Environmental Impact Assessment of Air-Purifying Paver Blocks Using Photocatalysis and  Sensors Technology

doi:10.21203/rs.3.rs-1822680/v1

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Environmental Impact Assessment of Air-Purifying Paver Blocks Using Photocatalysis and Sensors Technology

https://doi.org/10.21203/rs.3.rs-1822680/v1

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Air pollution is a major problem in India, and vehicular emissions cause about 27% of air pollution in urban areas. The major pollutants released from vehicles are carbon monoxide, carbon dioxide, nitrous oxide, photochemical oxidants, etc. The present investigation emphasizes the utilization of power plant waste materials effectively to replace the natural fine aggregate, leads to a new dimension of manufacturing concrete paver blocks. M-sand is replaced by bottom ash from 50–100%, and natural coarse aggregate is replaced with recycled coarse aggregates. Materials such as titanium dioxide (TiO₂) and recycled glass particles are also incorporated to improve the photodegradation of air pollutants. Concrete paver blocks were prepared and tested, and the compressive strength of the various mixes were compared with other research works. Real-time air quality is monitored using an Internet of Things (IoT) device developed to assess the performance of paver blocks laid on the roadside. The results concluded that bottom ash could be replaced with natural fine aggregate and recycled coarse aggregate can be replaced with natural coarse aggregate. Real time study results of air quality monitoring IoT device concluded that the pollution concentrations have been reduced up to 50%.

Photocatalysis

Titanium dioxide

Bottom Ash

Recycled Glass

Paver blocks

Air Quality Monitoring

Air pollution forms a major environmental crisis around the world. Every day, many harmful air pollutants are emitted from vehicles causes hazards for both living beings and the environment. Due to the increase in population and demand for naturally available raw materials, there is a tremendous escalation in the construction cost. It is necessary to focus on the reuse and recycling of waste materials dumped at the land sites as an alternative for construction material (Hopewell et al. 2009). The best solution for all these problems is to develop material that helps to control the air pollutants and waste materials utilisation that could deal with the problems associated with cost and environment.

This study aims to develop a sustainable paver block that satisfies photocatalytic action, strength and air purifying phenomenon. These blocks effectively minimise the harmful air pollutants and improves the land quality by proper utilization of industrial waste materials. The process of utilizing industrial waste like Bottom Ash (BA) and Recycled Coarse Aggregate (RCA) materials reduces the dumping of landfills. This paver block containing titanium dioxide could control air pollution caused by vehicular emission (Gopalan et al. 2020). They are highly stable materials and act as catalysts to initiate a photochemical reaction called the photocatalysis process.

Paver block is made with double-layer formation to increase the photochemical reaction by exposing the layer containing titanium dioxide to sunlight which is attempted in the present study. This double-layer paver block concept leads to infuse recycled glass particles in the facing layer to increase the photocatalytic reaction by retaining more daylight into the paver block. Other materials included in the base layer of eco-friendly paver block plays vital role in preventing pollutant runoff and providing better drainage systems in flood-prone areas. The shape of the paver block used in this study is rectangular with a thickness of 80 mm; as per (IS 15658 2006), the 80 mm thick paver block is recommended for medium traffic conditions. The dimension of the paver block is 200 mm x 100 mm x 80 mm. It consists of two layers: a facing layer (photocatalytic surface layer with titanium dioxide and recycled glass) of thickness 6 mm and a body layer of thickness 74 mm. In this research paper an attempt is made to achieve the maximum strength of paver block specimen using nanomaterials in concrete with optimal mix proportion and also tracking down the level of unsafe air contamination.

A study on the benefit of glass bead supports for efficient gas phase photocatalysis was carried out in a commercial and a synthesised photocatalyst by (Verbruggen et al. 2011). Preparing 2 mm glass beads with titanium dioxide as a thin layer to improvise the efficiency of illumination of TiO₂. (Kumar et al. 2019) have conducted a study on I-shape 80 mm recycled paver blocks for replacement with 10 mm size (0%, 15%, 30%, 45%, 60% & 75%) natural coarse aggregates by recycled coarse aggregates derived from construction and demolition waste. Replacing recycled concrete aggregates up to 60% results desired compressive strength, and water absorption value and no significant change is observed in 60% replacement levels. Research was conducted by (Antoni et al. 2017) on bottom ash replacement for fine aggregate in the production of paver blocks concludes, the paving blocks prepared with cement to bottom ash ratios of 1:3, 1:4, and 1:5 exceeds the target compressive strength of 40 MPa. (Singh and Siddique 2015) have carried out a study on the properties of concrete with bottom ash as fine aggregate in concrete. Concrete specimens were cast with 0%, 30%, 50%, 75%, and 100% replacement of river sand and 50% replacement of coal bottom ash, achieved highest compressive strength.

The light transmission property of glass cullets improved the photocatalytic activity efficiency of cementitious materials used in the concrete layers. Test results concluded that the increase in curing age decreases the photocatalytic activity. Recent Photocatalytic applications for Air Purification in Belgium by (Boonen and Beeldens 2014) with double-layer concrete blocks performance were compared with single layer concrete blocks for air purification. The increased humidity prevents the reduction of pollutant degradation. The replacement of natural coarse aggregate with the recycled aggregate up to 80% has achieved the target strength by employing a suitable mix design method and maintaining a good ultrasonic pulse velocity value.

