The slump test is a common and standard way of measuring workability and consistency in concrete. It can be performed in the laboratory or on site using a simple and inexpensive device known as the slump cone.
Several factors affect the slump of concrete: The fineness and distribution of aggregates, the moisture content of the mix, grading of aggregate, dosage of water reducing agents, super plasticizer admixtures and the time since the concrete was mixed. The time and method of testing is also a factor.
Slump values range from nearly zero, which means that the concrete is stiff and has almost no workability, to a degree where it is so wet and flowable that it collapses when removed from an inverted 12-inch-tall cone. The ideal slump is somewhere in between these two extremes, providing enough workability for easy placing and finishing but also having adequate cohesion to prevent segregation and loss of strength.
A Slump Cone is a frustum of a cone made from steel or plastic that is used to test the workability and consistency of concrete. The test involves filling the slump cone with concrete, removing it and taking a measurement between the top of the cone and the top of the concrete mass after it has slumped.
A concrete mass that has collapsed completely is called a collapse slump, while a slump where one side of the mass has dropped is called a shear slump. The shear slump indicates that the result is incomplete and that concrete needs to be retested.