Global economic growth causes an increase in natural resources exploitation, particularly in construction branch. The growing use of electricity contributes to climate change. Therefore, it is necessary to search the solutions, which will allow for reducing natural resources exploitation. One of the many opportunities to do that is the application of the recycled materials. The authors of the given article have analyzed three variants of construction solutions.
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One of the many opportunities to do that is the application of the recycled materials. The authors of the given article have analyzed three variants of construction solutions. One of them was the production of the walls of a building from reinforced concrete prefabricates with styrofoam insulation layer. The second variant for analysis were prefabricated walls from lightweight concrete, made of sintered clay aggregate with a foam core.
The third proposed variant was a system of multi-layered walls, which was made of lightweight concrete with granulated expanded glass aggregate GEGA. The main objective of the research was to assess the use of lightweight GEGA prefabricates, focusing on economic and technological aspects of the solution. The authors have analyzed the entire construction costs; ceilings and stairs were assumed as reinforced concrete elements.
In calculations, the weight of the elements was taken into account, as well as transportation and mounting costs. On the basis of this cost analysis, it was concluded that the use of prefabricated element, made of lightweight concrete with GEGA, could be a replacement for the solutions, widely applied until these days.
The analysis has also shown that the use of prefabricates with GEGA is sensible from the economic viewpoint, as it allows for saving construction time. Moreover, the solutions, proposed here, allow for saving natural resources and assuming a more environmentally friendly and caring attitude.
Science and technology development enable the implementation of innovative solutions in construction and architecture. Multiple changes in concrete production and prefabrication are being introduced.
At present, concrete as a modern composite is regarded not only as a construction material, but also as an insulation material or aesthetic architectural finish. Concrete properties depend on concrete mixture components.
It is also possible to modify cement binder by means of applying admixtures and additives or natural, artificial, or recycled aggregates alongside with sustainable development principles while obtaining components, producing ready-mix and prefabricating elements. New technologies in artificial lightweight aggregate production enable meeting complex requirements of the construction contractors as for strength, insulation, acoustic, fire-resistance, and aesthetic properties.
Currently, due to the possibility of the use of the additives and chemical admixtures, it is possible to obtain considerably higher strength parameters for lightweight concrete than is required by the standard.
Lightweight concrete and its modifications are subject to a great number of research at the moment [ 2 , 3 , 4 , 5 , 6 , 7 ].
Due to the possibility of application of the prefabricated elements, made of lightweight concrete as construction elements, it is necessary to design them with a great deal of precision and take into account the requirements that specifically apply to the type of construction. The components of a mix should be selected with the thought of safety of the future users of the construction and, also, the durability of the elements and their physical and mechanical properties.
Basic features of lightweight concrete, which make a difference, are lower volume density and better insulation properties [ 8 , 9 , 10 , 11 ]. The application of a lightweight aggregate, e.
Prefabrication gives great opportunities for public, residential, and industrial construction. The essence of this technology lies in the optimization of construction process, safety procedures improvement, limitation of the waste production, and minimization of exhaust gas emission. Moreover, the search of the effective methods of construction project realization in keeping with the aesthetic and comfort values of the constructed object is of high importance.
Prefabricated elements are widely used in residential construction as multi-layered walls, ceilings, and balcony panels due to their numerous advantages. The prefabricate production process led, in modern conditions, strictly following technological procedures, going on non-dependent on atmospheric conditions production floors, allows for receiving perfect quality products.
However, it is crucial to bear in mind the necessity of strict overall investment control and preliminary assessment of the difficulties while mounting. Economic analysis of the investment is also obligatory, so as to make sure of the financial reasonability of the project [ 26 ].
Table 1 presents a comparison of the building erection system by means of the method of performing all activities at the construction site and using prefabricated elements. Comparison between on-site and off-site construction based on [ 26 ]. The prefabricated multi-layer wall is frequently used in the prefabricated integrated residential buildings, which are characterized by easy installation and short construction time [ 27 , 28 , 29 ]. Figure 1 shows the process of manufacturing a prefabricated wall element.
Process of manufacturing of prefabricated wall elements [ 30 ]. Further analyzing the case of installing prefabricated walls in an apartment building, thermal conductivity aspects were considered.
Heat transfer coefficient for the walls was determined, while taking into account higher requirements, connected with thermal insulation in the countries with occurring problem of significant indoor and outdoor temperature difference. Table 2 shows the requirements for meeting for thermal conductivity of outer and inner walls of the residential building.
These requirements cannot be met by one-layer reinforced-concrete wall or brick wall. One could apply a thermal insulation layer of foam panels or mineral wool or use thermal insulation plaster in order to meet the latter thermal insulation requirements.
