A Study on Playful Work Design and Performance of Employees

Abstract

This paper\'s primary goal is to make an initial attempt to learn about and comprehend the various facets of concrete 3D printing. We have studied materials, printing parameters, finished and ongoing projects, and we have tested 3D printable concrete with materials that are readily available in our locality. This work examines a variety of historical data on mix design proportions, draws a general conclusion about the effects of mixture compositions on characteristics, particularly on the fresh and hardened stages of 3DPC, highlights those effects, and describes mix design methodologies. Right now, we continue to use a trial-and-error methodology, which is standard practice. In order to accomplish design goals that are common to particular 3D printer parameters and that should be widely accepted, we need to develop a set of standard guidelines.Here, the idea of manual extrusion—manually printing 3D objects with a hand-held extruder—is presented for experimental purposes.

Introduction

I. INTRODUCTION

3D concrete printing is a new age and an innovative construction technique that is progressively making its way into building construction sector to provide a secure, customized, aesthetics and duration of construction.As 3D printing became more widespread, the building sector adopted the technology to create homes and other construction projects. The benefits of on-site assembly, lower time and cost and improved quality are driving the daily growth of concrete 3D printing. The concrete specifically utilized for 3D printing, however retains the consistency feel of an aerated dough which having elements identical to traditional concrete.  Such 3D printed structures are globally constructed.There are no standards for construction of 3D printing and therefore there is list of researches being carried out. The material efficiency of additive manufacturing procedure is greater compared to traditional construction process [Joseph Pegna (1997)].  The use of cementitious materials in 3D printing is an emphasis on reasonable and sustainable choices. There are six possible replacement ratios of tailing to sand for a single nozzle printing technique. The ideal mixture contains about 30% mining tailings [Guowei Ma et al (2017)]. This technique reduces the industrial waste; reduce housing gaps and labour and energy costs [N.I. Vatin et al (2017)]. It is a cutting-edge technique that creates complicated shapes from 3D CAD designs without need for tools [Yi Wei Daniel Tay et al (May 2017)]. The latest advancements in 3D printing technology emphasize contour crafting as a revolutionary approach for building environmentally friendly dwellings. 3D printing and traditional construction methods will likely continue to evolve alongside each other in the future [Mehmet Sakin and Yusuf Caner Kiroglu (July 2017)]. In the industrial sector, 3D printing offers possibilities for automation, production acceleration. However, its potential in the building sector is restricted due to scarcity of materials and expensive processes [Isaac Perkins & Martin Skitmore (2017)]. The total amount of energy required for building construction, replacement, restoration, and demolition accounts for 48% of the world's yearly energy consumption. With 3D printing technology, energy usage and carbon emissions can be decreased [M K Dixit (2019)]. The combined effect of Industry 4.0 technology with 3D printing presents significant opportunities for more productive and sustainable construction. But the building industry has not completely embraced 3D printing technology, and incorporating robotic systems into large-scale construction projects is the main obstacle [S. El?Sayegh et al (March 2020)].  The demand for labor may be reduced by this technology, especially in nations with large immigration rates. This might not be helpful, in nations where building is the main sector and labor is less expensive. Additionally, 3D printing requires specialized knowledge and may require high-level positions [Md. Aslam Hossain et al (Oct. 2020)]. 3D printing could become a viable alternative to conventional methods, transforming industry management in remote, isolated, and expeditionary environments [S.J. Schuldt et al (March 2021)]. This technology requires 3D model design, optimized cement mortar, and careful mixing ratios.

It offers financial and ecological benefits, but its application depends on precision, material, cost, and duration [Asena KARSLIO?LU (March 2022)]. New design methodology that integrates fabrication and assembly of a flat print bed and a 3-axis gantry robot-equipped concrete extrusion 3D printer to create an overhanging, compression-dominated structure made of interlocking, modular 2.5D concrete segments. This formwork-free concrete 3D printing method allows for faster and easier customization of the geometry of overhanging concrete structures based on different site and structural design requirements [Alexander Lin et al (2022)]. 3D printing is the most flexible building technique, promoting creativity, error reduction, and a shorter supply chain. However, the lack of regulations and rules governing 3D printing production and usage raises concerns about public safety and the environment. The study suggests that appropriate laws and policies should be implemented alongside 3D printing to protect people and reduce environmental damage [Waqar et al. (Feb. 2023)].

