In this study, the basalt aggregates of grain size 0/3, 3/8, and 8/16 come from Diack

quarries located in the eastern limit of the Thiès Plateau, about 30 km from the city of Thiès. Diack’s basalt belongs to Miocene volcanism. Three textures have been identified for this material, namely, fine-grained, medium-grained, and coarse-grained one [12].

The sand was collected at the Beer borrow material source. It is mainly made up of silica sand in the form of coastal dunes, lagoon sediments, and red dunes dated to the Quaternary.

Limestone filler produced from calcareous rocks from Bandia quarries (consisting of a very hard yellowish sandstone limestone with a massive aspect) and sandstone filler from Toglou quarries (sedimentary formations dated to the Maastrichtian) are used in this study.

Litho-stratigraphic studies show that the Toglou quarries are made up of fine-grained siliceous cement sandstones. The deposit presents some heterogeneity marked by an alternance of hard and soft layers, covered by a lateritic cuirass [13]. Table 5 gives the specifications according to standard NF P 18-545 [14] as well as the grain sizes of the filler.

This method is one of the most used among the concrete composition calculation methods [15]. It enables to determine, according to the manœuvrability and strength criteria of the concrete defined in the specifications, the nature and the quantities of the components necessary to make one cubic meter of concrete.

For this study, CEM II/B-M 42.5 cement from Sococim Industries with a density (ρ_c) of 3.1 kg/liter was used. The cement quantity used is 350 kg/m³. The main parameters of the concrete used in this study are:

- the nominal strength in uniaxial compression at 28 days ( σ ′ n ) which is 30 MPa; the average compressive strength at 28 days targeted on site ( σ ′ 28 ) equal to the value of ( σ ′ n ) increased by 15%, that is: σ ′ 28 = 1.15 × σ ′ n = 34.5 MPa;

- An Abrams slump test value of A = 80 mm which characterizes the desired workability.

The Bolomey relation [16] that allows to determine the ratio between cement and water (C/E), is described by Equation (1).

σ ′ 28 = G × σ ′ c × ( C E − 0.5 ) (1)

where:

σ ′ 28 : average compressive strength desired (at 28 days) in MPa,

G : granular coefficient (0.6),

σ ′ : class of cement (MPa),

C : cement content in kg/m³,

E : water content on dry materials in liters for 1 m³,

So, the ratio C E = 1.565.

The grain size distribution of the aggregates used for the concrete and the partition curve of Figure 1 gives the different granular proportions. Figure 1 shows a composition of 58%, 8%, and 34% respectively for 8/16, 3/8, and 0/3 granular classes of the total dry volume of the aggregates.

Thus, the mass and volumetric proportions of the various components which should make up the theoretical cubic meter of fresh concrete are given in Table 6.

Theoretical bulk density of fresh concrete ρ_th = (2600/1000) = 2.600 kg/liter.

The particle size distribution curves of the basalt aggregates of 3/8 and 8/16 classes are respectively shown in Figure 4. Those of sand dune (0/1), basalt (0/3) and their mixture in equivalent proportion (50% of each), are shown in Figure 5.

The results of the geotechnical characterization of the aggregates are given in Table 8.

The respective particle size curves of the granular class 0/3 of basalt, limestone and sandstone are shown in Figure 6. These particle size distributions, carried

The index B designates the characteristics which meet the category B aggregates (NF P18-545 [14] ).

out by dry sieving, allow the determination of the quantity of fines (passing through a sieve of 0.063 mm) which can be obtained from this granular class (0/3) which is the smallest size particle produced in quarries in Senegal. It is this quantity that defines how many fillers can be produced. These grain size curves show that the percentage of passing through 0.063 mm sieve are 2%, 4% and 6% respectively for sandstone, limestone, and basalt. These percentages of fines obtained reflect the degree of hardness of these three geological materials.

After the sieving, respectively with 0.063, 0.125 and 1 mm of sieve diameter, the three fractions obtained are mixed in proportions specified to have the filler. Indeed, aiming to fill the microstructure of the concrete, the fillers were cut to a maximum diameter of 1 mm which is well between 0.125 and 2 mm.

Taking into account the measurements to be made after vibration, a volume of three (3) liters was chosen. The concrete components, which must correspond to this volume, serve as a reference formula from which we add limestone, basalt, and sandstone fillers in increasing proportions (2%, 4%, 6%, and 8%) compared to the cement content. Table 9 gives the details of sampling for determining the optimum filler addition.

