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Pozzolanic activity of metakaolins by the French standard of the modified Chapelle test: A direct methology

Publication . Ferraz, Eduardo; Andrejkovicová, Slávka; Hajjaji, Walid; Velosa, Ana Luísa; Silva, António Santos; Rocha, Fernando

This research was focused on the use of the modified Chapelle test as a direct laboratory methodology to access the pozzolanic activity of both experimental and commercial metakaolins. At the same time, this test was used in the evaluation of experimental metakaolins. This chemical test, performed during 16 hours at 90 °C, allows the quantification of portlandite fixed by the metakaolin sample. The calcium hydroxide that was not consumed is quantified by acid titration (HCl), and the test result is expressed in mg of fixed calcium hydroxide by g of metakaolin. According to this test, the pozzolanic activity of a metakaolin should not be less than 700 mg Ca(OH)2 / g metakaolin. The modified Chapelle pozzolanic activity of six commercial metakaolins was evaluated between 920 and 1560 mg Ca(OH)2 / g metakaolin. From the seven experimental metakaolins produced between 750 ºC and 940 ºC, a material with modified Chapelle pozzolanic activity value of 1240 mg Ca(OH)2 / g metakaolin was obtained, which is similar to some tested commercial metakaolins produced at industrial scale. The metakaolin produced at 800 ºC was ground, resulting in a particle size reduction of ≈ 4x less and a consequent increase of 21% in the pozzolanic activity.

2015Journal article

Open access

Synthetic zeolite pellets incorporated to air lime metakaolin mortars: Mechanical properties

Publication . Ferraz, Eduardo; Andrejkovicová, Slávka; Velosa, Ana Luísa; Silva, António Santos; Rocha, Fernando

In this study synthetic fine and coarse zeolite pellets were chosen in the development of air lime–metakaolin mortars for repairing ancient masonry to be used in conservation and restoration of cultural heritage. Synthetic zeolite was used due to their particular water adsorption properties and act as an artificial pozzolan promoting the development of hydraulic phases. Physical, chemical, mineralogical and microstructural tests were accomplished to characterize the materials used in mortars’ preparation. Flexural, compressive strength and dynamic modulus of elasticity tests were performed in mortars at 28, 90 and 180 days of curing. Incorporation of both fine and coarse zeolite pellets caused improvement of mechanical strength of mortars. The highest flexural strength value (∼0.5 MPa) was achieved in both mortars with fine zeolites pellets at 90 days and 20 and 30 wt.% metakaolin, and coarse zeolite pellets at 180 days and 30 wt.% metakaolin as lime replacement. 1.0 MPa was the highest compressive strength value obtained at 180 days for mortars with both fine zeolite pellets and coarse zeolite pellets, with 20 and 30 wt.% of metakaolin, respectively. Elasticity modulus ranged from 2.3 GPa to 3.9 GPa confirming the high deformation capability of these mortars. Zeolite pellets type A is a promise synthetic material that could be successfully used in air lime–metakaolin render mortars for applications in the conservation and restoration of cultural heritage.

2014-10-30Journal article

Restricted access

Influence of curing conditions on lime and lime-metakaolin mortars

Publication . Faria, Paulina; Martins, Ana Isabel G.

Air-lime mortars with or without pozzolanic components were largely used in historic buildings. Due to natural or accidental degradation it is often necessary the application of repair mortars, durable and compatible with the masonries of historic buildings. Within this context and associating the improvement of mortars characteristics to the necessity of sustainable construction practices, some mortars formulated with lime and the addition of pozzolans have been studied. In previous papers, the influence of some types of air-lime (powder hydrated lime or lime putty) and the addition of metakaolin in lime mortars have been presented. Each type of mortar presents its specificities. In pure lime mortars the setting occurs by carbonation and in lime-metakaolin mortars it occurs both by carbonation and hydration. A crucial question in order to optimize the characteristics of the mortars (and its applicability) is related with the curing conditions. This article describes an experimental campaign with different pure air lime mortars and lime-metakaolin mortars, cured under different conditions of relative humidity and CO2 content. Properties of the mortars, mainly in terms of mechanical behaviour and open porosity, capillary water absorption and drying capacity, are obtained, compared and discussed. The benefits in some properties revealed by the different mortars are correlated with the laboratorial curing conditions and with in situ applications possibilities.

2011-04Conference object

Open access