II. LITERATURE REVIEW

Joseph Pegna (1997) investigated a new additive manufacturing technique for construction automation, which simplified assembly operations. He investigated masonry constructions constructed by applying Portland cement and sand, revealing distinct mortar properties. Pegna also evaluated the potential for large-scale, solid freeform structure production.

Zeina Malaeb et al. (2015) stated that 3D concrete printing as a viable construction method. This method permits formwork-free construction of homes with the appropriate mix that meets architectural criteria. The printer works in three dimensions to efficiently construct walls and other structures. It optimizes the extrusion process by using a nozzle and trowels with a diameter of 2 cm. Experimentation revealed the appropriate mix: 125g cement, 80g sand, and 160g fine aggregates, plus performance additives, resulting in a compressive strength of 42 MPa.

C. Gosselin et al (2016) developed a new 3D printing method for ultra-high-performance concrete, combining various disciplines. Their innovation allows for large-scale, sophisticated structures to be built without the use of temporary supports, hence enhancing 3D printing in architecture. In addition, the technique allows structural components to be multifunctional.

Pshtiwan Shakor et al (2017) developed a cement mixture for Z-Corporation's 3D printing, hoping to replicate Z-powder. They assessed the mechanical properties using cubic specimens with varying saturation levels. The study proposes Z-Corp 150 as an alternative for Z-powder in 3D printing, enhancing compressive strength.

Guowei Ma et al (2017) investigated the use of cementitious materials in 3D printing with an emphasis on affordable and eco-friendly options. It develops a single-nozzle printing method and looks at six replacement ratios of tailing to sand. Thirty percent mining tailings is the ideal blend.

Hambach and Volkmer (2017) discussed 3D printing with fiber-reinforced Portland cement, a material recognized for its high flexural and compressive strength. They used aligned glass, basalt, or carbon fibers to increase strength, carefully controlling their alignment along the print path.

N.I. Vatin et al (2017) conducted a global assessment of additive technology in construction, focusing on its potential for waste reduction and cost efficiency. They studied fundamental printing technologies and market players with the goal of promoting innovative construction techniques in Russia. Key obstacles cited include a lack of regulations, industry expansion, and expensive equipment costs.

Yi Wei Daniel Tay et al (May 2017) investigated 3D printing, which is a toolless approach for sculpting complicated objects from computer models. It speeds up prototype manufacturing, reduces material waste, and revolutionizes building techniques, lowering prices and labor. The Singapore Centre for 3D Printing displays current advances, highlighting possible future research directions.
Mehmet Sakin and Yusuf Caner Kiroglu (July 2017) discussed 3D printing improvements, including contour crafting for sustainable housing. They highlight the reduced costs, reduced pollution, and safety benefits. The integration of BIM and 3D printing promises greater efficiency and design. BIM synchronizes 3D printing systems, defining future plans and generating revenue. The study forecasts that 3D printing will continue to evolve alongside traditional construction methods.

Ali Kazemian et al (2017) developed the workability of a new "printing mixture" for construction-scale 3D printing. It focuses on print quality, shape stability, and printability window, using measurements of printed layer size and surface quality. The study suggests an iterative laboratory testing approach that emphasizes printed layer characteristics rather than pump usage, allowing for compatibility with various concrete 3D printing systems.

Isaac Perkins&Martin Skitmore (2017) investigated 3D printing's potential in manufacturing for automation and waste reduction, but found limitations in construction owing to material constraints and pricing. Techniques like as contour crafting and concrete printing encounter scalability and practicality issues on large projects.

Refilwe Lediga&Deon Kruger (2017) investigated flexural strength and discovered a range of 13 to 16 MPa, with tension between layers resulting in a 36% drop in loading. Bonding between layers is critical in 3D concrete printing, with timing impacting adhesive strength and shrinkage being a concern. Optimizing mix design and nozzle diameter can improve buildability and compressive strength while meeting building codes over time.

Nils O.E. Olsson and Ali Shafqat (2019) highlighted the limited use of 3D printing in Norwegian construction, primarily for testing. Long-term, it is cost-effective, but it requires over 8 years of implementation and significant investment. Encouraging R&D support and collaboration among suppliers and contractors may aid in widespread adoption. 3D printing holds potential for non-standard building components, but more technological improvement is required.

