Plastic shrinkage cracking occurs when the rate of water evaporation from the surface of freshly placed concrete exceeds the rate at which bleed water can rise to the surface. This creates a volume deficit at the top layer, leading to tensile stresses that the "plastic" (unhardened) concrete cannot resist.
Aluform (Aluminium Formwork System) is widely adopted in high-rise and mass housing because it ensures high speed, dimensional accuracy, superior finish, and monolithic strength.
However, unsafe or early de-shuttering can cause cracking, honeycombing, deformation, accidents, and structural failure.
Therefore, Indian Standards (IS) provide guidance on timing, safety, stability, inspection, and quality during formwork removal.
Following standards should be considered during planning and execution:
IS 456:2000 – Plain & Reinforced Concrete Code
Clause 11.3 — Stripping time of formwork
Clause 13 — Concrete curing & protection
IS 3696 (Part 1 & 2) – Safety in Construction: Scaffolds & Working Platforms / Ladders
IS 4082 – Storage & Handling of Construction Material (Useful for stacking & handling Aluform)
IS 1200 (Part 5) – Formwork tolerances (good practice reference)
⭐ Always follow Project Specification + Consultant approval in addition to IS Code guidance.
De-shuttering depends on:
✔ Concrete Grade
✔ Temperature & Curing
✔ Member Type
✔ Structural Loading
| Structural Member | Minimum Time (Normal Weather) |
|---|---|
| Vertical sides of walls, columns & beams | 16 – 24 hours |
| Slab soffit (props left under) | 3 days |
| Beam soffit (props left under) | 7 days |
| Props for Slab up to 4.5 m span | 7 days |
| Props for Slab over 4.5 m span | 14 days |
| Props for Beams & Arches up to 6 m span | 14 days |
| Props for Beams & Arches over 6 m span | 21 days |
IS 456 also emphasizes that:
Concrete must gain minimum 70% of design strength before major de-shuttering.
Cube test report should be verified before stripping.
Before removing formwork, ensure:
✔ Required stripping time completed (as per IS 456)
✔ Cube strength achieved (70% or above)
✔ Proper curing done (IS-456 clause 13 compliance)
✔ No cracks, deflection or deformation visible
✔ Temp supports stable
✔ Barricading & safety arrangements ready
✔ Engineer / QA-QC approval taken
Isolate working zone
Display warning boards
Conduct toolbox talk
Provide lighting
Clear unwanted materials
Remove in sequence:
External wall panels
Beam side shutters
Stair side shutters
⚠ No hammering allowed
Use only approved Aluform release tools.
Release with drop-head / pin system
Keep props as per IS 456 duration
Do not force panels
Remove props in phased manner
Follow IS 456 prop retention rules
Confirm upper floors are safe
Clean using plastic / wooden scrapers
Do not bend, weld or hammer
Stack on flat stable surface
Segregate damaged panels
Must as per IS 3696:
Helmet
Gloves
Safety Shoes
Goggles
Reflective Jacket
Harness (working at height)
Close below working area
No movement under work zone
Use tag system
Avoid de-shuttering during rain/wind
Allow only trained workers
Use approved wrenches
Mechanical lifting if heavy
No gas cutting / welding on aluminium
Inspect tools daily
Check for:
✔ Honeycombing
✔ Surface voids
✔ Cracks
✔ Dimensional accuracy
✔ Alignment / Plumb
✔ Level
✔ Surface finish
(Refer IS 1200 Good Practice Guidance & Project Specs)
Verticality tolerance ±5 mm
Level tolerance ±5 mm
No structural cracks permitted
Honeycomb not acceptable
Repair immediately if found
Minor defects → polymer mortar repair
Honeycombing → remove loose concrete & repair with approved repair mortar
Severe defects → Consultant approval + NCR
Maintain repair records
Maintain following records:
📌 Cube Test Report
📌 De-Shuttering Checklist
📌 Safety Permit / Toolbox Talk
📌 QA/QC Inspection Report
📌 NCR / Corrective Action Records
Good documentation improves transparency, audit compliance & safety reliability.
❌ Removing form before IS time limits
❌ Ignoring cube strength
❌ Hammering aluminium panels
❌ Allowing people below working area
❌ No barricading
❌ Poor stacking damaging panels
Aluform de-shuttering is a critical structural & safety operation.
