skip to main content

SciTech ConnectSciTech Connect

Title: Identification of the hydrate gel phases present in phosphate-modified calcium aluminate binders

The conversion of hexagonal calcium aluminate hydrates to cubic phases in hydrated calcium aluminate cements (CAC) can involve undesirable porosity changes and loss of strength. Modification of CAC by phosphate addition avoids conversion, by altering the nature of the reaction products, yielding a stable amorphous gel instead of the usual crystalline hydrate products. Here, details of the environments of aluminium and phosphorus in this gel were elucidated using solid-state NMR and complementary techniques. Aluminium is identified in both octahedral and tetrahedral coordination states, and phosphorus is present in hydrous environments with varying, but mostly low, degrees of crosslinking. A {sup 31}P/{sup 27}Al rotational echo adiabatic passage double resonance (REAPDOR) experiment showed the existence of aluminium–phosphorus interactions, confirming the formation of a hydrated calcium aluminophosphate gel as a key component of the binding phase. This resolves previous disagreements in the literature regarding the nature of the disordered products forming in this system.
Authors:
;  [1] ;  [2] ;  [1] ;  [1]
  1. Department of Materials Science and Engineering, The University of Sheffield, Sheffield S1 3JD (United Kingdom)
  2. Solid-State NMR Group, Department of Chemistry, Durham University, Durham DH1 3LE (United Kingdom)
Publication Date:
OSTI Identifier:
22475497
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 70; 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:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; ALUMINIUM 27; BINDERS; CALCIUM PHOSPHATES; CALCIUM SULFATES; CEMENTS; CROSS-LINKING; GELS; HYDRATES; NUCLEAR MAGNETIC RESONANCE; PHOSPHORUS 31; POROSITY; SOLIDS