Improving insulation and energy efficiency in arid climate buildings with palm fiber-reinforced adob

2.78. t/m3

89% of the grains 89% are of fine to medium size (0.1 mm - 2 mm)

2.59. g/cm3 51%<0.08

Adobe Mixing Ratios To evaluate different sample mixtures, we carefully mixed the clay soil by hand with various parts of drinking water until we obtained a homogeneous adobe mixture. The percentage of water in the mixture varied between 23% and 25%, corresponding to a quantity of water ranging from 160 g to 1850 g. Seventeen different adobe mixes were prepared for this study; we compared an ordinary adobe brick mix without any additives (0%) to sixteen mixes containing four rates of natural fiber (0.25%, 0.50%, 0.75%, and 1% by weight of dry fiber) and four different fiber lengths (25 mm, 50 mm, 75 mm, and 100 mm). All data are shown in Table.3. The name of the sample includes two numbers, the first indicating the percentage by weight of fibers in the adobe and the second indicating the length of the fibers used in the preparation of the mixture. For each mix, three identical samples were prepared in order to repeat the tests three times. In total, 51 samples were made for each type of test, both thermal and mechanical Figure 3. Figure 4 shows two scanning electron microscopy (SEM) micrographs of fiber-reinforced adobe. The first image (a) reveals the composition of adobe made from dune sand and fibers. Sand particles, which have retained their

Figure 3. sample preparation a: adobe, b: palm fiber, c: samples [photo by author].

Figure 4. Image according to SEM. a: adobe fiber-reinforced. b: Fiber, x200 µm.

characteristic granular morphology, are predominantly larger than the fibers. This granulometric distribution influences the density, porosity and mechanical properties of the composite material. The second micrograph focuses on the fiber-matrix interface, showing significant roughening of the fiber surface. This morphological feature is crucial to the mechanical properties of the composite. As indicated in [46], increased roughness promotes better mechanical anchorage with the surrounding soil particles. This microscopic interlocking phenomenon improves fiber-matrix adhesion, increases resistance to raveling, enables better stress distribution and contributes to an increase in the material’s toughness. These microscopic observations provide valuable insights into the reinforcement mechanisms at work in fiber-reinforced adobe. Experimental Tests Mechanical test Uniaxial compression testing was carried out on the prepared samples to determine their compressive strength. Tests

of mechanical compressive strength were conducted according to EN:101511 [47], a loading speed of 0.01 MPa/s was selected. each specimen was subjected to an increasing load at constant speed until it failed, as illustrated in Figure 5.b. The flexural strength of the samples was determined in accordance with European standard EN1015-11 [48]. The test protocol involves applying a concentrated load to the center of a prismatic specimen, supported at both ends, as shown in Figure 4a. This configuration, known as a three-point bending test, creates a maximum bending moment at the center of the specimen. For our study, we used specimens of standard dimensions 40x40x160 mm³. Thermal properties We determined the thermal characteristics of the samples by conducting tests at the University of Adrar using an HM150 apparatus figure 6. Employs the thermal flow meter technique by the following standards: ASTM C518, ISO 8301, and DIN EN 12667 [49, 50]. We subjected the samples, measuring 400 × 400 × 40 mm³, to controlled measurements. (Fig. 8)

Figure 5. Experimental tests: (a) Bending test, (b) Compression test, and (c) Specimen failure after testing.

Building simulation To evaluate the impact of fiber-reinforced adobe on thermal insulation by selecting a typical building model from the Saharan region (Fig. 7). We incorporated fiber-reinforced adobe as an insulating layer on the ceiling and modeled the building’s thermal performance using TRNSYS 18 (Tab.4). The simulation allowed us to assess how fiber-reinforced adobe helps maintain

stable indoor temperatures in the extreme climate of the Saharan region. Two floor variants were investigated in this study. The first represents the standard waterproofing system commonly used in the Saharan region, while the second variant incorporates a fiber-reinforced adobe layer, as detailed in the table 5.

1.5. cm External

Plaster 15 cm Brick 5 cm Air Gap 10 cm Brick 2 cm Internal Plaster

2.5. cm Mortar Bed

10 cm Sand 3 cm Mortar 5 cm Reinforced Concrete 16 cm Concrete Slab 2 cm Plaster

2.5. cm Mortar Bed

13 cm Fiber-Reinforced Adobe 5 cm Reinforced Concrete 16 cm Concrete Slab 2 cm Plaster

Figure 8. Components of thermal seals. V1: Saharan seal. V2: Sealing with fibered adobe.

