United States Department of Transportation
i
Correlation of Slag Cement Composition with Durability of Portland Cement–Slag Concrete
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2021-04-01
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[PDF-8.74 MB]
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Edition:Final Report April 30, 2019-April 30, 2021
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Abstract:Three ordinary portland cements (OPC), three limestone cements (IL), and seven ground granulated blast furnace slags (GGBFS/slag) were used to investigate the heat generation, adiabatic temperature rise, sulfate optimization, sulfate durability (external and internal), and chloride durability in slag-blended cementitious systems. The as-received materials were characterized for their physical, chemical, and mineralogical composition using Blaine fineness, particle size distribution, specific gravity, X-ray fluorescence, and X-ray diffraction coupled with Rietveld refinement. The selected cements varied in their tricalcium aluminate, tricalcium silicate, sulfates, alkali, calcite contents, and fineness. Alumina content, magnesia-to-alumina ratio, sulfate levels and fineness were varied in the selected slags. A single slag substitution level of 60% was used throughout this study, as it is the most commonly used replacement level in massive concrete structural elements in the state of Florida. Adiabatic temperature rise of plain and slag blended concrete of a cementitious content of 665 lb/yd3 was measured using Type II(MH) cement, Type IL cement and their blends with slags of variable alumina content for a total of 10 concrete mixtures. Slag blended cementitious systems were optimized for sulfate content based on heat of hydration measurements according to ASTM C563 and adding hemihydrate as a partial replacement of slag. External sulfate durability was assessed using ASTM C1012 at a constant water-to-cementitious materials (w/cm) ratio. Delayed ettringite formation (DEF) was investigated using heat-cured mortar bars. Sulfate-optimized mixtures were also studied for sulfate durability. Chloride binding experiments were conducted on selected plain mixtures as well as slag-blended mixtures. Phase assemblage studies using quantitative X-ray diffraction and thermodynamic modeling were performed on pastes and mortars. The findings indicate the significance of the slag alumina content and magnesia-to-alumina ratio on adiabatic temperature rise. Limestone cement concrete generated lower adiabatic temperature rise than Type II(MH); however, for the slag-blended mixtures, incorporation of the same slag generated similar adiabatic temperature rise when blended with either cements. Sulfate demand of the slag-blended cementitious mixtures was influenced by cement C3A, C4AF and calcite contents, and slag alumina and magnesia contents as well as their particle size. External sulfate durability of the system appeared to be affected by the cement C3A and calcite content, and the slag alumina and the sulfate content. Expansion caused by DEF was suppressed when slag was used at 60% replacement level. Chloride binding was enhanced with increasing slag alumina levels and was negatively affected by the alkalis and limestone content of cement.
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