1. Introduction
Water, aggregate, cement and fine aggregate, called sand, are the materials used for making a concrete mixture. A new composite material called waste paper concrete (WPC) is created by incorporating waste paper (WP) into a concrete mixture. Nowadays, carbon dioxide gas (CO2) is emitted from construction sites due to cement usage, a significant concern for all nations. On the other hand, people's desire to live in an eco-friendly environment continues to grow. This study is conducted to address these issues. Moreover, excessive WP disposal can cause environmental pollution to occur. To reduce and prevent environmental pollution is by using WP in concrete production. WPC also reduces cement usage because it is an environmentally friendly construction building materialthat reduces pollution to occur, as defined by Ref. [1]. This WPC is a durable building construction material created using WP by combining with water and other materials, pouring them into a mould and then drying them before curing, whether air or water curing before experimental tests are conducted. WPC is a new material with a limited application range due to the fact that only certain percentages are allowed [2]. This is because higher percentages of WP are unsuitable, which might reduce the concrete strength, as stated by Ref. [2].
This WPC mixture is a well-insulated and durable material. Besides that, the previous experimental results show that WPC is a structurally and economically viable solution [3]. Due to the significant amount of recycled material, it is known as an environmentally beneficial material. It is also an adobe and fibrous new invention material [4]. Moreover, WPC could reduce the dead load of the main structure compared to normal concrete made up of water, coarse aggregate, cement and sand without WP content [5]. Various types of WP can replace regular WP, such as cardboard, magazine, pamphlet and any other types. Most WP found comes from paper mills or landfills [[6], [7], [8], [9], [10], [11], [12], [13]]. Apart from that, WPC may relate to a productive alternative to landfills, incinerators or other waste disposal methods and also a cost-effective product [14]. WP contains fibre material, which contributes to the mixed bulk, producing lightweight concrete. Utilising WP in structural concrete would be wise, contributing to reducing the adverse effects on the construction process. It is an essential source of cellulose and fibre, as well as one of the most prevalent types of waste found in all disposal and dump activity areas. Thus, a concrete mixture containing WP is a possible landfill problem solution by reducing WP disposal. Additionally [15], noted that incorporating WP in concrete can also lessen its density. This WP incorporation is the best way to use WP wisely and adequately. Therefore, it is selected to do more research on WPC by evaluating its material properties and characteristics in order to evaluate the potential for replacing conventional concrete usage [3].
WPC would provide several benefits and a broad range of construction and civil engineering applications. Subsequently, the inner walls in high-rise buildings in seismically active regions could use WPC because of its lightweight nature property. In addition, by utilising WPC in building construction, the structure's dead weight and the foundation depth required would increase, making it stronger, and the utilised steel number would be reduced, lowering labour, energy and material costs [16]. In conclusion, the production of WPC encourages WP recycling, particularly in communities that do not practice it. Therefore, it conserves landfill space and reduces chemical usage in new paper manufacturing and production processes [17]. This comprehensive review paper reviews the WP structure, WP's chemical and physical properties and the advantages of using WPC. Besides that, the experimental results of fresh, structural and durability properties of concrete containing WP, such as slump, modulus of elasticity, stress-strain and water absorption, are compared to conventional concrete without WP content based on previous research stated in this paper. Based on this comprehensive review, the novelty is the concrete strength becomes better with the inclusion of WP at 5% and 10%.
2. Waste paper structure
The cellulose microfibrils are elastic up to the point when they are broken with each other. Cellulose has an elastic modulus of 25 GPa, determined by the microfibrillar helix chiral angle. The modulus of elasticity could be estimated when the fibre is parallel strained to its axis. The angle of microfibrils is more prone to natural variation than any other angle, resulting in a closer mean value to the fibre axis. As a result, the fibre's modulus of elasticity is nearly identical to cellulose properties [18,19]. Almost all types of wood have chiral fibres. Fig. 1depicts the twisting and chiral curl of WP fibres resulting from the microscopic asymmetry image.
