Complete Concrete and Mortar: From Limestone to Foundation
⟁ cover painted for this edition — the source module carried no illustrations
Complete Concrete and Mortar: From Limestone to Foundation
Concrete is the most used building material on Earth. This campaign covers cement production, concrete mixing, mortar types, masonry, and reinforcement.
Chapter 1: Cement and Concrete Basics
Term
Definition
Components
Cement
Powder that hardens when mixed with water
Calcium silicates (from limestone + clay, fired)
Mortar
Cement + sand + water
Binding material for masonry
Concrete
Cement + sand + gravel + water
Structural building material
Aggregate
Sand (fine) and gravel (coarse)
Bulk filler, provides strength
Hydration
Chemical reaction of cement + water
Hardening process (not drying)
Curing
Keeping concrete moist during hardening
Critical for strength development
Material
Ratio (by volume)
Use
Strength
Mortar (Type N)
1 cement : 1 lime : 6 sand
General masonry
Moderate
Mortar (Type S)
1 cement : 0.5 lime : 4.5 sand
Structural masonry, below grade
High
Concrete (general)
1 cement : 2 sand : 3 gravel
Foundations, slabs, general
3,000-4,000 PSI
Concrete (strong)
1 cement : 1.5 sand : 2.5 gravel
Structural, columns
4,000-5,000 PSI
Lean concrete
1 cement : 3 sand : 6 gravel
Fill, non-structural
1,500-2,000 PSI
Chapter 2: Primitive Cement Production
Material
Source
Processing
Product
Limestone (CaCO3)
Quarry, river rocks
Burn at 1,650°F+
Quicklime (CaO)
Quicklime (CaO)
Burned limestone
Add water (slake)
Slaked lime (Ca(OH)2)
Hydraulic lime
Limestone with clay impurities
Burn at 1,650°F+
Sets underwater (hydraulic)
Natural cement
Cement rock (limestone + clay)
Burn at 1,800°F+
Natural cement (sets fast)
Portland cement
Limestone + clay (precise ratio)
Burn at 2,700°F (clinker) + grind
Modern cement
Pozzolan
Volcanic ash, brick dust, fly ash
Grind fine
Addite to lime (makes hydraulic)
Lime mortar (historical method): 1) Burn limestone in kiln at 1,650°F+ for 24-72 hours. 2) Result: quicklime (calcium oxide). 3) Slake: carefully add water (EXOTHERMIC, very hot, dangerous). 4) Result: lime putty (calcium hydroxide). 5) Age lime putty under water for weeks-months (improves workability). 6) Mix with sand: 1 part lime putty : 2.5-3 parts sand. 7) This is lime mortar (the mortar used in all construction before Portland cement). 8) Sets by absorbing CO2 from air (carbonation). 9) Slower setting than Portland cement but more flexible and breathable.
Chapter 3: Mixing and Placing Concrete
Factor
Specification
Why
Water-cement ratio
0.4-0.6 by weight
Lower = stronger (but harder to work)
Mixing time
3-5 minutes (thorough)
Even distribution of all components
Slump
3-5 inches (general)
Workability measure
Placement
Within 30-60 minutes of mixing
Begins setting; late placement = weak
Consolidation
Vibrate or rod (poke with stick)
Remove air voids
Finishing
Screed, float, trowel
Smooth surface
Curing
Keep moist 7-28 days
Hydration needs water to continue
Hand mixing concrete: 1) Measure dry ingredients (cement, sand, gravel) onto clean, hard surface or in wheelbarrow. 2) Mix dry ingredients thoroughly (shovel, turning pile). 3) Form crater in center. 4) Add water gradually (not all at once). 5) Fold dry material into water from edges. 6) Mix until uniform color and consistency (no dry pockets). 7) Consistency: should hold shape when squeezed but not be soupy. 8) Too wet = weak concrete (most common mistake). 9) Place immediately (don't let it sit). 10) Consolidate: poke with stick or rod to remove air bubbles.
Chapter 4: Reinforcement
Type
Material
Strength Improvement
Use
Difficulty
Rebar (steel bars)
Steel
Very high (tensile)
Foundations, columns, beams
Moderate
Wire mesh
Steel wire grid
Moderate
Slabs, flatwork
Low
Fiber (steel)
Short steel fibers
Moderate
Slabs, precast
Very low (mix in)
Fiber (synthetic)
Polypropylene fibers
Low-moderate (crack control)
Slabs
Very low (mix in)
Bamboo
Bamboo strips
Moderate
Where steel unavailable
Moderate
Natural fiber
Straw, hemp, sisal
Low (crack control)
Non-structural
Very low
Rebar placement: 1) Rebar goes where concrete is in tension (bottom of beams, bottom of slabs on ground). 2) Minimum cover: 3 inches from ground contact, 1.5 inches from formed surfaces. 3) Tie intersections with wire ties. 4) Support rebar on chairs or stones (keep off ground). 5) Overlap splices: minimum 40 bar diameters (e.g., 1/2 inch bar × 40 = 20 inches overlap). 6) Concrete is strong in compression, weak in tension. 7) Rebar provides tensile strength where concrete cannot.
Chapter 5: Common Projects
Project
Concrete Volume
Reinforcement
Form Complexity
Curing Time
Fence post footing
1-2 cubic ft
None (small)
Hole in ground
3-7 days
Slab (shed floor)
Thickness × area
Wire mesh
Simple edge forms
7-28 days
Foundation wall
Height × length × thickness
Rebar (horizontal + vertical)
Plywood forms
7-28 days
Steps
Variable
Rebar
Complex forms
7-28 days
Retaining wall
Variable
Rebar (heavy)
One-sided forms
28 days minimum
Cistern/tank
Variable
Rebar + waterproofing
Complex forms
28 days + waterproof
Reference Card
Water is the enemy of strength (too much water makes weak concrete; use the minimum water needed for workability). 2. Cure, cure, cure (keep concrete moist for at least 7 days; 28 days is better; uncured concrete is 50% weaker). 3. Concrete is strong in compression, weak in tension (it resists crushing but cracks when pulled; rebar handles tension). 4. Lime mortar breathes (lime mortar allows moisture to pass through; Portland cement traps moisture and can damage old buildings). 5. Mix dry first (thoroughly mix cement, sand, and gravel before adding water; dry pockets = weak spots). 6. Don't add water to stiffen concrete (if concrete is setting, adding water weakens it; mix a new batch instead). 7. Forms must be strong (wet concrete is heavy; weak forms bulge or blow out; brace thoroughly). 8. Concrete never stops getting stronger (hydration continues for years; 28-day strength is the design standard, but it keeps improving).
