CASE STUDIES
The following case studies are copyright documents provided for web viewing only.
Downloading or personal use of any information is strictly prohibited.
Investigation of Fire Damage in Concrete Bridge Abutments During Collapse of a Portion of Interstate 95
Collapse of a section of northbound Interstate 95 in Philadelphia, PA on June 11, 2023, from explosive fire from a commercial tanker truck carrying 8500 gallons of flammable cargo underneath the bridge has caused severe damage to the steel-concrete composite bridge structure above it let alone to disrupt one of the busiest interstates of the nation. As a result, numerous cores across various fire-damaged abutment walls at various elevations were examined by detailed petrographic examinations and compressive strength tests for assessment of the extent of fire damage. Stereo-microscopical examinations of lapped cross sections and fluorescent (UV)-light examinations of fluorescent epoxy-impregnated lapped cross sections were used for determination of depths of macro and microcracking from fire, whereas examinations of fluorescent epoxy-impregnated thin sections in high-power transmitted-light stereozoom microscope and petrographic microscope both equipped with fluorescent (UV) light facilities along with scanning electron microscopy and X-ray microanalysis of fire-damaged face of one of the most distressed cores were used for examinations of various microstructural and mineralogical changes induced during exposures to high temperatures from fire.
Cracking in Swimming Pool Plaster From ASR of Reactive Silica in Crushed Shale Coarse Aggregate in Shotcrete
Based on detailed petrographic examinations, cracking in the pool plaster is found to be due to expansion of the underlying shotcrete component due to potentially deleterious reactions of the crushed shale aggregate used in shotcrete in the presence of moisture. Expansion of shotcrete has put the well-bonded plaster skin in tension to cause development of tensile cracks that are thus wider at the exposed surface end of plaster and tapered downward into shotcrete. The plaster is found be present in sound condition without any chemical or physical deterioration and simply responded to the expansion of shotcrete by development of tensile cracks. Cracks, once formed, have provided the pathways for deeper migration of pool water to sustain deleterious reactions in shotcrete and, thus, continued expansion and cracking..
Beneficial Aspects of Protective Coatings for Concrete in a Marine Environment
Detailed petrographic examinations and through-depth water-soluble chloride and sulfate analyses were done on concrete cores from different structural elements of a wastewater treatment plant built in the early 80s, and located in close proximity to the ocean in Puerto Rico. Cores showed sound interior concrete, negligible water-soluble chloride and no external source for sulfate beyond the contribution from Portland cement - all thanks to the presence of a well-bonded protective coating. Delay in placement of coating, however, promoted carbonation, which wasn't advanced down to the top steel reinforcement to cause corrosion, thanks again to the coating for preventing further penetration of corrosive agents.
Rehabilitation of the Grand Central Terminal Train Shed, Park Ave, New York, NY
Constructed back in circa 1910-1920 with numerous repairs and rehabilitations since then, concrete cores collected from interior walls between train tracks in the historic Grand Central Station were examined through a plethora of laboratory investigations from petrography and determination of air-void parameters for assessing concrete composition and freeze-thaw durability, water-soluble chloride and sulfate analyses for determining depths of penetration of these potentially deleterious ions in concrete, to compressive strength tests. Such a comprehensive approach of concrete investigation provide the best assessment for short and long-term serviceability and durability of concrete in such a busy train station.
Laboratory Analyses of A Masonry Mortar From A Historic 1830’s Courthouse
In Washington, Virginia
Rappahannock County Courthouse is an antebellum courthouse built in 1834 by one of President Thomas Jefferson’s workmen at the University of Virginia, serving the Town of Washington, founded in 1799. As part of the renovation, a mortar sample was provided for detailed laboratory studies to determine the composition of mortar for assessments of a suitable replacement. A low-magnesian hydraulic lime mortar was detected having crushed silica sand and carbonated lime paste. Based on the calculated mix proportion of 1-part hydraulic lime to 2.2-part sand by volume, a suitable repointing mortar was judged to be a modern natural hydraulic lime (NHL) mortar, e.g., NHL 2 or NHL 3.5 – silica sand mortar, having the mix proportion of 1-part NHL to 2-part sand by volume.
Laboratory Investigation of a Reinforced Concrete Anaerobic Digester in a Wastewater Treatment Plant in Waynesville, North Carolina
The investigation is for a 60 foot diameter, 27 foot tall reinforced concrete anaerobic digester constructed around 1980s. The digester roof was removed and contents were mostly drained for plans to operate the digester for a different purpose. No protective coatings was used on the interior surfaces. The tank was evaluated for repairs and installation of possible protective coatings on the interior and exterior of the tank for future use.
Laboratory Analyses of Three Masonry Mortars
From The Historic Old Lehigh County Courthouse In Allentown, Pennsylvania
As part of renovation of the historic Old Lehigh County Courthouse in Allentown, Pennsylvania, three masonry mortar samples (#1, 3, and 4) were provided for detailed laboratory studies to determine: (a) the compositions and conditions of the mortars, and (b) assessment of suitable replacement mortars for the examined ones to be used for future restorations. Based on optical microscopy and SEM-EDS studies, all three mortars are determined to contain: (a) Portland cement as the major binder component, (b) variable proportions of dolomitic lime, which is mostly detected from high magnesia contents of pastes in SEM-EDS studies mainly in Mortars 3 and 4, and (c) siliceous sand. Overall hydraulicities of paste show higher values of cementation indices in Mortar #1 (mostly close to 1) compared to #3 (mean around 0.75), which, in turn, has overall higher values than the paste in Mortar #4 (mean around 0.5) indicating a progressively higher proportion of Portland cement added from Mortar #4 to 3 to 1. Consistent with magnesian composition of paste in the Mortars 3 and 4 detected in SEM-EDS studies, thermal analysis also detected brucite but only in Mortar #3 thus confirming the dolomitic lime addition at least in Mortar #3
XRD-XRF and Thermal Analysis of Soil
Systematic variations in chemical and mineralogical compositions of subsurface soil samples collected at regular intervals are routinely done by XRD, XRF, and thermal analysis. Due to the abundance of platy minerals (mica and clay), both exhibiting notorious preferred orientations, sample preparation for XRD is done both by conventional bulk sample powder diffraction of pulverized soil but in a special side-loading sample holder for random orientation of grains, and as a soil slurry in alcohol pulverized in McCrone micronizing mill for 10-minutes to create abundant size fractions of less than 10 micron in size, which is subsequently placed as slurry droplets on a zero background sample holder for the clay minerals to settle in random orientations from alcohol suspension. Such randomly oriented settled clay minerals from alcohol slurry provide better results than from the side-loaded sample, which, in turn, stillproduces better results than conventional pressed pellets.
