Contaminants Removal from Construction and Demolition Waste (CDW) with Water Jigs

Abstract

This study evaluates the viability of water jig for removing the impurities from CDW and the concentration of concrete aggregates from mixtures containing 10%, 20%, and 30% impurities (brick and gypsum), simulating the materials commonly found in CDW. Laboratory-scale jigging tests were conducted in single-stage jigging, and the products were characterized based on density > 2.6 g/cm³, water absorption, shape factor, and bulk density to evaluate the separation performance. It was noted that dense fractions consistently achieved high purity with less than 1% impurities and a concrete content of more than 99% and that more than 80% of dense material was recovered. These results demonstrate that water jigging is a technically viable method for producing recycled aggregates of sufficient quality for reuse in concrete while also reducing CDW disposal by more than 40% and contributing to the sector’s carbon footprint reduction. The findings confirm that even a single-stage jigging process can provide high-quality recycled aggregates, offering a simple and effective route for CDW beneficiation.

1. Introduction

Construction and demolition waste (CDW) is the most significant waste stream globally. It accounts for over 37% of total waste in the European Union (EU), highlighting the need for effective management and recycling [1]. EU waste management policies [2] aim to reduce the environmental and health impacts of waste and improve the efficiency of natural resources use. According to the Eurostat [3] report, the EU generated more than 4 tons of waste per person in 2020. In 2020, 39.2% of waste was recycled and 32.2% was landfilled in the EU, according to the study.

Considering the European Directive 2008/98/EC [4], which defines waste as “any substance or object that the holder discards or intends or is obliged to discard,” CDW potentially represents a significant waste of resources, both in materials and energy. Addressing the environmental aspects related to CDW, the reuse of materials should be prioritized, as disposal or incineration can pose ecological risks or lead to financial losses. Landfills, for example, occupy land and can cause air, water, and soil pollution, while incineration may emit air pollutants. According to a 2020 survey, the construction sector accounts for more than 30% of the total waste generated in Spain [3].

Reis et al. [5] demonstrated that CDW mainly consists of brick, ceramics, plastic, wood, concrete, bituminous mixtures, metals, plaster, and soil from material management. The authors also demonstrated the current applications of material recovered from CDW, including the production of sand, its use in pavements and roads, direct reuse in concrete mixing as recycled aggregates (RA), the manufacture of new concrete blocks, the production of cement, and the creation of adsorbents to treat contaminated water. They are the primary materials used in constructing pavements and roads, reducing the added value created by recycling.

1.1. CDW Processing

Many authors study CDW processing plants [6,7,8]. Typically, companies crush the CDW to reduce particle size and separate the inert portion, creating what is called “inert CDW.” During this process, they remove particles such as plastic, paper, wood, and metal parts (ferrous and non-ferrous) through methods like sieving, mats, or manual removal for materials that remain larger after size reduction. The “inert CDW” material contains bricks, tiles, gypsum, concrete, cement paste, and coarse aggregate [9,10]. About 76% of CDWs consist of solidified and inert materials [3].

Concrete and mortar make up the majority of construction and demolition waste (CDW), but they also contain a variety of contaminants that have a substantial impact on the quality of recycled aggregates. According to earlier research, bricks and ceramics are frequent pollutants that are frequently found in high concentrations as a result of masonry demolition. Because of their high water absorption and sulfate content, gypsum and plaster residues are especially harmful impurities that can affect the performance and longevity of recycled aggregates. Asphalt, glass, wood, plastics, and metals are other common impurities that are typically present in smaller amounts but are nevertheless harmful to aggregate quality [11]. These impurities change the density, porosity, and shape factor of recycled aggregates, increasing their absorption of water and decreasing their mechanical strength [12]. Because of this, a number of authors have emphasized the significance of separation methods, especially water and air jigging, in order to efficiently eliminate low-density contaminants like gypsum and brick and enhance the quality and suitability of aggregates made from CDW [13].

Studying the reuse of recycled aggregates (RA) directly in structural concrete mixtures, several authors explain that the main difficulty is adapting the material to the legislation and removing contaminants from recycled material [5,14,15,16]. Considering the vast range of environments and conditions to which these materials made from CDW can be exposed, their chemical composition (e.g., sulfate and chloride content) could compromise the performance of recycled concrete [5]. According to EN 1744-1 [17], the primary source of soluble sulfates in RA is the presence of gypsum, and the presence of sulfates has a linear relationship with the mass concentration of the gypsum in RA. Other authors [18,19] showed that the presence of contaminants, with a concentration higher than 1%, limits the application of RA in new concrete since they negatively influence the fundamental properties of the aggregates, such as size distribution, shape index, and bulk density.

