ASTM C805/C805M:13a pdf free download – Standard Test Method for Rebound Number of Hardened Concrete.
7.4 Fot readings to be compared, the direction of impact, horitontal, downward, upward, or at another angle, must be the same or established correction factors shall be applied to the readings.
7.5 Do not conduct tests directly over reinforcing bars with cover less than 20 mm 10.75 in.I.
Nota 10—The locatioii of reinhinenient may be established using reinforcement locators or metal detectors. Follow the manufacturer’s insLrucliuns fur proper operation of such des’ ices.
8. Procedure
8.1 I-fold the instrument firmly so that the plunger is perpendicular to the test surface. Record the orientation of the instrument with respect to horizontal to the nearest 45 degree increment. Use a positive angle if the instrument points upward and a negative angle if it points downward with respect to horizontal during testing (see Note II). Gradually push the instrument toward the test surface until the hammer impacts. After impact, maintain pressure Ofl the instrument and, if necessary, depress the button on the side of the instrument to lock the plunger in its retracted position. Read and record the rebound number to the nearest whole number. Take ten readings from each test area. The distances between impact points shall be at least 25 mm [I in.I, and the distance between impact points and edges of the member shall be at least 50 mm 12 in.I. Examine the impression made on the surface after impact. and if the impact crushes or breaks through a near- surface air void disregard the reading and take another reading.
Noii ti—Digital angk gages are available that can be attached to the body of the instrument to allow quick measurelitent of the angle ‘ith respect to horizontal. The recorded orientation wout4J be 0 degrees horizontal), ±45 degrees (inclined), or 90 (vertical). For esample. if the instrument points senically down during a test, thc angle would he reported as —90 degrees. If the angle is measured to hc 55 degrees upward from horizontal, the recorded angle to the nearest 45 degree increment would be +45 degrees.
9. Calculation
9.1 Discard readings ditiering from the average of lO readings by more than 6 units and determine the average of the remaining readings. If more than 2 readings differ from the average by 6 units, discard the entire set of readings and determine rebound numbers at 10 new locations within the test area.
9.2 If necessary, apply the correction factor to the average rebound number so that the rebound number is for a horizontal orientation of the hammer. Interpolation is permitted if corrections factors are not given for ± 45 degrees.