Improvement of biomass bottom ash properties by carbonation and pulverisation methods for application in cement-based materials

2.1. Standard natural sand

CEN Standard Sand is a specially designed material used in laboratory tests to measure the compressive strength of mortar. Its key feature is a tightly controlled grain size distribution, ranging from 0.08 to 2.00 millimetres. To ensure consistency, the sand is limited to a maximum moisture content of 0.2% and packaged in bags weighing 1350 grams, with a tolerance of +/- 5 grams. Table 1 show particle size distribution of sand according to EN 196-1.

2.2. Cement

Two types of cements were used, Portland cement type I of medium-high strength 42.5 MPa at 28 days with high initial strength and Portland cement with limestone type CEM II/B-L of medium strength 32.5 MPa at 28 days with normal initial strength. The main properties are shown in Table 2.

2.3. Biomass botton ash

Biomass bottom ash is the solid residue remaining after the combustion of biomass in a boiler or incinerator. This type of ash is found at the bottom of the combustion device and generally consists of the non-combustible materials that were not volatilised during the burning process. The composition of bottom ash can vary depending on the type of biomass used and the combustion conditions, but generally contains minerals such as silica, aluminium oxides, calcium, iron and other trace elements. Two types of biomass bottom ash have been studied, one mainly from eucalyptus (BBA-EU) and the other mainly from olive trees (BBA-OL). The main properties of the raw material are shown below.

For this investigation a maximum particle size of 2 mm was taken, typically (0 – 2) mm.

As illustrated in Figure 1, both BBA-EU and BBA-OL exhibit continuous granulometry in the (0-2) mm range with a particle size distribution similar to that of SNS. Furthermore, BBA-EU has a greater proportion of fine aggregates. For instance, 70% of BBA-EU particles pass through a 1 mm sieve, compared to 65% for BBA-OL.

Figure 1 Particle size distribution of BBA-OL, BBA-EU and SNS. 

Table 3 summarises the physical and chemical properties of BBA-OL and BBA-EU. The carbonated versions of both BBA materials display a significant change in both density and water absorption compared to their non-carbonated counterparts. The carbonation process leads to a substantial increase in density (17% for BBA-OL and 14.7% for BBA-EU) and a drastic decrease in water absorption (89% reduction for BBA-OL and 97% reduction for BBA-EU). This transformation is particularly noteworthy for mortar mix design, as the higher density and lower absorption of carbonated BBA could significantly influence the amount of mixing water required to achieve optimal workability.

The major components, silicon (Si) and calcium (Ca), are present in significant quantities (over 20%), which are typical of good binder materials and contribute to the necessary reactions. However, the presence of potassium (K) raises concerns about alkali-aggregate reaction (AAR), which can cause expansion due to gel formation upon water absorption (39Cuenca-MoyanoGM, CabreraM, López-AlonsoM, Martínez-EchevarríaMJ, AgrelaF, RosalesJ. 2023. Design of lightweight concrete with olive biomass bottom ash for use in buildings. J. Build. Eng.69. 10.1016/j.jobe.2023.106289). The impact of this will be further investigated in the dimensional stability tests.

The levels of water-soluble sulphate and acid-soluble sulphate were below the detection limit. The organic matter content likely results from incomplete combustion, which depends on the power plant’s efficiency (40CabreraM, GalvinAP, AgrelaF, CarvajalMD, AyusoJ. 2014. Characterisation and technical feasibility of using biomass bottom ash for civil infrastructures. Constr. Build. Mater.58:234–44. 10.1016/j.conbuildmat.2014.01.087).

2.4. Processed materials

2.4.2. Pulverised biomass bottom ash

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In order to obtain physical properties similar to cement, the biomass bottom ash from olive and eucalyptus were subjected to a process of crushing, sieving and grinding. The bottom ashes are more reactive by obtaining larger specific surface areas (31MorenoS, RosalesM, RosalesJ, AgrelaF, Díaz-LópezJL. 2024. Feasibility of using new sustainable mineral additions for the manufacture of eco-cements. Materials. 17(4). 10.3390/ma17040777, 42MaryoryA, CerónC, ArangoCG. Proyecto de investigación elaboración de unidades de mampostería perforada de concreto utilizando relaves provenientes de la minería de agregados.) Given the high friability ratio of these materials, the micronisation process to obtain BBA powder is not very costly in terms of energy.

