Concrete Admixtures: What They Are and When You Need Them

What Are Concrete Admixtures?

Admixtures are ingredients added to concrete beyond the basic mix of cement, water, sand, and gravel. They modify how concrete behaves during mixing, placement, or after it hardens. Think of them as performance enhancers—each one solves a specific problem.

Admixtures aren't optional extras for fancy projects. Many are standard practice:

• Air entrainment: Required in freeze-thaw climates
• Fiber reinforcement: Standard for driveways and patios
• Water reducers: Used in most commercial concrete

The 6 Main Types of Admixtures

1. Accelerators (Speed Up Curing)

Accelerators make concrete set faster. They're used when you need to finish quickly or when cold weather would slow normal curing.

When to use:

• Cold weather pours (below 50°F)
• When forms need to be removed quickly
• Fast-track construction schedules
• Repair work that needs quick turnaround

Common types:

• Calcium chloride: Most effective, but causes rebar corrosion—not for reinforced concrete
• Non-chloride accelerators: Safer for steel-reinforced work

Cost: $3-$8 per cubic yard

2. Retarders (Slow Down Curing)

Retarders delay setting time. They're essential when concrete needs to stay workable longer—hot weather, long hauls, or complex pours.

When to use:

• Hot weather pours (above 85°F)
• Long distance from batch plant
• Large pours that take hours to place
• Decorative work requiring extra finishing time

How it works: Retarders slow the hydration reaction between cement and water, giving you 1-3 extra hours of working time.

Cost: $4-$10 per cubic yard

3. Water Reducers (Plasticizers)

Water reducers let you use less water while maintaining workability. Less water means stronger, more durable concrete.

Why water content matters:

• More water = easier to work but weaker concrete
• Less water = stronger concrete but harder to place
• Water reducers give you both: easy placement AND strength

Types:

• Normal water reducers: Reduce water 5-10%
• Mid-range water reducers: Reduce water 10-15%
• High-range water reducers (superplasticizers): Reduce water 20-30%

Cost: $5-$15 per cubic yard depending on type

4. Air Entrainers (Freeze-Thaw Protection)

Air entrainers create microscopic air bubbles throughout the concrete. These bubbles give water room to expand when it freezes, preventing cracking and surface scaling.

When required:

• Any exterior concrete in freeze-thaw climates
• Driveways, patios, sidewalks in cold regions
• Any concrete exposed to deicing salts

Target air content: 5-7% for exterior flatwork

Cost: $2-$5 per cubic yard (often included in standard exterior mixes)

5. Fiber Reinforcement

Fibers are mixed into concrete to control cracking. They don't replace structural steel but significantly reduce shrinkage cracks.

Types:

• Synthetic fibers (polypropylene): Most common, controls plastic shrinkage cracks
• Steel fibers: Adds structural capacity, used in industrial floors
• Glass fibers: Specialty applications, decorative panels

When to use:

• Driveways and patios (standard practice)
• Slabs on grade
• Anywhere crack control matters

Cost: $3-$6 per cubic yard for synthetic; $15-$30 for steel fibers

6. Corrosion Inhibitors

These protect reinforcing steel from rust. Essential for concrete exposed to salt—coastal areas, parking structures, bridges.

When to use:

• Coastal construction
• Parking garages with salt exposure
• Bridge decks
• Any reinforced concrete near saltwater

Cost: $10-$25 per cubic yard

Admixture Combinations for Common Projects

Residential Driveway (Standard)

• Air entrainment (freeze-thaw protection)
• Synthetic fiber (crack control)
• Cost: ~$8-$12 per yard additional

Summer Pour (Hot Weather)

• Retarder (extend working time)
• Water reducer (maintain strength)
• Air entrainment
• Cost: ~$15-$20 per yard additional

Winter Pour (Cold Weather)

• Accelerator (faster set)
• Air entrainment
• Hot water in mix
• Cost: ~$10-$15 per yard additional

High-Performance Commercial

• High-range water reducer
• Corrosion inhibitor (if reinforced)
• Air entrainment
• Cost: ~$25-$40 per yard additional

How to Order Concrete with Admixtures

When ordering from a ready-mix plant, specify:

1. PSI strength: "4000 PSI"
2. Air content: "6% air" (for exterior)
3. Admixtures needed: "with fiber" or "with retarder"
4. Slump: How fluid you want it (4-5 inches typical)

Example order: "4000 PSI, 6% air, fiber mesh, 4-inch slump"

Can You Add Admixtures On-Site?

Some admixtures can be added at the job site, but it's not ideal:

• Water reducers: Can be added on-site by the driver
• Retarders: Can be added if concrete is stiffening
• Accelerators: Sometimes added in cold weather
• Fibers: Should be batched at plant for even distribution
• Air entrainment: Must be batched at plant

Plant-batched admixtures are more accurate and consistent. On-site additions are for adjustments, not primary dosing.

Common Admixture Mistakes

Adding Water Instead of Plasticizer

When concrete is too stiff, the temptation is to add water. This destroys strength. Always use water reducer or plasticizer to improve workability without sacrificing PSI.

Skipping Air Entrainment in Cold Climates

Non-air-entrained concrete will scale and spall after a few freeze-thaw cycles. If you're in a cold climate, air entrainment isn't optional—it's required.

Using Calcium Chloride with Rebar

Calcium chloride accelerator causes steel corrosion. If your concrete has rebar, use non-chloride accelerators only.

Over-Retarding in Decorative Work

Too much retarder can delay finishing for hours and cause surface defects. Start with minimum dosage and adjust.

The Bottom Line

Admixtures aren't exotic additives—they're standard tools that make concrete perform better. For most residential work, you want air entrainment (freeze protection) and fiber (crack control). For special conditions—hot weather, cold weather, long pours—specify the appropriate admixture.

Always discuss admixtures with your ready-mix supplier. They know local conditions and can recommend the right combination for your project.

Need concrete with the right admixture package? Contact Local Concrete Contractor. We specify the correct mix for your conditions—not just the cheapest option.