Simultaneous TGA and DSC analyses are done in a Mettler Toledo TGA/DSC 1 unit on 30-80 mg of moist soil sample in alumina crucible (70 µl, no lid) from 35°C to 1000°C at a heating rate of 20°C/min with high purity nitrogen as purge gas at a flow rate of 75.0 ml/min. Maximum weight losses occur due to loss of free and bound moisture from illitic clay within 200°C after which major endothermic peaks at 280-300°C and 540-550°C are related to dehydroxylation of illite and kaolinite.
Laboratory Investigation of a Precast Roof Assessment at a Biofilter in Moncure, North Carolina
A 2-year-old biofilter at the Arauco Wood Manufacturing Plant in Moncure, North Carolina was evaluated. The structure is 45’ ´ 165’ in plan area and includes 25’ tall cast-in-place reinforced concrete exterior walls and precast hollow core roof panels (HCPs) topped with a reinforced concrete slab (RCS). The function of the structure is to filter formaldehyde and exhaust from wood processing and manufacturing operations for pollution control. The hollow core roof panels (HCP) are the subject of this investigation.
SIDNEY R. YATES FEDERAL BUILDING, WASHINGTON D.C.
Founded in 1878-1880, the historic Sidney R. Yates Federal building is located in the National Mall in Washington, D.C. As part of the renovation process, three severely fragmented, damp, pigmented black mortar samples were provided from which one sample was selected for detailed laboratory testing to determine the type of mortar used, including composition and grain-size distribution of sand, type(s) of the binder(s) added, and volumetric proportions of binder(s) to sand.
Swimming Pool Plaster Discoloration – A Case Study From Field & Laboratory-Cured Plasters
Combined use of a chloride-based accelerator and a pigment increases the risk of discoloration compared to use of non- pigmented colored exposed aggregate plaster, or a plaster without a soluble chloride-based accelerator. The situation gets complicated by superposition of the actions of chemicals added to the pool water, which may bring imbalance between the pool water chemistry (alkalinity, pH, calcium concentration, LSI, etc.) and plaster. High temperatures in the spa can also enhance the rate of dissolution of soluble components from plaster and some pigments along with it. Extensive long-term laboratory testing of mockup plasters as the present short-term laboratory experiments are needed to evaluate the potential for discoloration of plaster by using a chemically-doped water which is representative of the pool water in service.
LABORATORY ANALYSES OF A MASONRY MORTAR FROM MARINE BARRACKS IN WASHINGTON D.C.
Founded in 1801 by President Thomas Jefferson and Lt. Col. William Ward Burrows Marine Barracks in Washington, D.C. is the oldest active post in the Marine Corps. As part of the renovation process, a ‘pointing mortar’ sample was provided to determine the type of mortar used, including composition and grain-size distribution of sand, type(s) of the binder(s) added, and volumetric proportions of binder(s) to sand.
LABORATORY ANALYSES OF MASONRY MORTARS FROM GEORGETOWN RESERVOIR IN WASHINGTON D.C.
The Georgetown Reservoir is a reservoir that is part of the water supply and treatment infrastructure for the District of Columbia. Four masonry mortars and a stucco sample were examined. Two mortars were retrieved from the exterior and interior of the Castle at east and north elevations and two others from the North Dome and Interior of the Meigs Vault. Detailed laboratory testing were done to determine the types of mortars used, including compositions and grain-size distributions of sands, type(s) of the binder(s) added, and volumetric proportions of binder(s) to sands used in the mortars,
INVESTIGATION OF SURFACE DISTRESS OF AN OUTDOOR CONCRETE SLAB
The investigation involved premature degradation of concrete sidewalks and roadway curbs in a residential development located at Norbeck Crossing in Silver Spring, Maryland. The alleged surface distress of concrete has ranged from: (a) various degrees of surface scaling of concrete as loss of the original finished surface of concrete and exposures of near-surface coarse aggregate particles, to (b) isolated occurrences of exposures of near-surface coarse aggregate particles as mortar lift-offs and/or pop outs, to (c) thin sheet-like scaling of the original finished surface where many such ‘sheets’ of finished surfaces are only loosely adhered to the main body. All these distress have reportedly occurred within two years of concrete placement between 2015 and 2017.
Delamination and Potential Surface Alteration Of An Indoor Concrete Slab-on-Grade – A Comprehensive Study From Two Concrete Cores &
An Incinerator Ash As A Potential Surface Contaminant
Delamination and surface erosion of an indoor concrete slab-on-grade at a metal recovery facility was investigated, which has suffered from premature delamination of hard trowel-finished surface of the floor at various areas, especially the areas subjected to heavy construction traffic including rubber tired front-end loaders and steel tracked equipment. Delamination occurred almost immediately once heavy equipment was on the slab. Trash burnt at a nearby incinerator was transported to the facility by a loader and dumped on the floor. Floors with a surface hardener at other facilities where this same procedure was performed have had no surface wearing issues.
