Characterization of Recycled Aggregates from Building Demolition Waste for Use in Road Infrastructures

Abstract

In light of rising environmental concerns, the rapid industrial recycling of building demolition waste material (BDWM) is now capable of supporting sustainable development in metropolitan regions. From this perspective, the current study investigated the geotechnical properties and applications of BDWMs as substitutes for natural materials (NMs) in road engineering infrastructures. For this purpose, the physical and geotechnical characteristics of both types of materials were initially examined, and then compared using laboratory-scale material comprehensive assessments such as sieve analysis (SA), the flakiness index (FI), the specific gravity test (Gs), the Los Angeles abrasion test (LAAT), Atterberg limits (AL), the water absorption test (WAT), the California bearing ratio (CBR), the direct shear test (DST), and the Proctor soil compaction test (PSCT). The BDWMs were collected from two locations in Iran. According to the results, the collected samples consisted of concrete, bricks, mortar, tile materials, and others. The CBR values for the waste material from the two sites were 69 and 73%, respectively. Furthermore, the optimum water content (OWC) and maximum dry unit weight (MDD) from the two sites were reported as 9.3 and 9.9% and 20.8 and 21 kN/m³, respectively, and the hydrogen potential (pH) as 9 and 10. The shear strength and CBR values indicated that the BDWM had a suitable strength compared to the NM. In terms of road infrastructure applications, the shear strengths were adequate for the analysis of common sub-base materials used in filling and road construction. Furthermore, the study’s findings revealed that BDWMs were suitable replacements for the NM used in road engineering operations and could make a significant contribution to sustainable development.

1. Introduction

Virgin materials, as the primary sources of natural resources, are widely used in engineering. Nowadays, some recycled waste materials have received a lot of attention because they can reduce demand for NM [1,2]. With faster urbanization, the consumption of building waste materials from old buildings has increased. Given Iran’s rapidly expanding population and construction industry, the use of virgin materials has increased significantly. Excessive exploitation of natural resources has resulted in increased costs and environmental damage. It is worth noting that the construction industry is now producing a significant amount of demolition waste worldwide [2,3]. As a result, disregarding such waste is likely to cause a slew of environmental issues in the future [1,4].

BDWMs are typically generated as solid waste, such as concrete, solids, bricks, ceramics, glass, plastics, bitumen, tiles, metals, rubbers, and so on, resulting from the demolition of numerous civic projects. In this context, statistics show that BDWMs produced by the construction industry account for 70, 46, 36, 30, and 78% of the total waste produced in Iran, Italy, Japan, Spain, and Australia, respectively [2,3]. Currently, most landfills near urban areas are overflowing with such waste materials [1,2,3,4]. As demonstrated by previous research, the reuse of this type of waste material appears to be beneficial in pavement and reclaimed asphalt engineering [5,6]. In recent years, the Iranian government has planned to replace approximately two million houses, followed by the construction and restoration of dilapidated urban fabrics over a three-year period, potentially leading to an increase in such waste in this region. Furthermore, some landfills in major cities across the country have overflowed. In this regard, there are two significant issues in recycling construction building waste materials: economic and environmental. Recycling reduces the amount of waste in these landfills and the use of natural materials [1,2,4]. Furthermore, these wastes could be stabilized with lime and cement to improve their engineering properties [7,8]. Overall, such waste can be used in all engineering applications.

The waste recycling rates of BDWM in various countries, such as Iran, France, Portugal, Spain, and Greece, are currently low, at 3, 14, 5, 17, and 5%, respectively, which is lower than the EU-27 average (46%) [9]. In contrast, the complex process of recycling to produce high-quality materials should become economically viable despite its high energy consumption. As a result, separation requires significantly more effort and expense, but little research has been conducted on building waste materials in landfills [10]. Furthermore, such materials have not been studied in terms of geotechnical properties or performance. The primary challenge for specific building waste materials has been economic profitability, which is influenced by factors such as labor and mechanization [11]. On-site building waste sorting has become increasingly popular for producing high-quality materials [12]. In recent years, the production rate of such waste materials has increased significantly [3,4].

