Concrete & Masonry

Concrete

Concrete is a mix of cement, aggregate (sand and gravel), and water that hardens (cures) into a rock-hard mass. Its strength is measured in psi (pounds per square inch) — common residential mixes run a few thousand psi.

Concrete is strong in compression but weak in tension — so it's reinforced with steel rebar or wire mesh to handle pulling and bending forces. That's why you see rebar in foundations and slabs.

Masonry

Masonry units are stacked and bonded with mortar:

• Concrete block (CMU) — structural walls and foundations.
• Brick and stone — structural and decorative.

Going Deeper (Intermediate)

Concrete = cement + aggregate + water, strong in compression but weak in tension — so it's reinforced with rebar or mesh. Strength is rated in PSI (≈3,000–4,000 for residential, higher for structural). Masonry = brick, CMU (block), mortar, and grout.

Advanced / Pro-Level

What controls concrete quality:

• Water-cement ratio — lower = stronger and more durable (but less workable); never add water on site to ease placement, it weakens the pour.
• Slump measures workability; curing (keep it moist ~7 days) develops the 28-day design strength; air-entrainment protects against freeze-thaw; admixtures accelerate/retard/plasticize.
• Rebar: sized in ⅛″ increments (#4 = ½″), Grade 60, with required concrete cover for corrosion protection.
• Masonry: CMU is 8×8×16 nominal, reinforced by grouting rebar into cells; mortar types N/S/M by strength; control/expansion joints manage cracking.

Practice Challenge

A crew adds extra water to a concrete truck to make it flow easier into the forms. What did they just do to the slab? (Answer: they raised the water-cement ratio, which lowers strength and durability and increases cracking/shrinkage — the slab won't reach its design PSI; workability should be fixed with admixtures/mix design, never by adding water on site.)

In Practice

Pour a structural slab with no rebar or mesh and it can crack and fail under load — because concrete is strong in compression but weak in tension. The steel carries the pulling forces.

Common Mistakes to Avoid

• Leaving out reinforcing steel where it's needed
• Adding too much water (it weakens the mix)
• Not curing the concrete properly

Takeaway: Concrete is strong in compression but weak in tension — so it's reinforced with rebar; masonry units are set in mortar.

Educational overview — specific grades, sizing, and structural uses come from the building code and the project's engineer and specifications.