Identiﬁcation of Methods of Reducing Construction Waste in Construction Enterprises Based on Surveys

: The article presents the analysis of the dependence between methods of reducing construction waste and the size of the construction enterprise. The analysis was carried out for the following construction products: steel, concrete, wood, and small-sized (ceramic, concrete) and ﬁnishing (ceramic and stone tiles) products. Based on the literature review, the 13 most frequently used methods of reducing construction waste were identiﬁed. Surveys were then conducted among 140 construction enterprises. The research was conducted in Sharjah in the United Arab Emirates. In order to test whether there is a relationship between the used waste-reduction method for a given construction product and the size of the enterprise, the Pearson chi-square test of independence was used. The null hypothesis and the alternative hypothesis were formulated, and the critical level of signiﬁcance α = 0.05 was adopted. The results were statistically signiﬁcant for 7 methods of reducing construction waste. The identiﬁed methods include appropriate storage, the training of employees in the ﬁeld of waste management, the use of monitoring systems, the appropriate transport and unloading of products, the appropriate involvement of subcontractors, the use of prefabricated elements, and the reuse of products on the construction site. Based on the conducted research, it was found that these methods are more often used with an increase in the size of the enterprise. The presented analysis emphasizes the urgent need to improve, integrate, and adjust the promotion of both the reduction of construction waste and the beneﬁts of this reduction in construction enterprises, especially those of the smallest size.


Introduction
The natural environment is constantly being exploited. In order to protect natural resources from destructive human activity, the concept of sustainable development was developed. It was first presented on 26 May 1969, by the United Nations (UN) in the report "Problems of the human environment". This report is considered to be a turning point in the perception of the devastating impact of humans on the environment [1,2]. Sustainable development aims to prevent the deepening destruction of the environment while at the same time satisfying the needs of mankind and enabling unlimited progress. The concept of sustainable development should be applied in all areas of human life [3]. The current assumptions of sustainable development were presented during the UN summit in New York on 25-27 September 2015, in a document entitled "Transforming our world: Agenda for Sustainable Development-2030". Sustainable Development Goals have been incorporated into the legislation of UN member states. In the regulation of the European Parliament and the Council of the European Union from 2011, a sustainable construction was introduced as a new basic requirement [4]. Since then, reusing and recycling construction products has not only become a choice but also a necessity. Countries theme to the existing knowledge: (1) production and delivery, (2) transport and storage, (3) construction, and (4) culture related [23].
The influence of the behavioral factor on the production of construction waste has been more widely studied and also confirmed in other scientific studies [24,25,29,30]. In 2004, a survey conducted in Singapore among general contractors identified four main sources of construction waste: (1) design, (2) production and delivery, (3) material management, and (4) construction [26]. The results of these both studies, which were carried out in 1994 and 1996, and following ones confirmed that the maximum number of sources of the construction waste occur at the design stage [23,[27][28][29]. Based on a subject literature review [21][22][23][24][25][26][27][28][31][32][33], 13 methods of reducing the amount of construction waste used in construction companies were found. These methods are discussed in detail in Table 1 in the next chapter. Waste segregation on the construction site Preventing contamination of products by providing containers for each type of waste. Non-contaminated waste can be recycled or reused; 10 Designation of a place for waste segregation Recovering products for reuse in the designated area, e.g., removing nails from wooden elements or crushing concrete elements;

11
Reuse of products on the construction site E.g., formwork timber used several times; use of concrete or ceramic and stone waste as rubble for temporary roads and pavements; 12 Delivery of products according to the schedule Reduction of storage time and the risk of damage; 13 Development of a waste-disposal plan Easier management of construction waste.
The aim of the conducted research and analyses is to find out whether the application of construction waste-reduction methods with regards to selected construction materials depends on the size of the enterprise. In terms of the number of people employed, the enterprises were classified into five groups: (1) from 1 to 9 employees, (2) from 10 to 49 employees, (3) from 50 to 99 employees, (4) from 100 to 249 employees, and (5) 250 employees and more. The analyses were based on the results of a survey conducted among engineers employed in construction companies. The research was conducted in Sharjah, United Arab Emirates (UAE). The analyzes were performed with the use of the SPSS 26 computer program.

