Non-Destructive Testing [NDT-CE]
It is often necessary to test concrete structures after the concrete has hardened to determine the structure is suitable for its designed use. Ideally such testing should be done without damaging the concrete. The tests available for testing concrete range from the completely non-destructive, where there is no damage to the concrete, through those where the concrete surface is slightly damaged, to partially destructive tests, where the surface has to be repaired after the test.
Nondestructive testing (NDT) are noninvasive techniques to determine the integrity of a material, component or structure or quantitatively measure some characteristic of an object. In contrast to destructive testing, NDT is an assessment without doing harm, stress or destroying the test object. The destruction of the test object usually makes destructive testing more costly and it is also inappropriate in many circumstances. NDT-CE, Non-Destructive testing in Civil Engineering plays a crucial role in ensuring cost effective operation, safety and reliability of reinforced concrete or pre-stressed concrete structures.
Non-destructive testing can be applied to both (concrete reinforced/ pre-stressed) old and new structures. For new structures, the principal applications are likely to be for quality control or the resolution of doubts about the quality of the material or construction. The testing of existing structures is usually related to an assessment of structural integrity or adequacy.
We at Struct Geotech have highly qualified and experienced personnel specialized in Non-Destructive testing techniques to encounter situations where NDT is needed, such as,
Quality control of pre-cast units or construction in situ
Removing uncertainties about acceptance of material
Confirming or negating doubt concerning workmanship
Monitoring of strength development in relation to concrete
Evaluation of defects(cracks, voids, honeycombing, etc) within a concrete structure
Determining the concrete uniformity before any expensive or disruptive tests
Determining the position, quantity or condition of reinforcement representative for quality assessment
Confirming or locating suspected deterioration of concrete due to various factors
Assessing the potential durability of concrete
Monitoring long term changes in concrete
Evaluation of remnant life analysis – RLA of concrete structures
Non-Destructive Testing [NDT-CE]
We at Struct Geotech have highly qualified and experienced personnel specialized in Non-Destructive testing techniques to encounter situations where NDT is needed, such as.
GPR–Ground Penetrating Radar Services
Struct Geotech conducts Geophysical Surveys using GPR-Ground Penetrating Radar for data acquisition and analysis of geotechnical, structural and environmental engineering applications. It is a cost effective method which is used for sub-surface exploration of roads/ highway, railways, runways or bridge, other concrete structures, for locating buried pipes, cables, conduits and ducts as well as ancient monuments in the area of Archeology and to find sub-grade of soil & their compactions of properties. The application areas are given ahead in detail. Ground penetrating radar is becoming an important component necessary for improving safety and productivity in the construction industry. In traffic infrastructure surveys the major advantages of GPR techniques are continuous profile, speed and accuracy. The use of this non-intrusive method provides an increased safety and avoidance of repair & replacement costs.
The Company has the Latest, Sensitive and Sophisticated GPR equipment which have been procured from preeminent International manufacturer, which is maintained and calibrated accordingly to provide precise data & results. The company has the most Qualified, Skilled & Experienced Engineers, who have been Trained according to the International Standards (ASTM, IS, BSI, IRC, ETC.) for conducting specialized Tests, which are of concern in the area of Quality Construction Engineering.
The system comprises an antenna emitting electromagnetic energy, and receiving the reflected energy from the surfaces as well as that from the inner layers, besides a processor. The energy reflected depends upon the type and nature of the antenna, and the materials involved – which depends on the dielectric constants. The energy reflected is transformed into visual images, which provide extensive data on the sub surface (inner) materials. GPR detects changes in EM properties (dielectric permittivity, conductivity, and magnetic permeability), that in a geologic setting, are a function of soil and rock material, water content, and bulk density. Struct Geotech uses appropriate antenna type, antenna frequency, antenna combination and configuration, analysis of polarization of the radiated electric field and the traces along which the measurements are performed to obtain a precise result.
Struct Geotech uses GPR extensively in Quality Control activities. It has been proved highly successful in road/ highway quality inspections, determining defects and voids in concrete structures, embedded reinforcement, quality of soil compaction, and other sub-surface details such as locating buried pipes, cables, conduits and ducts as well as ancient monuments in the area of Archeology. The Company collects and analyzes data densities which are not accessible using other conventional methods.
