Concrete is formed from three basic components: water, aggregate (rock, sand, or gravel), and portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates. this mix , or concrete mix, are going to be poured and harden into the durable material with which we are all familiar.
Components of a Basic Concrete Mix
There are three basic ingredients within the concrete mix:
- Portland Cement
- Water
- Aggregates (rock and sand)
Portland cement – The cement and water form a paste that coats the aggregate and sand within the mix. The paste hardens and binds the aggregates and sand together.
Water- Water is required to chemically react with the cement (hydration) and too provide workability with the concrete. the quantity of water within the mix in pounds compared with the quantity of cement is named the water/cement ratio. The lower the w/c ratio, the stronger the concrete. (Higher strength, less permeability)
Aggregates- Sand is that the fine aggregate. Gravel or crushed stone is that the coarse aggregate in most mixes.
Desired Properties of Concrete
- The concrete mix is workable:It are often placed and consolidated properly by yourself or your workmen.
- Desired qualities of the hardened concrete are met: for instance , resistance to freezing and thawing and deicing chemicals, water tightness (low permeability) , wear resistance, and strength. Know what you’re trying to realize with the concrete.
- Economy: Since the standard depends mainly on the water to cement ratio, the water requirement should be minimized to scale back the cement requirement (and thus reduce the cost).
Take these steps to scale back the water and cement requirements:
- Use the stiffest mix possible
- Use the most important size aggregate practical for the work .
- Use the optimum ratio of fine to coarse aggregate.
- Discuss the way to achieve your goals for the concrete together with your ready mix supplier.
Concrete Admixtures: most common Types and What they are doing
Admixtures are additions to the combination wont to achieve certain goals.
Here are the most admixtures and what they aim to realize .
Accelerating admixture-accelerators are added to concrete to scale back setting time of the concrete and to accelerate early strength. the quantity of reduction in setting time varies counting on the quantity of accelerator used (see your ready mix supplier and describe your application). calcium chloride may be a low cost accelerator, but specifications often involve a nonchloride accelerator to stop corrosion of reinforcing steel.
Retarding admixtures-Are often utilized in hot weather conditions to delay setting time. they’re also wont to delay set of harder jobs or for special finishing operations like exposing aggregate. Many retarders also act as a water reducer.
Fly Ash- may be a by product of coal burning plants. fly ash can replace 15%-30% of the cement within the mix. Cement and fly ash together within the same mix make up the entire cementious material.
- Fly ash improves workability
- Fly ash is simpler to end
- Fly ash reduces the warmth generated by the concrete
- Fly ash costs to the quantity of the cement it replaces
Air Entraining Admixtures- must be used whenever concrete is exposed to freezing and thawing, and to deicing salts. Air entraining agents entrains microscopic air bubbles within the concrete: when the hardened concrete freezes, the frozen water inside the concrete expands into these air bubbles rather than damaging the concrete.
- Air entrainment improves concrete workability
- Air entrainment improves durability
- Air entrainment produces a more workable mix
Water reducing admixtures-reduces the quantity of water needed within the concrete mix. The water cement ratio are going to be lower and therefore the strength are going to be greater. Most low range water reducers reduce the water needed within the mix by 5%-10%. High range water reducers reduce the combination water needed by 12% to 30% but are very expensive and infrequently utilized in residential work.
Engineers Blog 