Cement Dosage and Granular Class as Key Factors in the Properties of Pervious Concrete: A Comprehensive Study

In the context of rapid urbanization and population growth, soil impermeabilization presents significant environmental, developmental, and safety challenges [1-3]. It obstructs the natural infiltration of rainwater into aquifers, increasing surface runoff and flood risks during heavy rainfall [4, 5], while also disrupting local climate stability by limiting the exchange of heat and moisture. In response, urban stormwater management has shifted towards integrated strategies that restore natural hydrological processes like evaporation and infiltration [5]. Among these solutions, pervious concrete has emerged as a leading material [6]. Its porous structure allows water to pass through, reducing surface water accumulation during storms and directing it into the soil [6, 7]. Composed of aggregates, cement, and water, pervious concrete balances mechanical strength with high permeability, making it a sustainable choice for various outdoor applications. The American Concrete Institute (ACI) [6] provides guidelines on the composition of pervious concrete, specifying cement content between 270 and 415 kg/m³ and water-to-cement (W/C) ratios from 0.27 to 0.40. Pervious concrete primarily consists of coarse, uniformly graded gravel (1190–1880 kg/m³) and around 7% fine aggregates, typically sand, which improve compressive strength and durability [8-10]. Compressive strengths typically range from 2.8 to 28 MPa, as reported by several authors [7, 11-18], with water permeability rates between 81 and 730 l/min/m². These parameters are crucial in balancing water permeability and mechanical strength. Dynamic adjustments in component proportions and the careful selection of aggregate combinations enable designers to create pervious concrete tailored to specific project requirements. Our primary objective is to develop a pervious concrete mix that balances mechanical strength and water permeability while minimizing cement use to reduce costs and environmental impact [19]. Our study is guided by the following research questions: (1) How does varying cement dosage influence the trade-off between compressive strength and water permeability? (2) What impact does maximum aggregate size have on pervious concrete performance? (3) Can a high-performing mix be achieved using only natural aggregates and moderate cement dosages, without the need for additives?

By adhering to industry norms and carefully selecting gravel percentages, our study provides practical insights for improving pervious concrete formulations for large-scale applications. In previous research efforts, scholars have focused on enhancing pervious concrete formulations, emphasizing mechanical strength and water permeability. Huang et al. [20] compared granite and dolerite in pervious concrete compositions, finding that dolerite outperformed granite in imparting greater strength and permeability. Xu et al. [21] explored the influence of aggregate size and notch depth on fracture performance, demonstrating that larger particles improved resistance and fracture energy. Yu et al. [22] investigated the interaction among aggregate size, cement paste thickness, and compressive strength, observing an increase in strength with larger aggregate dimensions. Ćosić et al. [13] examined the effect of aggregate type and size, revealing that smaller aggregate fractions enhanced strength attributes and increased density. Mulyono and Anisah [23] explored the effects of water-cement ratios (0.27-0.34) and aggregate sizes, finding that smaller aggregates led to higher porosity but lower density, affecting both compressive strength and permeability. Yu et al. [24] investigated the optimization of pore structure in pervious concrete and found that reducing the porosity of smaller pores while maintaining larger ones enhanced both compressive strength and water permeability. Singh and Sidhu [25] examined the fracture and fatigue properties of pervious concrete with a 15-20% void ratio, concluding that high-strength pervious concrete (32-45 MPa) can be achieved while maintaining a high void ratio, suitable for heavy-load road applications. Singh et al. [26] developed a multi-criteria decision-making framework to optimize pervious concrete mixtures based on performance characteristics, providing guidelines for material selection. Boakye and Khorami [27] investigated the influence of calcined clay pozzolan and aggregate size on the mechanical and durability properties of pervious concrete, offering insights into optimizing strength and sustainability. Kaplan et al. [28] explored the use of recycled aggregates in lightweight pervious concrete, assessing the impact on mechanical properties and permeability.

