The potential for magnesia-based cements to improve the mechanical performance upon carbonation was recently identified. Key parameters were defined as drying, concentration and transport of CO_2 into the sample. However, the trials were performed on small-scale samples of cement paste only. Following this an investigation was then conducted to understand (a) whether the carbonation would occur in pressed masonry units, (b) whether an improvement in the mechanical properties of those units could be expected, and (c) what conditions give rise to the maximum level of carbonation. Hence this paper presents the following: (a) the effect of natural and forced carbonation on the mechanical properties of pressed masonry units containing natural aggregates or Lytag; and (b) the conditions which give rise to the maximum level of carbonation. The results presented indicate that the natural carbonation of magnesia cement-based masonry units was very limited while forced carbonation improved the mechanical performance of the systems substantially. The results also showed that the intermediate saturation level was optimal for the carbonation reaction to readily occur.
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