(de Melo et al. 2012) developed and evaluated the efficiency of photocatalytic pavement blocks in the laboratory. Modification of nanoparticles in the surface layer of concrete pavement for three different thicknesses and three different compositions of titanium dioxide were tested to reduce NO_x in the atmosphere. It shows that the porous structure of pavement affects the rate of NO_x reduction, and the efficiency could be increased by increasing the percentage of nanoparticles in it. The properties and structure of TiO₂ in air purification, self-cleaning, anti-fogging property and water purification performance while adding more titanium dioxide in the applications of photocatalysis were studied by¹². Novel applications on TiO2 surfaces for the wettability patterns analysis is performed. (Hüsken et al. 2009) have studied the photocatalytic concrete products for the evaluation of air purification. They analysed the degradation process of Nitric oxide (NO) in laboratory studies and observed the photocatalytic active concrete production. The study's inference includes a comparison of varying photocatalytic concrete products in the European market. (Andrade et al. 2009) have analysed the coal bottom ash as a replacement for natural fine aggregates on the properties of concrete, including bleeding, plastic shrinkage, and setting time. It was concluded that the setting time is affected by the replacement of bottom ash.

The wearing and abrasion resistance of concrete pavement containing ultrafine titanium dioxide particles was studied (Hassan et al. 2010). SEM and EDS were used to determine the performance of TiO₂ particles on the surface before and after wearing. This shows that 3% coating yields better results than the 5% coated surface. Decolourization of methylene Blue with TiO₂ under UV irradiation with a wavelength of 660 nm attained 92.3% of degradation efficiency after 160 minutes.

(Awadalla et al. 2011)have incorporated titanium dioxide in paver block to reduce indoor air pollution by reducing carbon dioxide in the atmosphere. The surface layer of the panel containing titanium dioxide to remove CO₂ reveals that its levels declined within 90days aging. (Gauvin et al. 2018) analysed the effect of porous building materials morphology and pore structure. The photocatalytic oxidation mechanism can reduce the pollutants in the air, by using two different porous structures like wood wool, cement board and autoclaved aerated concrete. The findings demonstrated the morphological and pore structure studies reveals a large effective area and increased roughness.

The durable property and purification performance of impregnated concrete with silicate and titanium dioxide was studied (Kim et al. 2019). Silicate and Titanium dioxide has a high effect after the impregnation of photocatalyst TiO₂. (Ramirez et al. 2010) Research on the porosity, roughness of the structure and wearing resistance concludes the removal efficiency of toluene was about 86%. (Augustyniak et al. 2021) conducted another study on the effects of ZnO nanoparticles on Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans bacteria. Mixed ZnO nanoparticles with cement mortar resulted in higher strength and low toxicity.

(Poon and Cheung 2007) have conducted experimental studies on nearby available waste materials with titanium dioxide to improve the removal of nitrogen oxides. Results indicate that the surface layer's porosity and the particle size distribution of materials are important in removing NO_x. (Padmini et al. 2009) Lower water-cement ratio and higher cement content has given higher compressive strength. Water absorption of recycled coarse aggregate was higher than the normal concrete, and increased aggregate size improved the strength of the concrete.

(Bica and de Melo 2020) The addition of glass on the surface layer of the concrete paver block enhanced the atmosphere's NOx reduction up to 17.90%. (Witkowski et al. 2021) have studied the experimental investigation of concrete carbonation depth. Results shows that photocatalysis effectiveness increases when titanium dioxide is modified to N- doped TiO₂. The nano titanium dioxide has a large area to volume ratio, which reduces the photocatalytic activity's performance. (Chu et al. 2021) Effect of natural and recycled aggregate packing on the properties of concrete blocks is reported. It might increase the compressive strength and performance by 31%. The reduction in nitrogen oxides was calculated using 70W and 300W UV light (Witkowski et al. 2019). Reduction of nitrogen oxide was found to be 45% and implemented on asphalt pavement on the road's surface.

(Yu et al. 2020) have studied the degradation efficiency on the intensity of UV radiation and the amount of TiO₂ percentage added to the pavement. (Rhee et al. 2018) had investigated nitrogen oxide reduction in the atmosphere when titanium dioxide was incorporated in the cementitious materials. The excess percentage of titanium dioxide reduced the compressive strength. It is concluded that the density of titanium dioxide and surface roughness of the products are important in the degradation efficiency of nitrogen oxides. (Staub de Melo and Trichês 2016) have carried out a study on the effects of nanoparticles in the mechanical properties and microstructure of concrete. By adding TiO₂ in concrete for improving the mechanical and microstructural behaviour. (Torres de Rosso and Victor Staub de Melo 2020) have developed a transparent photocatalytic cement-based recycled glass in paver blocks for metropolitan roads. Replacing mineral aggregates from 20–61% results in appropriate compressive strength.

The above literature review shows that the natural aggregates can be replaced by recycled coarse and fine aggregate by thermal power plant waste (bottom ash). The lower water-cement ratio enhances the compressive strength, and the water requirement of the paver block is higher due to the porous nature of recycled coarse aggregate and bottom ash. Titanium dioxide is the best photocatalyst, and it has some specific properties such as anti-fogging, self-cleaning, air purification, etc. Recycled glass particles enhance the effectiveness of NOx reduction when added to titanium dioxide. The porosity of the block surface layer plays an important role in reducing the pollutants. Double-layer blocks are more efficient than single-layer concrete blocks. The photocatalytic activity of titanium dioxide can be evaluated using dye degradation of Methylene blue. This solution can be degraded with the help of sunlight or UV light. The degradation efficiency can be identified using a UV-Visible spectrophotometer at a wavelength of 660 nm.

