Performance Study of Sustainable Concrete Containing Recycled Aggregates from Non-Selected Construction and Demolition Waste

By inergency On Mar 21, 2024

1. Introduction

Construction and demolition wastes (C&DW) currently pose significant global challenges, with approximately 10–30% of total waste being disposed of in landfill sites [1]. One of the most prevalent methods of C&DW disposal remains burial [2,3,4,5]. However, the excessive extraction of natural resources can have profound environmental repercussions [6,7,8]. Therefore, recycling such waste is imperative to reduce its volume, and utilizing these materials as sustainable resources can contribute to sustainable development. One effective strategy to increase recycling rates is by incorporating these wastes into concrete production.

Considering the preservation of ecosystems for future generations, integrating C&D wastes with virgin aggregates (VAs) in concrete manufacturing can yield substantial economic benefits. Unfortunately, a conservative stance or lack of supportive regulations regarding the use of recycled C&DW in concrete products has hindered their widespread adoption, leading to their underutilization in other applications. Addressing this issue, the utilization of waste as a sustainable construction material emerges as a crucial and viable endeavor [2,3,6,9,10].

Due to the increasing number of constructions in Karaj over the past decade, the generation rate of construction and demolition waste (C&DW) has significantly escalated. According to statistics released by the Karaj Municipality, approximately 6000 tons of C&DW are generated daily in this city. Against this backdrop, the present study aimed to analyze recycled concrete mixes using C&D aggregates sourced from different regions of the inactive waste landfill site in Line 4 of Hesar. As shown in Figure 1, Region 1 of this landfill contains materials accumulated from 1990 to 2005, representing old landfills in developing countries. Meanwhile, Region 2 showcases waste composition from 2005 to the present, representing new landfills in developing countries. Notably, approximately five million cubic meters of C&DW have accumulated at this landfill site since 1990. In Region 1, a relatively small amount of waste accumulated over 15 years, while in Region 2, C&DW accumulation exceeded that of Region 1 by more than 2.5 times over a period of 22 years, indicating a significant increase in waste production in recent years.

The extraction of C&DW samples from the landfill was conducted through four boreholes (BHs) and four test pits (TPs) with depths of 12 m, drilled into the aforementioned waste landfill site, as illustrated in Figure 1.

Regarding the impact of landfill age, no chemical evaluation was reported. However, this study presents the results of common essential chemical tests on aggregates used in concrete, considering old and new C&DW as well as virgin materials. Furthermore, rare experiments such as the Capon and British pendulum number (BPN) tests were conducted on concrete produced from the fine and coarse C&DW, with the obtained outcomes compared against acceptable criteria outlined in certain regulations for conventional concrete. Ultimately, the ultrasonic pulse velocities (UPVs) in the recycled concrete samples were compared with those of reference samples, and some correlations were proposed.

Numerous studies investigating the utilization of construction and demolition waste (C&DW) in concrete have encountered a range of limitations, as outlined in this section. Various factors, including people’s preferences, resource availability, and abundance, significantly influence the selection of materials for construction projects. Consequently, the age of a landfill can profoundly impact material selection [11,12]. Understanding the properties of C&DW in both old and new landfill sites is crucial for analyzing the mechanical performance of recycled concrete. To the best of the authors’ knowledge, there have been no recent reports on changes in these materials over the past 40 years or the effects of using old and new waste in concrete. Therefore, comprehending the effects of landfill age on material selection is essential.

Most researchers [13,14,15,16,17] have conducted common tests such as slump, density, compressive strength tests (CST), and so on, on conventional and recycled concrete. However, the use of some complementary tests, such as non-destructive ultrasonic pulse velocity (UPV), British pendulum number (BPN) for skid friction resistance, and Capon wide wheel abrasion tests for determining the characteristics of C&DW concrete made from fine and coarse non-selected C&D wastes, has been limited. Moreover, understanding the chemical properties of C&DW before their use in recycled concrete is essential, a factor often neglected in many studies.

Recent research has explored the utilization of various wastes in concrete, including rubber particles [18,19], palm oil clinker (POC) [20], glass powder, aluminum fibers [21], recycled concrete, brick aggregates [22], glass and carbon-fiber-reinforced polymers [23], reclaimed asphalt pavement [24], newspaper ash [25], and more. However, most studies have only examined a single type of selected C&D aggregates, often separated in recycling plants. Other mentioned wastes may be found in small amounts in specialized plants. Nevertheless, research on concrete composed of non-separated C&D aggregates (with different compositions), considering the physical–chemical properties prevalent in all industrialized countries, remains scarce.

