Strength and transport properties of metakaolin based alkali-activated mortar
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Date
2019-06
Authors
Lee Choon Wei
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Abstract
The feasibility and advantages of utilizing metakaolin (MK) as source material for
alkaline activated mortar (AAM) based on the strength and transport properties of the
resulting AAM have been evaluated. Varying silica modulus (SiO2/Na2O), Ms = 2.0, 2.2
and 3.3 was incorporated to prepare the alkaline activator with a combination of 10M
sodium hydroxide solution (NaOH) and sodium silicate solution (Na2SiO3). The
metakaolin used in this research was produced via calcination at 750˚C for 1 hour in an
electrical furnace. The mix proportions of the AAM was adopted from previous work
which was suited to the MK-based AAM based on series of trial mixes, with aggregate
to-binder ratio of 1.50, solid-to-liquid ratio of 0.80 and sodium silicate-to-sodium
hydroxide ratio of 2.50. A curing temperature of 75˚C for 24 hours was used based on
the previous research. This study showed that Ms had a significant effect on the mortar
strength. The mortar utilizing sodium silicate solution with Ms = 2.0 exhibits the highest
compressive strength from 3 to 28 days, where 28-day strength exceeding 68.1 MPa was
achieved. The compressive strength of the MK-based AAM decreases as the silica
modulus increases. The transport properties of the MK-based AAM was evaluated on the
mixture with Ms = 2.0 via porosity, initial surface absorption, rapid chloride
permeability, gas permeability and water permeability tests. The recorded values of
porosity, initial surface absorption, rapid chloride permeability, gas permeability and
water permeability at 28 days were 7.71%, 0.0055 ml/m2/s, 640 coulombs, 1.30 ×10-18
m2 and 1.55 ×10-11 m/s, respectively. Therefore, the strength and the transport properties
of the MK-based AAM are comparable with those of high strength Portland cement
concrete. Hence, the MK-based AAM has great potential in term of strength and transport
properties to ensure superior durability performance of concrete structure.