A water-reducing admixture (plasticiser) works by:
Choose the correct answer
Increasing water content
Adsorbing on cement particles to disperse them, reducing water demand for given workability
Accelerating cement hydration
Introducing air into concrete
Correct Answer
B. Adsorbing on cement particles to disperse them, reducing water demand for given workability
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Plasticisers / superplasticisers: surface-active agents (sulphonated formaldehyde naphthalene, PCE) adsorb on cement particles and impart negative charge → electrostatic and steric repulsion disperses cement grains → reduces water needed for given workability by 5–15% (normal WRA) or 12–30% (superplasticiser). Allows lower w/c without loss of workability.
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