First, the material was pre-crushed using a jaw crusher, then the material was fed into an aggregate abrasion testing machine, called Micro-Deval, with a ball charge of three different sizes and the BBA sample was subjected to 6000 revolutions per minute. 0.5kg of material and 5kg of abrasive load were introduced.. After this milling process, they were sieved through the 0.125mm sieve to obtain a powder with physical properties similar to cement. In figure 2 and in table 4 it can be seen how the grinding and sieving process makes the powder from BBA have characteristics similar to cement. The micronisation yields were 89.6% for olive BBA and 93.4% for eucalyptus BBA. In addition, to determine the pozzolanic activity of the BBA, the calcium quantity concentration through the Frattini test is presented in Figure 3.

Figure 2 Laser granulometry measurements of the particle size distribution. 

Figure 3 8 days and 15 days pozzolanicity test. 

The particle size distribution and specific surface area of hydration hardening materials is an important quality. There is a direct relationship between particle size distribution, specific surface area and the physical phenomena that occur during the setting time (43MichelF, CourardL. 2014. Particle size distribution of limestone fillers: Granulometry and specific surface area investigations. Particul. Sci. Technol.32(4):334–40. 10.1080/02726351.2013.873503). Other studies determine specific surface areas 2820cm²/g and 6600cm²/g for a particle size distribution that establishes that 8.85% and 30.5% of the particles are retained by the 10µm sieve. The mortar mixtures in this study determine that the higher mechanical strength is provided by the powder with higher specific surface area and smaller particle size, although it is not a definitive condition, since the chemical composition of these micronised materials, with reactive elements such as calcium or silicon, is a determining factor in their hardening capacity (44PapayianniI, AnastasiouE. 2012. Effect of granulometry on cementitious properties of ladle furnace slag. Cem. Concr. Compos.34(3):400–7. 10.1016/j.cemconcomp.2011.11.015, 45AgraTMS, LimaVME, BastoPEA, Melo NetoAA. 2023. Characterizing and processing a kaolinite-rich water treatment sludge for use as high-reactivity pozzolan in cement manufacturing. Appl. Clay. Sci.236. 10.1016/j.clay.2023.106870.).

The density of the powders from BBA is somewhat lower than that of conventional cement, in line with previous studies (46BeltránMG, AgrelaF, BarbudoA, AyusoJ, RamírezA. 2014. Mechanical and durability properties of concretes manufactured with biomass bottom ash and recycled coarse aggregates. Constr. Build. Mater.72:231–8. 10.1016/j.conbuildmat.2014.09.019, 47RosalesJ, CabreraM, BeltránMG, LópezM, AgrelaF. 2017. Effects of treatments on biomass bottom ash applied to the manufacture of cement mortars. J. Clean. Prod.154:424–35. 10.1016/j.jclepro.2017.04.024, 48CabreraM, GalvinAP, AgrelaF, CarvajalMD, AyusoJ. 2014. Characterisation and technical feasibility of using biomass bottom ash for civil infrastructures. Constr. Build. Mater.58:234–44. 10.1016/j.conbuildmat.2014.01.087). The chemical composition of the ashes showed a high content of SiO₂, CaO and Al₂O₃ so that hydration reactions are expected to be strong. Other works presenting XRFs of conventional cements and alternative cements with recycled additions have CaO, SiO₂ and Al₂O₃ sum of 89.4% or 83.17%, while the pulverised BBA samples of this research determined this sum as 78.79% for p-BBA-OL and 84.7% for p-BBA-EU (49SainzFA, RosalesJ, ManuelG, MontenegroC, ThomasC, FernandoG, et al.International Córdoba Eco-Concrete Conference Editors Organization Funding [Internet]. Retrieved from: www.uco.es/ucopress). A variation in the chemical composition of the original materials and the materials subjected to the pulverisation process was observed (table 3 and table 4). The screening of less friable particles that have not been pulverised in the milling process leads to the pulverised materials having a different composition to the original materials. The presence of SiO₂ and CaO was increased and the K₂O content was reduced, so that the hydration reactions are increased without significantly affecting the solidification rate. With regard to the presence of alkalis, which can be negative for the durability of cement-based materials, the amount of K₂O is between 8 and 4so there is no concern that this element is present at the amounts determined on p-BBA-OL and p-BBA-EU (50RosalesM, AgrelaF, Sánchez de RojasMI, CabreraM, RosalesJ. 2023. Optimisation of hybrid eco-efficient mortars with aggregates from construction and demolition waste and olive biomass ash. Constr. Build. Mater.400:132634. 10.1016/j.conbuildmat.2023.132634.).

