Sand used has been sampled from 3 manufactured quarries. In order to compare with natural sand, river (Sanaga) sand and pit sand have also been analyzed. Quarry manufactured sand, extracted from Nkoabang, Leboudi and Lobadjeck quarries. River Sand sampled from Sanaga River. Pit sand sampled from Okola and Lobo Quarries.

Regarding manufactured quarry sand, we carried out bulk sampling. At each site, samples were taken from the various piles and mixed together. In the laboratory, 2 kilograms of sand from each quarry were analyzed. Meanwhile, the natural sand (pit and river), which was also sampled in bulk, was collected from the construction site.

Our samples were first left exposed in the sun for 2 days and then spread out in a drying oven at 60˚C for 6 hours.

To determine particle size distribution, particles size analysis done has primarily used sieving. Essential tools include certified test sieves, shaker machines (vibratory/electromagnetic), sample splitters, precise balances, and cleaning brushes to ensure accurate results (Figure 1). The series of sieves used includes mesh sizes 160 µm, 315 µm, 630 µm, 1.25 mm, 2.5 mm and 5 mm (Figure 1(a), Figure 1(c)). Data are easily analyzed on Excel, Microsoft.

Fineness modulus serves as a measure of aggregate coarseness or fineness,

Figure 1. Sieving. (a) sieve column; (b) root and leaves of in river sand; (c) retained in 5mm sieve of M-sand; (d) sieving of sanaga (river) sand.

commonly used to optimize concrete mix design and maintain consistency. FM is an empirical numerical index that represents the average size of particles in an aggregate sample; it has been calculated according to French NORM [13].

FM = (Ʃ of cumulative % retained)/100 [14].

FM = (Ʃ of cumulative % series of sieves (160 µm, 315 µm, 630 µm, 1.25 mm, 2.5 mm, 5 mm))/100

A sample of aggregate is passed through a standard set of sieves. The percentage of material retained on each sieve is calculated, and a cumulative percentage is calculated by adding the percentages retained on all preceding sieves. The cumulative percentages are summed and divided by 100.

Typical fineness modulus values for sand [13].

1.8 < MF < 2.2: high workability and low strength. Good for mortar.

2.2 < MF < 2.8: satisfactory workability, good strength and no risk of segregation, good for concrete.

2.8 < MF < 3.2: High strength, weak workability with risk of segregation.

Sand with an FM greater than 3.2 is generally considered too coarse for high-quality, Workable concrete.

According to French and European standards [15]-[17], the value of FM is very useful for optimizing the mix design of concrete, mortar, and plaster. Sebsadji [18] highlighted the relationship between the global fineness modulus and the particle size distribution of concrete at the skeleton scale, using fractal dimension.

- For standard concrete, FM ≈ 2.2 - 2.8; range often cited as ideal is FM≈ 2.6 - 2.9 depending on the application [15].

- Aggregates for mortar and plaster are standardized [18]; FM depends on the type of mortar, often FM ≈ 1.5 - 2.2 depending on the application [16][17][19].

By visual inspection, it is observed that, manufactured sand is angular (Figure 1(c)), unlike river sand which is rolled. The angular shape increases the water demand of concrete and reduces its workability, often requiring the use of additives. Angular shapes increase strength primarily in construction materials specifically concrete and asphalt by enhancing mechanical interlocking and frictional resistance between particles; this reduces the workability of the concrete mix and increases its water demand to achieve a given slump. The sharp edges and rough surfaces of angular aggregates, often produced by crushing, lock together better than rounded, natural aggregates. This higher interlocking creates a denser, more stable matrix.

Visual inspection and sieving show that manufactured sand, compared to river and pit should be pure. Impurities observed in river and pit sand (Figure 1(b)) are organic elements including shell, bones, roots, leaves and twigs which can significantly reduce the strength of concrete and compromise its integrity and durability. The purity of manufactured sand is an important and great quality. To avoid weakness in concrete, mortar or plaster, element used for mixture, sand is characterized by purities. These organic impurities are highly deleterious to structural concrete. They retard the setting time of cement, inhibit the chemical hydration process, and leave physical voids upon decomposition. These voids create weak points that drastically reduce compressive strength and long-term durability [20][21].

The optimization of manufactured quarry sand used is the main objective of this research. Thus, sand from five samples of sand has been analyzed; three samples from manufactured quarries that we compared results to one river and two inland sand.

