Fiber reinforced polymers in pervious concrete - a state of the art review

Porous concrete, entitled also as permeable or pervious concrete, is a type of concrete that has interconnected voids that allow water and also air to go across it. It is widely used in the construction of pavements, parking lots, and sidewalks, among other applications, because of its ability to reduce stormwater drainage, better quality of the water, and decrease urban heat island effects. The addition of fibers to porous concrete has been the subject of numerous studies in recent years, with researchers examining the effects of diversified types and amounts of fibers on the material’s properties. Fiber reinforcement can enhance the strength, durability, and ductility of porous concrete, making it more suitable for use in structural applications. Polymer fibers, in particular, have shown promise in improving the properties of porous concrete. They can increase the material’s resistance to cracking, improve its flexural strength, and enhance its heat-absorbing property. However, the characteristics of polymer-reinforced porous concrete are not yet fully understood, and more research is needed to determine the optimal types and amounts of fibers for specific applications. Despite the potential benefits of fiber-reinforced porous concrete, there are also some challenges associated with its use. The addition of fibers can increase the material’s cost and complexity of production, and it may also affect its permeability and drainage capacity. Fiber-reinforced porous concrete represents an exciting area of research and development in the field of civil engineering. While the addition of fibers can enhance the material’s properties, more research is needed to determine the optimal types and amounts of fibers for specific applications. By addressing these challenges and continuing to refine the material’s properties, fiber-reinforced porous concrete has the potential to expand its use in a large spectrum of applications, including structural engineering, transportation infrastructure, and environmental protection.

Fiber-reinforced porous concrete represents an exciting area of research and development in the field of civil engineering.While the addition of fibers can enhance the material's properties, more research is needed to determine the optimal types and amounts of fibers for specific applications.By addressing these challenges and continuing to refine the material's properties, fiber-reinforced porous concrete has the potential to expand its use in a large spectrum of applications, including structural engineering, transportation infrastructure, and environmental protection.
Porous concrete is a type of concrete that has high porosity, which allows water to go across it with ease.It is also known as permeable concrete or pervious concrete [1].It was created in the 80's, in Japan, as an environmental friendly material, and then it spread around the world, including Europe [1].One of today's main general research objective is to reduce pollution, waste of materials and an environmental friendly material process industry [13].This type of concrete can be used instead of classic concrete and it allows us to recycle aggregates and to diminish energy consumption [2].One of the challenges of using porous concrete is its poor workability, which makes it difficult to produce precast products and apply it without the use of vibration equipment.To overcome this challenge, a ordinary permeable concrete can be produced by using a uniform size of aggregate and a low water-cement ratio.This helps to improve workability and compaction [1].If we add too much water, the concrete mix will segregate, while if we have too little amount of water, the mixture will form balls and will not mix properly.So, the mechanical properties of porous concrete depend on the mix ratios: water-cement, aggregate size and distribution, type and dosage of admixtures [7].Porous concrete typically has low compressive strength and stiffness compared to conventional concrete, but it can still be used for his structural performances in some applications [7].

Retaining walls
Retaining walls are a common feature in urban development projects, mostly in areas where we have uneven land and slopes.They are design to hold back soil and prevent it from sliding down, as well as to support, if necessary, a structure built on top of them [5].Traditionally retaining walls are constructed using masonry, concrete, stones and bricks, and can be designed also to satisfy the aesthetic needs of the surrounding landscape [5].

Permeable pavement
Green infrastructure involves the use of natural or engineered systems to manage storm-water its source.Cases of green infrastructure include vegetative roofs, construction elements that collects rain water, permeable pavements, and bio swales.These systems help to capture, store, and infiltrate storm-water on site, thereby reducing the amount of runoff that enters the urban drainage.In to these solutions, urban planning and design can also participates in decreasing the impact of impermeable surfaces on the water cycle.Strategies such as low-impact development, which emphasizes preserving natural features and minimizing the disturbance of existing landscapes, can help to reduce the amount of impermeable surface area in urban areas and promote more sustainable water management practice [10].

