Which one of the following materials is used as a bonding admixture?
🔬 Understanding Bonding Admixtures
A bonding admixture is a substance added to a cementitious mix (like concrete or mortar) or applied to an existing surface to improve the adhesion or "bond" between two layers. This is especially critical when applying new concrete or plaster to an old, hardened concrete surface, as a strong bond is difficult to achieve otherwise.
Mechanism: These admixtures are typically water emulsions of organic polymers. When added to the mix or painted on a surface, the polymer particles coalesce as the water evaporates, forming a thin, flexible film that acts as a powerful adhesive "bridge" between the old and new materials.
⚖️ Detailed Analysis of the Options
Let's evaluate each option to see how it fits the definition of a bonding admixture.
(c) organic polymers
Classification: This is the broad, correct chemical category for these admixtures. Common examples include Styrene-Butadiene Rubber (SBR), Polyvinyl Acetate (PVA), and acrylics. All of these are long-chain organic molecules (polymers).
(a) natural rubber
Classification: Natural rubber, in the form of latex, is a type of organic polymer. Natural rubber latex emulsions are used as bonding agents to improve adhesion and flexibility in cement mortars.
(b) synthetic rubber
Classification: Synthetic rubbers, such as SBR, are also organic polymers. SBR is one of the most common and effective bonding admixtures used in the construction industry for concrete repair and overlays.
(d) All option are correct
Why it's the best answer: Since natural rubber and synthetic rubber are both specific types of organic polymers, and all three are used as bonding admixtures, this option is the most complete and correct answer. It acknowledges that the specific examples (a and b) fall under the general category (c) and are all valid.
💡 Study Tips for Admixtures
- Bonding = Polymers: The fundamental principle is that organic polymers act as the "glue" in bonding admixtures.
- Rubber is a Polymer: Remember that both natural and synthetic rubbers are types of polymers. This helps connect the specific examples to the general category.
- Think of Concrete Repair: The most common use for a bonding agent is patching old concrete. You need a powerful glue to make the new patch stick, and that glue is a polymer admixture.