CT1

Concrete Ingredients – Detailed Notes

Cement • Water • Aggregates (Fine & Coarse) • Supplementary Cementitious Materials • Chemical Admixtures

High-Level Flowchart: From Ingredients to Fresh & Hardened Concrete

Figure 1: Ingredient-to-concrete flow.

At a Glance

Cement = Binder Aggregates = Skeleton Water = Reactant Admixtures = Tailoring

Rule of Thumb: Lower w/c → Higher strength & durability. Use water reducers for workability.

• Target strength drives w/c and cement content.
• Use clean, well-graded aggregates.
• SCMs improve durability.
• Admixtures adjust workability, set, air.
• Moisture corrections for batching.
• Early curing prevents shrinkage.

1) Cement (Binder)

Function: Hydrates with water to form C-S-H gel (strength) and CH (alkalinity). Types: OPC, PPC (fly ash), PSC (GGBS).

Key Property	Notes
Fineness (Blaine)	280–450 m²/kg; finer → faster strength.
Initial / Final Set	~30–45 min / 8–10 h.
Soundness	Low expansion to prevent cracking.
Early Strength	Better with lower w/c, accelerators.

Images: Cement Bag & Hydration Sketch (SVG)

Select cement based on exposure and durability needs.

2) Water

Function: Reacts with cement; aids workability. Use potable water, free from salts, oils, acids.

Key Check	Guidance
pH	≥ 6; neutral to alkaline.
Sulfates/Chlorides	Low to avoid corrosion.
Temperature	Cool for hot weather; warm for cold.

Diagram: w/c vs Strength

Tip: Use plasticizers to reduce water, maintain slump.

3) Fine Aggregate (Sand)

Function: Fills voids, improves finish. Use clean, well-graded sand, low silt.

Property	Notes
Grading	Continuous grading; blend if needed.
Silt Content	Low; wash to reduce water demand.
Shape	Rounded for workability; angular for strength.

Diagram: Sieve Grading Envelope

4) Coarse Aggregate

Function: Load-bearing skeleton; reduces shrinkage. Use angular, crushed stone, low flakiness.

Property	Notes
Nominal Size	20 mm & 10 mm; blend for packing.
Specific Gravity	~2.6–2.8 for siliceous rocks.
Moisture	Adjust for water corrections; SSD basis.
Strength	Low abrasion; free from clay.

Diagram: Moisture State & Water Correction

5) Supplementary Cementitious Materials (SCMs)

Function: Improves durability, reduces heat, enhances strength, lowers clinker.

SCM	Use	Benefits
Fly Ash	15–35%	Workability, sulfate resistance
GGBS	25–60%	Low heat, chloride resistance
Silica Fume	5–10%	High strength, low permeability
Metakaolin	5–15%	Early strength, color control

Ranges depend on specs and testing.

6) Chemical Admixtures

Function: Modify fresh and hardened properties.

Type	Purpose	Notes
Plasticizer	Increase slump	Check compatibility.
Air-Entraining	Freeze-thaw durability	Reduces strength.
Retarder	Delay set	For hot weather.
Accelerator	Early strength	For cold weather.
Shrinkage Reducer	Lower shrinkage	Crack control.

Image: Admixture Bottles (SVG)

Mix Design Snapshot

Target	Primary Lever	Support Levers	Watch-outs
Strength	Lower w/c	SCMs, curing	Workability loss
Workability	Paste, SP dosage	Aggregate shape	Segregation
Durability	Low w/c	SCMs, air	Poor curing
Economy	Aggregate packing	SCM replacement	Risk durability

Strength trend Workability trend Durability trend Economy trend

Quality Control & Field Checks

• Moisture: Adjust water for aggregates.
• Slump: Check consistency.
• Temperature: Measure fresh concrete.
• Air Content: For durability.
• Cubes: 7- & 28-day strength.

✓ Good grading reduces paste.
✗ Excess water harms durability.

Practical Checklist (Before You Pour)

• Confirm cement type & dry storage.
• Verify sand silt content.
• Blend coarse sizes.
• Calibrate batch scales; SSD basis.
• Check admixture compatibility.
• Set target slump.
• Plan curing; start ASAP.
• Ensure clean reinforcement.

Types of Cement — Properties, Uses, Pros & Cons

Quick reference notes with flowcharts, diagrams, and printable layout.

Overview Flowchart: Choosing a Cement Type

Figure: Decision flow to select cement type.

Quick Chips

OPC — Ordinary Portland Cement

PPC — Portland Pozzolana Cement

PSC — Portland Slag Cement

SR — Sulfate Resisting

RH — Rapid Hardening

Usage Summary

• OPC: General construction, small works.
• PPC: Sustainable, mass concrete, durable.
• PSC: Marine, chloride resistance, low heat.
• Rapid Hardening: Repairs, fast turnover.

