Chemical changes and phase analysis of OPC pastes carbonated at different CO2 concentrations

Chemical changes and phase analysis of OPC pastes exposed to accelerated carbonation using different concentrations of CO2 (3%, 10% and 100%) have been undertaken and compared with those of natural carbonation (≅0.03%). 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si M.A.S-N.M.R), Thermogravimetric analyses (TG) and X-Ray Diffraction (XRD) have been used for characterisation. The carbonation of the samples has resulted in a progressive polymerisation of CSH that leads to formation of a Ca-modified silica gel and calcium carbonate. The carbonation of CSH and portlandite occurs simultaneously and the polymerisation of the CSH after carbonation increases with the increase in concentration of CO2. When ≅0.03% and 3% CO2 are used, CSH gel with a lower Ca/Si than that of the uncarbonated sample, and quite similar for both samples remained. When carbonating at 10% and 100% of CO2, the CSH gel completely disappears. For every condition, a polymerised Ca-modified silica gel is formed, as a result of the decalcification of the CSH. From these results it can be deduced that among the different concentrations of CO2 tested, carbonation up to a 3% of CO2, (that is to say, by a factor of 100) results in a microstructure much more similar to those corresponding to natural carbonation at ≅0.03% CO2 than those at the 10% and 100% concentrations.

[1]  Kazusuke Kobayashi,et al.  Carbonation of concrete structures and decomposition of CSH , 1994 .

[2]  M. Cheyrezy,et al.  Concrete carbonation tests in natural and accelerated conditions , 2003 .

[3]  H. Hornain,et al.  Effect of Water-Cement Ratio of Cement Pastes on Microstructural Characteristics Related to Carbonation Process , 2000, SP-192: 2000 Canmet/ACI Conference on Durability of Concrete.

[4]  D. Michel,et al.  High-resolution solid-state NMR of silicates and zeolites , 1987 .

[5]  F. P. Glasser,et al.  Comparative studies of the carbonation of hydrated cements , 1989 .

[6]  G. Verbeck.  Carbonation of Hydrated Portland Cement , 1958 .

[7]  Christopher M. Dobson,et al.  Progressive Changes in the Structure of Hardened C3S Cement Pastes due to Carbonation , 1991 .

[8]  B. Johannesson,et al.  Microstructural changes caused by carbonation of cement mortar , 2001 .

[9]  L. Parrott.  Carbonation, moisture and empty pores , 1992 .

[10]  V. Lach,et al.  Long-term carbonization of the phases 3CaO.Al2O3.6H2O and 3CaO.Al2O3.SiO2.4H2 , 1972 .

[11]  W. Cole,et al.  Carbon Dioxide in Hydrated Portland Cement , 1960 .

[12]  H. Hilsdorf,et al.  Formation of Silica gel During Carbonation of Cementitious Systems Containing Slag Cements , 1989, "SP-114: Fly Ash, Silica Fume, Slag, and Natural Pozzolans in Concrete: Proceedings of the Third International Conference".

[13]  I. Richardson,et al.  The carbonation of hardened cement pastes , 1990 .

[14]  C. Dobson,et al.  29Si MAS NMR study of the hydration of tricalcium silicate in the presence of finely divided silica , 1988 .

[15]  C. Andrade,et al.  Relation between resistivity and corrosion rate of reinforcements in carbonated mortar made with several cement types , 1988 .

[16]  S. E. Pihlajavaara,et al.  Some results of the effect of carbonation on the porosity and pore size distribution of cement paste , 1968 .

[17]  Cruz Alonso,et al.  Efecto que el tipo de cemento y la dosificación del mortero ejercen en la velocidad de corrosión de armaduras embebidas en mortero carbonatado , 1987 .

[18]  Shigeyoshi Nagataki,et al.  Carbonation of Concrete with Fly Ash and Corrosion of Reinforcements in 20 Year Tests , 1989 .

[19]  Tadahiro Nishikawa,et al.  Chemical conversion of CSH in concrete , 1994 .

[20]  S. Pihlajavaara,et al.  Effect of carbonation on microstructural properties of cement stone , 1974 .

[21]  C. Dobson,et al.  Application of Selective 29Si Isotopic Enrichment to Studies of the Structure of Calcium Silicate Hydrate (C‐S‐H) Gels , 1994 .

[22]  X. Cong,et al.  29Si MAS NMR study of the structure of calcium silicate hydrate , 1996 .

[23]  C. Andrade,et al.  Corrosion of Reinforcing Bars in Carbonated Concrete , 1980 .

[24]  A. M. Dunster,et al.  An investigation of the carbonation of cement paste using trimethylsilylation , 1989 .

[25]  Peter A. Claisse,et al.  Permeability and pore volume of carbonated concrete , 1999 .

[26]  L. Parrott,et al.  Carbonation in a 36 year old, in-situ concrete , 1989 .

[27]  C. Dobson,et al.  The carbonation of OPC and OPC/silica fume hardened cement pastes in air under conditions of fixed humidity , 1993 .

[28]  R. L. Berger.  Stabilization of silicate structures by carbonation , 1979 .

[29]  E. Reardon,et al.  High pressure carbonation of cementitious grout , 1989 .

[30]  R. Rassem,et al.  29Si high-resolution NMR study of tricalcium silicate hydration , 1989 .

[31]  Y. F. Houst,et al.  Depth Profiles of Carbonates Formed During Natural Carbonation , 2002 .

[32]  D. Cocke,et al.  An FTIR and XPS investigations of the effects of carbonation on the solidification/stabilization of cement based systems-Portland type V with zinc , 1993 .

[33]  É. Lippmaa,et al.  Solid-state high-resolution silicon-29 chemical shifts in silicates , 1984 .

[34]  C. Page,et al.  Effects of carbonation on pore structure and diffusional properties of hydrated cement pastes , 1997 .

[35]  A. Benesi,et al.  Silicon‐29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates , 1989 .