Concrete durability is closely tied to its resistance to abrasion, a process where the surface deteriorates due to various physical impacts. This can include sliding, scraping, percussion, or the abrasive action of materials transported by water.
The impact of abrasion is significant in diverse settings, such as concrete pavements (roads and airfields), industrial floors, railway platforms, dockyards, and walkways. A standard test measures the abrasion loss of a concrete specimen exposed to an abrasive charge, offering insights into its relative resistance.
The test aims to determine the abrasion resistance of concrete under practical conditions. This involves subjecting 10 cm concrete cubes to air-driven silica sand, simulating the effects of abrasion.
The test operates by impinging an abrasive charge on the surface of concrete cubes. The resulting abrasion leads to a measurable loss in the mass of the cubes, termed as concrete abrasion loss.
The scale, with a minimum capacity of 5000 g, plays a crucial role. It should have a permissible variation of 15 g at a load of 5000 g.
This cabinet, detailed in Figure-1, consists of a wooden structure with a tightly closing door. A high carbon steel nozzle, 15 cm in length, is mounted 50.02 cm above the concrete surface. An annular copper or brass air tube, with specific dimensions, is integrated to ensure precision.
Figure-2 illustrates a conical galvanized iron hopper positioned atop the cabinet. It securely stores the sand charge pushed by air pressure. The nozzle assembly is connected to a pressure gauge, ensuring accurate measurement of air pressure supplied by a compressor.
The abrasive charge, driven by air pressure, conforms to specific standards and is sieved for optimal performance. Charges can be reused after passing through a 0.50 mm IS sieve.
The abrasion loss of concrete is determined under specific conditions, including an operating air pressure of 0.14 N/mm2, a defined abrasive charge, and a set quantity of charge (4000 g).
Prior to testing, 10 cm concrete cube specimens, cured for 28 days, are placed in an oven and rubbed with emery paper to remove laitance and expose aggregate grains.
The dry specimen is placed on the carrier, and the nozzle is positioned at the middle of one face. After exposing the specimen to the sand blast, the cradle is moved slowly between fixed points. The test is repeated on all four vertical surfaces, allowing mass loss calculation for each.
Test Calculation: Quantifying Mass Loss
The loss in mass is calculated as the difference between the mass before and after each test on one surface, providing a quantitative measure of abrasion.
Different categories of concrete surfacing are suggested to adhere to maximum abrasion loss values, offering broad guidance for durability.