NDT | apex

STRUCTURAL ENGINEERS

Residential | Commercial | Industrial

NON DESTRUCTIVE TESTING (NDT)

RCC | Masonry | Steel

RETROFITTING & STRENGTHENING

Design | BOQ | Execution

STRUCTURAL STABILITY AUDIT &

NON DESTRUCTIVE TESTING (NDT)

The general approach adopted to achieve the objectives of maintaining structural stability and enhancing safe service life of the structure under question can be explained as below:

Step 1: Inspection of available architectural & structural drawings/old test reports/any other relevant information/documents.

Step 2: Appropriate diagnosis of the building/structure by carrying out Condition Survey through Visual Inspection & Non-Destructive Testing (NDT), laboratory tests and soil testing, if required.

Step 3: Structural analysis & design calculations. This exercise is required to find design requirements for comparing existing parameters obtained from NDT.

Step 4: Suggesting suitable repair, retrofitting or strengthening methods with construction drawings and BOQ etc.

Step 5: Execution and supervision of remedial measures.

NDT of concrete, steel and masonry is a universally accepted tool to assess the health of structures or building health. NDT consists of a series of field and laboratory tests for quality assessment of structural components especially in case of hardened concrete and steel. It's major applications are:

Detailed Condition Survey
Addition or Alteration in Building Plan
Aged or Distressed Structures
Addition of floors
Change in usage than its intended purpose
Damages occurred due to Earthquakes or Fire etc.
Increasing Load Carrying Capacity
Marine Environment or other Chemical Attack
Quality Control during Construction
Residual Life Assessment (RLA) Studies
Other objectives as per specific requirements

NDT & OTHER TESTS AVAILABLE WITH US

Visual inspection is the most primary, economic and effective Non Destructive Technique to examine an object, an element or the entire structure. Since any structure which is under distress shows ample signs and an experienced examiner can understand the extent and vulnerability of distress up to a certain limit at the beginning itself.

Ref: IS 13311(Part2): 1992, ASTM C-805, BS 1881 Part 202

The Rebound Hammer test could be used for assessing:

The likely compressive strength of concrete
The uniformity of concrete
Quality of the concrete in relation to the standard requirements
Quality of one element of concrete in relation to another

Ref: IS 13311(Part1): 1992, ASTM C-597, BS 1881 Part 1

The Ultrasonic Pulse Velocity test could be used for establishing:

The presence of cracks, voids & other imperfections
Changes in the structure of concrete which may occur with time
Quality of the concrete in relation to the standard requirements
Quality of one element of concrete in relation to another

Reference: IS: 516-1959 (Reaffirmed 1999), IS 456: 2000, ASTM C39 & C42, AASHTO T22, SP 24

The Core sample test could be used to determine:

Compressive strength of concrete
Density of concrete & Porosity
Cement content
In addition, coring may also help to:
Physically verify actual depth/profile of a crack
Find the thickness of RCC slab where measurements cannot be done precisely.

Visual

Inspection

Rebound Hammer

Test

Ultrasonic Pulse Velocity (UPV) Test

Core Sample

Test

Cover Meter or Rebar Locator or Profometer Test

Carbonation

Test

Half Cell Potential

(HCP) Test

Ground Penetrating Radar (GPR) Survey

Ref: IS 456: 2000

When structural drawings are not available this tests helps:

To locate main bars as well as distribution steel bars.
To determine spacing between the bars
To estimate depth of concrete cover
To estimate diameter of bars
It can be used for both, quality control and building acceptance inspection survey

Ref: IS 456: 2000

Carbon-di-Oxide (CO2) present in the air slowly penetrates into the concrete cover and reacts with Calcium-Hydroxide. Though it is not self reactive but in presence of moisture it becomes reactive. It also reduces the alkalinity of the concrete and causes corrosion in reinforcement bars. This phenomenon is known as Carbonation and the depth up to which this carbonation front reaches is known as Depth of Carbonation. This test is conducted by using phenolphthalein indicator.

