Concrete 101: Everything You Need to Know

Before you calculate quantities or plan your pour, you need to understand what concrete actually is and how it works. This foundation knowledge prevents expensive mistakes—like adding too much water (permanently weakens concrete) or driving on a driveway too soon (causes surface damage).

This guide covers the fundamentals every DIYer needs to know. No prior construction knowledge assumed.

Table of Contents

1. What Concrete Actually Is
2. Concrete vs Cement
3. How Concrete Cures
4. Types of Concrete Mixes
5. Understanding PSI Ratings
6. Ready-Mix vs Bagged
7. What's a Yard of Concrete
8. Concrete Weight
9. Key Terms Glossary
10. Key Properties

What Concrete Actually Is

Concrete is a composite material made from three basic components:

Component	Percentage	Purpose
Cement	10-15%	Binding agent
Aggregates	60-75%	Bulk and strength
Water	15-20%	Activates chemical reaction

Cement is the "glue"—usually Portland cement, a fine gray powder made from limestone and clay.

Aggregates provide strength and volume:

• Fine aggregate (sand): Fills gaps between larger stones
• Coarse aggregate (gravel): Provides bulk strength

Water triggers the chemical reaction that transforms the mixture from a workable paste into hard stone.

The Standard Mix Ratio

The traditional ratio is 1:2:3—one part cement, two parts sand, three parts gravel (by volume).

When you buy pre-mixed bags at the store, these proportions are already measured and blended. You just add water.

Concrete vs Cement

This is the most common misconception. Cement is not concrete.

Term	What It Is	Example
Cement	Binding ingredient	Portland cement powder
Concrete	Finished product	Your patio, driveway

Think of it like baking:

• Flour is to bread as cement is to concrete
• Flour is essential, but you wouldn't call bread "flour"

When shopping, you want concrete mix, not cement. "Cement mix" is just cement powder—you'd need to add your own sand and gravel.

For a detailed comparison, see concrete vs cement.

How Concrete Cures

This is the most important concept to understand: concrete cures, it doesn't dry.

Hydration, Not Evaporation

When you add water to cement, a chemical reaction called hydration begins. The water doesn't evaporate—it chemically bonds with cement particles to form calcium silicate hydrate crystals.

These crystals are what make concrete hard and strong.

What this means practically:

Common Belief	Reality
"Let it dry out"	Actually weakens concrete
"More water makes it easier"	More water = weaker concrete
"It's cured when dry"	Strength continues building for weeks
"Rain is bad"	Light rain after initial set is fine (even beneficial)

The Curing Timeline

Time	Strength	What You Can Do
0-24 hours	~10-15%	Nothing—don't touch
24-48 hours	~20-25%	Walk on it (carefully)
7 days	~65-70%	Light use, no vehicles
28 days	~100%	Full design strength
90+ days	110%+	Continues gaining slowly

The 28-day rule is industry standard. Concrete reaches its specified strength (like 4,000 PSI) at 28 days under normal conditions. It continues strengthening after that, but 28 days is the benchmark.

Why Keeping Concrete Moist Matters

Since curing is a chemical reaction requiring water, keeping concrete moist during the first 7 days helps it develop maximum strength. Concrete that dries too fast can be 20-40% weaker than properly cured concrete.

Curing methods:

• Spray with water 2-3 times daily
• Cover with plastic sheeting
• Apply curing compound (forms moisture barrier)

For complete curing information, see how long concrete takes to cure.

Types of Concrete Mixes

Different projects need different mixes. Here's what you'll find at the store:

Standard/All-Purpose Mix

• PSI: 3,000-4,000
• Use for: Patios, sidewalks, general projects
• Brands: Quikrete Original, Sakrete Concrete Mix

High-Strength Mix

• PSI: 5,000+
• Use for: Driveways, footings, structural applications
• Brands: Quikrete 5000, Sakrete High Strength

Fast-Setting Mix

• PSI: 4,000
• Sets in: 20-40 minutes
• Use for: Fence posts, quick repairs
• Brands: Quikrete Fast-Setting, Sakrete Fast-Set

Crack-Resistant Mix

• PSI: 4,000
• Contains: Fiber reinforcement
• Use for: Large slabs, areas with soil movement
• Brands: Quikrete Crack Resistant

For detailed comparison, see types of concrete.

Understanding PSI Ratings

PSI (pounds per square inch) measures compressive strength—how much weight concrete can bear before failing.

Common PSI Ratings

PSI	Classification	Appropriate For
2,500	Low strength	Footings, fill (not recommended for slabs)
3,000	Standard	Patios, sidewalks, residential floors
3,500	Enhanced	General residential use
4,000	High	Driveways, garages, most applications
5,000	Very high	Heavy loads, commercial
6,000+	Industrial	Commercial, structural

Which PSI Do You Need?

Project	Minimum PSI	Recommended PSI
Patio	3,000	3,500-4,000
Sidewalk	3,000	3,500-4,000
Driveway	3,500	4,000-5,000
Garage floor	3,500	4,000
Foundation footing	2,500	3,000-3,500

Rule of thumb: 4,000 PSI handles almost any residential project. The cost difference is minimal—buy higher PSI unless budget is extremely tight.

Ready-Mix vs Bagged

You have two options for getting concrete: bags you mix yourself or ready-mix delivered by truck.

Bagged Concrete

How it works: Buy bags (40, 60, or 80 lbs), add water, mix in wheelbarrow or mixer.

Pros	Cons
No minimum order	Labor intensive
Work at your pace	More expensive per yard
Available anytime	Inconsistent batches possible
No scheduling needed	Physical work

Cost: ~$290 per cubic yard (using 80-lb bags at $6.50 each)

Ready-Mix Delivery

How it works: Concrete truck delivers pre-mixed concrete. You pour and finish.

