Abstract

The use of raw earth materials reduces the environmental impact of buildings, naturally regulates humidity and improves thermal comfort inside homes. This is why in recent years there has been a renewed interest in Senegal, for these so-called traditional materials but especially for compressed earth blocks (CEB). But the use of these blocks faces a number of problems including low tensile strength, shrinkage, cracking and lack of durability. The incorporation of Typha, which is an invasive plant in the rivers and lakes of northern Senegal, can help strengthen the matrix of these blocks. This article deals with the influence of crushed Typha on the mechanical behavior of laterite-based blocks. Several formulations based on Laterite, Typha and cement were made and CEB made with a CINVA-RAM type press. The mechanical characteristics were obtained from tensile, compression and bending tests on blocks containing between 0.5 and 1.5% Typha and 10% cement. The results show that Typha reduces the resistance of the blocks but within acceptable limits for the construction of non-load-bearing walls.

1. Introduction

Global warming, the depletion of fossil resources and the economic crisis are prompting construction players to turn to local and bio-sourced products. Indeed, the construction sector is responsible for more than 36% of total energy consumption and alone emits 39% of greenhouse gas emissions Figure 1. The cement industry alone causes between 5 to 7% of CO2 emissions worldwide Figure 2 In addition, a lot of waste is generated by this sector. This is the reason why in recent years there has been a renewed interest in our country, for these so-called traditional materials but especially for compressed earth blocks (CEB). Indeed, several works (TER stations, schools, hotels, etc.) are made in Senegal with this product, the use of which is unfortunately accompanied by shrinkage, cracking and low tensile strength. The incorporation of Typha in the material can overcome these drawbacks and fight against the proliferation of this plant which has become invasive in the River Valley. The use of aggregates derived from vegetable plants in the manufacture of building materials can contribute to effectively reducing greenhouse gas emissions thanks to their capacities to capture CO2 Figure 3 Most of the studies carried out on the addition of Typha in cementitious or earthen materials are oriented towards thermal insulation. This study, for its part, attempts to see its impact on the reinforcement of the cementitious matrix. Total particle size, Atterberg limits and methylene blue tests are carried out on the laterite and the particle size of the crushed Typha, its apparent density as well as its absorption rate are determined. The compressive, tensile and flexural strengths are determined from blocks of different formulations, produced with a CINVA-RAM type manual press.

2. Equipment and materials

The bricks used in this study were made using a manual press (Figure 1) of the CINVA-RAM type made with the help of local craftsmen.

The characteristics of the press are as follows:

• Force exerted by the operator: 60 daN

• Reduction rate: 1.7

• Compaction pressure: 2 MPa.

The best presses provide a pressure between 2 and 6 MPa, although lower pressures may suffice provided you obtain at least 0.7 MPa ⁴.

The laterite used comes from the lateritic quarry of Sindia, located in the region of Thiès, more precisely in the department of Mbour (Figure 2). It is chosen on the basis of its availability and abundance in the region.

The particle size analysis of the laterite shows that the curve is in the spindle of the soils suitable for use in CEB according to the XP P13-901 standard (Figure 3).

It contains the following percentages (Table 1):

This soil is not too clayey (% 2μm < 30%) which will avoid the risk of shrinkage cracking weakening the blocks.

The Atterberg limits (Table 2) and the classification on the Casagrande diagram of fine soils (Figure 4) show that the laterite of Sindia is a low plastic clay.

The results of the methylene blue test of the Sindia laterite shown below (Table ) show that it is a low plastic silty soil.

Sindia laterite is found in the spindle of soils suitable, according to their plasticity and liquidity indices, to be used in CEB according to the XP P13-901 standard (Figure 5).

The normal Proctor test of laterite gives an optimum water content of 13.4% for a maximum density of 1.915 t/m3.

Typha australis Figure 6 is defined as a genus of monocotyledonous plants commonly called cattails, widespread in aquatic or humid environments (rivers, lakes, backwaters, canals, etc.) at water depths not exceeding 1.5 m. It is found in both tropical and Mediterranean areas Figure 6.