Air pollution is a major threat to human health, and it has become a global issue in urban towns and cities. This study mainly focuses on developing an eco-friendly smart paving materials produced with industrial waste combined with nano-sized TiO₂ particles. Photocatalytic action of Titanium dioxide minimizing the air pollution is already established in many works of literature. However, the addition of TiO₂ infused with the glass cullets to control the air pollution levels and incorporating industrial waste in the double-layer concept of paver block is not yet attempted. Hence, the investigation was carried out to understand the optimal mixture combination that reduces the pollution level as well as the utilization of industrial waste.

The cementitious materials used in this study were Ordinary Portland cement 53 grade with a specific gravity of 3.15 and class F fly ash with a specific gravity of 2.20. Coal bottom ash (BA), a byproduct of thermal power plants, is used as a fine aggregate and locally available Manufactured Sand is used. The comprehensive research framework is presented in Fig. 1 which have the material properties, testing of paver blocks, implementation of paver blocks and performance study.

The size of bottom ash and M-sand used in this study passes through the sieve of size 4.75 mm, and its properties are given in Table 1. Figure 2 shows the gradation curve of Fine aggregate used in this study. RCA from building demolition waste was used as a coarse aggregate. Initially, they were crushed manually and sieved to a size between 6 mm, and 12 mm was used, and Table 2 gives the physical properties of RCA. Titanium dioxide and recycled glass were used on the surface layer of the block for an active mechanism of photocatalysis, and the properties obtained from literature(Reshma et al. 2021) is given in Table 3. RG was collected from the local glass industry dumping yard is crushed manually to the size passing through 2.36 mm sieve and retained on 300 µ sieve. The detailed methodology framework of the research is presented in Fig. 1.

Table 1

M Sand and Bottom ash Properties
Sl no	Properties	M-Sand	Bottom ash as aggregate
1.	Bulk density kg/m³	1755.21	1265
2.	Specific gravity under SSD condition	2.68	2.38
3.	Water absorption %	1.00	3.54
4.	Fineness modulus	5.97	6.39

Table 2

Recycled aggregate Properties
Sl No.	Properties	Range of Value
1.	Grading (mm)	6–12
2.	Bulk density kg/m³	1324
3.	Water absorption (%)	6.63
4.	Impact value (%)	37.70
5.	Abrasion value (%)	47.20
6.	Fineness modulus	7.46

Table 3

**Physical Properties of Titanium oxide**(Reshma et al. 2021)
Sl. no	Properties	Range of Value
1.	Colour	White
2.	Particle size	20 nano meters
3.	Crystalline structure	Amorphous
4.	Density	4.16
5.	Melting point (°C)	2120
6.	Solubility in water	Less than 1mg/ml at 28°C
7.	Boiling temperature(°C)	4850

2.1 PAVER BLOCK PREPARATION AND TESTING

The paver blocks of 200 mm x 100 mm x 80 mm were prepared with the facing and body layers. The dimension of the facing layer is 200 mm x 100 mm x 6 mm, and it consists of cement, Fly ash, bottom ash, M-sand, recycled glass, and TiO₂. The dimension of the body layer is 200 mm x 100 mm x 74 mm that consists of cement, fly ash, bottom ash, M-sand, and recycled coarse aggregate, as shown in Fig. 3.

This study used three different mix proportions to derive an optimal mix composition that would achieve suitable strength using recycled materials like RCA and BA. Titanium dioxide and recycled glass materials are used as a substance to degrade the pollutant existing in the air/atmosphere. Mixture with 0% BA consists of 100% M-sand as a fine aggregate, 50% BA consists of 50% bottom ash and 50% M-sand as fine aggregate, and 100% BA consists of 100% BA and 0% M- sand. Mixes with 100% RCA and 0% BA, 100% RCA and 50% BA and 100% RCA and 100% BA were prepared. The concrete mixture proportion is developed as per IS 10262:2019 method for both the facing and body layers. A water-cement ratio of 0.38 is used in the mixture composites. The details of various mix proportions used in this study are presented in Tables 4 and 5.

Table 4

Mix Proportion of Facing Layer
S.NO	% of bottom ash Replacement	Cement (Kg)	Fly Ash (Kg))	FA(Kg)		Glass (Kg)	TIO₂ (Kg)	Water Content (ml)
S.NO	% of bottom ash Replacement	Cement (Kg)	Fly Ash (Kg))	BA	M - Sand	Glass (Kg)	TIO₂ (Kg)	Water Content (ml)
1	0% of BA	0.033	0.014	-	0.088	0.131	0.004	18
2	50% of BA	0.033	0.014	0.044	0.044	0.131	0.004	19
3	100% of BA	0.033	0.014	0.088	-	0.131	0.004	21

