Temperature Analysis

Pervious Concrete Pavers (Perco-crete?):

3.1                Introduction:

Tests were performed at Arizona State University?s Solar Laboratory on two pervious concrete pavers during the month of September 2003. Frank Michiels from Michiels International supplied both pavers. The testing consisted of surface temperature measurements of one pervious paver in a dry state, one pervious paver in a wet state and a conventional concrete paver in a dry state. All three pavers were gray in color. Testing was performed on a flat horizontal surface with insulation placed under each paver. Surface temperatures were taken hourly by a Raytek? Ranger Infrared Thermometer; these measurements were taken over several days, however only a representative day is presented here.    

3.2       Test setup:

The following test setup was used for the purpose of measuring the surface temperatures of the paving materials:

bulletThe pavers were placed on 3? rigid insulation.
bulletTwo Perco-crete? pavers were used as samples.
bulletOne of these was wetted once, with approximately 10 fl. ounces (300 ml.) about 10 minutes before measurements were started.
bulletAll the tests were carried out without wetting the sample during the rest of the day.
bulletOne conventional concrete paver was also used, as a control block.
bulletAll the test blocks were kept in full sun, without any shading.

3.3       Test Procedure:

The surface temperatures of the pavers were taken hourly, using a Raytek? Ranger Infrared Thermometer.

The air temperature was taken from the weather station data at the given time. The measurements were carried out for three days to check for consistency of data. Readings were also taken through one night, to analyze the effect of heat loss for the test blocks.

 

Test Setup for Pervious Paving Materials

3.4       Results:

bulletThe Percocrete? wetted block performed considerably better than the Percocrete? dry block as well as the conventional concrete block (dry).
bulletWithin 10 minutes of wetting the block, a Δt of 19°F was recorded (The wetted block was 19°F cooler than the dry block.
bulletThe next hour, a Δt of 27°F was recorded. Subsequently, as the rate of evaporation decreased on account of loss of water, the Δt?s recorded were 16°F, 13°F, 6°F and 4°F; after this, the wetted block consistently recorded 1°F lower than the dry block.
bulletThe Percocrete? dry block recorded surface temperatures that were 1°F-2°F higher than the conventional concrete block, up to 3:00 pm in the afternoon.
bulletAfter 3:00 pm, the difference changed signs and the Percocrete? dry block recorded surface temperatures about 5°F to 3°F lower than the conventional concrete block until 5:00 pm, after which it consistently recorded 1°F lower than the conventional concrete block.

The following graph shows the temperatures recorded for a representative day:

Graph showing surface temperatures of paving materials

3.5                Conclusions:

Percocrete in its wet state significantly depressed surface temperature as compared to the conventional concrete paver. However, in its dry state its performance was only slightly better than the conventional concrete paver. The compressive strength of Percocrete seems to be very good. It is our understanding that percocrete can be easily stained, thus there is a wide range of colors available. In its wet state Percocrete was able to absorb and retain a large quantity of water, which is the reason why it depressed surface temperature so well. It also seemed able to wick water through the material at a rapid rate and no surface ponding was observed. Percocrete seems far superior to the conventional type of pervious concrete paving which use large voids in the material to move water through.

Harvey Bryan, Ph.D.,
Professor of Architecture
School of Architecture
Arizona State University
P.O. Box 871605
Tempe, AZ.  85287-1605
Tel:      (480) 965-6094
Fax:     (480) 965-0968
e-mail:  harvey.bryan@asu.edu