Table 4 Recycled powders physico-chemical characterization. 

Properties		p-BBA-OL	p-BBA-EU
Grain size distribution, R30 (µm) (%)		0.32	26.06
Real Density (kg/m3)		2589	2328
Blaine fineness (cm2/g)		5070	2660
Organic matter content (%)		2.42	2.06
Acid-soluble sulphate (% SO3)		0.131	0.049
Chloride content (%)		1.191	0.322
Main components XRF (%)
SiO2		33.09	63.82
CaO		40.41	12.07
K2O		7.92	4.18
MgO		5.74	2.61
Fe2O3		2.80	5.96
Al2O3		5.29	8.81
Na2O		0.38	1.33
P2O5		4.22	1.02
SO3		0.15	0.20

The results of the Frattini test showed that the p-BBA-EU is in the pozzolanic region in agreement with other previous studies in which bottom ash powder of organic origin were analysed (51FaleschiniF, ToskaK, ZaniniMA, AndreoseF, SettimiAG, BrunelliK, et al.2021. Assessment of a municipal solid waste incinerator bottom ash as a candidate pozzolanic material: Comparison of test methods. Sustainability (Switzerland). 13(16). 10.3390/su13168998). Other studies comparing organic waste used as biomass found that the calcination temperature can cause the ash to be in the pozzolanic or non-pozzolanic region. Calcination temperatures between 700ºC and 800ºC cause the biomass bottom ash to be located in the pozzolanic region (52Nahuat-SansoresJR, CruzJC, EscobarB, GurrolaMP, Ramírez-PintoCA, Garcia-UitzK. 2024. Evaluation of the pozzolanic potential of poultry litter ash calcined at different temperatures as a revalorized biomass waste. ACS Sustainable Resource Management. 1(5):950–7. 10.1021/acssusresmgt.4c00014). Other studies determine that the crystallinity of the minerals presented in the samples is indirectly proportional to the pozzolanic activity that the material may present. (53ZhouD, WangR, TyrerM, WongH, CheesemanC. 2017. Sustainable infrastructure development through use of calcined excavated waste clay as a supplementary cementitious material. J. Clean. Prod.168:1180–92. 10.1016/j.jclepro.2017.09.098). Pozzolanic oxides (SiO₂ +Al₂O₃ +Fe₂O₃) cause biomass ash to be located in pozzolanic or non-pozzolanic zones. p-BBA-EU has a sum of these three elements of 78.59% and p-BBA-OL presents a sum of 41.18%, being decisive for the area in which they are located, in accordance with previous studies that studied forest biomass ash (54JurićKK, CarevićI, SerdarM, ŠtirmerN. 2021. Feasibility of using pozzolanicity tests to assess reactivity of wood biomass fly ashes. Gradjevinar. 72(12):1145–53. 10.14256/JCE.2950.2020, 55VelardoP, Sáez del BosqueIF, Sánchez de RojasMI, De BelieN, MedinaC. 2024. Effect of incorporating biomass bottom ash and construction and demolition waste powder on the physical-mechanical properties and micro-structure of ternary-blended mortars. Constr. Build. Mater.432. 10.1016/j.conbuildmat.2024.136628).

2.5. Experimental scheme and dosages

In this study, two industrial by-products (BBA-OL and BBA-EU) were applied as partial substitutes for cement and sand in the manufacture of mortars.

First, material processing was carried out, consisting of material carbonation (BBA-OL-CA and BBA-EU-CA) and material micronisation (p-BBA-OL and p-BBA-EU). With each of the materials obtained, the manufacture of cement mortars was carried out with partial replacement of sand by carbonated and non-carbonated biomass bottom ash and partial replacement of cement by micronised biomass bottom ash.

The mortars were manufactured in accordance with EN 196-1. Standard CEN-NORMSAD (SNS) sand was used in all of them, and two different cements were used, CEM II B-L 32.5N for the control mortar and for the mortars in which a partial sand substitution was applied and CEM I 42.5 R in which a partial cement substitution was applied. The reason why two different cements were used was because the addition of 25% biomass bottom ash was intended to obtain a cement with a clinker content similar to CEM II B-L. For the substitution of sand by BBA, the density of the material was taken into account, and the substitution was carried out in volume. The dosage of the manufactured mortars is shown in Table 5.

