1. Introduction
In most cases, materials that are generated when new building and civil engineering structures are built, and also when current buildings and civil-engineering structures are renovated or demolished with deconstruction activities, are referred to as “construction and demolition waste” (C&DW). Such civil-engineering structures comprise every public building project such as street drainages, road or highways, bridges, utility plants, and dams [
1]. However, waste material generation is a prominent issue in construction projects, and the adverse effect of waste has influenced the management of C&DW in many countries. Shen et al. [
2] stated that C&DW is the major contributor to nearly 15–30% of the entire volume of waste that is disposed in several landfill sites in most countries, but this figure is bound to increase to approximately 40% when taking into consideration the amount of C&DW generated in construction per tonnes per day.
In construction sites, waste generated retains major quantities of C&DW produced every year in any construction sectors, and waste generated in construction sites initiate the result in cost factors for the contractors such as cost incurred in transportation, waste disposal, and procurement [
3,
4,
5]. However, it is expected that a drop in the volume of waste on construction sites can lead to a reduction in cost spent for raw material purchase and charges paid for disposal of the waste in landfill sites [
6]. However, it is acceptable worldwide that waste management is important to a sustainable construction economy, and this involves a procedure in which waste production is controlled and minimised by employing expert builders and contractors. For instance, in an estimation, it is opined that nearly 80% of waste stream created on site is recyclable and usable [
7,
8,
9].
However, the C&DW sector has greatly relied on factors such as increase in population, development in urban areas, and/or levies paid on landfills in some regions. Vergara and Tchobanoglous [
10] indicated that to avert the adverse effect of waste, suitable design and control is important. In addition, a proper structure for sustainable waste management implementation becomes an integral responsibility. This is a desirable trait in order to achieve a safe and protected environment in several countries [
11]. However, the key significance of a sustainable C&DW management strategies is to provide a tool for construction engineers, planners, and contractors to determine the best scenario for a sustainable minimisation of waste on construction sites [
12,
13]. Thus, the requirement for every construction industry with a good attribute of sustainable development is a sustainable C&DW management strategies [
14].
Consequently, managing C&DW implies eradicating the waste where feasible, reducing waste where realistic, plus possible reuse of the materials, which can turn out to be waste; thereby, a colossal part of C&DW can relentlessly be reused and recycled, and hence it preserves landfill size, for instance, waste generated from concrete or brick neglect or stones can be recycled into granular and fine aggregate, such as recycled aggregate concrete, cement, and floor thatches [
15,
16,
17,
18]. The UK Waste and Resources Action Programme (WRAP) in 2017 states that a good practice of material waste management gives a series of benefits that includes reduction in material and disposal costs, increase in competitive differentiation, increase in performance against corporate sustainability responsibility objectives, lower carbon dioxide (CO
2) emissions, meeting planning requirements, the complementary gains when combined with other aspects of sustainable design, and responses to and pre-empting public policy [
4,
5].
In China, the government establishes waste management policies and regulations that requires contractors to prepare and implement a waste management system and carry out on-site sorting of waste before certain payments are made, which is seen as tool to minimise waste incurred in construction projects [
14,
19,
20,
21]. However, in the absence of procedure in providing guidelines on how to produce a suitable waste management plan, the development of a waste management-mapping model that can be integrated before the commencement of construction activities and the provision of specification for the various handling measures for managing waste onsite is the cause of major waste production in the country [
22,
23,
24]. According to Poon et al. [
25], every regulation is required in the construction sectors to be followed and applied towards sustainable waste management, and there is a need to develop a holistic waste management system that is cost-effective, sustainable, and acceptable, with an emphasis on environmental conservation and good technological selection without the impact of the government regulations [
26,
27,
28].
In most cases, waste normally emanates during different life-cycle phases in construction, i.e., during the planning, construction, and demolition stages. Moreover, in procurement, not all the materials are used during construction, indicating that the leftovers may remain as waste that may not be accounted for [
23,
29]. In Nigeria, large volume of waste is generated in construction sites, especially in the Lagos metropolis. This is due to its position as Nigeria’s commercial nerve centre, with it continuing to experience rapid population growth, projected at 6–8% per annum. In this regard, the causes of materials waste in Nigerian construction sites include poor site supervision, design error, defective materials, unskilled labour, poor quality of materials, changes in design, specification errors, poor storage facilities, poor handling process, poor material scheduling, wrong suppliers’ advice, and bulk purchase that leads to excess and consequently contributes to waste generation in construction sites [
30,
31,
32].