Table 5

Mix Proportion of Body Layer
S.NO.	% of bottom ash Replacement	Cement (Kg)	Fly Ash (Kg)	FA (Kg)		RCA (Kg)	Water Content (L)
S.NO.	% of bottom ash Replacement	Cement (Kg)	Fly Ash (Kg)	BA	M -Sand	RCA (Kg)	Water Content (L)
1	0% of BA	0.415	0.178	-	1.080	1.368	0.277
2	50% of BA	0.415	0.178	0.389	0.530	1.368	0.282
3	100% of BA	0.415	0.178	0.778	-	1.368	0.289

Cement is replaced with 30% Flyash on every composition. The natural aggregates are fully replaced with recycled aggregates in all the mixture compositions, and the concrete mix is prepared in the concrete mixer. The base layer of the specimens was prepared with a homogenous mixture of all the required materials exactly and filled up to 74 mm into the steel moulds and compacted manually. The remaining 6 mm is filled with a suitable mixture containing TiO₂. The 6 mm layer is the facing layer of the paver block, which consists of semiconductor material, titanium dioxide and recycled glass material to enhance photocatalysis. It will act as an active surface layer that reacts with the sunlight to convert harmful gases into harmless ones. The specimens were cured at a temperature of 29°C and relative humidity of 78%. Totally 54 number of blocks were cast to ascertain the compressive strength and water absorption values. The compressive strength and water absorption tests were done as per the IS 15658:2006 procedure. Acceptable values for compressive strength of M40 grade concrete should have a minimum value of 40 MPa. As per IS 15658:2006 specifications, the water absorption value should not exceed 6% for the standard paver blocks.

The specimens were dried for 1 day after being removed from the moulds and kept under immersion curing process at room temperature. Specimens prepared with each mix were cured for about 7, 14, and 28 days to determine the paving blocks compressive strength and water absorption. The photocatalytic activity test was carried out with different samples to determine the indication of photocatalysis activity. The dye degradation test was done with the crushed specimens of different proportions to determine the degradation efficiency of Titanium dioxide. Finally, the photodegradation of pollutants was determined using an IoT device designed for air quality monitoring in real-time applications.

2.2 IOT DEVICE FOR AIR QUALITY MONITORING

The air quality monitoring on the paver block was conducted with the help of an IoT device. This device is included here to study the air purifying performance of the paver block and the reduction in the concentration of substances causing air pollution. However, in another way, dye degradation tests were performed on the paver blocks. This device was designed to use the IoT concept to study various pollutant parameters influence. Initially, the IoT device was kept at points where there was a need to know the air quality. Then the IoT-enabled device is connected with a mobile phone, which monitors the air quality through a mobile connectivity system. The IoT device estimates air quality values for the pre-set time intervals and these readings are tabulated as a database in the Excel CSV format. This air quality monitoring system includes some parameters such as air quality level, temperature, humidity, heat index, carbon monoxide (CO), carbon dioxide (CO_2), ethanol, ammonium (NH₄), toluene, acetone, and dust density of PM 2.5. Figure 4 shows the arrangement of IoT devices used for air quality monitoring in this research.

DHT11 digital temperature and humidity sensors are used and calibrated to the digital signal output of the temperature and humidity combined sensor. Dust sensor “GP2Y1010AU0F” is used in this monitoring arrangement to detect domestic house dust and cigarette smoke, etc. This device is also fitted with a GSM module and GPS receiver which automatically collects the real-time air quality data for communication and location identification purposes.

The thickness of the wearing layer should be at least 6 mm as per (IS:15658 − 2006 2006), and the thickness maintained in the wearing layer is measured to be 7.8 mm, which satisfies the tolerance limit. It consists of materials like Titanium dioxide and Recycled glass particles that serve as the surface layer of the paver block, which in turn enhances the property of photocatalytic reaction. The thickness of the paver block used in this study exceeds the actual measurement, but it satisfies the tolerance limit (IS:15658 − 2006 2006).

3.1 COMPRESSIVE STRENGTH OF PAVER BLOCKS

Compressive strength tests were applied to identify paver blocks' strength, quality, and characteristics. After 7, 14, and 28 days of curing, the specimens were tested for compressive strength. The specimens were placed on the 200T compression testing machine, and the load was applied gradually at the rate of 140 kg/cm²/minute (IS 516:2014) until the specimen fails. The maximum load was recorded, and by using the formula, the compressive strength of the paver block was determined, and results are depicted in Fig. 5.

From Fig. 5 it is obvious that at the end of 28 days, all the three mixes have attained suitable strength by replacing the coarse aggregate with RCA and fine aggregate with bottom ash. The bottom ash mix 100% replacement gives lower strength when compared to 100% M-sand mix. The 50% replacement of bottom ash to M-sand mix gives suitable strength similar to the 100% M-sand mix. Therefore, the thermal power plant waste (bottom ash) can be replaced up to 50% as fine aggregate, and the recycled coarse aggregate can be replaced fully as coarse aggregate in the concrete paver blocks. The compressive strength of this study is above 40 N/mm^2, and similar results were obtained in the study conducted by Torres de Rosso (Torres de Rosso and Victor Staub de Melo 2020) with a compressive strength of 44 N/mm². Hence these results are similar to earlier studies conducted with the replacement materials in the paver blocks production.

Water Absorption Test was carried out on the blocks after 28 days curing as per IS 15656: 2006 guidelines. The specimens were immersed in water for about 24 hours, and the wet weight was noted and dried for about 24 hours to measure the dry weight. By using the formula, the rate of water absorption can be calculated. As per IS 15656: 2006 codal provisions, the water absorption of paver block should not be more than 6%.

