Effects of treated miscanthus on performance of bio-based cement mortar

Bio-based miscanthus cementitious composites are potential promising sustainable building materials, however the organic matter and physical properties of miscanthus negatively influence their performances. In this study, physical milling treatment and heat treatments on miscanthus are investigated. Results show that the heat-treated miscanthus has a positive influence on compressive strength. The cavities of the parenchyma structure of miscanthus are easily filled with fresh mortar and tightly embedded in the mortar, resulting in the enhanced bonding interface. Besides, long fibre miscanthus (2–3 cm) has a better fibre-bridging effect than other forms of miscanthus, with an improvement in flexural strength of 24%. Physically treated miscanthus exhibits excellent heat-insulating performance, which is recommended for heat-insulating bio-mortar. The treated miscanthus significantly reduces the drying shrinkage, with a decrease of up to 25% at 90 days, compared to the untreated miscanthus. Graphical abstract Schematic diagram of the bonding interface between miscanthus fibre and mortar. Highlights Effects of treated miscanthus on bio-based miscanthus mortar are investigated Physically treated miscanthus is recommended for heat-insulating bio-mortar Heat-treated miscanthus has a positive influence on compressive strength Treated miscanthus significantly reduces the drying shrinkage of bio-mortar


Introduction
Miscanthus (Âgiganteus) is a perennial energy crop in Europe because of the high biomass yield and adaptation to European climate [1]. It only requires 2-3 times less water than other plants, which can grow in barren land [2]. The high photosynthesis rate makes miscanthus grow very rapidly and produces the dry biomass yield of [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] tons each year per hectare [3]. In the last decades, the cultivation of miscanthus as energy biomass has significantly increased, and approximately 100,000 ha have been used for the production of global miscanthus biomass [4]. Miscanthus is a lignocellulosic crop that is widely used as cellulose source in the paper industry [4], and also as an animal feed become of the high energy value of 17.7 MJ/ kg [5], and as possible biofuel energy for the electricity generation in Europe and the United States [6].
Nowadays, there is a growing interest in the application of renewable and cheap plant fibres in bio-based cement mortar, such as straw, hemp, coir and flax shives, etc. for sustainable building materials development [7,8] by using them as a promising bio-reinforcing material. The utilization of miscanthus as a fibre or an aggregate has gained great attention in Europe [9][10][11], for example, the lightweight fiberboards, plant pots and packaging materials made of miscanthus have been investigated in previous studies [12]. The advantages of using miscanthus fibre for the manufacture of bio-based cement mortar are that the miscanthus is usually renewable feature, abundance, widespread availability and rapid growth [11]. The research on bio-based miscanthus cement mortar aims to develop sustainable building materials, reduce the environmental impact and recycle wastes from agricultural factories [2,10]. Miscanthus has good thermal insulation and acoustical absorption properties because of the high porosity and lightweight properties [13]. Besides, the elastic modulus of miscanthus varies from 2 GPa to 8 GPa, which is usually stronger than other natural fibres, e.g. straw [14]. The cross-section of miscanthus shows that the parenchyma which provides thermic and acoustics insulation, and the epidermis, thick sclerenchyma and radial allocation of vascular bundles with relevance to very high firmness [10,14]. The miscanthus cement mortar exhibits excellent acoustic absorption and heat insulation properties in our previous studies [15]. Thanks to chemical compositions like silicon, miscanthus fibre is suitable to be used in building materials [14].
