Forensic methods are used to analyze brick masonry, refractory, and mineral problems. These methods include physical testing for properties related to performance. “Chemical testing” involved analytical methods to determine the root cause of problems. Optical and electron microscopy are useful with bricks and mortars in composition analysis.
Job Site Inspections – Structural Bricks and Furnace Inspections
After the property owner has noticed problems with bricks or mortar, a professional job site inspection is required to look for specific details and formulate a “root cause” hypothesis. Inspections are typically at ground level using telescopes if necessary. Roof inspections and inspections in bucket lifts may be required. Furnace inspections usually involve entry during a down time.
Structural Brick – Inspections
BrickExpert.org typically performs recognized field tests on-site during an inspection. Depending on the issues involved, the following tests may be warranted:
- Counts of affected bricks or mortar joints by type of defect.
- Photo surveys of the structures.
- Observation of weep holes and flashing protrusions from wall/drip edges.
- Soundness tests on bricks by tactile/tapping for surface defects including incipient/developing spalls.
- Soundness tests on bricks by Schmidt hammer for internal cracking.
- Sampling of efflorescence or surface stains for laboratory analysis.
- Water drop tests to determine the presence of coatings or sealants.
Schmidt Hammer Testing on Brick Veneer
If brick extraction is required, a sampling plan is formulated. There is no standard protocol for sampling of bricks from a structure, but a plan can be formulated using the general guidance/methodology of ASTM C823, Standard Practice for Examining and Sampling of Hardened Concrete in Constructions. Bricks are typically removed by an engineering company and sent to BrickExpert.org given protocols for packaging and shipping.
BrickExpert.org does not offer structural assessments or tests on brick assemblies (extracted or in-situ tests on panels). These services dealing with structural performance/capacity and safety must be provided by qualified structural engineers.
Detailed Information on Methods Below
Tests on Extracted Bricks and Mortar – Physical, Analytical, and Microscopic
- Physical tests described in national standards (ASTM and CSA).
- Analytical tests in investigations.
- Microscopic characterizations for composition and defects.
For Owners and Attorneys
Forensic investigations usually start with the question, “How good are the structural or refractory bricks involved?” Comparing properties to those specified in ASTM standards and product data sheets answers that question.
It is inappropriate and incorrect for any experts to test bricks extracted from a wall or taken from job site storage and make claims about qualifying as to Grade under standards.
It is frequently necessary to use analytical methods and microscopy. These tests for structural and refractory bricks answer questions such as (1) what is the source of efflorescence or other surface stains, (2) what is the future durability of bricks in a wall (for example, if interior insulation is retrofitted into an older building), (3) is my problem related to excessive thermal expansion of the bricks (for bricks of high sand content), and (4) are the bricks on my walls internally damaged? For refractory bricks, questions include: (1), do the bricks/monolithic materials meet typical data sheet values of chemistry, density, and refractoriness, (2) is the thermal expansion of the refractory as-advertised, is there excessive or unusual corrosion or surface buildup, are refractory anchors functioning as required, and is the refractory selection appropriate for the process? For mineral issues, characterization by approved regulatory methods may be required.
Analytical Tests in Brick Forensics, Refractories, and Mineral Issues
- X-ray florescence spectroscopy is typically used in determining the chemical analyses of bricks and mortar.
- X-ray diffraction reveals the mineral composition of the bricks and mortar for species generally present greater than one weight percent.
- Thermal analysis is particularly useful in identifying species where the species is present less than one weight percent. These methods, when coupled with evolved gas analysis, can determine the type of cleaner or the type of water/anti-graffiti coating used on bricks.
- Mercury porosimetry is used in durability predictions for bricks by revealing their pore sizes. It is also very useful in obtaining precise densities of small mortar specimens.
- Thermal dilatometry reveals the thermal expansion rates/coefficient of bricks. It is frequently used to determine the “firing temperature” of older clay bricks.
- Ion chromatography identifies substances that are water leached from bricks. In some cases, other chemical methods are used on leachate when “metal staining” is observed.
