Concrete aggregate behavior changes dramatically with temperature fluctuations, creating expansion and contraction forces that stress concrete structures throughout seasonal cycles. Understanding how different aggregate types respond to temperature changes helps construction professionals select appropriate materials and predict performance issues before they compromise structural integrity.
This technical guide explores the science of aggregate thermal expansion, seasonal temperature effects on concrete types, and strategies for managing temperature-driven stress in concrete structures.
The Physics of Aggregate Expansion
All materials expand when heated and contract when cooled. For concrete aggregate, this thermal movement follows predictable patterns but varies significantly based on mineral composition:
Coefficient of Thermal Expansion (CTE)
Each aggregate type has a characteristic CTE measured in microstrain per degree Fahrenheit (με/°F):
Limestone aggregates: 3.2-4.7 με/°F
Granite aggregates: 4.4-5.3 με/°F
Basalt aggregates: 4.2-5.1 με/°F
Quartzite aggregates: 6.6-7.4 με/°F
Sandstone aggregates: 5.8-6.9 με/°F
For reference, concrete paste (the cement and water mixture) typically exhibits CTE of 6.0-8.0 με/°F, depending on water-cement ratio and admixtures.
What These Numbers Mean
A concrete slab containing limestone aggregate with a CTE of 4.0 με/°F will experience:
50°F temperature change: 200 microstrain (0.02% length change)
100°F temperature change: 400 microstrain (0.04% length change)
For a 100-foot concrete slab, this translates to:
- 50°F change: 0.24 inches of movement
- 100°F change: 0.48 inches of movement
These movements create substantial internal stresses when restrained by foundations, adjacent structures, or internal reinforcement.
Seasonal Temperature Cycles and Aggregate Stress
Fall and spring create the most challenging conditions for concrete aggregate systems:
Daily Temperature Swings
Fall weather brings dramatic temperature variations:
Sunny October day: Surface temperatures may range from 35°F at dawn to 75°F in afternoon sun—a 40°F swing creating significant expansion and contraction.
Clear night cooling: Rapid temperature drops after sunset create thermal shock, with surface concrete cooling faster than interior mass.
Freeze-thaw initiation: Fall represents the transition to freeze-thaw cycling, where moisture in concrete pores freezes and expands, creating additional stress beyond thermal expansion.
Seasonal Cumulative Effects
Summer to Winter Transition: A concrete structure heated to 110°F in August cooling to -10°F in January experiences a 120°F temperature change. For a 100-foot slab with granite aggregate, this creates nearly 0.6 inches of potential movement.
Differential Expansion: Surface concrete responds quickly to temperature changes while mass concrete changes temperature slowly. This creates internal stress gradients even without external restraint.
Moisture and Temperature Interaction: Fall combines cooling temperatures with increased moisture, amplifying freeze-thaw damage potential when water trapped in aggregate pores freezes and expands.
Aggregate Type Selection and Temperature Performance
Different aggregate types offer varying temperature performance:
Limestone and Dolomite
Thermal Characteristics:
- Low to moderate CTE (3.2-4.7 με/°F)
- Good match with concrete paste thermal behavior
- Excellent dimensional stability
Temperature Performance:
- Minimal differential stress between aggregate and paste
- Reduced cracking from thermal cycling
- Good freeze-thaw resistance when properly air-entrained
Best Applications:
- Structures experiencing wide temperature ranges
- Thin sections prone to thermal stress
- Parking structures and bridge decks
- Regions with significant freeze-thaw cycles
Granite and Basalt
Thermal Characteristics:
- Moderate CTE (4.2-5.3 με/°F)
- Relatively good match with concrete paste
- High strength and durability
Temperature Performance:
- Some differential stress with paste
- Generally good thermal cycling performance
- Variable freeze-thaw resistance depending on porosity
Best Applications:
- Heavy-duty industrial floors
- High-traffic areas requiring wear resistance
- Structural concrete where strength is critical
- Moderate climate regions
Sandstone and Quartzite
Thermal Characteristics:
- High CTE (5.8-7.4 με/°F)
- Often poor match with lower CTE concrete paste
- Variable internal structure
Temperature Performance:
- Significant differential stress with paste
- Higher cracking risk from thermal cycling
- Freeze-thaw vulnerability in porous varieties
Best Applications:
- Mass concrete where thermal gradients are minimal
- Protected interior applications
- Architectural concrete where appearance is primary concern
- Warm climates with minimal freeze-thaw exposure
Recognizing Temperature-Related Aggregate Problems
Fall temperature swings reveal aggregate expansion issues:
Map Cracking (Pattern Cracking)
Appearance: Network of fine cracks resembling a map or alligator skin pattern on concrete surface.
Cause: Differential thermal expansion between aggregate and paste causes debonding at aggregate-paste interface. Repeated thermal cycling propagates cracks outward from aggregate particles.