M K Dixit (2019) discovered that buildings utilize 48% of global energy annually, with significant embodied energy in construction. 3D printing has the potential to reduce energy use and emissions, but it faces challenges in traditional construction processes. Future research should prioritize iterative design and implementation in order to fully capitalize on its benefits.

S. El?Sayegh et al (March 2020) studied 3D printing in construction, highlighting advantages such as constructability and sustainability, as well as dangers such as material printability and lack of regulation. They filled a literature void by addressing risk, which is a novel feature of 3D printing. While promising for sustainable building, full integration into construction faces obstacles, particularly with large-scale projects and robotic systems.

Md. Aslam Hossain et al (Oct. 2020) noticed the construction industry's shift toward automation, particularly 3D printing, to reduce labour costs. Its suitability is dependent on labour costs and a country's reliance on construction. However, knowledge and investment barriers may outweigh cost benefits in materials, labour, and time.

Lotfi Romdhane and Sameh M. El-Sayegh (Nov. 2020) examined 3D printing in construction, citing benefits such as speed, cost reduction, and design flexibility, as well as issues with materials and regulations. Despite the challenges, 3D printing has promise for the future of construction.

S.J. Schuldt et al (March 2021) reviewed 4491 papers on 3D-printed construction published between 1998 and 2019, indicating that it has the potential to replace traditional methods in remote regions. They highlighted seven essential factors, including materials and cost, and emphasized the necessity of technical advancements and case studies. The report emphasizes 3D printing's potential to alter industry management in remote regions with continuous investment.

Ning et al. (April 2021) used quantitative and qualitative research to investigate the current state, difficulties, and future directions of 3D printing (3DP). They investigate both technical and non-technical aspects, such as materials, processes, and societal implications. Their findings provide a theoretical underpinning for existing practices and future uses in building. However, constraints due to a lack of scientific publications may have an impact on the study's results.

Zhang D. et al (May 2021) demonstrated 3D printing's disruptive potential in construction, but its widespread adoption is impeded by material and technical obstacles. Despite its adaptability, current technology falls short of addressing industry requirements. Innovation efforts are underway, but the overall impact is questionable. Regulatory backing is critical for widespread 3D printing use in building.

Asena KARSLIO?LU (March 2022) investigated that advancements in technology are transforming the building industry, with 3D printing becoming increasingly popular for creating small-scale products and intricate structures. This technology requires 3D model design, optimized cement mortar, and careful mixing ratios. It offers financial and ecological benefits, but its application depends on precision, material, cost, and duration. Directed energy deposition and powder bed fusion are the best methods.

Alexander Lin et al (2022) invented a revolutionary design approach to create overhanging structures out of interconnecting concrete pieces using a flat print bed and a 3-axis gantry robot-equipped concrete extrusion 3D printer. Tested in a lab setting, this approach allows for quick customization without the need for formwork. In the future, piece-by-piece assembly ought to be the main focus to expedite construction.

A. Jandyal et al. (2022) has investigated that while 3D printing has advanced significantly, there are still problems that need to be addressed including material incompatibility and material expense. More attention needs to be paid to creating affordable printer technologies and materials that work with these printers in order to increase the number of applications for 3D printed items.

Y. Zhao (2022) looked at the negative effects of conventional building techniques on the environment and resource inefficiencies. Expanding upon these observations, 3D printing technology offers enormous possibilities for personalized constructions and tackles conventional construction obstacles. This study evaluates concrete 3D printing's developments in materials, equipment, defect management, and application contexts, providing suggestions for future growth. Concrete 3D printing emerges as a critical emphasis.

Waqar et al. (Feb. 2023) examined the effects of 3D printing on residential projects in Malaysia, stressing the necessity for restrictions while also noting the benefits to safety and the environment. Although there are hazards associated with regulatory limitations, integrating 3D printing into home construction offers innovation and efficiency. The report emphasizes how crucial it is to have legislation in place in tandem with improvements in 3D printing to guarantee public safety and environmental protection.

III. 3D PRINTABLE MATERIAL PROPERTIES

Cement-based 3D printing materials have the same composition as traditional materials. The nozzle's size limits the options available for choosing aggregates. You cannot utilize coarse aggregate larger than 2.36mm because of the limited nozzle dimension. The concrete in its fresh state goes through different stages such as selection of materials, mixing, pumping and deposition in a layer by layer.

