How Sulfates In Soil Affect Concrete Foundations

How Sulfates In Soil Affect Concrete Foundations

March 3, 2023

The Effects Of Sulfate In Concrete 

Sulfate is one of the most dangerous forms of deterioration that concrete faces. It infiltrates the concrete through cracks and begins to destroy the cement paste that holds it together. Once in the concrete, sulfate dissolves into water that is present and begins to draw it in. This excess water corrodes the anchor bolts that hold your home’s foundation in place, which can cause significant damage and loss of value. 

How Sulfate Damages Concrete 

Sulphate attacks concrete by chemically breaking down cement paste, causing it to expand and crumble. Sulfate-containing salts like sodium sulfate and calcium hydroxide react with hydration products in the cement paste. This causes gypsum to form, which increases in volume more than double the original volume. When sulfate is allowed to dry, it produces new compounds called ettringite that occupy empty space and cause the paste to crack. 

Sulfate And Concrete Slabs 

Sulfates can come from groundwater, soil, and runoff from industrial waste or from naturally decaying materials. They can also be present in sewage and household waste. When the sulfate reaches the foundation of a home, it will slowly attack the concrete slabs. It will begin with hairline cracks called “etching” and white, powdery stains called “efflorescence.”  

Sulfate And Concrete Foundations 

Sulfate damage is especially damaging to the foundations of buildings, which are susceptible to earthquakes and high winds. If the sulfate damage isn’t treated, the foundations can decompose and turn to rubble. Thankfully, most builders follow Code requirements and use a special Type V cement to ensure the proper level of density in the concrete after curing. However, some building contractors and suppliers ignore those requirements. As a result, concrete that is placed on soils with high sulfate levels result in it being weaker than necessary, allowing groundwater to inevitably seep into the concrete and transport sulfates.  

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