Scope of Application

Use indoor static pressure molded specimens to determine the permeability coefficient of extruded concrete, thereby assessing the quality of the extruded sidewall concrete.

Operating Instructions

1. Permeability tests are conducted in groups of three specimens, with the constant-head method being commonly used.

2. Two days before the test, the specimen must be properly installed: Place the test container with its open end facing upward on a level surface, insert the shims, then place the specimen inside the container. Fill the gap between the container and the specimen with expansive, fast‑setting cement mortar until it reaches the same height as the specimen.

3. Two days later, install the container holding the test specimen onto the base of the permeameter and connect the water supply line.

Saturation test: Maintain the water head 1 cm above the bottom of the specimen for 10 minutes; then raise the water head by another 1 cm and hold it for 1 minute, repeating this process until the top surface of the soil sample is flush with the water surface.

Determine the head difference between the upstream and downstream based on the design slope, and conduct three-level tests in equal increments within the designed head range. After each level stabilizes, record the seepage flow rate, duration, and water temperature three times, with each recording period lasting at least 10 minutes. Only when the permeability coefficients calculated from the three seepage flow rate measurements are of the same order of magnitude and the differences between them do not exceed 2 × 10⁻⁵ cm/s may the next test level proceed; otherwise, the duration should be extended until the seepage flow reaches a stable state.

Instruments and Equipment

Press or universal testing machine; the distance between the upper and lower platens shall be no less than 40 cm.

Steel test mold: φ150 × 300 mm; the inner walls of the test mold should be coated with a thin layer of mineral oil or release agent, as shown in Figure 1-1.

Steel pressure plate: φ147 mm, 20 mm thick; a handle can be installed in the center, as shown in Figure 1–1.

1. Column: 130 mm high, made of steel pipe with an outer diameter of 130 mm and a wall thickness of 12 mm, as shown in Figure 1-1.

Figure 1-1 Schematic Diagram of Specimen Formation

5. Platform scale: 10 kg, with a graduation value of 5 g.

6. Permeameter: Its structural diagram is shown in Figures 1–2.

7. Other: stopwatches, graduated cylinders, feeding funnels, material‑taking buckets, compaction tools, flat‑mold tools, etc.

Figure 1-2 Schematic Diagram of the Permeameter Structure

Specimen Molding and Curing

1. Sampling: During the construction of the sidewalls, collect approximately 60 kg of the mixed concrete that has not yet been treated with a rapid-setting agent from the discharge port of the concrete mixer and seal it in a container.

2. Immediately transport the collected samples back to the laboratory, thoroughly mix them, and then take no less than 2000 g to determine the moisture content of the mixture.

3. Based on the measured dry density and moisture content at the site, calculate the required mass of mixing material for each specimen according to the volume of the test mold—totaling three samples—which should then be portioned, sealed, and stored for future use.

4. In the weighed 1 portion of the mix, add the rapid-setting agent solution according to the design proportions and quickly mix thoroughly. Then, using a funnel, evenly distribute the uniformly mixed sample into the test mold in two batches. After each batch is added, use a tamping rod to compact the mixture around the sides of the test mold to prevent honeycomb formation along the mold walls. Remove the feeding funnel, level the surface of the sample, and carefully place the steel pressure plate flatly into the test mold.

5. Transfer the test mold containing one batch of mix to the lower platen of the compression testing machine, place a 130 mm high load transfer column on top, and ensure geometric alignment between the upper and lower platens of the compression testing machine, as shown in Figure 9.0.2-1.

6. Start the press and apply load continuously and uniformly at a rate of 0.1 MPa/s until the upper platen of the press is fully in contact with the top surface of the steel sleeve mold. After holding the pressure for 30 seconds, release the load. Remove the extruded specimen from the press and take off the force-transmitting column and the upper platen.

7. Repeat steps 4–6 of this clause to prepare two additional specimens.

8. Transfer the specimens with test molds into a molding chamber maintained at 20°C ± 5°C. After allowing them to stand for 24 hours, remove the test molds, inspect the specimen quality, and assign them unique identification numbers. If any chipped corners or missing pieces exceed 50 g in weight, the specimen shall be discarded and re‑molded.

9 After demolding, place the test specimens in a curing room for curing. The curing method for the test specimens shall be carried out in accordance with Section 4.1 of DL/T 5150—2001.

10. Cure the specimens in a curing room until they reach the specified age, then conduct permeability coefficient tests.

Test Treatment Results

2. For a given hydraulic gradient, the permeability coefficient shall be taken as the average of three test results. The test result shall be the average of the permeability coefficients obtained from three specimens under the design hydraulic gradient. If the ratio of the largest permeability coefficient to the smallest permeability coefficient among the three specimens exceeds 10, the test group must be repeated.

Implementation Standard: DL/T5422-2009