Due to economic issues, Senegal faces a major challenge in providing decent housing for all applicants. There is currently a housing deficit estimated at 125,000 units [1]. For decades, the construction industry has focused on developing new materials in order to minimize the environmental impact and improve building insulation envelopes.

In the building industry intended for residential use, the bricks designed with Portland cement are systematically chosen. For those bricks, the value chain from production to implementation on the various sites, requires significant resources and logistics. Almost all of the masonry in today’s buildings in the country is done with a combination of concrete, bricks and plaster consisting of cement, sand, gravel and water. The depletion of conventional aggregate deposits, the high construction costs as well as the negative effects of the cement industry on the environment are so many problems to be solved for a sustainable development.

The objective of this study is to propose an alternative to the use of Portland cement and crushed gravel for the construction of bricks by developing a sustainable method with the use of clay materials from Thicky in Thiès district. This area is well known for its significant potential of clay materials, for the production of fired clay bricks.

This work’s aim is, then, to enhance the value of local clay raw materials by developing widely distributed ceramic products.

The drilling and public works company (Société de Forage et de Travaux Publics (SFTP)) holds a prospecting authorization in this area with the goal of promoting the development of construction products based on local clay raw materials. SFTP carried out geophysical and geotechnical field studies which gave satisfactory results in terms of ceramic quantity and quality.

The production of bricks was made possible with the involvement of the SOFAMAC Company which optimized the use of yellow clays and gray clays for the production of several types of fired clay bricks whose physical, mechanical and thermal characteristics meet the standards in use.

The comparative study between a construction with classic concrete blocks in Portland cement and a construction with fired clay bricks has given results consisting in a lower cost, better preservation of the environment, greater thermal comfort and a considerable social impact.

The enhancement of thermal properties may strongly impact on the energy performance of the building, and the lightweight bricks for infill walls reduce building structural requirements [2].

The demands of the residential sector account for about 26.5% of the total energy consumed in the EU [3], with a large proportion of this energy used for heating, ventilating and air-conditioning.

The village of Thicky is located in Diass commune with approximately 34,829 inhabitants. The location of the study area (Figure 1) is characterized by rugged

terrains with a geomorphology consisting of small hills. The altitudes in the sector vary from 42 to 108 m. Located at 4 km west of the national road (RN1 Dakar-Kaolack) between the cities of Diass and Sindia, the Thicky area is characterized by clay hills.

Hydrographically, the area is crossed by small intermittent streams which flow at its pic of the rainy season. The rainy season lasts from July to September with rainfall of around 500 mm/year. The climate is Sudano-sahelian and the temperatures vary between 20˚C and 40˚C.

The clays and sands of Thicky belong to the Maastrichtian era and constitute, in this region, the stratigraphic level of the summit of the Diass Horst. Their facies are equivalent to the detrital levels (sands, sandstones) of the central part of the Horst [4]. Argillaceous series have long been known around the village of Thicky in the Ndangdang quarry, to the south. They belong to the undifferentiated Upper Cretaceous.

The chemical studies, carried out on the clay collected from various stacked piles, gave the results shown in Table 4.

Table 4 shows that Thicky clays contain three main chemical elements which are SiO₂, Al₂O₃, and Fe₂O₃. The other chemical elements identified have varying contents that do not exceed 2% with water content at around 5%. According to the analysis carried out, SiO₂ being unbound to Al₂O₃ decreases the binding power of clays, increases the porosity of the bricks once fired and lowers their solidity.

Alumina is an element which strengthens the plasticity of clay, and gives a mechanically resistant product. It also allows the products to withstand high temperatures. To have good fired products quality, the alumina content must vary between 10 and 30% what we have with Thicky clay. In contrast, CaO causes cracking in raw products exposed to air. Excess of CaO can cause swelling during firing and bricks breaking.

The dark red color reflects a higher Fe₂O₃ and MgO content in the clay, but a large amount of iron lowers its refractoriness.

Na₂O and K₂O lower the sintering temperature of the clay. The sintering constitutes the whole process of shrinkage, density and resistance increases of clays during the firing process.

Table 5 gives the water content of the two types of clays. An average of 5.45% is obtained.

The obtained results of the density tests are shown in Table 6. They show that the gray colored clays are less dense than the yellow colored ones.

The particle size curve show that the gray clays are less coarse than the yellow clays. Gray clays and yellow clays contain a fairly large amount of fine particles, of about 95% of the total mass.

