Abstract
Polymers have gained an extensive application due to their versatility of properties and benefits. Hence, the polymer blends and composites reinforced with different infusions at different scales, macro to nanofillers, can be fabricated, leading to specific tailormade applications. The main objective of this investigation is to overview the various studies carried out to reuse the waste materials like electroplating sludge, fly ash, etc. For the development of construction materials. This paper summarizes the use of polymers in composite material formulations for the development of building materials such as lightweight concrete, protective coatings, paver blocks, bricks, and structural components. Different tests, namely viscosity, density, flash point, amine value, and epoxy equivalent weight, were performed on polymers to find their suitability as binder materials. Various laboratory tests such as compressive strength, water absorption, tear resistance, flexural strength, and split tensile tests were carried out to determine the mechanical properties of the developed materials. By using polymers with the addition of sustainable filler and waste materials, the replacement of costly raw material can be achieved by more than 50% in the case of paver blocks, up to 60% in bitumen-polymer composite, 80% in case of lightweight concrete and polymer-based panels. This insight gives the framework for the selection of different materials, optimization of combining ratio of materials, and their testing for the development of polymer-based materials.
1. Introduction
Polymers assume a significant job in our everyday lives. Polymers can be clarified by parceling the word polymer to “Poly” which implies “numerous” and “mer” which means part or portion. Polymers are the developments of numerous particles, called monomers, as chains or other convoluted structures. They are one of the most valuable materials at any point made. Polymers can be rubbery or unbending and can be formed into an unending assortment of articles, extending from vehicle guards to squeezable jugs and delicate textures. Then comes the derived products from them which are called as polymer composite materials which are made by adding two or more polymers, filler materials, or reinforcing materials so that the blend obtained gives better product with large scale application [1, 2]. These engineered polymer composites offer properties such as high strength modulus to weight ratios which make the composites lightweight and relatively strong and toughened, with high resilience and cost-effectiveness.
Synthetic or artificial resins are scientifically produced resins, especially viscous materials, which transform through the curing process into rigid polymers. Resins undergo the curing transformation of the chemically active end groups. These synthetic polymers are manufactured and fabricated by the esterification of organic compounds [3]. The different types are broadly categorized into thermosetting and thermoplastic resins as shown in Figure 1. Here the word “resin” depicts the reactant or the product or sometimes both. Resin is a term used for one or two monomers in a copolymer and the other part of the polymer is known as a hardener.(i)Thermosetting Resin, also known as the thermoset or thermosetting plastic, is basically a petrochemical substance. These cannot be heated up again and liquified to be shaped differently once it gets hardened. Thermoset materials are generally more robust than thermoplastic materials; hence, they are better apt for application in high-temperature conditions [3].(ii)Thermoplastic Resin is also named thermo softening polymer, which becomes pliable or mouldable over a specific temperature condition and hardens upon cooling.
Taxonomy related to Polymer Composites: The main elements of the composite are fibers, fillers, and additives, etc. Each constituent plays an integral role in the formulation of different material composites specified for different functions. As depicted in Figure 2, the composite comprises the polymer base filler and reinforcing material. Polymer base can be of any type namely thermoplastic, thermosetting, and elastomer type. They can be of one component or two or more component polymers in regard to resin and hardener proportioning. The function of this blend is to provide a base for the reinforcing material by providing it with a chemical structure imparting the required shape for the fabrication of the composite. The selection of the blend altogether depends on the intent of the composite product usage [2, 3]. Reinforcement depicts the framework of composition and provides its the required bulk modulus, rigidity, and mechanical strength. Different types of reinforcements are filamentary in nature and occur in forms ranging from organic to inorganic fiber or on the basis of shape, i.e., either the elongated particle or continuous. Filler refers to the inert material which, when added to the mix or the base polymer, effectively enhances the composite structure by modifying its physical, chemical, mechanical, and thermal properties [1, 3]. This is achieved by improving ductility, temperature resistance, and surface appearance of the base material or desired product performance in different conditions. At the same time resulting in a reduction in the cost of the developed product [4–6].
