Journal
CEMENT & CONCRETE COMPOSITES
Volume 32, Issue 8, Pages 563-570Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.cemconcomp.2010.06.002
Keywords
Portland cement; Heavy metals; Compressive strength; Hydration
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The aim of this work is to investigate the effect of the addition of Cu, Cd, Ni, Pb and Zn nitrate salts on the compressive strength of a CEM I Portland cement. Concentrations of 0.018 01 0.18 mol/kg of cement of each trace element were tested. After 2 days age, the compressive strength was reduced by various extents by addition of heavy metals, with the exception of Ni. This difference is due to a delay in tricalcium silicate hydration (C(3)S) as shown by an isothermal calorimetry test. Trace elements also influence the 28-days compressive strength, whereas the measured degree of hydration of these cement pastes is the same. As shown by scanning electron microscopy and X-ray diffraction, Cu and Pb are predominantly absorbed in the calcium silicate hydrate gel (C-S-H) while Cd, Ni and Zn are mainly precipitated as hydroxides within the intergranular porosity. Thus, trace elements precipitated as hydroxides have only a slight effect on the compressive strength. In contrast, Cu and Pb cause an increase in mechanical resistance by changing the C-S-H nanometric assembly and its density. (c) 2010 Elsevier Ltd. All rights reserved.
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