Alkanolamines are additives used to increase the compressive strength of concrete.
Concrete strength can be enhanced by incorporating various additives, often referred to as admixtures. These materials are added during the mixing process and can significantly improve different properties of the concrete, including its strength. While many admixtures offer multiple benefits, some are specifically known for boosting concrete strength.
Alkanolamines
Alkanolamines, such as those found in products like SikaGrind®-200 and SikaGrind®-700, can increase the compressive strength of concrete by up to five MPa. They also improve the productivity of grinding aids used in cement production.
Types of Admixtures that Increase Concrete Strength:
While the reference text focuses on Alkanolamines, a comprehensive answer should include other important strength-enhancing admixtures:
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Accelerating Admixtures: These admixtures speed up the hydration process, leading to faster strength development, particularly in early stages. Examples include calcium chloride (though its use is often restricted due to corrosion concerns) and non-chloride accelerators.
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Superplasticizers (High-Range Water Reducers): By allowing for lower water-to-cement ratios while maintaining workability, superplasticizers contribute to denser, stronger concrete. Lower water-to-cement ratios are a key factor in achieving high-strength concrete.
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Supplementary Cementitious Materials (SCMs): Although not strictly "additives" in the sense of being added in small quantities, SCMs like fly ash, slag, silica fume, and metakaolin can react with the calcium hydroxide produced during cement hydration, forming additional cementitious compounds. This pozzolanic reaction refines the pore structure of the concrete, leading to increased long-term strength and durability. Silica fume is especially effective in producing very high-strength concrete.
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Polymer Admixtures: These admixtures modify the properties of the cement matrix and the interfacial transition zone (ITZ) between the cement paste and the aggregate, leading to improved bond strength and overall concrete strength.
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Shrinkage-Reducing Admixtures (SRAs): By reducing drying shrinkage, SRAs minimize cracking and internal stresses, ultimately contributing to improved durability and, indirectly, long-term strength retention.
Factors Affecting Concrete Strength:
It's important to remember that concrete strength is influenced by several factors beyond admixtures:
- Water-to-Cement Ratio (w/c): A lower w/c ratio generally leads to higher strength.
- Cement Type: Different cement types have varying strength development characteristics.
- Aggregate Properties: The type, size, and grading of aggregates affect concrete strength.
- Curing Conditions: Proper curing (maintaining adequate moisture and temperature) is crucial for optimal hydration and strength development.
- Mixing and Placement: Thorough mixing and proper placement techniques are essential for uniform concrete quality.
Conclusion:
Several additives can enhance the strength of concrete. Alkanolamines directly contribute to compressive strength. Additionally, superplasticizers, accelerating admixtures, supplementary cementitious materials, and polymer admixtures play significant roles in achieving higher concrete strengths by influencing hydration, workability, and the overall microstructure of the concrete. Understanding the specific effects of each admixture allows for tailored concrete mixes designed to meet specific strength requirements.