Use of Polymer in Civil Engineering: Polymeric materials are widely used in the construction industry in both structural and nonstructural applications. The main applications of polymer-based products are as follows: Admixture in concrete. Cables (used for pulleys to travel on-site). FRP (Fibre Reinforced Plastic) sheets. Piping materials for drainage, water, gas, industrial waste, sewage, and chemical plants. Ribs: As barriers to water movement occurring in walls and floor slabs. Adhesives and sealants: for woodworking and plumbing repairs. Cladding and decoration: on the exterior wall surface. Surface/barrier coatings. All paints contain a major portion as a polymeric binder.
In civil engineering, there are diverse uses of polymers in repair and rehabilitation of structures. Many R&D works across the globe have shown the dynamic involvement towards the improvisation of many building materials. These exhibit unparallel properties in terms of the processing, structure, performance, and properties (PSPP) in material science. This paper addresses the overview of past works with a framework for their development approach and their application in four different categories of polymer-based paver blocks/tiles, coatings, panels, and lightweight concrete [7–9].
2. Background
Systematic literature searching is acknowledged as the main approach for this review process. The input from different literature gaps and practical considerations, the adopted methodology for reviewing literature has been based on search strategies to retrieve articles that are potentially relevant [10–14]. Extensive investigations have been carried out by numerous researchers on the development of different sustainable construction materials. So, for better research problem emergence and identification of gaps, the literature review is categorized under four different applications of polymer-based construction material, namely lightweight concrete, protective coatings for concrete structures, paver blocks, tiles, bricks, and geopolymer panels subjected to flexural loading [15–19].
2.1. Polymer Based Construction Materials such as Bricks, Paver Tiles, and Paver Blocks
2.2. Polymer Modified Coatings for Concrete Structures
2.3. Polymer Based Light Weight Concrete
2.4. Polymer Based Ferrocement Panels Subjected under Flexural Loading
Literature Gaps and Emergence of Research Problem:
Previous studies have researched conventional binders and techniques for the reutilization of waste materials in different construction materials for example as partial replacement of raw material or filler in concrete or bricks. In Table 1 some of the methods are neither eco-friendly nor energy efficient. Other environmental concerns of handling and disposal are also there. Henceforth, there is a need to identify and study the use of suitable alternate binders that is polymers for stabilization of the composite mix and achieving an optimized combination, as shown in Table 2. For example, the problem of leaching heavy metals while using waste sludge in construction materials can also be solved effectively by using polymers as a binder [20–23]. Also, the major concern is to research for substitute material whose low emission is a binding agent for concrete to minimize the environmental impact caused by cement manufacturing. Many significant industries, for example, sealants, fibres, plastics, rubbers, adhesives, and caulking compounds, depend upon synthetic resins as they offer ease of prefabrication with the value-added energy efficiency of constructions and purpose for reuse and recycling of the obsolete, surplus, and scrap remaining material as shown in Table 3. However, many options are available in the market of waterproofing materials, but there is a need to go in-depth to explore other options of materials that provide a better life span and compatibility to structures [24, 25]. So, the development of an economic product for waterproofing that incorporates the beneficial properties of filler materials and polymers is needed to enhance the durability, as shown in Table 4.
3. Application of Polymer Composites as Construction Material
3.1. Paver Tiles, Blocks, and Bricks
Electroplating is one of the varieties of several techniques of metal finishing. Although the electroplating process has numerous applications, at the same time, it is considered among the 17 utmost polluting industries in India by CPCB (Central Pollution Control Board). The waste sludge generated by ETP (effluent treatment plant) of these electroplating industries is huge in quantity and comprises metal precipitates. This waste sludge can contain harmful pollutants like Ni, Ag, Sn, Cu, Zn, Cr, Pb, Cd, Fe, and ammonia, etc., and poses serious health risks [26]. The reclamation and recycling of these heavy metals from waste sludge are not feasible, therefore, causing disposal and dumping problems [27]. Currently, most of India’s hazardous waste ends up in landfills that are common waste disposal facilities and not specially designed. Due to this, heavy metals are leached into the environment and contaminating air, soil, and even drinking water and thereby causing serious health risks to general public.
