Physical and microstructural aspects of sulfate attack on ordinary and limestone blended Portland cements

Journal Article · Tue Dec 15 04:00:00 EST 2009 · Cement and Concrete Research

DOI:https://doi.org/10.1016/j.cemconres.2009.08.005· OSTI ID:21344734

Schmidt, Thomas ^[1]; Lothenbach, Barbara ^[1]; Romer, Michael ^[1]; Neuenschwander, Juerg ^[1]; Scrivener, Karen ^[2]

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1. Empa, Swiss Federal Laboratories for Materials Testing and Research, 8600 Duebendorf (Switzerland)
2. EPFL, Laboratory of Construction Materials, 1015 Lausanne (Switzerland)

The consequences of external sulfate attack were investigated by traditional test methods, i.e. length and mass change, as well as by a newly developed, surface sensitive ultrasonic method, using Leaky Rayleigh waves (1 MHz). The macroscopic changes are discussed and compared with thermodynamic calculations and microstructural findings (SEM/EDS). The results show that the main impact of limestone additions on resistance to sulfate degradation are physical - i.e. addition of a few percent in Portland cement reduces the porosity and increases the resistance of Portland cement systems to sulfate; but higher addition of 25% increase porosity and lower resistance to sulfate. The kinetics of degradation were dramatically affected by the solution concentration (4 or 44 g Na{sub 2}SO{sub 4}/l) and the higher concentration also resulted in the formation of gypsum, which did not occur at the low concentration. However the pattern of cracking was similar in both cases and it appears that gypsum precipitates opportunistically in pre-formed cracks so it is not considered as making a significant contribution to the degradation. At 8 deg. C limited formation of thaumasite occurred in the surface region of the samples made from cement with limestone additions. This thaumasite formation led to loss of cohesion of the paste and loss of material from the surface of the samples. However thaumasite formation was always preceded by expansion and cracking of the samples due to ettringite formation and given the very slow kinetics of thaumasite formation it was probably facilitated by the opening up of the structure due to ettringite induced cracking. The expansion of the samples showed a steady stage, followed by a rapidly accelerating stage, with destruction of the samples. The onset of the rapidly accelerating stage occurred when the thickness of the cracked surface layer reached about 1-1.5 mm-10-15% of the total specimen thickness (10 mm).

• OSTI ID: 21344734
• Journal Information: Cement and Concrete Research, Journal Name: Cement and Concrete Research Journal Issue: 12 Vol. 39; ISSN 0008-8846; ISSN CCNRAI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALI METAL COMPOUNDS
BUILDING MATERIALS
CARBONATE ROCKS
CEMENTS
CRACKS
DIMENSIONS
ELECTRON MICROSCOPY
FREQUENCY RANGE
GYPSUM
KINETICS
LAYERS
LIMESTONE
MATERIALS
MHZ RANGE
MHZ RANGE 01-100
MICROSCOPY
MICROSTRUCTURE
MINERALS
OXYGEN COMPOUNDS
POROSITY
PORTLAND CEMENT
RAYLEIGH WAVES
ROCKS
SCANNING ELECTRON MICROSCOPY
SEDIMENTARY ROCKS
SIMULATION
SODIUM COMPOUNDS
SODIUM SULFATES
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
SURFACES
THICKNESS