Mixing Concrete on Site

Maintaining Your Concrete Driveway

If you’re mixing concrete on site, the mixing area should be close to the pour area if possible, and your ingredients stockpiled nearby. Store bags of cement off the ground and cover them with plastic to keep them dry. Small quantities of sand can usually be purchased in bags at building supply yards. Larger quantities of both sand and gravel are sold by the ton or half ton by aggregate suppliers and delivered to the site in dump trucks. Spread tarps on the ground before the sand is dumped so that the moisture content of the sand is not affected by the moisture content of the soil, and so that rocks or soil are not accidentally shoveled up with the sand.

One of the most important things in mixing concrete is consistency from batch to batch. The ingredient weights and proportions are based on “wet” sand. Most sand that is sold for construction uses is “wet” sand, and the moisture that it contains has been accounted for in the recommended amounts of mixing water. If the sand you are using is “damp” rather than “wet,” and you are mixing ingredients by weight, reduce the quantity of sand in Table A by one pound, and increase the quantity of water by one pound. If your sand is “very wet,” increase the quantity of sand by one pound and decrease the water by one pound. The moisture content of sand is more difficult to adjust for when proportioning mixes by volume rather than weight.

Quick Tip 

• Damp sand falls apart when you try to squeeze it into a ball in your hand.
• Wet sand forms a ball when squeezed in your hand, but leaves no noticeable moisture on the palm.
• Very wet sand, such as sand exposed to a recent rain, forms a ball if squeezed in your hand, and leaves moisture on the palm.