Mayank's House — Concrete Grade Specifications

Concrete Grades — Quick Reference

Sheet 1 of 5

All grades per IS 456:2000 Table 2 · Nominal mix and design mix specified where applicable · M20 & M25 primary grades for this project

Standard Grade

M15

fck = 15 N/mm²

Char. strength15 MPa

Mix ratio (nom.)1 : 2 : 4

w/c ratio (max)0.60

Min. cement250 kg/m³

Slump50–75 mm

WorkabilityLow–Med

Min. cover40 mm

Exposure classMild

USE: Blinding / levelling course under footings & PCC. Not structural. Also mass filling.

★ Primary Grade — Slabs & Beams

M20

fck = 20 N/mm²

Char. strength20 MPa

Mix ratio (nom.)1 : 1.5 : 3

w/c ratio (max)0.55

Min. cement300 kg/m³

Slump75–100 mm

WorkabilityMedium

Min. cover30 mm

Exposure classMild–Moderate

USE: All slabs (GF, FF, roof), all beams (PB/GB/FB), staircase waist slab & landings. Standard RCC grade for this project.

★ Primary Grade — Columns & Footings

M25

fck = 25 N/mm²

Char. strength25 MPa

Mix ratio (nom.)1 : 1 : 2

w/c ratio (max)0.50

Min. cement320 kg/m³

Slump75–100 mm

WorkabilityMedium

Min. cover40 mm

Exposure classModerate

USE: All columns (GF + FF), isolated footings, combined footings, plinth beams PB. Higher grade for load-bearing compression members.

High Strength

M30

fck = 30 N/mm²

Char. strength30 MPa

Mix typeDesign mix only

w/c ratio (max)0.45

Min. cement340 kg/m³

Slump100–125 mm

WorkabilityHigh

Min. cover45 mm

Exposure classModerate–Severe

NOT used in this project. Reference only. Applicable for high-rise / seismic zone IV–V or severe exposure.

High Strength

M35

fck = 35 N/mm²

Char. strength35 MPa

Mix typeDesign mix only

w/c ratio (max)0.40

Min. cement360 kg/m³

Slump100–150 mm

WorkabilityHigh

Min. cover45 mm

Exposure classSevere

NOT used in this project. Reference only. Suitable for bridges, parking structures, industrial buildings, severe exposure.

Very High Strength

M40

fck = 40 N/mm²

Char. strength40 MPa

Mix typeDesign mix + admix

w/c ratio (max)0.35

Min. cement380 kg/m³

Slump125–175 mm

WorkabilityVery High

Min. cover50 mm

Exposure classVery Severe

NOT used in this project. Reference only. Used for pre-stressed members, high-rise cores, marine/industrial severe exposure.

Compressive Strength Comparison — All Grades

fck N/mm² at 28 days

M15

M20

M25

M30

M35

M40

          Characteristic compressive strength fck (N/mm²) at 28 days · IS 456:2000 Table 2
        

W/C Ratio Comparison

Lower = Stronger

0.60

M15

Max w/c = 0.60 · Mild exposure

0.55

M20 ★

Max w/c = 0.55 · Mild–Moderate

0.50

M25 ★

Max w/c = 0.50 · Moderate

0.45

M30

Max w/c = 0.45 · Moderate–Severe

0.40

M35

Max w/c = 0.40 · Severe

0.35

M40

Max w/c = 0.35 · Very Severe

Comprehensive Properties Table — All Grades

IS 456:2000 · SP 23 · IS 10262:2019

Property	M15	M20 ★	M25 ★	M30	M35	M40
fck (N/mm²) @ 28d	15	20	25	30	35	40
fck (N/mm²) @ 7d	10	13.3	16.7	20	23.3	26.7
Target mean str. fcm	21.65	26.6	31.6	38.25	43.25	48.25
Modulus of elasticity Ec (GPa)	27.4	22.4	25.0	27.4	29.6	31.6
Flexural strength fcr (MPa)	2.8	3.3	3.7	4.1	4.5	4.8
Tensile strength (approx.)	1.5	2.0	2.5	3.0	3.5	4.0
Nominal mix ratio C:S:A	1:2:4	1:1.5:3	1:1:2	Design	Design	Design
Max w/c ratio	0.60	0.55	0.50	0.45	0.40	0.35
Min. cement content (kg/m³)	250	300	320	340	360	380
Max cement content (kg/m³)	450	450	450	450	450	450
Min. cover — mild (mm)	20	20	20	25	30	45
Min. cover — moderate (mm)	30	30	30	35	40	50
Slump range (mm)	50–75	75–100	75–100	100–125	100–150	125–175
Density (kg/m³)	2400–2500 (all grades)
IS 456:2000 min. grade — mild	M15	✓	✓	✓	✓	✓
IS 456:2000 min. grade — moderate	—	M20 min.	✓	✓	✓	✓
Recommended for this project	BLINDING	SLABS/BEAMS	COLS/FTGS	NOT USED	NOT USED	NOT USED

