Technical Questions

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How is workability measured and specified?

Q. How is workability measured and specified?


A. The customary measure of workability is slump. ASTM C143 covers the determination of slump. The lowest acceptable slump is normally selected in preference to high slump due to a low w/cm and low amount of cementitious material, which are desirable; it also means less likelihood of segregation. The use of water-reducing admixtures, however, enables the preparation of concretes with a low w/cm and high slump values without adding more cementitious material and water and without segregation. Low slump is necessary in certain applications, such as slip-form paving, where concrete retains a certain shape without the need for formwork. On the other hand, a high-slump concrete may be necessary where complicated forms or closely spaced reinforcement is used. Under such conditions, it may be necessary to require self-consolidating concrete.


References: SP-1(02); ACI 238.1R-08; ACI PRC-211.1-22; ACI 301-20; ASTM C143

Topics in Concrete: Concrete Fundamentals; Mixture Proportioning; Placing; Self-Consolidating Concrete; Testing of Concrete

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