concrete blinding Sub-base/hardcore Sub-grade/natural ground... 

Similarly, the effective Hamiltonian holds for a double excitation of the bending mode, but involves the nondriven Hamiltonian of the slow mode (92). Within the sub-base (89c), it may be written... 

The damped effective Hamiltonian l holds for a single excitation of the fast mode and involves, according to some unitary transformations, a driven term that describes the intermonomer motion. Within the sub-base (89b), it may be given by... 

Bottom ash has a similar chemical makeup to fly ash but has a much coarser gradation. A recent study on its use as a sub-base material showed that it had sufficient engineering properties to perform adequately. 

Most surfaces of this kind now are laid on a sub-base of hard core, tarmac, or concrete in which has been installed adequate drainage for surface water over this is spread a shock-absorbing layer of porous rubber crumb, made from shredded tyres bonded together as flexible planar material of thickness 5 to 25 mm and supplied in the form of continuous rolls. The rubber layer may be laid loose or pegged, and sometimes is bonded to the sub-base with a moisture-curing polyurethane adhesive. 

Roads and walkways Concrete, slab, mesh reinforced Thickness, in. Sub-base, in. ... 

Liquid glass (sodium silicate) pulverized silicate Not known Compaction Soil compaction (sub-base of contaminated soil)... 

Because sub-bases are closer to the surface than subgrades and capping layers, they are more prone to damage by frost and their resistance to freeze-thaw cycles should be assessed [26.11] in the context of the conditions to which they will be subjected. 

A variety of binders are used for road bases and sub-bases, capping layers, soil stabilisation and soil improvement, depending on the availability of materials and local traditions. This section refers to factory blended mixtures of binders. In-situ treatment of materials, using lime and other binders is described in section 26.3. 

Future builders of solar ponds must make sure that their pond sub-base is adequately compacted and prepared for accepting a liner. 

The potential uses of soils after they are treated are as varied as the treatment options themselves [10-11]. The use depends on the quahty of the original material as well as the degree of treatment accomplished. Typical uses range from soil for sub-base, berms and general fill, to fill specifically for landfills, to feed stock for asphalt and concrete. 

In many metropolitan areas, the RCM source is from existing Portland cement concrete curb, sidewalk and driveway sections that may or may not be lightly reinforced. The RCM is usually removed with a backhoe or pay loader and is loaded into dump trucks for removal from the site. The RCM excavation may include 10-30% sub-base soil material and asphalt pavement. Therefore, the RCM is not pure Portland cement concrete, but a mixture of concrete, soil, and small quantities of bituminous concrete [159-161]. 

Due to the salt content and, in some cases, the low pH of BA and BS, these materials could exhibit corrosive properties. When using BA or BS in an embankment, backfill, sub-base, or even possibly in a base course, the potential for corrosion of metal structures that may come in contact with the material is of concern and should be investigated prior to use. 

The particle size distribution of milled or crushed RAP may vary to some extent depending on the type of equipment used to produce the RAP, the type of aggregate in the pavement, and whether any imderlying base or sub-base aggregate has been mixed in with the reclaimed asphalt pavement material during the pavement removal. 

Biczysko SJ (1985) Permeable sub-bases in highway pavement construction. Second Symposium UNBAR, University of Nottingham, Department of Civil Engineering... 

Dawson AR, Hill AR (1998) Prediction and implication of water regimes in granular basis and sub-baseS. Proceedings, International Symposium on Subdrainage in Roadway Pavements and Subgrades, Granada, Spain, Nov 11 -13, pp 121 -128... 

In some countries, particularly in the United Kingdom, the base, the sub-base and the capping layer (if it exists) are characterised as foundation layers or as pavement foundation. 

From the above, it is recommended that the subgrade works be conducted during periods where no rainfalls are expected and, if possible, that construction of unbound layers (base and sub-base) and the first asphalt layer be completed during the dry periods. 

The capping layer is the layer that is constructed between the subgrade and sub-base when the subgrade soil material is too weak. Its purpose is to improve the subgrade s bearing capacity and prepare an acceptable platform on which the pavement is to be constructed. The capping layer is usually needed when the subgrade GBR is lower than 5% and it is absolutely necessary when the GBR is lower than 2.5%. 

The sub-base is the first layer constructed, if necessary, over the subgrade (or the capping layer). This layer, certainly when the material used for its construction is the same as the base course material, is not a distinct layer. In a few countries, such as the United Kingdom, the sub-base indicates all the layers that are below the upper bound in bitumen or cement layers of the pavement. 

In the case where the sub-base functions as a drainage layer, the use of waterproofing membrane is necessary on the interface between a subgrade and a sub-base course. 

The thickness of the sub-base should be such that no high compressive and shear stresses develop in the subgrade under the influence of loads of worksite vehicles. The required thickness is determined according to the design methodology followed. 

In the case where the sub-base course is considered as an anti-frost layer, its thickness is determined (increased) from the depth of frost penetration and the overall resulting pavement thickness. 

Materials used for the construction of the sub-base course can be unbound or hydraulically bound aggregates obtained by processing natural or manufactured or recycled materials. In the case of hydraulically bound sub-base, the binder is cement, lime or fly ash. 

In fact, sub-base materials are the same as base course materials. In some countries, sand-gravels are also permitted to be used for the construction of the sub-base course. 

More information about sub-base materials is given in Sections 10.5.1 and 10.5.2. 

The base course layer is positioned between the sub-base course (or subgrade, if there is no sub-base constructed) and the asphalt layers. Together with the asphalt layers, in a typical flexible pavement, it constitutes one of the main two structural elements of the pavement. The base course layer performs the following functions ... 

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