Table 6

Water Absorption Results
SI NO	% of Replacement	Water Absorption (%)
1	0% of Bottom Ash	1.582
2	50% of Bottom Ash	1.085
3	100% of Bottom Ash	1.767

From Table 6, it is interpreted that all the three mixes show the percentage of water absorption lower than 6%, which satisfies the condition given in (IS:15658 − 2006 2006). Fly ash and Titanium oxides additives are of high fineness in their inherent characteristics. They act as a filler in improving the microstructure of concrete and thus reduces the water absorption properties of the matrix. While comparing all the three mixes, the water absorption rate is more for 100% bottom ash mix due to its high water-absorbing property and lower for 50% bottom ash and 50% M-sand mix series.

3.2 PHOTOCATALYTIC ACTIVITY TEST

An organic dye (Methylene blue solution) was dissolved in distilled water of 1:20 proportion, and 1–2 ml of prepared solution was dropped on the active surface layer containing titanium dioxide (TiO₂), and it is exposed to sunlight. Subsequently, the time required to degrade the colour of the Methylene blue solution is poured on the three paver blocks with and without RG. Normal blocks were noted to check the photocatalytic activity of the paver block containing titanium dioxide. The time taken details for the photocatalytic actions are shown in Table 4. In general, glass particles can generate an alkali-aggregate reaction, but these results change the curing and percentage of glass particles added to the concrete (Ke et al. 2018).

Table 7

Photocatalytic Activity
SI.NO.	Mix proportion		Time taken (min)
1	Facing layer with RG	Paver with 100% of BA, 0% of M-sand and 100%of RCA.	92
2		Paver with 50% of BA, 50% of M-sand and 100%of RCA.	90
3		Paver with 0% of BA, 100% of M-sand and 100%of RCA.	87
4	Facing layer without RG	Paver with 100% of BA, 0% of M-sand and 100%of RCA.	115
5	Paver block without facing layer	Normal paver block	NIL
6	Paver block without facing layer	Commercially available Store – brought paver block	NIL

The Methylene blue solution was dropped on six different paver blocks to determine its photocatalytic activity. From Table 7, it is concluded that the commercially available paver block and conventional type does not show any photocatalytic activity. In contrast, the blocks with titanium dioxide indicates photocatalytic activity through its colour degradation. Among the above mentioned, the efficiency of blocks with glass beads were better than those without glass beads. Further, the effectiveness of photocatalytic action was increased by adding glass beads along with titanium dioxide.

3.3 DYE DEGRADATION TEST

The dye degradation test was done to determine the degradation efficiency of the paver block having photocatalyst (Titanium dioxide, TiO₂) using a UV visible spectrophotometer. Initially, dilute Methylene blue solution with distilled water 1:20 proportion and 5gms of different proportions of paver block containing TiO_2, and recycled glass was crushed and added to the 50ml of prepared solution in four different beakers. The beakers with different proportions of paver block were kept under the sunlight, and the degradation efficiency was noted every 60 minutes. The dye degradation test conducted is presented in Fig. 6.

The degradation efficiency can be derived from the absorbance of the solution. The absorbance value can be identified using a UV-Visible spectrophotometer by placing Methylene blue solution as the reference.

ἠ = (A / Ao) x 100%

A = Absorbance obtained during 60min

Ao = Absorbance before reaction

Table 8

Degradation Efficiency of TIO₂ in Paver Block
Sl. No.	Wavelength	Time (min)	Absorbance (A₀)	Efficiency (%)
1	660	0	1.102	1.3
2		60	0.898	20
3		120	0.614	45.3
4		180	0.452	59.8
5		240	0.152	86.5

From Table 8, the degradation efficiency of the paver block containing titanium dioxide and recycled glass shows 86.5% performance. The degradation efficiency increases with the decrease in the absorbance rate of Methylene blue indicated by UV- V spectrophotometer. The rate of absorbance depends on the dilution rate of methylene blue. Figure 7 shows the degradation efficiency of modified Titanium oxide in paver block material.

The tungsten lamp as a source of visible light, at which the prepared photocatalyst 200 mg has been added under visible light irradiation. This is done in the presence of glass cullets with titanium oxide modified in aqueous solution. The experiment is carried out at different time intervals under visible light. Initially dark setup in the presence of photocatalyst in methylene blue dye has been stirred using a magnetic stirrer is maintained for 30 minutes in the absorption-desorption equilibrium of the surface of methylene blue, The solution has analysed wavelength at 660 nm and shows that absorption intensity increases with increasing concentration. After 80 minutes, methylene blue decolourised peak wavelength reduced compared to the initial dye concentration wavelength in zero minutes indicates the high activity in line with existing literature.

The mixture was ultrasonicated for 15 minutes at room temperature with 500 ppm methylene blue solution to scatter the solid catalyst particles. In a photoreactor, the mixture was swirled in the dark. A UV-visible spectrophotometer was used to measure the light absorbance of the samples obtained at different time intervals. At different TiO₂ concentrations, the difference in light absorbance at 600 nm of the drawn sample and the slurry was measured.

