What is sampling?
Concrete sampling involves the removal of materials from a concrete structure to enable property characterisation and off site assessment of durability and performance.
How does sampling work?
Concrete sampling removes cores, powders or broken sections with as little damage to the structure as possible to allow lab based assessment of materials properties, performance and durability. Typical tools for sampling include diamond tip cutters, drills and even a hammer and chisel.
What is sampling used for ?
Deterioration process | Defects | Control of repairs |
Can be applied to all deterioration processes where DT is required | Can be applied to all defects when a DT is required to correlate the defect with the deterioration process. |
How do I carry out sampling?
The first step to sampling a concrete structure is to decide which types of samples are to be taken and where they are to be taken from.
The selection of type of sampling to use (coring, broken, or powdered samples) for concrete analysis hinges on the goals of the investigation, the condition of the concrete, and the specific types of tests required.
BS EN 12504-1:2019 endorses coring for in-depth evaluations of concrete's structural integrity and material characteristics, especially in vital structural components where non-destructive methods are inadequate.
Broken samples, offering a more qualitative insight, are ideal for initial quality checks or exploring the causes behind failures in structures that are already damaged such as pop outs or spalling from the element.
For identifying the chemical makeup and detecting harmful substances, powdered samples are preferred, particularly in studies focused on chemical degradation mechanisms.
This approach to selection ensures that the sampling method aligns with the investigation's requirements, providing accurate and relevant data for assessing the concrete's condition. Identification and following of smart safety protocols during sample collection and handling, especially when dealing with compromised structures or when using tools is vital irrespective of the method used.
A simple procedure for coring based on BS EN 12504-1:2019 includes:
Evaluate the structure to select optimal coring sites, considering its layout and specific areas of interest while avoiding areas with superficial defects or non-homogeneous conditions.
Use a diamond-tipped core drill mounted on a stand to ensure stability and perpendicularity during drilling. The equipment should be capable of water cooling to minimize dust and prevent overheating.
Clearly mark the drilling locations, ensuring they are evenly distributed or strategically placed to sample specific areas of interest.
Secure the core drill in place and begin drilling at a low speed to establish a precise start, gradually increasing speed as the core begins to form. Water should be applied continuously to cool the drill bit and reduce dust.
Monitor the depth of the core to ensure it meets the requirements for the intended tests. The depth should be sufficient to allow for subsequent testing without influencing the results by edge effects.
Once the desired depth is reached, carefully withdraw the core from the hole, ensuring it is not damaged during removal.
If specified by the testing standards, prepare the core surfaces by sawing to create flat, parallel ends. This is crucial for compressive strength tests to ensure an even load distribution.
Before testing, condition the cores as required to standardize moisture content, which can significantly affect test results. This might involve sealing the core in plastic to prevent moisture loss or allowing it to equilibrate in a controlled environment.
Each core should be labelled with its extraction location, date, and orientation. Detailed records should be kept of the coring process, including equipment used, core dimensions, and any observations noted during extraction.
After coring, the holes left in the structure need to be repaired, especially if the structural integrity could be compromised. Use a repair material that is compatible with the existing concrete to ensure durability and performance.
A simple procedure for collecting broken samples from a concrete structure based on industry best practice is as follows:
Conduct a visual inspection of the structure to identify areas with visible signs of distress or failure, such as cracks, spalling, or exposed reinforcement.
Choose samples from areas that are representative of the distress observed. Consider the variability across the structure and aim to collect samples that reflect different degrees of deterioration.
Carefully remove pieces of concrete to avoid further damage to the structure and the sample itself. Use appropriate tools like chisels or hammers, ensuring not to induce additional fractures in the samples.
Collect samples of a size sufficient to perform the intended tests. Ensure to gather multiple pieces from various locations to account for material variability.
Label each sample immediately upon collection with details of the exact location, date of collection, and observed condition. This information is crucial for subsequent analysis and interpretation.
Wrap the samples in protective material to prevent loss of loose particles and further degradation during transportation. Use rigid containers to avoid mechanical damage.
