Low Calcium Fly Ash Based Geopolymer Concrete Long Term Properties

Geopolymer concrete has found extensive use in various applications, such as earth retaining structures and water-containing structures. Specifically, the properties of geopolymer concrete using low calcium fly ash are worth examining. Geopolymer concrete is composed of an alkaline liquid and source materials, which can be either natural minerals or by-product materials like fly ash.

This innovative concrete utilizes geopolymer as a binder instead of traditional Portland cement, primarily developed to mitigate the adverse environmental effects associated with the production of Portland cement. By employing geopolymer concrete, significant efforts have been made to minimize the detrimental impact of cement on the environment.

Low Calcium Fly Ash Based Geopolymer Concrete Properties

Geopolymer concrete possesses several notable properties, including high compressive strength, minimal drying shrinkage, low creep, and excellent resistance to both sulfates and sulfuric acid. It exhibits remarkable compressive strength, making it a durable and reliable construction material. The drying shrinkage of geopolymer concrete is significantly reduced compared to conventional concrete, mitigating the risk of cracking and structural damage.

Additionally, geopolymer concrete demonstrates low creep, meaning it experiences minimal deformation over time under sustained loads. This property enhances its long-term structural stability. Geopolymer concrete is highly resistant to sulfates, which are commonly found in soil and water, ensuring its durability in aggressive environments. Moreover, it exhibits exceptional resistance to sulfuric acid, making it suitable for applications in industries where exposure to corrosive substances is prevalent. These advantageous properties make geopolymer concrete an attractive alternative to traditional concrete in various construction projects.

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Geopolymer Concrete Compressive Strength

Geopolymer concrete has slightly lower strength compared to Portland cement-based concrete initially. However, over time, the compressive strength of geopolymer concrete significantly increases and can surpass that of Portland cement concrete in some cases. Similar to Portland cement, the curing condition plays a crucial role in determining the compressive strength of geopolymer concrete. Improper curing can result in a significant decline in strength. Research has shown that the compressive strength of geopolymer concrete decreases as the ratio of water to geopolymer solid material increases. This is because higher water content leads to the presence of excess water and the formation of larger microstructure pores.

Drying Shrinkage Effect Geopolymer Concrete

Drying shrinkage is an important property to consider in geopolymer concrete. Studies have shown that the drying shrinkage of geopolymer concrete increases with aging, but the rate of shrinkage decreases significantly. Interestingly, unlike Portland cement concrete, the drying shrinkage of geopolymer concrete decreases as the water-to-binder ratio increases.

This is contrary to the behavior of Portland cement concrete, where drying shrinkage increases with higher water-to-cement ratios. Under heat curing conditions, geopolymer concrete exhibits significantly smaller drying shrinkage compared to conventional Portland cement concrete. It is worth noting that, when considering a constant water-to-solid geopolymer material ratio, different curing conditions and temperatures at different times can result in varying drying shrinkage values.

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Creep of Geopolymer Concrete

The creep behavior of geopolymer concrete under heat curing conditions has been investigated, revealing an interesting relationship with compressive strength. It has been observed that as the compressive strength of geopolymer concrete improves, the creep coefficient decreases. The creep coefficient represents the ratio of creep strain to elastic strain. Conversely, the specific creep, which indicates the creep strain per sustained unit stress, increases as the strength of geopolymer concrete decreases. These findings provide valuable insights into the mechanical properties of geopolymer concrete and its performance under different conditions.

Sulfate Resistance of Geopolymer Concrete

Low calcium fly ash geopolymer concrete exhibits significant resistance to sulfate attack. To assess this resistance, tests were conducted under heat curing conditions, and various properties of the specimens such as compressive strength, mass, length, and surface appearance were observed. The compressive strength of geopolymer concrete exposed to sulfate attack did not show considerable variation.

The effect of sulfate attack on the mass of geopolymer concrete can be disregarded, as there was no significant change. Similarly, the dimensions of geopolymer concrete remained largely unaffected, as the observed expansion was lower than 0.015%, well below the threshold of 5% beyond which concrete is considered unable to resist sulfate attack.

Notably, low calcium geopolymer concrete did not exhibit any cracks, spalling, or expansion indications when subjected to sulfate attack. This can be attributed to the absence of expansive ettringite and gypsum, as well as the resistance of the geopolymerization product to sulfate attack. In contrast, conventional Portland cement concrete experiences the formation of expansive gypsum and ettringite, leading to cracking, expansion, and spalling. In summary, the sulfate resistance of low calcium fly ash geopolymer concrete can be attributed to the absence of expansive ettringite and gypsum, as well as the durability of the geopolymerization product against sulfate attack.

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Geopolymer Concrete Sulfuric Acid Resistance

Low calcium fly ash geopolymer concrete exhibits significant resistance to sulfate attack. To assess this resistance, tests were conducted under heat curing conditions, and various properties of the specimens such as compressive strength, mass, length, and surface appearance were observed. The compressive strength of geopolymer concrete exposed to sulfate attack did not show considerable variation. The effect of sulfate attack on the mass of geopolymer concrete can be disregarded, as there was no significant change. Similarly, the dimensions of geopolymer concrete remained largely unaffected, as the observed expansion was lower than 0.015%, well below the threshold of 5% beyond which concrete is considered unable to resist sulfate attack.

Notably, low calcium geopolymer concrete did not exhibit any cracks, spalling, or expansion indications when subjected to sulfate attack. This can be attributed to the absence of expansive ettringite and gypsum, as well as the resistance of the geopolymerization product to sulfate attack. In contrast, conventional Portland cement concrete experiences the formation of expansive gypsum and ettringite, leading to cracking, expansion, and spalling. In summary, the sulfate resistance of low calcium fly ash geopolymer concrete can be attributed to the absence of expansive ettringite and gypsum, as well as the durability of the geopolymerization product against sulfate attack.

Geopolymer concrete exhibits superior resistance to sulfuric attack when compared to ordinary Portland cement concrete. This improved performance can be attributed to the lower calcium content present in geopolymer concrete. Unlike Portland cement concrete, geopolymer concrete does not rely on lime during its production process, resulting in a reduced amount of calcium. As a result, geopolymer concrete is more effective in resisting the detrimental effects of sulfuric attack.

FAQs about Low Calcium Fly Ash Based Geopolymer Concrete