Current situation of construction material management at international Level Situación actual de la gestión de materiales de construcción en el ámbito internacional

The present research aimed to provide a broad overview regarding the management of construction materials. As a starting point, the conception of the set of actions that make up the materials management is described and its importance within the construction sector is pointed out; It also addresses the various obstacles that this sector currently faces when managing its materials, in a global scope, and which hinder the optimal development of the sector. Likewise, new management support technologies such as Radio Frequency Identification (RFID) web-based systems for materials management and data storage applications are described, offering a vision of the advantages and disadvantages involved in implementing these information technologies. In the same way, the most common support techniques for inventory control are outlined. It is concluded that the construction industry knows the concept of materials management, however, it still faces problems for the application of a correct execution of said concept; In addition, it is at an early stage in the adoption of new techniques and technologies to support the management of construction materials.

Recent studies have identified factors leading to deficiencies in construction material management. Soni 2015, points out issues derived from the communication among the persons who participate in the execution of the construction project, bad quality materials and lack of materials when they are needed (Soni et al., 2016). (Dakhli and Lafhaj, 2018), refers to problems concerning transport and deliveries, storage and inventory, and waste use and control (Dakhli and Lafhaj, 2018).
Since a company's material management is a key function for executing the project at a minimum cost (Soni et al., 2016), it is essential to mention and describe the components involved for its correct completion : planning, procurement, storage and control. It is crucial to say that the correct practice of construction material management increases the productivity of a construction project (Gurmu, 2018). Likewise, (Gurmu, 2018), recommends the implementation of new management practices by using the latest technologies for improving the productivity. Therefore, and with the purpose of correcting certain irregularities of material management systems, some construction companies, with a more formal organizational structure, are starting to implement a number of new systems, techniques and technologies, always aiming at optimizing construction materials, which in turn improves the project's productivity.
Radio Frequency Identification (RFID) is among these new technologies, which is a wireless communication technology using a configuration system of tags and readers (Bryan et al., 2015) to improve the delivery, receipt and localization of construction materials (Majrouhi, 2012). Another one is Web-Based Material Planning and Control (WB-MPC), whose purpose is to rely on an interactive interface that allows constructors to calculate and store materials and, at the same time, to plan and control their use (Afolabi et al., 2017). Furthermore, Zoho Creator is an app based on data storage concerning construction materials, whose purpose is the access, management and edition of these data (Karami and Danesh, 2018).
Among the newly implemented techniques, the inventory control is worth highlighting as a support of construction material management. The first is ABC analysis, which refers to the 80/20 rule or least significant rule that analyzes the items corresponding to a small portion of the inventory (around 20%), but representing the highest economic value (approximately 80% of the total cost), and vice versa (Macías et al., 2019). The second technique is the Economic Order Quantity (EOQ) analysis, which refers to the order size that will yield the lowest ordering and transport cost of an inventory material (Pal and Ahire, 2016). When this technique is applied during the company's planning stage, it can reduce the lack of materials, so as not to interrupt the execution process, and also optimize their supply cost (Elmas, 2017).
It is a fact that new techniques and technologies have transformed the construction industry (Afolabi et al., 2017) and that their implementation allows giving sophisticated solutions to the difficulties that the industry faces in relation to material management (Kasim, 2011). However, it is also a fact that this implementation has been slowpaced (Afolabi et al., 2017), due to different factors that are worth outlining to make their identification and subsequent elimination easier.

Search Methodology
The present research is based on a large review of the literature addressing the construction material management worldwide, starting with the general concept, delving deeper into its components and offering a review thereof. Moreover, it deals with the use of information technologies (IT), their benefits, advantages, disadvantages, and obstacles for their implementation, among others. A description of the general scenario on the subject will help evidencing the progress made in the last years, but it will also allow examining what aspects have stalled the construction material management, thereby distinguishing the causes of this standstill.
The study period was limited to the past ten years, in order to offer the largest and most updated research possible.
The main key words used in the search were: "construction material management" whose search results gave 4,330,000 items; "material management" with approximately 5,020,000 results; and "building materials" with around 5,770,000 resulting documents. It is necessary to clarify that the information from all these results was filtered. First, priority was given to the publishing date, designating the results according to the 10-year period mentioned above. Likewise, the publication relevance, that is, the number of citations, was taken as a reference. Finally yet importantly, the journal in which the document was published was revised, thereby prioritizing the journals with greater impact at global level.

