The Penetration Resisting Test
The penetration resistance test is used to measure the water content, the kind and quantity of cementitious material, the admixtures, and the impact of these factors on the concrete’s setting time. It also determines the concrete’s initial and final setting times in laboratories and on project sites. A sample of mortar that has been sieved is used for the test.
The initial setting time of cement is the point at which it starts to become less flexible and harden. But after the concrete totally hardens and loses its flexibility, the final setting time starts. ASTM C403M-16 states that the penetrating resistance of concrete can be used to calculate the starting and final times when it reaches 3.5 MPa and 27.6 MPa, respectively.
Certain elements, such as the fineness of the cement, the amount of salts in the sand, and meteorological conditions, can affect how long concrete takes to set. For example, cement requires 27°C to fully hydrate; however, the low temperatures of winter cause the hydration process to take longer.
Equipment
1. Container
Both the height and the lateral dimension must be at least 150 mm.
2. Needles for Penetration
The bearing surfaces of penetration needles, which are typically attached to the loading device, are 645, 323, 161, 65, 32, and 16 mm2.
3. Mechanism for Loading
It is employed to quantify the amount of force necessary to pierce the needles. The apparatus must have a minimum 600 N capacity and be able to measure the penetrating force with an accuracy of 10 N.
4. Tamping Rod
This is a straight, round steel rod that is about 600 mm long and 16 mm in diameter.
5. The pipet
It is employed to remove bleed water from the test specimen’s surface.
6. Thermometer
The fresh mortar’s temperature must be measured with a thermometer that can reach 60.5°C.
7. Stop Watch
Measuring the time with the stop watch .
Preparations of Sample
1. To conduct tests in the field, take a representative sample of the freshly laid concrete, from which three test specimens will be made.
2. Prepare the concrete and indicate its slump and air content for laboratory tests.
3. The concrete that has been filtered via a 4.75-mm screen will be utilized to prepare the specimens.
4. For each variable under consideration, create at least three distinct concrete batches in order to assess a material’s compliance with performance standards. Set up tests for each batch just once.
5. For additional tests, create three test specimens for each test variable from a single batch of concrete.
6. Note the moment the cement and mixing water make contact for the first time.
7. Using hand techniques, thoroughly mix the mortar on the non-absorptive surface. Determine the mortar’s temperature and note it.
8. Spread the mortar evenly throughout the container or containers.
9. Use one of the following methods to eliminate air pockets from the specimen: shaking the container, rodding the mortar, tapping the sides with the tamping rod, or setting the container on a vibrating table.
10. Lastly, even out the upper surface.
Concrete Setting Time Test Procedures
1. Use a pipet to remove bleed water from the specimen’s surface.
2. Choose the appropriate needle size for the penetration resistance device based on the mortar setting time.
3. Make sure the needle’s bearing surface touches the mortar surface.
4. Lower the device with a consistent, progressive vertical force until the needle pierces the mortar to a depth of 25±2 mm.
5. Record the amount of force required to drive the needle down to a depth of 25±2 mm.
6. Note the load application time, which is the amount of time that has passed when the cement and water first came into contact.
7. Determine the penetration resistance by dividing the force that was registered by the needle’s bearing area.
Precaution for Subsequent Penetration Test
Be cautious not to test further penetration in locations where prior testing have disrupted the mortar. Prior to performing the subsequent test on the sample used for the initial penetration test, the following safety measures must be taken into account.
1. There must be a minimum of 15 mm between needle impressions.
2. There should be a minimum of 25 mm and a maximum of 50 mm of free space between any needle impression and the container’s side, respectively.
3. Conduct the first test on standard concrete mixtures at laboratory temperatures between 20 and 25 °C after 3 to 4 hours have passed since the cement and water first came into contact. Tests should be conducted at intervals of 1.2 to 1 hour.
4. It is recommended to conduct follow-up tests at 1.2-hour intervals after the initial test, for concrete mixtures containing accelerators, after an elapsed time of 1 to 2 hours.
5. In the case of concrete mixtures that contain retarders, the first test may be deferred until four to six hours have passed.
6. Perform a minimum of six penetrations for every time-of-setting test, ensuring that the time intervals are long enough to yield a good penetration resistance against elapsed time curve.
7. Keep testing until one penetration resistance measurement approaches or surpasses 27.6 MPa.
Results of Graphing Tests
The pace of setting can be determined by plotting penetration resistance against elapsed time. Draw the penetration resistance y-axis vs elapsed time x-axis graph using a scale where a distance of at least 15 mm corresponds to each of the values of 3.5 MPa and 1 h. Find the starting and final setting times visually when the penetration resistance reaches 3.5 MPa and 27.6 MPa, respectively.
Source of Error
Results that are not indicative of the concrete sample under examination can be obtained due to a number of causes. To determine which points shouldn’t be included in the data analysis, the operator must use judgment.
1. The bigger particles in the mortar causing interference
2. The penetration zone has sizable voids in it.
3. Interference caused by neighboring penetrations’ impressions.
4. When penetrating, the instrument is not kept perpendicular to the test surface.
5. Mistakes made when interpreting load fluctuations in loading rate.