Compared to other natural fibres, miscanthus fibre has a significant difference from other plant fibres such as hemp, coir, and flax shives, which is the diameter of miscanthus fibre which is 10 times bigger than conventional coir. Because the inside and outside of the miscanthus fibre possess two different structures [10], as shown in Figure 1. The interior of the miscanthus fibre is composed of the high content of parenchyma, which provides excellent thermal insulation but also increases the water absorption capacity. Around the outer layer of the parenchyma has a stiff epidermis structure, which contains thick sclerenchyma and vascular bundles with a firm texture. The raw miscanthus is more like a particle than fibre, and direct use of untreated miscanthus fibre in mortar would reduce the mechanical properties of bio-based cement mortar [14]. The outer epidermis of the miscanthus fibre is stiff, mainly providing the strength for the miscanthus, which can be used as a natural reinforcing fibre in cement mortar. The internal surface of the miscanthus is the main contributor for reducing the thermal conductivity and sound absorption of cement mortar. Therefore, the outer and inner surfaces of miscanthus contribute different functionalities, and they are desired to be separated prior to being added in mortar.
The organic matter and physical properties (e.g. size and shape) of miscanthus show a negative influence on the performance of bio-based miscanthus mortar. Due to the high porosity of miscanthus fibre, it is sensitive to changes in humidity in the ambient environment. As a result, the drying shrinkage and wet swelling of miscanthus fibre will affect the performance of miscanthus mortar. The drying shrinkage of bio-based mortar is usually higher than that of normal-weight mortar [16]. Moreover, during ageing, the degradation of miscanthus fibre may occur as a consequence of the dissolution of the hemicellulose, cellulose and lignin [17]. The extractive compounds from miscanthus fibre such as polysaccarides, phenols and starch, are known to delay the cement hydration [18,19]. The weak bond between bio-based fibre and mortar interface is a key factor restricting the ultimate strength of bio-based mortar. Therefore, in order to reduce the drying shrinkage and improve the mechanical strength of miscanthus mortar, miscanthus fibre should be treated prior to using in bio-based cement mortar.
Some studies have been conducted to mitigate the degradation of biological materials recently. The heat treatment, i.e. a rapid decomposition of the organic matter in the absence of oxygen, is usually used for the treatment of bio-material which can decompose the organic matter and mitigate the influence of bio-material on cement hydration. Moreover, the heat treatment also addresses the dimensional instability and biodegradability, resulting in a significant reduction in the drying shrinkage of cement mortar [20]. Previous studies reported that the heat-treated apricot shell [21], wood [22] and oil palm shell [23] significantly increased the mechanical strength of bio-based cement mortar owing to the improvement in the bonding between the heat-treated aggregate and the mortar. But so far, the current literature mainly focuses on the direct use of miscanthus fibre in concrete, and the effects of heat treatment, size and shape of the miscanthus on the mechanical properties, microstructure and drying shrinkage of biobased cement mortar have been rarely investigated. In order to reduce the negative impact of organic matter, size and shape of miscanthus on the performance of bio-based cement mortar, optimized miscanthus pretreatment methods should be investigated for eco-friendly bio-based miscanthus mortar.
In this study, two methods are used to modify miscanthus fibre with heat treatment and physical treatment (ball milling). The raw miscanthus fibre is treated under nitrogen condition at 250 C for 2, 3 and 4 h for the heat treatment, and the ball milling is also used for the physical treatment of the miscanthus fibre. After ball milling treatment, 2-3 cm, 0.4-1.5 cm and <0.05 cm miscanthus are used as long fibre, short fibre, and powdery fibre, respectively. The physical properties, morphology and mineralogical phase of miscanthus fibre before and after treatment are evaluated. The effects of different forms of miscanthus fibre on the physic-mechanical properties, microstructure and drying shrinkage of bio-based cement mortar are investigated. The recommended miscanthus treatment method is obtained based on the present results.

