A Comprehensive Evaluation of Concrete Behavior Made with Date Seed as a Partial Replacement of Fine Aggregate

Concrete is a fundamental component in the construction of buildings and bridges. It consists of multiple raw materials: cement, aggregate (coarse and fine), water, and additives. Concrete grades are influenced by multiple factors, including the type of structure, environmental conditions, economic cost, and the quality of the used materials [1]. The key concrete characteristics include mechanical strength, durability, thermal properties, fire resistance and similar attributes, which significantly impact structural design decisions. There are important conditions that must be met in the concrete mixture. It must be homogeneous and workable. Therefore, the properties of materials and mixing methods have an effective effect [2]. Furthermore, durability is an important factor in concrete that must be taken into consideration to enhance the structure's lifetime. The durability factors give concrete the ability to resist degradation and maintain its shape, dimensions, and quality during its service life when exposed to harsh conditions such as weathering, corrosion, and attack by chemical substances [3].

In recent years, due to the development of industries, there has been a large amount of waste, which has prompted researchers to think about reusing these materials to reduce environmental pollution. In many studies on concrete, the primary target has become to obtain sustainable concrete at a lower cost while reducing undesirable CO₂ emissions by utilizing different materials as alternatives to concrete components. Organic and inorganic waste were involved as a replacement for fine or coarse aggregate. Inorganic waste such as (plastic, glass, ceramic, rubber, electronic waste, etc.) were investigated by many researchers [4-8]. Furthermore, researchers have explored the use of organic agricultural waste as a potential substitute for traditional aggregates in concrete production. These investigations were on sawdust, wood ash, cashew shells, sugarcane bagasse ash, papers and walnut shells [9-18] etc. Mohammed et al. [9] found that wood chipping improved workability but reduced strength. Al-Harshawi et al. [10] observed similar strength reductions with recycled wood waste replacing cement but noted excellent workability and a 25% weight reduction. Al-Saad et al. [11] successfully produced lightweight concrete using waste paper aggregates treated with cement or wood glue, achieving significant density reduction. Modani and Vyawahare [12] demonstrated the potential of utilizing untreated bagasse ash as a fine aggregate replacement. Hilal et al. [13] found that crushed walnut shells decreased concrete performance, with a 15% replacement yielding the best results. Priyadarshini et al. [17] used cashew shells as a partial coarse aggregate replacement in concrete, with a 10% substitution yielding optimal strength.

As concluded from the above-mentioned studies, agricultural wastes are suitable to use to produce eco-friendly lightweight concrete.

Date seeds (DS) are considered to be a large agricultural waste material in the Middle East, especially in Iraq and some Arab countries. After consumption of the date, seeds become agricultural waste and can contribute to environmental pollution if not properly managed. In many studies [19-23], researchers replaced the coarse aggregate with date seeds to produce concrete. The most important result was that increasing the DS reduced the workability of the concrete. In contrast, other studies found an enhancement in concrete strength when DS was added in a specific amount.

Adefemi et al. [19] explored the feasibility of using DS as a substitute for CG (crushed granite) in concrete production. Physical and mechanical characteristics were conducted of both materials for comparison. Ninety concrete cubes with varying CG to DS ratios (100:0 to 0:100) were prepared and evaluated for compressive strength after 28 days of water immersion. The results showed that partial replacement of CG by DS, up to 75%, yielded satisfactory compressive strengths, suggesting DS as a suitable alternative for lightweight concrete production in regions where it is readily available. Ahmed et al. [20] investigated the utilization of DS as a partial substitute for coarse aggregate in concrete, analyzing its impact on workability, density, and compressive strength under exposure to sodium chloride (NaCl) and sodium sulphate (Na₂SO₄) solutions. The incorporation of 2-4% DS as a replacement for coarse aggregate initially enhanced workability by 2%, but this improvement diminished over time. A slight reduction in density and compressive strength in plain water, while a more pronounced reduction in compressive strength was noted in salt solutions, especially after 28 days of exposure. Suggesting DS concretes susceptibility to salt damage. Palh et al. [21] explored the incorporation of DS as a partial substitute for coarse aggregate. Twenty-four cylindrical specimens were created, replacing coarse aggregate with 0%, 2%, 3% and 4% DS. The workability decreased as the DS content increased, primarily due to its larger surface area, while the compressive strength results were satisfactory at 2% and 3% replacement levels, suggesting that DS has potential as a feasible partial replacement for aggregate.

Gunarani and Chakkravarthy [22] studied date seed ash as an alternative to cement in certain proportions (2%, 4%, 6%, 8%, and 10%). A 2% date palm seed ash (DPSA) addition notably improves bond strength compared to ordinary Portland cement (OPC), however, optimal performance is attained with a 4% replacement. Shaikh et al. [23] replaced fine aggregate with crushed date seeds in concrete in four different percentages 1%, 2%, 3%, and 4%. Concrete incorporating 3% crushed date seeds achieved maximum compressive strength at 7 and 28 days.

