View source for OR/14/048 Results of fluid chemical analyses

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The full set of analytical data for the experiments is given in [[OR/14/048 Appendix 1 | Appendix&nbsp;1]]. The following sub-sections describe some of the more important changes that were observed in the chemistry between pre- and post-reacted solutions, and between ‘reactive’ (i.e. pressurised by CO<sub>2</sub>) and ‘non-reactive’ (i.e. pressurised by N<sub>2</sub>) experiments. Most reactivity was relatively early in the experiments, and so just the 40 day data are shown on the following figures.

In terms of a broad summary, the changes observed are consistent with our understanding of chemical reactions during CO<sub>2</sub>-cement reaction, and the data obtained for reaction of the NRVB matches data from other studies studying different cement formulations.

==Changes in pH==
The observed trends in pH (Figure&nbsp;7) over the course of the experiments were as follows:

:-&nbsp;&nbsp;The two starting solutions had very similar pH values.<br>
:-&nbsp;&nbsp;Solutions from the N<sub>2</sub>-pressurised experiments showed a very slight increase in pH at the end of the experiments.<br>
:-&nbsp;&nbsp;Solutions from the CO<sub>2</sub>-pressurised experiments however, showed a very marked decrease in pH to values of approximately 6.5–7.

[[Image:14048fig7.jpg|thumb|center|500px|  '''Figure 7'''        Changes in pH during the 40 day experiments (as measured at room temperature and pressure). Upper graph&nbsp;—&nbsp;nitrogen experiments, lower graph&nbsp;—&nbsp;CO<sub>2</sub> experiments.    ]]

Though the composition of the ‘young’ pore fluid with additional chloride was prepared based  on previous work (Francis ''et al.'', 1997<ref name="Francis 1997">FRANCIS, A J, CATHER, R, and CROSSLAND, I G. 1997. Development of the Nirex reference vault backfill; report on current status in 1994. Nirex Science Report S/97/014, United Kingdon Nirex Limited, 57p.</ref>), it ended up having a lower pH value (12.06) than an anticipated value in excess of pH&nbsp;13. The reasons for this are not clear, though in terms of representing the repository environment however, a slightly reduced pH is still relevant. As groundwater percolates through, and interacts with, the repository cement, the cement porewater composition will vary over time, and the pH will fall. Thus this porewater composition represents porewater compositions intermediate between ‘very young’ porewaters and ‘evolved’ porewaters.

The slight increase in pH in the N<sub>2</sub>-pressurised experiments appears to represent (at least partial) equilibration of the solution with Ca(OH)<sub>2</sub> and CSH phases in the sample of cement. Given the differences in solubility of these phases between lab pressure and temperature (P&T) and the P&T of the tests, then the observed slight variation in final pH is to be expected.

The large reduction in pH values in the CO<sub>2</sub>-pressurised experiments reflects equilibration of the solution with the fixed pressure of CO<sub>2</sub> in the autoclaves. This observation mirrors those from previous studies where CO<sub>2</sub> was reacted with samples of cement used to seal the gaps between steel borehole linings and the surrounding rocks (Rochelle ''et al.'', 2004<ref name="Rochelle 2004">ROCHELLE, C A, PEARCE, J M, BATEMAN, K, BIRCHALL, D J, CHARLTON, B D, REEDER, S, SHAW, R A, TAYLOR, H, and TURNER, G. 2004. Geochemical interactions between supercritical CO<sub>2</sub> and borehole cements used at the Weyburn oilfield.  ''British Geological Survey Commissioned Report'', CR/04/009, 22 p.</ref>, 2006<ref name="Rochelle 2006">ROCHELLE, C A, BATEMAN, K, MILODOWSKI, A E, KEMP, S J, and BIRCHALL, D. 2006. Geochemical interactions between CO<sub>2</sub> and seals above the Utsira Formation: An experimental study. ''British Geological Survey Commissioned Report'', CR/06/069. 86 pp.</ref>, 2007<ref name="Rochelle 2007">ROCHELLE, C A, MILODOWSKI, A E, SHI, J-Q, MUNOZ-MENDEZ, G, JACQUEMET, N, and LECOLIER, E. 2007. A review of the potential impact of CO<sub>2</sub> on the integrity of well infrastructure for underground CO2 storage. ''British Geological Survey Commissioned Report'', CR/07/204, 83p.</ref>). As the (acidic) CO<sub>2</sub> was present in excess, then it would have provided the dominant control of pH. Initially there would have been extensive reaction between the alkaline solution and the initial CO<sub>2</sub> that dissolved into it. This can be represented by a series of reactions; first CO<sub>2</sub> dissolution, then reaction of CO<sub>2</sub> with water, and finally neutralisation of hydroxyl ions:

