Abstract
This study involves the use of engineered synthetic aluminosilicates (ESA) in cement matrix to create a more controlled environment for carbonation and subsequent hydration. The ESAs were nano-engineered using sol-gel technology. This is the first-time engineered additives are added to control the reaction mechanism during early-age CO2 curing. Early age CO2 curing of Portland cement paste has proven to improve mechanical performance and durability. However, the later age performance is reduced due to the decalcification of hydration products. Furthermore, the reaction mechanisms during early-age CO2 curing are dependent on the curing environment. The principal focus was to control the carbonation reaction mechanism and enhance the later-age mechanical performance of the cement-based system independent of the curing environment.Two main ESA were developed in this research using organosilanes, tetraethoxysilane (TEOS) and functionalised organosilane, 3- minopropyltriethoxysilane (APTES). The two ESA behaved slightly differently, confirming the possibilities of altering the carbonation and hydration reaction mechanism. It was found that on 24 hours of CO2 curing, TEOS-based ESA cement samples (T-95-1%) improved the mechanical performance by 32% when compared to the control. On examining the evolution of hydration and carbonation products over a period of 28 days for T-95-1% and iterating it with the mechanical performance, it was realised that carbonation and subsequent hydration were enhanced by nucleation and seeding effect of the nano-carbonates formed on carbonation which when combined with pozzolanic reactions during hydration improved the mechanical performance. APTES-based cement samples, (AN1-95-1%) enhanced carbonation and subsequent hydration by creating a homogenously dispersed solution that prevents the formation of a barrier layer over the reactive surface hence there was a continuous reaction of either carbonation or hydration. Furthermore, the carbonates and hydrates formed were uniformly distributed throughout the depth of the mortar samples in the case of AN1-95-1% independent of the curing environment.
The surface carbonates (up to 5mm depth of the mortar samples) on 24 hours of CO2 curing were the highest for 28 days aged T-95-1% when compared to control samples. In the case of control samples, the decrease in carbonate content was proportional to the increase of portlandite with the increased depth of the mortar samples. This confirmed that carbonate content was formed due to the decalcification of hydration products. This was not the case of T-95-1%, the rate of decrease of carbonates was not proportional to the increase of portlandite. Hence, comparing the results of mortar samples with and without ESA, it was identified that the samples containing ESA prevented decalcification of hydration products and hence enhanced the mechanical performance.
This research hence sheds light on the possibilities to control the carbonation reaction in cement mortar samples by validating the controllability through investigation of the distribution of carbonation and hydration products across the depth of cement-based samples. The possibilities of an increase in carbon uptake (twice the amount when compared to control) without affecting the mechanical performance at a later age were shown.
Date of Award | 23 Feb 2023 |
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Original language | English |
Awarding Institution |
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Supervisor | Juliana Calabria-Holley (Supervisor) & Kevin Paine (Supervisor) |
Keywords
- Sol-Gel
- CO2 utilisation
- Engineered Synthetic Aluminosilicate
- Decalcification
- Carbonation
- Nucleation