The primary concern regarding removing gypsum and brick is the suitability of the recycled material for reuse. Gypsum can compromise the performance of recycled concrete, and the amount of sulfur compounds is minimal to ensure its chemical stability and avoid pathologies in adjacent concrete structures [5]. In terms of volume, bricks are the main components present in CDWs. They present low mechanical resistance, and when used as coarse aggregates in the formulation of concretes, their mechanical resistance decreases considerably, making it impossible to use them as structural concretes.

Research was carried out to identify a route for processing CDW with water jigs, as well as the removal of contaminants present in the material and the recovery of coarse aggregates (material with size range between 5 × 20 mm) for reuse as RA in concrete. The fine aggregates (material with size range between 0 × 5 mm) can also be recycled according to the authors but demands specific analysis as the separation to adapt the material for reuse [10,11,12,13,20]. This research has demonstrated that for the production of RA from CDW, it is necessary to crush the material to a fraction range from 5 × 20 mm and subsequently concentrate the material. The process enables the concentration of the denser material and the removal of contaminants that generally have a lower density, a larger form factor, and a bulk density that allows the separation of the material, generating a product that can potentially be reused as RA.

1.2. Jig Process

Ambrós (2020) [21] explains that the general scheme of most jigs consists of a container divided into two compartments, with one consisting of a separation chamber where feed particles are located on a supporting sieve and through which the water performs its oscillatory motion. The other compartment contains the mechanism that drives fluid pulsation, which is responsible for moving the bed during its passage by the jig. Figure 1 shows a schematic model of the water jig explained previously. The pulse wave can be produced mechanically through a plunger, pulsating water, or air intermittently fed into the jig vessel using a special valve. In some types of jigs, the relative motion between particles and water is obtained through the vertical displacement of the supporting sieve.

As proposed by F. Mayer [22,23], the “Jigging Potential Energy Theory” explains the stratification in the jigging process. This theory proposes a difference in gravitational potential energy between thoroughly mixed and stratified states concerning densities, and that the difference in potential energy is genuinely responsible for stratification in jigging.

The present work aims to demonstrate the possibility of removing contaminants from CDW with water jigs and concentrating the dense material mixed with the concrete. The viability of the jigging process for CDW management would allow for a reduction in the carbon footprint of the construction sector, a reduction in the volume of material to be sent to landfills, and the possibility of the economic recovery of this material. Three different tests were proposed with different amounts of contaminants (10%, 20%, and 30% in weight) to observe the product generated after the jig concentration process. Specific density and bulk density were measured in oven-dry conditions, and saturated, shape factors, water absorption, granulometric, and densimetric distribution tests were carried out; in addition, the manual analysis of the composition and quantification of the products generated in each test was performed to ensure the suitability of the material regarding the presence of contaminants.

2. Materials and Methods

2.1. Sample Preparation

The samples were prepared to represent the materials typically found in Inert-CDW and the contaminants that generate the most concern when found in RA. Concrete, brick, and gypsum were used to emulate these materials (concrete as a material to be recovered and cleaned, and gypsum and brick as contaminants). The bricks used were commercial ceramic blocks without structural or refractory functions. The concrete was made according to the Structural Concrete Instruction—EHE/08 [24], and the gypsum was formulated based on the specifications of EN13297-1 [25]. The materials were crushed in a jaw crusher (Wedag Española, S.A.) with a top size aperture of 20 mm and then classified with sieves to generate material with a 5 × 20 mm size range, considered coarse aggregates. The fine materials (0 × 5 mm) were not used and were separated for another study.

The content of brick, concrete, and gypsum in the jig was determined by manual weighing and sorting. After jig separation, each fraction was oven dried at 70 °C ± 8 h to remove the moisture, and individual components (bricks, concrete, gypsum) were separated by visual identification and hand picking. Each material type was weighed with precision balance (±0.01 g), and the percentage content was calculated relative to the total mass of the fraction. This approach ensured consistent and reproducible quantification of material purity across all tests.

2.2. Materials Characterization

• Form Factor

The form factor test was carried out according to the EN 933-4 standard [26]. The standard defines that 200 aggregates must be selected proportional to the mass fractions of 9.5 × 12.7 mm and 12.7 × 19.5 mm, constant in each sample. The selected grains are measured in their most significant longitudinal portion and smallest thickness with a caliper. Thus, the form factor is the average between the ratios of the values measured in each of the particles. Values approaching 1 mean particles with spherical characteristics, and values further from 1 mean particles with lamellar characteristics.