Fig. 1. Microscopic asymmetry image of WP fibres [20].Wood celluloses are fibrous substances of a primary constituent of WP to make it stronger. There are long sugar molecules that bind smaller sugar molecules together in cellulose [21,22]. β-D glucose sugar is used to make the cellulose chain connections. Cellulose fibres are linked together by hydrogen bonds, as delineated in Fig. 2. Furthermore, the chains form solid, hard crystalline zones that provide better support and balance. The hydrogen bonding between WP structures strengthens the WP [23]. It is composed of silica, calcium oxide, alumina and magnesium oxide elements.
Fig. 2. Elements in a cellulose fibre [21,22].2.1. Waste paper properties
Burgess and Binnie (2010) [24] argued that particular results and discussions could be produced with the precise selection of test materials and methodologies. The properties of WP, including humidity, temperature, radiation and pollution, should be investigated. The surrounding environment affects the hydrolysis and oxidation reactions resulting in the crosslinking breakdown process.
2.2. Chemical properties
Lignin, a non-cellulosic component, reacts more strongly in particular particles. But ironically, the fact that chemical probes are hard to discover and make the WP the most difficult to be monitored and quantified. Table 1 displays the WP's chemical composition.
2.3. Physical properties
Weight, substance or grammage is one of the essential properties of WP. The WP weight is calculated using a density conversion factor that changes g/m2 to g/inch2. Counting g/m2, p/ft2, or kg/ream of a specific dimension could be done. The size and weight of WP are important to determine its properties. The space amount of WP depends on the material weight. For example, a customer receives 1 kg of WP if he has 20 m2 of space. There are several ways to represent how many reams of a given weight are available from one pound. Basis weight is crucial for WP in terms of production rate. Table 2, Table 3 present the WP's grading and physical properties.
Table 2. WP's grading [23].
| Weight of passing (%) | Sieve size (mm) |
|---|---|
| 100 | 9.51 |
| 88 | 4.75 |
| 18 | 2.36 |
| 2 | 1.18 |
| 0 | 0.6 |
Table 3. WP's physical properties [21,27].
| Strength of bursting value (kPa) | Coefficient of friction static | Coefficient of friction kinematic | Value of tear resistance (mN) | Value of smoothness (mls/min) | Moisture content (%) | Absorption (%) | Value of thickness (μM) | Value of moisture (%) | Organic materials (%) | Density (kg/m3) | Inorganic materials (%) | Specific gravity (SSD) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 250–300 | 0.5–0.65 | 0.35–0.5 | 500–600 | 100–300 | 2.67 | 89 | 105–110 | 4–4.5 | 70 | 800 | 30 | 0.98 |
3. Advantages of waste paper concrete
Joo et al. (2012) [28] studied lightweight concrete made up of WP. It was concluded that WPC was lighter and more pliable than regular concrete without WP contents. Earthquake-prone areas might use WPC as a building material. By incorporating WP in concrete production, less pollution and landfills will occur. An experiment on energy-saving lightweight concrete utilising WP was conducted by (Subramani et al., 2015) [29] in order to learn more about the properties of WPC. The weight of each concrete sample was weighed, and it was found that WPC had the lightest weight compared to ordinary concrete. After the experiment was completed (Subramani et al., 2015), [29] concluded that WPC could be utilised for any walls that did not bear any load imposed (Ravindra et al., 2017). [30] experimented on developing and investigating the WPC cubes’ properties. WPC cubes were made of cement, sand and WP in various mixed proportions and were used to test the mechanical properties. It was found that WPC was easy to work with, lighter than standard concrete without WP contents and produced a high-quality finishing surface. WPC was studied and showed some interesting properties [31]. WPC had better density, water absorption property, compressive strength and fire resistance compared to regular concrete. Soundness and efflorescence tests were also carried out. According to the experimental test results, it could be concluded that WPC could be utilised for internal partition walls, slabs, columns and beams. Subsequently, WPC was a fantastic choice for building construction material since it had the best sound absorption and thus, could be used in large areas, such as halls and auditoriums, for better performance.
4. Fresh property of waste paper concrete
This section presents the slump results of WPC.