This research was used to understand the different photocatalytic degradation runs such as TiO₂ concentration initial methylene blue concentration. The initial TiO₂ concentration is measured to be 0.2 g/l. In contrast, the initial methylene blue concentration is 20 ppm, according to the first study conducted in this research. Before adding 2 ml of 500 ppm methylene blue, 0.01 g of TiO₂ was added to 48 ml of deionized water, and 0.2, 0.3, 0.4, and 0.5 g/l TiO2 concentrations were selected. Methylene blue concentrations were initially 20, 25, 30, and 35 ppm. Initially the methylene blue concentrations of 25 and 30 ppm were taken and TiO₂ concentrations of 0.3 g/l destroy the dye the faster, followed by 0.4 and 0.5 g/l, and finally 0.2 g/l. Experiments demonstrated that the initial methylene blue concentration and TiO2 concentration complicated the reaction rate. The pseudo-first-order reaction model fits the net desorption and degradation of methylene blue well.

At an early age, the inclusion of nano-TiO₂ powders greatly increased the hydration rate and enhanced the hydration degree of cementitious materials. TiO₂ was shown to be innocuous and stable during the cement hydration process. The overall porosity of the cement paste is reduced, and the pore size distribution changes as well. The physical and mechanical characteristics of cement-based materials were also influenced by the hydration rate acceleration and the microstructure change. Due to the inclusion of nano-TiO₂, the beginning and final setting times were reduced, and more water was required to maintain the standard consistency.

3.4 SEM ANALYSIS

Paver block with the composition of 50% bottom ash, 50% M-Sand, and 100% recycled coarse aggregate was examined, as it shows higher strength than the other two mixes. The sample paver block element of 1 cm was examined under the electron microscope, and high-resolution images were obtained with different magnifications.

The SEM image with the magnification of 300X with high electron tension of 15 Kv at 100 µm shows the body layer of the paver block, representing the homogeneous distribution of bottom ash and M-sand shown in Fig. 8. The materials were tightly packed together as there was no evidence of a contact zone. The absence of a contact zone infers nano particles' presence with the closely bonded dense structure. Further, the sample was studied under the magnification of 1000X with a working distance of 7.5 mm at 20µ m precision. The crack reveals the contact zone, and the white traces indicate the presence of titanium dioxide. The micro-holes in this image exhibit the porosity of the paver block. The porous structure is one of the factors that enhance the photochemical reaction. The hydration of Portland cement results in calcium silicate hydrate (C-S-H), calcium hydroxide (CH), and the capillary pore structure. The characteristics of the microstructure impact almost every physical property of concrete, including strength, elastic modulus, permeability, and shrinkage. Because of the agglomeration and lack of reactivity, it appears that the silica fume is either excessively thick or not properly incorporated into the paste. Unidentified silica fume should be used in future research.

Figure 9 shows the SEM image with the magnification of 500X at 20 µm with a working distance of 8 mm shows a bond between the facing and body layers. The titanium dioxide (white traces) demonstrates the facing layer, and the rough texture indicates the body layer. As there were no cracks and contact zone, the facing and body layers are firmly connected. Further, the sample is studied under the magnification of 2000 X with a working distance of 7.5 mm at 10 µm. The SEM photomicrograph of the paver block indicates the adsorption of carbon dioxide on the sample surface, and the morphology of particles is round and lighter. Due to its varied chemical formations, C-S- H colour and shape range from numerous hues of grey (Scrivener 2004). C-S-H in the groundmass (outer product) is darker, whereas C-S-H around cement grains (inner product) is lighter.

Figure 10 shows the SEM image with the magnification of 2500X at 10µm indicates the cloud-like structure that reveals the presence of titanium dioxide. The macro holes illustrate the slit in the structure. The drizzle demonstrates the fine glass particles incorporated in the paver block that enhances the photocatalytic reaction by refracting the UV rays. Further, the sample is studied under the magnification of 500X with a working distance of 7.5 mm at 20 µm. The micro-holes in this image indicate the porosity of the structure, and the white flakes represent the titanium dioxide. Usually, the nanoparticles like titanium dioxide will act as bonding agents and impart the compressive strength of concrete.

The SEM result indicates the pozzolanic reactivity of glass cullets with cement increased with respective surface area. The Pozzolanic activity is higher than using fly ash. It has released a high silica rate to react with calcium cation and hydroxide anion in an alkaline medium with increased C-S-H.

EDS examination would establish that these particles are TiO₂ and aid in determining their distribution throughout the microstructure, as presented in Fig. 11. Finally, there was no change in Ti concentration between the carbonated and non-carbonated mixtures. EDS may have detected Ti below the surface or inside the contact volume, resulting in no visible change. In any case, the data reveal no indication of TiO₂ shielding or covering at the surface due to carbonation.

3.5 FTIR ANALYSIS

The infra-red spectrum of 4000 cm^− 1 to 400 cm^− 1 is applied to the sample. The spectrum range is divided into two regions with 1500 cm^− 1 as a centre. Figure 12 presents the FTIR analysis of the paver block. The left-side region is known as a functional group from 4000 cm^− 1 to 1500 cm^− 1. This region was used to identify the functional group present in the material. The wavelength at which peak occurs and type of peak, i.e. (narrow peak or board peak) are noted. Based on the wave number at peak the functional group is determined. In this case, the peak is at 3433.03 cm^− 1, which is slightly board is obtained; this indicates O – H (Alcohol) and some traces of O – H (acids) and C – H. This shows the bonding of cementitious materials used in the paver block. The right-side region, called the fingerprint region, ranges from 1500 cm^− 1 to 400 cm^− 1. This region is used to identify an organic molecule present in the material. It contains complicated series of transmittance due to more bending vibrations.