In the manufacture of each of the mixtures, it was considered necessary to obtain a workability similar to that of the reference mortar. In this study, no superplasticiser additive was used, so, to achieve this parameter, the amount of mixing water was increased. The amount of mixing water was increased by adding a quantity of water added to achieve the workability of reference mortar (workability water).

The flowability value of the fresh mortar was determined by measuring the extension after a standardised shaking process. The workability of the reference mortar was 170 mm. In order to obtain a workability that did not differ by more than 10% from the value obtained for the reference mortar, the amount of water to be added to each mortar mixture manufactured was evaluated (table 5).

For the manufacture of each of the mortars, the saturation water of each aggregate was added (water absorption), it was observed that it was necessary to use more absorption water in the mortars manufactured with non-carbonated BBA. However, the carbonated ashes required more additional water to achieve a workability like the control. This added water may influence the mechanical properties subsequently obtained.

Figure 4 shows a scheme of the research development carried out, indicating the methodology applied to each material (processed and unprocessed) and the evaluated properties of the mortars manufactured with each standard used.

Figure 4 Experimental scheme. 

3.1. Mechanical behaviour: Compressive and flexure strength (EN 196-1)

The mechanical behaviour of the mortar mixtures described in previous sections was evaluated through the determination of compressive strength and flexural strength at curing ages of 2, 7, and 28 days. Two specimens were tested for flexural strength determination and four for simple compressive strength determination.

Figure 5 shows the results obtained for the flexural strength test, and Figure 6 shows the results for compressive strength. Additionally, Figure 7 illustrates the effect of carbonation in biomass bottom ash on compressive strength values at 2, 7 and 28 days.

According to Figure 5, the 28-day flexural strength for series 1 mortar mixtures was 7.03 MPa for the p-BBA-OL mortar mixture and 8.74 MPa for the p-BBA-EU mortar mixture. Compared to the reference mortar (7.59 MPa), a slight decrease of 7.42% was observed for the p-BBA-OL mortar mixture and an increase of 15.15% for the p-BBA-EU mortar mixture.

Regarding the 28-day simple compressive strength values obtained, as shown in Figure X2, series 1 mortars exhibited values of 32.76 MPa and 40.80 MPa for the p-BBA-OL and p-BBA-EU mortar mixtures, respectively. Compared to the reference mortar (36.50 MPa), a decrease of 10.26% was observed for the p-BBA-OL mortar mixture and an increase of 11.79% for the p-BBA-EU mortar mixture.

Both mortar mixtures with a 25% replacement of cement by BBA showed positive values, with mechanical strengths comparable to conventional cement. However, the different mechanical behaviour for each type of BBA applied may be attributed to their composition. BBA-OL ashes presented higher calcium and potassium values, whereas BBA-EU mixtures had higher Si content. The composition of BBA-OL indicated inert behaviour, similar to limestone filler, while the composition of BBA-EU suggested pozzolanic behaviour. (56PanesarDK, ZhangR. 2020. Performance comparison of cement replacing materials in concrete: Limestone fillers and supplementary cementing materials – A review. Constr. Build. Mater.251. 10.1016/j.conbuildmat.2020.118866).

Analysing the data shown in Figures 5 and 6 for series 2, a change in behaviour compared to series 1 was observed. The 28-day flexural strength values range from 3.76 MPa (50BBA-EU) to 4.88 MPa (25BBA-OL), reducing the strength compared to the reference mortar by approximately 35% for mixtures with 25% replacement and 50% for mixtures with 50% replacement.

Figure 5 Flexure strength results. 

Figure 6 Compressive strength results. 

Compressive strength values ranged from 10.13 MPa (50BBA-EU) to 20.46 MPa (25BBA-OL), with strength reductions of 40-50% for 25% replacement and 70% for 50% replacement.

This behaviour has been described in the literature by other authors and is attributed to the lower density of BBA, which increases the porosity of mortars, thereby reducing their mechanical strength. Additionally, the high-water absorption of BBA (10-12%) necessitated the addition of extra water during the mortar fabrication process, altering the water/cement ratio and reducing strength (57BeltránMG, BarbudoA, AgrelaF, JiménezJR, De BritoJ. 2016. Mechanical performance of bedding mortars made with olive biomass bottom ash. Constr. Build. Mater.112:699–707. 10.1016/j.conbuildmat.2016.02.065).

