Not a simple question. Not all concretes are made equal. Concrete must be designed (choice and amounts of cement, aggregates and additives) and correctly placed/cured depending on the exposure/working conditions. Unexpected conditions are always a risk, but at least the design should be made to the expected exposure conditions.

One way to spoil a concrete is to use water in excess, sometimes the use of cement in excess can become a problem.

Durability of Concrete depends on the following factors: Aggregate Type, Cement Content, Water-Cement (W/C) Ratio, Cement Type, Air Entrainment, Carbonation Process, Quality of Mixing Water, Influence of Crack, Depth of Cover to the Reinforcement, Age of Immersion, Diffusion of Salts Under Pressure, Wetting and Drying Cycles, Freezing and Thawing Cycle.

The main factors affecting the durability of concrete in seawater are:

1) Aggregate Type

2) Cement Content

3) Water-Cement (W/C) Ratio

4) Cement Type

5) Air Entrainment

6) Carbonation Process

7) Quality of Mixing Water

8) Depth of Cover to the Reinforcement

9) Age of Immersion

10) Diffusion of Salts Under Pressure

11) Wetting and Drying Cycles

12) Freezing and Thawing Cycle

Dear Dr. the following link may be useful

https://civil-engg-world.blogspot.com/2009/01/factor-affecting-durability-of.html?m=1

The deleterious reactions of sulfate become from this reason:

We know that gypsum was added to the clinker during grinding in the manufacturing of cement to prevent flash setting, So If gypsum exhausted beforeC3A The remaining C3A begins in hydration:

C3A + 6H → C3AH6

C3AH6 is stable –cubical crystals- with high sulfate resistance.

Calcium aluminate hydrate : Be at many forms before transforming to the stable state (C3AH6). It is probably forming hexagonal crystals (C4AH8, C4AH10, C4AH12) before the cubical crystals.

When the hexagonal crystals expose to sulfates (inside concrete from sand orexternal from soil or ground water) → react with it forming calcium sulfoaluminate → with increase in volume, depending on the amount of remaining aluminates and the concentration of sulfates → crack and deteriorate of the hardened concrete.

The transformation of calcium aluminates hydrate from the metastable hexagonal form to the stable cubical form is accompanied with – change in the density and size of the crystals – leading to decrease in the late ages strength of the cement paste due to

– lose the adhesion and cohesion in the microstructure

–increase the porosity of the hardened cement paste.

Dear Jabar,

I'll be brief with you:

I was noted that too. Because of varying conditions among countries in the world; that presented difficulties for study.

Generally, to improve durability of concrete you must check three important points:

1. Improvement interlocking between cement paste and aggregate, I will mean promotion the interfacial transition zone in concrete ( good adhesion and cohesion between concrete constituents).

2. Choose a sutabil type of aggregate to address the special environment conditions.

3. Increase strength of cement paste by using additives.

Best regards

Dear Dr. Doha M Al Saffar,

I completely agree with your interesting and valuable comment, thank you so much.

Dear Dr. Sales,

I have a master degree , but I didn't get the PhD degree. I'm hoping to do a PhD eventually.

Thank your for your sweet comments.

ALL the Best

Dear Dr. Doha M Al Saffar, from my point of view, You are Doctor of Science.

Dear Dr. Saleh,

thank you so much for the compliment!

Best regards

The quality of concrete depends upon so many factors. However, the degree of deterioration of concrete depends upon the strength and environmental factors. For instances, concrete with good strength, if placed in sulphate or chloride rich environment may deteriorate rapidly whereas if placed in normal condition may last long for more than 100 years (conditions applied). For the durability of concrete the strength of the concrete should be high and moreover, it should be dense with less porousness.

Thanck you for all. I want concrete to be durable in sever condition as in iraq environments . The adverse effects of sulpher salts are very bad with hot weather sorrounding.