A. Cementitious Materials

Because it is widely available and reasonably priced, Portland cement is the most widely used material in building; both for traditional concrete applications and 3D printed ones. Supplementary cementitious materials are used in place of certain Portland cement in order to lower CO2 emissions and minimize production costs while keeping an eye on the environment and the economics. A number of components that were formerly considered waste from manufacturing processes, such as fly ash, slag, and silica fume, are now recycled and used as binding agents in cement mixtures. The qualities of these additional cementitious elements influence printable concrete's pumpability, extrudability, and buildability.

B. Aggregates

Aggregates, one of the most crucial parts of 3D printed concrete, significantly affect as well as influence the quality of concrete (Rahul et al., 2020). River sand is becoming more and more scarce, thus manufactured sand has been utilized to fill its place. Concrete's workability, mechanical qualities, and durability have all been shown to be significantly impacted by aggregates, both experimentally and theoretically (Yaxin et al., 2022).

C. Fly Ash

One of the primary by-products of producing electricity from coal power plants, fly ash, is another substance that is utilized in place of Portland cement. Because it is more environmentally friendly to use recycled fly ash—which has already been created—instead of producing additional OPC and releasing needless CO2 into the atmosphere, this material is used in place of Portland cement.

D. Water-Binder Ratio

For printing, high performance concrete mixes with water to binder ratios of 0.21 to 0.41 are recommended. To complete the hydration process and get the best long-term durability and mechanical performance, low-w/b blends need more curing water (Gerrit et. al 2021).

E. Admixtures

To create printable concrete, a complex mix design containing exact additive proportions is required due to the conflicting rheological specifications for concrete printing. Any substance that is added to a cement mix—apart from water, cement, aggregate, and fibers—before or during the mixing process is referred to as an admixture. Admixtures can be used for a wide range of purposes, including minimizing slump, decreasing water content, accelerating or delaying set times, and enhancing workability, strength, and durability. For the purpose of additive manufacturing, a particular blend of admixtures, including retarders, water reducers, and accelerators, is needed.

F. Dynamon Sx 630 (Superplasticizer)

A modified acrylic super plasticizer for concrete, which has a lengthy workability period, a low water-to-cement ratio, and extremely high mechanical strength. Dynamon Sx is ideal for applications that require significant water reduction and excellent mechanical strength at early stages. Dynamon Sx is ideal for producing self-compacting concrete because of its outstanding workability.

IV. MIX DESIGN

An extensive series of experiments was required to arrive at the final ideal mix for concrete printing. Hand mixing method was used. Cement, sand, and water were the basic ingredients used in the initial testing combinations.  Trial combinations with different additions were then assessed and revised iteratively until a limited number of printing-suitable mixtures were obtained for a particular admixture. The procedure was then repeated with a different admixture to see which blend designs would work best for printing. Four trial mixtures totaling different material quantities and combinations were assessed. The most appropriate combinations were then tested for pumpability, extrudability, and buildability—the three essential characteristics of printable concrete—after extensive experimentation. A typical slump test was used to determine pumpability, a prototype extrusion nozzle was used to determine extrudability.

Table 1: Mix Design for River Sand

Table 2: Mix Design for M-Sand

V. TESTING PROCEDURES

A. Flowability Test

One important factor in assessing the printing performance of a concrete mixture is flowability. Ensuring that the paste is easily pumpable in the delivery system and depositable in the deposition system is the goal of flowability control. DYNAMON 630 superplasticizer was utilized to increase cement paste flowability while preserving compressive strength at low water content.

B. Extrudability Test

An adequate level of extrudability, or the ability for material to be constantly supplied through tiny pipes and deposited from nozzles at the printing head, is required of the cementitious materials used in 3D printing. The smooth grading of materials is the key to controlling the extrudability of concrete material for 3D printing. Following sieve analysis, the sand was graded into different sizes. Zone 2 and Zone 3 proportions were then achieved by combining the graded sand.

VI. RESULTS AND DISCUSSIONS

To arrive at the ideal combination that can be utilized for concrete printing, a long series of tests had to be carried out. The mix that can satisfy all necessary specified standards while having the lowest water-to-cement ratio is called the ideal mix. A number of mixes were evaluated for extrudability using different ratios of water to cement, superplasticizer, and dry constituents (sand, fine aggregates, and cement) in order to arrive at the control mix.