Parking lots and driveways
Pervious concrete allows rainwater to infiltrate into the ground, reducing stormwater runoff.This helps to replenish groundwater supplies and reduces the strain on drainage systems.Since water passes through pervious concrete, it helps prevent the accumulation of surface water on parking lots and driveways.This can improve safety by reducing the risk of hydroplaning and ice formation.

Landscaping projects and gardens
Allowing water to infiltrate through its porous structure is particularly beneficial in garden walkways, as it helps prevent water runoff and allows rainwater to reach the soil beneath.This promotes healthy plant growth by providing direct access to water and reducing the need for additional irrigation.By enabling water to penetrate the surface and reach the underlying soil, pervious concrete helps prevent soil erosion.Traditional impervious surfaces, such as solid concrete or asphalt, can contribute to erosion by channeling rainwater away from the soil.Pervious concrete acts as a natural erosion control measure, retaining water and reducing the risk of soil loss.

Greenhouse floors and foundations
By using pervious concrete for greenhouse floors and foundations, we can contribute to sustainable water management and minimize the strain on local drainage systems.Designed and installed correctly, it can provide sufficient structural support for greenhouse foundations and floors.It has the capacity to withstand moderate loads and offers stability for the greenhouse structure, equipment, and plant containers.However, it's essential to ensure proper engineering and design to meet the specific load-bearing requirements of the greenhouse.

Artificial reefs
Pervious concrete has been considered for use in artificial reefs due to its potential benefits in marine environments.While traditional concrete structures are often used for reef construction, porous concrete offers some advantages in certain scenarios.It provides a rough and textured surface that can serve as an attachment point for marine organisms such as corals, sponges, and other invertebrates.The porosity of the concrete allows water to flow through, which can create favorable conditions for the settlement and growth of marine life, enhancing the ecological value of the reef.

Porous Concrete Properties
If we increase the quantity of reused concrete aggregate in porous concrete can have an effect on its workability, from medium to low, which is a measure of its ease of placement, consolidation, and finishing.The workability of porous concrete is influenced by many elements, such as the type and quality of the RCA, the mix design of the concrete, and the method of placement and compaction [2].Reinforcing fibers in pervious concrete can help enhance its mechanical properties, reduce cracking, improve durability, and increase overall structural performance.However, it's crucial to consult with concrete experts or engineers experienced in pervious concrete to determine the most suitable fiber type and dosage for your specific application.Porous concrete reinforced with polypropylene fibers is a common approach to enhance the performance and durability of the material.[11] Polypropylene fibers are synthetic fibers that are often used as reinforcement in pervious concrete due to their improved properties.These fibers help control cracking in porous concrete.The fibers act as micro-reinforcement throughout the material, distributing stress and reducing the formation and propagation of cracks.This improved crack control helps maintain the structural integrity of the pervious concrete and minimizes potential damage caused by shrinkage or external loads.The addition of polypropylene fibers can improve the durability of porous concrete.The fibers enhance the material's resistance to weathering, abrasion, and impact.Polypropylene fibers are noncorrosive, making them particularly suitable for applications where the pervious concrete may be exposed to corrosive environments or chemical exposure.Unlike steel fibers, polypropylene fibers do not rust or deteriorate over time, ensuring long-term performance and reducing the risk of structural degradation.Using steel fibers in pervious concrete is another approach to reinforce the material and enhance its mechanical properties.Steel fibers provide additional strength, durability, and also crack resistance to pervious concrete.This type of fibers enhance the tensile strength of pervious concrete, making it more resistant to cracking and improving its overall structural integrity.The fibers act as reinforcement throughout the material, distributing stress and resisting tensile forces that can lead to crack formation and propagation.