Effects of composition and exposure on the solar reflectance of Portland cement concrete

Technical Report · Fri Dec 21 04:00:00 EST 2001

DOI:https://doi.org/10.2172/820773· OSTI ID:820773

Levinson, Ronnen ^[1]; Akbari, Hashem

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1. LBNL Library

Increasing the solar reflectance (albedo) of a paved surface keeps it cooler in the sun, reducing convection of heat from pavement to air and thereby decreasing the ambient air temperature. Simulations of the influence of pavement albedo on air temperature in Los Angeles predict that increasing the albedo of 1,250 km2 of pavement by 0.25 would save cooling energy worth $15M yr-1, and reduce smog-related medical and lost-work expenses by $76M yr-1. Most sidewalks and a small fraction of roads and parking areas are paved with portland cement concrete, which can be made quite reflective through suitable choice of cement and aggregate. Variations with composition and environmental exposure of the albedos of portland cement concrete pavements were investigated through laboratory fabrication and exposure of 32 mixes of concrete. Twenty-four mixes yielded substandard, ''rough'' concretes due to high, unmet aggregate water demand. The albedos of the remaining eight ''smooth'' concrete mixes ranged from 0.41 to 0.77 (mean 0.59). Simulated weathering, soiling, and abrasion each reduced average concrete albedo (mean decreases 0.06, 0.05, and 0.19, respectively), though some samples became slightly more reflective through weathering or soiling. Simulated rain (wetting) strongly depressed the albedos of concretes (mean decrease 0.23) until their surfaces were dried. Concrete albedo grew as the cement hydration reaction progressed (mean increase 0.08), but stabilized within six weeks of casting. White-cement concretes were on average significantly more reflective than gray-cement concretes. The albedo of the most-reflective white-cement concrete was 0.18 to 0.39 higher than that of the most-reflective gray-cement concrete, depending on state of exposure. Concrete albedo generally correlated with cement albedo and sand albedo, and, after abrasion, with rock albedo. Cement albedo had a disproportionately strong influence on the reflectance of concrete. Efflorescence and surface carbonation whitened some gray-cement mixes.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Assistant Secretary for Energy Efficiency and Renewable Energy. Office of Building Technology, State and Community Programs; Environmental Protection Agency (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 820773
• Report Number(s): LBNL--48334
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
54 ENVIRONMENTAL SCIENCES
CEMENTS
CONCRETES
CONVECTION
ENVIRONMENTAL EXPOSURE
FABRICATION
HEAT EXCHANGERS
HYDRATION
PAVEMENTS
PORTLAND CEMENT
RAIN
SAND
SOLAR REFLECTANCE ALBEDO PORTLAND CEMENT CONCRETE PAVEMENT WEATHERING ULTRAVIOLET LIGHT CONDENSATION SOILING ABRASION WETTING CEMENT AGGREGATE
SUN
WATER REQUIREMENTS
WEATHERING