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Title: X-AFm stabilization as a mechanism of bypassing conversion phenomena in calcium aluminate cements

Phase conversion phenomena are often observed in calcium aluminate cements (CACs), when the water-rich hydrates (e.g., CAH{sub 10}, C{sub 2}AH{sub 8}) formed at early ages, at temperatures ≤ 30 °C, expel water in time to form more compact, less water-rich structures (C{sub 3}AH{sub 6}). The phase conversions follow a path regulated by the thermodynamic stabilities (solubilities) of phases. Based on this premise, it is proposed that conversion phenomena in CACs can be bypassed by provoking the precipitation of phases more preferred than those typically encountered along the conversion pathway. Therefore, X-AFm formation (where in this case, X = NO{sub 3}{sup −}) triggered by the sequential addition of calcium nitrate (Ca(NO{sub 3}){sub 2} = CN) additives is identified as a new means of bypassing conversion. A multi-method approach comprising X-ray diffraction (XRD), thermal analytics, and evaluations of the compressive strength is applied to correlate phase balances and properties of CAC systems cured at 25 °C and 45 °C. The results highlight the absence of the C{sub 3}AH{sub 6} phase across all systems and the curing conditions considered, with enhanced strengths being noted, when sufficient quantities of CN are added. The experimental outcomes are supported by insights gained from thermodynamic calculations whichmore » highlight thermodynamic selectivity as a means of regulating and controlling the evolutions of solid phase balances using inorganic salts in CACs, and more generally in cementing material systems.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [1] ;  [4]
  1. Laboratory for the Chemistry of Construction Materials LC"2, Department of Civil and Environmental Engineering, University of California, Los Angeles, CA (United States)
  2. (United States)
  3. Department of Materials Science and Engineering, University of California, Los Angeles, CA (United States)
  4. (CNSI), University of California, Los Angeles, CA (United States)
Publication Date:
OSTI Identifier:
22475507
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 72; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINATES; ATOMIC FORCE MICROSCOPY; CALCIUM; CALCIUM NITRATES; CARBON NITRIDES; CEMENTS; COMPRESSION STRENGTH; HYDRATES; HYDRATION; PRECIPITATION; SALTS; SOLIDS; STABILIZATION; X-RAY DIFFRACTION