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Q. What is the most commonly used accelerating admixture and what precautions are necessary in its use? A. Calcium chloride. It should not be used in amounts in excess of 2%, preferably 1%, of the mass of cementitious material, and then only in solution form (ACI 306R). To minimize corrosion, calcium chloride should not be used in any steel-reinforced concrete or where there is an aluminum conduit in the concrete. Uncoated prestressing strands under tension are very vulnerable to corrosion with serious consequences. Calcium chloride decreases resistance to sulfates except when Type V (sulfate-resisting) cement is used and increases the expansion due to alkali-silica reaction (ACI 212.3R). Non-chloride accelerating admixtures are available and should be used in steel-reinforced concrete. References: SP-1(02); E4-12; ACI 212.3R-16; SP-288; ACI 222.3R-11; ACI 306R-16 Topics in Concrete: Admixture; Corrosion; Cold Weather; Durability
Q. What is the most commonly used accelerating admixture and what precautions are necessary in its use?
A. Calcium chloride. It should not be used in amounts in excess of 2%, preferably 1%, of the mass of cementitious material, and then only in solution form (ACI 306R). To minimize corrosion, calcium chloride should not be used in any steel-reinforced concrete or where there is an aluminum conduit in the concrete. Uncoated prestressing strands under tension are very vulnerable to corrosion with serious consequences. Calcium chloride decreases resistance to sulfates except when Type V (sulfate-resisting) cement is used and increases the expansion due to alkali-silica reaction (ACI 212.3R). Non-chloride accelerating admixtures are available and should be used in steel-reinforced concrete.
References: SP-1(02); E4-12; ACI 212.3R-16; SP-288; ACI 222.3R-11; ACI 306R-16
Topics in Concrete: Admixture; Corrosion; Cold Weather; Durability
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