Pros	Cons
Consistent quality	Minimum order (usually 1 yard)
Much less labor	Time pressure (60-90 min to finish)
Cheaper per yard	Delivery fees
Faster for large jobs	Requires helpers

Cost: $125-175 per cubic yard + $50-100 delivery

The Decision Matrix

Project Size	Bags Needed	Recommendation
Under 0.5 yards	Under 25	Bags
0.5-1 yard	25-45	Either (consider ready-mix)
1-2 yards	45-90	Ready-mix
Over 2 yards	90+	Definitely ready-mix

For complete comparison, see ready-mix vs bagged concrete.

What's a Yard of Concrete

Concrete is sold by the cubic yard. Understanding this measurement prevents ordering errors.

The Basics

One cubic yard = 27 cubic feet (3 ft × 3 ft × 3 ft)

Visualize it: About the size of a washer and dryer stacked together.

How Far Does a Yard Go?

Thickness	Coverage per Yard
4 inches	81 square feet
5 inches	65 square feet
6 inches	54 square feet

Example: A 10×10 patio at 4 inches thick needs about 1.2 cubic yards.

Bags to Yards Conversion

Bag Size	Bags per Cubic Yard
40 lb	90 bags
60 lb	60 bags
80 lb	45 bags

For detailed explanations, see what is a yard of concrete.

Concrete Weight

Concrete is heavy. Understanding weight helps with transport planning and structural considerations.

Weight Reference

Volume	Approximate Weight
1 cubic yard	4,000 lbs
1 cubic foot	150 lbs
80-lb bag (dry)	80 lbs
80-lb bag (mixed)	~86 lbs

Practical Implications

Pickup truck capacity: Most pickups can carry 1,000-2,000 lbs. That's roughly 12-25 bags of 80-lb concrete—less than one cubic yard.

Wheelbarrow loads: A full wheelbarrow of concrete weighs 400-600 lbs. Moving a yard of concrete means 7-10 very heavy wheelbarrow loads.

For complete weight information, see concrete weight.

Key Terms Glossary

Term	Definition
Aggregate	Sand and gravel in concrete mix
Air entrainment	Tiny air bubbles added to resist freeze-thaw
Bleed water	Water that rises to surface after pouring
Bull float	Large flat tool for initial smoothing
Control joint	Groove cut to control where concrete cracks
Curing	Chemical hardening process (not drying)
Edger	Tool that creates rounded edges
Expansion joint	Compressible material separating slabs
Finishing	Smoothing and texturing surface
Hydration	Chemical reaction that hardens concrete
Portland cement	Most common cement type
PSI	Pounds per square inch (strength measure)
Ready-mix	Factory-mixed concrete delivered by truck
Rebar	Steel reinforcing bars
Screed	Straight board used to level concrete
Slump	Measure of concrete workability/fluidity
Wire mesh	Welded steel grid for reinforcement

Key Properties

Understanding these properties helps you make better decisions:

Strength

Measured in PSI. Higher PSI = more weight capacity. Determined by:

• Mix ratio (cement content)
• Water-to-cement ratio (less water = stronger)
• Curing conditions (moist curing = stronger)
• Age (continues gaining strength)

Workability

How easy concrete is to pour and shape. Affected by:

• Water content: More water = more workable, but weaker
• Slump: Industry measure of workability (4-5 inch typical)
• Temperature: Hot weather reduces working time

Durability

How well concrete resists weather, chemicals, and wear. Improved by:

• Proper curing
• Air entrainment (for freeze-thaw)
• Appropriate PSI for use
• Surface sealing (optional)

Frequently Asked Questions

What's the difference between concrete and cement?

Cement is an ingredient in concrete. Concrete is the final product: cement + sand + gravel + water. Think of cement as flour and concrete as bread—you wouldn't call bread "flour." When buying at the store, look for "concrete mix," not "cement."

How long does concrete take to cure?

Concrete reaches about 70% strength at 7 days and full design strength (like 4,000 PSI) at 28 days. You can walk on it after 24-48 hours, but wait 7 days for light use and 28 days before driving vehicles on driveways.

What PSI concrete do I need?

4,000 PSI is the safe choice for almost any residential project. Use 3,000-3,500 PSI for patios and sidewalks if budget is tight. Use 4,000-5,000 PSI for driveways and areas bearing heavy loads.

How heavy is concrete?

Approximately 150 pounds per cubic foot or 4,000 pounds per cubic yard. An 80-lb bag yields about 0.6 cubic feet when mixed. This means a standard pickup truck can only carry about half a cubic yard at most.

Can you pour concrete in cold weather?

Yes, but with precautions. Concrete cures slowly below 50°F and can freeze (ruining it) below 30°F. In cold weather: use hot water for mixing, insulate forms, and cover with insulating blankets. Avoid pouring if temperatures will drop below 30°F within 48 hours.

Key Takeaways

1. Concrete ≠ Cement. Cement is an ingredient in concrete.

2. Concrete cures, it doesn't dry. Keep it moist for stronger results.

3. 28 days for full strength. Don't rush using it, especially driveways.

4. 4,000 PSI handles most projects. Don't overthink PSI selection.

5. More water = weaker concrete. Use only what's needed for workability.

6. Measure twice, pour once. Concrete mistakes are expensive to fix.

Next Steps

Now that you understand the basics:

1. Plan your project: Complete Concrete Guide
2. Calculate quantities: Concrete Calculator
3. Estimate costs: Concrete Cost Calculator
4. Compare products: Quikrete vs Sakrete
5. Browse all resources: Concrete Guides Hub