Division 3 - Concrete
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A structural material produced by mixing predetermine amounts of portland cement, aggregates and water, and allowing this mixture to cure under controlled conditions.
Define the "Quality of Concrete"
- Aggregate should consist of particles that have adequate strength and resistance to exposure conditions
- Concrete depends greatly on the quality of the paste. In properly made concrete, each particle of aggregate is completely coated with paste and all of the space between aggregate particles is completely filled.
- For given materials and conditions of curing the quality of concerete is determine by the amount of water used.
Some of the advantages of reducing water content are? (5)
- Increase compressive strength
- Increase water tightness
- Increased resistance to weathering
- Better bond between concrete and reinforcement
- Less volume change
List the different types of Portland cement.
- Type 10, Normal : General-purpose cement.
- Type 20, Moderate : Cement is used where precaution against moderate sulphate attack is important. It's uses include large piers and heavy retaining walls
- Type 30, High Early Strength : Cement provides high strenght at an early period, usually a week or less. It is used when forms are to be removed as soon as possible, and in cold weather to reduce the contolled curing time.
- Type 40, Low Heat of Hydration : Cement is used where the rate and amount of heat generated must be minimized. It developed strength at a slower rate than Type 10. It is used in massive concrete structures.
- Type 50, Sulphate Resisting : Cement is used only in concrete exposed to severe sulphate action. It us used principally where soils or ground waters have a high sulphate content.
What type of water can be used to mix concrete?
Almost any type of natural water that is drinkable and has no pronounced taste or odour is satisfactory as mixing water for making concrete. Also some water that is not fit for drinking may be suitable for concrete.
What is the used of Aggregate for concrete
Aggregate generally occupies 60 - 80% of the volume of concrete. It strongly influences the properties of concrete, its mix porportions and cost.
List eight (8) characteristics of Aggregate for Concrete.
- Abrasion and Skid resistance
- Resistance to freezing and thawing
- Chemical stability
- Particle shape and surface texture
- Bulk Denisity
- Absorption and surface Moisture
- Compressive Strength
Define "Air-Entrained Concrete"
Air-entrained concrete is produced by using either an air-entraining cement or an air-entraining addmixture. Unlike entrapped air voids, which occure in all concretes and is largely a function of aggregate, intentially air-entrained bubbles are extremely small in size.
What are the properties of Air-Entrained Concrete?(7)
- Freeze/Thaw Resistance
- Resistance to De-Icers
- Sulphate Resistance
- Abrasion Resistance
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