According to the distribution of the granular fractions, the results obtained

indicate that these clays consist mainly of 5% of clay fraction, 9% of fine silt, 22% of medium silts, 60% of coarse silts, and 4% of sand.

A slight variation was observed in particle size between the two types of clays (Figure 19).

The Atterberg limits results obtained on gray clays and yellow clays as well as on the mixtures between the two clays are presented in Table 7.

The plasticity index values vary between 20% and 40%. However, the yellow clays are less plastic than the gray ones. This plasticity decreases as the mass of the yellow clay increases in the mixture. This fact allows the yellow clays to be used as a degreaser in the mixture.

The plotting of the different values of Ip and ωL in Casagrande diagram [20] shows that the gray clays are considered as very plastic inorganic clays and the yellow clays as moderately plastic inorganic clays. However, their mixtures at the proportions by mass indicated in Table 9 lie between the two types of behavior.

The limestone content values found on gray clays and yellow clays as well as in the mixtures are presented in Table 8.

The different types of clays analyzed are classified as non-calcareous materials,

since their calcium carbonate contents do not exceed 10%. These results obtained constitute an advantage for the fired clay bricks production since a high content of limestone makes cracks appear on the final product.

The results obtained for the methylene blue and the grain size tests are given in Table 9. According to standard, the activity values obtained (A), only for the 100% of GC and 100% of YC, do not exceed 3. This shows that the clays tested are in the inactive range of clays.

The tests carried out suggest putting an emphasis on the grain size distribution of the clay, which has an influence on the stability of the structure. The values of Ip and ωL also allow us to classify materials by their plasticity and their consistency. Gray clay appeared to be more plastic than yellow clay, but they all have a hard consistency. The influence of grain size distribution is also evident on the kind of bricks obtained.

All the results obtained prompted the choice to produce fired clay bricks with a mixture of 50% of gray clay and 50% of yellow clay at a temperature of 950˚C for six (6) hours. This choice allowed the company to use now in its process the yellow clays which had previously been deposited in favor of the gray clays which were overexploited.

For the bricks manufacturing, the physical criteria and aspects which allow the validation of fired clay bricks manufactured industrially for construction are summarized in Table 10.

The bricks produced with 50% of gray clay and 50% of yellow clay, fired at 950˚C for 5 hours do not show any signs of bursting or any deformation observed. They present straight edges and uniform surfaces. The flexion measured between two parallel edges varies between 1 and 3 millimeters. The measured shrinkage values vary between 5.36% and 7.62%. These results give very acceptable appearance characteristics for the products manufactured.

The results obtained for the water absorption values on the bricks studied are shown in Table 11. They were found smaller than the tolerance of 15% provided by standard NF P 13-301. This suggests a good water absorption behavior for the

studied bricks. Figure 20 gives an example of a soaking brick in water.

A lower value of the water absorption capacity is always desired for good quality of clay bricks [21].

For the capillarity absorption of the bricks, as soon as this time has elapsed, the water raising by capillarity is measured from the marking line with a graduated ruler (Figure 21).

The capillarity absorption values obtained for the different types of fired clay bricks according to the standard are given in Table 12.

According to the results obtained on the 20 types of fired clay bricks produced by SOFAMAC, the capillarity absorption rates belong to the class of very poorly absorbent bricks according to standard NF EN 772-11.

The results of loss on ignition obtained after the bricks firing are shown in Table 13.

For the 20 types of bricks submitted to the test, the losses on ignition values are less than 10%. Johari et al. [22] found a LOI of 8.75% for the clay for manufacturing fired clay brick mixed with waste rice husk ash.

The maximum values allowed for a good quality of brick according to the standards ASTM C618 (1980) [23] are respectively 10% and 15%. So the values obtained comply with the standards and remain acceptable in order to avoid a

great deformation of the different bricks produced.

For the mechanical tests, if the laying face during the test is perpendicular to the perforations of the brick, the area occupied by those perforations is to be deduced in the calculations. To do this, a sand of a bulk density ρ = 1.5 g∙cm⁻³ is filled in the cells of the brick according to its laying direction. Once the cells of the brick are filled, the sand is weighed. The volume of sand extracted from the cells of the brick is given by the ratio of its mass to its bulk density. Knowing the height of the cells which is the same as the brick, the area occupied by the cells on the laying face would then be the ratio of the volume by the height of the bricks (Figure 22).