::::CO<sub>2(g)</sub>&nbsp;&nbsp;+&nbsp;&nbsp;⇔&nbsp;&nbsp;+&nbsp;&nbsp;CO<sub>2(aq)</sub>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[3]<br>
::::CO<sub>2(aq)</sub>&nbsp;&nbsp;+&nbsp;&nbsp;H<sub>2</sub>O&nbsp;&nbsp;⇔&nbsp;&nbsp;HCO<sub>3</sub><sup>-</sup>&nbsp;&nbsp;+&nbsp;&nbsp;H<sup>+</sup>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[4]<br>
::::OH<sup>-</sup>&nbsp;&nbsp;+&nbsp;&nbsp;H<sup>+</sup>&nbsp;&nbsp;⇔&nbsp;&nbsp;H<sub>2</sub>O&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[5]                                                                                   
Subsequently the rate of this reaction would have been dictated by the rate of production of OH<sup>-</sup> (or H<sup>+</sup> consumption) by the sample of cement. A consequence of these reactions is an increase in concentration of dissolved bicarbonate (see below). The actual final ''in-situ ''pH values within the experiments would have been lower than those measured in the laboratory. This is because the solutions degassed CO<sub>2</sub> as they were depressurised, increasing solution pH in the process.

==Changes in bicarbonate concentrations==
The observed trends in bicarbonate (Figure&nbsp;8) over the course of the experiments reflect the pH conditions. Initially no bicarbonate was added to the starting solutions. In the N<sub>2</sub> experiments where pH values were high, the stable dissolved carbon phase is carbonate rather than bicarbonate. However, concentrations of this would also have been low as; a)&nbsp;additional CO<sub>2</sub>  was not added to these experiments, b)&nbsp;high pH conditions and presence of Ca favour precipitation of all inorganic carbon as CaCO<sub>3</sub> minerals.

[[Image:14048fig8.jpg|thumb|center|500px|  '''Figure 8'''         Changes in HCO<sub>3</sub><sup>-</sup> concentrations during the 40 day experiments.    ]]

The presence of excess CO<sub>2</sub> caused pH values to decrease and reaction with hydroxyl ions. This caused the formation of significant amounts of bicarbonate ions, especially in the highest pH YNFP. The lower pH in these experiments would have meant that virtually all the dissolved inorganic carbon was bicarbonate. The high concentrations of bicarbonate would have facilitated saturation with carbonate minerals even for solutions of relatively low pH, provided that sufficient Ca was available in solution (see below).

==Changes in calcium concentrations==
The observed trends in Ca concentrations (Figure&nbsp;9) over the course of the experiments were as follows:

:-&nbsp;&nbsp;Solutions from the N<sub>2</sub>-pressurised experiments showed some variability. In broad terms however, they exhibited an increase in Ca concentrations for the
:&nbsp;&nbsp;&nbsp;‘young’ pore fluid, and approximately unchanged concentrations for the ‘evolved’ pore fluid.<br>
:-&nbsp;&nbsp;Solutions from the CO<sub>2</sub>-pressurised experiments also showed some variability. In broad terms they also exhibited an increase in Ca concentrations for the
:&nbsp;&nbsp;&nbsp;‘young’ pore fluid, and either unchanged or increased concentrations for the ‘evolved’ pore fluid.

[[Image:14048fig9.jpg|thumb|center|500px|  '''Figure 9'''         Changes in Ca concentrations during the 40 day experiments. Upper graph&nbsp;—&nbsp;nitrogen experiments, lower graph&nbsp;—&nbsp;CO<sub>2</sub> experiments.    ]]

It is not straightforward to explain all the trends in Ca concentrations in the N<sub>2</sub>-pressurised experiments. For the ‘young’ pore fluid, data from the 20°C experiment and starting fluid show broad similarities, but these values are much lower than for the two experiments at 40°C. This suggests that the phase controlling Ca concentrations (presumably either calcite, portlandite [Ca(OH)<sub>2</sub>] or a CSH phase) has a different solubility at these two temperatures, and may have undergone some dissolution to release Ca (see comments in the SiO<sub>2</sub> section below). The concentrations for the ‘evolved’ pore fluids show less variability and are around 2000&nbsp;mg/l. However, the concentrations seem to be slightly lower in the 40°C experiments compared to the starting fluid and the 20°C experiment.