Some studies have used different BDWMs instead of new material in engineering, such as recycled concrete aggregate (RCA) [13,14,15].

According to previous research on the uses of BDWM, there have been few studies on the use of BDWM, particularly in Tehran, for road construction purposes. As a result, the current study sought to address this gap in the related literature. It is worth noting that BDWM can be prepared at a lower cost and in less time, potentially having a significant economic and environmental impact. Determining the geotechnical properties of such materials and their applications in road engineering was the primary goal of this study. For this purpose, the BDWMs extracted from two sites in Tehran, Iran, were first exploited, and then a variety of geotechnical tests, such as the DST, CBR, Modified PSCT, WAT, FI, and SA, were used to assess them.

2. Methods and Materials

2.1. BDWM

The waste materials used in this study, specifically the BDWMs, were collected from two sites in Tehran province (Figure 1). Figure 2 illustrates the recycling process at the BDWM waste recycling plant. These materials came from the demolition of an old building.

The BDWMs were recycled at various stages, requiring significant effort and time, including crushing, measurement, categorizing, and pollutant removal [16]. The iron and steel components in this type of recycling were then separated by hand or magnets. The BDWMs were then crushed with a stone crusher, and the grains were classified as granules ranging in size from 0 to 30 mm and larger. Materials larger than 30 mm were also re-crushed to suit a variety of applications. Finally, the BDWMs were obtained.

Figure 3 shows the SA of the crushed materials. According to SA curves and the relationship between upper and lower limitations (as mentioned by Arul Arulrajah [9]), both grades of BDWM in the two sites are suitable for surface tracks and highway bases.

As shown in Figure 4, the BDWMs in both sites consisted of concrete, brick, glass, bituminous materials, and other components such as wood and mortar. The steel parts were also observed and separated using magnets. Figure 5 depicts the composition of recycled materials found at both sites.

2.2. NM

Natural materials were obtained from a mine in Tehran, Iran. Figure 3 shows the gradation of the NM. The gradation of the given materials was appropriate for use in surface tracks and highway foundations, meeting both minimum and maximum standards.

2.3. Experiments

The primary experiments were completed to assess the characteristics of the BDWM and NM (

Table 1. The BDWM and NM testing program.

Tests	Standards	Results	Tested Samples
SA	ASTM D422	Physical characterization analysis	BDWM, NM
Gs	ASTM D854		BDWM, NM
WAT	Conventional tests		BDWM, NM
FI	BS 812-105.1		BDWM, NM
LL and PL	ASTM D4318		BDWM, NM
LAAT	ASTM C 131		BDWM, NM
Modified PSCT	ASTM D 1557	Compaction analysis	BDWM, NM
CBR	ASTM D1883	Load-displacement curves analysis	BDWM, NM
DST	ASTMD5321	Shear strength analysis	BDWM, NM

). Furthermore, the laboratory tests were conducted in accordance with acceptable technical highway specifications in various countries, as well as the ASTM and BS standards. As a result, the experiments on the BDWMs were carried out using a variety of tests, including the specific gravity test (Gs) or density determination by a pycnometer in accordance with the ASTM-D854, Atterberg limits (AL), the particle-size distribution (PSD) test, the water absorption test (WAT), the modified Proctor soil compaction test (PSCT), the direct shear test (DST), the flakiness index (FI), the Los Angeles abrasion test (LAAT), and the California bearing ratio (CBR). As stated in ASTM D422-63As, the BDWM and NM underwent SA. Furthermore, two tests, the PSD and WAT, were performed on coarse-fine materials, while liquid (LL) or plastic (PL) limits were determined using fine materials (using ASTM-D4318). AL was also used as an empirical measure of critical water content [3,4]. Furthermore, the FI was applied in accordance with BS-812-105.1. The LAAT, a well-known test for determining the resistance of filling materials to force and abrasion, was also used to compare the quality of the two materials, BDWM and NM. According to ASTM-C131-03, the materials were then placed in a steel drum containing steel spheres that rotated in a limited manner. Notably, the given materials required low abrasion values for both construction and geotechnical applications. The modified PSCT was used to assess the relationship between the materials’ dry density and moisture content in accordance with ASTM-D1557. CBR tests were performed in accordance with ASTM-D1883-99 to determine load-displacement behavior and obtain the OWC and MDD. A DST apparatus (300 × 300 × 200 mm) at a shearing rate of 1 mm/min was then employed to assess the shear strength parameters of the BDWMs and NMs based on OWC. In this context, the samples were prepared in accordance with the MDD and based on ASTM-D5321 for the BDWMs and NMs, considering all three normal stresses. Following the consolidation phase, horizontal shear displacement was applied. The results were then presented, and the shear strength values for the BDWMs and NMs were determined. In the tests, water was added to the BDWM, and the waste was left for 24 h to absorb the water.

