Utilization of Wood Biomass Ash in Concrete Industry

*Nina Štirmer and Ivana Carević*

### **Abstract**

The use of energy from wood biomass plants results in the production of large quantities of wood biomass ash (WBA). Most of the WBA is disposed of and some are used as a soil supplement in agriculture. In the concrete industry, there is a high potential for substitution of certain components with suitable alternative materials. Depending on its physical and chemical properties, WBA can be used in concrete production as a partial replacement for cement or as a substitute for fine aggregates. The suitability of locally available WBA should be evaluated in terms of microtexture, chemical, and mineralogical composition. This paper presents the types of WBA produced by different combustion technology, the influence of WBA as a cement replacement on the properties of cement composites in the fresh and hardened state, an overview of the environmental impact of WBA cement composites, and the market opportunities and readiness for reuse of WBA as a new potential supplementary cementitious material.

**Keywords:** wood biomass ash, supplementary cementitious material, compressive strength, cement composites, concrete industry

### **1. Introduction**

The policy of promoting and increasing the use of wood biomass as a renewable energy source affects the increase in the amount of wood biomass ash (WBA) produced [1]. Comprehensive statistics on the annual production of WBA in the European Union are not available. However, Austria, Denmark, Germany, Italy, the Netherlands, and Sweden account for about 2.9 million t/y of biomass ash [2], while a survey conducted in Croatia revealed that about 25,414 t/y of produced WBA is landfilled [3]. Existing data estimated that Europe will generate up to 15.5 × 107 tons of WBA in 2020 [4], highlighting the urgency of strategic foresight in waste management. Currently, WBA is underutilized in the EU and mostly disposed of in landfills [5–8], resulting in additional costs and risks to the environment. The cost of biomass ash disposal ranges from 100 to 500 EUR/ton [9, 10]. About, 1.7 million EUR per year are paid for the disposal of WBA in Austria [11]. In the future, an increase in the cost of landfilling in the form of waste taxes or disposal fees, as well as difficulties in acquiring new landfills and stricter EU landfill directives, may be expected. Unsystematic management of WBA can lead to environmental pollution and potential risks to human health: WBA can be easily transported through the air and consequently cause health

problems related to the respiratory system of the population living in the vicinity of the landfill [12], while uncontrolled landfilling of WBA can lead to groundwater pollution through leaching of heavy metals from WBA or infiltration of rainwater [13]. European policies promote and stimulate green innovations in the reuse of waste as secondary raw materials to boost the market and new green business opportunities [14]. It is, therefore, necessary to find ways and methods for the application of WBA that are environmentally sound and economically justified. Previous studies [15–19] have shown that the resulting WBA can be reused in certain industries due to their properties and chemical composition, especially in the concrete industry. However, existing regulations and standards currently preclude the use of WBA in the concrete industry [20, 21].

The objectives of this chapter are: (1) to determine what types of combustion technologies are currently in use and what types of WBA are produced by each combustion technology, the properties of these WBAs, and the factors that most influence WBA properties, as well as the physical and chemical properties that could influence the use of WBA in cement composites; (2) to assess the influence of WBA as a cement replacement on the properties of cement composites in the fresh and hardened states; (3) to provide a brief overview of the environmental impact of the use of WBA in the mortar and concrete mixes; and finally (4) to identify the market opportunities and readiness for reuse of a new potential supplementary cementitious material (SCM).
