CDW QUANTIFICATION IN THE SEVERAL STAGES OF LIFE OF A BUILDING: IDENTIFICATION AND CHARACTERIZATION OF THE MAIN METHODS

Construction and demolition waste (CDW) represent, in mass, the largest fraction of the waste generated in many Brazilian cities. Quantifying this type of waste is an expensive task that still has to overcome some obstacles. Lack of management and irregular disposal are some of the main limiting factors. Thus, this work aims to identify CDW quantification methods as a basis for further studies of adaptation and/or development of specific methods for the quantification of the Brazilian CDW in the different life stages of a building. Publications were identified in scientific journals and events from the set of keywords: “estimate generation”, “quantification method”, “construction and demolition waste”, “construction waste” e “demolition waste”. The articles were classified in general criteria, type of residue evaluated, scale and public interest. At the end, 22 articles presenting methods of quantification of construction and demolition residues were identified. Methods for quantification of construction waste (CW) and CDW predominate among those identified, representing 41% each. Half of the studies adopt design data and 41% use regional data. Some of the methods identified cover both the interest of the builders and the public agencies, reaching 50%, however only 18% are specific of interest to the public management agencies. Related to the Brazilian CDW, only 2 publications were identified. Therefore, it is possible to verify that there is a gap in the development of Brazilian CDW quantification methods in the various phases, which could help construction companies and public agencies to improve the management of this type of waste.


INTRODUCTION
Construction and demolition waste (CDW) are generated in high volumes around the world. Estimating the quantities and composition characteristics of these wastes have been one of the challenges in the CDW management. Private and public construction works, beyond CDW generated by the population, are the sources of generation in Brazil, and in most countries around the world. Private and public civil works are responsible for all stages of waste management (segregation, storage and final destination) and CDW generated by the population are managed for the municipalities.
There are few CDW database in Brazil, restricted to surveys such as those conducted by the Brazilian Association of Public Cleaning and Special Waste Companies (ABRELPE, 2017) and the National Information System on Water, Sanitation and Solid Waste (SNIS), this one corresponds to a national information database fed by Brazilian recycling/ waste disposal plants, however known to be incomplete. 45 million tons of CDW were collected, in Brazil, by the municipalities (ABRELPE, 2017) in the 2016, allowing to infer a minimum average generation of 123,421 tons of CDW/day and 0.6 kg/person/day. These data, however, consider only the CDW collected by the municipalities, that is, generated by local population.
In Brazil, there are disposal places, called Voluntary Delivery Points, that receive waste generated by the population in quantities below 1 m³. It is necessary, however, to consider the occurrence of known irregular disposals, called "Vicious Point of Disposal" (OLIVEIRA et al., 2011;MMA, 2012), some points are informally mapped by the municipalities that collect the arranged materials, others however are dynamic or inaccessible.
CDW from private or public civil works needs to be managed by it is companies, which in Brazil in 2017 were over 126,000 (IBGE, 2017). Quantitative database of this CDW are scarce, being limited the declaration of these values to the local environmental agencies that do not always have online systems of treatment of these data.
The CDW composition characteristics are related to the type of work (building, highway, excavation), generation stage (construction, demolition or renovation), construction method (precast building system, engineered masonry, pillar and beam construction, steel/wood frame ), building age, waste management practices (source segregation or not) (Esa et al., 2017;Gálvez-Martos et al., 2018) and others. Waskow et al. (2019) perform statistical treatments to consolidate Brazilian CDW composition (Figure 1). These authors suggest a Brazilian average CDW composition composed basically of mortar (39%), concrete (14%) and ceramic (47%). However, according to the characteristics of the construction and/or building source of waste, as described in the previous paragraph, it is still possible to find divergent CDW compositions within a Brazilian state, such as Scoot Hood (2006) and Bernardes et al. (2008), or municipality, such as Oliveira et al. (2011) and Lima & Cabral (2013). Thus, it is necessary to know which CDW estimation methods are available in the scientific literature, whether there are proposed methods for Brazil, whether these methods are replicable in the Brazil regions or identify necessary adaptations. Thus, this paper aims to conduct a systematic survey of CDW generation estimation methods in the world and in Brazil, discuss them, identify potential input data sources for the identified models, evaluate their applicability and propose adaptations for the Brazilian case.