Definition of Construction Material Management
As a starting point, it is important to build an understanding of what construction material management is, and to know a little about the processes and actions involved. Therefore, a table (Table 1) has been generated to compare the definitions of different authors over the years.
The concepts coincide in four aspects that can be considered the most relevant ones: planning, procurement, storage and control (Madhavi and Varghese, 2013); (Phu and Aye, 2014).
According to Kasim & Anumba, the planning of materials provides the guidelines for the subsequent activities of the project, which has a great impact on the general plan. It is highly important to plan the access of materials to the site, in order to develop an efficient material management logistics (Kasim et al., 2005). That is where the relevance of this component lies, since the inappropriate planning of the material supply causes scheduling, cost and quality problems in the project (Chen and Nguyen, 2019).
Regarding the purchase of materials, a series of activities must occur successively and orderly for the correct execution: requisition of materials, consulting and comparing the suppliers, choosing the suppliers and negotiating with them, placing the purchase order and evaluating the supplier (Patel, 2011).
Storage is defined as the proper space, either closed or open, that is needed to provide security for the materials; this means protecting the materials against theft, loss or damage (Raibole and Waghmare, 2019). The place intended for storage must be located on a strategic point within the site to facilitate its access, because a badly located space has a negative impact on the project's productivity (Jusoh and Kasim, 2016).

N. B. Kasim 2010
Coordination function that is responsible for the planning and control of the material flow. In detail, it is a procedure comprising the procurement, delivery, waste manipulation and minimization, with the aim of guaranteeing the compliance with the requirements. (N. Kasim & Ern, 2010) Khyomesh V. Patel 2011 Process that coordinates planning, assessment of the need, supply, procurement, transport, storage and control of materials, waste minimization and profit maximization by reducing the cost of the material. (K. V. Patel, 2011) J.

Majrouhi Sardroud 2012
Management system designed to plan and control all the necessary efforts to ensure that the adequate quality and quantity of materials and equipment are properly and duly controlled, and at a reasonable cost, and to ensure its availability when necessary. (Majrouhi Sardroud, 2012) Calistus Ayegba 2013 Process for coordinating the planning by estimating the requisition supply, procurement, transport, storage and control of materials, reducing the waste and optimizing the profit by minimizing the cost of the material. (Ayegba, 2013).

Mahdi Safa 2014
Planning and control of the necessary activities to guarantee and confirm that the correct quantity and quality of materials and equipment are correctly specified, at a reasonable cost, and that they are available when needed. (Safa, 2014)

A. A. Gulghane 2015
Process that allows supplying the required goods and services to an organization in order to achieve their objectives of procurement, storage and movement of materials. (Gulghane & Khandve, 2015) Harsh Soni 2016 Key business function in charge of coordinating the optimal planning, supply, procurement, transport, storage and control of material, in order to provide a customer a predetermined service at a minimum cost. (Soni, 2016) Vikram The objective of the construction materials' control is to avoid generating a shortage and/or surplus of these materials on the site. This process is intrinsically related to the materials handling, distribution and use. The materials control can change according to how much the information technologies are actually used, since these technologies are capable of improving the process (Jusoh and Kasim, 2016).
It is imperative to manage the construction materials appropriately, because, in economic terms, these components represent more than 50% of the total cost of a construction project (Cengiz et al., 2017); (Georgekutty and Mathew, 2012); (Patel et al, 2015); (Patil, 2016). H. Nassir in 2010 affirms that a system that efficiently manages and controls the construction materials is able to increase the productivity of a project by up to 8% (Nassir et al., 2010.

Objectives of Material Management
The material management is important not only during the construction phase; it is also crucial to make a decision on the procurement of materials at the initial stage of the project planning and scheduling. Likewise, it is a key issue to rely on inventory management techniques during the execution phase, in order to supervise the material flow process periodically, and thus avoid losses, absences and delays (Patil and Pataskar, 2013). That is why material management pursues specific objectives, and their fulfillment allows an integral management process; these objectives are listed below: In order to fulfill these objectives, it is important to establish coordination and harmony among those in charge of the material management department, who in turn must be integrated and coordinated with the employees of other departments within the organization, and thus achieve an optimal construction project (Pal and Ahire, 2016).