Areas of Application for evaluation:
GPR is used for the following Applications:
|1.||Archaeological investigations||8.||. Pipes and cable detection|
|2.||Bridge deck inspection||9.||Rail ballast surveys|
|3.||Building condition assessment||10.||Road condition survey|
|4.||Contaminated land investigation||11.||Tunnel linings|
|5.||Evaluation of reinforced concrete||12.||Depth to bedrock and to the water table|
|6.||Forensic investigations||13.||Highway bridge scour studies|
|Road inspection:||Asphalt thickness, base evaluation & voids, spacing and location of slab reinforcement, their depth of cover, dowel bars, joining slabs and cracking and, for un-reinforced or widely spaced reinforcing, the position of cracks beneath slabs.|
|Concrete inspection:||Rebar locating, conduit, pt cables, slab thickness, voids & concrete cover, voids beneath the joints, cracking and delaminating of the concrete pavement, detecting and locating dowels and anchors around the concrete slab joints|
|Geology:||Ground water, bedrock profiling, bathymetry (measurement of the depth of bodies of water), karst mapping & stratigraphy, locating pipe lines, drums, tanks etc.|
|Bridge inspection:||Condition assessment, concrete cover, bridge deck thickness & concrete inspection, detecting scours around bridge piers, surveys on approaching slabs and bridge abutments, pavement damage, concrete cover of top layer of reinforcement, spacing between re-bars (reinforcement bars), position of tendons or tendon ducts, concrete damage, concrete and pavement properties.|
|Railway evaluation:||Ballast condition assessment, ballast thickness, to locate mud holes and ballast pockets and define the sub grade soil boundaries and also to detect if sub grade soil material has penetrated or mixed with the ballast.|
|Airfields Inspection:||Locating moisture trails & voids within, and below, concrete runways and taxiways, helipad,
Locating post-tensioning cables, conduits and reinforcing steel in concrete floors garages, bridges and buildings, Locating voids and delamination caused by corrosion or poor mixing of concrete roofs, Locating underground storage tanks below, Evaluating concrete and asphalt pavements, and locating sewer, water, gasoline, jet fuel, natural gas, glycol, steam and chemical buried pipelines and leaks in those lines, GPR has also been used in airport QC/QA surveys.
Permeability of Concrete is important when dealing with durability of Concrete (Concrete durability depends largely on the ease (or difficulty) with which fluids (water, carbon dioxide, oxygen) in the form of liquid or gas can migrate through the hardened concrete mass), particularly in those used for water retaining structures or watertight sub-structures. Structures exposed to harsh environmental conditions also require low porosity as well as permeability. Such adverse elements can result in degradation of reinforced concrete. Permeability test measures the ease with which liquids, ions and gasses movement can occur by flow, diffusion, or sorption. Generally the overall potential for moisture and ion ingress in concrete by these three modes is referred to as its permeability.
The increasing load on highway bridges due to increasing heavy goods vehicle traffic, aging, problems with the durability of structures, corrosion of reinforcement and acidic corrosion of concrete may lead to obstructions of traffic with ensuing severe economic damages. Effective and reliable condition assessment tools are an important part of the ongoing efforts to evaluate and maintain bridge structures. Testing of bridge in field or response observed (static response data) in field can be of help to device an analytical model that closely represents behavior observed in the field.
It becomes necessary to test existing bridge structures under the following circumstances–
- Bridge structure under stress
- Deterioration of structure over age and other factors
- Increase load bearing or carrying capacity
Once a full representation of the overall bridge condition is determined, appropriate and economical decisions regarding the possible rehabilitation or replacement of bridge members or the entire structure can be made.
Visual inspection, which is an essential precursor to any intended non-destructive test. An experienced civil or structural engineer may be able to establish the possible cause(s) of damage to a concrete structure and hence identify which of the various NDT methods available could be most useful for any further investigation of the problem.
The technical team at Struct Geotech has a vast experience in NDT-CE, following which they use different methods in assessing pre-stressed / reinforced concrete structures.
Rebound Hammer test is conducted to assess the relative strength and elasticity of concrete onsite based on the hardness at or near its exposed surface. Depending on the age of the concrete structure and carbonation effect some specialized investigation is suggested before conducting the test.
Ultrasonic Pulse Velocity Test is conducted to assess the quality of concrete which is suspected to have low compaction, voids (porosity), delamination or damaged material in concrete under test. Ultrasonic Pulse Velocity Test can also be used for the following applications:
- Estimation of Strength of Concrete
- Establishing Homogeneity of Concrete
- Studies on the Hydration of Cement
- Studies on Durability of Concrete
- Analysis of Surface Crack Depth
- Determination of Dynamic Modulus of Elasticity
Profometer/ Covermeter test is conducted to determine the presence of reinforcing bars, laps, transverse steel, metal tie, wires or aggregates with magnetic properties. It determines the size, depth and position of reinforcement buried in concrete.