[13] Incorporating steel fibers in pervious concrete increases its load-bearing capacity.The fibers help distribute loads and enhance the flexural and compressive strength of the material.This can be particularly beneficial in applications where the concrete may be subjected to heavy loads or vehicular traffic, such as in parking lots or driveways.Glass fibers can also be used to reinforce porous concrete.They are lightweight compared to other types of fibers, such as steel fibers.This lightweight characteristic makes them suitable for applications where weight reduction is desired, such as in elevated or lightweight structures.Also they have good thermal and electrical insulation properties.It can help reduce thermal conductivity in porous concrete, providing insulation against heat transfer.This can be advantageous in applications where temperature control is essential, such as in buildings or infrastructure.Glass fibers can also enhance the visual appeal of porous concrete.They can create a unique and attractive appearance when exposed at the surface, providing a decorative element to the material.Natural fibers offer environmental advantages as they are renewable, biodegradable, and derived from sustainable sources.Using natural fibers in pervious concrete aligns with sustainable construction practices and reduces the reliance on non-renewable resources.We can provide some degree of thermal insulation to pervious concrete.They help reduce thermal conductivity and can contribute to temperature regulation in structures or surfaces made with pervious concrete.Porosity, permeability, and compression resistance are important variables that can influence the performance of porous concrete.Porosity refers to the amount of void space or pores in the concrete, while permeability refers to the ease with which water can pass through the material [3].Taking into consideration both compression resistance and permeability, a specific requirement regarding the porosity can be selected for porous concrete.Based on the analysis presented, the optimal porosity range appears to be between 20% and 25%.Within this range, the compression resistance should be in the range of 10 to 20 MPa, and the permeability should be from 8 to 10 mm/s.This range can help to ensure that the porous concrete has the necessary strength and water permeability properties for its intended application [3].The characteristics of cement paste and the properties of porous concrete were studied through experimental tests [20].The results showed that the properties of the cement paste depend on the A/C ratio, the additives and the time of mixing the paste.Cement paste with high viscosity and consistency for the preparation of pervious concrete can be produced from an A/C ratio between 0.20 -0.25, by adding 1% superplasticizer additive and sufficient mixing.Good quality porous concrete with porosity 15-25% and compressive strength of 22-39 MPa is obtained using cement paste with a consistency of 150-230 mm and by vibrating the surface for 1 second with an energy of 90 kNm/m 2 .The same authors study how the resistance of the binder and the size of the aggregates influence the compressive strength and porosity of the porous concrete [21].To study how it influences the resistance of the binder, porous concrete test tubes were made in which 4 types of binders were used, having resistors between 30-130 MPa.The test tubes subjected to experimental tests had a porosity between 15-35%.To study how they influence the size of the aggregates, porous concrete test tubes were made in which aggregates with the following nominal dimensions were used: 5.13 and 20 mm.The results showed that for the same type of aggregate the rates of decrease of mechanical resistances due to the increase of porosity were the same regardless of the strength of the binder used.Experimental tests showed that the mechanical strength of pervious concrete is influenced by the size of the aggregates.The rate of decrease of the mechanical resistances of porous concrete with small aggregates is higher than that of concrete with large aggregates.For the same porosity, the mechanical resistances of porous concrete with large aggregates have values higher than those of concrete with small aggregates.In the paper "Evaluation of high-performance porous concrete properties" [15], the main purpose of the experimental tests was to evaluate the mechanical properties of high-strength porous concrete 3 sorts of large aggregates were used in the optimal porous concrete mixtures along with a suitable quantity of water and additives that increase the viscosity and thickness, and the porous concrete analyzed did not require vibration and special treatments.Experimental tests performed: compaction, consistency, porosity, permeability and mechanical tests such as bending strength and maximum strength.It was proposed to perform a mechanical test to study the effect of water reducing and thickening additives on the compaction of high-strength porous concrete, and the purpose of the proposed test was to evaluate the properties of porous concrete reinforced from the point of view of practical applications.The rate of maximum resistance has been assessed at 1, 3, 7, 14 and, respectively, 28 days since the implementation, at the standard temperature of 20 degrees Celsius and the relative humidity of 60%.Following the tests performed, the high-strength porous concrete has good workability, has not segregated or bled/ exudate.High-strength porous concrete has reached its maximum mechanical strength at a higher speed than classic porous concrete.The capacities of porous concrete regarding the compressive resistance and the water purification capacity were highlighted by Sung-Bum Park and Mang Tia in the work "An experimental study on the water-purification properties of porous concrete" [16].Two varieties of large aggregates were utilized in the production of porous concrete for test tubes: 5-10 mm and 10-20 mm, and 3 ratios were