Following IS 456 stripping guidelines, IS 3696 safety norms, IS 4082 handling rules, and strong QA/QC discipline ensures:
✔ Structural safety
✔ High-quality finish
✔ Zero accidents
✔ Faster progress
✔ Reduced rework
✔ Long-term durability
Disciplined execution = Safe Structure + Quality Construction 👍
Causes, Effects, Prevention & Indian Standards Explained**
Concrete cube strength is one of the most important quality parameters in construction. It indicates whether the concrete used on site is capable of carrying the designed load safely. However, in many projects, concrete cube test results show lower strength than the target or characteristic strength.
Low cube strength can lead to rejection of concrete, structural safety concerns, delays, and cost overruns. This blog explains all possible reasons for low cube strength, along with relevant Indian Standards (IS codes) and corrective measures.
Ensures structural safety
Confirms quality of materials and workmanship
Required for acceptance of concrete as per IS 456
Helps in quality control and assurance
📌 As per IS 456:2000, concrete strength shall be assessed by compressive strength tests on cubes.
| IS Code | Description |
|---|---|
| IS 456:2000 | Plain and Reinforced Concrete – Code of Practice |
| IS 516 (Part 1):2018 | Method of Tests for Strength of Concrete |
| IS 10262:2019 | Concrete Mix Proportioning – Guidelines |
| IS 383:2016 | Coarse and Fine Aggregates |
| IS 4031 | Tests on Cement |
| IS 1199:2018 | Workability Tests of Concrete |
Use of expired or low-grade cement
Sand containing excess silt, clay, or organic impurities
Poor-quality or flaky aggregates
Improper aggregate grading
📌 As per IS 383, aggregates must meet grading, shape, and cleanliness requirements.
Effect: Weak bond between cement paste and aggregates → reduced strength.
Extra water added on site for workability
No control on water measurement
Leakage of water during curing or mixing
📉 Higher w/c ratio increases porosity and reduces strength
📌 IS 456 recommends:
M20 → w/c ≤ 0.55
M25 & above → w/c ≤ 0.45
Mix not designed as per IS 10262
Excess sand or aggregate
Cement quantity reduced intentionally or unintentionally
Volume batching instead of weight batching
Effect: Concrete becomes either harsh or weak → low compressive strength.
Hand mixing not uniform
Insufficient mixing time in mixer
Segregation due to poor mixing
📌 IS 456 recommends mechanical mixing for uniformity.
No vibration or insufficient vibration
Manual rodding not done properly
Entrapped air voids inside concrete
📉 Every 1% air void can reduce strength by ~5%
📌 As per IS 516, cubes must be compacted properly using vibration or rodding.
Common mistakes during cube preparation:
Moulds not cleaned or oiled
Cubes not cast in three equal layers
Each layer not compacted with 35 strokes
Improper identification or marking
📌 Cube size as per IS 516:
150 × 150 × 150 mm
Cubes not submerged properly in water
Water temperature not maintained
Cubes removed early from curing tank
Interrupted curing
📉 Poor curing can reduce cube strength by 30–40%
📌 IS 456 requires continuous curing for at least:
7 days (OPC)
10 days (blended cement)
Compression Testing Machine (CTM) not calibrated
Load applied too fast or unevenly
Cube not placed centrally in CTM
Improper alignment of cube faces
📌 IS 516 specifies:
Loading rate: 140 kg/cm²/min (≈ 5.2 kN/sec)
Concrete strength increases with time.
| Age | Approximate Strength |
|---|---|
| 7 days | 65–70% |
| 14 days | 85–90% |
| 28 days | 100% |
📌 Misinterpretation of 7-day results often leads to confusion.
High temperature → rapid evaporation
Cold weather → slow hydration
Wind → surface moisture loss
📌 IS 7861 provides guidance for hot and cold weather concreting.
Concrete is considered acceptable if:
Average of 3 cubes ≥ characteristic strength (fck)
No individual cube < fck − 3 N/mm²
| Issue | Result |
|---|---|
| Extra water | Major strength reduction |
| Poor vibration | Honeycombing |
| Improper curing | 30–40% strength loss |
| Wrong mix | Non-uniform strength |
| Testing error | False low results |
✔ Use approved and tested materials
✔ Follow IS 10262 mix design
✔ Control water–cement ratio
✔ Ensure proper vibration
✔ Cure cubes correctly
✔ Use calibrated CTM
✔ Follow IS 516 testing procedure
Low concrete cube strength is not caused by a single factor but by a combination of material issues, workmanship errors, curing problems, and testing mistakes. Strict adherence to Indian Standards, proper supervision, and quality control can easily prevent cube failure and ensure durable, safe structures.
