Natural asphalt is divided into two groups ? lake asphalt and rock asphalt. We can obtain lake asphalt from lakes at Bermudez and Trinidad at depths which vary from 3-60 m.

Gypsum is hydrated sulphate of calcium and is a white crystalline substance. The percentage content of water and calcium sulphate in gypsum is 20.9 and 79.1 respectively.

Expanding cement is obtained by addition of an expanding medium like sulpho-aluminate to ordinary cement. Therefore, expanding cement expands while all or cements shrink. It is used to repair damaged concrete surfaces.

The ratio of percentage of alumina to that of oxide of iron in cement should not be less than 0.66. However, ratio of percentage of lime to those of iron oxide, alumina and silica should not be greater than 1.02.

Abrasives are broadly classified into two categories ? natural and artificial abrasives. Natural abrasives are those which occur in nature. Garnet, diamond and flint are examples of natural abrasives while silicon is an artificial abrasive.

The presence of alkali oxides and magnesium oxide badly affects quality of cement. It results in failure of concrete made from cement if amount of alkali oxides in it exceeds 1%.

Nitrocellulose glues are prepared from pyroxilin. pyroxilin is nitrated cellulose which is derived by treatment of cellulose with nitric acid.

An acid-resistant cement consists of acid-resistant aggregates like quartz, additives like sodium fluosilicate and soluble glass. Sodium fluosilicate added in acid-resistant cement increases resistance of cement to water and acid and also accelerates hardening process of soluble glass.

Neat?s foot oil is obtained by boiling fats and or parts of cattle with water. The specific gravity of this oil is 0.916. Neat?s foot oil is used for delicate mechanisms like clocks, sewing machines, etc.

Plastic bitumen consists of bitumen, a suitable inert filler and a thinner. The amount of inert filler in plastic bitumen is about 40-45%. Plastic bitumen is used to fill cracks in masonry structures.