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Performing a concrete slump test is a method to determine the consistency or viscosity of fresh concrete intended for construction. The test determines how quickly the concrete can be mixed, moved, and shaped into the required design.
Regular and periodic concrete slump tests are crucial in construction projects to ensure the produced fresh concrete meets the required consistency. Additionally, these tests help manage the amount of water and additives used during concrete mixing, contributing to the production of high-quality, strong, efficient, and safe concrete in construction projects.
Essentially, three types of slump exist: True, which denotes a uniform drop in concrete mass without disintegration; Shear, indicating lack of cohesiveness and susceptibility to segregation and bleeding, detrimental to concrete’s longevity; Collapse, signaling excessive moisture in the concrete mix, making it harsh and lean.
Concrete Slump Test Procedure
The mold for the concrete Slump test is a cone with a height of 300 mm (12 inches). The base measures 200 mm in diameter and has a smaller hole at the top of 100 mm (4 in). The base is set on a smooth surface, and the container is filled with concrete in three levels, whose workability will be checked.
Workers heat each layer 25 times using a typical 16 mm (5/8 in) diameter steel rod with a rounded end. When filling the mold with concrete, they level the top surface by striking it off (leveling with the mold top aperture) using a screening and rolling motion with the temping rod. They tightly hold the mold against its base during the procedure to prevent movement caused by the pouring of concrete, which they achieve by using handles or footrests brazed to the mold.
Immediately after finishing the filling and leveling of the concrete, workers slowly and carefully remove the cone vertically; this action causes unsupported concrete to slump. Slump refers to the drop in height of the center of the slumped concrete.
Workers measure the slump by placing the cone next to the slumped concrete and positioning the temping rod over the cone so that it extends over the slumped concrete. The scale indicates the drop in height from concrete to mold, with measurements typically taken to the closest 5 mm (1/4 inch).