Page 141 - New Trends in Green Construction

ALKALI-ACTIVATED MATERIALS FORMULATED FROM OLIVE GROVE BIOMASS FLY ASH
E. Bonet-Martínez, C. López-Mora, L. Pérez-Villarejo, D. Eliche-Quesada
Keywords: alkali-activate materials, biomass fly ash, olive grove, Circular Economy 1. Introduction
Alkali-activated materials or geopolymers are a new family of materials with low environmental impact which constitute a promising alternative to ordinary Portland cements (OPC). The search for industrially viable alternatives to the high emissions of gases produced by OPC is urgent. An aluminosilicate source is needed for the manufacture of these geopolymers, which can come either from raw materials, such as common clays or kaolin or from by-products or industrial waste, such as those used in this work. Fly ash from a plant that uses potassium-rich olive and pine biomass to generate electricity was used as a raw material to obtain sustainable geopolymers.
Up to the present moment, many researches have employed fly ash to obtain these materials, but the vast majority of them use ash from coal (Rakhimova and Rakhimov, 2019). It is necessary to deepen the investigation of the effect that the usage of olive grove biomass ash has on the formation of the geopolymer. In addition, the use of these ashes with biomass origin can help to reduce even more the environmental impact, by reusing an industrial waste and promoting the Circular Economy.
2. Materials and methods
For the development of these materials, metakaolin (MK) was used, obtained after firing kaolin acquired from the company Caobar (Guadalajara, Spain) at 750oC for 4 hours and olive grove fly ash (OGFA) provided by the company Aldebarán Energía del Guadalquivir S.L. (Andújar, Spain). For alkaline activation, a mixture of aqueous sodium silicate was used (Panreac S.A) and NaOH (reactive grade, 98 wt %, Panreac S.A). A NaOH solution (8.0 M) was prepared by dissolving in distilled water. The liquid/solid ratio utilized was 0.85. MK, replaced by different amounts of OGFA (25-100 wt %). The Si/Al molar ratio varies from 1.6 to 5.3 from pure MK up to 100 wt % OGFA. 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. Prior to the breakage of the ceramic samples, the average surface of the two faces was calculated and the maximum load reached between the average surfaces was divided and expressed with an accuracy of 0.1 MPa. The open porosity was determined by calculating the weight difference between the samples saturated in water and dry, divided by the volume.
3. Results and conclusions
The compression strength results obtained for pure MK geopolymers was 17.54 MPa after 7 curing days. Compared with the geopolymers obtained with different olive grove fly ash substitutions at the same curing ages, for 25% by weight, the mechanical resistance increased by 11.3% to 19.52
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New Trends in Green Construction