Basics Of Hydraulic Cement
Hydraulic cement consolidates by a reaction with water and develops a product that is water resistant. The hydraulic cements are hardened due to the chemical reaction with water. This reaction is known as hydration, during which the cement is mixed with water to produce hydrates of calcium and silica. These materials provide the cementing actions. Small quantities of alumina, iron, and sulfates are also present in the cement.
Composition of Hydraulic Cement
Chemical reactions occur when water is mixed with dry hydraulic cement. These chemical reactions produce chemical compounds that contain water, and trigger the hardening of the mixture. These compounds are not soluble in water. Thus the cement that has been hardened will preserve its hardness and strength even when in contact with water. These characteristics make the hydraulic cements suitable for buildings in or during wet climates, suitable for structures that remain in contact with water, and for several other applications. The main compounds in the hydraulic cement are:
•Tricalcium silicate: It hardens quickly, and is mainly responsible for the primary adjustment and initial strength of the material. The initial strength of the hydraulic cement increases with an increased quantity of this material.
•Dicalcium silicate: It hydrates and slowly hardens the material. It is responsible for the increase in strength after approximately one week of application.
•Tricalcium aluminate: It releases a considerable amount of heat in the initial days of the hydration and hardening. Gypsum is added that slows the hydration process to manage the hydration heat.
•Tetracalcium aluminoferrite: It decreases the requirement for a high temperature that is essential to chemically modify the raw material into cement clinker. Thus, the cement manufacture is facilitated. The concrete color is mainly due to the tetracalcium aluminoferrite.
The general application of hydraulic cement is for the repair of leaks and cracks. The cement ingredients cause expansion of the cement during drying. Thus, the small holes and leaks are filled with this material. Such repairs are often required at homes since the Portland cement slightly shrinks as it is dried. Basements and locations with humid atmosphere are particularly liable to leaks, and hydraulic cement is especially suitable for such usage. Other places may include: swimming pools, sewers, water pipes, dams, electric vaults, elevator pits, water tanks etc.
However, before applying the hydraulic cement it must be ensured that dirt, grease, oil, and other impurities should not be present on the surfaces. The results will be more effective if the hydraulic cement is added to clean and potable water, and properly mixed. The material should be forced into the required area using gloves, and filled to the complete depth.
Cautions and Limitations
•Hydraulic cement should not be applied when temperature is below 40°F or when it is expected to fall below 40°F within 48 hours (winter time).
•Do not apply over surfaces that are frozen or contain frost.
•The prepared mix should be used immediately.
•Avoid breathing the dust.
•Avoid any contact with eyes or skin.
•Silica inhaling may cause lung problems, although there is no real evidence silica is a carcinogen.
•The use of protective clothing: gloves or mask is recommended.