Laboratory Analyses of A Masonry Mortar From A 1940’s Industrial Building At Brooklyn Navy Yard,
New York
A plethora of Ca-Si-Al-Mg-Fe-based residual hydraulic phases (RHPs) are usually detected during SEM-EDS examinations of many historic hydraulic calcitic/magnesian/dolomitic lime mortars whose chemistry and mineralogy exceed far beyond phases commonly detected in non-hydraulic lime, natural cement, slag cement, early-age Portland cements, or binary cement-lime mixes used in many 19th century masonry constructions. These RHPs are testaments of lack of quality control of raw feeds, variability in compositions (impurity types and contents) of mica-clay-iron-alumina-silica impurities in calcitic/magnesian/dolomitic limestone feeds, and poor (uncontrolled) calcination processes employed. One such example is found, where a Ca-Mg-Al-Si-based hydraulic lime binder was used in the mortar, which was produced from calcination of an impure magnesian/dolomitic limestone raw feed.
Laboratory Analyses of Masonry Mortars From A Historic 19th Century Building in Washington, D.C.
Originally built in 1859 for William P. Trowbridge and used as federal office space since the early 1900’s, Trowbridge house is currently being renovated to serve as a presidential residence, specifically for the use of former presidents of the United States while visiting the capital city. Two bedding mortars, and one pointing mortar were examined to determine the compositions and conditions of the mortars, and assessment of suitable replacement mortars for the examined ones during future restoration.
Laboratory Analyses of A Masonry Mortar From The Third Presbyterian Church in Shadyside, Pennsylvania
Constructed circa 1897 to 1903, a feebly hydraulic dolomitic lime and natural siliceous-argillaceous sand mortar was detected for which two recommendations were provided for mock-up trials - an NHL-based mortar having 1-part NHL 3.5 to 2-part sand as the first trial and an ASTM C 270 Type O Portland cement-dolomitic lime-sand mortar as the second trial where sand to be used in restoration mortar must come from the nearby Allegheny river from which the original sand was used.
Petrographic examination of concrete cores from the historic (circa 1940’s) Normandie Hotel in San Juan, Puerto Rico
The Normandie Hotel is a historic building located in the Isleta de San Juan, in San Juan, Puerto Rico, which was opened on October 10, 1942 as a hotel, but as of 2021 remains unused and abandoned. Its design was inspired by the French transatlantic passenger ship SS Normandie in addition to featuring the same art deco design as the ocean liner that inspired it, and the hotel's original roof sign was one of the two signs that adorned the top deck of the SS Normandie, but were removed from it during an early refitting. It is an example of what came to be known as the Streamline Modern architecture style.
INVESTIGATION OF CONCRETE SIDEWALK SCALING
Surface scaling, as the loss of the original finished surface of concrete sidewalks exposing the underlying aggregates and paste across a housing development Traditions of America in Lititz, Pennsylvania has prompted this investigation. As a result, a concrete core was examined for detailed petrographic examinations to investigate all possible causes for surface distress from evaluation of concrete qualities to investigation of any workmanship-related issues to the potentially deleterious effects of deicing chemicals on the short and long-term durability of the sidewalk surfaces.
LABORATORY INVESTIGATION OF
EARLY 19TH CENTURY CALCINED CLAY-LIME SETTING
AND DOLOMITIC LIME POINTING MORTARS
FROM THE PERIMETER WALLS OF THE
HISTORIC EASTERN STATE PENITENTIARY IN PHILADELPHIA, PA
The Eastern State Penitentiary is a former American prison in Philadelphia, Pennsylvania. Constructed in 1822, the prison was operational from 1829 until 1971. At its completion, the building was the largest and most expensive public structure ever erected in the United States, and quickly became a model for more than 300 prisons worldwide. The prison is currently registered as a U.S. National Historic Landmark. As part of the renovation process, three reddish-brown original setting mortars were provided from interiors of the east, west, and south walls of the penitentiary after removing the exterior stone masonry units, along with a medium gray pointing mortar reportedly also from the original construction. The study determined compositions of sands and binders used, present conditions and micro-structural evolution of mortars during the last 200 years of service history, and eventually, assessed suitable repointing mortars to be used for restoration.
CRACKING OF PRECAST CONCRETE WALL PANELS
– A PETROGRAPHIC INVESTIGATION
Extensive cracking of precast concrete wall panels in the Liberty Terrace Apartments of University at Albany has prompted this investigation. As a result, two concrete cores were provided through full thickness of panel, one from over visible cracks, and another from a visibly sound location of panel for detailed petrographic examinations according to the procedures of ASTM C 865 to diagnose possible causes for cracking.
ASSESSMENTS OF CONCRETE COMPOSITION, CONDITION, STRENGTH, AND DEPTH OF PENETRATION OF CHLORIDE IONS IN A BRIDGE SUBSTRUCTURE FROM PETROGRAPHIC EXAMINATIONS,
COMPRESSIVE STRENGTH TESTS, & CHLORIDE ANALYSES OF
FOUR CONCRETE CORES & FORTY CONCRETE POWDERS
This report provides a representative cast study for assessment of overall composition, condition, compressive strength, and depth of penetration of chloride ions into a bridge substructure. CMC is involved in numerous similar projects of assessment of overall condition, performance, and long-term durability of many concrete bridge decks and substructures where petrographic examinations, air-void analysis, compressive strength, and depth of penetration of chloride ions are the common tests routinely performed to determine the concrete condition and diagnose potentially deleterious reactions in concrete from many decades of performance in a moist outdoor environment of freezing and thawing, which may have caused cracking, spalling, and corrosion of reinforcing steel in concrete.
LABORATORY ANALYSES OF MASONRY MORTARS FROM UNITED STATES MARINE BARRACKS IN WASHINGTON, D.C.
Founded by President Thomas Jefferson and Lt. Col. William Ward Burrows, the second commandant of the Marine Corps, in 1801, Marine Barracks in Washington, D.C. is the oldest active post in the Marine Corps. The Barracks is home to many nationally recognized units, including the Marine Corps Silent Drill Platoon, the Marine Drum and Bugle Corps, the Marine Band, the official Marine Corps Color Guard, the Marine Corps Body Bearers, and the site of the Home of the Commandants. Both Marine Barracks and the Historic Home of the Commandants were listed on the National Register of Historic Places in 1972. As part of the renovation, six masonry mortar samples across six different buildings of Marine Barracks were provided for detailed laboratory studies to determine the compositions and conditions of the mortars, and, assessments of suitable replacement mortars for restorations. The case study provides a comprehensive investigation of historic mortars and mismatched repointing mortars, emphasizing the need for laboratory testing of historic mortars for proper formulation of repointing mortars during restoration.
IMPROPER REPOINTING OF MASONRY MORTARS IN A HISTORIC MONUMENT – A CASE STUDY FROM MEMORIAL BELLTOWER AT NORTH CAROLINA STATE UNIVERSITY, RALEIGH, NC
Initiated in the 1920s and constructed through 1940s, the 115-ft. tall historic Memorial Belltower at North Carolina State University is a granite stone masonry tower, which stands as a symbol of inspiration to honor North Carolina State alumni killed in World War I. As part of the renovation process of this historic monument, two sets of masonry mortars were provided, one from the lower level of the tower constructed circa 1920s, and the second set from the upper level of the monument built circa 1940s. Mortars rom both levels showed the presence of Portland cement mortar, which was applied on the preexisting lime-based mortars. Portland cement mortar is found unsuitable for lack of lime, extensive microcracking, and grossly undersanded nature. A more appropriate mortar to be used with granite masonry units of the monument would be an ASTM C 270 Type M or S cement-lime mortar, which would not only provide more malleability, workability, and long-term durability than the present much harder, stiffer non-accommodative cement-only mortar but would be in conformance to common guidelines for masonry construction.
LABORATORY ANALYSES OF MASONRY MORTARS FROM FORT WASHINGTON, MARYLAND
Located in Prince George’s County, Maryland and constructed in 1809, Fort Washington guarded the nation’s capital until it was destroyed by its own garrison in August 1814 to prevent its capture by British forces advancing on Washington D.C. Reconstruction of the fort began in late 1814 or early 1815 and completed by 1824. As part of a recent renovation, a variety of masonry mortars encompassing a large time period from the original construction era in the early 19th century to later renovation episodes during 20th century were analyzed.
DISINTEGRATION OF MASONRY MORTARS FROM INFERIOR MASONRY CEMENT – A CASE STUDY FROM NOVA SCOTIA, CANADA
Unlike Portland cement-lime mortar mixes, which are carefully proportioned during field mixing of cement, lime, and sand, and individual components are well-defined by respective industry specifications, proprietary bags of masonry cements often lack such tight control on materials and mix proportions, which can result in some undesirable consequences in the masonry. A series of improprieties in a masonry cement mortar from high slag content in the masonry cement (and corresponding high sulfate in its paste released from slag hydration), to low lime content, low entrained air content in the cement, and high water content in mortar mixes have caused widespread softening, cracking, and disintegration of jointing mortars across many residential and commercial properties in Nova Scotia, Canada.
CHLORIDE AND CARBONATION-INDUCED CORROSION OF REINFORCING STEEL IN A CONCRETE COLUMN – A CASE STUDY
Exposed perimeter reinforced concrete columns at 4-story Mann Hall (constructed in 1963) in North Carolina State University has experienced corrosion of reinforcing steel in columns resulting in various levels of distress from vertical and horizontal cracking, delamination and spalls. Laboratory tests have determined the presence of elevated chlorides in some columns and deep carbonation, hence potential chloride-induced and/or carbonation-induced corrosion of steel in concrete to cause the distress.
PYRRHOTITE RESEARCH# 1:
PYRRHOTITE EPIDEMIC IN EASTERN CONNECTICUT - A CASE STUDY FROM ELLINGTON, CT
Widespread outbreak of deterioration of many residential concrete foundations due to oxidation of an iron sulfide mineral ‘pyrrhotite’ in the quarried aggregate stones has occurred in the state of Connecticut with many thousands of homes being affected. Here is a case study of one such outbreak in a residential concrete foundation.
PYRRHOTITE RESEARCH# 2:
PYRRHOTITE EPIDEMIC IN EASTERN CONNECTICUT - A CASE STUDY FROM TOLLAND, CT
Widespread outbreak of deterioration of many residential concrete foundations due to oxidation of an iron sulfide mineral ‘pyrrhotite’ in the quarried aggregate stones has occurred in the state of Connecticut with as many as 35,000 homes being affected. Here is a case study of one such outbreak in a number of concrete foundations across a school where two different constructions from circa 1998 and 2001 showed large variations in degree of deterioration, e.g., from extensive cracking of 1998 foundations to apparent sound condition of 2001 addition despite the use of same pyrrhotite-bearing aggregates in both constructions.
PYRRHOTITE RESEARCH# 3:
INVESTIGATION OF POSSIBLE PYRRHOTITE-RELATED DETERIORATION IN A RESIDENTIAL CONCRETE FOUNDATION IN MANSFIELD, CT
Not all pyrrhotite-bearing aggregates in eastern Connecticut have caused cracking and crumbling of foundations. Some foundations are present in apparently sound conditions at the time of investigation, despite the presence of similar pyrrhotite-bearing aggregates as seen in other deteriorated foundations from the same county. This indicates the role of moisture availability and moisture migration into concrete in causing pyrrhotite oxidation and subsequent cracking.
PYRRHOTITE RESEARCH# 4:
INVESTIGATION OF PYRRHOTITE-RELATED DETERIORATION IN A RESIDENTIAL CONCRETE FOUNDATION IN MANSFIELD, CT
Unlike the case study presented above (Pyrrhotite Research# 3), the present case from two other residential concrete foundations in Mansfield, CT showed extensive cracking of foundation from pyrrhotite oxidation and subsequent internal sulfate attack in concrete. Therefore, large variations in degree of deterioration is observed across various foundations, or even from the foundation from pyrrhotite-bearing crushed stone coarse aggregate particles used in concretes. Such variations are due to variations in the amount of pyrrhotite present, variable compositions and crystal structures of pyrrhotite which have affected the rate of oxidation, degree of moisture exposure during service, and various other factors.
PYRRHOTITE RESEARCH# 5:
INVESTIGATION OF POSSIBLE PYRRHOTITE-RELATED DETERIORATION IN A RESIDENTIAL CONCRETE FOUNDATION IN MANSFIELD CENTER, CT
This is another case study where despite the presence of potentially unsound pyrrhotite-bearing coarse aggregates that have shown oxidation and related distress in other foundations, the concrete foundation is present in sound, visually crack-free condition at the time of investigation. Unlike the other cases, pyrrhotite grains in crushed gneiss aggregate in this case are present in very finely disseminated forms with localized evidence of oxidation only in relatively coarser grains, indicating the potential influence of pyrrhotite grain size in oxidation and related distress.
CONCRETE SURFACE SCALING IN A RESIDENTIAL DRIVEWAY
Scaling i.e. loss of the original finished surface of concrete is a common problem in many residential driveways. Scaling can be due to inferior quality of concrete, improper workmanship, or exposures to potentially deleterious deicing chemicals especially at the early stages of construction prior to the attainment of concrete maturity. A major part of our investigations is to determine all probable causes of concrete scaling from petrographic examinations (ASTM C 856), air-void analysis (ASTM C 457), and chloride analysis (ASTM C 1152).
TUCK-POINTING MORTAR FORMULATION
Formulation of a tuck-pointing masonry mortar from calculated mix proportions of an existing mortar sample is a common test that CMC routinely performs on mortars from modern and historic structures. Here is a case study on determination of composition of a masonry mortar and a proposed mix for tuck-pointing mortar.
LABORATORY STUDIES OF A MASONRY MORTAR
Formulation of a tuck-pointing masonry mortar from calculated mix proportions of an existing mortar sample is a common test that CMC routinely performs on mortars from modern and historic structures. Here is a case study on determination of composition of a masonry mortar and a proposed mix for tuck-pointing mortar.
FAILURE OF ANCHORING GROUT & ASSOCIATED DISTRESS IN CONCRETE
Due to extreme moisture sensitivity of gypsum, a gypsum-based grout can distress when exposed to moisture during service by softening and expansion, and/or by causing potentially deleterious expansive chemical reactions with the aluminate components within the grout and/or within the surrounding concrete. Here is a case study on cracking of concrete around rail posts when a gypsum-based grout was used.
BLISTERING ON VCT FLOORING FROM OXIDATION OF PYRITE CONTAMINANT IN CONCRETE
Expansions associated with oxidation of pyrite contaminants in concrete surface have caused blistering on a VCT flooring. The present case study shows microstructural evidence of the mechanisms of pyrite oxidation and associated distress in concrete.
BLISTERING AND DE-BONDING OF EPOXY-TERRAZZO FLOORING - A CASE STUDY
Moisture is the essential ingredient to cause various flooring distress, e.g., from blistering to de-bonding to cracking. An epoxy-based terrazzo flooring, being inherently non-breathable to moisture, can cause moisture buildup and subsequent moisture-induced distress from disintegration of flooring adhesive to potentially deleterious alkali-silica aggregate reactions in concrete. Presented herein is a comprehensive case study, where moisture accumulation beneath an epoxy-terrazzo flooring, along with lack of an appropriate bonding agent has caused blistering and cracking of terrazzo floor. Fluid accumulated beneath a blister is extracted, and analyzed by IC-FTIR-XRF methods to determine high levels of alkalies, which are common byproducts of moisture migration through concrete slab to introduce additional levels of deterioration beyond moisture accumulation.
DETERIORATION OF CONCRETE FROM FLUE GASES IN A REINFORCED CONCRETE CHIMNEY
Deterioration of concrete can occur from high temperatures and chemically corrosive flue gases in a chimney. Here is a case study that investigates depths of concrete distress from changes in concrete properties due to exposures to high temperatures, and sulfur dioxide flue gases to cause external sulfate attacks, microcracking, and loss of paste around aggregate particles.
CHARACTERIZATION OF MASONRY MORTAR FROM HISTORIC ADAMS BUILDING, TULSA, OKLAHOMA
In an effort to gain a better understanding of the masonry mortar used in one of the most iconic buildings in downtown Tulsa, OK constructed circa 1928, a wide range of analytical techniques were used so that appropriate tuck-pointing mortar can be formulated.
SHEET SCALING OF CONCRETE SIDEWALK - A PETROGRAPHIC STUDY
Sheet scaling, where original finished surface of concrete slab is loosely adhered to the main body as thin sheets, is a common type of surface distress. This is common when finishing operations initiate prior to the cessation of bleeding, hence bleed water accumulates beneath the prematurely finished surface eventually leading to separation of the finished surface from the main body. A case study of one such distress is examined by petrographic examinations.
A CASE STUDY ON RELATIVE ROLES OF CONCRETE, CONSTRUCTION, AND SALT ON SEVERE SCALING OF CONCRETE SIDEWALK
Lack of air entrainment, improper finishing practices, and exposure to deicing chemicals especially at an early age are three common reasons for scaling of concrete sidewalks and other exposed slabs. Here is a case study showing roles of all three factors for severe scaling on selected sections pours of a sidewalk separated by construction joints from sound concrete
PERFORMANCE AND DURABILITY OF A CONCRETE PARKING GARAGE DECK - A PETROGRAPHIC STUDY
Petrographic examination is a powerful method to evaluate overall concrete quality, durability, and future performance of a parking garage, especially of the exposed deck, which is subjected to cyclic freezing and thawing and deicing chemicals.
INVESTIGATION OF PYRRHOTITE-RELATED DETERIORATION IN RESIDENTIAL CONCRETE FOUNDATIONS IN MANSFIELD, CT
Widespread outbreak of deterioration of many residential concrete foundations due to oxidation of an iron sulfide mineral ‘pyrrhotite’ in the quarried aggregate stones has occurred in the state of Connecticut with many thousands of homes being affected. Here is a case study of such outbreaks in a number of concrete foundations across eastern CT.
SHRINKAGE CRACKING OF AN INDOOR CONCRETE SLAB
From concrete materials to mix proportions, construction practices, depth-spacing-timing of placement of control joints, slab thickness, elastic modulus, etc. a variety of factors determine the potential for development of visible surface to even full-depth cracks on concrete slab by uncontrolled drying and/or plastic shrinkage.
LABORATORY STUDIES OF A HISTORIC MASONRY MORTAR FROM A CHIMNEY
Composition of a historic masonry mortar is determined from petrographic examinations and chemical analyses according to the procedures of ASTM C 1324. Proportion of binders and sand is determined from laboratory studies, which is then used as guidelines for formulation of an appropriate pointing mortar.
CONDITION EVALUATION OF CONCRETE WALKWAY AND ANCHORING GROUT
A wide range of laboratory techniques from optical microscopy to electron microscopy to chemical analyses, XRD, XRF, thermal analysis, and FT-IR spectroscopy were done for a comprehensive investigation of concrete quality and condition as well as distress of anchoring grout.
LABORATORY STUDIES OF CLAY BRICKS & MASONRY MORTARS FROM EARLY TO MID-20TH CENTURY - A CASE STUDY
Located in an industrial section at 325 Russell Avenue in Guilford County, High Point, North Carolina, the Langford Building was originally constructed in 1916 and has since received multiple episodes of additions and renovations. As a result, a variety of brick and masonry mortar samples were provided, spanning almost five decades of construction periods from the original 1916 vintage through 1950s to late 1960s, to determine compositions of bricks and mortars used during those periods. The samples were examined to determine the types of bricks and mortars present, materials and mix proportions of mortars, evidence of any physical or chemical deterioration of bricks and mortars during service, and recommendations for appropriate pointing mortar to be used in renovations. Bricks were tested for compressive strengths by using the methods of ASTM C 67 and petrography by ASTM C 856, whereas, mortars were studied by following the petrographic, chemical, and other ancillary methods of ASTM C 1324..
LABORATORY STUDIES OF A STONE AND MASONRY MORTARS FROM ROBERT C WEAVER FEDERAL BUILDING IN WASHINGTON D.C.
Located at 451 7 thStreet, SW in Washington, D.C. the Robert C. Weaver Federal Building is the headquarters of the U.S. Department of Housing and Urban Development (HUD). Constructed from 1965 to 1968 by the renowned architect Marcel Breuer, the building is recognized as the first federal building in the country to utilize precast concrete as the primary structural and exterior finish material, as well as the first fully modular design for a federal office building. As part of the renovation process, two sets of masonry mortar samples were provided for detailed laboratory examinations. The first set comprises two samples from the original 1960s vintage, and the second set of two samples reportedly came from 2019 construction. The purpose of this laboratory examination is to determine the compositions and mix proportions of mortars from the original 1960s and recent 2019 constructions and evaluate their compatibilities and suitability for long-term performance of masonry walls. Additionally, a dark gray, dense hard crystalline stone masonry sample from the building was provided in two small pieces to determine the stone type.
FAILURE OF A CONCRETE SEWER PIPE BY BACTERIAL ACID CORROSION - A CASE STUDY
The present study represents a classic case of bacterial sulfuric acid attack causing collapse of a concrete sewer pipe. Sewer environments impose a special type of chemical threat to Portland cement concrete whose products are similar to the products of deterioration of concretes exposed to acids or external sulfates, but the mechanism of distress is quite different as it is controlled by the bacteria colonies present within the sewer. Anaerobic bacteria present in sewer pipes can decompose many inorganic and organic sulfur compounds, releasing hydrogen sulfide gas to the interior sewer atmosphere above the sewer effluent. This gas is then absorbed by the moisture film on the interior pipe walls above the effluent, which contains aerobic bacteria (e.g., Thiobacillus). The aerobic bacteria colony in the aerated zone oxidizes the hydrogen sulfide gas to sulfurous and sulfuric acids, which then attack and dissolve the hardened cement paste. The result is the development of a chemically corroded concrete surface on the crowns and aerated portions of sewer pipes consisting of exposed aggregates standing proud against severely corroded cement paste.
INVESTIGATION OF POTENTIAL DAMAGING EFFECTS OF MAGNITUDE 6.0 TO 6.4 EARTHQUAKE ON EXTERIOR MASS CONCRETE COLUMNS OF CONCRETE POWER PLANT GENERATOR BASES IN A MARINE ENVIRONMENT IN GUAYANILLA, PUERTO RICO
A case study on evaluation of condition of an existing concrete after an earthquake along the subduction zone struck the south side of the ocean island arc environment of Puerto Rico generating seismic waves that has travelled to the nearby concrete power plant.
TESTING OF CONCRETE PRISMS & CYLINDERS FOR LENGTH CHANGE (ASTM C 157), CHLORIDE CONTENT (ASTM C 1218), CHLORIDE PERMEABILITY (ASTM C 1202), & AIR-VOID PARAMETERS (ASTM C 457)
As part of quality evaluation of concrete, besides petrographic examinations (ASTM C 295, and C 856), four commonly requested tests that we conduct are: length change (ASTM C 157), chloride content (ASTM C 1218), chloride permeability (ASTM C 1202), and air-void parameters (ASTM C 457).
LABORATORY TESTING OF A MASONRY MORTAR FROM A LATE 19TH CENTURY HISTORIC CHURCH IN PITTSBURGH, PENNSYLVANIA
The study involved evaluation of a historic masonry mortar sample from Church of the Ascension located at Ellsworth Avenue and Neville Street in the Shadyside neighborhood of Pittsburgh, Pennsylvania. Built in 1898, the church was added to the List of Pittsburgh History and Landmarks Foundation Historic Landmarks in 1971. The mortar was determined to be made using natural cement aka Rosendale cement, dolomitic lime (most probably used as lime putty), and a mixed sand consisting of crushed siliceous (quartz, quartzite) sand and natural (rounded) sand of dominantly argillaceous (shale, siltstone) and ferruginous components. The estimated volumetric proportion of natural cement to lime to sand is determined to be 1-part natural cement to less than 2-part lime to 7-part sand.
IMPORTANCE OF A COMPREHENSIVE TESTING STRATEGY FOR INVESTIGATION OF SURFACE SCALING OF OUTDOOR CONCRETE SLABS
Surface scaling of an outdoor concrete slab can occur from poor quality of concrete, improper construction practices, or, exposures to deicing chemicals especially prior to the attainment of concrete maturity. A simple petrographic examination of a scaled concrete core may show good air entrainment and no other obvious issues with concrete per se, as in the present case, except perhaps some finishing-related surface softening, but without doing a subsequent analysis of chloride contents at various depths, e.g., at least at the scaled surface region and in the interiors would not include the common potential deleterious roles of salts in surface scaling.
EARLY-AGE CRACKING OF A CONCRETE SLAB-ON-GRADE: A PETROGRAPHIC STUDY
Early-age cracking of a concrete slab-on-grade, e.g., prior to the attainment of at least a 7-day design compressive strength can occur due to a variety of reasons from settlement to plastic shrinkage to drying shrinkage. A detailed petrographic examination of a concrete core or a saw-cut concrete section can determination the reasons for such cracking.
LOWER-THAN-DESIGN COMPRESSIVE STRENGTH OF A CONCRETE CYLINDER: A PETROGRAPHIC STUDY
Higher-than-design air, clustering of air bubbles along aggregate-paste interfaces, higher-than-design water-cementitious materials ratios from higher-than-design water and/or lower-than-design cement contents, improper stone and/or sand proportions, improper aggregate type, grading, excessive dosages of fly ash, improper dosages of chemical admixtures, inadequate curing, early freezing of cylinder in an outdoor environment prior to moist curing - the reasons for the lower-than-design compressive strength of a cylinder are numerous, which only a detailed petrographic examinations can determine in a low-cylinder-strength investigation. Presented herein is a case study of one such effect, an important one, for lower-than-design cylinder strength of a project.
INVESTIGATION OF AN OUTDOOR SUSPENDED CONCRETE SLAB OF AN UNDERGROUND VAULT OF A SWIMMING POOL
Use of a non-air-entrianed concrete containing potentially alkali-silica reactive gravel coarse aggregate particles in an outdoor concrete slab exposed to percolation of chlorinated pool water, and winter freezing have taken its destructive tool. The concrete has developed extensive cracking primarily from cycling freezing and thawing of a non-air-entrianed concrete at critically saturated condition, which was subsequently followed by ready access of chlorinated water through freezing-related cracks to the sites of potentially alkali silica reactive gravel particles to cause such a reaction to further aggravate the condition. Despite attempts to save the slab with a dense topping, lack of a good bond of topping to the cracked substrate did not save the latter, requiring replacement as the only option for long-term serviceability of the vault.
LABORATORY STUDIES OF A MORTAR COATING FROM A FAILED PRESTRESSED CONCRETE CYLINDER PIPE (PCCP)
Investigation of failure of mortar coating in a prestressed concrete cylinder pipe (PCCP) is a commonly-requested laboratory study, which starts with detailed petrographic examinations of the mortar coating to evaluate the condition after interactions of soil and the surrounding environment to the pipe, which is then followed by determination of water-soluble chloride contents at successive depths from the exterior surface through the coating body to the interior wire cast surface regions, and finally physical tests involving water absorptions, specific gravity, and volumes of permeable voids in the coating to evaluate potential for penetration of deleterious elements through the coating to cause corrosion of the pipe elements leading to the failure.
LABORATORY INVESTIGATIONS OF LOWER-THAN-DESIGN COMPRESSIVE STRENGTHS OF CAST-IN-PLACE PROPRIETARY PILE GROUTS
The study involves investigation of lower-than-anticipated compressive strengths of 90 to 110 ft. deep cast-in-place grout piles from the Allen Tower in Houston, Texas, where a grout mix having a 28-day design strength of 6550 psi has reportedly produced 56-day cylinder strengths in the range of 4000 to 6000 psi, i.e. 60 to 90 percent of design strength even at 56 days. Additionally, strength testing of field grout samples showed lower-than-design strengths of about 40 out of 820 cast piles where strength variations were reportedly inconsistent.
LABORATORY INVESTIGATIONS OF CRACKING OF A PROPRIETARY ANCHORING GROUT AND SURROUNDING CONCRETE IN THE BALCONY SLABS OF A CONDOMINIUM
From cyclic freezing and thawing of a non-air-entrianed proprietary grout and/or the surrounding concrete to the continued expansive (e.g., sulfate-aluminate) reactions from the semi-plastic state (which was beneficial for the anchoring purposes) to the hardened state in the presence of moisture during service leading to expansions at the hardened state - a number of factors can introduce undesirable cracking in a proprietary anchoring grout and its surrounding concrete.