Timing: Often appears 3-10 years after placement, becoming more visible as seasonal temperature cycles accumulate stress.
Severity Indicators:
- Crack width (cracks wider than 0.020 inches indicate advanced deterioration)
- Crack density (cracks spaced closer than 6 inches suggest significant aggregate-paste incompatibility)
- Crack propagation rate (rapid worsening indicates ongoing thermal stress)
D-Cracking (Durability Cracking)
Appearance: Closely spaced cracks near joints, edges, and corners, forming a “D” pattern when viewed from above.
Cause: Freeze-thaw damage in saturated, porous aggregate particles near concrete surfaces exposed to water. Aggregate particles absorb water, freeze, expand, and crack surrounding paste.
Timing: Typically appears 5-15 years after placement in freeze-thaw climates. Fall moisture increases and winter freezing accelerate deterioration.
Critical Factors:
- Aggregate porosity (higher porosity increases susceptibility)
- Moisture access (edges and joints accumulate water)
- Freeze-thaw cycle frequency (more cycles accelerate damage)
Spalling and Scaling
Appearance: Surface concrete flaking or breaking away, exposing aggregate particles.
Cause: Combined effects of thermal cycling, freeze-thaw damage, and poor aggregate-paste bonding. Temperature-driven expansion of aggregate particles near the surface creates upward pressure, dislodging surface concrete.
Timing: Accelerates during fall and winter months when moisture and temperature cycling combine.
Progression:
- Initial surface crazing (fine cracks)
- Small-scale spalling (dime to quarter-sized areas)
- Large-scale delamination (hand-sized or larger areas)
- Deep spalling exposing coarse aggregate
Testing and Evaluation Methods
Professional assessment of aggregate temperature performance uses:
Laboratory Testing
ASTM C666: Freeze-Thaw Resistance
- Subjects concrete specimens to repeated freeze-thaw cycles
- Measures mass loss and dynamic modulus reduction
- Predicts field durability performance
ASTM C215: Resonant Frequency Testing
- Measures concrete elastic properties
- Detects internal damage from thermal cycling
- Provides non-destructive assessment method
ASTM C856: Petrographic Examination
- Microscopic analysis of concrete samples
- Identifies aggregate types and quality
- Determines extent of thermal damage
Field Testing
Core Sampling: Extract concrete cores to assess:
- Internal cracking patterns
- Aggregate-paste bond quality
- Moisture content and distribution
- Compressive strength retention
Ground Penetrating Radar (GPR):
- Non-destructive subsurface imaging
- Detects delamination and cracking
- Maps moisture accumulation zones
Thermal Imaging:
- Identifies temperature variations
- Locates areas with compromised thermal mass
- Detects moisture intrusion affecting thermal behavior
Preventing Temperature-Induced Aggregate Problems
Design Phase Strategies
Aggregate Selection:
- Match aggregate CTE to anticipated temperature exposure
- Specify freeze-thaw resistant aggregates for exposed concrete
- Require petrographic examination of proposed aggregates
- Prohibit high-porosity aggregates in freeze-thaw environments
Mix Design Optimization:
- Use air-entrainment admixtures (4-7% air content for freeze-thaw zones)
- Optimize water-cement ratio (≤0.45 for exterior exposure)
- Consider supplementary cementitious materials to improve paste quality
- Specify minimum cement content for durability
Joint Spacing:
- Reduce joint spacing in temperature-sensitive applications
- Use closer spacing (10-12 feet) rather than typical 15-20 feet
- Provide adequate relief for thermal movement
Construction Phase Controls
Material Testing:
- Verify aggregate compliance with specifications
- Test actual mix designs for freeze-thaw resistance
- Monitor concrete temperature during placement
- Document ambient conditions during critical pours
Placement Practices:
- Avoid placement during temperature extremes
- Control concrete temperature at placement (50-75°F optimal)
- Ensure proper consolidation around aggregate particles
- Achieve specified finish without overworking surface
Curing Protocols:
- Maintain adequate moisture for minimum 7 days
- Protect from rapid temperature changes during early curing
- Achieve target strength before first freeze exposure
- Apply curing compounds suitable for temperature exposure
Maintenance Strategies
Seasonal Inspection:
- Examine concrete after each winter season
- Document crack development and progression
- Monitor joint performance and movement
- Identify areas requiring repair before damage accelerates
Protective Treatments:
- Apply penetrating sealers to reduce moisture absorption
- Seal cracks before fall to prevent moisture intrusion
- Maintain joint sealants to control water access
- Consider protective coatings for severe exposure conditions
Drainage Management:
- Ensure positive drainage away from concrete
- Maintain drainage systems to prevent water accumulation
- Remove standing water that can freeze against concrete
- Clear ice and snow promptly to minimize freeze-thaw cycles
Regional Considerations for Aggregate Selection