Materials and Methods
The methods of reducing construction waste that are used in construction companies, which were identified based on the literature review, are presented in Table 1. The benefits of using each of them are also listed. Research was carried out for the following construction products: steel, concrete, wood, and small-sized (ceramic, concrete) and finishing (ceramic and stone tiles) elements.

Size and Structure of the Studied Population
The population of the studied enterprises consists of five subpopulations. Each of them includes enterprises with a certain number of employees. The groups have been derived from the population as per the characteristic of construction enterprises. In Sharjah, construction companies employ a limited number of people to keep low insurance and municipality fees, and they outsource work to subcontractors. The survey was conducted using the technique of personal interviews and telephone interviews due to the possibility of obtaining the most accurate data and immediate clarification of ambiguities in the obtained answers. The research was carried out in 140 enterprises of general contractors. The structure of the population is presented in Table 2.  Table 2 presents the number and percentage share of the enterprise sizes in the studied population. In the surveyed representative group, 42 enterprises (30%) employ from 1 to 9 employees, 41 enterprises (29%) employ from 10 to 49 employees, 15 enterprises (11%) employ from 50 to 99 employees, 20 enterprises (14%) employ between 100 and 249 employees, and 22 enterprises (16%) employ 250 employees or more. The largest sub-population includes enterprises that employ the least workers.
Research was also carried out with regards to the companies' experience in the market of construction works. The results of the surveys are presented in Table 3. Among the surveyed companies, 63 companies (45%) had 16 years or more of experience in the construction market, 42 companies (30%) had 11 to 15 years of experience, 25 companies (18%) had 6 to 10 years of experience, and 10 enterprises (7%) had between 1 and 5 years of experience. To sum up, the most numerous group were the oldest enterprises, with 16 years of experience or more.

Methodology of Identifying Methods of Reducing Construction Waste with Regards to the Size of the Enterprise
In the subject literature review, the correlation analysis of two variables is especially popular [34][35][36]. In the presented paper, the subject of the study is to determine the relationship between the method of reducing construction waste in relation to a given construction product and the size of the construction enterprise. For this purpose:

•
The answers of the respondents concerning the applied methods of waste reduction were qualified into five groups with regards to particular construction products. Each of these groups represented a certain size of an enterprise. In each group, the number of positive answers (YES) and the number of negative answers (NO) were determined; • In order to test whether there is a relationship between the waste-reduction method used in the case of a given construction product and the size of the enterprise, the Pearson chi-square (χ 2 ) test of independence was used [37]. This test is used to check the relationship between the two nominal variables X and Y. In the conducted research, the nominal variable X is the size of the enterprise, while the nominal variable Y is the answer Yes/No in relation to the tested reduction method.

•
The Pearson chi-square test is based on comparing the values obtained in the study (the so-called observed or empirical frequencies) with theoretical values calculated based on the assumption that there is no relationship between variables X and Y. The chi-square test statistic has the form of formula (1): where: Chi-square statistics were calculated using the SPSS-26 computer program. The chisquare statistic has a distribution of χ 2 with (r − 1)(c − 1) degrees of freedom. In the analyzed case, the number of degrees of freedom is 4. The p value determined for the chi-square test statistic is compared with the significance level α. The critical significance level of α = 0.05 was adopted in the analyzes.
The null hypothesis H 0 and the alternative hypothesis H 1 were formulated: p-the probability (the value of p is compared to the theoretical value of α) α-the significance level.
If p > α ⇒ it can be assumed that there are no reasons to reject hypothesis H 0 . This means that there is no significant relationship between the size of the enterprise and the use of the analyzed method of reducing construction waste. The result is statistically insignificant.
If p ≤ α ⇒ it can be assumed that there are reasons for rejecting hypothesis H 0 . Based on the tested sample, it can be assumed that there is a relationship between the size of the enterprise and the use of the analyzed method of reducing construction waste. The result is statistically significant.

Results
Calculations of the chi-square test were performed for all the tested methods of reducing construction waste in relation to all the analyzed construction products. Table 4 only presents those results that are statistically significant, namely the statistics of frequency and percentage rates of YES and NO responses as well as the calculated values of the χ 2 (4) test and probability p. Other calculation results, which are not included in the table below, show that there is no significant relationship between the size of the enterprise and the use of the analyzed method of reducing construction waste.

