Mortar Based on Dune Sand and Substitute Wood Sawdust: Physico-Mechanical Characterization and Relationship Between Properties in Young Age

The evolution of the current world forces us to rethink construction methods. Indeed, today, the construction sector consumes a significant amount of energy. It is responsible for about a quarter of carbon dioxide emissions, not to mention the depletion of non-renewable resources. This sector must therefore innovate to limit its impact on the environment while guaranteeing user comfort [1]. Several investigations have been attempted with the aim of using overabundant sand from the dunes in the construction sector, particularly in Algeria and Africa, which have been the subject of research [2].

The universal need to protect the environment and manage natural resources well requires establishing new laws and adapting new concepts. The recovery of natural materials and the recycling of waste are an effective means in the face of the economic and ecological constraints of recent years [3]. Faced with the context of environmental protection and like all industrial and household waste, waste from wood processing industries will have to be recovered and valued [4]. Many products already exist on the market, but knowledge in this field is still limited and studies must be carried out in order to better understand certain mechanisms and improve the properties of these materials [5].

The different results of the physical properties are grouped together in Table 3 and illustrated by figures ‘Figure 1’, ‘Figure 2’, ‘Figure 3 and Figure 4’.

Table 3. Effect of sawdust on the physical properties of mortar at a young age

1.png

Figure 1. Evolution of immersion absorption as a function of sawdust content at (7,14,21,28) days.

2.png

Figure 2. Evolution of porosity as a function of the sawdust content at (7,14,21,28) days

3.png

Figure 3. Evolution of the wet densities as a function of the sawdust content at (7,14,21,28) days

4.png

Figure 4. Evolution of dry densities as a function of the sawdust content at (7,14,21,28) days

3.1 Total immersion absorption and porosity

From “Figure 1” MS10% showed less absorption than MS0% at 7 and 28 days and moderately greater than MS0% at days 14 and 21, this decrease in absorption is due firstly to the presence of sawdust with their sizes larger than that of dune sand and secondly to the phenomenon of cement hydration and the composition of ettringites. On the other hand, the absorption of MS20% is always higher compared to other mortars except at 7 days it marked a slightly less absorption than that of MS0% at this age. Tend says that MS30% had the lowest absorption of other mortars at 7 and 28 days and greater than that of MS0% at 14 and 21 days.

From "Figure 2" MS10% and MS30% showed less porosity than MS0% on days 7-28. While MS20% scored less porosity than MS0% at 7 and 28 days to equal it at 14 days and score the greatest porosity at 21 days.

3.2 Wet and dry density

From 'Figure 3' The wet density of MS20% is always higher than those of other mortars except at 14 days it marked a wet density less than that of MS0% and greater than those of MS10% and MS30%. MS10% and MS30% mortars consistently scored less wet densities than MS0% and slightly higher than the latter at 21 days.

From "Figure 4" The dry densities of the three mortars (MS10%, MS20%, MS30%) marked consistently lower values than those of MS0%.

The relationships between early age strengths (compressive and tensile) and characteristic 28 days strengths can be influenced by the substitution of sand by sawdust. It has been observed through the results of these properties that they can present different values. In this part of the work, we explore the effect of sawdust content on these relationships at different ages, for compressive strengths and even for tensile strengths. These relationships between resistances are also situated in relation to those given by the regulations in force (BAEL [8], EC2 [9]).

• For the relationships between the compressive strengths at a young age and the characteristic strengths at 28 days, the following formulas Eq (1) were used; Eq (2) and Eq (3):

From « BAEL [8] »

$\mathrm{f}_{\mathrm{Cj}}=\frac{\mathrm{j}}{4,76+0,83 \mathrm{j}} \mathrm{f}_{\mathrm{C}_{28}}$              (1)

For f_c28 ≤ 40 MPa

From « EC2 [9] »

$\mathrm{f}_{\mathrm{cm}}(\mathrm{t})=\beta_{\mathrm{cc}}(\mathrm{t}) \mathrm{f}_{\mathrm{cm}}$          (2)

With $\quad \beta_{\mathrm{cc}}(\mathrm{t})=\exp \left[\mathrm{s}\left[1-\left(\frac{28}{\mathrm{t}}\right)^{1 / 2}\right]\right]$             (3)

Or

"s": is a coefficient which takes different values depending on the class of the cement, in which it is taken equal to 0.25 for our case (Cement CEM 42.5 N).