Structural Members — Grade Assignment

Sheet 2 of 5

Concrete grade specified for each structural element · Mayank's House G+1 · IS 456 Cl. 6.1.1

Grade Legend

M15

BLINDING ONLY

Non-structural · PCC base

M20

SLABS · BEAMS · STAIRS

Primary RCC structural grade

M25

COLUMNS · FOOTINGS

Load-bearing compression members

Project Rule:
All horizontal members (slabs, beams, stairs) → M20
All vertical members (columns, footings) → M25
Blinding / levelling courses → M15

Foundation Level

BELOW GF SLAB · SUBSTRUCTURE

PCC BlindingM15

75–100mm PCC under all footings and ground beams · non-structural · levelling course · prevents soil contamination of footing concrete

MPa

Isolated Footings F1–F6M25

All column footings · sizes 1200×1200×400 to 1800×1800×450mm · high grade for soil bearing + durability in contact with ground moisture

MPa

Combined Footings CF1–CF2M25

Combined footings at boundary columns · same grade as isolated footings · in contact with soil

MPa

Plinth Beams PB (300×450mm)M20

Tie beams at +450mm NGL · 7 beam lines × 3 spans · grade M20 per IS 456 · mild exposure class · 30mm cover

MPa

Ground Floor Structure

+0.00 TO +3.00m

GF Columns C1–C12M25

300×300mm · 12 columns · height 3000mm · primary compression members · higher grade ensures ductility & confinement

MPa

GF Beams GB (230×450mm)M20

All GF beams · 7 longitudinal + 4 transverse lines · T-beam action with slab · cast monolithic

MPa

GF Slab (125mm)M20

125mm two-way slab · all panels · T10@150 both ways · cast with beams in one pour

MPa

Staircase — Waist Slab + LandingsM20

150mm waist slab · GF & FF landings 150mm · T10@150 main bars · entire staircase M20 grade

MPa

First Floor & Roof Structure

+3.00 TO +6.45m

FF Columns C1'–C12'M25

300×300mm · same section as GF columns · grade M25 maintained throughout height for consistency

MPa

FF Beams FB (230×375mm)M20

Roof-level beams · reduced depth 375mm · lighter loading · M20 adequate for roof condition

MPa

Roof Slab (125mm)M20

125mm two-way slab · exposed to weather · 30mm cover (top) · waterproofing above · cast with FF beams

MPa

Brick Bat Coba / ScreedM15

50mm brick bat coba waterproofing screed on roof · non-structural · M15 or equivalent lean mix

MPa

Grade Assignment Summary — All Elements

COMPLETE PROJECT MATRIX

Element	Level	Grade	fck (MPa)	Cover (mm)	w/c max	Exposure	IS 456 Ref.
SUBSTRUCTURE
PCC Blinding	Fndn.	M15	15	—	0.60	Mild	Cl. 6.1
Isolated Footings F1–F6	Fndn.	M25	25	50	0.50	Moderate	Cl. 26.4.2
Combined Footings CF1–CF2	Fndn.	M25	25	50	0.50	Moderate	Cl. 26.4.2
Plinth Beams PB 300×450	Plinth	M20	20	30	0.55	Mild	Cl. 26.4.1
GROUND FLOOR
GF Columns 300×300	GF	M25	25	40	0.50	Moderate	Cl. 26.4.1
GF Beams GB 230×450	GF	M20	20	30	0.55	Mild	Cl. 26.4.1
GF Slab 125mm	GF	M20	20	20	0.55	Mild	Cl. 26.4.1
Staircase Waist + Landings	GF	M20	20	20	0.55	Mild	Cl. 33
FIRST FLOOR & ROOF
FF Columns 300×300	FF	M25	25	40	0.50	Moderate	Cl. 26.4.1
FF / Roof Beams FB 230×375	FF	M20	20	30	0.55	Mild	Cl. 26.4.1
Roof Slab 125mm	Roof	M20	20	30 (top)	0.55	Mild	Cl. 26.4.1
Brick Bat Coba Screed	Roof	M15	15	—	0.60	—	Non-str.

