Addition of sugar to concrete results in:

Detailed Explanation: Sugar Retards Setting by ≈4 Hours

Why B (Increase by about 4 hours) is correct: Sugar (saccharose/sucrose) is a very effective retarder for cement hydration. At a dosage of approximately 0.2% by mass of cement, it delays the initial setting time by about 4 hours. This is because sugar molecules adsorb strongly onto C₃S and C₃A surfaces in the cement particles, forming a thin coating that physically blocks water from reaching the unhydrated surface.

Sugar as a Retarder

Dosage (% by wt. cement)	Effect on Setting Time	Practical Outcome
0.05%	Delay of ≈1–2 hours	Mild retardation; slight extension
0.1%	Delay of ≈2–3 hours	Moderate retardation
0.2%	Delay of ≈4 hours	Significant retardation; the standard reference dosage
0.3%+	May cause permanent inhibition (never sets)	Excess sugar can permanently prevent setting — dangerous

Mechanism of Sugar Retardation

Step	What Happens
1. Sugar dissolves	Sugar dissolves in mix water; produces sucrose molecules in solution
2. Adsorption on cement	Sucrose molecules adsorb strongly onto C3S and C3A particle surfaces
3. Barrier formation	Adsorbed layer prevents water from accessing the reactive cement surfaces
4. Delayed hydration	C-S-H gel formation slowed; setting time extended by ≈4 hours
5. Sugar gradually deactivated	As Ca2+ ions build up, they displace sucrose; hydration resumes normally after delay

Practical Uses of Sugar as a Retarder

Situation	Why Sugar Retarder Is Used
Emergency site situations	Sugar is cheap and available; can buy time if ready-mix truck is delayed
Hot weather concreting	Combats the accelerating effect of high temperature
Exposed aggregate finish	Applied to the surface; retards surface paste; wash off later to expose aggregate texture

• Sugar at 0.2% by weight of cement increases setting time by approximately 4 hours.
• Excess sugar (>0.3%) can permanently prevent setting — a common cause of concrete failures when laborers add too much.
• Sugar is an economical emergency retarder; it acts by adsorption onto cement particle surfaces.