Northern Climates (Severe Freeze-Thaw)
Optimal Aggregate Types:
- Dense limestone with low porosity
- Hard, durable granite with minimal absorption
- Trap rock (basalt) with proven freeze-thaw performance
Critical Specifications:
- Maximum absorption: 1.5-2.0%
- Proven freeze-thaw durability (ASTM C666 durability factor >80 after 300 cycles)
- Low porosity measured by mercury intrusion porosimetry
Annual Temperature Range: -20°F to 90°F (110°F range requiring careful aggregate selection)
Moderate Climates (Occasional Freeze-Thaw)
Acceptable Aggregate Types:
- Most limestone and dolomite
- Granite and trap rock
- Some sandstone varieties with low absorption
Typical Specifications:
- Maximum absorption: 3.0%
- Freeze-thaw testing recommended but less critical
- Focus on aggregate-paste CTE matching
Annual Temperature Range: 15°F to 95°F (80°F range with lower risk)
Southern Climates (Minimal Freeze-Thaw)
Suitable Aggregate Types:
- Wide range including higher-porosity materials
- Local materials often acceptable
- Thermal expansion compatibility more important than freeze-thaw
Key Considerations:
- High temperature differentials (surface vs. mass concrete)
- Thermal shock from rapid cooling (summer thunderstorms)
- Aggregate-paste CTE matching for crack control
Annual Temperature Range: 30°F to 110°F (80°F range but with extreme surface temperatures to 130°F+)
Case Study: Aggregate-Related Failure Analysis
Project: 100,000 sq ft warehouse floor, 8-inch thick concrete slab
Location: Upper Midwest (severe freeze-thaw environment)
Issue: Extensive map cracking and corner spalling appearing 6 years after placement
Investigation Findings:
- Core samples revealed high-absorption sandstone aggregate (4.2% absorption)
- Petrographic examination showed aggregate-paste debonding
- Freeze-thaw testing of concrete achieved only durability factor of 42 (failure)
- Air content measured from cores: 2.1% (specification called for 5-7%)
Root Causes:
- Inappropriate aggregate for freeze-thaw environment
- Inadequate air-entrainment during construction
- High aggregate CTE mismatch with paste
- Poor drainage allowing moisture accumulation at slab edges
Remediation:
- Removed and replaced 15% of slab area (worst deterioration)
- Applied penetrating sealer to remaining slab
- Improved drainage to reduce moisture exposure
- Implemented protective coating system
Cost: $180,000 for remediation vs. $10,000 additional cost for proper aggregate selection during initial construction
Advanced Solutions for Temperature-Sensitive Applications
Fiber Reinforcement
Synthetic or Steel Fibers:
- Improves concrete ductility during thermal cycling
- Reduces crack width from thermal stress
- Provides residual strength after cracking begins
Dosage Rates:
- Synthetic fibers: 3-5 lbs per cubic yard
- Steel fibers: 25-50 lbs per cubic yard
Shrinkage-Compensating Cement
Mechanism: Expands slightly during curing to offset drying shrinkage and some thermal contraction.
Applications:
- Restraint-sensitive applications
- Parking structures and bridge decks
- Industrial floors with minimal joint spacing
Limitations: Does not eliminate thermal movement, only offsets portion of total movement.
Lithium-Based Admixtures
Benefits:
- Reduces alkali-silica reaction (ASR) potential
- Improves paste quality and density
- Can enhance freeze-thaw resistance
Use Cases: When reactive aggregates must be used or aggregate quality is marginal.
The IFTI Approach to Aggregate Assessment
IFTI provides comprehensive aggregate evaluation services:
Pre-Construction Assessment:
- Aggregate source evaluation and testing
- Petrographic analysis of proposed materials
- Thermal expansion testing and compatibility analysis
- Mix design review and optimization recommendations
Construction Phase Support:
- Fresh concrete testing and verification
- Core sampling and strength testing
- Temperature monitoring during placement and curing
- Documentation of compliance with specifications
Existing Structure Evaluation:
- Condition assessment and failure analysis
- Core extraction and laboratory testing
- Thermal imaging and GPR investigation
- Repair and remediation recommendations
Conclusion: Aggregate Selection Matters
Concrete aggregate thermal behavior fundamentally affects long-term concrete performance. Fall’s temperature fluctuations provide a preview of winter’s more severe thermal cycling, making autumn the ideal time to assess existing concrete and plan for new construction.
Proper aggregate selection matched to environmental exposure creates concrete structures that withstand decades of seasonal temperature cycling without significant deterioration. Conversely, inappropriate aggregate choices can lead to premature failure regardless of construction quality.
Contact IFTI for professional aggregate evaluation and concrete assessment. Our materials engineers and certified technicians provide the expertise needed to select appropriate concrete types and aggregates for your specific application and climate conditions.
Temperature changes are inevitable. Aggregate-related failures are preventable with proper material selection and construction practices.