Abstract
Geopolymers are a new class of binders based on alkali activation of natural and by-products raw materials. Their properties and eco-compatibility highly depends on the reaction system. The (Na,K)2O-Al2O3-SiO2-H2O system shows a distinguishing pseudo-zeolitic network structure, but reaction requires a high amount of activators. The aim of this work is to investigate how the use of forest biomass ash (FBA), as partial replacement material in the production of metakaolin (MK) based geopolymeric mortar, and affect its properties. FBA is a by-product of the combustion process of forest biomass in thermal power plants. Mortars with a FBA content of 0%, 10%, 20%, and 30% wt have been tested for workability, flexural, and compressive strength. Capillary absorption, micro-morphological features, thermal, and shrinkage behavior have been investigated. The addition of FBA allowed for a decrease in the use of alkaline activator up to 20%, while preserving the characteristic broad hump centered at approximately 28° 2θ Mechanical properties of the geopolymeric mortars decrease proportionally with metakaolin replacement, even if a compression strength of more than 35 MPa is still obtained with a FBA content of 30% wt. After thermal cycles of up to 700 °C, all of the mortars still retain their cohesiveness, with an overall loss of mechanical strength of about 80% of the initial value that can be attributed to the formation of microcracks as a consequence of the network strain and distortion due to dehydration and shrinkage.
Highlights
The use of forest biomass as fuel in thermal power plants is becoming a common practice due to its availability, low cost, sustainability, and renewability
In order to further increase the environmental sustainability of the process, it is necessary to reduce the fraction of forest biomass ash (FBA) that is currently land-filled
The aim of this work is to study the feasibility to use forest biomass ash as partial replacement material in the production of metakaolin (MK) based geopolymeric mortars in order to decrease the consumption of metakaolin, while simultaneously allowing to: 1
Summary
The use of forest biomass as fuel in thermal power plants is becoming a common practice due to its availability, low cost, sustainability, and renewability. In order to further increase the environmental sustainability of the process, it is necessary to reduce the fraction of forest biomass ash (FBA) that is currently land-filled. To achieve this target, new application fields, different from soil amendment, have to be found [2,3,4]. The development of more environmentally friendly materials based on the utilization of industrial waste materials or recycled materials in their manufacture is a nowadays focus It allows for reducing natural raw materials, water, and energy consumption, and it is driven by the increasingly more stringent environmental regulations [5,6]
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