9 Questions
What occurs when cement mixes with water in concrete?
Hydration, producing a calcium silicate hydrate (C-S-H) gel
What is the primary role of the calcium silicate hydrate (C-S-H) gel in concrete?
Acting as the 'glue' that binds everything together
What contributes to the mechanical interlocking of aggregates in concrete?
Rough surfaces of the aggregates
What is the primary binding mechanism between aggregates and cement paste in concrete?
Mechanical interlocking of aggregates and C-S-H gel
What is the role of fine sand particles in concrete?
Filling voids between coarse aggregates
What type of forces are responsible for the slight adhesion between cement paste and aggregate surfaces?
Van der Waals forces
What is not a direct result of the chemical reaction between cement and water?
Creation of a chemical bond with aggregates
What is the ultimate result of the combined effects of mechanical interlocking, packing, and friction in concrete?
Strong and durable concrete
What do the rough surfaces of aggregates contribute to in concrete?
Mechanical interlocking with C-S-H gel
Study Notes
Binding of Aggregates with Cement
- Aggregates do not chemically bond with cement particles in concrete, but instead get "stuck" through a physical process.
Cement Hydration
- A chemical reaction called hydration occurs when cement mixes with water.
- Hydration produces a calcium silicate hydrate (C-S-H) gel, which acts as the "glue" that binds everything together in concrete.
Packing and Friction
- Aggregates, particularly fine sand particles, fill the voids between larger coarse aggregates.
- This creates a dense packing where the rough surfaces of aggregates become mechanically interlocked with the hardened C-S-H gel.
- The interlocking shapes of aggregates contribute to a strong mechanical bond.
Interfacial Forces
- Weak attractive forces, such as van der Waals forces, exist between the cement paste (hydrated cement) and aggregate surfaces.
- These forces contribute to a slight adhesion, but are not the primary binding mechanism.
Overall Bonding Mechanism
- The combined effect of mechanical interlocking, dense packing, and weak attractive forces creates a strong bond between aggregates and hardened cement paste.
- This strong bond results in the overall strength and durability of concrete.
Learn about the process of cement hydration and how it leads to the binding of aggregates in concrete through a physical process aided by chemical reactions.
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