2.2.1. Granulometric and Densimetric Distribution

The particle size distribution of the material was determined by sieving the samples and analyzing the material retained on the 20 mm, 12.5 mm, 8 mm, and 5 mm sieves.

The densimetric distribution was carried out using sink and flow tests and was carried out with a solution of sodium polytungstate. Tests were conducted using samples with the following densities: 2.4 g/cm³, 2.5 g/cm³, 2.55 g/cm³, 2.6 g/cm³, 2.65 g/cm³, 2.7 g/cm³, 2.75 g/cm³, and 2.8 g/cm³. The density of the solution was measured with a manual Anton Paar Density Meter (DMA 35); 5 × 20 mm, 5 × 8 mm, 8 × 12.5 mm and 12.5 × 20 mm were analyzed.

2.2.2. Specific Density (OD), Saturated Specific Density (SSD), Apparent Density (OD), and Water Absorption

To calculate the characteristics densimetric and the impact of cement paste at different stages of material concentration, it is important to consider the product in its saturated condition. Compared to natural aggregates, the presence of cement paste, which has a lower density and high porosity, alters several key physical parameters when the material is saturated. Therefore, measurements of both bulk and specific gravity under saturated surface dry and oven-dry conditions, along with water absorption, were conducted by the procedures outlined in the ASTM C127-07 [27] standard, to assess how cement paste affects aggregate behavior.

The process selected by the standard is as follows:

At a temperature of 110 ± 5 °C, dry the sample in an oven till a constant mass is obtained. After that, cool in normal air at room temperature for 1 to 3 h. Test samples of size 37.5 mm, which is the maximum nominal size, but can be longer for larger sizes. Afterwards, submerge the aggregates in water for 24 ± 4 h at room temperature.

After removing the material from water, soak it in water until all the visible water films are removed. To obtain precise results, the larger particles should be wiped individually. Determine the mass of the saturated surface dry sample. Record this and all following weights with a precision of at least 0.5 g or 0.05% of the total sample weight, depending on which value is larger. After that, place the product immediately into the sample container to determine its Buoyant mass in water at 23 ± 2.0 °C.

Place the sample in an oven and heat it to constant mass at 110 ± 5 °C. Afterward, allow it to cool at room temperature for 1–3 h, or until a temperature where aggregates are cooled and are comfortable to handle. Once cooled, measure its weight and record it.

Specific Density (OD) (kg/m³)

$$997.5{\displaystyle \frac{A}{B-C}}$$

(1)

Specific Density (SSD) (kg/m³)

$$997.5{\displaystyle \frac{B}{B-C}}$$

(2)

Apparent Density (OD) (kg/m³)

$$997.5{\displaystyle \frac{A}{A-C}}$$

(3)

Water Absorption (%)

$$\left[{\displaystyle \frac{B-A}{A}}\right]\times 100$$

(4)

where

A = mass of oven-dry test sample in air, g;

B = mass of saturated surface dry test sample in air, g;

C = apparent mass of saturated test sample in water, g.

2.3. Jigging Equipment

The tests were conducted on a pilot water jig designed for laboratory tests, as shown in Figure 2. The piston (A) is driven by the engine (B), and the water is projected through the water duct (C) to the jig chamber (D) that has a measuring tape attached to locate the fractions of each test (enlarged in Figure 2). The frequency used in the tests is controlled by the electrical panel (E).

After the test, the material is collected manually from the top of the jig chamber according to the cuts defined in each test. After being removed from the jig chamber, the materials were dried in an oven at 70 °C ± 8 h, and each particle was manually separated to quantify the composition of each of the portions removed from the jig. After the jig efficiency tests (carried out previously, not exposed in this work), the jigging frequency was set at 35 pulses per minute, with an amplitude of 14 cm, and the detention time in the jig chamber of 3 min for each test.

2.4. Concentration Tests

Three different jigging tests were carried out.

Table 1. Parameters of materials inside the jig chamber.

Materials	Weight (kg)	Weight (Wt%)	Bulk Volume	Bed Height (cm)
Test—T1
Concrete	21.982	90%	94.0%	18
Brick	1.221	5%	3.5%
Gypsum	1.221	5%	2.5%
Total	24.424	100%	100%
Material ρ > 2.6 g/cm3	7.474	31%	31%
Test—T2
Concrete	19.541	80%	87.0%	18
Brick	2.442	10%	8.0%
Gypsum	2.442	10%	5.0%
Total	24.425	100%	100%
Material ρ > 2.6 g/cm3	6.644	27%	29%
Test—T3
Concrete	17.099	70%	78.0%	18
Brick	3.663	15%	12.5%
Gypsum	3.663	15%	9.5%
Total	24.425	100%	100%
Material ρ > 2.6 g/cm3	5.814	24%	26%

Contaminant Tests: 10%, 20%, and 30% (Wt%).

shows the materials, the weight, the concentration of each material in the tests, and the bed height generated in the jig chamber.