The combination that met all of the necessary characteristics for flowability, extrudability, buildability, and open time with the least quantity of water-cement ratio was found to be the most effective one. The dimension of the prototype nozzle was 3cmx3cm. The mix's ability to flow out of the nozzle continuously served as a visual test for the extrudability requirements. In order to boost strength while preserving the proper flowability, a superplasticizer was added with the purpose of lowering the water-cement ratio.

Four mixes were tested for river sand as well as m-sand as shown in table 1 &2. The results of the compressive strength test showed that samples 1, 2, and 3 of river sand had strengths of 41.68 MPa, 41.80 MPa, and 56.23 MPa, respectively. Samples of m-sand 1, 2, and 3 had strengths of 58.5MPa, 55.29MPa and 51.40MPa respectively. The desired compression strength of 40 MPa was met and exceeded by all of the combinations. The strengths of the printed concrete layers for m-sand were 29.25 MPa and 13.57 MPa for river sand, respectively. The best strength was evidently obtained with the least water-to-cement ratio. The slump-flow test was performed on the concrete mixtures to measure pumpability, the slump for river sand mixture was found to be 112mm and for m-sand was 110.5mm respectively. The buildability and shape stability were also assessed for the same mixtures with six layers.

Conclusion

According to the test results, high strength cement mortar is essential for concrete 3D printing and strong quality control of the materials and processes is crucial. The performance of the materials must be assessed in relation to their mechanical properties in order to create high performance 3D printed concrete. In order to meet the necessary specifications, the effect of additive materials such as binder and admixtures is also very important. Present research and development efforts are concentrated on generating a wide range of 3D printable construction materials, including sustainable and eco-friendly solutions. It will offer more versatility in construction projects and address both structural and environmental concerns.