Information and Communications Technologies in Construction Material Management
When the task of identifying and tracking the materials is automated, it facilitates the obtainment of adequate and accurate information concerning the availability of materials. This implies a decrease of the waiting time for materials that are not used, as well as a reduction of inefficient decision making due to lack of information (Majrouhi, 2012), thus contributing to the material management process. The most common methods for localizing and tracking construction materials suffer from various limitations; therefore, it is necessary to incorporate new technologies (Kereri, 2018), such as Information and Communications Technologies (ICT). According to Sánchez Duarte, ICT are the technologies used for the management and transformation of information and, particularly, the use of hardware and software that enable the creation, modification, storage, protection and retrieval of this information (Sánchez, 2008). A correct ICT implementation can deliver a more competent and productive material management process (Kasim and Ern, 2010).

Radio Frequency Identification (RFID) in Construction Material Management
RFID is a general term referring to the technologies that use radio waves to automatically identify a person, object or other information (Ren et al., 2011). A RFID system is mainly composed of a reader (transceptor) connected to an antenna and a set of tags (transpondent), which store information. The reader communicates with a computer through an app, which manages the data stored in the tags. The function of the antenna is to establish the communication between the reader and the tags. There are several types of antennas and tags, depending on the distance between the system and the objects to which the tags are attached (Valero et al., 2015), where readers can be at a range of up to 15 m from the tags. This technology is similar to the barcode system, but it differs in the sense that the RFID reader is capable to read more than one tag simultaneously and at a much larger distance, which makes it faster and more efficient.
The construction industry is applying RFID technology in different ways, but the most significant application is for material management (Hinkka and Tätilä, 2013). This approach consists in an integral GPS technology with RFID, with the aim of locating objects tagged in a real 3D plan. This means a great contribution to the material management process, because this tool is quite useful for facilitating and maintaining a real-time control of orders, stock of materials at the building site, entrance and exit from the warehouse, use, etc. (Lu et al., 2011). Likewise, the automated material management using this system replaces the traditional method with paper documentation, which can be tedious, inefficient and tardive. The application of this technology consists in using stationary antennas, which must be connected and installed in specific areas, such as in the entrance or exit of the warehouse, the construction site, among others. As soon as the tags attached to the materials reach the reading range of the readers, they are automatically identified and the information contained therein (including the GPS location of the corresponding reader) is transferred to a computer or server, where the project database is updated with the materials information, including their location (Majrouhi, 2012). There are also mobile or portable readers connected to the system, which can be transported by a person or mobile device to identify tagged items, either walking by or executing any other equipment. The main benefit of this integrated system is to ensure the availability of adequate materials in the right quantity, at the right place and when they are required, thereby reducing the search time for the materials, evaluating the inventory status, and reducing the waste of materials (Majrouhi, 2012). In contrast, the implementation of these technologies present certain disadvantages; one of them is the cost, which is a concerning issue for businesses. Moreover, the engineers, technicians and warehouse staff found that the implementation task for the new system was a little tedious, thus showing a certain reluctance and leaning towards the traditional material management system (Ren et al., 2011).
In 2012, studies were undertaken to evaluate the feasibility of these automated systems, and the results showed a saving of up to 3.1% of the total construction costs (Demiralp et al., 2012); this paved the way for implementing this system with new technologies. Such is the case for unmanned aerial vehicles (UAV), commonly called drones. A simple system was configured by installing a RFID reader on a drone, with the aim of tracking the materials located at the construction site, in order to control the material flow inside and outside of the warehouse and be able to rely on real time information about quantity, location, use, etc. The reader was a small device measuring 21 x 8.1 x 3.2 cm, whose weight was less than 500 g, which also provided a GPS positioning (Bryan et al., 2015). In relation to the selected drone, it had enough capacity to bear the weight of the RFID reader and its flight time was approximately 30 min.
The initial tests yielded positive results, that is, the combination of UAV and RFID technologies was successful; however, the researchers were faced with certain limitations such as the reading range of the RFID reader. The selection of a very small reader that could fly on top of the drone restricted the reading range, which was below 2 m. Furthermore, it was impossible to accurately control the speed and vision of the drone, thus making the task inside the site more difficult (Bryan et al., 2015).