Soil compaction is a fundamental geotechnical test used in civil engineering to determine how soil behaves when compacted at different moisture contents.
As per Indian Standards (IS), compaction testing helps us decide:
How much water (moisture) is required
How much density can be achieved
Whether soil is suitable for foundation, road, embankment, and backfilling works
The compaction test is carried out to:
Determine Maximum Dry Density (MDD)
Determine Optimum Moisture Content (OMC)
Control field compaction quality
Prevent settlement and failure
Improve shear strength and bearing capacity
Soil compaction tests in India are conducted as per:
| IS Code | Description |
|---|---|
| IS 2720 (Part 7) | Light Compaction Test |
| IS 2720 (Part 8) | Heavy Compaction Test |
| IS 2720 (Part 28) | Dry Density by Sand Replacement |
| IS 2720 (Part 29) | Core Cutter Method |
IS 2720 (Part 7)
Rammer weight: 2.6 kg
Height of fall: 310 mm
Number of layers: 3
Blows per layer: 25
Used for:
Light structures
Residential buildings
General earthwork
IS 2720 (Part 8)
Rammer weight: 4.9 kg
Height of fall: 450 mm
Number of layers: 5
Blows per layer: 25
Used for:
Highways
Runways
Heavy foundations
Used to check actual field density.
Suitable for coarse-grained soil
Determines in-situ dry density
Suitable for soft to medium cohesive soils
Simple and quick field test
MDD is the maximum dry unit weight of soil obtained at a specific moisture content during compaction.
👉 In simple words:
It is the highest density soil can achieve when compacted properly.
Why MDD is important:
Used as reference value for field compaction
Helps in calculating % compaction
Ensures structural stability
OMC is the percentage of water content at which soil achieves MDD.
Too little water → soil particles don’t rearrange
Too much water → water occupies voids
Correct water → best compaction
Moisture directly affects compaction.
As per IS 2720 (Part 2), moisture content is measured by oven drying method.
Helps identify OMC
Prevents over-watering or under-watering
Ensures uniform compaction
Reduces settlement and cracks
Moisture content (%) is calculated by:
Moisture Content (%)=Weight of dry soilWeight of water×100
| Soil Type | Moisture % |
|---|---|
| Sandy Soil | 6 – 12 % |
| Silty Soil | 10 – 20 % |
| Clayey Soil | 15 – 30 % |
(Values vary based on soil type and site condition)
Air-dry the soil sample
Add water in increments
Compact soil in mould using rammer
Measure wet density
Calculate dry density
Plot Dry Density vs Moisture Content curve
Determine MDD and OMC
Curve rises as moisture increases
Peak point = MDD
Corresponding moisture = OMC
After OMC, density reduces due to excess water
As per specifications:
Earthwork: ≥ 95% of MDD
Road subgrade: ≥ 97% of MDD
Embankment: As specified in drawings/contract
Soil compaction testing as per Indian Standards ensures:
Safe and durable construction
Proper load transfer
Reduced maintenance
Compliance with quality standards
MDD, OMC, and moisture control are the backbone of successful earthwork and foundation engineering.
Percentage of compaction indicates how well the soil is compacted in the field compared to the maximum dry density (MDD) obtained in the laboratory.
It is a key quality control parameter in earthwork, road works, and foundation construction.
Where:
Field Dry Density = Dry density obtained from field tests
MDD = Maximum Dry Density from lab compaction test (IS 2720 Part 7 / 8)
IS 2720 (Part 7) – Light Compaction (Lab MDD)
IS 2720 (Part 8) – Heavy Compaction (Lab MDD)
IS 2720 (Part 28) – Sand Replacement (Field Density)
IS 2720 (Part 29) – Core Cutter Method
| Type of Work | Required % Compaction (of MDD) |
|---|---|
| General Earth Filling | 90 – 95 % |
| Building Foundation Backfill | 95 % |
| Road Subgrade | 97 % |
| Pavement Layers / WMM | 98 % |
| Embankments | 95 – 97 % |
| Airport Runways | 98 % or more |
(Exact requirement depends on project specification and drawings)
Prevents excess settlement
Increases bearing capacity
Improves shear strength
Reduces water ingress
Ensures long-term stability
To calculate percentage of compaction:
Conduct lab compaction test → get MDD & OMC
Perform field density test
Sand Replacement Test
Core Cutter Method
Determine field dry density
Apply formula and compare with specified %
Improper moisture content (not near OMC)
Insufficient roller passes
Wrong compaction equipment
Thick soil layers (>200–250 mm)
Poor soil gradation
✔ Compact soil within ±2% of OMC
✔ Control layer thickness
✔ Maintain proper rolling pattern
✔ Re-test if compaction % is not achieved
Percentage of compaction ensures that soil in the field performs as designed in the laboratory.