METHODOLOGY
To achieve the objective of this paper was necessary identify quantification methods of the residue's generation adopting as way of identifying scientific papers the scientific portal Science Direct and internet search. The procedure for selecting articles of interest followed criteria, described below: -Search in the abstract of articles by set of keywords: "estimate generation", "quantification method", "construction and demolition waste", "construction waste" and "demolition waste"; -Selection of articles published in journals, congresses, symposia, events among others of which were the target of evaluation; -Discard of articles that presented only the characterization of the CDW or the determination of the generation rate; -Identification of the main characteristics of the developed method; -Classification of articles that meet the characteristics and objective of the work.
The classification of the selected articles followed criteria, such as: general data, type of residue evaluated, scale and public of interest. The criteria adopted in the mapping stage of the articles included in this study are presented in Table 1.

Criteria Scope
General data Author, year, country target of study.
Type of waste -Construction waste; -Demolition waste; -Construction and demolition waste (CDW).
Target audience -Construction company; -Government or state agency.

RESULTS AND DISCUSSION
The highest fraction of the identified studies adopts as a quantification method the constructed/demolished area multiplied by an average generation rate per area, corresponding to 59%. However, some of the authors complement this method with the insertion of other variables, such as Saez et al. (2014), which consider the life span of the building, in addition to density population, density of buildings by area, coverage of built and green area (BERNARDO et al., 2016;ZHENG et al., 2017). The relationship between the amount of material acquired and the average generation rate is considered by 23% of the authors (NAGALLI, 2012;JINGKUANG et al., 2012;LI et al., 2016;LLATAS & OSMANI, 2016;GHOSH et al., 2016).
The other methods adopted are based on the generation rate multiplied by the population (RHYNER & GREEN, 1988), multiple equations for several phases of building (COCHRAN et al., 2007), lifetime of the applied material and its exchange (COCHRAN & TOWNSEND (2010)) and Grey Model (GM) in conjunction with a Support Regression Vector (SONG et al., 2017).
More details about the methods adopted by the identified studies in the research are presented in final.
The first research results reveal the studies growth of construction and demolition waste (CDW) quantification methods from 2015 ( Figure 2). The results obtained also suggest that the United States were the pioneers in the search for quantification methods, being responsible for 4 of the first 5 studies identified. Initial results suggest that the first studies of quantification methods development aimed to quantify construction and demolition residues, that is, the generated residues in building construction and its demolition ( Figure 3). Construction phase residues (construction waste, CW) were the target of subsequent studies, in chronological order, however both CDW and CW represent 41% of all identified studies. Project scale studies predominate among those identified, representing 50%. The quantification methods on a regional scale represents 41%, followed by methods that meet both scales (9%). Corroborating these data, the evaluation of the target audience of the study shows that construction companies may be the largest beneficiaries of most identified studies (82%), including the methods where both target audiences are met. Figure 4 presents more details about the results obtained.  Brazil, Lebanon and India are other studied countries that have more than one study. Studies focused on Brazilian waste focused only on construction waste, however those developed in Lebanon and India focused on CW/DW and DW/CDW, respectively. Table 2 summarizes the main information from the works that suggest CDW quantification methods. The information is classified into the following categories: Author: Description of the authors and publication year, according to scientific citation.
Country: Description of the country where the study is applied or where the CDW quantification method is developed.
Origin: Describes the origin of the waste considered in the study and method of quantification, which can be the stages of construction, renovation and demolition individually or independently.
Equation Scale: Describes the scale of application of the proposed quantification method. The work (construction, demolition or renovation) classifications as municipal, state, national are adopted.
Input data source: Describes the source of information that feeds the CDW quantification methodologies proposed by the authors.
Period: Describes the applied period and/or the expected for proposed applicability CDW quantification methodology.
Method Description: Describes information that complementary previous classifications and supported the analysis of methods applicability to Brazilian scenario. Likewise, the information in this topic helps identify useful information the discussions about methods to be used in Brazil.
As can be seen, some authors converge on their quantification methods. Rhyner & Green (1988) and Yost & Halstead (1996) adopt the average generation rate or estimated population quantity.
Other authors adopted data on measures of expansion and/or built/demolished area, such as Cochran et al.  Not Specified Aimed at the construction waste. Evaluating and simulate the CW generation in new condominiums constructions in Spain. The development of the method is based on the CDW generated amount, an area covered by the constructions and the expected duration/time of the work. Thus, the authors obtained final result of generating CDW according to the duration of a work with those characteristics.
Kern et al.
Brazil CW Municipal -On-Site Data Collection.