Type — Properties — Uses

Type	Properties	Uses
OPC (43/53 grade)	Predictable strength, moderate heat	Buildings, pavements, slabs
PPC	Lower heat, sulfate resistance	Mass concrete, marine
PSC / GGBS	Low heat, chloride resistance	Ports, coastal structures
Rapid Hardening	High early strength, high C3S	Repairs, precast, winter
Sulfate Resisting	Low C3A, sulfate resistance	Foundations, sewage works

Notes on Grades

OPC grades (33/43/53) indicate 28-day strength (MPa). Select based on design.

Specialty Cements

Type	Properties	Uses
White Cement	Low iron, aesthetic finish	Architectural, terrazzo
High Alumina	Rapid strength, heat resistant	Refractory, rapid repairs
Oil-well	Sets under pressure, high temp	Well cementing
Hydrophobic	Repels moisture	Monsoonal supply, mortars
Expansive	Offsets shrinkage	Grouting, crack control

Pros & Cons

Type	Pros	Cons
OPC	Predictable, cost-effective	Higher CO2, heat
PPC	Durable, low CO2, economical	Slower early strength
PSC	Chloride resistance, low heat	Limited availability
Rapid Hardening	Fast turnover	Higher cost, heat
Sulfate Resisting	Sulfate protection	Costlier, niche use

Cement Components & Hydration

Figure: Clinker phases and hydration products.

Selection Checklist

• Check exposure (sulfate/chloride).
• Assess early strength needs.
• Consider heat control for mass concrete.
• Evaluate sustainability (SCM %, CO2).
• Verify local availability.
• Trial mixes for compatibility.

Compatibility & Quality Control

Notes for site engineers:

• Storage: Keep cement dry, use FIFO.
• Compatibility: Trial mixes for admixtures.
• Batching: Use SSD aggregates, correct moisture.
• Testing: Check strength, fineness, setting time.

Aggregates — Detailed Notes

Types • Classification (size, shape, texture, moisture) • IS:383 grading zones • Shape indices & formulas

Decision Flowchart — Choose Aggregate Type & Quality Checks

Figure: Selection & QC flow for aggregates.

Types of Aggregates (by Source)

• Natural: River sand, crushed rock (granite, limestone).
• Manufactured: M-sand, crushed gravel/stone.
• By-products: Blast furnace slag, steel slag, ash.
• Recycled: Recycled Concrete Aggregate (RCA).

Classification & use per IS:383.

Classification — Size (Coarse & Fine)

Fine: Passes 4.75 mm IS sieve (sands). Grading zones I–IV (IS:383).

Coarse: Nominal sizes: 10, 12.5, 16, 20, 40, 63 mm. Graded: 12.5/16/20/40 mm.

Key Definitions

• Max Size: Smallest sieve where 100% passes.
• Nominal Max: Most material passes.
• Single-sized: Retained on one sieve.

Shape & Surface Texture

• Shape: Rounded, sub-angular, angular, flaky/elongated.
• Texture: Smooth (less bond); rough (better interlock).
• Effect: Angular increases strength, water demand; rounded improves workability.

Shape/texture affects mix design & workability.

Moisture States & % Moisture

Aggregates' moisture affects batch water:

• Oven-dry (OD): No moisture (lab use).
• Air-dry (AD): Some internal moisture.
• Saturated Surface Dry (SSD): Pores full, no surface water.
• Wet: Free surface water.

% Moisture:
(Mass_wet - Mass_od) / Mass_od × 100

Correct batch water: Target water − (Free moisture × Aggregate mass). Use SSD basis.

Grading Zones for Fine Aggregates — IS:383

Grading limits for fine aggregates (percent passing, IS:383 Table 9):

IS Sieve	Zone I (%)	Zone II	Zone III	Zone IV
10.0 mm	100	100	100	100
4.75 mm	90–100	90–100	90–100	95–100
2.36 mm	60–95	75–100	85–100	85–100
1.18 mm	30–70	55–90	75–100	90–100
600 μm	15–34	35–59	60–79	80–100
300 μm	5–20	8–30	12–40	15–50
150 μm	0–10	0–10	0–10	0–10

Crushed sands may have higher 150 μm passing. See IS:383 for tolerances.

Practical QC & Specification Tips

• Test sources for grading, shape, mechanical properties (IS:383).
• Use SSD basis; correct for moisture (IS:2386 Part 3).
• Control flakiness for structural surfaces.
• Blend sizes for packing, reduce paste demand.

