| บทคัดย่อ |
Alkali activated material has been considered as a high potential construction material for replacing or reducing cement usage. However, proper curing at specific temperatures is necessary for optimizing the alkali activated material’s strength and durability performance. In this work, a novel technique for curing alkali activated material is proposed based on the ohmic heating principle by passing electrical current through the just casted alkali activated paste. With this method, the alkali activated paste was rapidly cured right from the start. As a result, it set very quickly (∼15 min) compared to hours for setting for the controlled sample without ohmic heating. Moreover, the compressive strength (22.9 MPa) and flexural strength (0.42 MPa) of the 80 °C ohmic cured samples for 90 min were significantly improved compared to the non-heated sample (compressive strength of 0.68 MPa and unmeasurable for flexural strength). The prolonged mechanical properties (7-day age) were also increased, with the compressive strength (47.0 MPa) nearly double and the flexural strength (1.32 MPa) almost quadruple, compared to the controlled sample. The reasons for the quick setting and enhanced mechanical strengths cannot be related to microstructures from the SEM image analysis. However, the FTIR analysis showed that ohmic heating accelerated early geopolymerization. The Al-O-Si bonding (the absorption band at ∼ 948 cm−1), the backbone of the geopolymeric structure, was found to increase almost linearly with the ohmic heating time (R2 of 0.93). Rapid formation of the geopolymeric structure was thus responsible for the quick setting and the early and prolonged strength enhancement. Furthermore, this ohmic curing technique does not require the addition of conductive fillers, such as carbon fiber, since ionic conduction from the presence of alkali and hydroxide ions is sufficient to induce ohmic heating. Nevertheless, the carbon fiber addition to alkali activated pastes led to strength enhancement. In addition, this technique is not limited to a lab-scale sample but can be extended to cure alkali activated material in large-scale construction. |
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