Tuesday, November 29, 2022

How to Prevent Reinforcement Corrosion on Site?

 
 
   

 

In this article, we will discuss how to prevent reinforcement corrosion on site.

Summary: 

Corrosion of steel bars is highly detrimental to reinforced concrete elements and might undermine their serviceability and even cause structural failure. However, various precautions can be taken to prevent the corrosion of steel bars on construction sites.

Concrete having high quality and low permeability is very essential for controlling different corrosion mechanisms. Therefore, although conventional concrete is not fully impermeable, paying proper attention to various aspects of construction such as workmanship, concrete mixtures, and curing can make sure the production of low-permeability concrete with excellent quality.

These practical measures are important for designers and site engineers to protect against reinforcement corrosion.

 

 


 

  A. How to Prevent Reinforcement Corrosion on Site?  

1. Water-Cement Ratio (w/c ratio)

Low-permeability concrete can be made by involving a low w/c ratio which, in return, can deliver better reinforcement protection. ACI 318M-11 Building Code provisions for structural concrete suggest a maximum w/c ratio of 0.40 and minimum concrete strength of 35 MPa for concrete uncovered to moisture and an external source of chlorides from deicing chemicals, salt, brackish water, seawater, or spray from these sources.

Furthermore, ACI 357R- 84 delivers a similar water-to-cement ratio, as shown in Table 1. Therefore, it is suggested to employ a concrete strength of 42 MPa as long as the concrete surface is expected to degrade severely.

Water/ Cement Ratios And Concrete Compressive Strength for Three Weather Conditions

Zone Maximum w/c ratio Concrete compressive strength (fc’) MPa
Submerged 0.45 35
Splash 0.40 35
Atmospheric 0.40 35

 

 

2. Content

The binding capacity of CO2 and CL is raised as cement content is improved. However, if the portion of cement is raised without analysis, the water/cement ratio, curing, and compaction quality will have a more effective effect on chloride and carbonation penetration compared with cement content. Therefore, it is suggested by ACI 357R-84 that minimum cement content of 356 Kg/m3 could be utilized for a corrosive environment.

 

How To Prevent Reinforcement Corrosion On Site?

 

3. Cement Type

Cement composition involves concrete durability greatly. For instance, as the content of tricalcium aluminate (C3A) in Portland cement increases, corrosion resistance is enhanced greatly. This is because chloride ions’ reaction with the hydrated tricalcium sulfoaluminate makes insoluble Friedel salt in the hardened cement paste.

However, the effectiveness of C3A drops when the quantity of chloride content is more as C3A reacts only with a specific amount of chloride. Moreover, concrete resistance to sulfate attack is reduced by improving C3A content. That is why ACI 357R-84 suggests employing ASTM I, II, and III (Canadian Standard Association (CSA) 10, 20, and 30) cement type but with C3A content varying between  4-10 %.

 

Cement Type

 

 

4. Pozzolans

Pozzolans

 

Admixtures

 

 

Aggregates

 

water-soluble chloride ion content

 

Concrete Cover Thickness

 

Compaction

 

 

Protective Coatings

 


 

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