Dear Dr. Jabbar

I think one of the most important reasons for concrete deterioration is the improper W/C ratio. Regards

The corrosive action of chlorides is due to the formation of chloroaluminate hydrates, which causes softening of concrete. Sulphate ions can enter into chemical reactions with certain constituents of concrete, producing sulphoaluminate hydrates and gypsum, which cause the expansion of concrete.

Fom my point of view, the essential factors affecting the durability of concrete in seawater are:

1- Aggregate Type, 2- Cement Content, 3- Water-Cement (W/C) Ratio, 4-Cement Type, 5- Air Entrainment, 6-Carbonation Process, 7- Quality of Mixing Water, 8- Depth of Cover to the Reinforcement, 9- Age of Immersion

10- Diffusion of Salts Under Pressure, 11-Wetting and Drying Cycles and 12- Freezing and Thawing Cycle

Concrete deterioration can be the result of a combination of two issues

1. placement

2. service condition

Examples of deterioration: cracking, spalling, leaking, premature or excessive wear, scaling, settlement, deflection and disintegration.

Understanding deterioration modes and their cause are necessary to set up a successful strategy.

Whatever the causes of deterioration, careful analysis, supplemented by testing, is vital to the success.

For example, to avoid the aggressive action by sulfates on concrete. One of the solutions that provide the best protection is a dense and well-compacted concrete. The low permeability of dense concrete prevents or greatly restricts the entry of the harmful materials into the pores of the concrete. Therefore, the strength of concrete is the most property to be tested and must be designed to achieve the required degree of impermeability and resistance to aggressive action.

Not a simple question. Not all concretes are made equal. Concrete must be designed (choice and amounts of cement, aggregates and additives) and correctly placed/cured depending on the exposure/working conditions. Unexpected conditions are always a risk, but at least the design should be made to the expected exposure conditions.

One way to spoil a concrete is to use water in excess, sometimes the use of cement in excess can become a problem.

Durability of concrete may be defined as the ability of concrete to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties. Different concretes require different degrees of durability depending on the exposure environment and properties desired. For example, concrete exposed to tidal seawater will have different requirements than an indoor concrete floor. Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete.

Seawater Exposure:  Concrete has been used in seawater exposures for decades with excellent performance. However, special care in mix design and material selection is necessary for these severe environments. A structure exposed to seawater or seawater spray is most vulnerable in the tidal or splash zone where there are repeated cycles of wetting and drying and/or freezing and thawing. Sulfates and chlorides in seawater require the use of low permeability concrete to minimize steel corrosion and sulfate attack. A cement resistant to sulfate exposure is helpful. Proper concrete cover over reinforcing steel must be provided, and the water-cementitious ratio should not exceed 0.40.

Chloride Resistance and Steel Corrosion: Chloride present in plain concrete that does not contain steel is generally not a durability concern. Concrete protects embedded steel from corrosion through its highly alkaline nature. The high pH environment in concrete (usually greater than 12.5) causes a passive and noncorroding protective oxide film to form on steel. However, the presence of chloride ions from deicers or seawater can destroy or penetrate the film. Once the chloride corrosion threshold is reached, an electric cell is formed along the steel or between steel bars and the electrochemical process of carrions begins.

The resistance of concrete to chloride is good; however, for severe environments such as bridge decks, it can be increase by using a low water-cementitious ratio (about 0.40), at least seven days of moist curing, and supplementary cementitious materials such as silica fume, to reduce permeability. Increasing the concrete cover over the steel also helps slow down the migration of chlorides. Other methods of reducing steel corrosion include the use of corrosion inhibiting admixtures, epoxy-coated reinforcing steel, surface treatments, concrete overlays, and cathodic protection.

Resistance to Alkali-Silica Reaction (ASR):  ASR is an expansive reaction between reactive forms of silica in aggregates and potassium and sodium alkalis, mostly from cement, but also from aggregates, pozzolans, admixtures, and mixing water. The reactivity is potentially harmful only when it produces significant expansion. Indications of the presence of alkali-aggregate reactivity may be a network of cracks, closed or spalling joints, or movement of portions of a structure. ASR can be controlled through proper aggregate selection and/or the use of supplementary cementitious materials (such as fly ash or slag cement) or blended cements proven by testing to control the reaction.

