Curling and Warping of Concrete Pavements – Ride Quality Impacts and Mitigation Strategies Thomas Van Dam, Ph.D., P.E. Arizona Pavements/Materials Conference November 18, 2015
Acknowledgements This presentation is partially based on a presentation given at the National Concrete Consortium meeting in Spring 2015 – Presentation made with Tyler Ley of OSU and some of his slides are used in this presentation
And partially based on a presentation given by Jason Weiss of Oregon State University at the Spring 2015 meeting of the National Concrete Consortium
Volumetric Changes in Concrete Pavements Concrete is sensitive to volumetric changes caused by – Changes in moisture including moisture gradient – Changes in temperature including temperature gradient
These changes can impact the ride quality, support by the foundation, and development of stress in jointed concrete pavements
What is Curling/Warping? It is when the edges/corners of a concrete slab deflect upward or downward due to moisture and/or temperature gradient – Curling is commonly related to temperature – Warping is commonly related to moisture
positive curvature
negative curvature
Why Do Pavements Curl/Warp? Curling and warping occur when there is a differential volume change between the top and bottom of the slab This occurs due to temperature or moisture gradients that exist between top and bottom
Moisture
From Tyler Ley
Temperature
dry
cold
wet less dry
less cold
wet
hot
less wet
less hot
Volume Change From Temperature Varies throughout the day – Hotter on top than bottom during the day – Cooler on top than bottom during the night
Important if there is significant temperature gradient from the top to the bottom of a pavement
Volume Change From Temperature Aggregate accounts for about 60 to 75% of the concrete volume – Coefficient of thermal expansion (CTE) of aggregates dominates CTE of concrete • Pure limestone ~ 3 x 10-6 in/in/°F • Quartzite ~ 6.5 x 10-6 in/in/°F
Cement volume – Cement paste CTE ~ 10.5 x 10-6 in/in/°F
The CTE of concrete is dependent on the mixture
Volumetric Changes Due to Moisture Loss of water over time due to evaporation from exposed surface – Overall volume contracts – Bottom of slab remains “wet” under most circumstances
Strains are primarily influenced by the volume and nature of paste porosity
Impact of Pores Gel pores (2 – 5 nm) –Related to paste volume. Big impact on shrinkage as relative humidity is reduced. We have little control on the size of these pores. Capillary pores (5 nm – 10 μm) – Critical to transport properties and strength. Impact on drying shrinkage at high relative humidity ( > 70%). Controlled by w/cm and curing. Entrapped/entrained air – Effect strength and freeze-thaw durability Based on Weiss 2015
As the Cement Hydrates (w/cm = 0.45) Chemical Shrinkage Water/Capillary Pores Gel Water/Pores
Hydration Products
Unhydrated Cement
From Weiss 2015
Taking a Closer Look
From Weiss 2015
Degree of Saturation and Relative Humidity
From Weiss 2015
Shrinkage Mechanism Menisci pull against void walls at air/water interface
From Peter Taylor
Capillary Pores, Drying Rate, and Magnitude of Shrinkage 100% rH
Air
Capillary
Gel
Capillary Pores, Drying Rate, and Magnitude of Shrinkage 90% rH
Air
Capillary
Gel
Capillary Pores, Drying Rate, and Magnitude of Shrinkage 80% rH
Air
Capillary
Gel
Capillary Pores, Drying Rate, and Magnitude of Shrinkage 50% rH
Air
Capillary
Gel
Reversible and Irreversible Shrinkage
From Mindess, Young, and Darwin 2003
Effects of Wetting and Alternate Wetting and Drying
From Kosmatka and Wilson 2011
What Does this Mean? As concrete dries, some of that volume change will never be recovered Rain can reduce moisture gradients but not stop warping Since the pavement dries out faster on the surface this causes upward curvature
Warping from drying not as significant
Warping from drying expected to be significant
Studying Slab Curvature in the Field? Documented by Chang et al. (2010) in FHWA Tech Brief (FHWA-HIF-1-010) Applied to LTPP SPS-2 Site in Arizona by Karamihas and Senn (2012) (FHWA-HRT-12-068) Larger study of LTPP data is underway – Contractor is NCE – Looking at SPS-2 and GPS-3 sites
Let’s Look at One Arizona Section SPS-2 Section 040215 Jointed concrete pavement: 15 ft joint spacing Lane width: 12 ft PCC thickness: 11 inches DGAB Thickness: 6 inches PCC MOR: 550 psi Maximum aggregate size: 0.75 inch Total cementitious content (20% FA): 500 lbs w/cm: 0.47 Average RH = 40% Lots of profile data on this site
IRI Progression for Section 040215
No cracking, faulting, or spalling
Slab Curvature (Section 040215) Slab Width (180 inches)
IRI Progression (Section 040215)
What Can We Do About This? Reduce joint spacing Reduced paste content – Lower cement paste, less shrinkage, less deflection
Internal curing – It may delay the shrinkage
Shrinkage reducing admixtures Diamond grinding ARFC?
Diamond Grinding Removal of thin surface layer of hardened concrete using closely spaced diamond saw blades Results in smooth, level pavement surface Longitudinal texture with desirable friction and low noise characteristics For warping, timing is critical
Diamond Grinding Equipment
Diamond Grinding
Diamond grinding can provide a 65% to 70% improvement over the pre-grind profile!
Noise and Concrete Pavements
Next Generation Concrete Surface
From Rasmussen 2012
Tire/Pavement Noise Reduction Diamond grinding can reduce noise by 5 to 8 dbA on average Removes discrete frequencies that create the whine The next generation concrete surfacecan be as quiet as the quietest AC pavements – Diamond grinding has excellent acoustic durability
Next Generation Concrete Surface
Timing of First Grind?
Is this where we diamond grind
Conclusions Temperature and moisture gradients result in slab curvature – Worse in dry environments
Drying shrinkage is an important driving force for upward curvature of concrete slabs – Reduce paste content
Slab curavature seems to increase to a point and then stops – Diamond grinding will restore serviceability
Questions? Thomas Van Dam
[email protected] 775-527-0690