Slag Cement Facts What is Slag Cement?

How Does Slag Cement Improve Resistance to Alkali-Silica Reaction (ASR)? 
ASR occurs when the alkalis in portland cement react with certain reactive aggregates to 
form an expansive gel that causes the concrete to crack, swell and prematurely 
deteriorate. Slag cement mitigates ASR by reacting with the alkalis in portland cement 
and making them unavailable for reaction. It also lowers the permeability of the concrete, 
reducing the water available for reaction and, in some cases, lowering the total alkali 
content of the cement paste. 
How Does Slag Cement Mitigate Sulfate Attack? 
Sulfate attack occurs when sulfates, found in seawater and some soils, react with the 
tricalcium aluminate in portland cement. This causes an expansive reaction and resulting 
deterioration of the concrete structure. Slag cement helps in two ways: 1) reduced 
permeability reduces the ingress of deleterious sulfates into the concrete; and 2) slag 
cement does not contain tricalcium aluminate, and thus lowers the total amount available 
for reaction. The use of slag cement with a Type I portland cement can provide 
equivalence to a Type II (moderate sulfate-resistant) or even a Type V (high sulfate-
resistant) cement. 

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Slag Cement Association: Slag Cement Facts 
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How Does Slag Cement Help in Reducing Heat and Cracking in Mass Concrete?
Mass concrete applications require limitations on the temperature differential between the 
surface and center of concrete to guard against thermal cracking. Slag cement reduces the 
rate of heat rise in proportion to its quantity in a mixture. Generally, high replacement 
rates are required (50 to 80 percent) to meet low heat of hydration requirements for mass 
applications. 
How Does Slag Cement Affect the Early Age Properties of Concrete? 
 
Slag cement improves the workability, placement and consolidation of concrete. This 
results in easier and better finishing, and helps ensure proper consolidation of the placed 
material.
Time of initial set is generally extended by one to three hours at room temperature when 
slag cement is used (depending on several factors including the portland and slag cements 
used, the substitution rate and chemical admixtures). Time of set differences normally 
become insignificant above 85 degrees F. At low temperatures, time of set can be 
extended significantly, but the addition of conventional accelerators can greatly reduce or 
eliminate this.
Early age strength properties (three to seven days) are lower for slag cement concrete 
compared to OPC concrete. But by 28 days—and often much sooner—slag cement 
concrete normally exhibits higher strength than OPC concrete.
 
Slag cement is compatible with chemical admixtures in a similar manner to OPC 
concrete. Slight adjustments in admixture dosages may be necessary to achieve desired 
results.