Raw materials
The CEM I 52.5 R Portland cement is used as binder (ENCI, the Netherlands). The commercial expanded silicate (ES) is used as aggregates. To obtain a good particle packing, four sizes of the ES are used with the size of 0.09-0.3 mm, 0.5-1 mm, 1-2 mm and 2-4 mm in this study. The specific density and crushing strength of the ES are 2.26 g/cm 3 and 12-22 MPa [24], respectively. The raw miscanthus fibre with a length of 1-3 cm is supplied by NNRGY Company (The Netherlands). The micrographs of the miscanthus obtained by a Scanning Electron Microscopy (SEM) scanner are shown in Figure 2. The external surface is stiff and smooth epidermis texture with round micropores (Figure 2a), which provides the strength and toughness for the miscanthus fibre. The internal surface of the miscanthus is a parenchyma structure ( Figure  2b), which provides good thermal and sound absorption properties [10]. Fly ash and silica fume are used as supplementary cementitious materials. CEN-NORM sand satisfying European standards (EN 196-1) is used as fine aggregates. The polycarboxylate ether superplasticizer is used to improve the workability of the fresh mixture.

Treatment of miscanthus
The schematic diagram of the treatment methods of the miscanthus fibre is presented in Figure 3. Generally, the pyrolysis temperature of miscanthus biomass varies from 200 C to 400 C [25]. The miscanthus easily turns to ash under high-temperature condition, the low-temperature pyrolysis is selected in the present study. The raw miscanthus is placed in a vacuum furnace under nitrogen condition at 250 C for 2 h, 3 h and 4 h.
For the ball milling, the external surface of the miscanthus is used as the long fibre and short fibre, while the porous internal surface is used for the powdery miscanthus. The detailed process of ball milling is as follows: 10 milling balls with the diameter of a 30 mm are placed in each porcelain ball mill pot, and then 40 g miscanthus is added to per ball mill pot. The ball milling is run with a milling speed of 300 rpm for 10 min. After ball milling, the long fibres (2-3 cm), short fibres (0.4-1.5 cm) and powdery (<0.05 cm) miscanthus are obtained by a sieving machine, as shown in Figure 4.

Mix proportion and specimen preparation
The treated miscanthus, including heat-treated 2 h (M-2), 3 h (M-3) and 4 h (M-4), long fibre (M-LF), short fibre (M-SF) and powdery miscanthus (M-P) are used to replace the untreated miscanthus (M-0) by volume. A 1.5% V/V of the miscanthus is added to the mortar. The gradation distribution of the ES aggregate refers to our previous study [24], the contents of cement, fly ash and silica fume refer to the lightweight aggregate concrete [26]. The powdery miscanthus cannot be submerged in water for the pre-wet treatment, the same volume water of 24-h water absorption of the powdery miscanthus is added to the fresh mixture. The fresh mixture is compacted by a striking shaker. After that, all mixtures are covered with a plastic film and demoulding after 24 h, and then stored in the laboratory with a temperature of 20 ± 2 C and relative humidity of !95%. The mix proportions of mortar are shown in Table 1.

Test methods
The density of 100 Â 100 Â 100 mm 3 sample at 28 days is measured following EN 1015-6. The water absorption and porosity of 100 Â 100 Â 100 mm 3 sample at 28 days are determined according to ASTM C642-13. The compressive strength and flexural strength of 40 Â 40 Â 160 mm 3 sample at 28 days are determined according to EN 196-1, with a loading rate of 2400 N/s and 50 N/s, respectively. The average value of three samples is recorded as the final result. The specific density of the miscanthus fibre is determined by using an AccuPyc II 1340 gas pycnometer. The microscopic images of the miscanthus fibre before and after treatment are observed by SEM (Phenom ProX). The 100 Â 100 Â 100 mm 3 sample at 28 days are ovendried at 105 C for 24 h to a constant mass, and then the surface midpoint position of the sample is used for the thermal conductivity measurement by ISOMET 2104, three surfaces are determined for each sample. The    23.55 the laboratory with a temperature of 20 ± 2 C and relative humidity of 65 ± 3%, and then the drying shrinkage is determined by using a digital micrometer gauge with a distinguishability of 0.001 mm according to DIN 52450.

Physical properties of the treated miscanthus
The physical properties of the treated miscanthus fibre are shown in Table 2. As expected, heat treatment reduces the density of the miscanthus, whereas, the ball milling (physical) treatment has a negligible effect on the density. The density of heat-treated miscanthus at 2-hours, 3-hour and 4-hour are reduced by 13%, 24% and 39%, respectively, as compared to the untreated miscanthus (M-0). This may be attributed to the organic matter being pyrolyzed and a carbon skeleton and microporous structure are formed during the process, which leads to a reduction in the mass loss of the bio-materials [27]. The results also show that the powdery miscanthus and heat-treated miscanthus have a higher water absorption than other forms of the miscanthus. However, the long fibre and the short fibre miscanthus possess lower water absorption because the parenchyma structure with high water absorption is separated from the miscanthus surface.

Morphology
The SEM micrographs of the miscanthus fibre after 4-hour heat treatment are shown in Figure 5. The surface colour of the heat-treated miscanthus turns from yellow to black, which indicates that the oxygen in the organic matter is decomposed and more carbon is formed [28]. Cracks appear along the longitudinal direction of the stem due to the dehydration of the miscanthus (Figure 5a). Moreover, the surface peeling is observed on the external surface of the miscanthus. Similar to the external surface, cracks also occur on the surface of the parenchyma structure and the fragment of the cavity is peeled off from the parenchyma, a dispersed laminated structure is formed on the internal surface (Figure 5b). The increased surface cracks by heat treatment provide paths for the flowing mortar to penetrate the interior of the cavity of the miscanthus [29], making the miscanthus more tightly embedded in the mortar to achieve a better bonding interface.

