4.10
Types of Cement II
Portland blast-furnace cement is made by blending Portland cement clinker with granulated blast-furnace slag, which accounts for 25 to 65 percent of t…
Intergrinding Portland cement clinker with granulated blast-furnace slag, a by-product of the iron-making process, produces slag cement.
It can be used to construct large structures designed to resist the attack of chlorides and sulfates.
White cement, made from chalk and china clay containing fewer quantities of iron and manganese oxides, has a distinctive white color and can be used to create facades with excellent aesthetics.
Adding colored pigments that are not detrimental to the concrete with white cement produces colored cement.
Expansive cements, such as Types K, M, and S, are produced by combining Portland cement with an expansive agent and a stabilizer. This prevents shrinkage cracking through controlled expansion due to early ettringite formation during hardening.
Air-entrained Portland cement uses smaller quantities of air-entraining materials to form millions of microscopic air bubbles within the cement matrix.
This provides spaces for water to expand into when it freezes, preventing cracking caused by freeze-thaw cycles.
Waterproof Portland cement incorporates water-repellent substances, ensuring structures exposed to moisture are protected against water infiltration.
Q1: What is slag cement and what are its main applications?
Slag cement is produced by intergrinding Portland cement clinker with granulated blast-furnace slag, a by-product of iron-making, which comprises 25 to 65 percent of the cement's weight. It is particularly suited for large structures designed to resist chloride and sulfate attack, and performs well in marine environments due to its superior sulfate resistance and lower heat of hydration.
Q2: How do white and colored cements differ from standard Portland cement?
White cement is made from chalk and china clay with fewer iron and manganese oxides, producing a distinctive white color suitable for aesthetically important applications like facades and precast panels. Colored cement is created by adding pigments to white cement. Both are more expensive due to stringent production requirements to avoid impurities and achieve color uniformity.
Q3: What are expansive cements and how do they prevent cracking?
Expansive cements, including Types K, M, and S, combine Portland cement with an expansive agent and stabilizer. They expand during early hardening to compensate for drying shrinkage, preventing shrinkage cracking through controlled expansion due to early ettringite formation. Type K provides general shrinkage control, Type M offers sulfate resistance, and Type S is designed for high sulfate exposure.
Q4: How does air-entrained Portland cement protect concrete from freeze-thaw damage?
Air-entrained Portland cement incorporates smaller quantities of air-entraining materials to form millions of microscopic air bubbles within the cement matrix. These bubbles provide spaces for water to expand into when it freezes, preventing cracking caused by freeze-thaw cycles and improving concrete durability in cold climates.
Q5: What makes waterproof Portland cement resistant to moisture?
Waterproof Portland cement incorporates water-repellent substances such as calcium stearate or aluminum stearate mixed into the Portland cement clinker during grinding. These additives enhance the cement's resistance to moisture penetration, making it suitable for structures exposed to water and ensuring protection against water infiltration.
Q6: Why does slag cement develop strength more slowly than ordinary Portland cement?
Portland blast-furnace cement has lower early strength compared to ordinary Portland cement despite similar fineness and setting times. However, it achieves comparable strength later on. Its lower heat of hydration makes it particularly suitable for mass concrete structures where reduced heat generation is beneficial.
Q7: Which cement types are best suited for marine and mass concrete applications?
Slag cement is ideal for marine environments and mass concrete structures due to its superior sulfate resistance and lower heat of hydration. Its ability to resist chloride and sulfate attack makes it particularly valuable for coastal structures, while its reduced heat generation prevents thermal cracking in large concrete pours.