Although there are few alternative solutions known, these all are difficult to continue. Within these, firstly, reclamation and recycling of harmful metals from the waste sludge are neither possible nor feasible. Secondly, after converting into ash by burning, this waste sludge can be used as a fractional substitute for fine aggregates in cement concrete. In this process, the maximum percentage is used up to 20%, and in the process of converting sludge to ash again, there is a possibility of air pollution. The cement industry of the world emits approximately 7% of global greenhouse gases [28]. Thirdly waste sludge can also be used as a partial replacement for clay in the manufacturing of bricks. The maximum percentage used is up to 30% in this process and the burning of bricks again causes air pollution. The brick production industry is considered to be the key contributor to the fast deterioration of air quality. Recently, attention has shifted to the use of polymers as other building materials. Polymers provide great opportunities for advances in building materials research and material property improvements [29]. The construction industry is one of the chief consumers of polymer composites. The potential benefits of polymers include high strength, high durability, fatigue efficiency, versatility, and low maintenance costs. The present construction industry is searching for superior quality materials with properties of durability, lightweight, easily installed, and also adaptable. Polymers are extensively used in the construction industry due to their exceptional strength-to-weight ratio, protecting properties, durability, and flexibility [30]. Stabilization and solidification remain unique strategies used to modify risky waste into an ecologically stable and friendly product [4]. To solve this universal problem, an attempt has been made to develop a unique process that is simple and eco-friendly for preparing durable and lightweight polymer-based construction materials like bricks/tiles/slabs from the most polluting waste sludge of electroplating industries. The process includes the leaching of heavy metals within the permissible limit and protects the environment from air, water, and soil pollution. The process does not require any burning/heating of sludge as well as it does not consume any natural resources such as soil and water. Finally, the process can replace up to 50% of sludge by weight without leaving any residual. Therefore, the process is helpful indeed and has a lot of applications in the environmental aspects. The flow chart for the design approach is mentioned in Figure 3.
3.1.1. Selection of Polymers
To find out the suitable polymer and its hardener, the following tests are required to be carried out as tabulated in Tables 5 and 6.
3.2. Procedure
In the present investigation, the polymers were successfully used as binders for the stabilization and solidification of electroplating waste sludge. The details of the different attempts/experiments are given below. Trial 1: The waste sludge, after drying and pulverization, was used as a replacement for cement of cement concrete. Different grades of concrete, such as M15 and M20, are prepared by percentage replacement of 5%, 10%, 15%, and 20%. After testing cubes for 7 days and 28 days, it was observed that the maximum replacement possible was 15%. After this, the compressive strength of concrete starts decreasing. Therefore, the percentage of waste sludge in the final product made with concrete is less than 5%. Trial 2: The waste sludge was converted into ash after burning and used as a sand replacement in the making of cement concrete. Different grades of concrete, such as M15 and M20, are prepared with percentage replacement of 10%, 15%, 20%, 25%, and 30%. After testing cubes for 7 days and 28 days, it was observed that the maximum replacement possible was 25%. Therefore, the percentage of waste sludge in the final product made with concrete is less than 10%. While converting the sludge into ash again, there is a danger of emission of harmful gases into the atmosphere. Trial 3: Waste sludge was also used as a partial replacement of clay in the manufacturing of bricks. The maximum percentage used is up to 30% and these bricks are required to be burned at 1000 °C. While burning bricks again, there is a possibility of release of poisonous gases into the environment. To manufacture the construction materials from the waste sludge, the following are the important steps which are to be followed.