Mix Design — M20 & M25

Sheet 3 of 5

Nominal mix for site use · Design mix proportions per IS 10262:2019 · OPC 53 grade cement · 20mm downgraded coarse aggregate

M20 Mix Design — Slabs, Beams, Stairs

Nominal 1:1.5:3 · Or design mix per IS 10262

fck N/mm²

0.55

max w/c

300

min. cement kg/m³

100

slump (mm)

OPC 53 Cement

320 kg

320 kg/m³

Fine Aggregate

640 kg

640 kg/m³

Coarse Aggregate

1150 kg

1150 kg/m³

Water

176 L

176 L/m³

Admixture

1.5 kg

Optional SP

Total volume per m³	~2290 kg/m³
Nominal ratio C:FA:CA	1 : 2.0 : 3.6
Coarse agg. max size	20mm downgraded
FA zone	Zone II (IS 383)
Air content	1.5–2.0%
Admixture (if used)	Plasticiser @ 0.3% of cement wt.
Target mean fck	26.6 N/mm²
Standard deviation σ	4.0 N/mm² (IS 456 Table 8)

M25 Mix Design — Columns & Footings

Nominal 1:1:2 · Or design mix per IS 10262

fck N/mm²

0.50

max w/c

340

min. cement kg/m³

slump (mm)

OPC 53 Cement

360 kg

360 kg/m³

Fine Aggregate

580 kg

580 kg/m³

Coarse Aggregate

1100 kg

1100 kg/m³

Water

165 L

165 L/m³

Admixture

1.8 kg

SP recommended

Total volume per m³	~2210 kg/m³
Nominal ratio C:FA:CA	1 : 1.6 : 3.1
Coarse agg. max size	20mm (columns) / 20mm (footings)
FA zone	Zone II–III (IS 383)
Air content	1.5%
Admixture	Superplasticiser @ 0.4% cement wt.
Target mean fck	31.6 N/mm²
Standard deviation σ	4.0 N/mm² (IS 456 Table 8)

Material Specifications — All Ingredients

IS CODE REFERENCES

Material	IS Code	Grade / Type	M20 Qty / m³	M25 Qty / m³	Quality Requirement
Cement	IS 12269	OPC 53 Grade	320 kg	360 kg	Fresh, no lumps, <30 days from mfr.
Fine Aggregate (Sand)	IS 383	Zone II or III	640 kg	580 kg	FM 2.4–2.8 · silt <4% · clean river sand
Coarse Aggregate	IS 383	20mm downgraded	1150 kg	1100 kg	Clean, hard, durable · elongation <15%
Water	IS 456 Cl. 5.4	Potable quality	176 L	165 L	pH 6–8 · TDS <2000 ppm · no sulphates/chlorides
Admixture (if used)	IS 9103	Plasticiser / SP	Optional 1.5 kg	Recommended 1.8 kg	Compatible with OPC · manufacturer data sheet
Mineral Admixture	IS 3812 / IS 1489	Fly ash / PFA	Optional ≤30%	Optional ≤20%	Replace cement partially for workability improvement

Curing Regime & Strength Gain

Sheet 4 of 5

IS 456:2000 Cl. 13 · Minimum 7-day moist curing for OPC · 28-day design strength · Strength gain percentages vs time

Strength Gain vs Time — M20 & M25

OPC 53 GRADE CEMENT · TYPICAL CURVE

M20 — Strength Gain

1 day

16%

~3.2 MPa

3 days

40%

~8 MPa

7 days

67%

~13.4 MPa

14 days

80%

~16 MPa

28 days ★

100%

20 MPa

90 days

115%

~23 MPa

M25 — Strength Gain

1 day

16%

~4 MPa

3 days

40%

~10 MPa

7 days

67%

~16.7 MPa

14 days

80%

~20 MPa

28 days ★

100%

25 MPa

90 days

115%

~29 MPa

Note: Strengths are characteristic values · Actual mean strength = fck + 1.65σ · 7-day strength test used as indicative check only · 28-day test is the acceptance criterion per IS 456

