Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 26 стр.

UptoLike

Составители:

Рубрика:

immediately after mixing. The usual, composition is 1 part cement to 3 parts

sand. A dense cement mortar should not be used for bedding and jointing low-

strength bricks.

Lime-Cement or Compo Mortars. - Compo is a mixture of lime, cement

and sand. It is usual to mix the lime mortar and then to gauge this mixture with

the necessary proportion of Portland cement immediately before the mortar is

required for use. Only non-hydraulic lime should be used for this class of

mortar. The addition of cement increases the hydraulicity of the mortar, besides,

increasing its strength and the rate of hardening is therefore accelerated. The

gauging also increases the workability of the mortars. The proportions vary

from 1 part cement: 2 to 3 part lime: 9 to 12 parts sand. Eminently hydraulicand

magnesian limes should not be ganged with cement.

Strength of Mortar. - Cement mortar produces the strongest brickwork,

non-hydraulic lime mortar is approximately half the strength of that in cement

mortar, and the strength of eminently hydraulic mortars is intermediate between

that of cement and non-hydraulic lime mortars. The strength of compo mortars

depends upon the cement content and may be very little less than that of cement

mortar.

Properties of Mortars

Workability is an important property of mortars, particularly of those

used in conjunction with unit masonry of high absorption. Workability is

controlled by the character of the cement and amount of sand. For example, a

mortar made from 3 parts sand and 1 part slaked lime putty will be more

workable than one made from 2 parts sand and 1 part Portland cement. But the

3:1 mortar has lower strength. By proper selection or mixing of cementitious

materials, a satisfactory compromise may usually be obtained, producing a

mortar of adequate strength and workability.

Water retention — the ratio of the flow after 1-min standard suction to

the flow before suction — is used as an index of the workability of mortars. A

high value of water retention is considered desirable for most purposes. There

is, however, a wide variation in water retention of mortars made with varying