Abstract
This paper investigates the influence of CO2 concentration (ambient and 5%) and duration of exposure on the carbonation, alkali content and pH of alkali activated concrete (AAC) and mortar produced from a ggbs based alkali activated cementitious material (AACM). Depth of carbonation was measured at regular intervals by the standard phenolphthalein indicator test method. The alkali content, mineralogy, and pH of the AAC in its carbonated and non-carbonated zones was determined by XRD, XRF, EDS and pH analysis. The effect of carbonation on physical properties (porosity, shrinkage) and mechanical properties (compressive strength) of alkali activated concrete (AAC) and mortar (AAM) together with their corresponding Portland cement-based specimens (PCC and PCM) was determined.The results show significantly high pH (between 10 and 10.5) at the carbonated zone of AAC and AAM. The high pH at the carbonated zone of AAC and AAM depicts sufficient alkalinity within the zone to prevent reinforcement corrosion due to carbonation. The alkalis Na+, K+, Al3+ and Mg2+ are more abundant in AAC and AAM which boost its alkalinity relative to the control PCC and PCM. The phenolphthalein test is more sensitive for detecting the carbonation of alkalis Ca(OH)2 and C–S–H which are predominant in PCC and PCM.The long-term depth of carbonation is lower in AAC than the control PCC under ambient CO2 exposure, but it is greater under accelerated carbonation (5% CO2) when kinetically unstable reactions occur, and bicarbonate is also formed. Results on the total drying and carbonation shrinkage, carbonation rate, and compressive strength are also reported which show the dominant influence of porosity of AAC and PCC.
Published Version
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