Formwork Striking Times

IS 456:2000 TABLE 11 · MINIMUM PERIODS

Member	Min. Period	Condition
Walls, columns, vertical faces of beams	24–48 hrs	Temp ≥15°C
Soffits of slabs (props left)	3 days	Span ≤4.5m
Soffits of slabs (props left)	7 days	Span >4.5m
Soffits of beams (props left)	7 days	Span ≤6m
Soffits of beams (props left)	14 days	Span >6m
Props to slabs (span ≤4.5m)	7 days	—
Props to slabs (span >4.5m)	14 days	—
Props to beams and arches	14–21 days	Span dependent

Curing Protocol — Step by Step

IS 456 Cl. 13 · MANDATORY

Immediate Surface Protection

Immediately after casting and initial set (~2–4 hrs), cover all exposed surfaces with wet hessian cloth / polythene sheet. Prevent rapid evaporation — critical in hot/windy site conditions at Dehradun (summer max 38°C).

0–4 hrs

Water Curing — Slabs

Flood-cure all slabs by ponding water. Build earthen bunds around slab edges. Keep ponded at all times. Minimum depth 25mm of standing water. Replenish twice daily. Required duration: 7 days minimum for OPC (14 days recommended for exposed roof).

7–14 days

Water Curing — Columns & Beams

Wrap exposed column and beam surfaces with wet burlap/hessian. Keep continuously wet with regular wetting schedule (minimum 3× per day). Alternatively use curing compound (IS 9103) applied immediately after stripping formwork. Minimum 7 days.

7 days min.

Footing Curing

Backfill excavation immediately after 48-hr initial curing and moist soil ensures ongoing curing. For exposed portions, use ponding or wet hessian. M25 footings require full 7-day curing before applying backfill loads.

7 days

Curing Compound (Alternative)

Approved curing compound per IS 9103 may be used as alternative to wet curing. Apply 2 coats immediately after finishing while surface is still moist. Do not use on construction joints or surfaces to receive further concrete / plaster.

Immediate

Hot Weather Precautions

When ambient temperature exceeds 35°C: chill mixing water with ice (target concrete temp ≤30°C at discharge). Shade aggregates. Pre-wet formwork. Schedule pours for early morning or night. Increase curing frequency to 4–5 times daily.

When T >35°C

28-Day Strength Achievement

Design strength achieved at 28 days. Cube test results should confirm fck before imposing full service loads. Do not load slabs until formwork striking criteria met. Maintain construction records of pour dates per member.

28 days ★

Quality Control & Testing Protocol

Sheet 5 of 5

IS 456:2000 Cl. 15 & 16 · IS 516 compression testing · IS 1199 workability · Acceptance criteria · Sampling frequency

Sampling & Testing Frequency

IS 456:2000 TABLE 14 · MINIMUM SAMPLES

Concrete Volume	No. of Samples	No. of Cubes per Sample	Total Cubes
1–5 m³	1	6 (3 @ 7d + 3 @ 28d)	6
6–15 m³	2	6 per sample	12
16–30 m³	3	6 per sample	18
31–50 m³	4	6 per sample	24
>50 m³	4 + 1 per 50m³	6 per sample	Variable

Cube size: 150mm × 150mm × 150mm per IS 516
Curing of cubes: Demould at 24 hrs · water-cure at 27±2°C till test date
Test ages: 7 days (indicative) + 28 days (acceptance)
Machine: Compression testing machine calibrated per IS 1828