Typha produces seeds when mature. The inflorescence has the shape of a candle 15 to 20 cm long, brown in color when ripe, inside which the flowers are very numerous and tight. Each candle can contain between 20,000 and 700,000 seeds hence its high reproductive capacityFigure 7

The particle size is obtained by dry mechanical sieving, using standard square-mesh sieves, from a crushed sample (Figure 7) and previously passed through a 10-mesh sieve.

The results show the coarse nature of the plant particles used, indeed a refusal at the 2 mm sieve equal to 77.20% is observed (Figure 8).

The bulk density of Typha aggregates is 52.88 kg/m3. A significant mass absorption of water by immersion of 230% in 24 h was observed for ground Typha fibres (Figure 9). This hydrophone character also observed for Kenaf fibers ⁸ and flax straw ⁹ is due to the porosity and the presence of hemicellulose in these plants.

Different mixtures were prepared (Table 4) in order to estimate the influence of the mass of Typha on the mechanical behavior of CEB. Blocks were made from four formulations (S90C10; S89.5C10T0.5; S89C10T1 and S88.5C10T1.5).

All formulations contain 10 % cement.

For each composition, 3 blocks of 29.5×14×8 cm3 (Figure 10) were prepared to measure the mechanical characteristics. After the tests, an average value was retained.

3. Results and discussions

The mechanical tests were carried out on the CEB. The compression tests were carried out using a hydraulic press with a pressure force of up to 1500 kN and the splitting and bending tests on a press with a maximum force of 50 kN. The load is applied continuously and smoothly at a speed of 0.02 mm/s until failure.

The results of the tensile (Figure 11), compression (Figure 12) and 3-point bending (Figure 13) tests are shown below.

Tensile test results show a decrease in strength with the addition of Typha. In fact, it has a value of 0.28 MPa without Typha and drops to 0.14 MPa with 0.5% Typha; 0.12 MPa with 1% fiber and 0.14 MPa for 1.5% addition. Typha is found to cause BTC to lose more than 50% of its tensile strength.

The compressive strength of blocks without Typha is 4.36 MPa, which is well above the minimum strength of 2 MPa set by most standards. That of the Typha reinforced blocks goes from 1.26 MPa for 0.5% fiber and to 1.31 MPa for 1.5%. This gives a resistance loss of more than 68%.

The results of the bending test show a decrease in strength as the amount of fiber increases. The resistance increases from 0.44 MPa with 0.5% Typha to 0.31 MPa for 1.5% addition. This gives a resistance loss of more than 57%.

These results show that the incorporation of Typha fibers reduces the mechanical characteristics of the blocks. Indeed, the cementitious matrix based on hydraulic binder corresponds to an assembly of solid phases, mainly hydrates. The entanglement of these hydrates ensures the cohesion of the materials, and gives this matrix the role of a real glue, at the origin of sometimes very high mechanical performance.

However, Typha being very porous, its incorporation into the cementitious matrix increases the proportion of voids and at the same time constitutes an obstacle to the deployment of chemical bonds and therefore reduces the resistance of the material.

The compressive strength values obtained remain modest overall because Houben and Guillaud, 1994 ¹⁰ recommended at least 2 MPa for blocks stabilized with cement. However, they may be sufficient for a one-storey building or a building with non-bearing walls.

Regarding the flexural strength, the addition of 0.5 and 1% of Typha complies with the American standard ¹¹ which reports that the minimum value of the flexural strength 3 points must be greater than 0.34 MPa for a BTC to be suitable for use in construction.

In addition, the fibers are used for the purpose of preventing the propagation of cracks.

4. Conclusion

This work shows that reinforcing the blocks with Typha results in modest mechanical resistance. This means that these blocks can be used for certain ground-floor buildings, buildings with non-load-bearing walls or for separating walls. The incorporation of this fiber in earthen construction materials has a real interest because it participates in the transformation of Typha and thus reduces the nuisances linked to its development.

In perspective, a thermal characterization of the compressed and reinforced earth blocks of Typha will be carried out to evaluate the variation of the parameters according to the different formulations. As well as a treatment of Typha fibers is envisaged to reduce their mass absorption.

References