EFFECT OF CARBONATION CURING ON FIBER-CEMENT PRODUCTS BASED ON MGO-SIO2 SYSTEMS GONZALO MÁRMOL, JULIÁN E.M. BALLESTEROS, JULIANO FIORELLI, HOLMER SAVASTANO JR. University of Sao Paulo, Faculty of Animal Science and Food Engineering, Department of Biosystems Engineering, Duque de Caxias Norte Street, 225, 13630-000 Pirassununga, SP, Brazil ABSTRACT Thin fiber-cement (FC) plates made out of MgO-SiO2 binding systems and reinforced with polypropylene (PP) and cellulosic (pine) pulp, produced by a slurry-dewatering and pressing technique, were mechanically and physically characterized. Samples were cured under two different conditions: steam water curing at 55 o C and high CO2 concentration (20% by volume). To evaluate the mechanical performance of the cementitious based material and the possibility to be reinforced for fiber-cement production, 4 point-bending test was used. Also apparent porosity (AP), bulk density (BD) and water absorption (WA) were assessed. In order to study the effects of carbonation on the materials, and their performance over time, cycles of accelerated ageing were used. The analyzed materials showed excellent flexural strength and toughness, which were maintained after ageing. Carbonation helped to increase flexural strength and physical properties, becoming an attractive method to improve fiber-cement products made with this alternative binder. KEYWORDS: MgO-based cement; carbonation; matrix densening INTRODUCTION Accelerated carbonation has been shown to be capable of improving cementitious matrices for fiber cement (FC) application (Almeida et al., 2013; Pizzol et al., 2014; Purnell et al., 2001; Santos et al., 2015). The main effect of carbonation on hydrated Portland cement paste is the conversion of portlandite [Ca(OH)2] into calcite and vaterite (CaCO3). This reaction increases the density of the matrix, (Frías and Goñi, 2013; Mo et al., 2015; Morandeau et al., 2015; Zha et al., 2015), making it more rigid and stronger. It also strengthens the fiber-matrix interface, but this can modify the fracture mechanism, often leading to a reduction in the deflection during flexural test, despite significant increases in the modulus of rupture (MOR) and modulus of elasticity (MOE) (Almeida et al., 2013; Pizzol et al., 2014; Purnell et al., 2001; Santos et al., 2015). Reactive periclase binders can also harden by carbonation, sequestering CO2 as part of the process of making construction materials (Unluer and Al-Tabbaa, 2015, 2014, 2013; Vandeperre and Al-Tabbaa, 2007). When MgO is carbonated in the presence of water, hydrated magnesium carbonates (HMC) are produced, with general formula xMgCO3.Mg(OH)2.yH2O (Botha and Strydom, 2001; Lanas and Alvarez, 2004). These compounds bind both water and CO2 and thus create a very large additional solid volume, giving them a much greater potential than Portland cement in terms of overall carbonated binder efficiency. The transformation of brucite into HMC, identically to what occurs for Ca(OH)2 when turns into (CaCO3), increases strength of the hydrated pastes. Therefore, the aim of this work was to study the behavior of FC elements made out of blends of MgO-SiO2 reinforced with both polymeric (polypropylene) and lignocellulosic (pine pulps) considering:  The effects of the early-age carbonation on the cement matrix and the fiber-cement composites,  The evolution of mechanical and physical properties after accelerated ageing and  The thermodynamic stability of the possible obtained hydrated magnesium carbonates in the matrix. IIBCC 2018 · CONFERENCE PROCEEDINGS 123 iibcc.biz