Abrasion Resistance: Concrete is resistant to the abrasive affects of ordinary weather. Examples of severe abrasion and erosion are particles in rapidly moving water, floating ice, or areas where steel studs are allowed on tires. Abrasion resistance is directly related to the strength of the concrete. For areas with severe abrasion, studies show that concrete with compressive strengths of 12,000 to 19,000 psi work well.

Yes, the degree of deterioration of concrete depends upon the strength and environmental factors. For instances, concrete with good strength, if placed in sulphate or chloride rich environment may deteriorate rapidly whereas if placed in normal condition may last long for more than 100 years (conditions applied).

Dear Dr. Salim , Thank you so much for your interesting and deep answer. I am indeed got a lot of knowledge from your valuable comments.

Yes, the concrete must be designed (choice and amounts of cement, aggregates and additives) and correctly placed/cured depending on the exposure/working conditions. Unexpected conditions are always a risk, but at least the design should be made to the expected exposure conditions.

I completely agree with that, Different concretes require different degrees of durability depending on the exposure environment and properties desired. For example, concrete exposed to tidal seawater will have different requirements than an indoor concrete floor. Concrete ingredients, their proportioning, interactions between them, placing and curing practices, and the service environment determine the ultimate durability and life of concrete. Seawater Exposure:  Concrete has been used in seawater exposures for decades with excellent performance. However, special care in mix design and material selection is necessary for these severe environments. A structure exposed to seawater or seawater spray is most vulnerable in the tidal or splash zone where there are repeated cycles of wetting and drying and/or freezing and thawing. Sulfates and chlorides in seawater require the use of low permeability concrete to minimize steel corrosion and sulfate attack. A cement resistant to sulfate exposure is helpful. Proper concrete cover over reinforcing steel must be provided, and the water-cement ratio should not exceed 0.40. Chloride Resistance and Steel Corrosion: Chloride present in plain concrete that does not contain steel is generally not a durability concern. Concrete protects embedded steel from corrosion through its highly alkaline nature. The high pH environment in concrete (usually greater than 12.5) causes a passive and noncorroding protective oxide film to form on steel. However, the presence of chloride ions from deicers or seawater can destroy or penetrate the film. Once the chloride corrosion threshold is reached, an electric cell is formed along the steel or between steel bars and the electrochemical process of carrions begins. The resistance of concrete to chloride is good; however, for severe environments such as bridge decks, it can be increase by using a low water-cementitious ratio (about 0.40), at least seven days of moist curing, and supplementary cementitious materials such as silica fume, to reduce permeability. Increasing the concrete cover over the steel also helps slow down the migration of chlorides. Other methods of reducing steel corrosion include the use of corrosion inhibiting admixtures, epoxy-coated reinforcing steel, surface treatments, concrete overlays, and cathodic protection. Resistance to Alkali-Silica Reaction (ASR):  ASR is an expansive reaction between reactive forms of silica in aggregates and potassium and sodium alkalis, mostly from cement, but also from aggregates, pozzolans, admixtures, and mixing water. The reactivity is potentially harmful only when it produces significant expansion. Indications of the presence of alkali-aggregate reactivity may be a network of cracks, closed or spalling joints, or movement of portions of a structure. ASR can be controlled through proper aggregate selection and/or the use of supplementary cementitious materials (such as fly ash or slag cement) or blended cements proven by testing to control the reaction. Abrasion Resistance: Concrete is resistant to the abrasive affects of ordinary weather. Examples of severe abrasion and erosion are particles in rapidly moving water, floating ice, or areas where steel studs are allowed on tires. Abrasion resistance is directly related to the strength of the concrete.