3.2.1. Step by Step Procedure
(1)Collection of waste sludge from the electroplating process industry.(2)The waste sludge may contain moisture up to 20-30%, so it is needed to make it dry under the sun for 2-3 days till moisture content of less than 5% is achieved.(3)The dried waste sludge consists of lumps. So, it requires to be broken down into powder using a pulverization process. After pulverization, the sludge is required to sieve in a 600-micron sieve for uniform size.(4)After taking the perfect quantity of polymer (Polyurethane/Epoxy) resin in a container as per the table below, add sludge up to 25% of the required quantity as per the table below. Then start mixing of contents with a stirrer for five minutes at a speed of 2000 rpm. Add another 25% of the sludge and mix the contents for five more minutes at a speed of 4000 rpm. Add another batch of 25% of the sludge and mix them at a speed of 6000 rpm for five more minutes. Finally, add the remaining 25% of the sludge and mix the contents for five minutes @8000 rpm.(5)After proper mixing of polymer resin and sludge, the required quantity of suitable hardener as per the tables below is added and mixed for one minute @8000 rpm to obtain a slurry.(6)Finally, pour the slurry into a mould (Paving tiles/Paver blocks/Bricks) after giving a wax/silicone coating to the mould.(7)Allow the mould to cure at a temperature of 27°C for one day.(8)Remove the mould and cure the products (Paving tiles/Paver Blocks/Bricks) at a temperature of 27°C for 07 days.The outcomes of the product developed can be stated as follows:(i)The developed paver tiles, paver blocks, and bricks, as shown in Figure 4 contain 50% of waste sludge and meet all the requirements of paver tiles, bricks, and blocks as per BIS standards (IS 13801-2013, IS 3495-1 to 4 (1992) and IS 15658 : 2006. The process includes the leaching of heavy metals within the permissible limit and protects the environment from air, water, and soil pollution. The process does not require any burning/heating of sludge as well as it does not consume any natural resources such as soil and water.(ii)These developed materials are durable, lightweight, flexible, chemical resistant, soundproofing, and have glossy finish as compared to conventional products such as concrete paver tiles, concrete paver blocks, and brunt clay bricks available in market.(iii)Industrial Application: The process does not require any burning/heating of sludge as well as it does not consume any natural resources such as soil or water. This unique process can replace up to 50% of sludge by weight without leaving any residual. Therefore, the process is helpful, efficient, and cost-effective indeed and has a lot of applications in the environmental and health aspects. The developed products are also beneficial for the pavements/building construction. Therefore, this process has greater industrial value and can be easily scaled up.
3.3. Protective Coating for Concrete Structures
Water permeation in concrete structures results in degradation of structural components leading to the corrosion of reinforcing steel of the structure, thus affecting the durability. The conditions of freezing and thawing aggravate the deterioration process, which in turn shortens concrete structures’ life. Generally, a preventative approach of waterproofing is adopted that extends the service life of concrete components hence avoiding the additional incurred cost of repair and maintenance or retrofitting of subcomponents. This paper presents a review of these approaches of waterproofing concrete structures with different materials and additives in various forms such as membranes, coatings, integral mixing, pore liner penetrants, and pore blocker tests to evaluate the waterproofing efficiency of concrete. It demonstrates the advancements in concrete waterproofing research, explaining the taxonomy highlighting the frequency collection of different materials or additives used and also the tests applied. The review also delineates various surface treatments and their effect on the physiomechanical properties of concrete elements. The main technique adopted is the surface treatments in the form of coating and membranes. As per a study carried out by Foti et al. (2018) [31], it was summarised that the polyurethane foams are appropriate for use in masonry walls because of their advantageous characteristics, speed of installation, and reduction in processing costs resulting in the reduction of the total cost. It was found out that the collapse is extended for higher values of the load in diagonal compression testing for the case of masonry with foam, and the observed deformations are similar to the M2-mortar masonry.
Such a study provides the researchers a detailed construct of research and thus helps to carry out the work in lesser explored approaches by developing new materials or composite materials for sustainable use in increasing the serviceability of the infrastructure. The methodology for the development of the coating is summarised in Figure 5. One such example of practically formulating the composite mix for the development of coating is shown in Figure 6.
In terms of outcomes of the manufactured product, it can be concluded that the developed membrane will have higher resistance to water permeability along with great thermal and sound insulation properties. The developed membrane will be eco-friendly and UV resistant.
3.4. Light Weight Composite Concrete
Composite Concrete with Synthetic Resin is analogous to ordinary cement concrete, but it comprises finer aggregates; however the different binder is totally substituted with a Synthetic Resin. Synthetic Resin composite contains no cement or water. The aggregates are bonded together by the addition of polymers. The properties of Synthetic Resin composite are mainly determined by the quantity and properties of the type of polymer (synthetic resin and hardener) in the composite concrete. Ordinary Portland cement is nowadays under precarious criticism because of the associated carbon dioxide (CO2) emissions released into the atmosphere. So, it is the need of the hour to research for substitute material that is a low emission binding agent for concrete to minimize the environmental impact caused by cement manufacturing. Many significant industries, for example, sealants, fibres, plastics, rubbers, adhesives, and caulking compounds are depending upon synthetic resins offering ease of prefabrication with value-added energy efficiency of constructions and purpose for reuse and recycling of the obsolete, surplus and scrap remaining material. As per the experimental investigation carried out by Foti, D. (2016) [32], it was concluded that the reinforcement in the concrete beam made with PET AND CFRP is arranged as continuous bars and strips, respectively, limiting the presence of the crack and avoid the corrosion process in reinforced concrete structural elements. Hence, the specimens reinforced with CFRP strips exhibit better behavior.