The results of brick measurements, failure loads, and compressive strength value are compiled in Table 14. The test is carried out using a classic concrete press, operating with a hydraulic pressure system which moves the lower part upwards until the brick breaks (Figure 23).

The compressive strength of the bricks mainly depends on the mineral structure, which strongly depends on the raw materials, drying and firing process (e.g. increasing/decreasing temperature rates, soaking time, and moisture content [24]. The sintering and mechanical properties of the clay brick samples depend on the optimum conditions maintained at the time of their manufacturing.

To meet the requirements of standards NF DTU 20.1 [25] and NF DTU 20.13 [26], the compressive strength average specifications are given according to the following rules:

· For fired clay bricks with horizontal perforations, the average compressive strength must be greater than or equal to 2.8 N∙mm⁻²;

· For fired clay bricks with vertical perforations, the average compressive strength must be greater than or equal to 4 N∙mm⁻²;

· For other bricks, the average compressive strength must be greater than or equal to 10 N∙mm⁻².

According to the requirements of these standards, all the bricks with horizontal perforations tested (Amsa 4, Amsa 4 bis and BR200) show satisfactory results.

Bricks with vertical perforations have satisfactory results and are much better than bricks with horizontal perforations. This is due to the fact that the axial stresses applied on bricks with vertical perforations are absorbed over their entire height from the total area of the network of partitions forming the bricks cells, while for bricks with horizontal perforations, the stress is applied along a surface with a large void below.

The thermal characterization of bricks method allows the thermal conductivity and the thermal effusivity of the material to be determined in a short time (Figure 24).

Knowing the conductivity of the material which is 0.427 W∙m⁻¹∙K⁻¹ and that of unventilated air which is 0.024 W∙m⁻¹∙K⁻¹, it’s possible to determine both the conductivity and the resistivity of the cellular wall brick. For illustration, we have chosen two types of bricks (BR200 and BS200) and the results are shown in Table 15.

In comparison with the usual bricks made in cement in Senegal whose thermal conductivity values vary between 0.47 and 1.2 W∙m⁻¹∙K⁻¹, the use of fired clay bricks for construction present more satisfactory results and must be favored for better sustainable development.

In light of the various fieldwork and laboratory tests carried out, the area of Thicky has great potential for gray clays and yellow clays. Geophysical surveys and geotechnical tests carried out on the area have shown that the clay formations locally change to sandy clays or even clayey sands. However, these sandy-clay formations can locally include clay but most often at great depth, more than 10 m below the surface.

Chemical analyses of the clay materials show that they contain mainly SiO₂, Al₂O₃, and Fe₂O₃.

The grain size distribution shows a composition of 5% of clays, 9% of fine silts, 22% of medium silts, 60% of coarse silts, and 4% of sands. The gray clays show slight variations compared to the yellow ones with natural content of water of 5.09 and 5.82% respectively. The plasticity index varies between 24% and 30% with a low level of limestone.

The shrinkages measured on the manufactured bricks vary between 5.36% and 7.62% for water absorption between 6.4% and 11.9%. The capillarity absorption of water oscillates between 0.01% and 0.12% and the loss on ignition values varying between 7.02% and 10%. The compression tests on the bricks give satisfactory results depending on the type of brick tested.

In terms of thermal behavior, the tests performed on the fired clay brick give a thermal conductivity and effusivity of 0.42 W∙m⁻¹∙K⁻¹ and 746.47 J∙K⁻¹∙m⁻²∙s^−1/2 respectively.

The quality of clays used in the brick industry varies due to chemical, mineralogical, grain size and technological properties. The diversity of compositions and the heterogeneous nature of raw materials cause variations in fired product characteristics. The results obtained in this study show that the fired clay brick industry has been highlighted as an optimal sector for developing new materials in order to minimize environmental impact and improve building insulation envelopes.

This research project was supported by SFTP MINING SN Sarl (Société de Forage et de Travaux Publics), and SOFAMAC (Société de Fabrication des Matériaux de Construction).

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Diao, I., Diagne, M. and Dia, I. (2021) Characterization of Fired Clay Bricks for an Economic Contribution of the Exploitation of Thicky Clay Deposit. Materials Sciences and Applications, 12, 389-416. https://doi.org/10.4236/msa.2021.129027