Laboratory Services

Petrography is one of the most effective methods used to evaluate building materials. Unlike other techniques, petrographic examination of hardened concrete can determine the root cause of deterioration and identify risk factors that would impact durability of the material.

By combining our in-house petrography capabilities with informed remedial and durability engineering solutions, we can provide a detailed insight into the health of your structure. This can aid in the development of targeted remediation strategies, as well as mix design verification at the time of construction.

Applications include:

Concrete

Concrete petrography plays a critical role in durability assessments of existing structures. Our experienced petrographers can determine the constituents of the cement paste, classify the aggregate/sand type, map crack/ microcrack patterns, identify secondary deposits and more. Through this process, we can ascertain which deterioration mechanisms have occurred, are currently in progress or are likely to initiate. These include, but are not limited to:

• Alkali-silica reaction (ASR)
• Delayed ettringite formation
• Sulfate attack
• Acid attack
• Soft water attack

Heritage

When matching historic mortars and renders, knowing the composition of the original materials is paramount to creating an ideal match. Duratec’s petrographic team can determine the aggregate mineralogy and cement constituents of the sample, as well as the air content of the mortar. From the petrographic and wet chemistry data, the percentage of portland cement, hydrated lime and sand in the existing mortar is calculated, aiding in the mix design for remedial mortars and renders.

Aggregate

Understanding the potential for particular aggregates to undergo alkali-silica reaction (ASR), or have undesirable constituents, is crucial when determining suitability for use.
Aggregate petrography is used to analyse both coarse and fine aggregate to classify the rock/mineral types present and identify these deleterious constituents. The results of the analysis break down the weighted percentages of the rock and existing minerals in the sample, and these percentages can be compared to specifications to determine if the sample is suitable for use.
The MEnD Laboratory offers NATA Accredited aggregate petrography in accordance with ASTM C295 and AS 1141.26.

Other materials

Building material without standard testing methods can still be evaluated by petrography to determine its condition and properties. For example, bricks are tested to determine causes of cracking/spalling or degree of firing. Grouts can be looked at to determine their constituents and degree of hydration. Our optical microscopy facilities can also be used for forensic investigations of coatings, metals and ceramics.

Chemical analysis of concrete can provide vital information on the potential for chloride-induced corrosion of steel reinforcement and the likelihood for deterioration by sulfate attack.

• AS1012.20.1: Determination of Chloride and Sulfate in hardened Concrete and Aggregates – Nitric Acid Extraction Method
• AS1012.20.2: Determination of Water-Soluble Chloride in aggregates and Hardened Concrete
• BS 1881 Part 124 Section 12.1: Determination of Chloride Content (Acid Soluble)

• AS1012.20.1: Determination of Chloride and Sulfate in Hardened Concrete and Aggregates – Nitric Acid Extraction Method
• BS 1881 Part 124 Section 12.2: Determination of Sulfate Content

X-ray diffraction (XRD) is an analytical technique used to speciate the crystalline phases in a material. A sample is prepared and placed into an X-ray Diffractometer, an instrument which exposes it to X-rays at different angles.

Industries used in

• Mining and Exploration: Determine the minerals that contain the metal of interest
• Ore Processing: Help to understand the phase changes that occur during metal extraction to retain high yields
• Construction Materials: Identify relative concentration of key phases in cement clinker or potentially deleterious phases in aggregate
• Soil Science: Speciate the clay fraction of soils and determine if swelling clays are present

Technique limitations

• Powdered Sample: As samples are typically powdered for XRD, the spatial information of where certain phases occur in the sample is lost
• Detection Limit: If a phase occurs in the sample at a concentration <1%, it may be lost in the background and not picked up by the technique
• Overlaps: Overlaps between mineral phases can be difficult to speciate in XRD. Additional information like sample chemistry can help rectify this issue, but not always. In these situations the experience of the operator is critical in phase determination.

Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) is an instrument used to determine the chemical composition, texture and microstructure of a given material. Individual particles at the micron scale can be imaged and chemically speciated (to a degree) using the technique.

SEM-EDS can be coupled with other techniques like X-ray Diffraction (XRD) if determining a samples mineralogy and chemical composition are both required.

Industries used in

• Mining and Exploration: Confirmation of the metal of interest and finding its location within the sample
• Ore Processing: Determine liberation of the metal of interest throughout various processing stages
• Construction Materials: Diagnose specific mechanisms of deterioration in hardened concrete when coupled with optical microscopy
• Health and Safety: Work to identify composition of respirable particles

Technique limitations

• Analysis Area: SEMs can operate at very high magnifications and typically require very little sample. As such, the data collected may not be representative of the bulk sample
• EDS Data: EDS is reasonably accurate with regard to the chemical elements identified (there are a few overlaps but an experienced operator can determine which element to select). However, the concentrations given are relative rather than absolute.
• Lighter than Carbon: Chemical elements that are lighter than carbon are not detected by SEM-EDS. This can be an issue when analysing samples that are known to contain Lithium, as the element is ‘invisible’ on the instrument. Typically other techniques are coupled with SEM-EDS when testing these types of samples