Concrete Tests and Procedures
Welcome back to our series on concrete testing! In our previous discussion, we delved into the crucial tests performed on fresh concrete to assess its properties and quality during the early stages of construction. Now, we'll shift our focus to the next phase—testing of hardened concrete.
Testing the hardened state of concrete is paramount in ensuring the longevity, structural integrity, and performance of concrete structures over time. A variety of specialized tests are conducted to comprehensively evaluate different aspects of hardened concrete.
In this article, we'll provide a comprehensive overview of the key tests performed on hardened concrete, shedding light on their methodologies, significance, and the relevant ACI (American Concrete Institute) or ASTM (American Society for Testing and Materials) standards that guide these procedures. By understanding these tests and their outcomes, engineers and construction professionals can make well-informed decisions to uphold the quality and durability of their concrete creations.
Without further ado, let's delve into the world of hardened concrete testing and explore the various types of tests that play a vital role in ensuring the reliability of concrete structures.
1. Compressive Strength Test
The compressive strength test evaluates a concrete's ability to withstand axial loads. Cylindrical or cubic specimens are cast from fresh concrete and cured under standard conditions. The specimens are then loaded in a compression testing machine until failure occurs. The maximum load is divided by the cross-sectional area to determine the compressive strength.
Relevant Standard: ASTM C39 / C39M - Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.
2. Flexural Strength Test
The flexural strength test assesses a concrete's bending capability. A beam specimen is prepared and loaded at its center point until failure. The load-deflection relationship is recorded to calculate the flexural strength of the concrete.
Relevant Standard: ASTM C78 / C78M - Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading).
3. Splitting Tensile Strength Test
The splitting tensile strength test evaluates a concrete's tensile strength perpendicular to the loading direction. A cylindrical specimen is loaded diametrically until failure occurs, and the tensile strength is calculated.
Relevant Standard: ASTM C496 / C496M - Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens.
4. Water Absorption Test
The water absorption test determines the porosity of concrete. Dry specimens are weighed, then immersed in water for a specific duration. Afterward, the specimens are re-weighed to determine the water absorption.
Relevant Standard: ASTM C642 - Standard Test Method for Density, Absorption, and Voids in Hardened Concrete.
5. Ultrasonic Pulse Velocity Test
The ultrasonic pulse velocity test assesses concrete uniformity, cracks, and voids using ultrasonic waves. The travel time between transducers is measured to determine wave velocity.
Relevant Standard: ASTM C597 - Standard Test Method for Pulse Velocity Through Concrete.
6. Rebound Hammer Test
The rebound hammer test estimates concrete compressive strength. A rebound hammer is pressed against the concrete surface, and the rebound distance is measured.
Relevant Standard: ASTM C805 / C805M - Standard Test Method for Rebound Number of Hardened Concrete.
7. Chloride Permeability Test
The chloride permeability test evaluates concrete's resistance to chloride ion penetration, which can cause corrosion. Concrete specimens are exposed to chloride solution, and the penetration depth is measured.
Relevant Standard: ASTM C1202 / C1202M - Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration.
8. Rapid Chloride Migration Test
The rapid chloride migration test measures the rate of chloride ion migration through concrete under an electric field.
Relevant Standard: ASTM C1202 / C1202M - Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration.
9. Carbonation Depth Test
The carbonation depth test determines the depth of carbonation in concrete. Freshly broken concrete surfaces are sprayed with phenolphthalein solution, and the depth of color change indicates the carbonation depth.
Relevant Standard: ASTM C1218 - Standard Test Method for Water-Soluble Chloride in Mortar and Concrete.
10. Shrinkage Test
Shrinkage tests assess concrete volume changes due to drying and autogenous shrinkage. Different methods, such as drying shrinkage and length change measurements, are used to measure shrinkage.
11. Permeability Test
The permeability test evaluates concrete's resistance to fluid flow. Methods include constant head and falling head tests.
Relevant Standard: ASTM C1202 / C1202M - Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration.
12. Durability Tests
Durability tests assess concrete performance under specific conditions. For example, freeze-thaw resistance is evaluated using ASTM C666 / C666M, and alkali-aggregate reactivity is assessed using ASTM C1260.
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