used in the preparation of the mixture A/C-aggregate, for each gravels, as follows: 30%, 40% and 50% respectively.The capacity of porous concrete to purify water is analyzed by the amount of organisms attached to its surface, as well as by the amount of phosphorus and nitrogen removed.The amount of organisms is analyzed indirectly by the amount of dissolved oxygen consumed by them.Experimental tests found that the compressive strength of porous concrete is higher when the size of the aggregates and the A/C -aggregate ratio are small.Chemical analysis noted that porous concrete made from gravels with small and high porosity aggregates has a superior ability to remove phosphorus and nitrogen from water.This is due to the large specific surface of the porous concrete in question.How the consistency of the cement and the type of aggregate influence the mechanical and acoustic characteristics of the porous concrete has been studied by experimental tests [17].Porous cement concretes were prepared with the following consistency levels in turn: 80%, 110% and 140% respectively.Aggregates from the following gravels were used in the porous concrete mixture: 8-13 mm and 13-19 mm respectively and light aggregates from the following gravels: 4-8 mm, 8-12 mm and, respectively 12-19 mm.How additives affect the physical and sound-related properties of porous concrete has also been studied.The acoustic characteristics of porous concrete were analyzed by studying the configuration of the layers that make up the test tubes, those test pieces being made of a single layer and 2 layers, respectively.The parameters used to evaluate the test tubes were: porosity, compressive strength and sound absorption coefficient.Based on the results of experimental studies, a porous concrete is created that absorbs noises with an absorption coefficient of approximately 1 with the minimum value of the sound absorption coefficient for 2-layer test tubes greater than 0.60 at a frequency of 400 Hz or more and taking into account the required tolerances [17].A research project has been carried out to create a special porous concrete that is fragmented into small pieces in shock actions, but which retains a resistance reserve.This type of porous concrete is intended for protective walls and buildings that were designed to enhance safety [22].Porous concrete with high compression resistance has been prepared by modifying recipes and compaction techniques.The test tubes made from the proposed mixture were analyzed by mechanical tests on a meso and macro scale, by CT, by microscopic analysis and by X-ray analysis.When making this type of porous concrete, in addition to the large mechanical resistors, the high porosity is essential for the formation of multiple cracks that lead to the fragmentation of the concrete.Experimental tests showed that the degree of compaction and the dimensions of the aggregates have a predominant influence on the mechanical properties of the special porous concrete.The influence of silica dust on the mechanical properties of the proposed porous concrete does not was significant [22].How porosity affects compressive strength was also analyzed by creating a mathematical model that would characterize it.The mathematical model involves the analysis of empirical results and theoretical derivatives [18].The mathematical model for porous concrete is derived from Griffith's Theory.And the results are similar to the results of the experimental tests.The paper showed that the proposed mathematical model can determine the compressive strength of porous concrete depending on its porosity.The paper showed that the proposed mathematical model can determine the compressive strength of porous concrete depending on its porosity.Also through a mathematical model, the phenomenon of carbonation of porous concrete was described.[19].It is based on physic-chemical processes in which the transfer of ions through the carbon-moisteal-calcium dioxide route is modeled.The rate of dissolution of calcium hydroxide and mass equations are modified to could describe more precisely the chemical process.A method of solving the system of nonlinear parabolic equations is proposed, which is called the finite volume method.The paper presents numerical simulations of the porous concrete carbonation process, carbonation is presented at normal speed and higher speed, respectively.In the paper "Investigation of the permeability of porous concrete reconstructed using probabilistic description methods" [23], the authors present the analysis of the spatial distribution of gaps in porous concrete that influence their physical properties such as mechanical resistors or permeability.This is done by C.T. and using lower probability functions.With the help of lower probability functions, different porous concrete test tubes are rebuilt with a variety of ways of distributing the gaps.It is analyzed whether the real test tubes and the reconstructed test tubes show the same behavior.The results of the study confirm that the test tubes rebuilt using the probabilistic optimization process proposed by the authors have, statistically, properties identical to the original models and show material behavior similar to them.Reconstructed test tubes can be used in numerical tests to reduce the number of real experimental tests that consume time and material resources.
