Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 19 стр.

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UNIT 3

CEMENTITIOUS MATERIALS

Cementations materials include the many products that are mixed with

either water or some other liquid or both to form a cementing paste that may be

formed or molded while plastic but will set into a rigid shape. When sand is

added to the paste, mortar is formed. A combination of coarse and fine

aggregate (sand) added to the paste forms concrete.

TYPES OF CEMENTITIOUS MATERIALS

There are many varieties of cements and numerous ways of classification.

One of the simplest classifications is by the chemical constituent that is

responsible for the setting or hardening of the cement. On this basis, the silicate

and aluminate cements, wherein the setting agents are calcium silicates and

aluminates, constitute the most important group of modern cements. Included in

this group are the portland, aluminous, and natural cements. Limes, wherein the

hardening is due to the conversion of hydroxides to carbonates, were formerly

widely used as the sole cementitious material, but their slow setting and

hardening are not compatible with modern requirements. Hence, their principal

function today is to plasticize the otherwise harsh cements and add resilience to

mortars and stuccoes. Use of limes is beneficial in that their slow setting

promotes healing, the recementing of hairline cracks. Another class of cements

is composed of calcined gypsum and its related products. The gypsum cements

are widely used in interior plaster and for fabrication of boards and blocks; but

the solubility of gypsum prevents its use in construction exposed to any but

extremely dry climates. Oxychloride cements constitute a class of specialty

cements of unusual properties. Their cost prohibits their general use in

competition with the cheaper cements; but for special uses, such as the

production of spark proof floors, they cannot be equaled. Masonry cements or

mortar cements are widely used because of their convenience. While they are,

in general, mixtures of one of more of the above-mentioned cements with some

admixtures, they deserve special consideration because of their economies.

Other cementitious materials, such as polymers, fly ash, and silica fume, may