In addition, inadequate involvement of non-regulatory sectors in the collection of the waste, lack of sustainable waste management plan, and the valuation of waste that could begin from the design processes is not usually considered in construction in Nigeria, and poor implementation of a sustainable procurement system is one of the major influencing factors to waste generation [
33,
34,
35].
However, the participation of informal private sectors in the disposal of waste has made the environment civilised, but in order to have accurate data of the amount of waste being generated, a proper survey should be examined [
36,
37,
38]. According to the survey carried out by the Waste Management Authority in Lagos (LASMA), the landfill sites have been regulated to ensure waste material handling and control system over a decade. In the survey report, there are five landfill sites in Lagos metropolis in the three major sites and several temporary sites, where all types of waste are disposed including waste from demolition and construction [
39,
40]. The composition of this waste comprises concrete, reinforcement steel, plywood, plastics, and other packaging materials. According to Aboginije [
3], waste from concrete, reinforcement, and wood is indicated as the highest waste generated in Nigerian construction projects, generating rates that range between 15–20%, while soil and stones, plastic, and packing materials are the least, with 2–4% generating rates, as indicated in
Figure 1.
According to Ajayi et al. [
41], the process of handling of waste involves identifying waste stream, evaluating waste on-site, deciding the final destination of waste materials, segregating waste, and careful studying of the handling procedures on-site. The waste streams are the flow of the waste that are specified right from their sources through recovery and recycling to the final disposal. However, waste framework and legislative structure must be instituted if any sustainable waste sector is to be achieved [
42,
43]. Many countries are now developing a waste framework directive to curb the adverse effect of waste. According to a report by the European Environmental Agency, most of the EU has established and implemented a framework that can lead to a recycling rate of about 90% [
26]. Recently, the Nigerian government aimed at developing a sustainable waste management legislation to curb the generation and adverse effects of waste on its environment, but there are still problems yet to be tackled in terms of this reality [
44,
45]. In addition, the waste management system must be understood and accepted by all concerned before its implementation. Thus, staff training, communicating with staff, and obtaining their commitment towards ensuring waste management plans is actualised are essential parts of the implementation processes [
46].
In this study, the main purpose was to carry out a holistic investigation with the intention of assessing the current C&DW management strategies implemented to minimise waste in the Nigerian construction projects.
5. Conclusions
This study set out to investigate the C&DW management strategies implemented in the Nigerian construction projects. The reviews of literature identified C&DW management strategies implemented throughout the life cycle phases of the construction projects that consist of the establishment of waste separation and collection techniques, and appropriate specifications on reusable, reclaimable, and recycled materials. Likewise, provision for deconstruction and disassembly in the design phase; BIM implementation; government intervention through increased landfill tax; off-site preparation, pre-assembly, and prefabrication; reduction of waste at the material source; improving the on-site waste management plan; and adding waste minimisation in contractual clauses can contribute to C&DW management. In addition, provision for efficient procurement in the design phase; provision for off-site construction in the design phase; provision for material optimisation in the design phase; re-use of materials as backfills; on-site sorting of materials; avoidance of late drawings, revisions, and submissions; and complete and unambiguous contract documents can make a difference to the management of waste. The use of standard dimensions and sizes in design, provision of detailed information on drawings, and avoidance of frequent design changes were also indicated in this study.
From the survey results obtained from respondents, the major waste management strategies implemented included re-use of materials as backfills; off-site preparation, pre-assembly, and prefabrication; provision of detailed information on drawings; and BIM implementation. The results show that the level of utilisation of some of these approaches is moderate, especially the adoption of modularity in construction projects in Nigeria, which is still below standard, while many of the procurement procedures and their implementation are still deficient in reducing waste in the country. However, the waste management still has some basic sustainability traits.