MgAl-layered double hydroxide as smart nanofiller for cement-based materials

Reference Presenter Authors
04-022 Marinalva Aparecida Alves-Rosa Alves-Rosa, M.A.(Instituto de Química/UNESP); Almeida, A.A.(Instituto de Química/UNESP); Santos, R.M.(Instituto de Química/UNESP); Pulcinelli, S.H.(Instituto de Química/UNESP); Santilli, C.V.(Instituto de Química/UNESP); Layered double hydroxides (LDH) are described by the general formula [M(1-x)2+ Mx3+ (OH)2]layer [Ax/nn-1 zH2O]interlayer, where M2+ and M3+ are metal cations occupying the octahedral interstices of the layers while An-1 represents anions embedded in the interlayers of the lamellar edifice. They are a family of anionic clays that have received attention because of their important ability of structural regeneration after thermo-decomposition. This so called memory effect involves the reversible recrystallization of LDH from mixed oxides obtained by collapse layered structure during calcination. In this communication we studied the LDH memory effect induced by the contact with cement water. This memory effect has shown advancements in adsorption capacity of different anions, such as chloride ions which damages the durability of concrete. Additionally, the LDH can eliminate the cement pores due to the volumetric expansion of the particles caused by regeneration, filling small pores and improving the mechanical resistance. Here LDH-MgAl nanoparticles with different precursor anions (carbonate and nitrate) were prepared aiming to elucidate and control the kinetics of LHD reconstruction in the cement water and the effect of this smart nanofiller in the final cement characteristics. Surface areas increased after calcination from 93-321 m2/g for LHD prepared with carbonate and from 58-147 m2/g with nitrate. XRD patterns showed the pristine LDH structure disappears after calcination at 500 °C and the LDH reconstruction occurring in cement water. The SAXS in situ measurements of the mixed oxides revealed the reappearance of the diffraction signals of lamellar structure after 40 and 60 min of contact with cement water in the LDH with carbonate and nitrate, respectively. The controlled change of recovery time of the LDH can be an advantage in adjusting of the kinetic cure of concrete and its mechanical properties.
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