This article is about ASTM C495 and Standard Test Method for Compressive Strength of Lightweight Insulating Concrete.
aSTM c495 pdf free Download and Technical Guide
ASTM-C495-Free-Download-PdfWhat is ASTM C495?
ASTM C495 is a standard test method that is used to determine the compressive strength of concrete cylinders. The full title of this standard is “Standard Test Method for Compressive Strength of Lightweight Insulating Concrete”.
This test method involves casting cylindrical specimens of lightweight insulating concrete, curing them under specific conditions, and then subjecting them to a compressive load until failure occurs. The compressive strength is then calculated by dividing the maximum load at failure by the cross-sectional area of the cylinder.
ASTM C495 provides a standardized procedure for testing the compressive strength of lightweight insulating concrete, which is commonly used in construction for thermal insulation purposes. This standard can be used by engineers, contractors, and testing laboratories to ensure that the concrete being used in a project meets the necessary strength requirements.
ASTM C495 Sampling
ASTM C495 sampling is a crucial step in the procedure for testing the compressive strength of lightweight insulating concrete. The standard specifies that the sampling should be done in accordance with the applicable provisions of Practice C172, which outlines recommended procedures for sampling fresh concrete.
However, there are some exceptions to be noted while sampling fresh lightweight insulating concrete according to ASTM C495. If the concrete is being pumped, the sample can be taken by filling a bucket of around 10 quarts (9 liters) capacity by passing through the discharge stream of the concrete pump hose being used to place the concrete.
The bucket should be filled at the point of placement of the concrete, and care should be taken to ensure that the sample is representative of the pour, avoiding the beginning or ending of the discharge from the equipment.
Once the sample is obtained, the test specimens should be prepared as described in Section 6 of the standard, by filling them with a scoop of lightweight insulating concrete dipped from the bucket. It’s important to note that the sample should not be remixed before preparing the test specimens.
By following the recommended procedures for sampling, you can ensure that the lightweight insulating concrete samples used for compressive strength testing are representative of the overall mixture, and that the test results accurately reflect the performance of the concrete in the construction project.
ASTM C495 Test Specimens
The following information provides guidelines for preparing and testing lightweight insulating concrete specimens to determine their compressive strength.
To begin, cylindrical test specimens should be used, with a diameter of 3 6 1/16 inches (75 6 1.6 mm) and a length of 6 6 1/8 inches (150 6 3 mm). The base of each specimen should be perpendicular to the longitudinal axis within the limits prescribed in 6.8.
It is recommended to obtain at least four test specimens for compressive strength tests from each sample of lightweight insulating concrete.
When molding the specimens, the concrete should be placed in two approximately equal layers. After placing each layer, tap the sides of the mold lightly with a rubber mallet until the surface of the layer has subsided approximately to a plane. Overfill the mold when placing the second layer but do not rod the concrete.
Immediately after filling the molds, strike off the specimens and cover them in such a manner as to prevent evaporation without marring the surface. If desired, cover the filled mold with a glass or metal plate to obtain a surface that will be suitable for testing without capping and with a minimum of grinding. It is also desirable to place the filled mold in a moist room if one is available. If this is done, protect the surface from dripping water.
It is important to not remove specimens from molds until danger of damage to the specimens has passed. In any event, remove specimens from the molds within 7 days after molding.
For the first 24 hours after molding, maintain the specimens at a temperature of 70 6 10°F (21.1 6 5.5°C). After 24-26 hours, store the specimens in a moist condition at a temperature of 73.4 6 3°F (23.0 6 1.7°C). Do not expose specimens to a stream of running water nor store in water, unless a saturated lime (calcium hydroxide) solution is used. After 7 days, store the specimens at a temperature of 70 6 10°F and a relative humidity of 50 6 30% for 18 days.
After twenty-five days of molding, dry the specimens in an oven at 1406 5°F (60 6 2.8°C) for 3 days. Cool specimens to room temperature and test for compressive strength at an age of 28 days.
Before testing, check the surfaces of the specimen that will be in contact with the bearing surfaces of the testing machine within 0.02 in. (0.5 mm). If the bearing surfaces depart from a plane more than 0.02 in. (0.5 mm), grind them to conform to this tolerance or cap in accordance with Practice C 617. Cap surfaces to be plane within 0.002 in. (0.05 mm). Check the planeness of the bearing surface of the specimen by means of a straightedge and feeler gage, making a minimum of three measurements on different diameters of the specimen. Make sure the surface of the specimen in contact with the lower bearing block of the testing machine does not depart from perpendicularity with the longitudinal axis of the cylinder by more than 1° or the combined departure of the two bearing surfaces from perpendicularity by more than 3°.
To determine the diameter of the specimens, measure two diameters at right angles to each other at about mid-height of the specimen and average them. Use these dimensions in computing the cross-sectional areas. Determine the height of the specimen to the nearest 0.01 in.
ASTM C495 Procedure
To conduct a compressive strength test on concrete cylinders, the following procedure should be followed:
- Specimen Preparation: a. Retrieve the concrete cylinders that have been stored in a moist room at a temperature of 73.4 ± 3°F for 28 days. b. Remove the cylinders from the molds within 7 days of casting. c. Check the surfaces of the specimens to be in contact with the bearing surfaces of the testing machine within 0.02 in. (0.5 mm). If the bearing surfaces depart from a plane more than 0.02 in. (0.5 mm), grind them to conform to this tolerance or cap them in accordance with Practice C 617. d. Determine the diameter and height of the specimens to the nearest 0.01 in. (0.3 mm).
- Placing of Specimen: a. Clean the bearing faces of the upper and lower bearing blocks of the compression test machine and of the test specimen. b. Place the test specimen on the lower bearing block and carefully align the axis of the specimen with the center of thrust of the spherically seated block. c. As the spherically seated block is brought to bear on the specimen, gently rotate its movable portion by hand so that uniform seating is obtained.
- Rate of Loading: a. Continuously apply the load without shock at a constant rate such that the maximum load will be reached in 65 ± 15 s. b. Record the maximum load sustained by the specimen. c. Note the type of failure and the appearance of the concrete.
It is important to follow the procedures carefully and ensure that the equipment used is in good condition to obtain accurate and reliable results.
ASTM C495 Calculation
The calculation to determine the unit compressive strength of the concrete involves dividing the maximum load sustained by the specimen during the compression test by the average cross-sectional area of the specimen. The result is recorded to the nearest 10 psi (69 kPa).
For example, if the maximum load sustained by the specimen is 200,000 pounds and the average cross-sectional area of the specimen is 28.27 square inches, then the unit compressive strength of the concrete would be:
Unit compressive strength = Maximum load / Average cross-sectional area Unit compressive strength = 200,000 / 28.27 Unit compressive strength = 7,072 psi
Therefore, the unit compressive strength of the concrete in this example is 7,070 psi, rounded to the nearest 10 psi.