- Ultrasonic detection of internal flaws/cracks using a pulse – eco technique (Pundit).
Forensics/Mix Composition – Mortars, Coatings, Mineral Paints, and Early Concretes
The key issues in masonry mortar analysis are mortar mix (cement – lime – sand ratio or binder – sand ratio), cement type, and identity of constituents. Masonry buildings built before about 1900 used either lime/sand or natural cement/lime/sand mortars. After about 1900, Portland cement mixes became available, and early masonry cements were introduced.
It is well-known that repair mortar must be “compatible” with the original mortar used in a structure. What this really means is that stiff or rigid (high elastic constant) mortar can damage bricks over time leading to cracking in or spalling on the bricks. This is particularly true for structures with bricks made before about 1950 that may include softer bricks or those formerly known as “commons”.
Similar considerations apply to pointing mortar applied over older or historic mortar. Further, physical properties of mortar including vapor permeance are used by engineers in predicting moisture movement through and moisture accumulation in brick masonry walls. Wall designs and repair strategies always attempt to avoid moisture accumulation in walls.
There are three levels important of a mortar investigation:
- Basic Level – What is the Mortar Mix? This investigation seeks information to include cement ID, mortar mix composition, and a chemical look at constituents. The investigation uses a part of ASTM C1324 and includes a microscopic examination in the cement identification and a determination of the sand chemical analysis – since the sand analysis determines sand color and dramatically affects mortar color.
- Intermediate Level – What are the Chemical Analyses and Mineralogical Characteristics of the Mortar? This investigation seeks a full chemical and mineralogical characterization for a historic building mortar, as is appropriate for a protected building – such as one on the National Register. This investigation uses methods covering a large scope of ASTM C1324. Usually the Basic Level results are included in this analysis.
- Full Characterization – What are the Physical Characteristics of the Mortar and Has There Been Salt Attack/Mineral Alteration? This investigation employs physical tests to provide engineering properties and to look for corrosion (salt/attack). This investigation usually includes 1 and 2 above, and it provides a full scope of information as provided in ASTM C1324. Color measurements on hardened repair and original mortars are available using computerized instrumentation.
Similar analysis techniques are used in analysis of mineral paints, cementitious coatings/pargeting, and historic concrete.
Microscopy in Forensics
There are various levels of microscopy used in forensic examination of bricks and mortars. Simple examination with a magnifying glass or a stereo microscope (at magnifications of 2-50X) are generally insufficient to see most internal features. Stero microscopy is NOT the same as “petrographic” microscopy/examination.
Petrographic examinations are performed on thin section of masonry specimens so that constituents, their spatial distribution, and porosity can be seen requiring magnifications of 5-200X. A typical petrographic microscope used by BrickExperts.org is shown below.
When chemical information is needed or when greater magnification is required, scanning electron microscopes (SEM) are used. In brief, the image in a SEM is often detected when electrons impact the surface and are “back scattered”. Since the beam is “rastering” across the surface, a two dimensional picture of the specimen is obtained with very high magnifications possible. Another consequence of the electrons impacting the specimen is the generation of X-rays characteristic of the elements in the electron impact area of the specimen. The technique of analysis is called “Energy Dispersive X-ray Analysis” or EDAX. A SEM used by BrickExperts.org is shown below.
A scanning electron microscope photomicrograph of a brick below shows:
- Quartz particles (dark gray) surrounded by a continuum of vitreous material and pores (black). The amount of quartz can affect the thermal expansion behavior of the brick.
- White streaks of iron oxide (hematite) – it is a red brick.
- Bright angular inclusions (magnetite) – there was reduction firing or “flashing”.
- Irregular orientation of back pores over the field – it is a molded brick.
A SEM photomicrograph of a pointing mortar specimen:
A low magnification photomicrograph of a masonry pointing mortarobtained using a petrographic microscope/polarized light shows the degree of carbonation (light areas between sand grains), below:
A dry prssed refractory brick microstructure viewed in reflected light microscopy is shown below: