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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 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 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 many thousands of homes being affected. Here is a case study of one such outbreak in a number of concrete foundations across a school.
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.
PETROGRAPHIC EXAMINATIONS AND AIR-VOID ANALYSIS OF CONCRETE
Petrographic examinations (ASTM C 856) and air-void analysis (ASTM C 457) of hardened concrete are two most commonly requested tests of CMC. Here is a case study of one such project where both test methods were applied.
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.
SLAB SURFACE DELAMINATION
Excessive air in a slab intended to receive a hard troweling operation inevitably leads to delamination. Here is a case study showing delamination from accidental dosage of air entraining chemical causing as much as 20 percent air in concrete.
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.
EPOXY TERRAZZO FAILURE FROM CONCRETE SLAB ON GRADE
Moisture and improper preparation of surface are two common causes of failure of terrazzo floor. A case study on failure of epoxy terrazzo from a concrete slab-on-grade finds evidence of both players in causing blistering and de-bonding of terrazzo.
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.
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.