Современные проблемы промышленного и гражданского строительства на занятиях английского языка. Кузьмина Е.В. - 27 стр.

UptoLike

Составители:

Рубрика:

proportions of cement and lime and with varying limes. The ‘‘Standard

Specification for Mortar for Unit Masonry’’ requires mortar mixed to an initial

flow of 100 to 115, as determined by the test method, to have a flow after

suction of at least 75%.

Strength of mortar is frequently used as a specification requirement, even

though it has little relation to the strength of masonry. The strength of mortar is

affected primarily by the amount of cement in the matrix. Other factors of

importance are the ratio of sand to cementing material, curing conditions, and

age when tested.

Volume change of mortars constitutes another important property.

Normal volume change (as distinguished from unsoundness) may be considered

as the shrinkage during early hardening, shrinkage on drying, expansion on

wetting, and changes due to temperature. After drying, mortars expand again

when wetted. Alternate wetting and drying produces alternate expansion and

contraction, which apparently continues indefinitely with Portland-cement

mortars.

PORTLAND-CEMENT CONCRETE

Portland-cement concrete is a mixture of Portland cement, water, coarse

and fine aggregates, and admixtures proportioned to form a plastic mass

capable of being cast, placed, or molded into forms that will harden to a solid

mass. The desirable properties of plastic concrete are that it is workable,

placeable and no segregating, and that it set in the desired time. The hardened

concrete should provide the desired service properties:

1. Strength (compressive and flexural)

2. Durability (lack of cracks, resistance to freezing and thawing and to chemical

attacks, abrasion resistance, and air content)

3. Appearance (color, lack of surface imperfections)

Each of these properties affects the final cost of the mix design and the

cost of the in-place concrete. These properties are available from normal-

weight, lightweight, and heavyweight concretes.

1. Discussion: Your ideas about the material.