Discussion
The analysis of the results of the calculations included in Table 4 helped to indicate methods of reducing waste, the application of which depends on the size of the construction company, to be indicated with a probability greater than 0.95. A significant statistical dependence was found for seven methods of reducing construction waste, namely appropriate storage, employee training in the field of waste management, use of monitoring systems, appropriate transport and unloading of products, appropriate involvement of subcontractors, use of prefabricated elements, and the reuse of products on the construction site. In all these cases, the statistic Chi2(4) > 9.487, and p < 0.05. No statistically significant correlation was found for the other six methods of reducing construction waste, namely ordering products to size and in the appropriate quantity, the security of the construction site, waste segregation on the construction site, the designation of a place for waste segregation on the construction site; timely delivery, and having a waste disposal plan. In all these cases, the value of the statistic Chi2(4) > 9.487, and p > 0.05. This means that the application of a given reduction method does not depend on the size of the enterprise. A detailed summary of the test results is provided in Table 5.  Table 6 lists the construction products for which a statistically significant correlation was found between the method of reducing construction waste and the size of the enterprise. Moreover, for each construction product, the strength of this relationship (PW) was determined. The frequency of the affirmative answer (YES) indicated by the respondents was adopted as a measure of this strength. The following designations were adopted: PW = 1 when the frequency is ≤60%, PW = 2 when the frequency is between 61% and 75%, and PW = 3 when the frequency is between 76% and 100% Table 6. Construction products for which a statistically significant correlation was found between the method of reducing construction waste and the size of the construction enterprise.   Based on the results of the research, the following conclusions were drawn: 1.
Out of the 13 analyzed methods, a statistically significant correlation between the size of the enterprise and the method of reducing construction waste was found in the case of seven methods. These include appropriate storage, the training of employees in the field of waste management, the use of monitoring systems, the appropriate transport and unloading of products, the appropriate involvement of subcontractors, the use of prefabricated elements, and the reuse of products on the construction site (justification in Table 4). As the size of the enterprise grows, these methods are used more frequently; 2.
Each group of analyzed methods of waste reduction includes construction products for which no statistically significant correlation was found between their use and the size of the enterprise. No such dependence was found with regards to the method of: • Appropriate storage in the case of steel and concrete; • Training of employees in the field of waste management in the case of steel, concrete, and wood; • Appropriate transport and unloading of products in the case of steel, concrete, and wood; • Appropriate involvement of subcontractors in the case of concrete and ceramic and stone tiles; • Use of prefabricated elements in the case of concrete, wood, and ceramic and stone tiles; and • Reuse of products on site in the case of steel.

3.
The use of seven separate methods of reducing construction waste in enterprises of certain sizes is as follows: 3.1. In enterprises employing 250 or more employees, the following methods are used: 3.1.1. Most often (PW = 3): • Appropriate storage in relation to small-sized products, wood, and ceramic and stone tiles; • Training of employees in the field of waste management in the case of small-sized products; • Use of monitoring systems in the case of steel, concrete, ceramic and stone products; • Appropriate transport and unloading of products in relation to small-sized products; and • Appropriate involvement of subcontractors in the case of smallsized products and wood.
3.1.2 Often (PW-2): • Use of monitoring systems in the case of small-sized products and wood; • Appropriate involvement of subcontractors in the case of steel products; and • Reuse of products on the construction site in the case of smallsized products and wood.
3.1.3. Rare (PW = 1): • Use of prefabricated elements in relation to steel and small-sized products; • Reuse of products on the construction site in the case of concrete products and ceramic and stone tiles.

3.2.
In enterprises employing from 100 to 249 employees, the following methods are used:

Most often (PW = 3):
• Appropriate storage with regards to small-sized products, wood, and ceramic and stone tiles; • Training employees in the field of waste management with regards to small-sized products; • Use of monitoring systems in relation to all the groups of analyzed construction products; • Appropriate transport and unloading of products with regards to small-sized products; • Appropriate involvement of subcontractors with regards to steel products; and • Reuse of products on the construction site with regards to concrete, small-sized products, wood, and ceramic and stone tiles;

Rare (PW = 1):
• Appropriate involvement of subcontractors with regards to smallsized products and wood; • Use of prefabricated elements with regards to steel and smallsized products.

3.3.
In enterprises employing from 50 to 99 employees, the following methods are used: 3.3.1. Most often (PW = 3): • No such cases were observed.