The construction industry will face different confronts in terms of material application and manufacturing in the next few years, and polymer-based materials are the solution for it as they provide cost-effective answers to various scenarios. The basic prerequisite for high strength-to-weight ratio materials along with different high-quality architectural features is the driving forces for switching from conventional materials to polymer-based composite materials. Likewise methodology for the development of the approach of polymer-based lightweight concrete is shown in Figure 7 below.
Fillers include Silica sand, electroplating sludge, calcite, dolomite, and Flyash, and thermoplastic fibers include polyester fibre and polypropylene fibre. Basically, resin is a combination of polyol and harder, and fillers are added to reduce cost and achieve desirable properties in Table 7.
The outcomes of the developed lightweight concrete can be summed up as follows:(i)The properties of synthetic resin composite concrete are better than normal concrete in terms of lightweight, flexure strength, chemical resistance, and soundproofing, etc.(ii)Addition of thermoplastic fiber will enhance the engineering properties of Synthetic resin composite.(iii)Synthetic resin composite concrete will have more shock-absorbing characteristics. They can be used for the foundation of heavy machines, which produce lots of vibration during the run.(iv)If the resin dosage is high, it will give a glossy appearance but becomes costly.(v)Forming Pu matrix composite resin having 1.2–1.3 density where epoxy resin matrix composite having 1.9–2.1(vi)Consumption of fillers in epoxy resin is nearly twice as compared to Pu resin for the same quantity of volume(vii)Pu resin composite may be used as precast because top surface covering is required during casting.(viii)Synthetic resin composite can get 100% strength in 7 days and 70-80% of strength in just 24 hours, whereas 80–90% strength in 7 days and 100% strength in 28 days of conventional concrete.(ix)Only Room temperature curing is required for gaining strength, so it diminishes water utilization as compared to conventional concrete, as shown in Figure 8.
3.5. Polymer Based Panels under Flexural Loading
Many of the research work studies have concentrated on conventional panels made with conventional mortar. There is a need to recognize and analyze the use of suitable resin materials or their mix blends by incorporating their desired properties and hence developing the further proficient product for replacing conventional panels.
None of the investigations have perceived the extent of using the advantages of manufactured resin composite innovation as a growing structural member. Moreover, the panels generally use wire mesh, and there is a need to explore advanced innovative solutions to replace traditionally used wire mesh, which are efficient and, at the same time, sustainable in its application. Hence, aligning the research in this direction, the development and application of PET mesh have been proposed in the ongoing investigation. New endeavors and investigation of the advancement of resin and developed PET mesh for basic application ought to be taken so as to improve the mechanical properties. Henceforward, there is a deep requisite for the design, fabrication, and development of such material, which encompasses all the advantageous properties of the material with the addition of the polymer and also exploits the properties of PET waste as mesh for increasing the effectiveness in different situations making it a resourceful product in terms of mechanical strength, insulation properties, and better durability. As per Foti, D., and Lerna, M. (2020) [33], a feasibility study was conducted to depolymerize PET and use it as a replacement for sand in cement paste. Experiments were performed to study the effect on the mechanical and thermal properties of the modified paste. Great enhancement in different properties, such as heat transfer, was observed finally.
The properties of polymer-based panels are superior to conventional panels in terms of mechanical and durability point of view. The effect of reinforcing PET wire mesh will enhance the engineering properties like the flexural strength of polymer panels. Polymer panels can be used for secondary roofing panels, railway sleepers, bridge decks, concrete crack repairs, waste-water pipes, pavement overlays, parking, decorative construction panels, etc. Figure 9 shows the development approach for polymer-based panels, and Figure 10 shows the real image of testing of flexural panels.