2008-2013
Aiming at quantifying construction waste, the method considered the amount of waste generated in the construction of 20 buildings in Brazil. At the end uses the variables the number of apartments per floor, apartment area, area per floor, construction system and waste reuse. Bakshan et al. (2015) Lebanon CW Municipal -On-Site Data Collection.
Not Specified Aiming at construction waste, it estimates the amount of generated waste by material type in kilograms per square meter from data from other authors.
Not Specified Aiming the construction waste, the method was based on condominiums built in Spain. The input parameters were the number of residential units per condominium, the area of each unit and the quantified waste generation per unit and per area. Thus, the authors established factors for calculation of mass generation and volume.
Lu et al.
China CW -Chinese Statistics Yearbooks; -China Statistical Yearbook on Construction.

Estimated for 2014
Aiming at the CDW, the authors adjusted the equation cited by other authors based on individual building area, renovation and demolition criteria, and the waste generation rates for each of these steps.
Li et al.
China CDW National -Uniformat II classifying building specifications, cost estimating, and cost analysis in the U.S. and Canada.
Not Specified Aiming at demolition residues, the estimate was based on a mathematical modeling and has as a return which residues of the work are the most significant, quantitatively. This method considers the CDW composition, including the corresponding fraction of other types of waste, such as packaging.

2009-2012
The modeling carried out aims to evaluate the effectiveness of design actions and the minimization of waste generation in the construction of the building. Data such as the waste expected and generated are related.

2003-2013
The method is not restricted only to quantifying CDW generated over a period of time, but also to quantifying the area required for CDW management such as construction, recycling and disposal. The authors used input data such as built-up area, urban area covered by road system, urban area with green coverage, increase of buildings over a year, average of floors per building and other related data.

2013
Aiming demolition residue quantification, the adopted method is based on other authors works introducing some changes in the quantification equation. The authors adopted as calculation criteria the total area of demolitions in a given region, generation rate per area and the proportion of the type of building to be demolished in under study region Table 2 -List of articles with proposed methods of quantification of construction, demolition and/or renovation waste. The main information of each article is described in columns, allowing to establish relations and further discussions.

Source: Authors.
More simplified methods are adopted by Bakshan et al. (2015) and Tamraz et al. (2012), who use the built-up area as a reference for their estimates. Lu et al. (2016) presents estimates in more detail, predicting generation by stage (construction, renovation and demolition).
Studies conducted in Brazil are restricted to estimates based on quantifications of previous project generations, as presented by Nagalli (2012) and Kern et al. (2015).

CONCLUSION
The constructed/demolished area ratio and the generation rate per square meter can be considered most widespread method, however it is difficult to infer about its greater accuracy.
It is concluded that the development of segregated quantification methods for the construction and demolition phases separately could improve the management of the CDW either in project management or in public management.
The evolution of CDW quantification methods occurs slowly, given the year of the first study.
There is a development gap in quantification methods of CDW in numerous countries, including Brazil.
A few sources national data may support the use of methods used for country (population x average generation rate) or regional (urban expansion x average generation rate) scale. Local scales, however, lack the development of methods that allow the estimation of quantities and characteristics of the Brazilian CDW, which still does not exist.