Efecto de la incorporación de diferentes arcillas del sur de España en el desarrollo de sistemas cementantes de cenizas de biomasa de pinar y olivar-metacaolín activados alcalinamente

Resumen

The global warming is caused by the emission of greenhouse gases and is one of the great problems of the society. The manufacture of Portland cement involves the use of a large amount of energy resources and the use of fuels, which implies an environmental impact that affects different areas: the exploitation of quarries, the emission to the atmosphere of particles and high amounts of CO2. 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, being considered 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. The development of this material is environmentally sustainable, using as raw material byproducts and industrial wastes, it require less energy consumption than Portland cement and significantly reduces CO2 emissions. In this research, the effect of the incorporation as a source of aluminosilicates of different calcined clays of Bailén (Jaén, Spain) has been studied, in alkaline-activated cementing systems that use as base materials metakaolin (MK) and the residue, pine-olive pruning bottom ash (CFB). As an alkaline activator, a solution of sodium hydroxide (NaOH) in an 8 M concentration and sodium silicate solution (Na2SiO3) have been used. In addition to the geopolymers containing 33.33 wt % of MK, 33.33 wt % of CFB and 33.33 wt % of different clays, the control geopolymer containing MK and 33.33 wt % of CFB, and only MK as precursor has been prepared. The Si / Al molar ratios of alkaline-activated materials vary from 1.6 to 2.7 depending on the precursors used. The geopolymers were cured in a climatic chamber at 60 ° C in a saturated atmosphere of water for 24 hours. Subsequently, they were demoulded and cured at room temperature for 28 days. After the curing period, the geopolymers have been characterized using Fourier transform infrared spectroscopy and X-ray diffraction. Physical properties, such as bulk density, apparent porosity and water absorption, mechanical properties such as compressive strength, and thermal properties, such as thermal conductivity, have been determined. 314 The results indicate that the replacement of 33.33 wt % of MK by different types of clays produces an increase in bulk density, decreasing apparent porosity and water absorption, according to the real density data of the precursors. With respect to compressive strength, all geopolymers have better mechanical properties than the control geopolymer, with compressive strength values greater than the minimum required standard value (10 MPa) applied for construction materials for structural purposes. All geopolymers have low thermal conductivity values, ranging between 0.23 and 0.27 W / mk, which make them good insulating materials. Therefore, it can be concluded that the biomass bottom ashes and the different types of calcined Bailén clays are suitable raw materials to replace the metakaolin in the manufacture of geopolymers, since the construction materials obtained have adequate technological properties.