Carbonation Depth Test
(Phenolphthalein Indicator Test)

Measurement of the depth of carbonation in concrete using phenolphthalein indicator — assessing the rate of CO₂ penetration and remaining alkalinity protecting the reinforcement from corrosion.

Overview

What is the Carbonation Depth Test?

The Carbonation Depth Test determines the depth to which concrete has carbonated — losing its alkalinity due to reaction with atmospheric CO₂. Carbonation reduces the concrete pH from ~13 to below 9, destroying the passive oxide film on reinforcing steel and initiating corrosion when the carbonation front reaches the rebar.

Conducted as per BS EN 14630 and IS 13311, the test uses phenolphthalein indicator sprayed on freshly exposed concrete cores or drilled holes. Carbonated zones remain colourless while uncarbonated zones turn pink/purple. Global Lab measures carbonation depth at multiple locations and correlates with rebar cover depth to assess remaining service life.

Simple & Reliable

Phenolphthalein spray test is the industry-standard method for carbonation depth.

Service Life Assessment

Comparing carbonation depth with rebar cover depth indicates remaining time to corrosion initiation.

Multiple Measurement Points

Tests conducted at multiple locations across structure for representative mapping.

Combined Cover Depth

Carbonation depth measured alongside rebar cover depth for accurate service life prediction.

NABL Certified Reports

All results issued on NABL-accredited letterhead per BS EN 14630.

Rehabilitation Planning

Results used to plan targeted repair, coating or cathodic protection strategies.

Test in Action

Carbonation Depth Test — Site Images

Phenolphthalein Applied to Fresh Core

Carbonation Measurement

Carbonation Depth Recorded at Multiple Points

Test Procedure

How the Carbonation Depth Test is Conducted

1

Core Drilling or Hole Drilling

A 50mm diameter core is extracted or a hole is drilled to expose fresh concrete at the test location.
2

Phenolphthalein Application

Phenolphthalein indicator solution (1% in ethanol) is immediately sprayed on the freshly exposed concrete surface.
3

Depth Measurement

After 30–60 seconds, the boundary between the colourless carbonated zone and the pink uncarbonated zone is measured with a digital calliper.
4

Multiple Location Testing

Process is repeated at minimum 5 locations across the structure for representative carbonation mapping.
5

Service Life Assessment & Reporting

Carbonation depth vs rebar cover depth comparison is made. Remaining service life estimated. NABL report issued within 24 hours.

Standards & Specifications

Applicable Test Standards

Standard	Title	Scope	Type
BS EN 14630	Products and Systems for the Protection and Repair of Concrete Structures — Determination of Carbonation Depth	Carbonation Test	British Standard
RILEM CPC-18	Measurement of Hardened Concrete Carbonation Depth	Carbonation	RILEM
IS 13311	Non-Destructive Testing of Concrete — Recommendations	General NDT	Indian Standard
fib Bulletin 34	Model Code for Service Life Design	Service Life	fib

Applications

Where is the CAPO Test Used?

Assessment of aging RCC buildings in urban areas with high CO₂ levels

Pre-repair survey to quantify extent of carbonation-induced corrosion

Service life assessment for structures approaching end of design life

Investigation of spalling and cracking attributed to rebar corrosion

Monitoring of carbonation progression in structures over time

Assessment of concrete repair materials and coatings for carbonation resistance

Why Choose Global Lab

Our Advantages

NABL Accredited ReportsLegally valid service life assessment certificates for insurance and legal proceedings.

Combined Corrosion PackageCarbonation + Half-Cell + Cover Depth + Galva Pulse as a complete corrosion audit.

Service Life EstimationOur engineers provide written service life predictions based on carbonation rate.

Pan-India CoverageField engineers across 7 lab locations for rapid site deployment.

Fast TurnaroundOn-site results immediately; NABL report within 24 hours.

Rehabilitation RecommendationsWritten recommendations for repair strategy based on carbonation findings.

Carbonation Depth Test(Phenolphthalein Indicator Test)