4. Conclusion and Outlook
The significant findings of the present study and the application of polymer composites can be summarised as mentioned below:(1)The developed polymer-based paver tiles, paver blocks, and bricks contain more than 50% of waste sludge and meet all the requirements of paver tiles, paver blocks, and bricks as per BIS standards (IS 13801-2013, IS 3495-1 to 4 (1992) and IS 15658 : 2006.(2)These developed materials are durable, lightweight, flexible, chemical resistant, sound proofing, and have a glossy finish as compared to conventional products such as concrete paver tiles, concrete paver blocks, and brunt clay bricks available in the market. The process does not require any burning or heating of sludge, and it does not consume any natural resources such as soil or water.(3)This process can replace more than 50% of sludge by weight of the conventional material used in brick formation without leaving any residual. Therefore, the process is helpful, efficient, and cost-effective indeed and has a lot of applications in the environmental and health aspects. In regard to industrial application, the developed products are beneficial for pavements, walkways, and parking lots, as well as in building construction. Therefore, this process has greater industrial value and can be easily scaled up.(4)In case of polymer-based coatings, the characteristics of polymer composite coatings entirely depend on the chemical structure of the base material, such as bitumen, epoxy, cement, and the interaction between base-resin-hardener and reinforcement and filler matrix. The whole process of polymer composite coating development makes it evident that these increase the life of the substrates and which in turn decrease the related maintenance costs to the infrastructure. Along with the enhancement in mechanical performance because of infusion with polymers, the coatings offer great resistance against weathering effects, UV effects, and waterproofing properties also are developed. The noteworthy facts concluded from this paper act as a guide for forthcoming research to develop protective coatings for different substrates such as concrete, steel, and timber.(5)In case of polymer-based lightweight concrete, the developed material has better mechanical properties providing early strength in 7 days as compared to normal concrete. The compressive strength ranges from 20 MPA to 80 MPA entirely depending upon the grade and type of polymer used, which fulfill the minimum criteria of structural concrete (>17 MPa) as per relevant ASTM codes. The density of composite is less as compared to normal concrete making it lightweight and having good flexure and toughness. The work discussed provides a technical reference of specifications for the design and development of polymer-based materials.(6)The developed polymer-based panels contain more than 50% of the fly ash and also use PET bottles as reinforcement. The resultant will be more durable, lightweight, and environmentally friendly. The vast majority of study has been done on conventional panels. Synthetic resin act as a binder that replaces cement which is the main binding constituent in conventional concrete, which have greenhouse gas emissions. Polymer panels can be used for secondary roofing panels, which will enhance the life of low-cost housing and also helps in reducing industrial waste, like fly ash, PET water bottles, etc.
Although, polymer composites offer a great range of sustainable and superior construction materials in terms of processing, structure, performance, and properties (PSPP). One of the main difficulties faced in developing composite is handling the usage of polymers. The temperature susceptibility and pot life of polymers is the reason for less workability of the mix obtained, leading to futile trials during fabrication of composite. But there is still a vast scope and potential that is unexplored in this field of material science in regard to polymer composites. Surely, with the advent of technologies and manufacturing processes, there can be more refined forms of materials that sustain the various complex loading conditions, weather constraints, etc.
Future scope: Future scope of the development of these materials remains vast as more replacement of waste materials can be achieved with the potential use of polymers. Many such future scope applications can be explored in depth.(i)Utilization of acrylic resins in different finishes, binder in paint formulations, sealants, caulks, and safety glazing.(ii)Concrete-polymer hybrids, polymer-impregnated concrete, and sulphur concrete.(iii)Epoxy for different adhesives, binders, durable protective coatings and overlays, and fillers to patch voids or Rebar coatings in reinforced concrete.(iv)Structural upgrade of steel members.(v)Repair and rehabilitation of reinforced concrete members, wood members, and masonry walls.(vi)FRPs for cladding, column wrapping, domes, fencing, masts, pipes, roofing, tanks, and towers.(vii)Poly(vinyl butyral) (PVB) to be used as the optically clear vibration-stopping inner layer in top-of-the-line laminated glass soundproofing windows, etc.
Data Availability
The data used to support the findings of this study are included in the article. Should further data or information be required, they are available from the corresponding author upon request.
Disclosure
The study was performed as a part of the Employment Jimma University, Ethiopia.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Acknowledgments
The author thanks NITTTR Chandigarh for his appreciation and technical assistance in completing this experimental work. The authors thank Jimma Institute of Technology, Jimma University, Ethiopia, for his support in draft corrections.