The analysis of the three manufactured quarry sand shows that, amount of particles distribution according to size varies little from on sieve to the other (Figure 2). Average distribution shows a maximum percentage of particles retained on 2.5 mm mesh sieve; i.e., 18.49%. Sieves 5 mm, 2.5 mm, 1.25, 0.63, 0.315, and 0.16 have average distribution of 16.2%, 18.49%, 14.9%, 13.2%, 13.6 and 17.12% retained respectively; we consider these results closes (Table 1). The distribution of particles is almost equilibrated according to size from 0.16 mm to 5 mm sieve. We can observe that manufactured quarry product is constituted to about 1/3 of fine, 1/3 of medium and 1/3 of coarse sand. It is then complicated to classify manufactured sand in fine, medium or coarse category. In general, sand is used in concrete, mortar or plaster. To be high quality, proper proportion of sand as well as water and cement are critical in the mixture. To consider quantity of sand, it has to be classified in fine, medium or coarse. It is then clear that, we cannot use manufactured quarry sand as it is. It can also be observed that, a proportion of 6,496% (sieve 0.08 mm) of this sand is dust generated by drilling crushing and grinding; the necessity of washing and cyclone treatment are then essential to optimize quality.

Considering river and pit sand, the classification is clear (Figure 3 and Figure 4). River sand analyzed is constituted to retained from 0.315, 0.63 and 1.25 sieves; what gives a total of about 80%. This range of sieve classified river sand as medium aggregate required for concrete. Pit sand analyzed shows that retained on 0.8, 0.16 and 0.315 is made with about 93.5% of fine particles; what ranges it in the category of fine sand (Figure 4) mandatory for mortar. From 0.08 and 0.16 sieves, the retained is about 80%, good range for aggregate to mix high quality plaster.

Table 1. Distribution of particle size in percentage for each quarry.

Figure 2. Cumulative curve from manufactured quarries sand.

Figure 3. Cumulative curve from river (Sanaga) sand.

Figure 4. Cumulative curve from pit quarries sand.

Fineness modulus calculated from the different sample of sand gave results of Table 2.

Table 2. Values of fineness modulus from different sample.

FM obtained from manufactured quarries is greater than 3.2 (Table 2). Quarry sand is then considered as too coarse for high quality workable concrete.

Sand from river has FM of 2.591; what offers a satisfactory workability. Concrete mixed with this sand is the required quality with good strength and no risk of segregation.

Sand from pit quarries of Okola and Lobo has FM lower than 1.8; what is typically used for finishing applications rather than structural concrete.

We decide to separate particle at a mesh 0.315. Considering the sieving of manufactured sand at a mesh of 0.315, sand retained include particle size from 0.315 to 5 mm; mixed of medium and coarse sand. The calculation of fineness modulus from the formula FM=(Ʃ of cumulative % retained)/100 is applied.

According to French norm NFP 18-540, we should use series of sieves 160 µm, 315 µm, 630 µm, 1.25 mm, 2.5 mm, 5 mm. Since particles with size lower than 0.316 are not included, retained percentage of 160 µm is excluded.

FM = (Ʃ of cumulative % series of sieves (160 µm, 315 µm, 630 µm, 1.25 mm, 2.5 mm, 5 mm))/100.

Fineness modulus calculated for these sands are grouped on the Table 3.

Table 3. Fineness modulus for sample of manufactured quarry sand.

Table 4. Fineness modulus (FM).

Retained sand is coarse, and angular, ranging from 0.315 to 5 mm in size. These jagged, large particles lock together to provide superior structural strength for driveways, pouring slabs, foundations, and footings; what fulfills the conditions of good sand for concrete. The percentage of this coarse and medium sand is about 76% of the row sample (Table 4).

The passing sand which represents about 24% is finer and can be used for smooth finishes in walls, stucco, and mortar masonry. This offers smoother, more compactable results for coating, whereas “sharp sand” is better for high-strength structural.

Table 5. Cumulative percentage of sieve (2.5; 1.25; 0.63; 0.315 mm).

From the row sample of manufactured sand, it is possible to have 76% of coarse sand to mix good concrete providing superior structural strength (Table 5). The 24% of sand remaining constitutes fine sand which is interested to make mortar and plaster for smooth coating.