Thus, once the sampling settled up, the test is carried out for the three types of fillers in order to know their effect on the concrete. Figure 7 shows the optimum for each type of filler. It is 4.2% for basalt, 3.8% for limestone and 2.3% for sandstone. Two (02) values framing the optima on the three different curves and the value of 5% for limestone were then used to know the behavior of the concrete beyond the optimum. Seven (7) formulas were then used to be compared to the reference formula (composition without filler).

Table 10 presents percentages of filler implemented in order to investigate the effect they would have on the physical, chemical, and mechanical properties of hydraulic concrete.

The optimization enables to define the quantities of fillers that can be incorporated into the microstructure of concrete without exceeding the cubic meter of concrete. It should also be noticed that these quantities are linked to the fineness (specific surface) of the filler as well as to their actual density.

The test is carried out in accordance with standard NF EN 12350-2 [17]. It consists in compacting by chipping the fresh concrete in a mold having the shape of a cone. When the cone is removed vertically, the slump test of the concrete allows its consistency to be measured. A batch of concrete for seven (7) cylindrical specimens of dimensions 160 mm in diameter and 320 mm in height is made for each given formula. The results obtained on the different formulas used are shown in Figure 8.

Figure 8 shows that the slum test decreases with the addition of filler. For formulas with the addition of basalt and limestone fillers, the slump test values are smaller to that of the reference formula. This could be explained by the fact that basalt and limestone generate much more fines than sandstone does because of their mineralogical composition. However, it is important to notice that, despite

the addition of filler, the concrete produced still remain in the slump class S2 of plastic consistency (from 50 to 90 mm with a tolerance of ±2 mm). The addition of filler, therefore, does not affect the need for water in the mixture.

The test is carried out according to standard NF EN 12390-2 [18]. Six (06) specimens are made to determine the unconfined compressive strength of concrete at 7 and 28 days (Figure 9).

Figure 10 gives the variation of the bulk density of the fresh concrete according to the addition of x (%) of filler.

The slight increases in density compared to that of the reference formula show that the fillers have been well incorporated into the concrete (its voids), hence the improvement in compactness. However, beyond the optimum for limestone

filler (5%), the decrease in density results in an increase in volume because the cubic meter of concrete is exceeded at this percentage.

Bleeding occurs when a freshly mixed cement-based material starts to settle. It is the phenomenon of exudation of the mixing water from concrete before it starts its setting (X P18-468) [19]. The bleeding and the water evaporation of concrete affect plastic shrinkage cracking.

This process is often due to an insufficiency of fines, an excess of vibration or high water content.

The total bleeding is expressed by the ratio RT (mm/min), and is calculated by Equation (4):

R T = E c totale V beton (4)

with: E c total = ∑ E i   and   V concrete = m 2 − m 1 D ,

Ec_total: total cumulative volume of water (ml),

V_concrete: volume of the concrete sample (l),

E_i: volume of water sampled (ml) at time t_i,

m₁: mass of container (g),

m₂: mass of sample and container (g) at the start of the test,

D: density of fresh concrete (kg/l),

R_T: total bleeding of the concrete (mm/min).

The curves for variation of bleeding E_i as a function of time (t) are given in Figure 11.

Figure 11 shows that the curve of the reference formula is above the curves of the formulas with addition of filler. The latter, being more or less overlapped,

show a natural variation in the quantities of water sampled (E_i) depending on the type, and quantity of filler. The curves show overall that the bleeding of the concrete is reduced by the addition of filler. Topsu and Elgun [20] show that concrete mixes containing high cement contents yielded minimum quantities of bleeding and concrete mixes containing more mixing water yielded the maximum amount of water evaporation.

Thus, the finer and more absorbent the filler, the more it reduces bleeding. The reduction in the bleeding of the concrete is a favorable consequence of the incorporation of filler in it because it allows stabilization of the concrete used. The filler is more absorbent because its incorporation into the concrete increases the specific surface.

Figure 12 gives the bleeding in a sample and the recovery of water taken.

The values of the total bleeding as well as their corresponding stabilization percentages are given in Table 11. These percentages are calculated according to the bleeding value of the reference formula (4.2 mm/min).