"f_cm": Average compressive strength at 28 days.

• And in the same way for the relations between tensile strengths at young age and characteristic strengths at 28 days.

•  For the relationships between compressive strengths and tensile strengths Eq (4) and Eq (5).

From « BAEL [8] »

$\mathrm{f}_{\mathrm{tj}}=0,6+0,06 \mathrm{f}_{\mathrm{Cj}}$              (4)

From « EC2 [9] »

$\mathrm{f}_{\mathrm{ti}}=0,30(\mathrm{fcj})^{2 / 3}$           (5)

5.1 Relationships between compressive strengths at young age and characteristic strengths at 28 days

The results are grouped together in the Table 5 below and shown diagrammatically in the Figures 7-9, which follow.

Table 5. Compressive strengths at (7, 14 and 21) days as a function of sawdust content

The values of the compressive strength at 7 days are higher than those of BAEL [8] and EC2 [9] for the different sawdust contents.

The values of the compressive strength at 14 days are higher than those of BAEL [8] and EC2 [9] except for the sawdust content of 30%.

The values of the compressive strength at 21 days are lower than those of BAEL [8] and EC2 [9] for the sawdust contents of 20% and 30% and higher for the other two contents 0% and 10%, but the most remarkable which is closer for the latter.

7.png

Figure 7. The relationships between the 7-day compressive strengths and the characteristic 28-day strengths as a function of the sawdust content

8.png

Figure 8. The relationships between the 14-day compressive strengths and the 28-day characteristic strengths as a function of the sawdust content

9.png

Figure 9. The relations between the compressive strengths at 21 days and the characteristic strengths at 28 days as a function of the sawdust content

5.2 Relationships between early tensile strengths and characteristic 28-day strengths

The results are grouped together in the Table 6 below and shown diagrammatically in the Figures 10-12 which follow.

Table 6. Tensile strengths at (7, 14 and 14) days as a function of sawdust content

10.png

Figure 10. The relationship between the tensile strengths at 7 days and the characteristic strengths at 28 days as a function of the sawdust content

11.png

Figure 11. The relationship between the tensile strengths at 14 days and the characteristic strengths at 28 days as a function of the sawdust content

The values of the tensile strength at 7 days are higher than those of BAEL [8] and EC2 [9] for the different sawdust contents.

The values of the tensile strength at 14 days are higher than those of BAEL [8] and EC2 [9] for the different sawdust contents especially at 0%.

12.png

Figure 12. The relationship between the tensile strengths at 21 days and the characteristic strengths at 28 days as a function of the sawdust content

The values of the tensile strength at 21 days are lower than those of BAEL [8] and EC2 [9] for the sawdust contents of 10%, 20% and 30% and higher for the content 0%.

5.3 The relationships between compressive strengths and tensile strengths

The results are grouped together in the Table 7 below and shown diagrammatically in the Figures 13-16 which follow.

The curves for the experimental results are trend lines. And the curves of the results calculated by the formulas of BAEL and EC2 are curves following these formulas.

Table 7. Compressive and tensile strengths as a function of sawdust content at (7, 14, 21 and 28) days

13.png

Figure 13. Relationship between compressive strengths and 7-day tensile strengths

14.png

Figure 14. Relationship between compressive strengths and tensile strengths at 14 days

The preceding curves show the Ts-Cs relationships for MSs with different sawdust content (0%, 10%, 20%, 30%) at 7, 14, 21 and 28 days. We notice that the differences between the regulatory curves and the experimental curves of the MS are very important with very acceptable regression qualities Ts-Cs (R2 = 0.9628, R2 = 0.7956, R2 = 0.9007 and R2 = 0.9974) respectfully at (7, 14, 21 and 28) days. These relationships always give overestimated values compared to those of the regulations.

It can be seen that the Rt-Rc relationships are influenced by the sawdust content at different ages.

15.png

Figure 15. Relations between compressive strengths and tensile strengths at 21 days

16.png

Figure 16. Relationship between compressive strengths and tensile strengths at 28 days

The authors thank the LGCH research laboratory at the University 8 May 1945 (Guelma) and the pedagogical laboratory of the civil and hydraulic engineering department (Guelma) for their technical support during the experimental work.