Concrete properties: water-cement ratio, curing, strength, creep

One-line orientation

Concrete’s behavior — how it cures, why a lower water-cement ratio is stronger, and why it needs steel — drives most of the qualitative concrete questions on the exam.

Key points

• Curing is hydration, not drying. Strength comes from a chemical reaction between cement and water that releases heat and causes shrinkage. Keep the concrete moist (e.g., cover with plastic sheeting); rapid drying weakens it.
• Design strength at ~28 days. Concrete keeps gaining strength after placement; the standard benchmark is about 28 days.
• Water-cement ratio controls strength and workability. Less water generally raises strength but makes the mix harder to place.
• Strength:
  • Compressive: typically 3,000–4,000 psi, ranging roughly 2,000–20,000 psi for ordinary work (ultra-high-strength mixes go higher).
  • Tensile: weak — concrete cracks in tension, so steel reinforcement carries tensile loads.
• Why steel and concrete work together: they expand and contract at similar rates, and concrete’s alkalinity helps protect embedded reinforcing steel from corrosion.
• Creep: long-term deformation under sustained load — distinct from immediate elastic deflection.
• Environmental note: concrete carries a large carbon footprint from cement manufacturing heat and transport.

Confusions / comparison

Property	What it means	Exam takeaway
Cures by hydration	Chemical reaction with water (releases heat)	Keep moist — do not let it dry out to cure
Lower w/c ratio	Less water per cement	Stronger but less workable
Compression	Resists crushing	Concrete’s strength — ~3,000–4,000 psi typical
Tension	Resists pulling apart	Concrete’s weakness → add steel
Creep	Deformation under sustained load	Long-term, slow; not the initial deflection
Shrinkage	Volume loss as it cures/dries	Drives cracking → control joints, temp bars

Related

→ Cement types & admixtures (this topic): how superplasticizers hold workability at low w/c · Reinforcing & prestress (this topic): how steel carries the tension concrete can’t · Mixes & joints (this topic): shrinkage control via joints.