However, while these studies significantly advanced our understanding of the impact of aggregate size and cement dosage on pervious concrete, they often relied on complex formulations, including the use of recycled materials, chemical admixtures, or mineral additives. For example, Raimon et al. [29] utilized marble waste and fly ash to improve compressive strength, but this approach increased material complexity and cost. Shen et al. [30] proposed an ultra-high-performance paste to achieve high compressive strength (up to 60.93 MPa) while maintaining permeability, but the use of advanced materials further elevated production costs. Similarly, Mulyono and Anisah [23] found that adjusting the water-cement ratio and aggregate size improved permeability, but their use of additional components like superplasticizers increased formulation complexity. These approaches, while effective, often present practical challenges when applied in large-scale projects where cost and simplicity are critical. Our investigation focuses on the relationship between cement dosage and maximum aggregate size (Dmax) and their combined impact on the properties of pervious concrete. By examining twenty formulations with varying cement dosages (250 to 350 kg/m³) and Dmax values (8, 10, 12.5, and 20 mm), we aimed to find an optimal balance between mechanical strength, as indicated by compressive strength, and hydrological efficiency, represented by water permeability. Achieving this balance is challenging due to the typically inverse relationship between compressive strength and permeability. Unlike previous studies that incorporated recycled materials, chemical admixtures, or mineral additives to enhance performance, our study takes a distinct approach by eliminating these additional components. Instead, we focus on optimizing natural aggregate sizes and moderate cement dosages to maintain both performance and cost-efficiency. This not only minimizes production costs and CO₂ emissions associated with cement use but also provides a scalable and sustainable solution for high-performance pervious concrete. Our work is particularly well-suited for large-scale, low-cost applications where economic and environmental constraints are crucial, offering a simpler, more accessible alternative without sacrificing essential performance metrics like strength and permeability.

The different constituents of the pervious concrete are chosen according to the recommendations of the ACI [6] and the volume dosages of the different constituents are then calculated concerning the Eq. (1):

$1 m^3=\frac{M_c}{\rho_c}+\frac{M_g}{\rho_g}+\frac{M_s}{\rho_s}+V_w+V_v$            (1)

where, M_c, M_g, and M_s (kg) are the masses of cement, gravel, and sand, respectively ρ_c, ρ_g, and ρ_s (kg/m³) are their densities. V_w (m³) is the volume of water, and V_v (m³/m³) is the volume of voids. Several formulations are tested (Table 5). The water/cement and sand/gravel ratios were maintained across all formulations. This ensured uniformity in the mixing process while allowing the analysis of cement dosage impact (W/C=0.36, S/G=0.07).

Table 5. Mixture proportions

The mixing sequence: followed the same procedure for all pervious concrete compositions, ensuring consistency across samples. The concrete was prepared using an electric mixer with a nominal capacity of 65 litres. The following steps outline the precise mixing sequence and durations:

- Initial Mixing: The dry cement and aggregates were added to the mixer and blended for 60 seconds. The water-to-cement (W/C) ratio was kept constant at 0.36 across all formulations, ensuring consistent hydration across the different cement dosages. The sand-to-gravel (S/G) ratio was also kept constant at 0.07, which helped to maintain a stable proportion of fine to coarse aggregates throughout the mix.

- First Water Addition: After the dry materials were mixed, 70% of the total water was added to the mixer, and the mixture was blended for 30 seconds.

- Final Water Addition: The remaining 30% of the water was then added, and the entire mix was blended for another 60 seconds to achieve full hydration and uniform consistency.

Compaction and Vibration: The fresh pervious concrete was poured into cylindrical molds with dimensions of (11×22 cm) Nine samples were prepared for each concrete composition. The concrete was placed into the molds in three layers, and after each layer, the mold was subjected to 5 seconds of vibration using an electric vibrating table to compact the concrete and minimize air voids. After the final layer, the top of the mold was leveled to ensure a consistent initial height of 220 mm. The weight of each sample was measured to ensure consistency in initial porosity. This step ensured uniformity in samples with similar aggregate particle sizes and compositions.

Curing Process: The molds were sealed in plastic bags for 24 hours to prevent moisture loss during the initial curing phase. After demolding, the samples were immersed in water at 25℃ for a period of 28 days to achieve full curing. This curing process was critical for the development of the mechanical and permeability properties of the concrete.

Slump Test: The workability of the pervious concrete was evaluated using an Abrams cone, following EN 12350-6 [32]. The concrete was placed into a truncated cone mold (base diameter: 20 cm, top diameter: 10 cm, height: 30 cm) in three layers, with each layer compacted 25 times using a 16 mm diameter metal rod. The slump was measured by comparing the height of the demolded concrete to the original height of the mold. This method was chosen for its simplicity and effectiveness in providing quick feedback on the workability of the concrete mix, ensuring consistent results across all formulations.

