Mix design requirements

The Federal Aviation Authority (FAA) has its own recommendation and mix design requirements on dense AC. Since it is a globally recognised authority, brief information regarding the AC mixtures proposed is given here. 

Table 6.5 Mix design requirements - recommendations for slurry surfacing on airfields...

To prevent the surrounding air from mixing with the supply air, the air shower should use air-permeable filter material with a harder, load-bearing, nonflammable outer shell and an inner layer of softer material with a high air resistance. This design requires that the supplied air be filtered. 

Scale-up techniques for using the results of pilot plant or bench scale test w ork to establish the equivalent process results for a commercial or large scale plant mixing system design require careful specialized considerations and usually are best handled by the mixer manufacturer s specialist. The methods to accomplish scale-up will vary considerably, depending on whether the actual operation is one of blending, chemical reaction tvith product concentrations, gas dispersions, heat transfer, solids suspensions, or others. 

For continuous reactors, plug-flow designs require smaller volumes and hence smaller inventories than mixed-flow designs for the same conversion, as discussed in Chapter 5. 

The most widely used application of water-reducing admixtures is to allow reductions in the water-cement ratio whilst maintaining the initial workability in comparison to a similar concrete containing no admixture. This, in turn, allows the attainment of a required strength at lower cement content to effect economies in mix design. 

Recognized mix design procedures (or existing standard mixes) are used to produce a plain concrete meeting the requirements of workability, strength and cohesive character using available materials. 

Such requirements can often be met by specially designed mixes for individual jobs, almost always involving a compromise in sand-aggregate ratio and water content. However, even with good mix design the incidence... 

Interlocking construction blocks are also a promising field for sulphur concretes. The various types of blocks produced allow easy construction. The close reproduction of mould shape is a major advantage mortarless construction has been employed, allowing use of unskilled labour. Improvements in mix design should lead to a reduction in the quantity of binder required and thus a reduction in cost. 

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