In the paper "Effect of CO2 on porous concreteness" [24], the author presents the influence of carbon dioxide on porous concrete.The study is performed by experimental tests, with porous concrete test tubes stored for 30 days in rooms with a concentration of 30% and 10% carbon dioxide, respectively.Other test tubes are kept in the air, where the carbon dioxide concentration is 0.03%.The results of the experimental tests showed that the lowest values of the compressive resistance were obtained in test tubes kept in rooms with a carbon dioxide concentration of 30% and 10%, respectively, for 30 days.In test tubes kept in rooms with high concentrations of carbon dioxide for 1 year, the values of the compressive resistance decreased by less than 10%.The primary element that affects the contraction of porous concrete is the concentration of carbon dioxide followed by air humidity.Porous concrete exposed to air for 1 year at a relative humidity of 50, 75 and 100%, respectively, increased its insignificant volume.The influence of additives on used to optimise the mechanical properties and durability of porous concrete used in paving was also studied [25].The influence of different types of additives on the mechanical strength and anti-exfoliation properties of porous concrete is analyzed.The effects of the additives on the characteristics of the pores, on the permeability, on the mechanical resistors and on the anti-exfoliation properties of the porous concrete were analyzed using C.T. The relationships between permeability, mechanical strength, anti-exfoliation properties and pore characteristics were analyzed.The additives used to prepare porous concrete test tubes were: superplasticizer additive, silica smoke, micro silica, slag, nano silica, graphene oxide and carbon nanotubes.The porosity of pervious concrete varied significantly based on the type of additives used during its preparation.This indicates that the density value of the concrete is not sufficient to characterize its porosity when the cement mortar utilised in its production is altered.The permeability of porous concrete prepared with different additives was more than 131%.The use of suitable additives may improve the mechanical strength of porous concrete, and the effect of the same additive on improving the resistance to compression and bending has not been completely consistent.There was no obvious relationship between the mechanical resistances of porous concrete with different additives and the characteristics of pores, which shows that cement mortar has a greater impact on mechanical strength than on pores.The use of additives can improve the anti-exfoliation properties of porous concrete.The anti-exfoliation properties of slag concrete were relatively good, while in concrete with superplasticizing additive they were very weak.The anti-exfoliation properties of porous concrete prepared with different additives had little to do with the characteristics of the pores and its mechanical strength.Based on the observations made after the experimental tests, the authors recommend the following procedures to improve the anti-exfoliation properties and mechanical strength of porous pavement concrete: choice of suitable additives, reduction of porosity to meet the permeability conditions, choice of water-cement ratio depending on the type of additive [25].In the paper "In-situ pore size investigations of loaded porous concrete with non-destructive methods" [26], the authors present non-destructive tests on porous concrete from the manufacturer Ytong.The volume of pores and their size distribution are analyzed.The following non-destructive methods are used: nuclear magnetic resonance analysis and X-ray computed tomography analysis.The test tubes are subjected to gradually increasing pressures.The results obtained from the 2 non-destructive methods were comparable and complementary.In the case of both non-destructive methods it was observed that the pores in the test tubes decreased by a radius of 0.1 mm when increasing applied pressure.In both non-destructive methods it was observed that small pores increased by a radius of approximately 0.0001 mm when the pressure increased.The results of the CT analysis showed that at high pressure some pores they collapse, and the growth of small pores is not the primary cause of element fracture, but by collapsing pores and remnants of material.
In the paper "Studies on the sound absorption characteristics of porous concrete based on the content of recycled aggregate and target void ratio" [27], the authors present the analysis of the physical and mechanical properties and the sound attenuation capacity of the porous concrete, this analysis being based on the target porosity and the content of recycled aggregates.The aim of the study is to reduce the noise caused by road traffic, rail traffic and activity in residential areas and central areas of cities, respectively, the purpose of the study is to prepare concrete with recycled aggregates from waste from demolished concrete structures.The compressive strength of porous concrete decreased rapidly when the target porosity exceeded the value by 25%, and the content of recycled aggregates was exceeded by 50%.The results of the study showed that the difference between the target porosity and the real porosity of the porous concrete is 1.7%.In the scenario of pervious concrete prepared with reprocessed materials, the noise absorption coefficient has optimal values for porosity of 25%.The amount of recycled aggregates had little influence on the value of the noise absorption coefficient.A porous concrete prepared with recycled aggregates that absorb noise efficiently has the following optimal characteristics: the porosity is 25% and the content of recycled aggregates is 50%.