From Table 6, fineness modulus of row and separated sand by sieving are presented. It clearly appears that, row manufactured quarry sand (A) has fineness

Table 6. Fineness modulus for row and optimized samples.

modulus more than 3.2; what means this sand is too coarse for high-quality, Workable concrete. It is generally unsuitable for high-quality, workable concrete because it creates harsh, unworkable mixes prone to segregation and honeycombing. In some condition, this sand can be used when looking for very strength concrete, or can be just rejected. Sand sample (B) separated with 0.315 mm sieve has average of 3.14 for Fineness modules which is comprised between 2.8 and 3.2, what means it provides with high strength to the concrete. Sand with a fineness modulus (FM) around 3.0 is classified as coarse sand, ranging between 2.9 and 3.2, indicating a relatively high average particle size suitable for producing high-strength, low-shrinkage concrete. While excellent for structural concrete, this sand may require more cement and water to maintain workability compared to medium sand. The separation at 0.315 means that 0.163 mm sieve is excluded to the calculation of FM, because the retained from this sieve is considered to be zero. Sand sample (C) constituted with retained by sieve 0.315 mm and passing of 5mm sieve; what means retained from 0.163 mm and 5mm sieve are removed, and then are not considered for the calculation of FM. Sand with a fineness modulus of around 2.63 is generally classified as medium sand. It falls within the desirable range (2.3 - 3.1) for creating quality concrete, offering a good balance between workability and strength. An FM of 2.63 indicates that the average particle size is well-balanced, sitting at the transition point between fine and medium sand, typically falling within the ideal Zone. Sand with this modulus specifically between 2.2 and 2.8 is known to produce concrete with high workability and low segregation. The particle distribution is likely favorable, reducing the need for excess water and allowing for higher strength and durability.

The production of medium sand suitable for good concrete leads simultaneously to the production of the fine sand needed for mortar. This dual-production method is a highly efficient approach to construction material sourcing, maximizing resource utility by aligning the production of medium-grade sand (essential for concrete) with the finer byproduct needed for mortar and plastering. By utilizing crushed rock or aggregate, this process creates a sustainable, zero waste approach, as all fractions of the crushed material are tailored to specific, in demand construction applications.

The fraction constituted by passing of 0.63 mm sieve, provide us with fine sand with an average fineness modulus of 1.63. It is considered very fine sand and is ideal for general structural mortar, and can be used for specific finishing plastering applications, provided it is clean and properly graded [11]. According to standard building codes [11][22], the recommended FM range for plastering sand is 1.2 to 2.2.

This statement highlights the shift toward sustainable, high-performance construction materials by emphasizing that manufactured sand is not just a substitute for river sand, but often a superior alternative due to its controlled production process. The crushing process allows for precise control over the particle size distribution, ensuring a mix of fine, medium, and coarse fractions that provide denser packing in concrete. Different fractions can be utilized for different purposes: finer fractions can be used for plastering or as mineral fillers, while coarser fractions (up to 4.75 mm) are used as concrete aggregates. Modern crushing methods, such as Vertical Shaft Impactors (VSI) produce angular or cubical particles, which provide superior interlocking compared to the rounded particles of river sand, leading to higher compressive strength and better durability.

Manufactured sand is processed in a controlled factory environment, reducing contaminants. Unlike river sand, which often contains silt, clay, and organic matter, M-sand is clean. This absence of impurities helps in preventing the reduction of cement strength and prevents corrosion of reinforcement steel. The chemical and mineral composition is consistent throughout, eliminating the variations often found in natural sourcing.

While initial processing requires investment, the overall project cost is often reduced. M-sand can be produced near construction sites significantly reducing the high logistics costs associated with transporting river sand. Proper grading and shape often allow for a lower cement-to-sand ratio, saving on overall material costs while achieving the same or higher strength.

The sieve analysis reveals that the raw manufactured quarry sands (Leboudi, LogBadjeck, Nkoa-Abang) display an atypical, overly uniform particle size distribution: Fine Particles (~1/3), Medium Particles (~1/3) Coarse Particles (~1/3) This nearly equal tri-distribution (roughly 33% each of fine, medium, and coarse fractions) makes it impossible to classify the raw product into a standardized single category.

For high-quality concrete, mortar, or plaster, the sand must be clearly classifiable to ensure a dense particle packing layout:

Highly optimized for structural concrete, with 80% of its particles retained on medium sieves (1.25 mm to 0.315 mm), yielding an ideal fineness modulus (FM) of 2.591. This ensures excellent workability and no risk of segregation.

Distinctly fine, with up to 93.5% of particles are into the fine category. While unsuitable for structural concrete (FM < 1.8), it is mandatory for high-quality finishing plasters and mortars.

Raw manufactured sand contains an average of 6.496% ultra-fine micro-dust (0.08 mm sieve) generated during drilling and crushing. This excess of micro-fines increases water absorption and weakens the cement-aggregate bond, demonstrating that raw quarry sand cannot be used in its as-received state. Washing and cyclone treatments are mandatory to strip away this micro-dust.