{"id":9721,"date":"2023-05-30T08:36:25","date_gmt":"2023-05-30T08:36:25","guid":{"rendered":"https:\/\/cimsa.com.tr\/en\/?p=9721"},"modified":"2023-07-05T10:19:11","modified_gmt":"2023-07-05T10:19:11","slug":"what-is-sulfate-attack-on-concrete","status":"publish","type":"post","link":"https:\/\/cimsa.com.tr\/en\/what-is-sulfate-attack-on-concrete\/","title":{"rendered":"What is Sulfate Attack on Concrete?"},"content":{"rendered":"\n

In the 2000s, the perception of concrete began to change. In addition to focusing on high strength, the production of concrete with long-term durability has started to gain importance. As long as concrete is in service, it must maintain the required strength and be durable enough to withstand both chemical and physical effects. Concrete with long-lasting durability can only be produced if all of the inputs are carefully controlled. One of the durability problems that can occur in the medium- and long-term is sulfate attack. In this article, we will discuss how sulfate attack on concrete occurs and what must be done to prevent it.<\/p>\n\n\n\n

What is Sulfate Attack?<\/h2>\n\n\n\n

Sulfate attack is a form of expansion and cracking of concrete due to penetration of SO4<\/sub> ions. When concrete cracks, permeability increases, and water penetrates more easily, thus accelerating the deterioration.<\/p>\n\n\n

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\"what-is-sulfate-attack\"<\/figure><\/div>\n\n\n

Picture 1. <\/strong>Sulfate Attack<\/p>\n\n\n\n

Sometimes the expansion of concrete may cause serious structural problems, such as the displacement of building walls due to horizontal thrust by an expanding slab.
Sulfate attack can also take the form of a progressive decrease in the strength and loss of mass due to loss of cohesiveness of the cement paste.<\/p>\n\n\n

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\"mortar-subjected-to-sulfate-attack\"<\/figure><\/div>\n\n\n

Picture 2.<\/strong> Mortar Subjected to Sulfate Attack<\/p>\n\n\n\n

How does Sulfate Attack on Concrete Occur?<\/h2>\n\n\n\n

There are 3 fundamental reasons for the reaction known as sulfate attack or sulfate effect that results in harmful expansion in harden concrete:<\/p>\n\n\n\n

1.         C3<\/sub>A phase in cement,<\/p>\n\n\n\n

2.         Groundwater or seawater-borne sulfate<\/p>\n\n\n\n

3.         Portlandite (Calcium Hydroxide), a product of cement hydration<\/p>\n\n\n\n

One of these three factors must be prevented in order to stop the expansion caused by sulfate attack on concrete.<\/p>\n\n\n

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Picture 3.<\/strong> Sulfate Attack Formation<\/p>\n\n\n\n

The ground water in clay soils and seawater contains sulfate ions that are harmful to concrete. Calcium hydroxide (CH) and alumina-bearing phases in hardened cement paste are susceptible to sulfate attack. If the C3<\/sub>A content of the cement is more than 5%, monosulfate hydrate (C3<\/sub>A\u22c5CS\u22c5H18<\/sub>) will be formed in hardened cement paste. If the C3<\/sub>A content of the cement is more than 8%, the hydration products will also contain C3<\/sub>A\u22c5CH\u22c5H18<\/sub>.<\/p>\n\n\n\n

When SO4<\/sub> penetrates in, both these phases hydrates react with CH and SO4<\/sub>, converted to the high-sulfate form ettringite.<\/p>\n\n\n\n

Ettringite that forms in the stable structure of hardened concrete results in harmful expansion and the formation of cracks.<\/p>\n\n\n\n

Depending on the cation type associated with the sulfate solution (i.e., Na+<\/sup>, K+<\/sup>, or Mg+2<\/sup>), both CH and C-S-H may be converted to gypsum by sulfate attack.<\/p>\n\n\n\n

What\u2019s more, sulfate combines with free MgO resulting in the deterioration of the calcium-silica-hydrate gels (C-S-H) that provide binding to cement paste. The result is a negative effect on concrete strength.<\/p>\n\n\n\n

What are the Sources of Sulfate?<\/strong><\/strong><\/h3>\n\n\n\n