Web-Based Material Planning and Control Model
The purpose of the WB-MPC model is to rely on an interactive interface based on the web, providing a tool for professionals in charge of construction materials that helps them calculate and store quantities of these materials, while simultaneously planning and controlling their use. The system was designed to show any deficit in the quantities of specific construction materials through periodical short texting systems or by E-mail. In this system, the construction project manager and certain users can access the form of the element by logging in to the webpage. The project manager or any other authorized employees have access to critical data or information dealing with the use of materials on the site, which contributes to the transparency of the project. The system also has a messaging network where users can send clarifications to the project manager regarding the works (Afolabi et al., 2017). (Figure 1) shows the design of the architectonic system.

Zoho Creator and its Material Management Application
Zoho Creator is a collaborative environment for making and using relational database artifacts, with regard to relations between entities and object-relational ones (VanZandt, 2017). This app is based on data storage, in this case, related to construction materials under predictable crisis conditions created by the app itself. It is a minimalist tool developed under an easy-to-use code. Its main objective is to easily access, manage and edit large quantities of materials data (Karami and Danesh, 2018). (Figure 2) shows the Zoho Creator's fields The app's main fields are dates and places in which the materials must be stored, according to the information facilitated at the working place and the decision made by the project managers. These fields are related to when and where the construction materials should be stored, and when and how many materials are to be used. This app certainly helps project managers to easily manage large amounts of data.
Two actors are needed for using the app: one of them is the person in charge of the materials in the warehouse, who receives the materials and accepts or rejects them according to the quality (the material's acceptance or rejection report can be generated in the app). The same person enters the necessary information of the materials (name, quality, quantity, supplier's data, etc.) in the Zoho Creator database. Once the data input is accomplished, they are immediately available for the second actor, the project manager, who will rely on the necessary information, in real time, for making decisions about how to use the materials, thus making their management easier, even when dealing with large amounts of materials (Karami and Danesh, 2018).
An evaluation of 21 app users (students of architecture and construction science) showed that the app fulfilled the expectations of the users by 85%. The drawback here is that the study was made with students, thus it is not possible to guarantee that the app used in real construction cases will be equally satisfactory.

Support Techniques for Construction Material Management
The inventory control is a key component of the material management process. It refers to a subsystem that guarantees the supply of the necessary inventory quantity and quality at the right time; in turn, this subsystem avoids superfluous inventory investment (Patil and Pataskar, 2013). Although there are different techniques to help in the optimal accomplishment of this inventory control, those considered predominant are ABC and EOQ analysis.

ABC Analysis
The ABC analysis is one of the most commonly used approach for classifying inventories (Desai and Patel, 2019). (Pal and Ahire, 2016). In order to calculate the cost or monetary value of the materials, you only need to multiply the quantity of material by its unit price.

The analysis technique is based on the principle that a reduced portion of construction materials represents the highest monetary value of a construction project inventory; while the greatest amount of materials of this inventory represents a small part of its monetary value
• "A" classified materials, which make up for 5% to 10% of the inventory items, represent 70%-75% of the inventory cost. • "B" classified materials, which make up for 10% to 15% of the inventory items, represent 10%-15% of the inventory cost. • "C" classified materials, which make up for 70% to 80% of the inventory items, represent 15%-10% of the inventory cost (Mohopadkar and Patil, 2017).
The position of the elements in the different categories shows that "A" classified items must be strictly controlled, while "B" classified items could undergo a medium-level control; and "C" classified items can be controlled in a much more flexible way (Pande and Sabihuddin, 2015).
The case studies carried out demonstrated that the main advantage of this inventory control technique is that, compared to any other method or technique, it is the most inexpensive. The observed disadvantage is that ABC analysis does not provide the items' critical nature with absolute certainty, that is, it only creates an idea about the inventory value (Shet and Narwade, 2016).

