Fundamentals of building Chap 8

Question 1

most characteristic type of mor-tar is

Answer 1

cement–lime mortar

made of portland cement,
hydrated lime, an inert aggregate,
and water.

Question 2

portland cement

Answer 2

is the bonding agent in the mortar. Its composition and manu-facture are described in more detail beginning on page 518 of this book . (Only portland cement Types I, II, and III are recommended for use in masonry mortars.) Mortar made only with portland cement, however, is Òharsh,Ó meaning that it does not ß ow well on the trowel or under the brick, so lime is added to impart smoothness and workability.

Question 3

Lime

Answer 3

is produced by burning limestone or seashells (calcium carbonate) in a kiln to drive off carbon dioxide and leave quicklime (calcium oxide).
quicklime is then slaked by allow-ing it to absorb as much water as it will hold, resulting in the formation of calcium hydroxide, called slaked lime or hydrated lime.

Question 4

Blended hydraulic cements,

Answer 4

ASTM C595, are blends of portland cement with other cementitious materials, such as blast furnace slag, that may be used in place of ordinary portland cement alone in the cementÐlime mortar mix.

Question 5

Masonry cements and mortar ce-ments

Answer 5

re prepackaged cements that do not require the addition of lime by the mason on the job site. Their main advantages are convenience, consis-tency (since they are premixed), and good workability. Masonry cements are proprietary formulations that may contain portland cement or blended hydraulic cements, lime or other plas-ticizing ingredients, and other ad-ditives. Formulations vary from one manufacturer to another, but all must comply with ASTM C91.

Question 6

In order to achieve a workability equivalent to that of conventional cementÐlime mortars, masonry cement mortars are formulated with

Answer 6

air-entraining admix-tures that result in a higher air content in the cured mortar than cementÐ lime mortar. This reduces the bond strength between the mortar and the masonry unit to about half that of conventional mortar, which means that the flexural and shear strength of the wall is reduced and the wall is more permeable to water.