Questions about concrete and cement..

What is the difference between cement and concrete??

• Cement and concrete often are used interchangeably, but cement is actually an ingredient of concrete.
• Concrete is basically a mixture of aggregate and paste while aggregate are sand and gravel or crushed stone; the paste is water and portland cement. .
• Cement comprises from 10 to 15 percent of the concrete mix. Nonetheless, measuring exact volumes of the materials is difficult. Thus, the mix proportions are usually expressed as the weight of each material required in a unit volume of the concrete production,usually in kg/m.
• Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years. This means that concrete gets stronger as it gets older.
• So, there is no such thing as a cement sidewalk or a cement mixer; the proper terms are concrete sidewalk and concrete mixer.

What does it mean to 'cure' concrete??

• Curing is one of the most important steps in concrete construction as the proper curing greatly increases concrete strength and durability.
• Concrete hardens as a result of hydration, which is the chemical reaction between cement and water. But, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range.
• During the curing period, from 5 to 7 days after placement for conventional concrete, the concrete surfaces needs to be kept moist to permit the hydration process.
• New concrete can be wet with soaking hoses, sprinkles or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.

Can it be too hot or too cold to place new concrete??

• Temperature extremes make it difficult to properly cure concrete.
• On hot days, too much water is lost by evaporation from newly placed concrete.
• If the temperature drops too close to freezing, hydration slows to nearly a standstill. Under these conditions, concrete ceases to gain strength and other desirable properties.
• so, the temperature of new concrete should not be allowed to fall below 10 ºC.

Will concrete harden under water??

• Portland cement is a hydraulic cement which means that it sets and hardens due to a chemical reaction with water. Consequently, it will harden under water.