Short-Term Lay-Up

Membranes that are laid-up for less than two weeks should follow shortterm lay-up procedures. These procedures are designed to minimize fouling, scaling, and microbial growth on the membranes. General procedures are given below. 

Upon shut-down of the RO, the membranes should be flushed with feed water under minimal pressure (see Chapter 13.1.1) or with RO-permeate or better quality water. Flushing with higher-quality water will help remove foulants and scale and better preserve the membranes. While flushing, the air from the system should be vented. 

When the pressure vessels are filled, the valves should be closed to prevent air form entering into the system. 

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Fig. 7 shows that the values from the second laboratory tend to be lower than those from the first for both types of cross-ply lay-up, while those for the unidirectional lay-up agree fairly well. The scatter still seen in the R-curves for the cross-ply laminates with a single fracture surface topography (Fig. 7) can probably, at least in part, be attributed to different amounts of fibre-bridging (compare Fig. 1). Another factor is micro-cracking in front of the delamination that may make accurate determination of the delamination length difficult. This would also offer an explanation for the steep rise seen in the R-curves of those specimens for which the delamination does not deviate into the unidirectional plies. This is discussed in detail in [6]. Small (local and short-term) deviations of the delamination into the unidirectional plies not recognised in the visual inspection of the fracture surfaces might also contribute to the scatter by temporarily reducing Gic. Finally, the oscillating interlaminar - intralaminar type of delamination propagation could also account for some of the observed scatter. The analysi > presented in [4] concludes that the intralaminar G is considerably smaller than the...

A possible approach to this problem is as follows. The customer/designer must decide on the performance required from the arterfact/structure in terms of short/long-term mechanical, thermal and electrical properties, mass and environmental resistance. From this information he/she can select possible fibre and matrix types, using the information in this book, decide on the lay-up or directional nature of the reinforcement and select a suitable fabrication route. Logically, for a given set of properties, the materials which fulfil the conditions and are the least expensive and easiest to process will be chosen. 

Cement-based mortars set chemically, they harden hydraulically by the addition of water, they bind by the reaction of the cement with water in air and even under water, and are water resistant after cming. To take into account the need for more and more short-term completion of construction, in recent years rapid construction adhesive mortar based on special cements have been developed increasingly. The joints of these adhesive mortars may already be filled up just horns after the laying of the tiles (Geiss 2006a). 

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