All tests were carried out with ternary mixtures, where the concentration of each contaminant mixed with the concrete varies. In the first test (T1), 90% of the material in the jig chamber is concrete, 5% gypsum, and 5% brick, totaling 10% of contaminants. The second test (T2) comprises 80% concrete, 10% gypsum, and 10% brick, totaling 20% of contaminants. The third test (T3) was 70% concrete, 15% gypsum, and 15% brick, totaling 30% contaminants. The material presented as “Material ρ > 2.6 g/cm³” in Table 1 is a dense material mixed in the concrete densimetric analysis, which could possibly be replaced as coarse aggregates in new concrete formulations. This material is mixed in the whole range of concrete particles inserted in the batch and is used as a parameter of the process efficiency in this study.

Figure 3 displays the flowchart for the three tests conducted. Made of concrete, gypsum, and brick ranging from 5 to 20 mm, the tests were performed in a single jigging stage, producing three different products. Each material was collected in 6 cm layers within a jigging bed, representing 33% of the total volume of each material’s chamber. Tests T1, T2, and T3 (shown in red in the figure) were conducted separately using the same jigging parameters, with variations in the amount of each element to simulate a C&DW with different contaminant concentrations and produce three distinct products. The jigging bed for all tests was 18 cm deep, with the light material located in the first 6 cm (18–12 cm), the medium-weight material in the middle 6 cm (12–6 cm), and the densest material at the bottom of the bed, comprising the last 6 cm (6–0 cm), which terminates at the jig sieve.

After the jigging process, the materials were manually removed from the chamber, and each particle was manually separated to analyze and quantify each portion of material generated. The materials were used in pure form (without the presence of material adhered to the particles).

3. Results and Discussion

3.1. Physical Characterization of Materials

3.1.1. Physical Properties Analysis

Table 2. Values obtained for the bulk density, specific density (OD and SSD), form factor, and water absorption of the materials used during the tests.

Material	Specific Density (OD) (g/cm3)	Specific Density (SSD) (g/cm3)	Bulk Density (g/cm3)	Water Absorption (%)	Form Factor
Concrete	2.04 ± 0.01	2.13 ± 0.01	1.37 ± 0.01	4.93 ± 0.03	2.19
Brick	1.77 ± 0.02	2.03 ± 0.02	1.03 ± 0.01	13.26 ± 0.04	3.49
Gypsum	1.11 ± 0.02	1.62 ± 0.02	0.64 ± 0.01	46.92 ± 0.08	2.22

indicates the values taken for specific density in saturated (SSD) and oven-dried (OD) form, bulk density, water absorption, and the form factor of materials. The bulk density of the materials is directly proportional to the shape factor, due to the packaging capacity of the particles within the jig chamber. A higher form factor means a material with a lamellar particle, which prevents the material from packing. The material’s packing capacity is higher with a shape factor closer to 1 [28]. This material has the possibility of better packing, thus leaving fewer spaces (voids) between the particles and increasing the bulk density value.

The physical properties of concrete, brick, and gypsum show significant differences essential for understanding their behavior in separation and recycling processes. Concrete displays the highest specific density among the three materials in oven-dried (2.04 ± 0.01 g/cm³) and saturated surface-dry (2.13 ± 0.01 g/cm³) states. Brick exhibits slightly lower values (1.77 ± 0.02 g/cm³ OD, 2.03 ± 0.02 g/cm³ SSD), and gypsum shows the lowest densities (1.11 ± 0.02 g/cm³ OD, 1.62 ± 0.02 g/cm³ SSD), indicating it is the least dense and most porous of the materials tested. Bulk density values follow a similar pattern, reinforcing the trend seen in specific density. Concrete exhibits the highest bulk density at 1.37 ± 0.01 g/cm³, indicating a compact structure with minimal void space. Bricks, with a bulk density of 1.03 ± 0.01 g/cm³, are lighter due to their internal porosity [28]. Gypsum, with a bulk density of only 0.64 ± 0.01 g/cm³, is significantly less dense, indicating a loosely packed and highly porous structure.