EVALUATION OF SERVICE LIFE OF CONCRETE WALL IN A WASTEWATER TANK: A PETROGRAPHIC STUDY
Interaction of chemicals in a wastewater tank with the surrounding concrete wall of the tank can lead to various alterations of concrete. The depth of such alterations depend on the density, water-cementitious materials ratio, consolidation, and other factors that control the resistance of penetration of chemicals into concrete. Usually, leaching of calcium hydroxide component of cement hydration occurs at the exposed surface, along with increased paste porosity from continued leaching of calcium-silicate-hydrate, carbonation, chemical alterations of paste depending on the chemicals stored the tank, discoloration, etc. Petrographic examinations of cores drilled from the aerated, transitional, and submerged portions of the tank wall, along with chemical analysis of wastewater contaminants from ion chromatography of concrete from successive depths of wall can determine the serviceability of the tank from the condition of concrete and depth of penetration of chemicals.
CONDITION EVALUATION OF AN INDOOR CONCRETE SLAB-ON-GRADE WHICH WAS EXPOSED TO FREEZING AT ITS EARLY STAGES OF CONSTRUCTION
It is not uncommon for an indoor concrete slab-on-grade exposed to freezing, snow etc. during the winter weather placement at the early stages of its construction. A detailed petrographic examination of a core from such a slab can eliminate any concerns related to early freezing and other environment-related as well as construction and concrete-related factors that can affect the long-term serviceability of the slab.
FAILURE OF STUCCO CLADDING IN A CONDOMINIUM COMPLEX - A PETROGRAPHIC STUDY
Cracking, blistering, de-bonding from the substrate as well as within the coats, and discoloration are the four common types of failure occur in a stucco cladding. A detailed petrographic examination and chemical analyses of a saw-cut section of stucco from a distressed area can determine the reasons for failure from evaluation of the stucco materials, proportions, construction practices to the effects of the environment.
SURFACE SCALING OF AN OUTDOOR SWIMMING POOL DECK - A PETROGRAPHIC STUDY
Despite almost 90 years of advancement and understanding of the importance of having air entrainment in an outdoor concrete slab exposed to cyclic freezing and thawing, we still see cases where an outdoor slab placed a harsh weather condition has missed air entrainment - the necessary ingredient for durability and survival of a slab in the winter weather condition especially around a swimming pool deck. The present case shows one such negligence.
INVESTIGATION OF SPALLING OF BALCONIES IN TWO 22-STORY HIGH-RISE BUILDINGS IN AN OCEANFRONT ENVIRONMENT IN
PUERTO RICO
Concrete construction in a marine environment requires careful attention to the details starting from the use of a dense, low water-cement ratio, air-entrained, near-impermeable durable concrete to adequate concrete cover over reinforcement and use of epoxy-coated reinforcement to combat corrosion of moisture, chloride, oxygen and other corrosive agents from the environment. Petrographic examinations, along with chemical analysis of concrete are routinely done to evaluate condition of an existing concrete and corrosion-related spalling as in the present case.
CRAZE CRACKING OF A TROWEL-FINISHED CONCRETE SLAB-ON-GRADE: A PETROGRAPHIC STUDY
From the network of fine, closed polygonal-shaped craze cracks to large continuous cracks on a concrete slab on grade can occur from drying shrinkage of slab due to loss of water from the concrete to the environment. A number of factors starting from the concrete materials to mix proportions to placement, finishing, curing practices, slab thickness, substrate condition, placement environment (temperature, wind speed, humidity), control joint depth-spacing-timing of placement, amount and depth of reinforcement, etc. control the amount of water loss, and hence shrinkage, and related cracking. Petrographic examinations of a core from a cracks concrete slab investigate many of these factors and their potential role in causing excessive drying shrinkage of concrete slab.
EFFLORESCENCE AND SPALLING OF A FLAGSTONE PAVER - A PETROGRAPHIC STUDY
Despite natural tendency of a flagstone paver to break in flat parallel pieces along its internal fissile planes of bedding as in sandstone, or planes of weakness (cleavage) as in slate, a careful choice of flagstone along with a careful choice of jointing mortars around the pavers create a durable paver slab that can be serviceable even in a moist and harsh outdoor environment. However, occasional flaking of paver can occur in a moist outdoor environment of freezing if the bonds to the jointing mortars are weak, which, in turn, is controlled by a careful choice of the mortar mix compatible with the paver in question.
COATING FAILURE FROM STUCCO FACADE OF A HISTORIC COURTHOUSE
Extensive peeling of paint from around an 18th century courthouse in Charleston, South Carolina has been investigated from an extensive array of testing of stucco substrate, and paint, from optical microscopy through SEM-EDS, XRD, XRF, TGA-DSC, gravimetry, image analysis, to FTIR studies of paint to determine use of an alkyd-resin based paint susceptible to saponification in an alkaline environment as opposed to common latest or acrylic-based paint, along with use of a dolomitic hydraulic lime-based binder in the stucco, and absence of a bonding agent across the elevations to cause extensive paint failures.
LABORATORY ANALYSES OF A CEMENT-LIME MORTAR FROM A HISTORIC PRISON IN FAIRFAX, VA
As part of the renovation process of Old Fairfax County Jail in Fairfax, Virginia, a cement-lime mortar sample was analyzed to determine grain-size distribution of sand, compositions and microstructures of carbonated cement-lime paste, and volumetric proportions of cement, lime, and sand. The sample was analyzed by comprehensive laboratory examinations by following the methods of ASTM C 1324 and RILEM, including optical microscopy, scanning electron microscopy and X-ray microanalyses (SEM-EDS), chemical analyses (gravimetry), X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analyses (TGA, DTG, DSC), and ion chromatography.