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Title: Acid attack on hydrated cement — Effect of mineral acids on the degradation process

During acid attack on concrete structural components, a degraded layer develops whose properties as a protective barrier are decisive for durability. {sup 29}Si NMR spectroscopy and {sup 27}Al NMR spectroscopy were used with XRD to investigate the degraded layer on hardened cement paste exposed to HCl and H{sub 2}SO{sub 4}. The layer comprises an amorphous silica gel with framework silicates, geminate and single silanol groups in which Si is substituted by Al. Amorphous Al(OH){sub 3} and Fe(OH){sub 3} are present. The gel forms by polycondensation and cross-linking of C-A-S-H chains at AlO{sub 4} bridging tetrahedra. In the transition zone between the degraded layer and the undamaged material, portlandite dissolves and Ca is removed from the C-A-S-H phases maintaining their polymer structure at first. With HCl, monosulphate in the transition zone is converted into Friedel's salt and ettringite. With H{sub 2}SO{sub 4}, gypsum precipitates near the degradation front reducing the thickness of the transition zone and the rate of degradation.
Authors:
; ;
Publication Date:
OSTI Identifier:
22475516
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 74; 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; ALUMINIUM 27; ALUMINIUM HYDROXIDES; CEMENTS; CONCRETES; CROSS-LINKING; GYPSUM; HARDNESS; HYDROCHLORIC ACID; IRON HYDROXIDES; LAYERS; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; POLYMERS; SALTS; SILICA GEL; SILICATES; SILICON 29; SULFURIC ACID; WEAR RESISTANCE; X-RAY DIFFRACTION