Site management approach to reduce material waste

Transcription

1 Site management approach to reduce material waste U. E. L. Souza (1); A. C. Andrade (2) (1) (2) Dept. of Civil Construction Eng., Escola Politécnica, Universidade de São Paulo, Brazil Abstract Material waste has been an important issue to be addressed in order to reduce environmental impacts of the building construction activities. The extra mass of materials expended (Souza et alii, 1999 [8]) can be as large as 25% of the amount prescribed by the design. In this context, Brazilian construction companies have been trying to implement actions aiming to improve materials management. This paper describes a case study where the authors coordinated an experience, in a building construction site in São Paulo, where a new management approach was adopted. Based on an extensive database, collected from more than one hundred construction sites, weekly meetings were held, gathering together site and subcontractor managers, in order to evaluate the previous week job performance, to define actions to be implemented to improve the job process, and to define goals to be achieved in the next week. Due to the objective tools used, the main contractor and the subcontractor were induced to act as partners, and the detected material waste index was smaller than the minimum value of the available database. This paper describes this experience (the method adopted, information and decisions related to every week meeting) concerning the target of reducing concrete blocks waste. Keywords Materials Waste; construction management 1 Material waste in the building construction process Several researches indicate that material waste in the building construction industry is very significant. Enshanssi [3] obtained a 5.2% waste value for common bricks, in 86 sites studied in the Gaza region; Skoyles [6] verified the value of 7% for concrete blocks waste in one building site, Pinto [4] presented a value of 13% for block waste and Soibelman [7] obtained median values of 52%. Therefore, this is a very important subject, both in terms of the revenue the contractor can get from the site activities or in terms of the amount of natural resources that is consumed in the building construction process.

2 In order to discuss block waste, this paper firstly defines material waste and then it describes the level of brick/block waste the authors found for laying blocks activity job. 1.1 Material waste: concept A worker wastes material every time he/she spends an amount of material above the essentially necessary amount to produce a job. For example, if 110m³ of concrete is demanded to produce a 100m³ concrete structure, 10m³ of concrete were wasted (Figure 1). One can observe that the waste can appear under different natures: over embodied material or debris. Figure 1 Concrete waste and its nature. This paper measures material waste as follows: where: MLP RMQ TNM RMQ TNM MLP = x100 (1) TNM = material loss in percentage = real material quantity used = theoretically necessary material In the case of brick/block waste, the embodied parcel (Figure 2.a) is seldom detected; the waste normally appears in the nature of debris (Figure 2.b). a) b) Figure 2 Brick/block waste: a) embodied waste; b) debris.

3 1.2 Figures about bricks/blocks waste The authors coordinated a very expressive research where almost one hundred construction sites were evaluated in terms of material waste measurement. Table 1 indicates the results for brick and block waste. The position measure (median), dispersion measures (minimum and maximum values) and the sample size (n) are presented. Table 1 Brick and block waste in the Brazilian building construction (Agopyan, 1998 [1]) Material Material Loss in Percentage (MLP) Medians Minimum values Maximum values Bricks/blocks n The waste figures analysis indicated the main factors causing the waste (Figure 3) were: inadequate transportation of blocks; low quality materials; bad storage conditions; inappropriate equipment used to cut the blocks. Figure 3 Some factors inducing an increase in brick and block waste.

4 2 Case study context 2.1 Sustainable construction as a goal Several meetings, papers, policies and laws have pointed out the building construction process must be improved in terms of reducing the environmental impacts it implies. The Brazilian Construction Industry demands an amount of material more than one hundred times bigger than the amount demanded by the Automobile Industry, for example. It also produces 2/3 of the urban residues PINTO [5]. Therefore, contractors should be induced to reduce material waste. Both the new laws and the increasing awareness about these issues have provided a more demanding client in terms of building construction. The developers and the contractors realized that improving resources management is a must in the new context. 2.2 Concima company Concima is a medium-sized developer-contractor firm that has an special concern with its construction process management. This company participated in another research, as a partner of the University of São Paulo USP, studying labor productivity. After obtaining the ISO 9002 certification, Concima set environmental preservation as a task to be accomplished. In order to help the company improving its environment management skills, without reducing its competitiveness, the Construction Departament of the University of São Paulo (PCC-USP) was invited to develop a new site management approach to be used by Concima. 2.3 PCC-USP previous experience related to material waste management The environmental impact caused by the construction activity is one of the concerns of PCC- USP. During three years, PCC-USP coordinated a national effort, in 12 different Brazilian states, study more than 100 building construction sites, that allowed an ample and detailed diagnostics about material waste in the Brazilian construction activity. After this study, a method providing a fast and continuous material consumption control (Andrade, 1999 [2]) was developed for many services/materials. So, the PCC-USP was prepared to develop a continuous process management to reduce material waste in the Concima building constructions sites. This method, and the results obtained, are presented in this paper. 2.4 A partnership to reduce waste The amount of material used in a certain construction task is influenced by several decisions taken by some agents, as one can see on Figure 4. Figure 4 presents the agents involved in the Concima building site management.

