Use of biomass fly ash as partial replacement in the manufacture of mortars

(1)

Conclusions

Use of biomass fly ash as partial cement replacement in the manufacture of mortars

Zengfeng ZHAO

1*

_{, Luc COURARD}

1

_{, Frédéric Michel}

1

_{, Sébastien REMOND}

2

1. Department of ArGEnCo, GeMMe Building Materials, Urban and Environment Research Unit, University of Liège,

Belgium

2. Civil and Environmental Engineering Department, EA 4515 - LGCgE, IMT Lille Douai, Université de Lille, France

Materials

The cement used in mortars was Ordinary Portland Cement (CEM I 52.5 N) provided by CBR Company. The density of cement CEM I 52.5 N measured by helium pycnometer was 3.12 g/cm3_{. A siliceous CEN standard sand (corresponds to European standard EN 196-1)} was used as natural sand with the density of 2.66 g/cm3_{. The biomass fly ash used was} collected from combustion of 100% wood pellets (Electrabel Company). The density of biomass fly ash was 2.73 g/cm3_{measured by helium pycnometer, which is lower than} Portland cement. Chemical composition of biomass fly ash was determined by X-ray fluorescence. The major chemical elements of the biomass fly ash were oxygen, silicon, calcium, aluminium and iron. The biomass fly ash had higher calcium, magnesium, phosphorus, potassium, and lower silicon, aluminium, iron compared with the classical fly ash (Table 1). Laser granular analysis of cement and biomass fly ash showed that D50 of the biomass fly ash was 33.39 µm while D50 of the cement was 11.14 µm. The biomass fly ash contained a lower proportion of fine particles (1 µm to 30 µm) than cement. The BET specific surface area of biomass fly ash (2.61 m2_{/g) was two times larger than that of cement} (1.29 m2_{/g) according to BET method, which is due to the irregular shape and higher porosity} of biomass fly ash.

Four mortars were made with CEM I 52.5 N being replaced by the same mass of biomass fly ash at replacing levels of 0%, 10%, 20%, 30% and 50% (noted M0_52.5, M10_52.5, M20_52.5, M30_52.5, M50_52.5 respectively). Table 2 shows the compositions of all studied mortars. A precise mixing procedure was followed according to standard EN 196-1.

Experiments

After mixing, the consistence of fresh mortar was measured by flow table with Abrams’ mini-cone (h=60mm, D=100mm, d=70mm) according to standard EN 1015-3. The preparation of specimens (40mm × 40mm × 160mm) for mechanical strength tests was followed in accordance with standard EN 196-1. The flexural and compressive strengths of hardened mortar were determined in accordance with standard EN 196-1. These two mechanical tests were carried out with an INSTRON 5585 (loading capacity of 200 KN) after being cured 7, 28 and 90 days in water.

Authors would like to thank the Electrabel Company for providing us biomass fly ash and CBR Company for providing us cement. Authors would also like to thank European Regional Development Fund and Wallonia Region for financial support through the project Feder Ecoliser (ÉCOLIants pour traitement de Sols, Etanchéité et Routes).

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In this paper, the feasibility of using biomass fly as a supplementary cementitious material was investigated. Mortars with different percentages of substitution (0%, 10%, 20%, 30% and 50%) of cement by biomass fly ash were manufactured, and then the fresh properties (slump) and mechanical properties (compressive strength and flexural strength) were studied. The results showed flexural and compressive strengths of mortars after 28 days decreased when the substitution of cement by biomass fly ash increased. However, when 20% biomass fly ash was added, the mechanical strength was around 76.8% of the reference mortar. Further detailed investigations are in progress to address the application of these biomass fly ashes. These include tests of strength/durability for obtaining sustainable biomass fly ash based mortar formulations.

Introduction

Results

Introduction

Biomass is widely used as a renewable energy source, which accounts for more than 4% of the total energy consumption in the European Union and it will be increased in the future. The combustion of biomass or co-combustion of biomass with coal can reduce coal consumption and minimize the global CO2emissions. However, the storage of biomass fly ash occupies land area and increases the risk of contamination of groundwater. Biomass fly ash has been used for several purposes such as fertilization in agriculture and atmospheric pollution control.

In this paper, the feasibility of using biomass fly ash as a supplementary cementitious material was investigated. The biomass fly ash from combustion of 100% wood pellets were collected from industrial power plant located in Belgium. The physicochemical properties of fly ashes were characterized by different techniques such as laser diffraction spectroscopy, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The biomass fly ash was irregular in shape. Mortars with different percentages of substitution (0%, 10%, 20%, 30% and 50%) of cement by biomass fly ash were manufactured, and then the fresh properties (slump) and mechanical properties (compressive strength and flexural strength) were studied.

Research main objectives

To investigate the feasibility of using biomass fly ash as a supplementary cementitious material in mortar and to define a relationship between different percentage of substitution of cement by biomass fly ash and the mechanical properties of mortar.

Acknowledgements

Results

The slump flow of mortars decreased when the substitution of cement by biomass fly ash increased (Fig. 1). This trend could be due to the higher specific surface area of biomass fly ash compared with cement. Thus, part of the mixing water was expected to be adsorbed by biomass fly ash and thereby the free water quantity decreased, leading to a significant loss of workability. The fresh density of mortar decreased as the substitution of cement by biomass fly ash increased, which is certainly due to the lower density of biomass fly ash compared to cement.

Fig. 2 present the flexural and compressive strengths of mortars (average values obtained by three measurements for flexural strength and six measurements for compressive strength). Both flexural and compressive strengths of mortars after 28 days decreased when the substitution of cement by biomass fly ash increased. This result is in agreement with the dilution of cement when part of the cement is substituted by unreactive or slightly reactive compounds. The compressive strength of mortars (M10_52.5, M20_52.5, M30_52.5 and M50_52.5) after 28 days are 87.7%, 76.8%, 58.4% and 26.8% respectively compared with the reference mortar (M0_52.5). Therefore, the mortar with substituting amounts up to 20% is still acceptable with respect to flexural and compressive strength.

Fig. 2 Mechanical properties as a function of mortars: left (flexural strength), right (compressive strength)

Table 1 Chemical compositions determined by XRF

SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total Classical fly ash 49.3 1 27.7 7.9 0.1 1.6 1.4 0.8 4 0.3 6.6 100.4 Biomass fly ash 24.7 0.4 5.3 3.2 1 9.3 25.8 2.3 7.9 4.9 9.7 94.3 CEM I 52.5 N 20.2 0.5 4.8 3.3 0.1 1.8 64.2 0.3 0.5 0.4 1.1 100

Table 2 Compositions of mortars

M0_52.5 M10_52.5 M20_52.5 M30_52.5 M50_52.5

Sand (g) 1350 1350 1350 1350 1350

Cement (g) 450 405 360 315 225

Biomass fly ash (g) 0 45 90 135 225

Efficient water (g) 225 225 225 225 225

Eeff/(C+B) 0.5 0.5 0.5 0.5 0.5

Fig.1 Slump as a function of mortars 0 20 40 60 80 100 120 140 160 180 200 M0_52.5 M10_52.5 M20_52.5 M30_52.5 M50_52.5 S lu m p f lo w (m m )