Lighting gains based on lamp type are presented as follows: The figure 9 illustrates the percentage of occupancy intensity, equipment use, and lighting in a Saharan building during a typical day, from 1 a.m. to midnight. Occupancy levels fluctuate, peaking during daylight hours and decreasing at night. Equipment use increases with occupancy. Lighting use follows a similar trend, increasing as daylight diminishes and peaking in the evening. Energy Needs We assessed the cooling energy demand during summer to maintain indoor conditions at 27 °C and 50% relative humidity, and the heating energy demand in winter to maintain 20 °C. These comfort conditions are defined by the Algerian thermal regulation standard DTR C3.4. [51] Figure 9. Occupancy intensity. Internal Gains The sensible power dissipated per person is estimated at 100 W/person according to the current standards (DTR34) [51]

Research Uncertainty and Limitations This study presents certain limitations and uncertainties. The hypothesis of a uniform distribution of palm fibers simplifies reality. However, ensures a replicated experimental framework. We conducted our tests with three replicates per mixture, thereby reducing the influence of random errors, although total variability may not be fully accounted

for. Modeling has taken into account only floor variation, which highlights its specific role but does not reflect all actual conditions. Finally, the energy assessment is based on DTR regulatory comfort temperatures (25°C in summer, 20°C in winter), although occupant preferences may differ. These limitations serve to delineate the scope of the present study while simultaneously highlighting directions for future research.

19.11. MPa [54], and doum fiber achieved 19.91 MPa at 1%

[55]. Lavender straws, used at a higher dosage of 6%, yielded

3.9. MPa [56]. Sawdust fibers at 1% reached 8.11 MPa [57],

and neem straw at 2% attained 6.35 MPa [58]. These comparisons highlight that while palm fibers may not attain the very high compressive strengths of specific agricultural residues like crushed wheat straw or doum fiber, they still offer a viable and sustainable reinforcement, especially when dosage and fiber length are carefully optimised. Flexural Strength Figure 11 shows the flexural strength of adobe samples as a function of the dosage (0%, 0.25%, 0.5%, 0.75%, 1%) and length (25, 50, 75, 100 mm) of incorporated palm fibers, compared to a control sample without fibers.0% The results reveal a substantial improvement in flexural strength for all fiber dosages. The 1% dosage showed the most pronounced increase, ranging from 20% to 45%. The 0.75% dosage follows closely with an improvement ranging from 13% to 43%. The 0.5% dosage shows a moderate increase from 12% to 20%. Even the lowest dosage of 0.25% shows a positive increase, albeit more modest, from 4% to 20%. These data highlight the significant influence of palm fiber dosage on the flexural strength of adobe. Fiber length has an important role to play, particularly for the 1% dosage, where the effect is most noticeable. The addition of palm fibers considerably improves the bending strength of adobe. This improvement depends on both the dosage and the length of the fibers used. This

reinforcement not only increases mechanical strength, but also delays the appearance and propagation of cracks in the material. It is essential to stress that the homogeneity and uniform distribution of the fibers guarantees a consistent improvement in mechanical properties throughout the material. In our study, palm fiber–reinforced adobe achieved a flexural strength of up to 1.7 MPa, positioning it favorably among both natural and synthetic fiber reinforcements reported in the literature. For comparison, lower strengths have been reported for red millet fiber (0.17 MPa) [22], barley straw (0.28 MPa) [28], waste tire textile fiber (0.285 MPa) [59],, wool fiber (0.139 MPa) [60], eucalyptus pulp (0.45 MPa) [29], alfa fiber (0.488 MPa) [29], polypropylene fiber (0.83 MPa) [61], banana fiber (0.95 MPa) [61], sawdust fibers (0.4 MPa) [57], lavender straws (0.28 MPa) [56], neem straw at 2% (0.65 MPa) [58], doum fiber (0.412 MPa) [55], and crushed wheat straw (0.78 MPa) [54]. Palm fibers also compare closely with wheat long straw (1.42 MPa) [54], although they fall below alfa fiber in some cases (2.01 MPa) [38] and hemp fiber (3.11 MPa) [62]. These findings highlight palm fibers as a highly promising natural reinforcement for adobe, particularly in hot and arid regions, offering an effective and sustainable means of improving mechanical properties while supporting local resource use.