(Mikhaylov et al. 2009) observed N₂O₃ species on Titanium oxide surface only during NO and O₂ adsorption studies initiated by the reaction between NO and NO₂ species on titanium oxide surface also suggested the Bands in the 3600–3750 cm-1 range have been assigned to isolated hydroxyl groups, while Bands in the 3600-2500cm-1 range are due to the adsorption of the un-dissociated water molecule, -OH oscillators involved in H-bonds. Under the high dehydrated condition, P25-TiO₂ has six isolate hydroxyls with bands at 3734, 3715, 3688, 3671, 3658 and 3640 cm-1, which the 3734, 3715, 3688, 3671and 3640 cm-1 are assigned to frequencies bonding on anatase phase present in P25 and the 3658 cm-1 is ascribed to the dominated hydroxyl on rutile. The six isolate hydroxyls (3734, 3712, 3688, 3671, 3658 and 3640 cm-1) on the P25 surface are selective toluene adsorption. The best alkali-activated curing method has a good setting and mechanical properties with existing common cement. The formation of materials functional groups has been confirmed FT-IR analysis.

3.6 AIR QUALITY MONITORING USING IoT DEVICE

The location selected to implement the paver block for this study is Poonamallee, West part of Chennai, India, with 13.044° N, 80.106° E. This location near a road junction of 5 m from the edge of the road has more traffic volume and pollution is chosen as the area of interest. Figure 13 shows the implmentation of paver blocks and an air quality monitoring system. The data collected using IoT devices were used to analyze the effectiveness of paver block in reducing the pollutants in the air. The paver blocks containing TiO₂ have been arranged on the floor, covering 16 m². The device was placed at the centre and at an interval of 0.5 m, 1 m, 1.5 m, and 2 m on either side of the arrangement to collect the data at respective positions. Figure 13 shows the site's location where air quality is monitored.

Carbon monoxide is one of the prime parameters considered in this study as it causes harmful effects on the environment and living beings. This study analyzes the air quality around the paver block system. CO comes under the category of good if it ranges from 0–1 ppm as per the air quality index of India (CPCB 2014). From Fig. 14 (a), it is noticed that the CO levels at the centre range from 0–1 ppm, whereas the CO levels at a distance of 2m from the paver block range from 2–3 ppm. This shows the clear difference and reduction in CO levels when the device was placed at the centre of the arrangement.

Carbon dioxide is a gaseous pollutant and not as harmful as carbon monoxide but creates an overabundance of greenhouse gases, which causes many ill effects on the environment. Figure 14 (b) shows that CO₂ ranges from 300–500 ppm at the centre and 800–900 ppm at 2 m from the paver block. Hence the carbon dioxide levels too were lowered.

Ethanol in the gas phase produces the same hydrocarbons and nitrogen oxides. It emits carbon dioxide and greenhouse gases while burning. Reduction in ethanol, in turn, reduces CO and CO₂ levels. From Fig. 15 (a), it is clear to notice a visible reduction in the levels of ethanol at the centre of the paver block than at 2 m from the arrangement of the paver block. Figure 15 (b) shows that the ammonium levels were reduced at the centre compared with 2 m from the paver block.

The concentration of toluene reduces gradually at the centre, which helps in reducing the pollution rate in the atmosphere - refer to Fig. 16 (a). Acetone causes many health issues like headaches, dizziness, vomiting, nausea, etc. Such issues can be reduced by lowering acetone levels in the atmospheric air. Figure 16 (b) shows that the paver block containing titanium dioxide reduces such harmful pollutants in the air.

Parameters such as carbon dioxide, carbon monoxide, acetone, toluene, ammonium, and ethanol are analyzed, and various graphs have been plotted with the data obtained from the study area. In this study, temperature and humidity affect the concentration of pollutants. If humidity increases, the concentration of pollutants also increases and vice versa. From the graphs, it can be concluded that all the gases mentioned above in the atmosphere were reduced when the IoT device was placed at the centre of the arrangement of the paver block. Initially, the concentration of CO and CO₂ in this study area was in the moderately polluted category as per the air quality index. The concentration of the mentioned pollutants was high at 2 m from the paver block. It reduced gradually as the device position was moved from the distance of 2 m to the central position of the arrangement. This indicates that the arrangement of paver blocks containing TiO₂ reduces the concentration of pollutants in the air to a certain extent.

This experimental study on the paver blocks using recycled coarse aggregate and byproduct of thermal power plant (bottom ash) making the product sustainable. Using recycled products and the thermal power plants waste reduces pollution at the dumped site. Moreover, incorporating the photocatalyst titanium dioxide into the paver block reduces the pollutants in the air since the vehicle exhaust emissions contain carbon monoxide, nitrogen oxides, hydrocarbons, etc. This study results will help to reduce carbon monoxide, carbon dioxide, toluene, ammonium, acetone, and ethanol in the atmosphere and further, the concentration of CO is reduced up to 50%.