Often (PW-2):
• Appropriate storage with regards to wooden products; • Use of monitoring systems with regards to steel, concrete and wooden products; • Appropriate involvement of subcontractors with regards to steel and wooden products; and • Reuse of products on the construction site with regards to wood, and ceramic and stone tiles.

Rare (PW = 1):
• Appropriate storage with regards to small-sized products and ceramic and stone tiles; • Training employees in the field of waste management with regards to small-sized products; • Use of monitoring systems with regards to small-sized products and ceramic and stone tiles; • Appropriate transport and unloading of products with regards to small-sized products; • Appropriate involvement of subcontractors with regards to smallsized products; • Application of prefabricated elements with regards to steel and small-sized products; and • Reuse of products on the construction site with regards to concrete and small-sized products.

3.4.
In enterprises employing from 10 to 49 employees, the following methods are used: 3.4.1. Most often (PW = 3): • No such cases were observed.

Often (PW-2):
• Appropriate storage with regards to wood and ceramic and stone tiles; • Training employees in the field of waste management with regards to small-sized products; • Appropriate transport and unloading of products with regards to small-sized products; and • Reuse of products on the construction site with regards to concrete products.
3.4.3. Rare (PW = 1): • Appropriate storage with regards to small-sized products; • Use of monitoring systems with regards to all the groups of analyzed construction products; • Appropriate involvement of subcontractors with regards to steel, small-sized, and wooden products; • Use of prefabricated elements with regards to steel and small-sized products; and • Reuse of products on the construction site with regards to smallsized products, wood, and ceramic and stone tiles.

3.5.
In enterprises employing from 1 to 9 employees, the following methods are used: 3.5.1. Most often (PW = 3): • Appropriate transport and unloading of products with regards to small-sized products; • Reuse of products on the construction site in relation to concrete, small-sized, and wooden products.

Often (PW-2):
• Reuse of products on the construction site with regards to ceramic and stone tiles.
3.5.3. Rare (PW = 1): • Appropriate storage with regards to small-sized products, wood, and ceramic and stone tiles; • Training employees in the field of waste management with regards to small-sized products; • Use of monitoring systems with regards to all the groups of analyzed construction products; • Appropriate involvement of subcontractors with regards to steel, small-sized, and wooden products; and • Use of prefabricated elements with regards to steel and smallsized products.

Conclusions
The subject of the study was to determine the relationship between 13 methods of reducing construction waste and the size of the construction enterprise in relation to selected construction products. The selected construction products included steel, concrete, small-sized products, wood, and ceramic and stone tiles. Enterprises were divided into groups according to the number of employees, namely from 1 to 9 employees, from 10 to 49 employees, from 50 to 99 employees, from 100 to 249 employees, and for 250 employees and more. Employee surveys were conducted in enterprises belonging to the designated groups. The values of the chi-square test for the significance level of 0.05 and the degree of freedom 4 confirmed a statistically significant correlation between the size of the enterprise and seven methods of reducing construction waste, which included appropriate storage, the training of employees in waste management, the use of monitoring systems, the appropriate transport and unloading of products, the appropriate involvement of subcontractors, the use of prefabricated elements, and the reuse of products on the construction site. The dependence between the use of waste-reduction methods and the size of the enterprise did not always apply to all tested construction products, e.g., no statistically significant correlation was found in relation to steel and concrete in the case of the appropriate storage method. For the remaining six methods of reducing construction waste, no statistical correlation was found between the application of these methods and the size of the enterprise, but this does not mean that these methods were not used. The use of these methods or their non-application may be influenced by other factors that are not included in these studies.
In further research, it is recommended to focus on behavioral motives that can have a large impact on the use of methods that reduce construction waste in construction enterprises.
Studies presented in this paper make a significant contribution to the existing research concerning the reduction of construction waste. In conclusion, based on the conducted research, it was found that the bigger the enterprise, the more methods of reducing construction waste were applied. It can be assumed that larger construction enterprises have more human resources and financial support to plan, organize, and implement more methods of reducing construction waste than smaller enterprises. Therefore, it is crucial that governmental bodies will support reduction of construction waste by providing necessary trainings and financial support and will effectively require it. Thus, the presented analysis emphasizes the urgent need to improve, integrate, and adjust the promotion of the reduction of construction waste and the benefits of this reduction in construction enterprises, especially those of the smallest size.