**5. Market readiness of the WBA use as supplementary cementitious material**

In order to explore the market readiness and capacity for using WBA as SCM in the concrete industry, a questionnaire was conducted among 11 concrete producers (SMEs) from Croatia with an approximate annual concrete production of at least 12,000 m3 to a maximum of 300,000 m3. The purpose of the questionnaire was to conduct a qualitative study of concrete and cement production and the views of SMEs on the reuse of WBA in their plants. According to the results of the survey, the most common strength classes in concrete production are C25/30 and C30/37 (each represented by 91%), followed by 64% of concrete use of strength classes C20/25, C35/45, and C40/50 (**Figure 7a**). The compressive strength of concrete is a common and important property in the design of concrete structures. In addition to compressive strength as a basic property of concrete,

**Figure 7.**

*(a) Concrete production share with respect to the compressive strength class; and (b) cement type share in the concrete production.*

all respondents indicate water permeability. Other main properties most tested on hardened concrete are freeze-thaw resistance with or without de-icing salt (82%), wear resistance (82%), and chemical resistance (73%).

The average amount of cement used in concrete ranges from 295 to 340 kg per 1 m3 of concrete. 27% of the respondents use mineral admixtures in the production of concrete namely silica fume, coal fly ash, and metakaolin. The most common types of cement used in concrete production are shown in **Figure 7b** (multiple answers were possible): of the 15 types of cement on the market, blended cements are the most common: CEM II /A(B)-M(S-V) and CEM II /A(B)-S with 45% of use, CEM II /A(B)-M(S-LL, V-LL) with 27%, CEM II /A(B)-LL with 18% and CEM III /A(B, C), with 18%. Blended cements contain waste products as SCMs to replace clinker as the main source of CO2 emissions in concrete production [69]. By using SCMs could result in CO2 reduction of about 400 million tons per year [70]. These can be easily replicated as a possible circular solution for WBA management, which was recognized by concrete producers: 55% of respondents are familiar with the problem of WBA management and 91% of them are interested in using WBA in their plants. Concrete producers emphasized ensuring a consistent chemical and physical WBA quality to ensure the quality of the concrete produced.

Considering the current quantities of WBA in Croatia (25,414 tons per year [3]) and the data from the questionnaire analysis of cement and concrete production, all WBA can be used in cement and concrete production with regular quality control. For example, if 10% of cement is replaced by WBA, it is possible to reuse 1500 t of WBA per year in only one concrete plant with an average production of 50,000 m3 concrete/year. This means that in the four concrete plants the whole amount of the finer WBA can be used, while the coarser fraction can be used as a substitute for the fine fraction of aggregates (sand).

### **6. Conclusions**

According to all observed trends, waste ash from wood biomass combustion is expected to increase and the regulatory framework for waste management is becoming more stringent. In the design and planning phase of biomass power plants, it is important to determine the amounts of WBA generated and to find sustainable solutions for WBA management during the life cycle of the power plant. In the concrete industry, there is a high potential for substitution of certain components by adequate alternative materials, and in that context, the use of WBA has been examined. This paper presents comprehensive research of the properties of WBA necessary for its use as SCM in concrete. Based on the review of existing research and results of experimental testing shown in the paper, it can be expected that WBA reduces the workability of the cement composites, noting that cement replacement up to 10% has no significant effect on the consistency. This is probably due to the morphology of WBA, high alkali content, and LOI values. Increased setting time can also be expected, although results vary depending on the type of WBA used. For WBAs with a high CaO content, it is necessary to check the free CaO as it may affect the volume stability and durability properties of the cement composites. The comparison of the compressive strength of mortars and concretes shows a significant variability and influence of the different WBAs used on the compressive strength after 28 days with a tendency to decrease the compressive strength with a higher proportion of WBA.

*Utilization of Wood Biomass Ash in Concrete Industry DOI: http://dx.doi.org/10.5772/intechopen.102549*

The main logistical and long-term challenges that need to be considered when establishing an industrial symbiosis for sustainable WBA management are to ensure consistent WBA quality (proper storage and transportation of WBA from power suppliers to concrete producers); different types of WBA collection in power plants (e.g. mixing with water), which could affect WBA properties (self-hardening) and the need for additional pre-treatment of some WBA samples (e.g., grinding and/or screening) due to inefficient combustion of wood biomass or due to wood impurities, which could negatively affect durability properties.