Air Content Test: The air content of the fresh concrete was measured using an 8-liter aerometer, following NF EN 12350-7 [33]. This instrument gave a direct reading of the occluded air content as a percentage. Measuring air content is critical for understanding the workability and permeability of the concrete, as it directly affects the performance of the pervious concrete in its final application.

Compressive Strength Test (fcm): Was tested on cylindrical specimens (11×22 cm) according to EN 12390-3 [34]. A ZWICK press was used, applying a constant loading rate of 0.5 MPa/s. Each specimen was coated with ISO-9001 certified surfacing mortar to ensure accurate test results. Compressive strength is a key indicator of the mechanical performance of concrete, and this method provides a reliable and standardized way to measure it.

Splitting Tensile Strength Test (fct): Was evaluated using the splitting tensile strength test on cylindrical specimens (11×22 cm) in accordance with NF EN 12390-6 [35]. The loading rate was 0.05 MPa/s. This test was chosen because it offers a practical and efficient method for determining tensile strength, avoiding the complexities associated with direct tensile tests, while still providing accurate data on the material's tensile behavior.

Water Permeability Test: Was measured using a custom-designed constant load permeability apparatus [36-38]. Water was introduced at a constant height of 220 mm above the specimen, and the flow rate was measured after 60 seconds. The permeability (K) was calculated using Darcy's law (Eq. (2)). This method was selected because it closely simulates real-world drainage conditions, providing an accurate measure of the concrete’s hydrological efficiency. The constant head test was specifically chosen for its ease of execution and reliability in laboratory settings.

$K=\frac{(V \times L)}{(h \times S \times t)}$             (2)

where, V (mm³) is the volume of water moving vertically through the cylindrical specimen (11×22 cm); t is the time 60 seconds (t=60); L is the height of the test tube (220 mm); S is the cross-section of the specimen and h (mm) is the constant height of the water (h=220 mm).

Porosity and Density: Porosity and 28-day density were determined according to ASTM C1754/C1754M-12 [39]. Samples were air-dried for 72 hours, then fully saturated in water for 48 hours. The dry weight Asec (kg) and floating weight Bhydro (kg) were measured. Porosity P (%) and density $\rho$ (kg/m³) were calculated using Eqs. (3) and (4) with $\rho$w the density of water at 25℃ being used as a constant. The conversion factor K used was 1,273,240 mm³/kg according to ASTM C1754/C1754M-12 [39].

$P=\left(1-\left(\frac{K\left(A_{\text {sec }}-B_{\text {hydro }}\right)}{\rho_w d^2 L}\right)\right) 100$            (3)

$\rho=\frac{K A_{s e c}}{d^2 L^2}$            (4)

Electrical Resistivity: The electrical resistivity of water-saturated specimens was measured (two-point method) using a resistivity meter. After being soaked for 24 hours, two moistened sponges were placed between the specimens and the meter’s plates, and readings were taken after a 5-minute stabilization period. This method was chosen as it provides an indirect measure of pore connectivity.

This study explored the impact of aggregate size and cement dosage on the properties of pervious concrete, focusing on the balance between compressive strength, permeability, and electrical resistivity. The findings highlight the following key points:

(1) The ideal formulation involves a cement dosage of 300 kg/m³ and D_max of 10 mm. This combination provides high compressive strength (fcm>12 MPa) and satisfactory permeability, while maintaining adequate durability indicated by moderate electrical resistivity. This configuration achieves a balance between mechanical performance and drainage efficiency.

(2) Smaller aggregate sizes (D8 and D10) improve compressive strength due to better compaction and particle cohesion. Larger aggregates (D20) increase permeability but reduce strength, making them less suitable for structural applications.

(3) Higher cement dosages improve cohesion and strength but reduce permeability. Moderate dosages (300 kg/m³) are sufficient to achieve a balance, meeting mechanical and hydrological requirements without the need for additives.

(4) Higher porosity correlates strongly with increased permeability, facilitating water drainage. However, excessive porosity diminishes mechanical strength, emphasizing the need for careful mix proportioning.

(5) Smaller aggregate sizes and higher cement dosages decrease resistivity, enhancing durability. However, higher porosity in 8 mm aggregates leads to increased resistivity, suggesting that these mixes may be more susceptible to degradation over time.

The findings support the research objectives by demonstrating that a high-performing mix can be achieved using only natural aggregates and moderate cement dosages.