3. Results of Basic Laboratory Testing for the Identification of BDWM and NM Properties

In this study, the physical properties of the NMs obtained from mines near Tehran, Iran, and the recycled BDWMs obtained from the two sites were assessed.

Table 2. Engineering properties of the BDWM and NM.

Materials	Gs (Coarse)	Gs (Fine)	WAT (Coarse) (%)	WAT (Fine) (%)	PL (%)	LL (%)	FI	LAAT (%)	MDD (kN/m3)	OWC (%)	CBR (%)	C (kPa)	Φ (°)
BDWM (Site 1)	2.75	2.65	4.0	6.2	20.4	29.3	15.2	31.3	20.8	9.3	73	60	41
BDWM (Site 2)	2.73	2.62	4.1	7.1	21.5	31.2	15.6	35.2	21	9.9	69	59	43
NM	2.79	2.72	0.9	1.0	5.4	10.4	11.0	25.0	27	6.2	89	64	45

summarizes the experimental results from the two sites for further comparison. They were small-scale and only concerned Tehran, Iran, so field experiments were necessary to generalize the results to field conditions. The study’s perspective and limitations are presented below. Furthermore, the results of this study were compared to previous research.

3.1. WAT

The WAT results of the BDWMs used in urban projects have been evaluated in relation to some engineering applications. In this study, the BDWM’s water absorption capacity was investigated.

Previous studies have shown that the WAT values of BDWM fluctuate between 1 and 10% but rarely exceed 3%. The given conditions were also applicable to the NMs used in the current study. As evidenced by [17], BDWMs containing concrete and bricks may be porous. Furthermore, the water absorption of the recycled materials for each site in specific proportions was discovered to be approximately 6.2–7.1 and 4.0–4.1 times greater than the NMs containing fine and coarse grains, respectively. According to the FHWA, the absorption values of the BDWMs were approximately 3–5% higher than those permitted for highway construction. Fine-grained materials with parts smaller than sieve No. 40 were used to test the AL at both sites. In light of this, the LL and PL for recycled BDWM were lower.

The fine materials in the CBs were mixed with water to form a viscous paste that was then used to increase the PI value. Because the clay content in other sites was low, there were some challenges to the viability of the BDWMs, so cohesion was a desirable characteristic. The results showed that the recycled waste materials had a lower specific density and a higher tendency to absorb water than the natural ones, owing to the presence of mortar. As a result, combining the BDWMs with others or using a small amount of fine NMs may help address this issue. It was important to conduct the necessary tests on the mixture containing cohesive and high-quality materials in varying percentages in order to assess its suitability for a variety of applications.

3.2. FI

In this study, the FI was used for the materials in the bituminous mixtures, and the BDWM value ranged from 15.2 to 15.6 in extracted samples. Furthermore, the grains contained fewer elongated materials. Thus, they appeared more efficient when compressed. On the other hand, they may be suitable for use as base materials in normal state roads and pavements, with a maximum value of 35.

3.3. LAAT

The LAAT was used to determine the abrasion and impact resistance of the materials. The LAAT results for the BDWM showed that the number of coarse grains in concrete and brick was not significantly higher than that of the NMs. In this study, the LAAT outcomes for the BDWMs were approximately 25–40% higher than those of the NMs, indicating that the latter were more resistant to abrasion. Despite this, the state road authorities approved the maximum values for the sub-base and base at 40. To improve the performance of recycled materials for road paving and underlayment, they needed to be combined with other appropriate aggregates.