3.
Modified Porous Concrete Polymer-modified porous concretes are becoming popular in construction due to their improved mechanical properties, durability and sustainability, compared to traditional concrete.Total void ratio, permeability and compressive strength are three important properties to consider [8].The use of polymer latex and polymer powder can improve the properties of the porous concrete.When added to the mix, it can enhance its adhesion, flexibility and workability.These concretes also have higher compressive, tensile and flexural strengths than traditional porous concretes due to the presence of the polymer [8].The possibility of making a porous concrete using aggregates from recycled crushed concrete waste was studied [28].Porous concrete from recycled aggregates has permeability and acceptable mechanical resistors.The optimal mixtures of porous concrete used in the manufacture of test tubes were made, in turn, from ordinary aggregates and recycled aggregates.The following experimental tests were performed: porosity, determination of the permeability coefficient, mechanical tests to determine bending and compressive strength.The effect of the reused materials on the porousness, mechanical strength and permeability of the proposed porous concrete was also analyzed.To improve the mechanical properties of the analyzed porous concrete, polymer powders (butadiene styrene) and latex were introduced into the mixtures.Porous concrete made with reused materials exhibited lower compressive strength when compared to porous concrete made with regular aggregates.The conclusions of the study show that the porosity of concrete with recycled aggregates was higher than that of concrete with ordinary aggregates.The addition of polymers in the concrete mixture led to a small increase in the porosity of the concrete regardless of the type of aggregate used.Also, the addition of polymers led to a significant increase in the compressive strength of porous concrete with ordinary aggregates by 57% and porous concrete with recycled aggregates by 79%, respectively.The preparation of porous concrete with recycled aggregates and the addition of polymers leads to the realization of an acceptable porous concrete with porosity and acceptable mechanical resistors."Investigation on polymer-rubber aggregate modified porous concrete" [29] has a porous concrete prepared with polymer-based aggregates from rubber waste, which is intended for pavements with non-slip material.Concrete made with polymer-based aggregates has been subjected to experimental tests to study its mechanical strength, material curves (stress-deformation), abrasion resistance and impact resistance.The results of the experimental tests showed that concrete with aggregates based on rubber polymers, having the optimal ratio between aggregates based on polymers and mineral aggregates, has a bending strength and a compressive strength greater than porous concrete with ordinary polymer-based aggregates.The impact energy dissipation capacity of porous concrete with materials based on rubber polymers is higher.Also ductility, abrasion resistance and impact resistance of this type of concrete are improved.The porosity and permeability of this type of concrete meet the OGFC standards (Open Graded Fraction Course).Through experimental tests, the study "Thermal conductivity and mechanical properties of porous concrete materials" [30] aims to analyze the influence of the water-binder ratio, replacement of cement with flying ash and incorporation of water-reducing additives on thermal insulation capacity and mechanical strength in porous concrete with a density of 600 kg/m3.It was observed that porous concrete prepared with a water-binder ratio of 0.32, containing 30% fly ash and 0.65% water reducing additive achieved optimal mechanical and thermal performance.Due to this optimal mixture with which the analyzed porous concrete was prepared, the following properties were obtained: the compressive strength measured at 28 days is 4.37 MPa, the water absorption rate is 12% and the thermal conductivity coefficient is 0.116 W/mK.Generally, porous concrete with a density of 600 kg/m3 and cast in a 150 mm layer meets the requirements of mechanical strength and thermal insulation in order to be used as a thermal insulation layer on the circulating terrace roofs.The porous concrete studied is efficient in terms of production costs and can be used in various fields.The effects of the use of pumice as an option for ordinary aggregates were analyzed to improve the mechanical characteristics (compressive, bending, tensile strengths, hardness, roughness) and physical ones (density, different types of conductivity, specific heat) of pervious concrete, by experimental tests.The physical and mechanical properties of porous pumice stone are compared with the results of other experimental studies and with the A.C.I.The usage of pumice stone in