Acceptance Criteria — IS 456:2000 Cl. 16

BOTH CONDITIONS MUST BE SATISFIED

CONDITION 1 — Individual Cube

              Individual cube strength (28d) ≥ fck − 3 N/mm²

              For M20: Each cube ≥ 17 N/mm²

              For M25: Each cube ≥ 22 N/mm²

CONDITION 2 — Mean of Group

              Mean strength of group of 4 consecutive samples ≥ fck + 0.825σ

              For M20 (σ=4.0): Mean ≥ 23.3 N/mm²

              For M25 (σ=4.0): Mean ≥ 28.3 N/mm²

REJECTION CRITERIA

              If either condition fails → STOP pour on that element

              Conduct core tests per IS 516 Part 4

              If cores fail → demolish and reconstruct element

Complete QC Checklist — Site Quality Assurance

PRE-POUR · DURING POUR · POST-POUR

Stage	Check Item	Method / Frequency	Acceptance Criterion	Status
PRE-POUR CHECKS
Pre-pour	Cement quality — date of manufacture	Visual + dispatch note	<3 months old · no lumps	CHECK
Pre-pour	Aggregate sieve analysis	IS 2386 · each new consignment	Zone II/III · CA 20mm max	CHECK
Pre-pour	Water quality test	IS 456 Cl. 5.4 · once per source	pH 6–8 · TDS <2000 ppm	CHECK
Pre-pour	Rebar inspection — dia, cover, ties	Visual 100% before pour	Per approved drawings	MANDATORY
Pre-pour	Formwork check — alignment, levels	Theodolite / spirit level	±5mm tolerance	MANDATORY
Pre-pour	Cover blocks in position	Visual 100%	Correct cover per element type	MANDATORY
DURING POUR CHECKS
During pour	Slump test at point of discharge	IS 1199 · min. every 2 m³ or change of batch	M20: 75–100mm · M25: 75–100mm	EACH POUR
During pour	Cube samples (150mm)	IS 516 · per Table 14	3 @ 7d + 3 @ 28d per sample set	EACH POUR
During pour	Concrete temperature at discharge	Thermometer · each batch	≤30°C (hot weather) · ≥10°C (cold)	CHECK
During pour	Compaction — vibrator needle immersion	Visual · at every point ≤500mm c/c	No voids · no segregation · vibrator not touching rebar	CONTINUOUS
During pour	Level & thickness control (slabs)	Depth gauge / screed rails	±5mm on design thickness	CHECK
During pour	Concrete free-fall height	Visual	≤1.5m — no segregation	CHECK
POST-POUR CHECKS
Post-pour	Curing start time	Record time — within 4 hrs of casting	Wet hessian / polythene within 4 hrs	MANDATORY
Post-pour	7-day cube test result	IS 516 · accredited lab	M20: ≥13.4 MPa · M25: ≥16.7 MPa (indicative)	RECORD
Post-pour	28-day cube test result	IS 516 · acceptance criterion	Per IS 456 Cl. 16.1 (both conditions)	ACCEPTANCE
Post-pour	Surface defects inspection	Visual after stripping formwork	Honeycombing <25mm depth permitted (treat with approved grout)	CHECK
Post-pour	Dimensional check after formwork removal	Tape measure / plumb	±10mm position · ±5mm level	CHECK

Common Defects & Remediation

SITE GUIDE

Defect	Cause	Treatment	Prevention
Honeycombing	Poor compaction · high w/c	Chip out >25mm · grout pack	Proper vibration · slump check
Segregation	High w/c · excessive vibration	Demolish if structural	Reduce w/c · limit vibrator time
Plastic cracking	Rapid drying · no cover	Wet curing · surface sealer	Cover immediately after cast
Cold joints	Long time between pours	Core test · if weak → demolish	Complete pour before initial set
Low strength cubes	High w/c · poor curing	Core tests per IS 516 Part 4	Strict w/c control · 7-day cure
Corrosion (future)	Low cover · carbonation	Anti-corrosion coating	Maintain minimum cover

Applicable Indian Standards

CODES OF PRACTICE

IS Code	Title
IS 456:2000	Plain & Reinforced Concrete — Code of Practice (4th Rev.)
IS 10262:2019	Concrete Mix Proportioning — Guidelines (2nd Rev.)
IS 516:1959	Method of Tests for Strength of Concrete
IS 1199:1959	Methods of Sampling & Analysis of Concrete (Slump, VB etc.)
IS 383:2016	Coarse & Fine Aggregates — Specification (3rd Rev.)
IS 12269:2013	OPC 53 Grade Cement — Specification
IS 8112:2013	OPC 43 Grade Cement — Specification
IS 9103:1999	Admixtures for Concrete — Specification
IS 3812:2003	Pulverised Fuel Ash (Fly Ash) — Specification
IS 1489:1991	Portland Pozzolana Cement — Specification
IS 2386:1963	Methods of Test for Aggregate for Concrete (Parts 1–8)
IS 875:1987	Code of Practice for Design Loads (All Parts)
SP 16:1980	Design Aids for Reinforced Concrete to IS 456
SP 23:1982	Handbook on Concrete Mixes