Comparing the values obtained for both types of BBA, mortars made with BBA-OL showed higher flexural and compressive strength values than those made with BBA-EU. This may be due to the granulometry of the BBA used as sand substitutes. BBA-EU contained a higher amount of material with a granulometry below 125 microns compared to BBA-OL. Rosales et al. (2023) (50RosalesM, AgrelaF, Sánchez de RojasMI, CabreraM, RosalesJ. 2023. Optimisation of hybrid eco-efficient mortars with aggregates from construction and demolition waste and olive biomass ash. Constr. Build. Mater.400:132634. 10.1016/j.conbuildmat.2023.132634.) demonstrated that mortars with sand substitutions by BBA exhibited higher mechanical strengths when the fraction below 125 microns was removed.

Regarding the values obtained for series 3 in the flexural and compressive strength tests, shown in Figures 5 and 6, a similar behaviour trend to series 2 was observed, with strength reductions compared to the control. Analysing the 28-day flexural strength values, they ranged from 3.68 MPa (50BBA-EU-CA) to 6.33 MPa (25BBA-OL-CA). The strength reduction was 16% and 25% for mixtures with 25% replacement (BBA-OL and BBA-EU) and 50% for 50% replacement.

Analysing the simple compressive strength values, they ranged from 10.62 MPa (50BBA-OL-CA) to 27.15 MPa (25BBA-OL-CA), with strength reductions of 25% and 38% for mixtures 25BBA-OL-CA and 25BBA-EU-CA, and 70% and 57% for mixtures 50BBA-OL-CA and 50BBA-EU-CA.

Figure 7 shows the increase in strength over time due to the carbonation of BBA. The samples with 25% replacement exhibited a 32% (25BBA-OL-CA) and 40% (25BBA-EU-CA) increase in 28-day simple compressive strength. The 50BBA-OL-CA mortar mixture showed very similar strength values to the non-carbonated mortar, with a slight decrease of 5%. The 50BBA-EU-OL sample exhibits a 55% increase.

Figure 7 Effect of carbonated biomass bottom ash on compressive strength at 28 days. 

The positive effect of carbonation shown in previous studies (58López-ZaldívarO, Mayor-LoboPL, Fernández-MartínezF, Hernández-OlivaresF. 2015. Improved cement mortars by addition of carbonated fly ash from solid waste incinerators. Mater. Construcc.65(319). 10.3989/mc.2015.07114) was not clearly seen in the compressive and flexural strength values obtained in this work. Mainly due to the need to use a higher amount of water in mortars with BBA-CA. The strength reduction in the 50BBA-OL-CA sample was due to the large amount of extra water added to maintain the workability of the sample, significantly increasing the water/cement ratio. The remaining mixtures exhibited a considerable increase in simple compressive strength at all ages due to the carbonation effect. Carbonation increases the density of BBA, reduces their absorption, and improves the physical properties of the mortars. Similar behaviours have been described applying carbonate recycled aggregates (59ZhangJ, ShiC, LiY, PanX, PoonCS, XieZ. 2015. Influence of carbonated recycled concrete aggregate on properties of cement mortar. Constr. Build. Mater.98:1–7. 10.1016/j.conbuildmat.2015.08.087).

3.2. Determination of the capillary water absorption coefficient of hardened mortar

The water absorption coefficient (WAC) due to capillary action was determined for hardened mortars containing BBA as a replacement for sand or cement, with and without carbonation treatment according to EN 1015-18. The calculated coefficients are presented below in Figure 8.

Figure 8 Water Absorption Coefficient. 

A preliminary analysis based on the percentage of aggregate replacement with BBA reveals that mixtures with 50% BBA exhibit higher water absorption coefficients compared to mortars with 25% BBA. Studies have demonstrated that the incorporation of highly porous industrial by-products significantly increases the porosity in hardened cement mortars (47RosalesJ, CabreraM, BeltránMG, LópezM, AgrelaF. 2017. Effects of treatments on biomass bottom ash applied to the manufacture of cement mortars. J. Clean. Prod.154:424–35. 10.1016/j.jclepro.2017.04.024) and that low substitutions (10-20%) can improve mortar durability by reducing water absorption due to decreased porosity. However, higher substitutions (30-50%) tend to increase these values (60PantićV, ŠupićS, Vučinić-VasićM, NemešT, MaleševM, LukićI, et al.2023. Effects of Grinding Methods and Water-to-Binder Ratio on the Properties of Cement Mortars Blended with Biomass Ash and Ceramic Powder. Materials. 16(6):2443. 10.3390/ma16062443.)

