Concrete blocks are porous and can take in moisture. The moisture will eventually cause the blocks to crumble. To prevent this, you can cover the concrete blocks with a mortar made from slag cement. Slag cement is a mixture of clinker and limestone that helps give the concrete mixture strength and makes it more durable over time. Here’s how to replace crumbling cement blocks using slag cement.

Slag is a by-product of the smelting process used to make iron, and is made up of various minerals. Slag cement can be used at full replacement for portland cement, or it can be blended with portland cement to form a blended cement. The amount that can be used in slag cement depends on the type of concrete being made, and it is important to consult your local ready-mix producer. Since slag is not as strong as portland cement, it must be used in moderation.

Step 1

Mix your mortar according to directions on the bag of cement you are using. If you are blending portland and slag cement, start by mixing two parts portland to one part slag. You will have to experiment with these amounts until you get the result you want. Mix the mortar with a hoe in a clean wheelbarrow. Add water gradually until you get a consistency that seems right for what you are doing. The best way to learn this is by trial and error; if it doesn’t seem right, add more water or more mortar mix until it does.

Step 2

Use a mason’s trowel to spread mortar onto the exposed ends of your blocks where they will meet other blocks. First

Slag cement can be used in mortar to replace Portland cement. The general rule is that you can replace up to 30% of the Portland cement but no more. This means for an 80 lb bag of Portland you can add up to 24 lbs of slag cement.

Slag cement is a byproduct of the iron smelting process and is used as a partial substitute for portland cement in concrete mixes. Slag also improves the durability of concrete by reducing permeability, inhibiting corrosion and increasing resistance to freeze thaw conditions. Slag works similar to portland cement in that it reacts with water to form a hard matrix that will bind together aggregates.

Slag Cement

Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of portland cement. It is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious properties when ground into fine particles. Slag cement was introduced in Europe in the early 1900s for use as a supplementary cementitious material in concrete. In the mid-1940s, it was first blended with portland cement to form blended cements; and in the late 1960s, GGBFS from the steelmaking industry was used to manufacture blended cements. Slag cement is commonly found in ready-mixed concrete, precast concrete, masonry, soil cement and high temperature resistant building products. While there are many applications and benefits of slag cement, a few are highlighted below and detailed information sheets are located here.

Use Concrete with Slag Cement

Slag cement reduces permeability, increases durability and offers better long-term strength properties compared to portland cement concrete. Use it in combination with portland or blended cements

Slag cement, originally known as ground granulated blast-furnace slag, begins with the production of iron. The heart of the process is the blast furnace that refines iron ore into iron. The ingredients are heated to nearly 1500 degrees Centigrade to form two components: molten iron and molten slag. Molten slag floats on top of the iron and is drawn off separately.

When cooled, it becomes a glassy material of mostly calcium silicate and other compounds, including gypsum, which is added during grinding. This material is then ground into a fine powder to produce slag cement.

Today’s slag cement is a finely ground powder, gray in color and in many ways similar to Portland cement in its chemistry. However, it has a special feature: When mixed with water and allowed to harden, it turns into a product that is stronger and more durable than Portland cement concrete. Slag cement requires nearly 90 percent less energy to produce than Portland cement.

The use of slag cement has demonstrated long-term performance enhancements allowing designers to reduce the environmental footprint of concrete while ensuring improved performance and increased durability.

Slag Cement Association (SCA) member companies supply ground granulated blast-furnace slag

Slag cement is a hydraulic cement formed when granulated blast furnace slag (GGBFS) is ground to suitable fineness and is used to replace a portion of portland cement. It is a recovered industrial by-product of an iron blast furnace. Molten slag diverted from the iron blast furnace is rapidly chilled, producing glassy granules that yield desired reactive cementitious properties when ground into cement fineness.

Slag cement has actually been used in concrete projects in the United States for over a century. Its earliest use was documented in 1774, when it was combined with lime and water to make mortar used in the construction of Fort Pitt, a British fortress during the French and Indian War. Slag cement use became more common after the early 1900s, when scientists discovered how its chemistry contributes to concrete durability.

Slag cement, or ground granulated blast-furnace slag (GGBFS), has been used in concrete projects in the United States for over a century. Earlier usage of slag cement in Europe and elsewhere demonstrates that long-term performance is enhanced in many ways.

Slag cement is commonly found as a supplementary cementitious material (SCM) – a material used to replace a portion of portland cement. Slag cement typically contains 30-70% blast furnace slag.

Slag cement can contribute to achieving LEED points to help your project attain this globally-recognized sustainability certification.