4.1. Slump
Balwaik and Raut (2011) [32] experimented on concrete containing 0%, 5%, 10%, 15% and 20% of WP to replace Portland cement partially. The slump test was conducted according to IS 1199–1959 and increased to 5% cement replacementwith WP, while above 5%, the slump value decreased. The slump value increased from 69 mm to 71 mm and decreased from 71 mm to 58 mm in M − 20 concrete, while for M − 30 concrete, the slump value increased from 50 mm to 52 mm and decreased from 52 mm to 45 mm. The high absorption limit of WP caused the concrete workability to decline. Increasing the content of WP required more water to achieve the targeted slump value. Adding a high amount of water rather than admixtures can improve the WP concrete workability. Thus, economical concrete could be achieved. The physical properties, carbon content and the amount of WP addition affected the concrete reduction workability. The diminishing water demand became larger, increasing WP content to about 20%. The concrete mix proportion and slump value are shown in Table 4 and Fig. 3.
Table 4. Concrete mix proportion for M − 20 and M − 30 [32].
| Mix | WP (%) | Cement (kg/m3) | CA (kg/m3) | FA (kg/m3) | W/C Ratio |
|---|---|---|---|---|---|
| M-20 | 0 | 383 | 1220 | 550 | 0.5 |
| 5 | 364 | 1220 | 550 | 0.5 | |
| 10 | 345 | 1220 | 550 | 0.5 | |
| 15 | 326 | 1220 | 550 | 0.5 | |
| 20 | 307 | 1220 | 550 | 0.5 | |
| M-30 | 0 | 426 | 1220 | 550 | 0.5 |
| 5 | 405 | 1220 | 550 | 0.5 | |
| 10 | 383 | 1220 | 550 | 0.5 | |
| 15 | 362 | 1220 | 550 | 0.5 | |
| 20 | 341 | 1220 | 550 | 0.5 |
Fig. 3. Slump value [32].In other previous research, Ilakkiya and Dhanalakshmi (2018) [33] studied the fresh property by performing slump tests on concrete containing 0%, 5%, 10% and 15% of WP contents. The slump cone was uplifted vertically and gradually after the fresh concrete was fully compacted. Shock and vibration-free were ensured when the slump test was conducted. When the WP was added up to 10%, the slump value increased, but the slump decreased when more than 10% added WP. The increased slump values were shown by the 5% and 10% WP addition compared to 0% addition from 75 mm to 78 mm for 5% and 80 mm for 10%. There was a decrease in the slump when the WP addition was 15%, from 80 mm to 72 mm.
Zaki et al. (2018) [21] conducted slump tests following ASTM C143-12 on five WPC mixes containing 0%, 5%, 10%, 15% and 20% of WP as partial addition by weight of cement. One of the significant highlights characterising fresh concrete properties was the workability which could be described as concrete measurement ability to be transported, handled and mixed with fewer air voids. The slump value increased at 5% WP partial addition and decreased at above 5%, as delineated in Fig. 4. The water demand rose to about 20% in addition of WP content. The concrete slump value and fresh density decreased because of the WP's high water absorption property due to the high content of WP. More water is needed to acquire a similar slump as well as adding superplasticiserimproved the concrete workability containing WP. More addition of paper will lower the density value. The percent of superplasticiser used is affected by the WP content. The superplasticiser percentage used depended on the WP content. It had been affirmed that including WP has an apparent opposing effect on the slump and fresh density, which demanded higher water or chemical admixturequantity to maintain the slump value possible as well.
Fig. 4. Slump value [21].Ramesh and Chandu (2018) [34] conducted an experimental program to explore WPC fresh property with 0%, 50% and 100% replacement of coarse aggregate with WP by performing slump tests on the fresh concrete mixtures. The concrete mix will be intended to evaluate the concrete having the necessary workability and characteristic strength at the very least of proper strength of concrete mix and should be equivalent to characteristic strength in addition to 1.65 times the standard deviation. The fresh concrete uniform workability was checked by conducting slump tests from batch to batch. In this study, an experimental activity of concrete was conducted, where coarse aggregate was replaced with WP. This undertaking contained a test perception where the correlation between conventional concrete, WPC 50% and WPC 100%. As the results obtained, the slump value increased by 47.06% with WPC 50%, while for WPC 100%, the slump value increased by 88.24% compared to the slump of conventional concrete. The slump value of fresh concrete increased as well as increased WP, which was replaced with coarse aggregate. The higher the coarse aggregate replacement with WP, the higher the slump value.
