Concrete acid effects

The results of the literature survey, private discussions, and the responses to mail and telephone inquiries have indicated that very little qualitative or quantitative information is available dealing specifically with the effects of acid deposition on PCC structures, but there is a considerable amount of information available indicating that acids and acid waters have a significant effect on the durability of concrete. This effect may not be sudden or dramatic, but it is a cause for concern. 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

Prevention Methods of prevention already summarised may be used singly or in combination. Elimination of sulphur and certain of its compounds are most effective but more recently more resistant materials such as polythene or asbestos are used to replace iron and concrete where acid corrosion in severe. 

Picric acid, in common with several other polynitrophenols, is an explosive material in its own right and is usually stored as a water-wet paste. Several dust explosions of dry material have been reported [1]. It forms salts with many metals, some of which (lead, mercury, copper or zinc) are rather sensitive to heat, friction or impact. The salts with ammonia and amines, and the molecular complexes with aromatic hydrocarbons, etc. are, in general, not so sensitive [2], Contact of picric acid with concrete floors may form the friction-sensitive calcium salt [3], Contact of molten picric acid with metallic zinc or lead forms the metal picrates which can detonate the acid. Picrates of lead, iron, zinc, nickel, copper, etc. should be considered dangerously sensitive. Dry picric acid has little effect on these metals at ambient temperature. Picric acid of sufficient purity is of the same order of stability as TNT, and is not considered unduly hazardous in regard to sensitivity [4], Details of handling and disposal procedures have been collected and summarised [5],... 

Addition of admixture to obtain higher strengths In this situation the small amount of reported work indicates that where the water-cement ratio is reduced, the shrinkage and creep of the concrete is also reduced. Figure 1.50 shows the effect of a hydroxycarboxylic acid plasticizer on the creep of the concrete where the material has been used to effect a reduction in the water- cement ratio without any other changes in the mix design. Thus it seems that the reduction of the water-cement ratio will compensate for the increases in creep observed in the data above. 

Fig. 1.50 The effect of a hydroxycarboxyiic acid water-reducing agent on the creep of concrete when used to lower the water-cement ratio (Rodrigues).

Dampproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. In the case of materials based solely on calcium and aluminum stearates, stearic acid in solid or emulsion form, bitumens and hydrocarbon resins, there will be no effect on the properties of the plastic concrete with regard to air content, workability, mix design parameters, etc. When water-reducing admixtures or accelerators are included in the formulation, the effect on the concrete will be a function of the particular type of material used (see relevant section). The wax emulsions do appear to have an effect on the properties of the plastic concrete because of the lubrication effect of the very small... 

Table 4.7 Effect of a stearic-acid-based dampproofer on the compressive strength of concrete...

Table 7.5 presents a comparison of the results obtained from concrete batches produced on the same plant with and without admixtures. The table summarizes data collected over a 6-month period for two concretes of differing slump values (50 mm and 75 mm). It can be seen that the hydroxycarboxylic-acid-based normal water-reducing admixture produced no effect on the standard deviation for the 50 mm slump mixes, whilst an increase is noted for the higher-workability mixes. 

Hatchett fused the ore with potassium carbonate. When he took up the melt with boiling water, a brown residue remained. When nitric acid was added to the yellow filtrate, a copious white precipitate was thrown down. The preceding experiments shew, said he, that the ore which has been analyzed consists of iron combined with an unknown substance and that the latter constitutes more than three fourths of the whole. This substance is proved to be of a metallic nature by the coloured precipitates which it forms with prussiate of potash and with tincture of galls by the effects which zinc produces when immersed in the acid solutions and by the colour which it communicates. .. to concrete phosphoric acid, when melted with it. . . . He mentioned that it retained oxygen tenaciously and that the oxide was acidic. Although the specimen Hatchett analyzed was very small, he hoped to get more soon from a gentleman now in England (Mr. Smith, Secretary to the American Philosophical Society). This was evidently Thomas P. Smith, who died in 1802 (53). 

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