These differences are crucial in influencing the separation efficiency of these materials in gravity-based processes like jigging. Water absorption data offers additional insight into the porosity of the materials. Gypsum stands out with a water absorption rate of (46.92 ± 0.08)%, confirming its high porosity and water-retaining ability. Bricks absorb (13.26 ± 0.04)% water, also indicating a porous internal structure. Concrete, with a significantly lower absorption rate of (4.93 ± 0.03)%, is denser and less permeable. The variation in water absorption directly impacts how these materials behave in water-based separation systems, affecting settling velocity and overall separation performance [21].

3.1.2. Granulometric Distribution

The particle size distribution of the material is demonstrated in Figure 4. After comminution, the materials formed fine particles (understood as the fraction of the material that presents a range of 0 × 5 mm). In total, 33% of the concrete, 22% of the bricks, and 19% of the gypsum were classified as fine materials and were not used in this study, but were separated by sieving and stored for future studies.

Concrete is composed of coarse aggregates (high-strength particles), fine aggregates (particles that are mixed with the cement), and cement paste (low-resistance material). During comminution, the concrete tends to fracture in the interstitial zones, which favors the formation of completely liberated coarse aggregate particles and mixed particles, which are formed by aggregates with cement paste attached. Particles composed of only cement paste tend to fracture randomly, forming the finest materials. After granulometric analysis, concrete exhibited 14.7% of particles with a size range of 5 × 8 mm, 26.1% with a size range of 8 × 12.5 mm, and 25.5% with a size range of 12.5 × 20 mm.

As a result of the original shape in which they are sold, bricks tend to fracture into lamellar particles with more elongated shapes, and form particles with larger fractions (12.5 × 20 mm) as shown. Bricks comprised 7% of particles with the size range 5 × 8 mm, 21.8% with the size range 8 × 12.5 mm, and 49.1% with the size range 12.5 × 20 mm, comprising the most significant portion of the material.

Due to its greater water composition, gypsum presents more formation of fines, and due to its low resistance, it tends to form particles randomly. Gypsum had 8.3% particles with a size range of 5 × 8 mm, 12.5% with a size range of 8 × 12.5 mm, and 28.4% with a size range of 12.5 × 20 mm.

3.1.3. Densimetric Distribution

The following densities were used for the sink-and-flow test: 2.4 g/cm³, 2.5 g/cm³, 2.55 g/cm³, 2.6 g/cm³, 2.65 g/cm³, 2.7 g/cm³, 2.75 g/cm³, and 2.8 g/cm³. This was carried out in each of the granulometric ranges of the concrete (5 × 20 mm, 5 × 8 mm, 8 × 12.5 mm, and 12.5 × 20 mm). Figure 5 shows the mass obtained from concrete at different density and size ranges.

The concrete exhibits a high densimetric variation, ranging from 2.4 to 2.8 g/cm³, due to the segregation mechanism of its materials. Recycled concrete typically includes coarse aggregates (high-density particles), fine aggregates (sand), and cement. Material with a density below 2.6 g/cm³ is either cement paste thoroughly mixed with fine aggregates or coarse aggregates with a layer of cement paste attached, which significantly lowers its specific density and increases water absorption. This can make it impossible to reuse as RA in new concrete mixtures, due to certain regulations and specifications.

The material with a density higher than 2.6 g/cm³ is fully liberated coarse aggregates or coarse aggregates with a thin layer of cement paste. Concrete tends to fracture in the interstitial zones (ITZs) due to the difference in resistance between the aggregates and the cement paste. ITZs were the parts of concrete with the lowest strength, which allows the recovery of the aggregates and their possible reuse as RA if composed of material with a density above 2.6 g/cm³.

From Figure 5, it can be observed that more than 50% of the material that makes up the concrete with the size ranges of 8 × 12.5 mm and 12 × 20 mm is light materials (with a density below 2.6 g/cm³), which are composed of agglomerates of fine aggregates completely involved with cement paste. Such behavior is not observed in the fraction with the size range of 5 × 8 mm due to the randomness in the fractures that occur in the thinnest portions of the generated material, where a considerable variation in densities ranging between 2.4 g/cm³ and 2.8 g/cm³ are extant.

The brick and the gypsum were not subjected to the sink–float test, as they do not have considerable densimetric variations, due to their homogeneity. Their densities were defined in the density test.

3.2. Jig Concentration Tests

In

Table 3. Recovery and ratio values of concrete, brick, gypsum, and dense material (>2.6 g/cm³) obtained from jigging tests T1–T3. Recovery (%) represents the percentage of each component recovered in a specific jigging fraction (light, middling, dense) relative to its total amount in the feed. Ratio (%) represents the relative composition of each fraction, i.e., the proportion of each material within that layer after jigging.