0.15. W/m·K for 0.5%, and the reduction further increased

to 0.2 W/m·K and 0.45 W/m·K for fiber contents of 0.75% and 1%, respectively. Compared to values reported in the literature for other natural fiber reinforcements, palm fibers show competitive thermal performance. For example, wheat long straw at a 2% dosage yielded a thermal conductivity of 0.411 W/m·K [54], and hemp shiv at a 6% dosage reached a much lower value of 0.2 W/m·K [63]. While hemp-based materials exhibit superior insulation, the use of palm fibers remains a sustainable and effective solution, especially in arid regions where such resources are abundant and locally available. These results clearly demonstrate that reinforcing adobe with palm fibers significantly enhances its thermal characteristics by effectively reducing its thermal conductivity. Figure 13 shows the variation in the specific heat capacity of the samples as a function of fiber content and length. Improvements of 1.56%, 5%, 7.81%, and 12.5% were recorded for fiber dosages of 0.25%, 0.50%, 0.75%, and 1%, respectively. These results demonstrate the positive effect of palm fibers on improving the specific heat capacity of adobe, a key parameter that plays an important role in thermal insulation and heat storage. Adobe with a higher specific heat can absorb more heat during the day without significantly raising their temperature. As a result, the indoor temperature increases more gradually during peak heat periods, effectively delaying or reducing the intensity of heat reaching the interior. This delay in temperature changes, known as thermal lag, leads to a more stable indoor temperature throughout the day.

Thermal Properties Figure 12 presents the results of the thermal conductivity tests conducted on adobe samples reinforced with varying percentages and lengths of palm fibers. An apparent decrease in thermal conductivity was observed, demonstrating the positive effect of palm fiber addition in enhancing the thermal insulation performance of adobe. The thermal conductivity dropped from 1.15 W/m·K (reference sample without fibers) to 0.65 W/m·K in the best-performing mix, which included 1% palm fiber with a length of 100 mm. Specifically, a reduction of

Thermal Insulation of The Building The variation in the internal temperature of the building for the two variants, compared to the external temperature

during a summer period, is illustrated in Figure 14. A significant daily temperature difference between day and night was observed, reaching up to 17°C, with a maximum temperature of 45°C, highlighting the severity of the climate. For Variant 1, with the Saharan sand-based waterproofing, the temperature difference between the exterior and interior does not exceed 3°C. In contrast, for Variant 2, with a floor waterproofing system incorporating fiber-reinforced adobe, the temperature difference reaches 7°C, representing an improvement of 133%.

Figure 15. variation in temperature on both sides of the floor.

Figure 15 shows the variation in temperature on both sides of the floor, external and internal, for the two variants. In Figure 15.a, we observed a difference between the temperatures on the two sides, with a notable daily variation. However, in Figure.15b, we recorded that the temperature on the internal side remains relatively independent of the temperature on the external side. The variation in the internal and external surface temperatures of the floor for the two variants during the period starting in August is presented in Figure 16. It was observed that the temperature on the internal side for Variant N°2(with adobe) figure 16a remains nearly stable, while for Variant N°1(Fig. 16.b), it fluctuates between 47°C and 38°C. In contrast, the temperature on the external side reaches up to 62°C, with a significant daily temperature difference of 33°C. This highlights the highly aggressive effect of the climate in arid and hot regions on construction materials, particularly cement-based products. Therefore, adobe presents an ideal solution for floor insulation in buildings, protecting against the effects of external temperatures. Energy Balance Figure 17 presents the energy needs for cooling (Fig. 17.a) and heating (Fig. 17.b) for two construction variants: V1, which uses sand, and V2, which incorporates fiber-reinforced adobe as the terrace sealing material. Regarding cooling needs, Figure 14. a shows that the summer period extends approximately six months, from May to October. However, the winter lasts around five months, from November to March. It shows the significant

Figure 16. variation in temperature on both sides of the floor in summer period.

thermal demand of the examined location, defined by an extended hot season, emphasizing the necessity for efficient building insulation.