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Long Term Properties of Geopolymer Concrete with Low Calcium Fly Ash

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Geopolymer concrete has been employed in many applications for example earth retaining structures and water containing structures. Properties of geopolymer concrete with low calcium fly ash is discussed. Geopolymer is composed of alkaline liquid and source materials which is either natural mineral or by product material for example fly ash. Geopolymer is a binder that is used instead of Portland cement and it produced because of efforts which were conducted to reduce detrimental environmental impact of Portland cement.

Fig.1: Reinforced Geopolymer Concrete

Properties of Geopolymer Concrete with Low Calcium Fly Ash

Following are the properties of geopolymer concrete which are discussed:

Compressive Strength of Geopolymer Concrete

It is demonstrated through tests that, geopolymer strength achievement is slightly lower than that of Portland cement based concrete. However, the compressive strength of the former will substantially increases as time goes by and it surpasses Portland cement concrete compressive strength in some occasions. Curing condition largely influence compressive strength of geopolymer concrete and is similar to Portland cement. If it is not cured properly its strength will be decline considerably. It is proven that, the compressive strength of geopolymer concrete is decreased as the ratio of water to geopolymer solid material increases. This is because high amount of fee water will be present and eventually larger amount of microstructure pores will be created.

Fig.2: Geopolymer Concrete Compressive Strength Test

Drying Shrinkage of Geopolymer Concrete

Drying shrinkage is another important property which needs to be considered. It is shown that the geopolymer concrete drying shrinkage is increases with aging but the speed of drying shrinkage declines greatly. As far as water to solid geopolymer material is concern, it is demonstrated that drying shrinkage of the geopolymer concrete is decreased as the ratio of water to binder material is increased. This is surprisingly opposite of Portland cement concrete which its drying shrinkage increases with increasing water to cement ratio. It is reported that the drying shrinkage of geopolymer concrete under heat curing condition is considerably smaller than the conventional Portland cement concrete shrinkage. It should be said that, at constant water to solid geopolymer material ratio, various curing condition and temperature at different times will lead to different drying shrinkage values.

Creep of Geopolymer Concrete

Geopolymer concrete creep is studied under heat curing condition and it is reported that, the creep coefficient of geopolymer concrete, which is the ratio of strain of creep to elastic strain, is decreased as the compressive strength of geopolymer concrete is improved. Similarly, the specific creep which is equal to creep strain per sustained unit stress increases the decreasing geopolymer concrete strength.

Sulfate Resistance of Geopolymer Concrete

Low calcium fly ash geopolymer concrete possess substantial resistance against sulfate attack. The sulfate resistance is explored through tests under heat curing condition and compressive strength, mass, length, and surface appearance of the specimens observed to evaluate geopolymer concrete sulfate resistance. It is noted that, there was not considerable variation in compressive strength of geopolymer concrete exposed to sulfate attack. The effect of sulfate attack on mass of geopolymer concrete can be ignored. Similar to the sulfate aggression on geopolymer concrete mass, the dimension of geopolymer concrete is extremely low. This can be observed from geopolymer expansion which is lower than 0.015% much smaller than 5%; expansion value above which concrete is considered to not possess the ability to resist sulfate attack. Low calcium geopolymer concrete subjected to sulfate attack has not shown any cracks, spalling, and expansion indication. It can be said that, the main factor that make the low calcium fly ash geopolymer concrete sulfate resistance is due to not only the absence of expansive ettringite and gypsum but also the product of geopolymerization is not subjected to sulfate attack. However, this totally opposite in conventional Portland cement concrete in which expansive gypsum and ettringite are formed and lead to cracking, expansion, and spalling of concrete.

Geopolymer Concrete Sulfuric Acid Resistance

It is shown that resistance of low calcium geopolymer concrete against sulfuric acid aggression is better than that of normal Portland cement concrete. The surface suffers damages and erosion. If the concentration of sulfuric acid is increased, concrete deterioration will be more extreme and severe. Figure-3 geopolymer concrete specimen which subjected to 2% sulfuric acid for one year and as it can be observed from the figure that the specimen experienced damages and deterioration. The effect of sulfuric attack on compressive strength of geopolymer concrete is based on the concentration of the acid and exposure period. The compressive strength reduction will be greater provided that the acid concentration is high and the period in which geopolymer concrete is subjected to the sulfuric attack is longer. With regard to concrete mass variation, it is noted that geopolymer concrete loss about 5% of the mass before it exposed to sulfuric attack and it is smaller than that of Portland cement concrete.

Fig.3: Damaged Geopolymer Concrete Specimen Due to Sulfuric Acid Attack

Finally, the better performance of geopolymer concrete to withstand sulfuric attack compared with ordinary Portland cement concrete is due to low amount of calcium content in the material by which geopolymer concrete produced, and because geopolymer concrete does not produced from lime as it is the case with Portland cement concrete, therefore, the amount of calcium will be lower. Read More: Geopolymer Concrete - Eco Friendly Construction Material Glass Fiber Reinforced Concrete (GFRC) - Properties and Applications in Construction Works
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