What test is commonly used on-site to assess the workability (consistency) of freshly mixed concrete?

• A. Slump flow test
• B. Slump test (ASTM C143)
• C. Compressive strength test
• D. Penetration test

Answer: (B)

The main idea here is measuring how workable freshly mixed concrete is, right there on the job site. The slump test (ASTM C143) is designed exactly for that purpose. It uses a hollow truncated-cone mold filled with fresh concrete in three layers, each layer tamped to compact the mix. When you lift the mold straight up, the concrete should settle a certain amount. The difference between the mold height and the settled height is the slump value. A larger slump means the mix is more workable; too little slump means the concrete is too stiff to place easily, while an excessively high slump can indicate too much water and potential strength loss or segregation. This test is simple, quick, and standardized for field use, making it the go-to on-site check for workability.

The other tests aren’t as suited for this on-site check of consistency. Slump flow tests measure how far a concrete mix spreads and are typically used for self-consolidating concrete, not the standard workability in general site pours. Compressive strength testing is for hardened concrete to determine strength, not fresh-mix workability. Penetration tests aren’t the common field method used to gauge freshness or consistency of the mix.