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Resistance to weathering and the somewhat synonymous term durability have been used by different authors with meanings varying from very narrow to very broad. In the paper on Resistance to Weathering—General Aspects, published in the 1955 edition of this special technical publication  C. H. Scholer presented a detailed outline of the various factors that may influence concrete durability. This outline subdivides the factors under five major groups as follows : 1. Constituent materials. 2. Construction practices. 3. Physical properties of the hardened concrete. 4. Nature of exposure. 5. Types of loads. As Scholer pointed out, not all of the factors listed under these headings are of equal importance in their effect upon weathering, and it is still true that many important ones are not as yet well understood, though there has been notable progress in our knowledge in the last decade. Bauer  states that durability of concrete is affected by (1) alternate wetting and drying, (2) freezing and thawing, (3) heating and cooling, (4) capillary water, (5) deposition of salts by percolating water, (6) dissolving of certain products (principally calcium hydroxide) by percolating water, (7) the dissolving of cement by certain acids, and (8) chemical reaction between certain constituents of aggregates in high-alkali portland cements. Troxell and Davis  add mechanical wear or abrasion to this list. Waddell  begins his list of categories of agencies of destruction with “Deficiencies or weaknesses of the concrete itself, resulting from failure to follow the five fundamentals of good concrete construction.” He goes on to point out that these weaknesses, although not actually damaging to the concrete in themselves, may make the concrete more vulnerable to the other three categories which are cyclic forces of the weather, chemical or mechanical attack by outside agencies other than weather cycles, and reaction between the constituents of the concrete itself.
Arni, H. T.
Materials engineer, Nat. Bureau of Standards, Washington, D. C.