As observed in table 2 and table 3, untreated BBAs exhibit high absorption percentages, and the accelerated carbonation process to which they were subjected improved this characteristic, resulting in significantly lower absorption percentages for BBA-CA. Based on the above and analyzing the data in Figure 8, it can be seen, particularly with BBA-EU samples, how the use of BBA-CA as an aggregate replacement reduces the WAC of hardened mortars, resulting in less permeable and more resistant mortars, as shown in figure 6 and previous research (61SkeviL, BakiVA, FengY, ValderrabanoM, KeX. 2022. Biomass bottom ash as supplementary cementitious material: the effect of mechanochemical pre-treatment and mineral carbonation. Materials. 15(23). 10.3390/ma15238357).

On the other hand, replacing part of the cement with BBA shows a notable decrease in WAC (62BeltránMG, BarbudoA, AgrelaF, JiménezJR, De BritoJ. 2016. Mechanical performance of bedding mortars made with olive biomass bottom ash. Constr. Build. Mater.112:699–707. 10.1016/j.conbuildmat.2016.02.065) compared to mortars where aggregates were replaced with BBA, with the p-BBA-OL sample presenting the lowest value at 0.13.

3.3. Dimensional changes

Dimensional changes of the mortar mixtures were recorded throughout the curing process following the guidelines of UNE 83831. Square section samples measuring 2 cm per side and 28.5 cm in length were used, and length variations were measured with micrometric precision at different maturity stages: at 2, 7, 14, and 28 days. During the hardening process, these specimens are embedded with two metal pieces which serve as reference points for subsequent length measurements. Once the specimens have been fabricated, their changes in length are measured using a length comparator. This comparator consists of an adjustable-height steel frame equipped with a micrometre with a precision of 0.003 mm. A steel bar is used to calibrate the apparatus. To evaluate the dimensional changes, all mixtures were subjected to two curing environments: one in a Dry Chamber (60% humidity and 20ºC) and the other underwater condition. The results of these changes are presented in Figures 9 and 10.

Figure 9 Dimensional change (dry chamber). 

Figure 10 Dimensional change (under water). 

In the dry chamber, the mortars experience a loss of moisture to the dry environment, which causes significant contraction, as evidenced in most samples shown in Figure 9. This contraction results from the evaporation of water contained in the mortar pores, reducing the total volume of the material and generating internal stresses that contribute to further dimensional reduction. Specifically, for the present work, the dimensional changes were found between -697µm/m and 4189µm/m, with mortars containing BBA-EU substitutions, both carbonated and non-carbonated, showing the highest shrinkage values at 28 days.

On the other hand, when mortars are submerged in water, they have the capacity to absorb additional water, causing the material to swell due to the water entering the pores, which promotes hydration products and thus increases the total volume. The results presented in Figure 10 confirm this, as previously analyzed, with mortars containing higher percentages of incorporated BBA showing a higher water absorption coefficient and therefore presenting the greatest expansion values.

In summary, shrinkage in dry conditions is mainly due to moisture loss, while expansion underwater is attributed to water absorption and the continuous hydration of the cement. The dimensional changes of the mortar in these two environments depend on how the material interacts with moisture, the specific curing conditions, and the physicochemical properties of the substitutions in the mixtures.

It was observed that the dimensional changes produced in the mortars at early ages were more variable in dry chamber curing conditions than submerged, similar results were obtained in previous studies (Manu). The use of BBA as a partial sand substitute led to a higher dimensional instability in the mortars compared to the results obtained with the control mortar. The carbonation of the material produced a decrease in these dimensional variations, mainly due to the reduction of the absorption of the material at source. The use of p-BBA as a partial cement substitute did not lead to significant modifications with respect to the control mortar (50RosalesM, AgrelaF, Sánchez de RojasMI, CabreraM, RosalesJ. 2023. Optimisation of hybrid eco-efficient mortars with aggregates from construction and demolition waste and olive biomass ash. Constr. Build. Mater.400:132634. 10.1016/j.conbuildmat.2023.132634.).