Gently clean the samples to remove dirt, debris, or loosely attached particles without altering the sample's surface or internal structure.
Examine the samples to determine their suitability for the intended tests. This might involve measuring dimensions, assessing the condition, and noting any peculiarities.
Document the cleaning and preparation process, noting any changes in the sample's condition or any anomalies observed. This documentation can be crucial for interpreting test results.
Choose appropriate tests based on the condition of the samples and the investigation's objectives. Common tests include visual examinations, compressive strength tests, or petrographic analysis.
Ensure the collected samples are representative of the overall condition of the concrete structure, considering both deteriorated and relatively intact areas.
A simple procedure for collecting broken samples from a concrete structure based on industry best practice is as follows:
Choose areas suspected of chemical deterioration or where composition analysis is necessary, focusing on both distressed and undisturbed zones.
Create a sampling strategy that covers the entire structure to ensure comprehensive analysis.
Ensure drills or grinders are clean and equipped with appropriate bits (diamond or carbide) to prevent sample contamination.
Attach dust collectors or employ wet methods to minimize dust generation.
Wear dust masks or respirators, safety glasses, and gloves to protect against drilling hazards and powdered concrete.
Decide on the sampling depth to penetrate beyond surface layers and obtain a representative sample.
Directly store the collected powder in clean, labelled containers to avoid contamination and moisture absorption.
Clearly label each sample with location, sampling depth, date, and any observations. Keep detailed records of all sampling locations.
If necessary, condition samples to standardize moisture content or eliminate volatile components.
Measure the quantity of powder to ensure adequacy for the tests, adhering to each method's requirements.
Opt for suitable chemical analysis techniques like XRF for elemental analysis or XRD for mineralogical studies.
Provide laboratories with comprehensive sample information and objectives to facilitate accurate analysis.
What equipment and expertise are required for sampling?
For concrete sampling, whether coring, collecting broken samples, or preparing powdered samples, each method requires specific equipment and expertise to ensure accurate and representative results.
Coring, necessitates the use of diamond core drill rigs, which are available from manufacturers like MK Diamond, Golz, and Husqvarna. These rigs, combined with water management systems for slurry disposal and dust extraction heads for clean operation, are essential for obtaining core samples with minimal structural impact and health risks. Expertise in safely operating this equipment, along with knowledge of where to core without compromising structural integrity, is crucial.
Figure 4. Diamond core drill rig (MK Diamond), water management system (Hilti) and dust extraction head (Bosch) for concrete coring
Collecting broken samples is less equipment-intensive but requires a keen eye to select representative areas of distress within the concrete. Basic tools like hammers and chisels are used to remove pieces of concrete, which are then analysed to understand the material properties or structural issues present.
Powdered samples, geared towards chemical analysis, demand precision in collection to avoid altering the sample's composition. Tools like drills or grinders must be used carefully, with samples stored immediately to prevent contamination. The expertise here lies in understanding the chemistry of concrete and its deterioration mechanisms to ensure the powdered samples are prepared correctly for analysis.
What are the advantages of sampling?
General advantages of sampling of concrete structures for identification of deterioration include:
Enables comprehensive assessment thorough evaluation of concrete properties such as compressive strength, permeability, and density which are essential for verifying the structural integrity and durability of concrete structures.
Through various sampling methods, hidden defects, and areas of potential failure within the concrete can be identified early, allowing for timely remediation and extending the lifespan of the structure.
Sampling provides empirical data to validate compliance with design specifications and building codes, ensuring that the constructed facility meets the required quality standards.
In older structures, sampling can provide insights into the materials and construction techniques used, aiding in preservation efforts and informing maintenance strategies. By understanding the existing condition of concrete, engineers can design appropriate retrofitting or upgrading measures to enhance the structure's performance and safety.
Each concrete sampling method—coring, broken, and powdered samples—serves specific analytical needs with its own set of advantages. Coring is invaluable for in-depth structural integrity and material property assessments, offering comprehensive insights necessary for evaluating critical structural components. It's particularly effective for analysing the concrete's internal condition and its compatibility with embedded materials.
