Water for the building industry

The requirements for water used in the building industry for preparation of a concrete mix and mortar are not stringent. The majority of natural waters can be used except for swampy, muddy, mineral and wastewaters. Water used for the preparation of concrete mixes (so-called concrete or mixing water) is added to concrete in relatively small quantities and thus even higher amounts of certain constituents may not have negative effects. 

Aggressive waters are divided into several groups  

Waters with a low content of salts. The most important process is leaching of soluble constituents of material. As far as concrete is concerned, particularly the release of Ca(OH)2 during the hydration of cement should be borne in mind. 

Acid waters. Waters of this group contain mineral or organic acids which dissolve calcium components of concrete, which are thus removed from it. Acids whose calcium salts are quite soluble (HCl, HNO3) corrode concrete more quickly than those whose calcium salts are insoluble. The pH of water should not decrease below 6.7. 

Sulphate waters. The influence of these waters, mostly groundwaters, on concrete is the most intensive. The main reason for the destruction of concrete by sulphate waters is the reaction of sulphate anions with tricaJcium aluminate to form the already mentioned strongly hydrated compound. This compound crystallizes in needles with a considerable increase in volume. Due to the considerable crystallization pressure the concrete cracks, becomes porous and the destructive effects of aggressive water penetrate deeper through the cracks formed. 

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