Test	Component	Feed (%)	Light Product		Middling Product		Dense Product
			Recovery (%)	Ratio (%)	Recovery (%)	Ratio (%)	Recovery (%)	Ratio (%)
T1	Concrete	90.0	15.3	66.0	29.0	95.4	55.7	99.6
	Gypsum	5.0	92.1	18.0	6.4	1.0	1.3	0.1
	Brick	5.0	76.0	16.0	21.3	3.5	2.1	0.2
	>2.6 g/cm3	31.0	5.0	9.2	12.7	12.9	82.3	45.9
T2	Concrete	80.0	18.6	46.8	32.8	90.1	48.6	99.4
	Gypsum	10.0	94.1	29.5	5.4	1.8	0.6	0.1
	Brick	10.0	75.1	23.7	23.4	8.0	1.5	0.3
	>2.6 g/cm3	27.0	2.7	2.3	17.0	15.8	80.3	55.9
T3	Concrete	70.0	4.9	13.5	34.7	75.2	60.4	99.4
	Gypsum	15.0	98.6	58.1	1.3	0.6	0.6	0.2
	Brick	15.0	47.1	28.4	51.8	23.4	1.1	0.4
	>2.6 g/cm3	24.0	1.9	1.7	12.6	9.2	85.6	47.2

, the values obtained for products generated in each test are shown. The material was divided into groups that underwent three different tests: T1, T2, and T3. T1 had 10% concrete weight contaminants, T2 had 20% contaminants, and T3 had 30% contaminants. Each test generates three different products: light products (LPs), which remain at the top layer in the jigging equipment after the test; middling products (MPs), where the product remains in the middle layer in the jigging equipment; and dense products (DPs), where the material comprises the bottom layer in the jig.

The light products from all three tests showed the effective separation of low-density materials. The light product from test 1 (LP1) contained 66% concrete, 18.0% gypsum (92% feed gypsum), and 16.0% bricks (76% feed bricks). The light product from test 2 (LP2) demonstrated similar trends with 46.8% concrete, 29.5% gypsum (94.1% recovery), and 23.7% brick (75.1% recovery). The light product from test 3 (LP3) showed the highest gypsum concentration at 58.1% (98.6% recovery) with 13.5% concrete and 28.4% brick. All light products contained minimal dense material (<5% of feed), confirming the effective separation of low-density components, and the jig theory as explained.

Concrete, in particular, showed a significant percentage of partially liberated aggregates in the middling products. The middling product from test 1 (MP1) retained 3.5% brick, 1% gypsum, and 95.4% concrete from the feed. With 90.1% concrete, 1.8% gypsum, and 8% brick, the middling product from test 2 (MP2) showed a similar pattern. The middling product from test 3 (MP3) had the lowest concentration of concrete (75.2%), but due to the higher levels of pollution in the feed, there was a noticeable increase in brick content (23.4%). Between 9% and 16% of dense materials (>2.6 g/cm³) were caught by these middling layers, indicating an intermediate quality proportion that could be further reinserted into the jig circuit to obtain more fully freed dense aggregates.

The dense products had a high purity (>99% concrete) across all tests. The dense product from test 1 (DP1) contained 55.7% of the feed concrete with only 0.1% gypsum and 0.2% brick. The dense product from test 2 (DP2) and the dense product from test 3 (DP3) showed similar purity (99.4% concrete) while recovering 48.6% and 60.4% of feed concrete, respectively. These products comprised 80–86% of dense material (>2.6 g/cm³), consisting mainly of fully liberated aggregates with minimal cement paste, making them suitable for direct recycling in new concrete formulations. Contaminant levels remained below 1% in all dense products.

Generated Material Analysis

The tests were conducted on different compositions of CDW mixtures producing dense materials of high purity (>99% of concrete), confirming the effectiveness of lab-scale water jigging for the separation of multi-component mineral fractions. These results are consistent with the above-mentioned [11,12,13,21,22,23] studies, demonstrating the capability of gravity-based separation methods to concentrate effectively mixed CDW inputs. In line with previous research [12], which demonstrated that water-based jigging can produce recycled aggregates (RAs) with a concrete content exceeding 99.5% when contamination levels are moderate, the application of lab-scale hydraulic jigging proved successful in separating concrete from contaminants such as gypsum and brick. The different grain size distributions and physical characteristics of the three phases account for the observed performance. Brick broke into coarser, lamellar particles that partially functioned as ragging material, dilating under pulsation and allowing the downward migration of denser concrete grains. In contrast, gypsum, which is finer and less dense, stratified toward the upper layers. Concrete has intermediate particle sizes, but it is denser and less porous than other materials. It is always concentrated in the dense fraction. The interaction of particle size distribution, density, and morphology supports the high purity (>99% concrete) seen in the dense products.

