Concrete Mix Ratio
Making concrete can be complicated unless you follow the right method. There are four basic ingredients needed to make a good concrete mix, and it is really important to obtain the right concrete mix ratio as well. The four ingredients are water, sand, cement and aggregate. The combined concrete mix ratio is measured in cubic feet and is equal to a single cubic yard of concrete. Mixing is key to obtaining the right concrete mix ratio. Mixing the concrete can be done by hand in a big plastic tub, bucket or wheelbarrow, or in a portable rotating cement mixer.
Cement is a fine powder that is white in color and is made up of lime, silica, iron and aluminum. It is available in different types, usually Type One through Type Five. Type One cement is the best for most construction needs and it can be bought in standard sized bags that contain one cubic foot of concrete that weighs around 95 pounds. To arrive at the correct concrete mix ratio, the ratio of cement to sand is important when it comes to finding out the compressive strength of the concrete. A ratio of 3:1 of sand to cement will give a concrete mix ratio with more than 3000 pounds per square inch or PSI, which is more than plenty for most small jobs.
Aggregate is simply crushed rocks, which is classified under fine, medium and course. Aggregate will be added into making the cement, and it will take up about three fourths of the concrete volume. Course aggregate will make the volume of cement needed less while not sacrificing the strength of the concrete too much. The only disadvantage is that it will give the surface of the cement a rough finish once it hardens.
The strength of concrete is inversely related to the water to cement ratio, and for this reason it should always be kept under .60. If the ratio is higher than this, the mixture will be more fluid and will lack good surface and strength qualities.
The hydration process begins after the water has been added into the mix. A chemical reaction takes placethat causes the cement to cure or harden if your concrete mix ratio is right. It is then poured and compacted to get rid of any trapped air. To make sure the mix is uniform; it can be vibrated as well. Too much vibration, however, will cause the heavier aggregates to form a residue at the bottom while the fluid-like paste will rise to the top, so this should be done carefully.
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