Mineralogical phase analysis
The cellulose chain molecule in the amorphous area is irregularly arranged, resulting in a diffuse reflection and no peaks are generated [30]. The X-ray Diffraction (XRD) patterns of the untreated and heat-treated miscanthus fibre are presented in Figure 6. The results show that both untreated and heat-treated miscanthus are amorphous and a distinct peak appears between 25 and 26 , which may be ascribed to the presence of graphite. Bio-materials such as peanut, walnut and chestnut, etc. have typical peaks at 22.6 because of the presence of crystalline cellulose [30]. Previous studies show that the crystalline cellulose of peach and apricot shells decreases after heat treatment and the appearance of wide graphitic peaks at the diffraction angle of 26.7 [21]. The reduction in the crystallinity of cellulose is mainly caused by the absence of oxygen in the heat-treated bio-materials [31].

Density
As shown in Figure 7(a), the treated miscanthus reduces the demoulding and oven-dry density of the mortars. Moreover, as the duration of heat treatment increases, the density gradually decreases. Because the heat treatment increases the microporous structure of the miscanthus over time [25]. Under the same fibre volume fraction, the amount of the heat-treated miscanthus adds to the fresh mixture is lower (Table 1), and consequently, the density of the mortar is reduced. The oven-dry density of the reference mortar (M-0) is 1498.4 kg/m 3 , and the M-4 mixture obtains the lowest oven-dry density of 1439.1 kg/m 3 , which is reduced by 4%, compared to the M-0 mixture. For physical treatment, the M-SF results in more reduction in density of mortar, compared to the M-LF and the M-P, with a decrease of 2.3%. This may be attributed to the weak bond between the smooth external surface of miscanthus fibre and the mortar resulting in more micropores in the interfacial transition zone (ITZ) [15,29]. Heat treatment is more advantageous than the ball milling treatment in reducing the density of bio-based miscanthus mortar.

Water absorption and porosity
As shown in Figure 7(b), the 24-hour water absorption of the miscanthus mortar varies from 8% to 11%, and the porosity was between 17% and 22%. The treated miscanthus significantly decreases the water absorption and porosity of the mortar. The water absorption and porosity of the M-P mixture decrease by 26% and 24%, respectively, compared to the M-0 mixture. After ball milling, the small particle of the miscanthus is more easily wrapped by the mortar, which results in a decrease in the porosity and water absorption [32]. For the heat treatment, with the increase in the pyrolysis duration, the hydrogen and oxygen elements gradually decrease, and the carbon element gradually increases due to the decomposition of organic matter, which results in the improvement in the bonding ability with the mortar interface [21], and consequently, reducing the porosity and water absorption of mortar.

Thermal conductivity
The thermal conductivity of the mortars varies from 0.557 W/(mÁK) and 0.725 W/(mÁK), as shown in Table 3. The treated miscanthus significantly reduces the thermal conductivity, volume heat capacity and thermal diffusivity of mortar. The thermal conductivity of the M-4 and M-LF mixtures is reduced by 19% and 23%, respectively, as compared to the M-0 mixture. This may be attributed to the fact that the heat treatment increases the microporous structure of miscanthus and reduces its density [25]. When the particle size of the miscanthus fibre is decreased, they are more easily and uniformly dispersed into the mortar and formed tiny closed voids, resulting in an improvement in the heat absorption capacity of the miscanthus mortar. It can be concluded that the physically treated miscanthus (M-LF and M-SL series) is recommended for the manufacture of heat-insulating biobased mortar.

