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The Science of Concrete
Volume Basics
Concrete is sold by the Cubic Yard. One yard is exactly 27 cubic feet. Understanding this helps you visualize your project size.
Measurement Tips
Measure your area at least twice. For thickness, check multiple spots. An extra 1/2 inch can change concrete needs significantly.
Bag Conversions
An 80lb bag covers 0.6 ft³, meaning you need 45 bags for 1 cubic yard. 60lb bags require 60 bags per yard.
Reinforcement
Rebar or wire mesh doesn't just stop cracks; it holds the concrete together when it does crack. For driveways, #3 rebar at 16 inches on center is standard.
Sub-Base Prep
Concrete is only as strong as what it sits on. 4 inches of compacted 3/4" minus gravel is the best way to prevent sinking and shifting over time.
Curing Process
Concrete doesn't dry; it cures through a chemical reaction. Keeping it wet for the first 7 days (hydration) can result in a 50% stronger slab.
Job Site FAQ
Q. What is the standard thickness for a driveway?
For residential cars, 4 inches is standard. For trucks or trailers, 6 inches with rebar reinforcement is highly recommended.
Q. How much extra should I order?
A 10% waste factor is the industry standard. It covers sub-grade variations, spillage, and concrete left in the mixer.
Q. What does PSI mean in concrete?
PSI stands for Pounds per Square Inch. It measures the compressive strength. 3,000 PSI is common for sidewalks, while 4,000 PSI is better for driveways and structural walls.
Q. How many yards are in a full concrete truck?
Most standard ready-mix trucks carry between 9 and 11 cubic yards of concrete. Small-load fees usually apply for orders under 3 or 4 yards.
Q. Do I need a vapor barrier under my slab?
If the slab is for an interior living space (like a garage or basement), a 10-mil or 15-mil poly vapor barrier is essential to prevent moisture from seeping up through the concrete.
Q. When should I cut control joints?
Control joints should be cut within 6 to 18 hours after pouring, or as soon as the concrete can support the weight of a saw without raveling. Joints should be 1/4 the depth of the slab.
Q. How much does a yard of concrete weigh?
A single cubic yard of concrete weighs approximately 4,000 pounds (2 tons). Ensure your subgrade and forms can handle this immense weight.
Q. What is the difference between cement and concrete?
Cement is an ingredient in concrete. Concrete is a mixture of cement, water, and aggregates (sand and gravel). Think of cement as the flour and concrete as the cake.
Latest Concrete Insights
Professional tips, calculation guides, and industry secrets to make your next project a success.
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Calculating Driveway Yardage
Learn how to account for sub-grade variations and curves in your next driveway pour.
The 10% Waste Rule
Why ordering exactly what you calculate is a recipe for disaster on the job site.
Choosing the Right PSI
From 2500 to 4000 PSI - which strength is actually required for your specific project?
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