Question

What will you propose for a concrete mix design to be used in constructing a bridge pier during a cold winter month. The bridge is designed to be constructed on a site where sulfate attack on the concrete is a problem. In this project, high cost is not allowed and the concrete’s cost must be priority without lowering quality.

Answer 1

Temperature does play a large role in the usability and strength of concrete. Consolidated is well-versed in finding the right mix of concrete for the cold temperatures of winter and even early spring because the company has been doing this for decades.Another important factor in working with concrete during the colder weather months is the quality of the concrete mix itself. The right “recipe” is needed in order to ensure concrete will perform properly.

TIP: Although concrete sets more slowly when the air temperature is colder, concrete can still be quite workable if you follow these essential steps in preparing the curing site:

• Never place concrete on frozen ground, ice or snow
• Thaw the ground for a couple of days using heat pipes and blankets or electric blankets
• Triple wrap corners and protrusions
• Remove standing water; bleed water needs to evaporate or be removed by a squeegee or vacuum
• Keep setting concrete covered until it is cured – consider a temporary enclosure.

Sulphate attack on concrete is a chemical breakdown mechanism where sulphate ions attack components of the cement paste. The compounds responsible for sulphate attack on concrete are water-soluble sulphate-containing salts, such as alkali-earth (calcium, magnesium) and alkali (sodium, potassium) sulphates that are capable of chemically reacting with components of concrete.

To prevent the sulphate attack on concrete, we must understand the factors which affect the sulphate attack.

Main factors affecting sulphate attack are:

1. Type of Cement and its Content

The most important mineralogical phases of cement that affect the intensity of sulphate attack are: C3A, C3S/C2S ratio and C4AF.

2. Fly ash addition

The addition of a pozzolanic admixture such as fly ash reduces the C3A content of cement.

3. Types of Sulphate and its Concentration

The sulphate attack tends to increase with an increase in the concentration of the sulphate solution up to a certain level.

4. Chloride ions

Other factors:

• The level of the water table and its seasonal variation
• The flow of groundwater and soil porosity
• The form of construction
• The quality of concrete

Control of Sulphate Attack on Concrete

Following measures help to control sulphate attack:

1. The quality of concrete, specifically a low permeability, is the best protection against sulphate attack.

• Adequate concrete thickness
• High cement content
• Low w/c ratio
• Proper compaction and curing

2. The use of sulphate resisting cements provide additional safety against sulphate attack

Exposure	Concentration of water-soluble sulphates in soil percent	Concentration of water-soluble sulphates in water ppm
Mild	<0.1	<150
Moderate	0.1 to 0.2	150 to 1500
Severe	0.2 to 2	1500 to 10000
Very severe	>2	>10000

Thank you. Hope you understand. If you have any doubts comment me. Upvote me..