All test conditions in the current study produced dense products (DPs) that were over 99% pure concrete with very slight brick and gypsum traces. This is consistent with findings [12,13], which found that even with cement paste and brick present, traditional jigging produced substantial concrete recoveries from mixed CDW. Interestingly, T3 produced over 99.4% concrete in the dense fraction despite greater contamination, but DP1 recovered 60.7% of input concrete with just 1.3% gypsum and 2.1% brick.

Good operational resilience is also suggested by the consistency of separation across different contamination levels. Higher contaminated mixtures, such as T3, experienced a minor decrease in efficiency, with only 1.9% of the LP3 with a density greater than 2.6 g/cm³ ending up in the light fraction, compared to 5% in T1. This decline suggests less accurate stratification under feed settings that are more varied. Such behavior is in line with the operational difficulties, which found that more heterogeneity in CDW mixes might decrease the precision of density-based separations like jigging and lessen the clarity of stratification. The results demonstrate that, even at the laboratory scale, hydraulic jigging provides a practical and effective method for recovering high-purity recycled aggregates from CDW mixes, with reliable results across a range of feed compositions. A single jigging stage is adequate for producing high-quality recycled aggregates, although multi-stage jigging can enhance purity and recovery [11,13]. Our findings show that merely one step of water jigging may provide goods that are very dense and have fewer than 1% contaminants.

Table 4. Characterization of physical parameters for the materials used in the tests.

Sample	Specific Density (SSD) (g/cm3)	Specific Density (OD) (g/cm3)	Bulk Density (OD) (g/cm3)	Water Absorption (%)	Form Factor
T1	1.66 ± 0.02	1.50 ± 0.02	1.71 ± 0.02	8.08 ± 0.05	2.12
T2	1.76 ± 0.03	1.64 ± 0.04	2.05 ± 0.05	13.01 ± 0.02	1.82
T3	1.84 ± 0.04	1.63 ± 0.02	2.10 ± 0.03	14.67 ± 0.22	1.95
DP3	2.52 ± 0.04	2.49 ± 0.06	1.44 ± 0.06	4.78 ± 0.04	2.19

shows the values of specific density (SSD), density oven-dried (OD), bulk density (OD), water absorption, and the form factor of feed samples T1, T2, and T3, in comparison with the dense materials that were recovered. Due to the homogeneity between the dense materials that were generated in each of the tests, in Table 4, DP3 was chosen to compare the physical parameters and analyze the improvement in the indicators obtained after the jigging process.

To assess the influence of particle geometry on the physical behavior of the product, a shape factor analysis was conducted on the fraction of feed in each mix. The average shape factors obtained for each mixture were 2.12, 1.82, and 1.95 for T1 to T3, respectively. T2 exhibits the lowest shape factor, indicating a predominance of finer or more equidimensional particles at this replacement level. Conversely, T1 and T3 show relatively higher values due to the following: For T1, low substitution, where coarse aggregates (which may be more elongated or angular) dominate the shape factor. For T3, higher substitution increases the proportion of lamellar brick particles, which tends to contribute to higher form factors due to their irregular geometry. This behavior suggests that particle geometry in composite mixes is not solely dependent on substitution percentage but also on how different materials fracture, mix, and interact during the preparation stage. The analysis confirms that the de form factor of the DP3, where the contaminants’ presence is less than 1% and the coarse aggregates’ natural form, increases the value.

The densities and water absorption are directly proportional to the contaminant ratios. The water absorption increases with the weight percentage of contaminants, as brick and gypsum are more porous than concrete [29].

Specific density (OD) increases from (1.50 ± 0.02) to (1.66 ± 0.02) g/cm³, and bulk density increases from (1.71 ± 0.02) to (2.10 ± 0.03) g/cm³ when contamination increases from T1 to T3. Water absorption also increases dramatically at the same time, rising from (8.08 ± 0.05)% in T1 to (14.67 ± 0.22)% in T3. As a result of increased contamination levels or lower-quality fractions, T3 shows more absorptive and potentially less dense microstructures, reflecting the changing composition and porosity of the recycled materials. Comparing these values with the DP3 analysis, it is possible to observe the increase in density values due to the drastic reduction in contaminants present. If the DP3 values are compared with the concrete analyzed in Table 2, it is possible to observe an increase in more than 21% and 14% in the specific gravity (OD) and (SSD) values, respectively. This phenomenon is explained by the removal of less dense particles that were separated in the MPs and LPs, concentrating the particles with a density > 2.6 g/cm³ in the DMs.

