How to Control Water When We Make the Concrete

To strengthen samples and to promote hydration, soak concrete in water (after it is set).
Wet sand may carry considerable water, so the amount of mix water should be reduced to compensate.
Air bubbles in the molds will become weak points during strength tests. They can be eliminated by:
I. Packing theconcrete.
ii. Tapping the sides of the mold while filling the mold.
iii. "Roding" the concrete inside the mold with a thin spatula.
Special chemicals called "water reducing agents" are used to improve workability at low water to cement ratios and thus produce higher strengths. Most ready-mix companies use these chemicals, which are known commercially as super plasticizers. They will probably be willing to give you some at no charge.
You can buy a bag of cement from your local hardware store. A bag contains 94 lb. (40kg) of cement. Once the bag has been opened, place it inside a garbage bag (or two) that is well sealed from air. This will keep the cement fresh during the semester. An open bag will pick up moisture and the resulting concrete may be weaker. Once cement develops lumps, it must be discarded. The ready mix company in your area may give you cement free of charge in a plastic pail.