Ref: as per ASTM C876 -1991

(Re-approved 1999)

During process of corrosion, when reaction starts between steel and concrete, rebar gives away electrons from the anode (where oxidization occurs) to the cathode (where reduction occurs). The positive ions formed at the surface of the anode will react and create corrosion by-products. This electro-chemical reaction creates a potential difference, and consequently a corrosion current, between the anodic and cathodic areas at the surface of the steel reinforcement. This current, or the potential difference is measured by the half-cell potential and risk of corrosion is assessed.

The word GPR stands for Ground Penetrating Radar. As the name suggests it is a radar for sub surface/underground explorations. Ground can be rock, soil, concrete, wood, ice and anything non-metallic.

The common applications of GPR are to detect:

Underground utilities i.e. plastic/metal/concrete pipes and cables.
Internal voids and conduits in concrete/RCC slabs
Defects under RCC layers/slab/floors
Hidden ducts and trenches
Historic constructions/ underground remains
& many other applications

Load Test

Ultrasonic Test (UT) for Steel Elements

Ultrasonic Thickness Measurement (UTM) for Steel Elements

Dye-Penetrant Test

Liquid Penetrant Test

(DPT/LPT) for Steel

Ref: IS 456: 2000

Generally, Non Destructive Testing (NDT) with core testing is employed for assessment of hardened concrete or existing RCC structures. However,if the observed results do not impart adequate confidence about the strength and quality of a particular element or area of the building, Load Tests can be conducted for better impression about actual load carrying capacity of the same.

Ref: Reference AWS D1.1

This test involves introducing beams of high frequency sound waves into the materials to detect flaws in the material. Ultrasonic Testing (UT) is used to inspect weld defects, surface flaw or internal defects, de-lamination in metal plates etc. Ultrasonic uses (ultra) sound waves to detect internal discontinuities ranging from cracks to disbonds. Ultrasound can be used on almost any material to locate discontinuities from large disbonds, down to the smallest defects.

This test involves introducing beams of high frequency sound waves into the materials to detect flaws in the material or to measure the material thickness. Thus, the Ultrasonic Testing is used to inspect weld defects, surface flaw defects, and for comprehensive UT thickness survey to determine the thickness of steel plates (webs & flanges), where it is not possible to measure the thickness manually due to inaccessibility on the other side / face of the plate.

Reference ASTM E-165

Surface breaking of welds may be tested using many NDT techniques, However, Liquid Penetrant or Dye Penetrant Testing (DPT/LPT) is used for being economic and relatively easy to conduct on areas with difficult access.

The Liquid Penetrant Test kit comprises of the following items:

Penetrant

Cleaner

Developer

When penetrant solution is applied to the surface of a pre-cleaned component. The liquid is pulled into surface-breaking defects by capillary action and an indication of carck is formed.

Magnetic Particle Test (MPT) for Steel

Sonic Integrity Test or Pile Integrity Test

Soil Bearing Capacity

(SBC)

Surveying &

Leveling

MPI is a NDT technique for detecting surface and shallow sub-surface discontinuities. It is used to inspect ferromagnetic materials (those that can be magnetized materials such as iron, cobalt, nickel and some of their alloys) for defects that result in a transition in the magnetic permeability of a material. The magnetic lines of force travel through the material and defects such as crack or voids cannot support as much flux, and force some of the flux outside of the part. Magnetic particles distributed over the component will be attracted to areas of flux leakage and produce a clearly visible indication directly on the surface of the part.

Ref: IS 14893: 2001

Since pile construction as well as the final product are mostly invisible, their integrity is always under question. In fact, experience has shown that in piles, all kinds of flaws (such as short length, necking/bulging etc. ) may occur. The purpose of integrity testing

is to discover such flaws before they can cause any damage.

Pile Integrity or Sonic Integrity Testing is a non destructive technique to evaluate integrity of pile shafts.

In geotechnical engineering, bearing capacity is the capacity of soil to support the loads applied to the ground. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil. It is important to determine the soil bearing capacity (SBC) for foundation design.

Leveling and surveying is an essential part of planning of any project. Leveling is a process of determining the height of one level relative to another. It is used in surveying to establish the elevation of a point relative to a datum, or to establish a point at a given elevation relative to a datum.