5 %! " # '! $ ( $! $ " & $ & % ' $ # $! % #$ & Figure 4 The material consumption control and the relationship among the construction site and other agents involved in the constructive process. 3 Case Study 3.1 West Park Residential West Park Residential Project holds 452 apartments in 38, m². It is constituted by three 15-floor towers and four 17-floor towers. Each tower has 4 apartments per floor and each apartment has 2 or 3 bedrooms. The towers structure is composed by concrete walls, molded "in loco", and steel reinforced concrete slabs; the internal masonry adopts concrete blocks layed with multiple use mortar; the internal covering uses mortar plaster, in the cold areas, and gypsum plaster, in the other areas. The external covering will be constituted by a pigmented and texturized mortar. The building site is very large and the access conditions are good. Trucks have access to the site interior. The material discharge is done by a tower crane. 3.2 Blockckwork: execution and evaluation Blockwork is a construction job that generates a considerable amount of waste. More than that, the masonry units account for the major part of the masonry costs. Consequently, it is important to control blocks consumption. Masonry, in the case study, uses concrete blocks and mortar. The concrete blocks are received and immediately transported up to the several building floors, where they are stocked and, later, layed by the masons. The blocks waste evaluation was done by means of a sampling approach. A certain number of blocks ("A") were marked in the stock. After a week, the amount of marked blocks ("B") in the new walls (Figure 5), and the remaining market blocks in the stockpile ("C") were determined. Waste id calculated as: ((A- (B+C))/A)*100.

6 Figure 5 Marked blocks in the stock and in the wall 3.3 Defining a target for the blocks consumption Brazilian construction sites presented MLP values running from 3% to 48%. The case study site and process management was defined in terms of becoming similar to the sites which MLP were close to the minimum value, that is, 3%. Once the Concima site managers agreed in establish a consumption process as close as possible as the defined one, Table 3 indicates the consumption rate the authors considered to be feasible to reach in the case study. The index was adopted as a target to be addressed. Material Table 2 Target block consumption rate for the case study. target Concrete Blocks Waste < 3% Material Loss in Percentage (MLP) comments the authors consider that it would be possible, as far as the material consumption management follows the planned actions, to reach a waste rate smaller than the one presented by the best national performance detect by PCC-USP in the former research (see Table 1). 3.4 Blocks consumption management Beside the initial meeting, when the target of reaching to a MLP smaller than 3% was established and the production process features were defined, once a week meetings were scheduled. The idea was: every Friday the week performance expressed in terms of the a meeting would be held to evaluated and plan actions for the next week with the goal of reduction blocks waste eventually detected. 3.5 Results and analysis The authors participated on 6 meetings before leaving to the site managers the task of keeping on reducing material waste.

7 In the first meeting as stated before, the target MLP was defined; more than that, several recommendations were placed in order to define good practices and human motivation to minimize blocks waste. In the next five weekly meetings, the week MLP was calculated (see Table 3) and all the participants discussed it and planned actions for the next week: cycle 1 showed a very good MLP; the authors believe that the first meeting influenced the foreman in his efforts to avoid the worker under his command to waste material; cycle 2 presented a bad MLP. The reasons for this unexpected performance was the workers turnaround. For the next week it was recommed to improve the new workers training; cycle 3 showed a good performance again; cycle 4 was not as good as it could be. Problems with the masonry design were detected: the upper parts of the doors (Figure 6) and windows were not correctly defined, and several blocks had to be cut to fit to the walls dimensions. A new design definition was provided to fix this mistake; cycle 5 again, bring MLP to the expected level; cumulatively, the MLP reach 3,2%, and the managers believed next weeks would be good. They expect the final goal (MLP < 3%) would be met. Table 3 Results of concrete blocks waste Cycle MLP 1 st 0,60 2 nd 6,51 3 rd 1,65 4 th 3,80 5 th 1,71 ALL 3,21 Every week, in a meeting, new directives were established to improve the rates detected. Some Figure 6 Concrete blocks cut on top of door.

8 4 Final comments and acknowledgements The proposed method proved to be easy to use. The "decision bases on figures" approach was approved both by the site superintendent and the foreman. The masons also were able to understand the goals and to accept the target MLP as their target. The method also demonstrate to be important to reduce material waste. In the case study the MLP value, during the six weeks the work was tracked by the authors, was as small as the minimum national MLP previously detected. And we believe the final performance would be even better once the approach to manage blocks consumption kept on being adopted. The ideas presented in this paper have been successfully used, by some researchers of PCC-USP, in other case studies, not just for block work. The authors belive that confidence in terms of the reachable performance and its continuous evaluation can provide a strong tool to help construction managers to reduce material waste. 5 Acknowledges The authors acknowledges Finep, Senai And Capes by their support to the on going research effort to reduce material waste in construction. 6 References 1. AGOPYAN, V. et al. Alternativas para a redução do desperdício de materiais nos canteiros de obras. São Paulo, 1998 (Relatório final: vol. 1 ao 5). 2. ANDRADE, A. C. de. Método para quantificação das perdas de materiais em obras de construção de edifícios: superestrutura e alvenaria. São Paulo, p. Dissertação (Mestrado) Escola Politécnica, Universidade de São Paulo. 3. ENSHANSSI, A. Materials control and waste on building site. Building Research and Information, vol. 24, number 1, PINTO, T. P. Desperdício em xeque. Revestimento. São Paulo: Pini, p Suplemento. 5. PINTO, T.P. Entulho de construção: problema urbano que pode gerar soluções. Revista Construção São Paulo, v.9, n.2325, p.23-26, ago., SKOYLES, E.R. Materials wastage a misuse of resources. Building Research and Practice, CP 67/76, oct SOIBELMAN, L. As perdas de materiais na construção de edificações: Sua incidência e controle. Porto Alegre, Dissertação (Mestrado em Engenharia) - Curso de Pós- Graduação em Engenharia Civil - Universidade Federal do Rio Grande do Sul. 8. SOUZA, U.E.L.; AGOPYAN, V.; PALIARI, J.C. Conhecendo as perdas de materiais na construção. Revista Qualidade, Sinduscon-SP, n.20, p.34.