PERMEABILITY OR WATER FLOW OF HOT MIX ASPHALT

Transcription

1 Test Procedure for PERMEABILITY OR WATER FLOW OF HOT MIX ASPHALT Texas Department of Transportation TxDOT Designation: Tex-246-F Effective Dates: November 2004 April SCOPE 1.1 Use this test procedure to evaluate the permeability of Permeable Friction Course (PFC) hot mix asphalt. High Permeability of PFC mixtures is critical, as the primary purpose of the use of PFC is to drain water off the pavement surface to reduce splash & spray and hydroplaning to improve the wet pavement friction. There are two parts to this test procedure Part I is an empirical field procedure measuring permeability or water flow rate as water channels onto the pavement surface with the use of a cylindrical, permeameter type device Part II is a procedure performed in the laboratory to evaluate the permeability of laboratory compacted specimens. 1.2 The values given in parentheses (if provided) are not standard and may not be exact mathematical conversions. Use each system of units separately. Combining values from the two systems may result in nonconformance with the standard. PART I TIME OF WATER FLOW OF COMPACTED HOT MIX ASPHALT PAVEMENT 2. SCOPE 2.1 Use this empirical test procedure for PFC pavements under construction or on PFC roadways already constructed to test and verify that the compacted mixture has adequate permeability. 3. APPARATUS 3.1 Cylindrical field permeameter, used to channel water onto the pavement surface, equipped with a pipette graduated in divisions of 1.0 in. (25mm) (See Figure 1). 3.2 Stopwatch or timing device, used to record the time of travel of water in the pipette graduated in divisions of 1.0 seconds. CONSTRUCTION DIVISION /04 04/09

2 3.3 Plumber s putty, used to seal the field permeameter to the pavement surface. 4. PROCEDURE 4.1 Select an area of the compacted PFC hot mix asphalt pavement after it cools down immediately following roller compaction or of any roadway already constructed. Remove any debris on the pavement surface that can hinder the sealing of the permeameter to the surface of the mat. 4.2 Turn the permeameter upside down, so that the bottom of the outer circular base ring is facing upwards then place a ring of plumber s putty onto the surface of the outer circular base ring. Use an adequate amount to create a watertight seal between the permeameter and the pavement surface. 4.3 Turn the permeameter upside down and push it onto the pavement surface. Use enough force to create a watertight seal between the permeameter and the pavement surface where the plumber s putty penetrates the surface voids of the pavement surface. 4.4 Trim and remove any excess plumber s putty inside the permeameter. 4.5 Push on the excess plumber s putty outside the permeameter with the use of a thumb or finger against the outer circular base ring to tighten the seal between the pavement surface and permeameter. 4.6 Fill the permeameter with water approximately 1 2 in. (25 50 mm) above the top marking on the pipette. 4.7 Start the timing device when the water level reaches the top marking on the pipette. 4.8 Stop the timing device when the water level reaches the bottom marking on the pipette. 4.9 Record the time the water traveled from the top marking on the pipette to the bottom marking on the pipette. Typical range normally less than 20 seconds for newly constructed PFC mixtures. CONSTRUCTION DIVISION /04 04/09

3 Figure 1 Field Permeameter Used to Measure Water Flow Rate PART II LABORATORY WATER FLOW RATE 5. SCOPE 5.1 Use this test procedure to measure the time of water flow through laboratory compacted PFC specimens. 6. APPARATUS 6.1 Cylindrical laboratory permeameter, used to direct water through a laboratory compacted specimen, equipped with a graduated pipette in divisions of 1.0 in. (See Figure 1). 6.2 Stopwatch or timing device, used to record the time of travel of water in the pipette graduated in divisions of 1.0 seconds. CONSTRUCTION DIVISION /04 04/09

4 7. SPECIMEN 7.1 Laboratory Molded Specimen: Prepare in accordance with Tex-205-F and Tex-241-F, with a diameter of 6 in. (152 mm) and a height of approximately 4.5 in. (115 mm). 7.2 Core Specimen: With a diameter of 6 in. (152 mm) and height no greater than 4.5 in. (115 mm). 8. PROCEDURE 8.1 Place test specimen in the cylindrical laboratory permeameter. Figure 2 is a drawing of the permeameter used for laboratory testing. 8.2 Secure rubber clamps around the permeameter at the top and bottom edges of the test specimen Place the clamps such that the top and bottom edges are approximately in the middle of the location of the clamps Tightly secure the clamps such that water does not flow around the test specimen. Water must flow through the test specimen. 8.3 Fill the permeameter with water approximately 1 2 in. above the top marking on the pipette. 8.4 Start the timing device when the water level reaches the top marking on the pipette. 8.5 Stop the timing device when the water level reaches the bottom marking on the pipette. 8.6 Record the time the water traveled from the top marking on the pipette to the bottom marking on the pipette. CONSTRUCTION DIVISION /04 04/09

5 Figure 2 Laboratory Permeameter Used to Measure Water Flow Rate CONSTRUCTION DIVISION /04 04/09