References & Standards

• IS 383: Grading zones, limits (Table 9).
• IS 2386: Tests for size, shape, absorption (Parts 1, 3).
• Lab guides for aggregate testing.

Tests on Aggregates – Detailed Notes

Sieve analysis • Shape tests • Angularity • Specific gravity • Absorption • Mechanical tests • Soundness • Deleterious materials

Overview Flowchart: Aggregate Testing Sequence

Figure: Typical testing sequence for aggregates (IS standards).

1) Sieve Analysis (Grading Test)

Purpose: Determine particle size distribution for grading classification (IS 2386 Part 1).

Procedure: Dry sample, sieve through IS sieves, weigh retained on each, calculate % passing.

% Passing = (Cumulative mass passing / Total mass) × 100

Plot grading curve; check against IS 383 zones for fine aggregates.

Mean Dimension, Flakiness & Elongation Index

Mean Dimension (Dm)

Average of length (L), breadth (B), thickness (T):

Dm = (L + B + T) / 3

Flakiness Index (FI)

Percentage of particles with thickness < 0.6 × Dm (IS:2386 Part 1).

FI (%) = (Mass of flaky particles / Total mass) × 100

Procedure: Gauge particles for thickness; weigh flaky portion.

Elongation Index (EI)

Percentage of particles with length > 1.8 × Dm (IS:2386).

EI (%) = (Mass of elongated particles / Total mass) × 100

Acceptance: Lower FI & EI preferred; check combined limits (IS:383).

Angularity Number

Measures angularity via voids in compacted aggregates (IS:2386 Part 1).

Angularity number = (% voids) − 33

Rounded aggregates ~33% voids; higher number = more angular (0–12 range).

Why Angularity Matters

• Angular aggregates improve interlock, strength, but increase water demand.
• Used in bituminous mixes, concrete bases.

Example: Flakiness & Elongation

Sample (10–20 mm), total mass = 10,000 g:

• Flaky mass = 1,200 g → FI = 12%.
• Elongated mass = 300 g → EI = 3%.

IS:383 requires combined FI+EI check (clause 5.3).

Formulas & Diagrams

Percent Passing

% Passing = (Mass passing sieve / Total mass) × 100

Bulk Density & Voids

Voids (%) = (1 − Bulk density / Particle density) × 100

Shape Thresholds (Schematic)

4) Specific Gravity & Water Absorption

Specific Gravity: Ratio of aggregate density to water (IS 2386 Pt3).

SG = (Mass OD / (Mass SSD - Mass in water))

Water Absorption: % increase in mass due to water in pores.

Absorption (%) = ((Mass SSD - Mass OD) / Mass OD) × 100

Use pycnometer or wire basket method; limits in IS 383.

5) Mechanical Tests

Aggregate Crushing Value (ACV)

Measures resistance to crushing (IS 2386 Pt4).

ACV (%) = (Mass passing 2.36mm / Total mass) × 100

Aggregate Impact Value (AIV)

Resistance to impact.

AIV (%) = (Mass passing 2.36mm / Total mass) × 100

Los Angeles Abrasion Value (LAAV)

Abrasion resistance.

LAAV (%) = (Mass lost / Original mass) × 100

Limits: ACV <30%, AIV <30%, LAAV <40% for concrete (IS 383).

6) Soundness Test

Purpose: Durability against weathering (IS 2386 Pt5).

Procedure: Cycles of sodium/magnesium sulfate immersion and drying; measure mass loss.

Soundness Loss (%) = (Mass lost / Original mass) × 100

Limits: <12% for Na2SO4, <18% for MgSO4 (5 cycles).

7) Deleterious Materials Test

Purpose: Check for clay, silt, organic impurities (IS 2386 Pt2).

Silt Content: Settling test for fine aggregates.

Silt (%) = (Volume of silt / Volume of sample) × 100

Organic Impurities: Color test with NaOH.

Limits: Silt <3%, organic not darker than standard.

8) Bulk Density & Voids

Bulk Density: Mass per unit volume (loose/rodded, IS 2386 Pt3).

Bulk Density = Mass / Volume

Voids: Space between particles.

Voids (%) = (1 - Bulk Density / SG) × 100

Used for volume calculations in batching.

9) Explanatory Diagram: Sieve Analysis Setup (Schematic)

Figure: Basic sieve analysis process.

10) Practical Tips & References

• Use representative samples (IS 2430).
• Frequency: As per IS 383 for QC.
• Acceptance: Check against IS 383 limits.

Standards: IS 2386 (Parts 1-8) for test methods; IS 383 for limits.

Ask for PDF version or specific IS extracts.