The trends in Ca concentrations in the CO<sub>2</sub>-pressurised experiments show certain similarities to data from the N<sub>2</sub>-pressurised experiments. However, the increases in the ‘young’ pore fluid experiments are much larger than in the N<sub>2</sub>-pressurised experiments. Given the lower pH in these experiments, then portlandite and CSH phases would not be stable, and so the phase buffering Ca concentrations seems likely to have been calcite. The higher Ca concentration in the 20°C experiment compared to the 40°C experiments may reflect the higher solubility of CO<sub>2</sub> at lower temperatures (leading to slightly more acidic conditions, and a higher solubility of calcite). However, this is a somewhat tentative conclusion as CO<sub>2</sub> solubility also increases with pressure, and it is less easy to judge at this stage how much influence increasing the pressure would have&nbsp;—&nbsp;though data from the 40°C experiments suggests that this is smaller than for temperature). The Ca concentrations for the ‘evolved’ pore fluids are approximately double those of the ‘young’ pore fluids. Though the data are somewhat scattered, they also seem to show a slightly higher value at 20°C compared to 40°C. If the Ca concentrations were also buffered by calcite as per the ‘young’ pore fluid experiments, then it is not clear why one set of values are approximately twice those of the other.

==Changes in magnesium concentrations==
The observed trends in Mg concentrations (Figure&nbsp;10) over the course of the experiments were as follows:

:-&nbsp;&nbsp;Solutions from the N<sub>2</sub>-pressurised experiments showed no detectable dissolved Mg.
:-&nbsp;&nbsp;Solutions from the CO<sub>2</sub>-pressurised experiments however, showed a very marked increase in Mg concentrations (50–100&nbsp;mg/l) compared to the starting
:&nbsp;&nbsp;&nbsp;solutions.

No useful Mg data were obtained from the N<sub>2</sub>-pressurised experiments because the concentrations were below the detection limits. This is consistent with previous studies that show that highly alkaline conditions stabilise brucite [Mg(OH)<sub>2</sub>], the low solubility of which is very effective in removing Mg from solution.

[[Image:14048fig10.jpg|thumb|center|500px|  '''Figure 10'''         Changes in Mg concentrations during the 40 day CO<sub>2</sub> experiments.    ]]

The CO<sub>2</sub>-pressurised experiments show a very different situation, with increases in Mg concentrations in all the experiments. This is due to leaching of Mg from the cement driven by the low pH caused by the presence of CO<sub>2</sub>. The phase in the cement that is dissolving is probably brucite, which is anly stable under alkaline conditions. That Mg concentrations after 40 days reaction vary by about an order of magnitude between the experiments, may reflect variable degrees of leaching of the cement samples. As per the Ca data (see the previous section), a possible (though tentative) explanation could be that the experiments were not yet at equilibrium, and that complete leaching of Mg from the cement cores would require timescales in excess of 40 days to be completed. Data from 12 month long experiments (to be described in a subsequent report) may help clarify this issue.

==Changes in silica concentrations==
The observed trends in SiO<sub>2</sub> concentrations (Figure&nbsp;11) over the course of the experiments were as follows:

:-&nbsp;&nbsp;The only N<sub>2</sub>-pressurised experiment that showed any dissolved SiO<sub>2</sub>  was the 20°C ‘young’ pore fluid experiment.
:-&nbsp;&nbsp;All solutions from the CO<sub>2</sub>-pressurised experiments however, showed significant amounts of dissolved SiO<sub>2</sub>.

In the N<sub>2</sub>-pressurised experiments the general lack of dissolved SiO<sub>2</sub> can be explained by equilibrium with respect to CSH phases. The high pH conditions within these experiments maintain the stability of CSH phases within the cement. These phases moderate both SiO<sub>2</sub> and Ca concentrations, such that significant concentrations of either are mutually exclusive. Thus elevated SiO<sub>2</sub> concentrations can only happen when Ca concentrations are relatively low, and vice versa. This exclusivity has been noted in previous work (Savage ''et al.'', 1992<ref name="Savage 1992">SAVAGE, D, BATEMAN, K, HILL, P, HUGHES, C, MILODOWSKI, A, PEARCE, J, RAE, E, and ROCHELLE,    C.  1992.  Rate  and mechanism of the reaction of silicates with cement pore fluids. ''Applied Clay Science'', 7, p 33–45.</ref>). It would be expected that if the 20°C ‘young’ pore fluid experiment had run for longer and Ca concentrations started to increase, then there would have been a related decrease in SiO<sub>2</sub> concentrations.

