What is acid attack?
Due to its alkaline nature, concrete is vulnerable to acid attack, a condition where the cement paste components deteriorate upon exposure to acidic substances.
This process primarily dissolves calcium hydroxide, although other compounds within the cement paste or aggregates may also be adversely affected.
Acid attack on concrete typically happens in environments where the pH level drops below 6.5.
Understanding the interaction between concrete's alkaline properties and acidic environments is crucial for protecting structures from the deleterious effects of acid exposure.
What causes acid attack on concrete structures?
Acid attack on concrete is a critical concern in specialized settings such as waste disposal centres and industrial buildings, where the material is often exposed to strong acids.
The severity of acid attack depends on several factors, including the type of acid involved (with sulfuric, nitric, hydrochloric, and acetic acids being notably aggressive), the concentration of the acid, and the duration of exposure.
Additionally, the condition is influenced by the pressure and velocity of contaminated groundwater flow, which can exacerbate the penetration of acidic substances into the concrete.
The vulnerability of concrete to acid attack is also significantly affected by its composition and structure. A high water-to-cement (w/c) ratio, low cement content, and the use of limestone aggregates can increase the susceptibility of concrete to damage from acid exposure.
To safeguard structures in environments prone to acid attack, it is essential to consider these factors during the design and construction phases, employing strategies that reduce the concrete's permeability and enhance its resistance to chemical degradation.
What are the signs of acid attack on concrete structures?
Loss of material.
How can I identify acid attack on concrete structures?
Visual survey | Non-destructive testing | Destructive testing |
How can I prevent acid attack on concrete structures?
Enhancing concrete's resistance to acid attack involves optimizing its mix design for chemical durability. Key factors include maintaining a low water-to-cement (w/c) ratio, high cementitious materials content, good workmanship and suitable aggregate gradings for reduced porosity.
Incorporating cement replacement materials like ground granulated blast-furnace slag (GGBS) and selecting aggregates resistant to acid attack is also vital.
Additionally, applying protection measures , such as concrete coatings or impregnations, can act as a barrier, preventing acidic substances from permeating the concrete when environmental conditions are known to be aggressive.
