Page 43 - New Trends in Green Construction

SUSTAINABLE GEOPOLYMERS FROM METAKAOLIN AND OLIVE-PINE BOTTOM ASH
D. Eliche-Quesada, P. García Cobo, E. Bonet-Martínez, L. Pérez-Villarejo, E. Castro
Keywords: geopolymers, biomass bottom ash, mechanical properties, thermal properties, sustainability 1. Introduction
The manufacture of Portland cement involves the usage of a large amount of energy resources and the use of fuels which implies an environmental impact (Deja et al., 2010). The search for new alternative or green cements is necessary to limit such emissions. The most promising green cement is alkaline cement, or geopolymeric cement, due to its properties and low environmental impact. As a result, it is considered as the cement of the future. They are obtained by the chemical interaction between strongly alkaline solutions and silicoaluminates of natural origin, as clays, or artificial, as industrial by-products (Duxson et al., 2007).
Olive crop and its associated industry generate a series of wastes or by-products such as olive pruning, olive bone and olive pomace that, given their energy potential, can be used as fuel, generating another residue, ash. Most of the ash generated are deposited in landfill, causing a negative effect on the environment. This work proposes a new potential applicationfor olive-pine bottom ash through its valorization in new geopolymeric cements as a substitute for the metakaolin.
2. Materials and Methods
The raw materials used in this work were metakaolin (MK), obtained by calcining, at 750oC for 4 hours, kaolin from Caobar, whose mines are located in the province of Guadalajara, Spain and olive-pine bottom ash (OPBA) supplied by the plant Aldebarán Energia del Guadalquivir S.L., located in Andújar (Jaen, Spain). For alkaline activation, a mixture of aqueous sodium silicate was used (Panreac S.A.; 8,9 wt % Na2O, 29,2 wt % SiO2 and 61,9 wt % H2O) and NaOH (reactive grade, 98 wt %, Panreac S.A). The NaOH solution (8.0 M) was prepared by dissolving 400-841 m sodium hydroxide beads in distilled water. The liquid/ solid ratio used was 0.85. MK was replaced by different amounts of OPBA (25-100 wt%). Pure MK was used as control. The Si/Al molar ratio varies from 1.6 to 5.3 from pure MK up to 100 wt % OPBA. The samples were cured under controlled conditions (60 oC and 99% relative humidity) for 24 h. The specimens were then demolded and kept at ambient conditions for 7 days of curing. Bulk density was determined by Archimedes method. Tests on compressive strength were performed according to UNE-EN 772-1 (UNE-EN 772-1, 2011) on a MTS 810 Material Testing Systems laboratory press. Thermal conductivity was determined at 10 oC using a FOX 50 Heat Flow Meter to TA Instruments accordance with ISO 8301.
3. Results and Conclusions
The bulk density data of the geopolymers after 7 days of curing indicated that the bulk density of the pure MK, control geopolymers was 1269 kg/m3. The replacement of MK by increasing amounts (25-100 wt%) of olive-pine bottom ash produced an increase in the bulk density of the geopolymers, increasing up to 1324 kg / m3 with the incorporation of 25 wt% of waste up to 1437
43
New Trends in Green Construction