The percentages of stabilization are respectively 26% for basalt, 29% for limestone, and 36% for sandstone fillers. This is linked not only to their different water absorption coefficient at 24 hours (ωA24) but also to the kinetics of their water absorption because bleeding is measured within two hours after the preparation of the concrete. For Elyamany et al. [21], filler type has a significant effect on the segregation resistance and bleeding resistance of self-compacted concrete and flow-able concrete.

The test is carried out in accordance with standard NF EN 12390-3 [22]. The unconfined compressive strength of concrete is an important parameter in measuring the durability of concrete. It is measured at seven (7) and twenty-eight (28) days of concrete curing (NF P18-430-2/NF EN 12390-2 [23] ). The maximum load reached is recorded and the compressive strength is calculated by Equation (5):

R c = F A c (5)

R_c: compressive strength, expressed in MPa (N/mm²);

F: maximum load causing failure, expressed in Newton (N);

A_c: surface of the section of the test specimen to which the compressive force is applied (mm²).

The variations in the compressive strength of the basic formula and the different other concrete formulas at 7 and 28 days of age are given in Figure 13.

Figure 13 shows that, compared to the reference formula, the formulas with mineral addition to the optima have higher strengths at 7 and 28 days. It’s observed that addition of filler has a positive effect (so called “filler effect”) on strength and strength development of concrete. This effect is not chemical but is due to the filling of the voids of the matrix grains by the fillers whatever their nature.

Thus, the formulas with the addition of sandstone filler have higher compressive strength than those with the addition of limestone which in turn are superior to those with the addition of basalt filler.

Indeed, these results can be explained by the fact that the sandstone filler are chemically cleaner than the other two (value of methylene blue 4.27 < 10 g/kg). In addition, the silica grains (main components of sandstone filler) constitute nucleation sites, which gives a better distribution and homogenization of the hydrated cement products.

For formulas with the addition of limestone filler, the low hardness of the filler (much lower than that of sandstone filler) as well as their relatively high harmfulness compared to that of sandstone, are largely balanced by their “binding” activity effect. Here, the compressive strengths are controlled by this chemical effect. Indeed, CaCO₃ and the aluminates of the cement (C₃A, C₄AH₁₃) would react chemically in presence of water to form a hydrated calcium mono-carbo-aluminate C₃A∙CaCO₃∙11H₂O, which crystallizes in fine hexagonal pads thus increasing the quantity of hydrated products.

For the formulas with the addition of basalt filler, despite their hardness, the strength, lower than those of the other two formulas, appears to be a consequence of the relatively high harmfulness of these fillers. In fact, in addition to having no binding activity, the relative importance of the methylene blue value influences the mechanical performance of the concrete. Here, hardness and compactness are responsible for the improvement of the compressive strengths compared to the reference formula. Esfahani et al. [24] in comparing various types of filler (steel filler, cast iron filler, and stone powder filler) on mechanical properties of concrete show that inclusion of stone powder filler increased the concrete’s strength.

For Moosberg et al. [25], the fillers can interact with cement in several ways, to improve particle packing and give the fresh concrete other properties, and even to reduce the amount of cement in concrete without loss of strength.

The compactness of concrete is the most important parameter to take into account to ensure its durability in front of physical and chemical attacks. It is equal to the ratio of the absolute volume of all the components of hardened concrete to the volume of their container. In other words, it is the ratio of the apparent density (ρ_a) of the hardened and dried concrete over the bulk density (ρ_r), Equation (6).

The degree of compaction is determined in accordance with standard NF EN 1097-6 [26].

C = ρ a ρ r × 100 (6)

ρ a : concrete apparent density (kg/l);

ρ r : concrete bulk density (kg/l);

C : degree of compaction (%).

The results obtained are shown in Figure 14.

Figure 14 shows that the values obtained on the compactness of formulas with mineral additions are greater than that of the reference formula. For the optima, the best compactness is obtained with sandstone filler (2% and 3%). THE batches with limestone filler (3% and 4%) have a greater degree of compaction than those of the formulas with the addition of basalt filler (4% and 5%). These degrees of compaction values are well correlated with the values of unconfined compressive strengths. Limestone filler speeds up hydration reactions and provide a finer porous structure [27]. The values obtained also show that it should not go beyond 4% with limestone because the compressive strength values as well as the degree of compaction decrease.

The filler addition to concrete plays a good role due to its positive influence on viscosity and segregation resistance. The powder added has an important effect on the concrete mobility and on the hardening rate in the first hour of curing.