Purpose of application,
- Quality control, to ensure correct location and cover to reinforcing bars after concrete placement
- Investigation of concrete members and locating reinforcement as a preliminary to some form of testing, such as, core extraction or UPV
- Location of buried ferromagnetic objects other than reinforcement
Electrochemical Half-cell Potentiometer test provides a relatively quick method of assessing reinforcement corrosion over a wide area without the need of wholesale removal of the concrete cover. Quantitative measurements are made so that a structure can be monitored over a period of time and deterioration can be noted. Areas of usage include marine structures, bridge decks, abutments and so on. Used in conjunction with other tests, it has been found helpful when investigating concrete contaminated by salts.
The method of testing consists of determining the depth of the carbonated layer on the surface of hardened concrete by means of an indicator. Carbonation of concrete occurs when the carbon dioxide, in the atmosphere in the presence of moisture, reacts with hydrated cement minerals to produce carbonates, e.g. calcium carbonate. The carbonation process is also called depassivation. Carbonation penetrates below the exposed surface of concrete extremely slowly. The significance of carbonation is that the usual protection of the reinforcing steel generally present in the concrete due to the alkaline conditions caused by the hydrated cement paste is neutralized by carbonation. Thus, if the entire concrete covering the reinforcing steel is carbonated, corrosion of the steel would occur if moisture and oxygen could reach the steel.
This test is used to determine the compressive strength of a concrete core, which has usually been extracted from an existing structure. The value of compressive strength can then be used in conjunction with other measured properties to assess the condition of the concrete.
Using a masonry saw, the core is first trimmed to the correct test length, which varies upon the standard being adopted. Following trimming, the core will have its ends either ground perfectly flat,
or be capped in a material to produce a smooth bearing surface.
After the prescribed curing has taken place, the specimen is then crushed to failure noting the maximum load achieved. From the values of load and dimensions, the compressive strength of the core can be calculated.
For those in the construction industry, one of the options available for testing piles using non-destructive testing (NDT) method is by using wave equation-based pile testing. The most common forms of nondestructive testing of deep foundations used by Struct Geotech are based on pulse echo testing, which goes by variety of names:
- Low strain integrity testing or Pulse or Sonic Echo Test, or Low Strain Dynamic Test
- Dynamic load testing (high strain dynamic testing) which is used to check capacity & quality of piles, and serves as an alternative to static load testing, which is also technically a non-destructive test.
Other methods used for nondestructive testing of deep foundations used by Struct Geotech are,
- Static pile load testing:
- Kenteledge load test Method
- Reaction beam load test method/ Rock Anchoring Method
- Lateral load test
- Pullout load test
- Bi-Directional load testing
These non-destructive testing method’s for concrete pile testing (test or working pile) are conducted to determine the quality components required for the structural and geotechnical engineer for further evaluation, such as, Pile length, Pile capacity, skin friction, end bearing, displacement, stresses, integrity, settlement, flaws, inclusions & necking or bulging.
Struct Geotech background results from specialized experience(of more than 3000 concrete piles) in non-destructive method in pile testing since 2006.From bridges to telecommunication towers and buildings, encompassing all kind of infrastructural projects consisting of deep pile foundations, we offer clients the experience and capabilities needed to assist them in successfully performing a variety of projects.
All civil engineering structures are initially designed depending on certain design criteria, such as design loads, allowable stresses etc. But, damage due to an extreme event is always possible in a structure during its design life. Sometimes, undetected and un-repaired damage may lead to structural failure demanding costly repair and a huge loss of lives. Therefore, the problem of maintenance and repair of existing engineering structures involves damage detection at an early stage. For massive structures like bridges, dams, flyover, ROB, RUB, chemical plants, thermal & nuclear plants, etc that were constructed some 20 - 40 years ago, it is necessary to test its functionality under the present load situation and quantify damage if any. Since it involves huge expenditure to demolish and reconstruct them, it is important to valuate the residual life- RLA of these structures.
Going on the NDT-CE experience, Struct Geotech has been considered one among the best firm providing NDT of concrete structures, which is a basis for the evaluation of Residual Life Assessment/ Remnant Life Analysis- RLA Studies. We use many methods which are traditionally used for flaw characterization and measurement of residual stress. Combining these inputs many parameters, including mechanical properties, factor of safety in design, conservative operation of unit, inaccuracy in data extrapolation, overestimation of corrosion effects etc, would be assessed.
Therefore, Struct Geotech follows a standard damage/ degradation detection algorithm which includes four different stages of analysis, as follows:
- Detection of damage (Damage can be defined as the change in structural performance, which can be identified in terms of discrete Cracks or a weak zone formation and a consequent stiffness reduction) if present in the structure.
- Determination of the geometric location of the damage.
- Quantification of the severity of the damage.
- Prediction of the remaining service life of the structure.
Degradable mechanisms of Concrete Structures:
Efflorescence & leaching
Alkali –aggregate reaction
Concrete- Freeze/thaw cycling
Conventional reinforcing- Corrosion
Soil/structural issues- Differential settlement
Soil erosion (scour)