3.4. Modified PSCT

The BDWM compaction curves were determined, and they were similar to the NM curves. Figure 6 depicts the Modified PSCT results, which show that the OWC of the BDWMs was higher, ranging from 9.3 to 9.9 for the two sites, and their MDDs were 20.8 and 21, respectively, which were lower than the NM ones. Given the high percentages of CBs and RCA, the OWC was close to 10%. The amount of WA in the materials also had a negative effect on their parameters. As a result, as the WA of recycled BDWMs increased, so did the OWC, while the MDD decreased. The amount of water to reach the BDWMs with OWC and MDD could thus give rise to high water consumption rates in geotechnical constructions.

3.5. CBR

According to the suggestions, the CBR value approved by the state road authorities for the sub-base and base aggregates was at least 80%. As a result, CBR values less than 80% could be mixed with natural materials to make the best use of recycled BDWM with higher performance while improving road sub-base layers. Using stronger additives is one method for improving material quality. This technique involves adding additives with appropriate strength to raw materials in order to improve their quality. In this study, using this method with BDWM materials to improve the CBR value was recommended. Given that determining the amount of additive necessitates several additional tests, and this section is not defined in this project, additional information has not been provided in this study, and more complete details on how to use this method will be provided in future studies.

Recycled BDWMs with California bearing ratio test results significantly lower than this value may have engineering applications, such as filling embankments [9]. The California bearing ratio test results in this study and at the two sites were 69–73%. The differences in CBR results between the two sites were caused by slight variations in strength and material composition. Overall, the CBR value for the given depot was comparable to that for natural grains [9]. Recycled BDWMs had a lower CBR than NMs. Figure 7 and the California bearing ratio test results show that the curves for the BDWMs and the NMs at the initial displacements are similar. Despite this, the curves show a slight divergence as the level of displacement increased. The NMs were further thought to have higher CBR values than the BDWMs.

3.6. Strength Behavior of BDWM and NM

The DST results revealed that the curve trends for the BDWM and NM were nearly identical. Figure 8 shows the Mohr–Coulomb failure envelope lines. In granular materials such as sand, very dense sand, and pre-consolidated clay, the sample volume initially decreased and then increased as soil particles moved on each other and the soil expanded, which could be commonly used in civil engineering with reference to peak friction and residual values of 40–48 and 32–36 degrees, respectively [17]. In accordance with the behavior of the samples, the DST results for the BDWM indicated that they met the shear resistance requirements for use as geotechnical materials. The rising trend in normal stress was also found to reduce the tendency for dilation, which is consistent with these findings. The values showed high continuity in appearance because they had significant RCAs, which were strengthened by more hydration from absorbing water from the mixture. Additionally, some previous studies [18] reported similar RCA values. The presence of CBs and fine clay in these blanks created a paste with high adhesiveness when combined with water under compression, resulting in higher apparent cohesion than other blanks. The small amount of bitumen-containing RAP also contributed to the cohesion. In terms of the BDWM’s shear strength parameters, they were not necessary for base and sub-base applications because the minimum internal friction angle required did not exceed 35 degrees.

4. Comparing Using BDWM with Similar Trends

Table 3 compares the waste characteristics, including Cc, Cu, LAAT, and BDWM strength values, to those described in the literature. The geotechnical properties of the BDWMs resembled the average results of previously investigated materials. Furthermore, previous studies using various recycled materials reported LAAT outcomes ranging from 28 to 42.5%. The LAAT results for BDWM waste materials in this study were also between 34.5 and 35.3%. As a result, they appeared to be efficient under compression and suitable for base materials in standard state roads and pavement applications, with a maximum value of 35. Notably, these conditions and values were met during this study. Considering the unit weight of the NM, the MDD of the BDWM was 19.5 kN/m³, which was similar to the values reported for recycled ones in the related literature. Resistance parameters were also compared to similar studies. However, some studies did not mention waste resistance or provided insufficient information. The mean values of cohesion, internal friction angle, and CBR in this study were also 62 kPa, 43 degrees, and 71%, respectively, which differed little from previous research on similar materials. The minor differences between wastes in various references are due to changes in waste composition. In general, the obtained results indicate that the geotechnical properties of the BDWM were similar to those of the recycled ones studied previously. Figure 9 shows that the OWC and MDD values of different wastes vary depending on their location and composition and must be considered when designing projects.