Matching field density with MDD is essential for safe and durable construction.
Water is one of the biggest enemies of buildings. If waterproofing is not done properly, structures face problems like leakage, dampness, corrosion of steel, mould growth, paint peeling and structural deterioration.
That's why waterproofing is a critical step in buildings, from foundations to roofs.
This blog explains all major types of waterproofing used in modern construction — with advantages, applications and Indian Standard (IS) recommendations.
A rigid/semi-flexible waterproof coating made using cement, sand, polymer additives, and waterproofing chemicals.
Includes acrylic, polyurethane, and rubber-based liquid membranes applied with a roller, brush, or spray.
A protective coating made using bitumen mixed with polymers.
Bitumen membranes available in self-adhesive rolls or torch-on sheets.
A high-performance waterproof coating forming an elastic, durable membrane.
Synthetic rubber (EPDM) and thermoplastic polyolefin (TPO) membranes used for high-end roofing systems.
Uses chemicals that penetrate into concrete and block capillaries by forming crystals.
Brick Bat Coba (BBC) is a traditional waterproofing system used mainly for flat RCC roofs in India.
It uses broken bricks (brick bats) mixed with cement–sand mortar to create a slope for easy water drainage, followed by a waterproof plaster layer.
Follows recommendations from:
From Elasticity to Failure: A Civil Engineer's Guide to the TMT Steel Stress-Strain Curve
Reinforcement steel (TMT bars) is the backbone of RCC structures. To evaluate its performance under tension, a tensile test is conducted, and the results are represented on a stress–strain curve. This curve explains how steel behaves under increasing load — from elastic stage to final failure.
Indian Standard IS 1786 governs the mechanical properties of reinforcement bars in India. Understanding this curve is essential for civil engineering students, site engineers, consultants, quality control teams, and contractors.
It is a graph plotted during a tensile test:
This curve helps us understand:
✔ Strength
✔ Ductility
✔ Elasticity
✔ Yielding
✔ Failure pattern
The curve is divided into six important phases:
| Grade | Yield Strength (Fy) |
| Fe 415 | 415 MPa |
| Fe 500 | 500 MPa |
| Fe 500D | 500 MPa Higher ductility |
| Fe 550 | 550 MPa |
| Fe 550D | 550 MPa |
| Fe 600 | 600 MPa |
This is the most important property in design of beams, slabs, columns, and foundations.
This region provides:
| Grade | Ultimate Tensile Strength (Fu) (MPa) |
| Fe 415 | 485 |
| Fe 500 | 545 |
| Fe 500D | 565 |
| Fe 550 | 585 |
| Fe 550D | 600 |
| Fe 600 | 660 |
High elongation = better ductility = preferred for seismic design.
| Property | Meaning | Why Important |
| Yield Strength (Fy) | Start of permanent deformation | Used for structural design calculations |
| Ultimate Tensile Strength (F_u) | Maximum load capacity the steel can bear | Shows the safety margin and reserve strength |
| Elongation | Total strain (deformation) before fracture | Indicates ductility and is crucial for earthquake resistance |
| Bend/Rebend Test | Bending quality of the rebar | Ensures workability on site and prevents brittle failure during fabrication |
After necking:
But design standards use engineering stress–strain curve.
✔ Ensures safe selection of TMT bars
✔ Helps in earthquake-resistant design
✔ Prevents brittle failure
✔ Ensures ductility in beams and columns
✔ Helps engineers understand collapse mechanism
| Grade | Yield (Fy) (MPa) | UTS (Fu) (MPa) | Elongation |
| Fe 415 | 415 | 485 | 12% |
| Fe 500 | 500 | 545 | 12% |
| Fe 500D | 500 | 565 | 14.5% |
| Fe 550 | 550 | 585 | 10% |
| Fe 550D | 550 | 600 | 16% |
| Fe 600 | 600 | 660 | 10% |
The stress–strain curve of reinforcement steel reveals the complete behavior of TMT bars under load—from elastic deformation to final fracture. Understanding this curve helps engineers choose the right grade of steel, ensure safety, improve ductility, and meet IS 1786 requirements for long-lasting structures.
🏗️ “Surface Area of Concrete Ingredients – Strength, Workability & Durability” Concrete performance does not depend only on grade or ...