EOQ Analysis
The analysis technique of Economic Order Quantity (EOQ) refers to the order size that yields the most inexpensive total ordering and transport cost of an inventory material. The purpose of this technique is that construction companies do not place unnecessary orders, thus not generating superfluous or excessive ordering costs; and at the same time, that they do not generate a small number of orders with large quantities of materials to prevent storage and/or maintenance cost overruns (Pande and Sabihuddin, 2015).
The economic order quantity is calculated with (Equation 1).
Using this tool has many advantages. In 2009, Deepak Karoriya stated that the cost of a construction project could be reduced with the EOQ analysis (Karoriya and Pandey, 2018). On the other hand, Mahant y Patil declared that the joint application of ABC and EOQ analysis techniques on a construction project produces cost savings and prevents material waste (Soni et al., 2016). In turn, in 2013 and following a case study on a construction project, Ashwini indicated that the total inventory cost was reduced after adopting EOQ analysis (Patil and Pataskar, 2013). In 2017, Elmas suggested that the application of this method during the planning phase could reduce sold out materials, thus not altering the process within the company, in addition to cutting down the materials' supply costs (Elmas, 2017).

Obstacles in the Implementation of Construction Material Management
The currently used practices in the construction industry to manage the materials and procedures for controlling them are quite unsatisfactory, because they are labor-intensive, irregular and error-prone (Gulghane and Khandve, 2015). The project managers, who are responsible for the construction material management, show difficulties when it comes to solving problems with the current practices (Kasim, 2015). These situations lead to inadequate material management practices, thus causing many problems at the time of executing the system or process. (Table 2) lists the different problems that the material management encounters at international level. • Materials are inadequately obtained and stored and a lack of inventory control is perceived. (Madhavi & Varghese Mathew, 2013) Myanmar N. L. Phu 2014 • Unavailability of the necessary material. • Not enough storage space and inefficient control thereof.
• Material price fluctuations. • Lack of systematized control in the use of materials. • Theft, robbery and vandalism. (Phu & Aye Mya, 2014)

Discussion
With the aim of achieving a competitive construction industry in the face of other sectors, it is essential to remain at the forefront in the implementation of new techniques and technologies for supporting the material management, regardless of the industry's business strata. However, it is not that simple to implement this in different business strata, because it is impossible to equate the facilities of medium and large business with those of micro and small business. The former rely on a more formal organizational structure, better human resource and greater capital investment, while the others have precarious organizational structures, less human resource and limited capital. Consequently, smaller construction companies suffer from underdevelopment in relation to the management of their materials.
It is noteworthy that the economic factor appears as one of the main barriers for adopting these new tools, but, on the other hand, the economic factor is also one of the greatest driving forces for establishing new methods of construction material management, because they allow optimizing the financial resources. Therefore, the economic capital plays the leading role in the optimization of a construction project by means of material management.

Conclusions
The construction industry has already consolidated the concept of material management, as well as its implicit processes. This is perceived in the definitions pointed out by different authors in different countries: they all agree with the fact that the main pillars for properly managing materials are: planning, procurement, storage and control. Nevertheless, despite knowing the concept and processes involved, it is clear that the construction industry has not been able to execute them to its full extent, because it faces different barriers that prevents it from achieving a satisfactory completion. At the international level, the predominant issues range from aspects regarding the logistics, organization, economics or investment to exogenous factors affecting the construction projects.
In the last decade, and for the sake of compensating these inconsistencies, the construction industry has started to bet on IT implementation and the use of new control techniques, which, although they do offer potential benefits, they are still in the development stage. The technologies such as radiofrequency identification, web-based • Poor storage of materials. • Improperly manipulated materials.
• (Santelices, 2019) management models and data storage apps, as well as inventory control techniques such as ABC and EOQ analysis (which are not entirely new, but are gaining increasing importance) are the new tools used by construction companies, with the aim of overcoming the weak points in their material management processes.
There is no doubt that the construction material management has yet problems to solve, so it is crucial to emphasize the overcoming of these obstacles. First, in order to find a solution to any of the problems it is necessary to identify the causes generating them. Consequently, the present research leaves the door open for delving deeper into the factors originating these problems. This is feasible by undertaking case studies dealing with companies from the construction industry in their different strata, with the aim of detecting endogenous and exogenous causes that generate the existing problems when it comes to implement the material management within the construction companies.