Concerning the use of coarse C&DW in concrete production instead of coarse virgin aggregates (VAs), previous studies have shown that low replacement ratios do not significantly alter the physical and chemical properties of concrete [15,26,27]. However, limited research has explored the effects of fine recycled aggregates from C&DW on concrete. Previous studies have identified excessive water absorption as the primary hindrance to the use of fine C&DW in new concrete production.

Ultrasonic pulse velocity (UPV) is a recognized non-destructive testing method to estimate the mechanical properties and internal cracks of concrete materials. Despite this, studies implementing this technique to determine the characteristics of recycled concrete made from fine and coarse non-selected C&DW are scarce. This situation is even more pronounced for the British pendulum number (BPN) for skid friction resistance and wide wheel abrasion (Capon) tests, as illustrated in Table 1. Moreover, understanding the chemical properties of C&DW before its use in recycled concrete is crucial, a consideration often overlooked in many studies.

To address the above limitations, the current study investigated non-separated C&D materials for new concrete production with different mix compositions. Recycled materials and virgin aggregates were employed in the present study.

Nowadays, construction waste has significantly increased due to urbanization and economic development. Consequently, the production of construction waste has reached a critical juncture where landfills near urban areas are overflowing with these materials, emphasizing the urgent need for recycling on a global scale.

With the rise in construction material prices and the recognition of the limitations of natural resources, there is a growing awareness of the importance of preserving national capital for future generations. Additionally, participation in recycling programs, while safeguarding the environment, has become paramount. Therefore, the management and recycling of construction waste have become increasingly important and necessary worldwide.

Given the significance of this issue, researchers worldwide are dedicating considerable efforts to studying the recycling of construction waste and its integration into construction projects, aiming to reintroduce these materials into the construction sector and mitigate the unsustainable depletion of natural resources. In this context, several research gaps and innovations are being explored, including:

Utilizing aggregates from non-selected construction and demolition waste (C&DW) as a sustainable material.
Exploring the potential of concrete made from non-selected C&DW to contribute to sustainable development.
Investigating the effects of landfill age on construction waste properties.
Assessing the impact of fine aggregates and addressing issues related to excessive water absorption.
Understanding the properties of C&D waste in both old and new landfill sites.

Addressing these research gaps and advancing our understanding of construction waste recycling will play a crucial role in promoting sustainability in the construction industry and mitigating environmental degradation.

3. Comparison of Some Waste Aggregates with C&DW Aggregates in Previous Studies

The geotechnical characterization of C&DW in the present article is compared with a previous study and presented in Table 4. This table outlines the geotechnical characteristics of C&D waste, including scaling index, grading, specific gravity, water absorption, and Los Angeles abrasion of the recycled aggregates.

The geotechnical properties of the studied C&DW depot in Karaj city were found to be similar to the average results of various C&DW studies. Moreover, the Los Angeles abrasion loss of the C&DW in the present study was found to be between 35–42%, while the flakiness index value ranged from 16–17%. This indicates that the particles have relatively fewer elongated aggregates, resulting in higher efficiency under compression. Therefore, these materials are still acceptable for usage as a base material, with a maximum value of 35, in road construction according to normal state road authorities and pavement applications. The water absorption of natural materials does not exceed 3%, while it varies from 1 to 10% for the C&DW materials. Thus, the existing conditions and values remain consistent with this study.

Considering that C&DW includes concrete and brick bits in specific proportions for each BH, the water absorption in this study is roughly 4.6 times higher than that of natural materials for coarse aggregates and 7.8 times higher for fine aggregates. According to the specific weight of natural materials, the dry unit weight of C&DW ranges from 19.69–21.3 kg/m³.

Given that the density of different materials is affected by the amount of water absorption, the optimal humidity in this study is approximately 7.8%, which is similar to other studies. The comparison of some geotechnical parameters of C&DW with other studies is shown in Table 4. Therefore, in the current study, the geotechnical parameters of C&DW are comparable to the recycled aggregates of other studies. According to Figure 4, the maximum unit weight of C&DW is lower than that of virgin materials, while its optimal water content is higher than that of virgin materials.

In the present study, the comparison of geotechnical characteristics such as scaling index, grading, Los Angeles abrasion, specific gravity, and water absorption of the C&D waste and recycled aggregates with previous studies is shown in Table 4.