However, these solutions will generate additional costs and will make the walls thicker. Additional construction works, connected with thermal insulation, will cause construction deadlines prolongation. Therefore, an alternative solution lies in using multilayer prefabricated elements, which are made of lightweight concrete. Figure 2 presents the types of prefabricated walls. The types of layers, thickness of the layers, the values of thermal conductivity coefficients, and thermal resistivity values were determined to compare and analyze the values of the heat transfer coefficients for the three types of a vertical outer wall.
The walls with the ordinary concrete post and the post, made of concrete with expanded clay aggregate were compared, as well as the ones made of concrete with fly ash aggregate and with granulated foam glass aggregate.
The total thermal resistivity R T of the flat construction component, consisting of homogeneous insulation layers, perpendicular to the direction of the heat flow should be calculated according to Equation 1. The values of thermal resistance R si , R se [ 32 , 33 ] were assumed according to Table 4.
Heat transfer coefficient of the wall was calculated according to the Equation 4. The main assumption was the maximum heat transfer coefficient U max could not be higher than 0. The research of different variants of the project realization and the proposal of the optimal one leads to the choice of the best solution from the point of view of the chosen criterion. In order to optimize costs, it is advised to prepare construction cost estimation, including all costs calculation labor, materials, equipment, indirect costs, and profit for the solutions in question.
In the case of time optimization, it is necessary to analyze workload for each process within the proposed solutions. The objective of the analysis, presented in the following part of the article, is to compare the labor cost and time needed for mounting the elements of the construction. Three solutions have been proposed, for which the costs and time of realization were analyzed. The object was selected, the bill of quantities was prepared, assumptions for calculation were made, and a cost-estimate calculation was carried out in order to determine the cost of raising a building in a raw state by means of prefabricated technology and the use of three types of materials.
Three solutions were analyzed. The aforementioned methods were applied on an actual construction site. Subsequently, the economic, environmental, and social benefits of prefabricated concrete application in residential construction were analyzed.
A sandwich wall contains an insulating layer of polystyrene. In addition, the wall has elements for transporting and arranging elements. Table 5 provides detailed information. Solution 2 is an assembly of the object, using prefabricated layered elements, with a lightweight concrete core of sintered and expanded clay Leca.
In addition, the wall has transporting and arranging elements. Solution 3 consists of assembling the object with sandwich elements with a lightweight concrete core from granulated expanded glass aggregate, with an insulating layer of ultra-light concrete containing perlite and granulated expanded glass aggregate from the outside.
Gypsum plaster was used in the inside. The wall has elements, which enable the transport and arrangement of elements. In Table 5 , one can see the examples of the walls alongside with heat transfer coefficient.
As an example, a multi-family, five-story, three-frame residential building was subjected to economic, technological, and organizational analysis Figure 3. There are 30 residential premises with a total usable floor area of The built-up area is The building is constructed of prefabricated elements in large-panel technology.
The structural arrangement of the load-bearing walls is transverse, their spacing is 3. On the last storey of the building, masonry, prefabricated, and wet cast elements were used. Structural walls of the underground and above-ground storeys are made of 15 cm thick prefabricated reinforced concrete elements.
A multi-family, five-story, three-frame residential building. Source: own photo of the authors. On the basis of the project documentation, a bill of quantities BOQ was prepared, the range and quantity of certain works, needed for the raw object state, were determined. In both BOQ and estimation the production cost of the walls, ceilings and stairs were calculated Table 6.
The assessment was made on the basis of [ 37 ] and individual calculations [ 38 ]. It was assumed that, given retail prices would include labor, material, equipment costs, as well as indirect costs and profit for a mounting unit of each element [ 39 ].
For the walls, the retail prices concerned three proposed solutions 1—3. It was assumed that the production of the ceilings and stairs would be, in each case, as for solution 1 prefabricated reinforced concrete. List of structural elements for five storeys of the building, unit prices and total cost of walls, ceilings and stairs according to solutions 1, 2, 3.
The cost of making the above range of the building shell walls, ceilings, stairs from reinforced concrete precast elements is , The cost of the same scope of works from precast lightweight concrete, which was made of sintered and expanded clay, is 1,, The cost of prefabricated lightweight concrete works is 1,, Solution No.
Table 6 , Figure 4. Cost of making walls, ceilings and stairs in the building implemented according to three solutions. The following assumption was made: in each case, the construction of five floors of the building, five to 14 employees are employed depending on the scope and nature of technological processes. The expenditure of time given in Table 6 was determined on the basis of Material Expenditure Catalog KNR [ 40 ] and own analyzes [ 38 , 41 ].
Based on the information contained in Table 7 and Figure 5 , it can be concluded that the expenditure of working time for the technology of assembling the object according to solutions 2 and 3 are similar and significantly differ from the expenditure of time for solution 1.
This is due to the fact that the structural elements—prefabricated concrete lightweight, made of sintered and expanded clay and lightweight concrete precast elements, made of GEGA, have similar weight and they are definitely lighter than reinforced concrete precasts.
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