[[Image:14048fig11.jpg|thumb|center|500px|  '''Figure 11'''         Changes in SiO<sub>2</sub> concentrations during the 40 day experiments. Upper graph&nbsp;—&nbsp;nitrogen experiments, lower graph&nbsp;—&nbsp;CO<sub>2</sub> experiments.      ]]

The CO<sub>2</sub>-pressurised experiments show a very different situation, with the dissolved SiO<sub>2</sub> concentrations in the 80–100&nbsp;mg/l range. The lower pH in these experiments would destabilise CSH phases, releasing both SiO<sub>2</sub> and Ca to solution. The broad consistency in dissolved SiO<sub>2</sub> concentrations suggests equilibrium with a common secondary Si phase, which in this case is likely to be silica gel formed through the breakdown of CSH:

::::Ca<sub>5</sub>Si<sub>6</sub>O<sub>16</sub>(OH)2.9.5H<sub>2</sub>O&nbsp;&nbsp;+&nbsp;&nbsp;5 CO<sub>2</sub>&nbsp;&nbsp;⇒&nbsp;&nbsp;5 CaCO<sub>3</sub>&nbsp;&nbsp;+&nbsp;&nbsp;6 SiO<sub>2</sub>&nbsp;&nbsp;+ &nbsp;&nbsp;10.5 H<sub>2</sub>O&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[6]
::::CSH (e.g. tobermorite)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;calcite&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; silica

Only the ‘evolved’ pore fluid experiments contained appreciable dissolved SO<sub>4</sub><sup>2-</sup>, and the observed trends in SO<sub>4</sub><sup>2-</sup> concentrations (Figure&nbsp;12) over the course of the experiments were as follows:

:-&nbsp;&nbsp;All the N<sub>2</sub>-pressurised experiments showed large decreases in concentrations, and this was particularly marked in the 20°C experiment.
:-&nbsp;&nbsp;A similar pattern of decreases was found in the CO<sub>2</sub>-pressurised experiments, however the decreases in concentration were not as great as for the
:&nbsp;&nbsp;&nbsp;N<sub>2</sub>-pressurised experiments.

The concentration decreases in the N<sub>2</sub>-pressurised ‘evolved’ pore fluid experiments suggests that a secondary phase containing SO<sub>4</sub><sup>2-</sup> was being formed. Fluid chemical data alone cannot  uniquely identify this phase, but possibilities could include an ettrignite group phase (due to the high pH) or gypsum (due to the high Ca concentrations). That about 15–20% more of the phase appears to have formed at 20°C compared to 40°C is suggestive that its solubility has a fairly strong dependence on temperature.

[[Image:14048fig12.jpg|thumb|center|500px|  '''Figure 12'''          Changes in SO<sub>4</sub><sup>2-</sup> concentrations during the experiments.          ]]

The concentration decreases in the CO<sub>2</sub>-pressurised ‘evolved’ pore fluid experiments again suggest that a secondary phase containing SO<sub>4</sub><sup>2-</sup> was being formed, and a similar dependence on temperature was observed. The generally higher concentrations however, indicate that less of this phase formed compared to the N<sub>2</sub>-pressurised experiments (about 60% of that in the N<sub>2</sub>-pressurised experiments). The presence of CO<sub>2</sub> in these experiments would have made the pore water slightly acidic, and if the same phase was controlling SO<sub>4</sub><sup>2-</sup> concentrations as in the N<sub>2</sub>-pressurised experiments, then its solubility has a dependence on acidity as well as temperature. However, the slightly acidic pore fluid would have made phases such as ettringite unstable. This suggests that either: a phase such as gypsum was controlling SO<sub>4</sub><sup>2-</sup> concentrations, or that ettringite had formed but it was partly protected inside the remaining unreacted parts of the cement block. If the latter were the case, then further reaction of the cement would be expected to release the SO<sub>4</sub><sup>2-</sup> to solution.

Fluid chemical data alone cannot uniquely identify this phase, but possibilities could include an ettrignite group phase (due to the high pH) or gypsum (due to the high Ca concentrations). That more of the phase appears to have formed at 20°C compared to 40°C is suggestive that its solubility has a fairly strong dependence on temperature.