Compressive strength and flexural strength
The compressive strength and flexural strength of the mortars are shown in Figure 8. The results show that the treated miscanthus significantly increases the compressive strength of the mortar. Moreover, the compressive strength of mortar containing heat-treated miscanthus improves as the heat treatment duration increases. However, considering the energy consumption and exhaust emissions caused by heat treatment, it is not preferred for treating miscanthus. The 28-day compressive strengths of the M-LF and M-P mixtures are increased by 17% and 26%, respectively, compared to the M-0 mixture. The results also show that the M-LF and M-P significantly improve the 28-day flexural strength of the mortar, with an increase of 24% and 12%, respectively, as compared to the M-0 mixture. The low strength and large particle morphology of the untreated miscanthus play the role of voids, which results in weak bonding with the mortar [10]. The untreated miscanthus increases the air voids of the mortar, resulting in a reduction in mechanical strength.  The cross-sections and SEM images of the miscanthus mortar are shown in Figure 9. For the M-0 mixture, a small amount of mortar is observed on the smooth external surface of the miscanthus (Figure 9a), indicating the smooth external surface of the miscanthus is difficult to form a good bond with the mortar. However, for the M-P mixture, the parenchyma structure of the miscanthus is filled with mortar and tightly embedded in the mortar (Figure 9b), the infiltrated mortar in the parenchyma structure is bonded together, which is beneficial to the improvement of mechanical strength of the mortar.

Improvement mechanism of strength
Microcracks are usually observed in the ITZ of the untreated bio-based aggregate, such as apricot shell [33], wood [34] and oil palm shell [35], etc. The weak bond between the bio-based aggregate and the mortar significantly affects the mechanical strength of bio-based concrete. As shown in Figure 10, the crack appeared between the smooth surface of the untreated miscanthus and the mortar (Figure 10a), and the crack width was about 25-30 lm. However, the fresh mortar can penetrate and fill the cavity of the miscanthus due to the high porosity of the parenchyma structure. The heat-treated miscanthus not only has a rougher surface but also increases the cracking of the miscanthus. Therefore, more surface cracks and cavities are filled with the mortar (Figure 10b), the ITZ may be improved owing to better adhesion between the mortar-miscanthus interface, resulting in an improved mechanical strength. The size of the long (short) fibre is significantly thinner (80%-90%) and smaller (50%-86.7%) than the untreated miscanthus, the mortar containing long (short) fibre had small cracks with a width   of 5-10 lm in the ITZ (Figure 10c). The irregular cavities near the parenchyma surface are easily filled with fresh mortar (Figure 10d) and the powdery miscanthus is tightly embedded in the mortar, which results in a good interface. The flexural failure mechanism of miscanthus mortar is proposed and shown in Figure 11. The smooth surface of natural fibre tends to produce weak bonding with mortar, which results in that the fibre is easily pulled out without stress transfer [17]. When the crack propagates to the untreated miscanthus fibre, it is more easily pulled out due to the weak fibre bridging effect (Figure 11a). For heat treatment, an increase in the surface roughness of the miscanthus and the adhesion to the mortar occurs, which results in the heat-treated miscanthus is more difficult to be pulled out from the mortar, and thus the crack passes across the heat-treated fibre (Figure 11b). The long miscanthus fibre can stop the growth of cracks thanks to the crack bridging effect [36] (Figure 11c), which results in a   significant increase in the flexural strength. However, the short fibre has limited ability to capture cracks compared to long miscanthus fibre. When the crack reaches the short fibre, the crack that is adjacent to the short fibre easily penetrates through the macroscopic crack (Figure 11d). Because of the miscanthus powder has a good bond with the mortar, and when the damage of mortar, the crack passes through the low-strength parenchyma structure (Figure 11e). Therefore, it can be concluded that the longfibre miscanthus can be used to significantly improve the flexural strength of mortar, as compared to the direct use of the untreated miscanthus.

Microstructure
The SEM micrographs of the surface texture and the ITZ of the miscanthus are shown in Figure 12. The results show that the mortar is present on the longitudinal texture of the untreated miscanthus and a small amount of mortar is observed on the surface (M-0). Some surfaces of heattreated miscanthus are covered with mortar (M-4). For long fibre, a smooth cross-section is observed on the surface of the mortar when the miscanthus is pulled out from the mortar (M-LF). It is clear to see that the crack occurs at the ITZ between the untreated miscanthus and the mortar (M-0). However, a good bond is observed at the interface between the heat-treated miscanthus and the mortar (M-4). The interface between the thin long miscanthus fibre and the mortar also has the crack, but the crack is smaller than the untreated miscanthus (M-LF).
The crack development process of bio-based miscanthus mortar is shown in Figure 13. The results show that the failure of mortar depends on the characteristics of the miscanthus, lightweight aggregate strength, as well as interfacial adhesion between the miscanthus and the mortar. The microscopic pores easily appear on the surface of the mortar around the miscanthus. The crack is developed along with the weak bonding interface under external load  and the low-strength miscanthus is also penetrated by the crack. When the crack passes through the lightweight aggregate, the failure of mortar occurs. Therefore, an effective method to improve the mechanical strength of the miscanthus mortar is to increase the bonding ability between the miscanthus and the mortar by heat treatment and physical treatment.