Table 3. Comparison of waste properties in the present study with the literature.

Cases	Types of Aggregates					Properties of Waste
		Cu	Cc	MDD (kN/m3)	LAAT (%)	C (kPa)	φ (°)	CBR (%)
Current Research (Site 1)	BDWM	28.1	1.2	19.51	35.3	61	42	69
Current Research (Site 2)	BDWM	28.3	1.21	19.35	34.5	63	44	73
Arulrajah et al., 2013 [9]	RCA	31.2	0.9	19.13	28	44	49	-
Herrador et al., 2012 [19]	RCA-RAP-CB	30	1.29	-	34	-	-	-
Cerni et al., 2012 [20]	CD waste	85.71	1.93	25.7	37	-	-	-
Nasiri et al., 2024 [21]	CD waste	29.4	1.32	19.5	42.4	70	34	59
Strider et al., 2023 [6] (AASHTO Hammer)	CDW1	86.7	2.5	18.4	-	60	51	-
Strider et al., 2023 [6] (Vibrating Hammer)	CDW1	86.7	2.5	18.4	-	59	52	-
Delongui et al., 2018 [5]	CDW	20.3	0.6	18.7	57	-	-	-

Table 3. Comparison of waste properties in the present study with the literature.

Cases	Types of Aggregates					Properties of Waste
		Cu	Cc	MDD (kN/m3)	LAAT (%)	C (kPa)	φ (°)	CBR (%)
Current Research (Site 1)	BDWM	28.1	1.2	19.51	35.3	61	42	69
Current Research (Site 2)	BDWM	28.3	1.21	19.35	34.5	63	44	73
Arulrajah et al., 2013 [9]	RCA	31.2	0.9	19.13	28	44	49	-
Herrador et al., 2012 [19]	RCA-RAP-CB	30	1.29	-	34	-	-	-
Cerni et al., 2012 [20]	CD waste	85.71	1.93	25.7	37	-	-	-
Nasiri et al., 2024 [21]	CD waste	29.4	1.32	19.5	42.4	70	34	59
Strider et al., 2023 [6] (AASHTO Hammer)	CDW1	86.7	2.5	18.4	-	60	51	-
Strider et al., 2023 [6] (Vibrating Hammer)	CDW1	86.7	2.5	18.4	-	59	52	-
Delongui et al., 2018 [5]	CDW	20.3	0.6	18.7	57	-	-	-

Figure 9. Comparison of compaction parameters of the construction industry waste in the present study with other research [5,6,20,21].

Figure 9. Comparison of compaction parameters of the construction industry waste in the present study with other research [5,6,20,21].

5. Possibility of Using BDWM for Road Engineering

The use of recycled BDWM benefits both the economy and the environment in a variety of engineering applications and geo-environmental infrastructure.

Because most cities pay little attention to waste management, BDWM ends up in a variety of locations, including landfills and on the side of the road. If more attention is paid to these materials, costs can be reduced through energy conservation and waste management. Currently, using such materials in engineering can help reduce project costs. According to previous research, BDWM could be used instead of NM. Recycling such waste saves natural resources and prevents future problems. These wastes are commonly used for landfill cover and embankment slopes, asphalt materials, fill materials, geosynthetic structures, building materials, and bio-retention ponds [22,23,24,25,26,27,28,29,30]. Some important applications for these recycled materials include landfills and slopes, geo-synthetic reinforced infrastructure, pavement materials, and road pavement design using roller-compacted concrete pavement. Some of the possibilities for using BDWM in road engineering applications are listed below.

5.1. Slopes and Filling Materials

The materials obtained at various stages of recycling BDWM are useful in a variety of applications. BDWM can be used alone or in conjunction with natural materials for road slopes.