Teixeira’s findings [29] show that concrete aggregates recovered by a two-stage water jigging technique can achieve higher physical quality, and the results are consistent with these findings. High-quality material was indicated by the specific densities of the recovered fractions above 2.6 g/cm³ and low water absorption values. The potential for jigging to generate recycled aggregates appropriate for use in new concrete applications is reinforced by the growing trend in density and the comparatively steady form factor, particularly when operating parameters are optimized.

Additionally, the findings show that there is a definite connection between the qualities of the materials, the jigging parameters and the quality of the recycled aggregates produced. Under the applied jigging conditions (35 pulses/min, 14 cm amplitude, 3 min residence), the concrete, which has a higher density and lower porosity, always moved to the dense fraction. On the other hand, the gypsum, which has a lower density and a higher water absorption, accumulated in the light fraction. Brick, which has an average density and a higher form factor, was only partially stratified in the intermediate layer. The chosen process settings encouraged stable stratification, resulting in products with more than 99% concrete in the dense fraction and less than 1% contaminants. This shows that the way water jigs separate things depends on how the jig is configured and the qualities of the CDW components.

4. Future Trends

In our current situation, where the complexity of extracting new materials for civil construction and the production of construction and demolition waste (CDW) are increasing due to globalization and societal development, discovering new ways to reuse these materials is becoming essential. This creates opportunities to reintegrate these materials into the construction supply chain. Understanding the large volume of waste generated, its heterogeneity, and the contaminants found in recycled materials from CDW—which mainly hinder their reuse in more valuable applications—research on how to purify this material and develop different passive materials for reuse in various products appears to be the most practical approach to reduce landfilling and the disposal of CDW.

Viewing the process as an economic cycle, the next steps in research on this material should focus on assessing the physical and chemical suitability of these materials according to regulations for civil construction materials. Following this, the performance of these materials should be tested in new applications, such as in different concrete formulations, using the recovered material as aggregates, in high-performance concrete, or ceramic materials. Additionally, new options should be explored, such as using these materials as absorbents in liquid effluent treatment, which could make investment in plants and recycling processes for this material more attractive and economically feasible.

After laboratory-scale analyses of all the suitability and characteristics of this material, it is necessary to carry out a pilot-scale plant to understand the transfer of this process to an industrial scale. Due to the heterogeneity of CDW and the large volume generated, several variables will prove to be fundamental to adapting this process to be suitable for use in industrial plants.

5. Conclusions

The main conclusions of this paper are as follows:

Observing the materials (gypsum, brick, and concrete) in the context of managing the inert portion of the CDW, when the materials are crushed to a top size of 20 mm, they generate a minority portion of fine material (0 × 5 mm), with a majority of its particles being in the size range of 5 × 20 mm.

This study demonstrates the technical viability of utilizing water jigging as an efficient method for recovering high-quality recycled aggregates (RAs) from mixtures of concrete, gypsum, and brick found in construction and demolition waste (CDW). The laboratory-scale experiments showed that even at contamination levels as high as 30 wt%, water jigging consistently produced a dense fraction with more than 99% concrete purity and less than 1% impurities, making the recovered material suitable for reuse in concrete production.

The results confirm that the main determinants of separation efficiency are bulk density, particle density, and shape. Concrete was successfully separated from brick because of its lamellar fracture and from gypsum because of its low density and high porosity. In a single jigging stage, more than 80% of the dense fraction (ρ > 2.6 g/cm³) could be recovered, and its physical characteristics (specific density and water absorption) were similar to those of natural aggregates.

This investigation underscores the wider environmental and industrial importance of water jigging, in addition to its technical confirmation. Facilitating the recovery of clean aggregates may diminish construction and demolition waste discharge by over 40%, lessen the carbon footprint of the building industry, and bolster circular economy initiatives. These findings indicate operational robustness across varying contamination levels, which is essential for practical applications where CDW composition is very changeable.

It is possible to generate final products with low impurity contents, and a purity grade of over 99% concrete. This concentrate has a high enough purity to be used as recycled aggregate.

The tests proved that the values of the shape factors and the bulk densities of the materials are directly responsible for concentrating the materials within the water jig process.