PeTrographic Analsis

Petrography is an important branch of petrology that focuses on the in-depth study of rocks and their characteristics. The goal of petrography is to understand the mineral content, texture, and structure of rocks, which helps to classify them into different types (e.g. shale, sandstone, limestone, granite, quartzite etc.).

Petrography usually begins with the field notes or sampling taken at the rock outcrop and includes the examination of hand specimens. The petrographer uses a petrographic microscope to conduct a detailed analysis of minerals, including the texture and structure, which provides important insights into the origin of the rock. The analysis is usually performed by a qualified geologist.

In a modern petrographic lab, various tools and techniques are used to study rocks in detail. Electron microprobe analysis, atom probe tomography, and whole rock chemical analysis using techniques such as X-ray fluorescence, atomic absorption, and laser-induced breakdown spectroscopy are used to get an accurate picture of the mineral composition of the rock. X-ray diffraction can also be used to analyze individual mineral grains when optical means are not sufficient.

Another important aspect of petrography is the analysis of fluid inclusions within mineral grains. By heating the mineral grains on a petrographic microscope, the petrographer can determine the temperature and pressure conditions that existed during the formation of the minerals.

Petrography plays a crucial role in the study of rocks and provides valuable insights into the mineral content, texture, and structure of rocks, which helps to classify and understand their origin.

Petrographic analysis can also determine the present condition of previously placed concrete, identifying the root cause of surface scaling, spalling, and aggregate pop-outs, and explaining the causes of concrete degradation. The analysis can also be used to assess the air content, water/cement ratio, density, and permeability of the material. Additionally, petrographic analysis can reveal the root cause of low compressive strength, compare hardened concrete to known mix designs, and assess fire damage.

Petrographic analysis of concrete

Petrographic analysis answers several important questions about the material being evaluated, such as whether the materials used match the concrete mix design, if the air content and porosity are correct, if the material has cured correctly, and if there is evidence of deleterious degradation. The analysis can also determine the geological origin of the stone being evaluated, it’s composition and suitability for use as a construction material. Petrographic analysis is also used to identify alkali silica reactivity, which is particularly problematic when found in concrete, often resulting in product failure through expansion.

Several test methods are performed as part of petrographic analysis, including Petrographic Analysis (ASTM C856), Air Void Analysis (ASTM C457), FTIR Analysis, Petrographic Analysis of Natural Stone (BS EN 12407), Petrographic Analysis of Agglomerated Stone (BS EN 14618), Petrographic Analysis of Natural Stone Tiles (BS EN 12057), and Petrographic Analysis of Slate and Roofing Tiles (BS EN 12326-2), Petrographic Description of Aggregate (BS EN 932-3), Detailed Petrographic of Aggregate (BS BS 812-104). These tests provide detailed information about the composition and characteristics of the material being evaluated.

Petrographic analysis is a valuable diagnostic tool that can help understand the mineralogy of materials and evaluate the integrity of concrete and other geological materials. The analysis is performed by independent and reputable organizations, and provides a wealth of information about the material being evaluated.

SEM Petrographic

Scanning Electron Microscopy (SEM) is a powerful analytical tool that can be used in conjunction with petrographic analysis to gain a deeper understanding of geological samples. SEM can be used as a stand-alone service or in support of other petrographical analyses and descriptions.

SEM is capable of analyzing a wide range of sample types, including small rock chips, polished thin-sections, and other materials. It offers a range of benefits, including the detailed characterization of clay mineralogy and other microcrystalline components and their associated microporosity.

One of the primary uses of SEM in petrographic analysis is to elucidate paragenetic relationships. SEM allows for the investigation of zoning and chemical variability within cements, providing valuable information about the formation and evolution of geological samples.

Another useful application of SEM in petrographic analysis is the systematic and automated collection of images for pore image analysis. This technique can provide valuable data on the porosity and permeability of geological samples, which is essential for the evaluation of hydrocarbon reservoirs.

SEM can also be used to prepare petrographical montages for deep zoom imaging. This allows for high-resolution imaging of geological samples, providing a detailed view of their morphology and structure.

Perhaps one of the most significant advantages of having SEM capabilities in-house is the ability to offer a rapid turnaround/hotshot analysis of samples. Many geological materials can be analyzed with a minimum of preparation, with samples only needing to be dry. In the case of samples containing liquid hydrocarbons, light cleaning is also required.

SEM analysis can reveal the detailed morphology and inter-relationships of clay minerals that may not be clearly resolved in thin-section/optical microscopy. This makes SEM a valuable tool for understanding the complex mineralogy of geological samples.

Backscattered electron SEM imaging can be used to investigate the zoning and chemical variability within cements, which may not be detectable with thin-section imaging. This technique, combined with energy dispersive X-ray analysis, allows for the identification of variations in mineral chemistry and compositional zoning within the cement. This information can be used to subdivide and correlate cementation episodes between samples, as well as provide insights into diagenetic conditions such as redox. The Z-contrast variations evident in SEM images also provide valuable information on mineral chemistry.

In conclusion, SEM is an essential tool for petrographic analysis, offering a range of benefits for the characterization and understanding of geological samples. Its ability to provide high-resolution imaging and detailed information about the structure, porosity, and mineralogy of samples makes it an indispensable tool for the geological sciences.