The cost of normal concrete paver block as per the market rate is ₹ 10. The presence of photocatalyst (TiO₂) and recycled glass increases the price of the paver block to ₹ 13, which is higher than the cost of a conventional concrete paver block. The cost analysis of the paver block is presented in Table 9 for different mixes used in this research. Cost-benefit analysis shows that the Paver blocks made with TiO₂ and recycled glass are economical and effective in controlling the air pollution. The utilization of industrial waste materials like fly ash, bottom ash and recycled aggregate provides a proper disposal solution. Though the price of the block is higher, the photocatalyst and the recycled glass makes the block more efficient in reducing the harmful effects of the pollutants and helps in the transformation of a sustainable environment.

Table 9

Cost analysis of the Material
Material used	Price per Kg (in ₹)	Price for the quantity used
Material used	Price per Kg (in ₹)	Mix 1	Mix 2	Mix 3
Cement	7.0	3.14	3.14	3.14
Fly ash	1.20	0.23	0.23	0.23
Recycled coarse aggregate	1.40	1.91	1.91	1.91
Bottom ash	2.0	-	0.86	1.73
M Sand	4.50	5.25	2.58	-
Titanium dioxide	280	1.12	1.12	1.12
Recycled glass beads	5.50	0.72	0.72	0.72
Total price		12.37 ~ 12.50	10.71 ~ 11.00	8.85 ~ 9.00

Air pollution is a major health hazard that Indian society is facing today. Titanium dioxide-based paver block would reduce the pollutants in the air by converting harmful gases to harmless ones. Natural resource degradation is also a major environmental threat that can be reduced by using alternative materials. Fine aggregate can be replaced by coal bottom ash, and coarse aggregate can be replaced efficiently by recycled coarse aggregate. The photocatalytic activity of glass cullets with titanium oxide improves the efficiency of dye degradation of wastewater treatment and the removal of air pollutants. The efficiency of photocatalyst is active in the visible region and surface layers of paver blocks. The luminescence nature of glass cullets incorporated titanium oxide catalyst is easily recycled and recoverable.

It was found that 50% replacement of fine aggregate by bottom ash and 100% replacement of coarse aggregate by recycled coarse aggregate gives better compressive strength and water absorption at the end of 28 days. The utilization of bottom ash and recycled coarse aggregate in concrete paver blocks aids the sustainability of construction materials. Such endeavors further lead to more green technologies in the construction industry. The maximum strength of 43 MPa was attained by the paver block having 50% bottom ash and 50% M-sand. The water absorption rate is high for the 100% bottom ash mix due to its water-absorbing capacity. Usage of titanium dioxide in paver block reduces the pollutant level in the air to a certain extent and incorporating glass on the surface layer enhances its property of pollutant reduction. The titanium dioxide-based paver block has 86.5% efficiency on degrading methylene blue under sunlight within 240 minutes, which indicates photocatalysis activity on the paver block.

The accurately measured harmful pollutants like carbon di oxide and global warming causes carbon monoxide and measured corrosion causing electrolytes acetone to have been removed effectively and it is monitored using sensor-based IOT devices and results are agreed with the existing literature. Then photocatalytic removal of these materials has been utilized industrials textile wastewater contamination of cationic dye like methylene blue decolourisation have been checked in UV-visible spectrophotometer absorption wavelength at 660 nm.

Air quality monitoring on titanium dioxide-based paver block infers that the concentration of CO reduced up to 50%. Thus, the environmental effects from the power plant waste like bottom ash are significantly lowered, and the cost of fine aggregate is reduced by the substitute of waste material from the thermal power plant. These paver blocks can be used in footpaths, car parking, cycle tracks etc. Further, these blocks can also be used at locations where medium traffic conditions with high traffic volume prevail.

Ethical Approval

Not Applicable

Consent to Participate

Not applicable

Consent to Publish

All the authors are consented to publish the work

Authors Contributions

P. P (Professor) contributed to problem identification, literature collection, experimental design, and manuscript preparation. C.C.G(Associate Professor) contributed to Experimental design, data analysis, interpretation of results. B.A (Professor) involved in problem identification, literature collection, data analysis, manuscript preparation. S. K. (U.G. Student) contributed to Experimentation, data analysis, manuscript preparation. N. H. (U.G. Student) contributed to Experimentation, data analysis.

Funding

No Funding, self-funding

Competing Interests

On behalf of all authors, the corresponding author states that there is no conflict of interest

Availability of data and materials

Not Applicable

Note to preprint

It is state that the manuscript "has not been submitted to a preprint server prior to submission on ESPR"

Acknowledgments

The authors would like to acknowledge the Centre for Energy Research, Chennai Institute of Technology, Chennai, India, for providing the fabrication and testing facilities, financial support, and other important aspects of the work.

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Environmental Impact Assessment of Air-Purifying Paver Blocks Using Photocatalysis and Sensors Technology

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Abstract

Figures

1. Introduction

2. Materials And Methods

2.1 PAVER BLOCK PREPARATION AND TESTING

2.2 IOT DEVICE FOR AIR QUALITY MONITORING

3. Results And Discussions

3.1 COMPRESSIVE STRENGTH OF PAVER BLOCKS

3.2 PHOTOCATALYTIC ACTIVITY TEST

3.3 DYE DEGRADATION TEST

3.4 SEM ANALYSIS

3.5 FTIR ANALYSIS

3.6 AIR QUALITY MONITORING USING IoT DEVICE

4. Conclusions

Declarations

References

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