Figure 9. Sample of powdered concrete for XRD testing
Powdered samples excel in chemical analysis, providing detailed information on the concrete's composition and potential chemical deterioration mechanisms. This approach is critical for understanding the chemical health of the concrete, guiding maintenance strategies, and remediation efforts effectively.
What are the disadvantages of sampling?
General disadvantages of sampling of concrete structures for identification of deterioration include:
Some sampling methods, especially coring, are invasive and can compromise the structural integrity if not performed with precision and requires subsequent repair to restore the structure's condition.
The need for specialized equipment and expertise, particularly for coring, results in higher costs associated with sampling. This can be a significant factor in budget-sensitive projects.
While some sampling methods are quick, the preparation, execution, and analysis of samples, especially for comprehensive tests, can be time-consuming, potentially delaying project timelines.
Sampling locations may be constrained by the accessibility of the area of interest within the structure, potentially leaving critical areas untested.
The interpretation of test results requires expert knowledge. There's a risk that the data obtained from sampling might be misinterpreted, leading to incorrect conclusions about the structure's condition.
The process of sampling, particularly when involving the removal of large cores, unsafe structures or the generation of dust and waste material, can involve significant health and safety risks.
Any drilling, grinding or coring work into existing structures faces the risk of exposing undeclared/unknown asbestos or other dangerous compounds.
Each sampling method come with distinct disadvantages that need to be considered. Coring, is the most expensive due to the need for specialized equipment and expertise. It's also invasive, potentially compromising the sampled area's structural integrity, and carries the risk of damaging embedded materials, necessitating careful planning and subsequent repair.
Broken samples, while quick and cost-effective, offer limited insight compared to more detailed methods. They are best suited for preliminary assessments, with their usefulness diminishing when in-depth or quantitative data is needed. This method may not provide a full picture of the concrete's condition across a structure, especially in areas not visibly distressed.
Powdered samples, critical for chemical analysis, face challenges regarding contamination risk. This risk is particularly pertinent when collecting samples at different depths, which can compromise the accuracy of depth profile analyses. The method requires meticulous handling to preserve the integrity of the sample's composition, crucial for reliable chemical analysis results.
These disadvantages underscore the importance of selecting the appropriate sampling methods based on the specific objectives of the concrete investigation, balancing the need for detailed information against the potential impact on the structure, risks to those carrying out the survey and the associated costs.
How accurate is sampling?
The reference of position of samples in concrete structures must be well identified, because it will have influence on the applicability of all test results. The accuracy each of individual result will varying based on the type of test and the procedures used to carry it out.
What are the limits of sampling?
Concrete core sampling is an essential technique for evaluating the structural integrity of concrete structures, offering detailed insights into material properties. However, its applicability has certain boundaries and scenarios where it's not recommended. Core sampling provides only a localized assessment of concrete, potentially overlooking broader structural conditions. Its invasive nature necessitates limiting the number of cores to maintain structural integrity, as each core extraction introduces a potential weak point that must be repaired, altering the structure's original state.
Sampling is particularly challenging in unstable or dangerous structures, where additional damage could pose safety risks. In environments containing hazardous materials like asbestos, core sampling could expose individuals to health hazards, necessitating careful consideration and alternative methods. Moreover, in highly reinforced or aesthetic areas, coring could compromise structural performance or visual integrity.
For these reasons, if possible, non-destructive testing (NDT) methods are increasingly specified. Using robotic equipment to collect samples from unsafe areas to protect the health and safety of operatives is also becoming more popular. These alternatives provide valuable insights without the drawbacks of physical core extraction, allowing for a safer and broader evaluation of concrete's condition without compromising structural safety or integrity,
Ancillary information
Maturity of test: > 10 years
Qualification & interpretation : Inspector
Service disruption: Yes
Preliminary works: No
Time consumption Low (< one hour)
Cost Low
Access to element 1 face