==Changes in chloride concentrations==
The observed trends in Cl<sup>-</sup> concentrations (Figure&nbsp;13) over the course of the experiments bear many similarities to the SO<sub>4</sub><sup>2-</sup> concentrations, and were as follows:

:-&nbsp;&nbsp;All N<sub>2</sub>-pressurised experiments showed decreases in Cl<sup>-</sup> concentrations relative to the starting solutions, but the decreases in the 20°C experiments were
:&nbsp;&nbsp;&nbsp;far larger than in the 40°C experiments.
:-&nbsp;&nbsp;All the CO<sub>2</sub>-pressurised experiments also showed decreases in Cl<sup>-</sup> concentrations relative to the starting solutions, and the decreases in the 20°C
:&nbsp;&nbsp;&nbsp;experiments were again far larger than in the 40°C experiments. Concentration decreases in these experiments were slightly larger compared to the
:&nbsp;&nbsp;&nbsp;N<sub>2</sub>-pressurised experiments.

Although Cl<sup>-</sup> is considered conservative in many studies, this is not the case when dealing with highly alkaline cementitious solutions, as several Cl<sup>-</sup> containing phases are stable at high pH. The high pH values in the N<sub>2</sub>-pressurised experiments are consistent with the stability of Cl<sup>-</sup> containing phases such as hydrocalumite and Friedel’s Salt, and the reduction in dissolved Cl<sup>-</sup> concentrations suggests that this type of phase formed during the experiments. The large decreases in the 20°C ‘evolved’ pore fluid experiment (approximately 13&nbsp;g/l) suggests that a significant amount of secondary phase formed. The smaller decreases in the 40°C experiments suggests that the solubility (or stability) of this phase has a strong dependence on temperature.

The CO<sub>2</sub>-pressurised experiments show a very similar situation, but with slightly larger  decreases in Cl<sup>-</sup> concentrations. At first sight such decreases would seem at odds with the low pH in these experiments, but they are consistent with other experimental studies (Rochelle ''et al.'', 2006<ref name="Rochelle 2006"></ref>, 2009<ref name="Rochelle 2009">ROCHELLE, C A, MILODOWSKI, A E, LACINSKA, A, RICHARDSON, C, SHAW, R, TAYLOR, H, WAGNER, D, BATEMAN, K, LÉCOLIER, E, FERRER, N, LAMY, F, JACQUEMET, N, SHI, JI-Q, DURUCAN, S, and SYED, A S. 2009. JRAP-14: Reactions between CO<sub>2</sub> and borehole infrastructure, report on laboratory experiments and modelling. CO<sub>2</sub>GeoNet project report for the European Commission, deliverable JRAP-14/3, 138p.</ref>). The previous work found significant formation of a Cl-rich phase inside partially-reacted blocks of cement, which was concentrated particularly on the internal side of a major reaction front, and where high pH conditions would have existed. This could explain why minerals stable under alkaline conditions could exist (albeit for a limited time) within a block of cement submerged within slightly acidic water. If this were the case, then further reaction of CO<sub>2</sub> with  the  cement  would  be  expected  to  consume  the  remaining  Ca(OH)<sub>2</sub> and  CSH  phases, reducing pH within the (reacted) cement block, destabilising the Cl-rich phase, and releasing Cl<sup>-</sup> back to solution. That the CO<sub>2</sub>-pressurised experiments apparently favour the formation of a Cl<sup>-</sup> containing phase may suggest that the phase may also be part of a solid-solution series, one end-member of which may contain carbonate. Also, the similar pattern of SO<sub>4</sub><sup>2-</sup> concentrations in the ‘evolved’ pore fluid experiments may be an indication that the phase also has a sulphate end-member (see the mineralogical information in the following sections).

[[Image:14048fig13.jpg|thumb|center|500px|  '''Figure 13'''          Chloride behaviour in 40 day static batch experiments. Note decreases relative to the starting solutions, especially at 20°C. Note also that concentrations in the YFNP experiments are too low to be visible on these plots. Upper graph&nbsp;—&nbsp;nitrogen experiments, lower graph&nbsp;—&nbsp;CO<sub>2</sub> experiments.      ]]

==References==
<References/>     
[[Category: OR/14/048 Results of laboratory carbonation experiments on Nirex Reference Vault Backfill cement | 09]]