IS-18

Producing Concrete Block with Slag Cement

Concrete Block

While only a few basic methods are used in the initial forming of concrete block, there are many methods of curing. Depending on the temperature and length of curing, slag cement proportioning may change. Some of the properties that slag cement can impart are:

  • An architecturally appealing lighter color
  • A finer, tighter surface texture or more swipe
  • Reduced efilorescence
  • Decreased permeability
  • Increased compressive strengths

How Does Slag Affect Color?

Slag cement is lighter in color than portland cement. Block manufactured with slag cement will therefore have a lighter finished color. The higher the percentage of slag cement used, the lighter the color will be. If the block remains unpainted or unsurfaced, the lighter color is often viewed as a positive enhancement.

How Does Slag Cement Affect Surface Texture?

Due to the fine grind and glassy structure of slag cement, the surface texture of con­ crete block is tighter and may increase swipe. Some manufacturers have report­ ed reduced cycle times when slag cement is used.

How Does Slag Cement Affect Ellforescence?

Slag cement combines with calcium hydroxide and soluble salts in portland cement, locking them in the paste and reducing their migration to the surface of the unit during curing and in service, thus helping to reduce efllorescence.

How Does Slag Cement Affect Permeability?

When slag cement is used as part of the cemen­ titious material in a concrete block mixture, it reacts with calcium hydroxide (Ca(OHh ) to form additional calcium silicate hydrate (CSH). CSH is the glue that provides strength and holds concrete together. The additional CSH produced modifies the pore structure of the paste resulting in lower permeability. The level of improvement is proportional to the percentage of slag cement in the mixture

How Does Slag Cement Affect Compressive Strength?

The curing temperature affects the compressive strength of concrete block in mixtures containing slag cement: the higher the curing temperature of the block, the higher the percentage of slag cement that can be used. Typical slag cement replacement levels for optimum strength in concrete block are between 20 percent and 50 percent.

Proportioning Block Mixture with Slag Cement

Concrete block manufacturers who have successfully incorporated slag cement in their products have used slag cement in ranges from 20 to 50 percent of cementitious material.


A cube of concrete block, mode with slag cement, awaiting shipping.


Concrete block machine producing block with slag cement.


Color comparison of a block made without (left) and with (right) slag cement.

Stay Connected with SCA

Sign up for our newsletter.

Join us on Facebook.

Follow us on Twitter.