Concrete durability tests(Initial Surface Absorption Test )
Several tests are conducted to evaluate concrete quality and durability. Initial surface absorption tests are one of these tests. Increasing of concrete permeability will be associated with the ingress of aggressive liquid and gases such as chloride and sulfate. The ingress of chemicals such chloride will result in steel corrosion, and this, in turn, will reduce the durability of concrete. Initial surface absorption test measures the rate of water flows into concrete per unit of area for a specified duration at a constant applied head.
Various factors could affect the test result such as moisture condition, concrete mix, aggregate, surface finish and type, age of concrete, cracking, water type, and temperature. Figure 1 showing the apparatus used in the initial surface absorption test.
- Test at least three concrete samples or three locations. Selected concrete surface shall not contain cracks, oil, or grease.
- Oven-dried specimen: place the specimen in the oven (105 c) until it reaches the constant mass. Once the specimen reaches a constant mass, remove it from oven and put it in the cooling cabinet. The temperature cabinet shall have a temperature similar to room temperature.
- No-oven dried specimen: in laboratory leave the specimen for 48 h at a temperature of 20±2 C. at field protect the concrete surface from water for 48 h and from the sun for 12 h.
- Fix the cap and attach the flexible tube at the inlet and the outlet. The level head of water shall be 180-200 mm, as shown in figure 2. the final configuration of the test shall be as shown in figure 3.
- Close the tap and fill the reservoir with water. The temperature of the water shall be 20 c. Open the valve and allow the water to fill the cap. Remove all trapped air in the cap by pinching the capillary tube. Refill the reservoir to maintain the water head of 180 mm to 220 mm.
- Take the measurement at 10 minutes, 30 minutes, and 1 hour. Lift the capillary tube above the water level to avoid the overflow of water. At the end of specified intervals place the capillary tube horizontally at the same level as the water in the reservoir. Close the tap and allow water to flow to the capillary tube. When the meniscus reaches the scale, start the stopwatch, and measure the number of the division after 5 seconds. Determine the period to estimate the movement of water from table 1.
- Measure the number of scale divisions traversed by water for the period selected from table 1. if the division's measure for 30 seconds or 2 mins multiply the results by 2 or 0.5 respectively to transfer to 1 min period. Record the actual scale unit traversed per minute, which is equal 0.01 times the number of divisions which water traversed for the specified period, and this is the initial surface water absorption ml/(m2.s).