References

[1] Pegna, J., 1997. Exploratory investigation of solid freeform construction. Automation in construction, 5(5), pp.427- 437. [2] Bhattacherjee, S., Rahul, A. V., Santhanam, M. (2020). “Concrete 3D printing – progress worldwide and in India” The Indian Concrete Journal, Vol. 94, No. 9, pp. 8-25. [3] Wolfs, R.J.M., Bos, F.P. and Salet, T.A.M., 2019. Hardened properties of 3D printed concrete: The influence of process parameters on interlayer adhesion. Cement and Concrete Research, 119, pp.132-140. [4] Giridhar, G., Prem, P.R. and Kumar, S., 2023. Development of concrete mixes for 3D printing using simple tools and techniques. S?dhan?, 48(1), p.16. [5] Patel, N., Bhatt, K., Thesiya, D., Vora, R. and Ranjanna Srinivas, A., 2017, December. A design, development and mechanical characterization of FDM machine. In Proceedings of 10th international conference on precision, Meso, micro and nano engineering (COPEN 10). Indian Institute of Technology, Madras, Chennai, India (pp. 107-112). [6] Brochu, O., Murray, G. and Rivera, P., 2020. Enhancing the Interlayer Bond in Printed Concrete Structures (Doctoral dissertation, Worcester Polytechnic Institute). [7] Bhattacherjee, S., Basavaraj, A.S., Rahul, A.V., Santhanam, M., Gettu, R., Panda, B., Schlangen, E., Chen, Y., Copuroglu, O., Ma, G. and Wang, L., 2021. Sustainable materials for 3D concrete printing. Cement and Concrete Composites, 122, p.104156. [8] Ma, G. and Wang, L., 2018. A critical review of preparation design and workability measurement of concrete material for large-scale 3D printing. Frontiers of Structural and Civil Engineering, 12, pp.382-400. [9] Sudhakrishnan, J., PJ, R.N. and Mathew, M., 2023. 3D Printable Concrete: Mixture Design, Simulation & Test Methods. [10] Malaeb, Z., AlSakka, F. and Hamzeh, F., 2019. 3D concrete printing: machine design, mix proportioning, and mix comparison between different machine setups. In 3D Concrete printing technology (pp. 115-136). Butterworth-Heinemann. [11] A. V. Rahul, Development of Cementitious Materials for Extrusion-Based 3D Printing (2020). [12] Gosselin, C., Duballet, R., Roux, P., Gaudillière, N., Dirrenberger, J. and Morel, P., 2016. Large-scale 3D printing of ultra-high-performance concrete–a new processing route for architects and builders. Materials & Design, 100, pp.102-109. [13] Shakor, P., Sanjayan, J., Nazari, A. and Nejadi, S., 2017. Modified 3D printed powder to cement-based material and mechanical properties of cement scaffold used in 3D printing. Construction and Building Materials, 138, pp.398-409. [14] Hambach, M., Rutzen, M. and Volkmer, D., 2019. Properties of 3D-printed fiber-reinforced Portland cement paste. In 3D concrete printing technology (pp. 73-113). Butterworth-Heinemann. [15] Sakin, M. and Kiroglu, Y.C., 2017. 3D Printing of Buildings: Construction of the Sustainable Houses of the Future by BIM. Energy Procedia, 134, pp.702-711. [16] Kazemian, A., Yuan, X., Cochran, E. and Khoshnevis, B., 2017. Cementitious materials for construction-scale 3D printing: Laboratory testing of fresh printing mixture. Construction and Building Materials, 145, pp.639-647. [17] Perkins, I. and Skitmore, M., 2015. Three-dimensional printing in the construction industry: A review. International Journal of Construction Management, 15(1), pp.1-9. [18] Lediga, R. and Kruger, D., 2017. Optimizing concrete mix design for application in 3D printing technology for the construction industry. Solid State Phenomena, 263, pp.24-29. [19] Olsson, N.O., Shafqat, A., Arica, E. and Økland, A., 2019, May. 3d-printing technology in construction: Results from a survey. In 10th Nordic conference on construction economics and organization (Vol. 2, pp. 349-356). Emerald Publishing Limited. [20] Dixit, M.K., 2019, June. 3-D printing in building construction: a literature review of opportunities and challenges of reducing life cycle energy and carbon of buildings. In IOP Conference Series: Earth and Environmental Science (Vol. 290, No. 1, p. 012012). IOP Publishing. [21] El-Sayegh, S., Romdhane, L. and Manjikian, S., 2020. A critical review of 3D printing in construction: Benefits, challenges, and risks. Archives of Civil and Mechanical Engineering, 20, pp.1-25. [22] Hossain, M.A., Zhumabekova, A., Paul, S.C. and Kim, J.R., 2020. A review of 3D printing in construction and its impact on the labor market. Sustainability, 12(20), p.8492. [23] Romdhane, L. and El-Sayegh, S.M., 2020. 3D printing in construction: Benefits and challenges. Int. J. Struct. Civ. Eng. Res, 9(4), pp.314-317. [24] Schuldt, S.J., Jagoda, J.A., Hoisington, A.J. and Delorit, J.D., 2021. A systematic review and analysis of the viability of 3D-printed construction in remote environments. Automation in Construction, 125, p.103642. [25] Ning, X., Liu, T., Wu, C. and Wang, C., 2021. 3D printing in construction: current status, implementation hindrances, and development agenda. Advances in Civil Engineering, 2021(1), p.6665333. [26] Karsl?oglu, A., Hanifi Alkayis, M. and Inanc Onur, M., 2022. 3D printing technology in construction sector: A short review. In 2nd International Conference on Applied Engineering and Natural Sciences (pp. 548-552). [27] Lin, A., Goel, A., Yeo, C., Chung, J., Dai Pang, S., Wang, C.H., Taylor, H. and Kua, H.W., 2022. Compressive load-dominated concrete structures for customized 3D-printing fabrication. Automation in Construction, 141, p.104467. [28] Jandyal, A., Chaturvedi, I., Wazir, I., Raina, A. and Haq, M.I.U., 2022. 3D printing–A review of processes, materials and applications in industry 4.0. Sustainable Operations and Computers, 3, pp.33-42. [29] Waqar, A., Othman, I. and Pomares, J.C., 2023. Impact of 3D printing on the overall project success of residential construction projects using structural equation modelling. International Journal of Environmental Research and Public Health, 20(5), p.3800.

Copyright

Copyright © 2024 Shreyas Savaikar, Shrushti Parab, Ikhlas Nadaf, Faruq Anwar, Vishwesh Shet, Smita Aldonkar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.