Concrete Workability

Workability Test Methods for Self-Compacting Concrete

Self-compacting concrete (also self-leveling, super workable, or self-consolidating concrete) presents new challenges for the measurement of workability. Since self-compacting concrete is capable of flowing readily under its own weight, its yield value is near zero. Therefore, in measuring the workability of self-compacting concrete, yield stress is a less important parameter than it is for conventional concrete. Although the yield stress of self-compacting concrete is still evaluated, other properties related to plastic viscosity and segregation resistance must also be examined.

Since, at the time of this writing, self-compacting concrete remains a nascent technology with limited widespread use, particularly in the Unites States, no tests have been formally standardized, although several tests are finding widespread use. Since there is generally no agreement on dimensions and materials for the devices described below, the tests cannot beeasily specified. It must be noted here that self-compacting concrete, in contrast to conventional concrete, is a proprietary, engineered product and not a commodity product. As such, it is more likely to be the subject of performance-based specifications. Researchers studying the use selfcompacting concrete have developed laboratory tests to understand more fully the movement and consolidation of self-compacting concrete. Such laboratory experiments, like the one presented by Tanaka et al. (1993), are typically intended solely for research and are not reported in this document.

Workability tests for self-compacting concrete can be broadly split into three categories: filling ability tests, passing ability tests, and segregation resistance tests. Each test described below fits into one or more of these categories. In accordance with the NIST classification scheme, the tests for self-compacting concrete typically fit into the confined flow and free flow test categories. As previously discussed, many rotational rheometers are capable of measuring selfcompacting concrete. In addition to the test methods described below, the free orifice (orimet) test can be used for self-compacting concrete.

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