Malik (2013) [35] researched M − 25 concrete behaviour with a 0.45 water-to-cement ratio by replacing cement with 0%, 5%, 10%, 15% and 20% WP and performing slump tests according to IS 1199–1959 on each concrete mixture. The WP disposal issue might decrease from time to time and enhance concrete performance by using WP in concrete. A high level of silicon dioxide (SiO2) in WP might strengthen the concrete. 0.45 water-to-cement ratio was used in M − 25 concrete grade. Increasing WP content affected the concrete workability by decreasing the slump value. 5% cement replacement with WP recorded the highest slump value and above 5% replacement gradually decreased the slump value. The fresh concrete workability decreased due to cement's lower water absorption than WP particles. Table 5 and Fig. 5 show the concrete mix proportion and slump value.
Table 5. Mix proportion [35].
| WP (%) | WP (kg/m3) | W/C Ratio (kg/m3) | Water (kg/m3) | Cement (kg/m3) | Fine Aggregate (kg/m3) | Coarse Aggregate (kg/m3) |
|---|---|---|---|---|---|---|
| 0 | 0 | 0.45 | 191.6 | 425.80 | 543.5 | 1199.36 |
| 5 | 21.29 | 0.45 | 191.6 | 425.80 | 543.5 | 1199.36 |
| 10 | 42.58 | 0.45 | 191.6 | 425.80 | 543.5 | 1199.36 |
| 15 | 63.87 | 0.45 | 191.6 | 425.80 | 543.5 | 1199.36 |
| 20 | 85.16 | 0.45 | 191.6 | 425.80 | 543.5 | 1199.36 |
Fig. 5. Slump value [35].Gallardo & Adajar (2006) [9] investigated the workability of concrete containing 0%, 5%, 10% and 15% of WP replacement with fine aggregate. The concrete mix proportion was a procedure by which one shows up at the correct combination of cement, aggregate and water to make concrete according to the specifications. One reason for mix proportioning was to get a product that would play out the most fundamental prerequisites for the workability of fresh concrete. 75–100 mm (3–4 inches) is the desired slump range of all mixes. The mixes that did not fall in the slump range were remixed and more water was added. Using an alternative material known as WP was studied by observing the feasibility. Based on the study results, the concrete workability reduced with above 10% partial fine aggregate replacement with WP, but the concrete workability increased with 5% and 10% replacement compared to 0%. Percentage replacement higher than 10% resulted in the slump value reduction. The presence of silica compound in WP was essential because of its main role in structuring and bonding the concrete bond. During experimental procedures, there was a problem with the concrete mix workability caused by the high water absorption rate of WP. Extra water was the permanent solution for this sort of issue as well as the higher water content will reduce the concrete strength. The type of superplasticiser used in the concrete mixtures containing WP was ASTM Type D/G. This superplasticiser played roles by producing higher concrete strength and workability and producing lower density at a lesser water content. The validation of this experiment was valid and approved for 0% replacement of WP in a concrete mixture. The slump value of concrete containing WP decreased as the replacement percentage increased along with the admixture addition. WP could be used in concrete by replacing partial fine aggregate, producing low-cost housing projects. Table 6 and Fig. 6 show the specimen mix proportion and slump value.
Table 6. Specimen mix proportion [9].
| WP (%) | WP (kg) | Cement (kg) | White Sand (kg) | 3/4 Gravel (kg) | Water (kg) | Water Adjustment (kg) | Total Water (kg) | Superplasticizer (ml) |
|---|---|---|---|---|---|---|---|---|
| 0 | 0 | 20.80 | 28.28 | 42.08 | 7.20 | −0.50 | 6.70 | 208 |
| 5 | 0.74 | 20.80 | 27.02 | 42.08 | 7.20 | 1.50 | 8.70 | 208 |
| 10 | 1.50 | 20.80 | 25.76 | 42.08 | 7.20 | 1.50 | 8.70 | 208 |
| 15 | 2.24 | 20.80 | 24.48 | 42.08 | 7.20 | 2.0 | 9.20 | 208 |
Fig. 6. Slump value [9].Based on research by Ravindra et al. (2015) [36], the amount of WP increased in four preliminaries as T-1, T-2, T-3 and T-4, corresponding to 0%, 10%, 15% and 20% addition of WP in M − 25 concrete mixtures. WP had naturally high water absorption characteristic and thus, needed preliminary testing to achieve a workable mix. The slump value was recorded between 70 mm and 80 mm and declined with the rising of WP content. 10% of WP addition reduced the slump value by 6.3% and stayed consistent at 6.3% with 15% addition compared to 0% but diminished at 20% addition by 12.5%. It could be concluded that 10% utilisation of WP in the concrete mix might be conveniently permitted. Compared with the control mix, the expense of concrete production was reduced by 1.5%, 2.2% and 3.0% with 10%, 15% and 20% addition of WP, respectively. Table 7 shows the optimum percentages of WP for the slump.