Among the most significant benefits of recycling such wastes are their application as filling materials, improvements to land and natural resources, and reductions in primary and environmental costs, transportation costs, and energy consumption rates.

5.2. BDWM in Geo-Synthetic Reinforced Road Construction

Geogrids could improve the geotechnical properties of these wastes. As a result, geo-grids could be used as an alternative in various applications.

5.3. Pavement Materials

Pavements are made up of several layers that transfer and support loads from the surface to the underlying layers. These materials typically consist of concrete slabs or asphaltic products on a base system.

Natural crushed materials are commonly used in pavement construction to form the sub-base or base layers, but recycled materials, such as BDWM, can be environmentally beneficial. As a result, the recycled BDWMs were suitable for both rigid and flexible pavements. Their properties determined their suitability as road pavement materials (Table 2). The laboratory-scale study results for these waste materials were then compared to some existing standards. According to ASTM-D1241, the SA of NMs and BDWMs was adequate for highway base and surface tracks. Because of the use of recycled materials for sustainable development, BDWMs increase construction speed while also lowering costs and energy consumption rates.

The RCCP, which is a combination of water, cement, and appropriate earth materials, could be applied as zero-slump concrete using the roller compaction operation [31]. These materials, specifically BDWMs, could be used in the production of RCCP and road construction to accelerate and reduce project costs, such as energy consumption, transportation, and infrastructure and pavement layer improvement [32]. As a result, the construction could become more valuable, and the thickness of pavement layers could decrease. As a result, RCCP was suggested for use in storage facilities, parking lot construction, airports, amusement park spaces, and pavement and road infrastructure. The use of RCCP for the pavement project proved to be more cost-effective. The process of recycling BDWM and producing RCCP from recycled materials has both engineering and environmental benefits.

6. Conclusions

This study investigated the physical and geotechnical properties of recycled BDWM obtained from two Iranian sites. To characterize the recycled materials, BDWM samples were collected and evaluated on a comprehensive laboratory scale. The study findings can be summarized as follows:

• According to basic laboratory testing and identification of the BDWM from the study sites, the average composition was brick, concrete, mortar, tile, and others.
• In the current study, the physical properties of the NMs were compared to those of the recycled BDWMs, which were obtained from mines in Tehran, Iran. The mean particle size distribution at each site was then compared to the FHWA’s lower and upper limits. The SA results also revealed that the BDWMs were suitable for road base applications according to ASTM-D1241 and could be combined for highway sub-base and base.
• In this study, the LAAT values of the BDWM were 31.3–35.2%, while the FI score was 15.2–15.6% for the two sites. On the other hand, the BDWM’s FI, the Gs of the coarse and fine parts, uniformity and curvature coefficients, total LAAT values, OWC, and MDD all met the NM’s specified maximum amount.
• According to the experimental tests conducted in this study, the WAT values of the BDWM were 4 and 6.6 times higher than those of the NM for coarse and fine materials, respectively.
• The California bearing ratio values for the BDWM were 69–73%. The recycled materials also had a lower CBR than the NM. The state road authorities approved California bearing ratio values for sub-base and base materials of at least 80%. To achieve higher performance from recycled BDWM, those with CBR values of less than 80% could be mixed with NM.
• Considering the high percentage of CBs and RCA, the MDD and OWC were also 20.9 kN/m³ and 9.6%, respectively. As evidenced in previous research, the WAT values of the BDWM varied between 1 and 10%.
• In comparing the direct shear test results for the BDWM and NM, the curve trends were comparable. The values appeared to have good cohesion, which was enhanced by hydration via water absorption from the given mixture. Another reason for the cohesion was the low concentration of RAP in the samples.

To summarize, BDWM from old structures and depots can be a viable alternative to NM in a variety of applications, including fillings, base and road infrastructure, backfilling walls, concrete parts, infrastructure reinforced with geosynthetics, asphalt, RCCP, landfills, slopes, and others. It should be noted that some wastes require further investigation due to the high content of specific materials, such as wood, and there are restrictions on using these materials in engineering projects. The use of cement, lime, and nanomaterials to improve BDWM in road engineering is beneficial and should be explored further in future research.