Although date seeds are widely available in Iraq as agro-waste material, their use in concrete production has not been considered in studies or construction. A significant gap remains in the comprehensive evaluation of DS durability and heat resistance, especially as a replacement for fine aggregate.

Therefore, in the current work, DS was incorporated as a partial substitute of fine aggregates with 1.25%, 2.5%, 3.75%, and 5% by volume. Slump, dry density, water absorption, compressive strength, splitting tensile strength, and flexural strength were evaluated. Additionally, durability was also investigated including rapid chloride permeability, elevated temperature, Schmidt rebound hammer, and ultrasonic pulse velocity test.

3.1 Fresh concrete test (Slump test)

After the process of mixing the concrete ingredients was completed and the required homogeneous texture was achieved, a slump test was performed to assess the workability and consistency of the fresh concrete. This test was conducted according to ASTM C143-03 [27] on all the concrete mixtures as illustrated in Figure 4.

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Figure 4. Slump test

3.2 Hardened concrete tests

The effect of adding DS on the specimens' mechanical behavior was evaluated through several tests on the hardened concrete. These tests included dry density, water absorption, compressive strength, and splitting tensile strength, flexural strength, Schmidt rebound hammer, and ultrasonic pulse -velocity as non-destructive techniques for the last two tests, respectively. Eighteen 100 mm cubic specimens, nine 100×200 mm cylindrical specimens, and three 100×100×400 mm prisms were cast for each concrete mixture. The measurement of concrete dry density at 28 days was performed on cubic specimens according to ASTM C642-97 [28] and water absorption, also following ASTM C642-97, after a 28-day curing period. Compressive strength was determined according to BS 1881: Part 116 [29] (Figure 5) using a universal load testing machine. The average splitting tensile strength of three concrete specimens (cylinders) was tested at 7, 28, and 56 days according to ASTM C 496- 96 [30] as illustrated in Figure 6. The center-point loading test was implemented to compute the flexural strength of concrete prisms at age 28 days conforming to ASTM C293-02 [31] as in Figure 7. A Schmidt rebound hammer test, conforming to ASTM C805 [32], was conducted on concrete cubes before compressive strength testing (Figure 8). Ultrasonic pulse velocity UPV was determined by measuring the travel time of a 50-54kHz pulse transmitted through the concrete specimen by the electro-acoustical transducer. The pulse velocity was calculated based on the known path length [33]. The pulse velocity of cubes was tested using an ultrasonic device shown in Figure 9 following ASTM C 597-02 [34].

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Figure 5. Compressive strength test

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Figure 6. Splitting tensile strength test

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Figure 7. Flexural strength test

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Figure 8. Schmidt rebound hammer test

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Figure 9. Ultrasonic pulse velocity test

3.3 Durability of concrete tests

The effect of adding DS on the durability of concrete was evaluated through several tests. These tests were chloride permeability and elevated temperature which are described in the following subsections.

3.3.1 Rapid chloride permeability test (RCPT)

The RCPT, a method for measuring chloride ion penetration in concrete, was performed as follows. Disc-shaped specimens, 100 mm in diameter and 50 mm high, were cut from 100×200 mm cylinders after a 28-day curing period, conforming to ASTM C1202 [35] and AASHTO T277 [36]. The borders of the specimens were coated with sealing material before being placed in the device. A constant 60V DC was maintained across the sample ends throughout the test for 6 hours, as shown in Figure 10. The sample had one end immersed in a 3% sodium chloride (NaCl) solution and the other end in a 0.3M sodium hydroxide (NaOH) solution. Readings were taken every half an hour. After 6 hours, the specimen was removed, and the total amount of charge (coulombs) that had passed through the sample was computed as in Eq. (1).

$\begin{aligned} C_f=900 & \left(A_0+2 A_{30}+2 A_{60}+2 A_{90}\right. \left.+2 A_{120}+\ldots \ldots+2 A_{330}+2 A_{360}\right)\end{aligned}$               (1)

where, C_f represents the total charge flow through the concrete cell in coulombs, calculated by integrating the current, A_t (amperes), measured at time t (minutes) under a constant 60V DC voltage. The total charge, measured in coulombs, passing through the concrete specimen was used to assess chloride penetration resistance according to the criteria outlined in Figure 11.

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(a)

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(b)

Figure 10. Rapid chloride permeability test, a) Chloride permeability test diagram [37], b) Chloride permeability current study device

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Figure 11. RCPT rating measured in Coulombs per ASTM C1202 [37]

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Figure 12. Electric furnace used for elevated temperature test

3.3.2 Elevated temperature

Three cube samples were examined for each different heat value, 150℃, 300℃, and 450℃. Cubes were weighed, subjected to a one-hour heat at each specified temperature in an electric furnace (Figure 12), cooled, reweighed, and following assessed for compressive strength. The effect of the elevated temperature was evaluated using Eq. (2) [38].

Percentage weight loss $=\frac{w_1-w_2}{w_1} \times 100(\%)$              (2)

where, $w_1=$ cube weight before subjected to heat, ($g$), $w_2=$ cube weight after subjected to heat ($g$).