Table 7. Optimum percentages of WP for the slump.
| References | Percentages of WP (%) | Optimum percentages (%) |
|---|---|---|
| Balwaik & Raut (2011) [32] | 0%, 5%, 10%, 15%, 20% of WP as partial replacement of cement | 5% |
| Ilakkiya &Dhanalakshmi (2018) [33] | 0%, 5%, 10%, 15% of WP addition | 5%, 10% |
| Zaki et al. (2018) [21] | 0%, 5%, 10%, 15%, 20% of WP as partial addition by weight of cement | 5% |
| Ramesh & Chandu (2018) [34] | 0%, 50%, 100% replacement of coarse aggregate with WP | 50%, 100% |
| Malik (2013) [35] | 5%, 10%, 15% and 20% replacement of WP with cement | 5% |
| Gallardo & Adajar (2006) [9] | 0%, 5%, 10%, 15% of WP replacement with fine aggregate | 5%, 10% |
| Ravindra et al. (2015) [36] | 0%, 10%, 15%, 20% addition of WP | 0% |
5. Mechanical properties of waste paper concrete
This section presents the mechanical properties of WP concrete, such as compressive strength, flexural strength and splitting tensile strength.
5.1. Compressive strength
Jung et al. (2015) [37] evaluate the suitable WP replacement on cement mortarreplaced with WP at 0%, 5%, 10%, 15% and 20% replacement against the cement weight. The cement mortar explored different avenues regarding the WP to find an optimum mixing ratio of different W/C ratios and the impact of compressive strength as per WP replacement ratio. The trials were separated into 45%, 60%, 75% of W/C ratios to evaluate the mortar mechanical and physical properties with the change of W/C ratio, replacement rate and type of WP. Mortar using waste newspaper recorded the highest compressive strength compared to mortar using waste advertisement flyer and waste copying paper. This highest strength was due to the high absorption rate of the newspaper and the best combination of the cement composite. The 5% replacement to cement weight showed the highest compressive strength compared to 0%, 10% and 15% replacement because hydrate formations actively occurred when the WP was replaced in a small amount.
In a separate study, Jung et al. (2015) [37] investigated the significance of the interaction between the strength change graph in the mortar test and the concrete brick test value. The compressive strength of concrete containing WP with 0%, 10%, 15% and 20% of cement weight was measured with three different W/C ratios of 60%, 70% and 80%. The concrete size was based on the Korean brick size standard as per KS F 4004. All the compressive strength were over 8 MPa, which were in accordance with the KS standard. At 28 days, the best W/C ratio was 70% with a mixture containing 10% WP, which also recorded the highest compressive strength compared to 0%, 15% and 20% WP and 60% and 80% W/C ratios. The higher absorptive force of WP caused the bond strength between the WP and cement paste to weaken.
Asha et al. (2017) [38] examined the effect of replacing coarse aggregate replaced with WP by volume in concrete ranging from 0%, 2.5%, 5%, 7.5%, 10% and 12.5%. The IS 10262: 2009 standard was used to produce two types of concrete grades comprising the M20 and M25 concrete mixes. Additionally, concrete's toughened properties were also investigated. The WP replacement of aggregates was deemed acceptable as the percentage limit for replacing aggregates was under an acceptable range for both M20 and M25 concrete grade mixes. Although the government did not approve this concrete type, the proposed mixes could be used in the construction industry and also serve as an excellent option to apply affordable WP for construction purposes.