and the physical properties of the new plastics can be changed and improved 

 through the manufacturing process and the addition of additives and plasti- 

 cizers. 



(4) Geotextile Filters . The development, investigation and testing 

 of fabrics is fragmented and there are many activities overlapping in effort. 

 The manufacture of filter fabric is changing in some instances due to the 

 ongoing development of nonwoven fabrics with controllable thickness, elonga- 

 tion, and filtration capabilities. Methods are being investigated to char- 

 acterize fabric as to the size and shape of openings and the details of 

 clogging of the fabric. Tear propogation in fabrics is being studied. 

 Mechanical property analysis to indicate the amount of deformation that a 

 fabric will undergo is being performed. Information about anchoring to 

 indicate the required friction between the fabric and the soil is also being 

 investigated. Filtration mechanisms (and particularly the soil structure 

 arrangement resulting from the waterf low) , flow rate, permeability, and 

 piping are being evaluated and laboratory test methods are being recommended. 

 The results of these investigations and others that will come along in the 

 future will provide data for expanded and better use of fabrics. 



h. Protective Systems . 



(1) Coatings . One of the principal means of preventing deteriora- 

 tion of structures is through the use of protective coatings. Coatings may 

 be specified on a formulation basis, on a performance basis, or by a combina- 

 tion of the two. The formulation-type specification does not take advantage 

 of the manufacturer's experience and formulating knowledge, the responsi- 

 bility for obtaining a suitable coating being the specification writer's and 

 his technical sources. The principal alleged merit of a performance- type 

 coating is that it does take advantage of the manufacturer's knowledge and 

 experience and may be a real advantage if the manufacturer is highly ex- 

 perienced in formulating coatings for the particular contemplated usage. A 

 principal difficulty with performance-type specifications is that acceptance 

 tests, which purport to show that a coating is satisfactory for a specific 

 use, must necessarily be finished in a short time and frequently have little 

 significance in predicting actual performance. Performance tests include 

 flexibility, hiding power, immersion resistance, gloss, resistance to weather 

 or salt spray tests. 



The development of improved coating systems involves three areas of 

 investigation and testing: surface preparation, coating application tech- 

 niques and improved materials. In many situations environmental constraints 

 have required innovations and improvements in all three areas of coating 

 systems development. 



(a) Surface Preparation . Surface preparation is accomplished 

 in many ways: solvent cleaning, hand and power- tool cleaning (wire brushing), 

 pickling, flame cleaning and blast cleaning (sandblasting). 



Good coating performance requires good adhesion to the structure surface. 

 Preparing the surface for coating application is critical. In solvent 

 cleaning, mineral spirits are frequently used but must be sufficiently 

 refined as to not leave oily residues upon evaporation. Solvents that leave 



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