Drying shrinkage and mass loss
The drying shrinkage and mass loss of mortar are shown in Figure 14. The results show that the treated miscanthus significantly decreases the drying shrinkage and mass loss of the miscanthus mortar. Moreover, most of the drying shrinkage and mass loss of the miscanthus mortar happen within the first two weeks. This is due to the high water absorption and porosity of the miscanthus mortar, which results in a dramatic reduction in the relative humidity [37]. At 90 days, the drying shrinkage of the M-LF and M-P mixtures are 831 le and 788 le, respectively, which are reduced by 21% and 25%, respectively, compared to the M-0 mixture. Previous studies show that the drying shrinkage of oil palm shell concrete [38] and wood sand concrete [39] at 90days are about 450-550 le and 1200-1900 le, respectively. Therefore, the drying shrinkage of the miscanthus mortar in this study is acceptable compared to those bio-based concretes.
The drying shrinkage is generally caused by the loss of water in the capillary from the interior of concrete [40][41][42], which is related to relative humidity [43,44] and porosity [45,46]. Under the same conditions, low porosity concrete usually has less drying shrinkage [47]. The large particle aggregates are prone to dry shrinkage than small particle aggregates [48]. Therefore, mortar containing powdery miscanthus has a smaller particle size and less porosity than mortar containing untreated miscanthus, which results in a significant reduction in the drying shrinkage.

Relationship between mass loss and drying shrinkage
The relative humidity inside the concrete may affect the drying shrinkage [45]. The mass loss of concrete can be used to evaluate relative humidity [40], especially for the high water absorption aggregate [49]. As shown in Figure 15, the relationship between drying shrinkage and mass loss can be divided into three stages. In the first stage, the mass loss increases significantly with a small drying shrinkage due to the rapid loss of free water from the larger pores of the miscanthus mortar. The treated miscanthus reduces the mass loss of the miscanthus mortar in this stage because of the reduction in porosity of mortar. In the second stage, a good linear relationship is observed between drying shrinkage and mass loss. The similar trend is observed in other previous studies [40,43,47]. The drying shrinkage of concrete increases with the mass loss increases [50]. This is attributed to the decrease in the relative humidity in the internal capillary results in the increase in drying shrinkage. In the third stage, the mass loss of mortar is maintained at a steady-state, while the dry shrinkage rate is gradually reduced [45].

Conclusions
The organic matter and physical properties (size and shape, etc.) of miscanthus fibre have negative effects on the performance of bio-based miscanthus mortar. In order to produce more sustainable miscanthus mortar, the effects of heat-treatment, size and shape of the miscanthus on the performance of miscanthus mortar are investigated in this study. Heat treatment and ball milling methods are used to modify miscanthus fibre. The physical properties,  mechanical strength, microstructure and drying shrinkage of bio-based miscanthus mortar are investigated. The following conclusions can be drawn: 1. The heat treatment significantly reduces the density of the miscanthus fibre and increases the water absorption, which is not recommended for the treatment of miscanthus. After heat treatment, the crack occurs on the surface of the miscanthus and the fragment is peeled off from the surface. The short fibre (0.4-1.5 cm) and long fibre (2-3 cm) reduce the water absorption of the miscanthus. 2. The treated miscanthus significantly decreases the density, water absorption, porosity and thermal conductivity of the mortar. After ball milling, the small particle of the miscanthus is more easily wrapped by the mortar, which results in the decrease in the water absorption and porosity of the M-P mixture. 3. The treated miscanthus significantly improves the compressive strength of the mortar. The irregular cavities of the parenchyma structure of the powdery miscanthus are easily filled with fresh mortar and tightly embedded in the mortar, which results in an enhanced bonding interface. Moreover, the long fibre miscanthus has a better fibre-bridging effect than other forms of the miscanthus. 4. Powdery miscanthus and long fibre miscanthus are superior in reducing the drying shrinkage, thermal conductivity and improving the mechanical strength of the miscanthus mortar, which are the recommended forms for applying miscanthus in sustainable bio-based cement mortar.