the mixing of porous concrete leads to their porosity and to their decrease modulus of elasticity.By using pumice stone, porous concretes with tensile strength greater than those prescribed by the A.C.I. [31]."An experimental study on the hazard assessment and mechanical properties of porous concrete utilizing coal bottom ash coarse aggregate in Korea" [32] analyzes the physical properties and toxicity of aggregates based on coal ash.Also, the mechanical characteristics of pervious concrete with a varied aggregate content based on coal ash are analyzed.In porous concrete prepared with aggregates based on coal ash, their porosity and permeability changed slightly, but the resistance to compression and bending decreased.For an aggregate based on coal ash content of more than 40%, the compressive strength of porous concrete decreased sharply by 11.7-27.1%,and bending strength decreased by 26.4%.As the aggregate based on coal ash content increased, the test tubes were predominantly destroyed by crushing the aggregates and less by crushing the binder or by breaking the surfaces.Improvements such as the incorporation of reinforcement materials or tougher aggregates based on coal ash are needed to use in the preparation of porous concrete.Following laboratory tests, aggregates based on coal ash meet the characteristics of solidity and abrasion resistance imposed by specific rules.Following the leaching test, it turned out that both aggregates based on coal ash and porous concrete prepared with them meet environmental standards.A study that makes a new type of ecological porous concrete that is prepared mainly with industrial by-products was treated in "A novel eco-friendly porous concrete fabricated with coal ash and geopolymeric binder: Heavy metal leaching characteristics and compressive strength" [33].When preparing the new type of porous concrete, bottom ash from coal was used as an aggregate, and as a geopolymer binder.The new type of porous concrete has been subjected to experimental tests, analysing the compressive strength and disposal capacity of heavy metals (heavy metal leaching).Experimental results showed that the concentrations of heavy metals removed from the ash in porous concrete were below the values established as evaluation criteria.Geopolymers used as binders prevented the diffusion of heavy metals from ash.Based on the experimental results, an empirical formula was created by which the relationship between the porosity of the new type of concrete and its compressive resistance is expressed.The study concludes that porous concrete made with ash and geopolymer is able to efficiently retain heavy metals as solidified / stabilized products.Light porous concrete can be prepared using only solid residues.The purpose of this type of concrete is to improve the compressive strength in the first days after commissioning and to reduce the consumption of resources during the preparation of the mixture as well, can be put into operation in a short time [34].This type of mixture was obtained by sintering (process of gluing metal, ceramic powders, etc. following their heating and pressing) the following substances: aluminum powder, flue gas desulphurization gypsum, carbide slag and red mud.The result was a cement material, which was then mixed with other industrial residues, such as fly ash, thus obtaining the paste for light porous concrete that can be put into operation quickly.The raw material used in the preparation of this type of porous concrete comes only from industrial residues.The results of the experimental tests showed that light porous concrete from industrial residues has a minimum thermal conductivity of 0.15 W/mK.The compressive strength measured at 28 days is 3.57 MPa for light porous concrete from industrial residues with a density of approximately 600 kg/m 3 .The compressive strength measured at 4 hours is 1.31 MPa, and the one measured at 1 day is 1.57MPa.These values are higher than the compressive strength at 28 days of ordinary light porous concrete.In conclusion, lightweight porous concrete prepared from industrial residues has a smaller impact on the environment than slightly obscured porous concrete [34].The paper [35] presents a prototype of bio-receptive porous concrete covered with vegetation that is subjected to heat transfer, ventilation and air conditioning tests, using water as an energy transfer medium.The coils for energy transfer were evenly distributed in a cylindrical formwork.At the hardening of the porous concrete poured into the respective formwork, a plant of the species Lolium perenne was sown, which was hydroponic irrigated and increased for 60 days.The cylindrical porous concrete test tubes covered with vegetation was connected to an air duct, air from 3 centrifugal fans.Experimental tests were performed on the test piece in which it was heated, cooled, humidified and dehumidified to determine its heat transfer capacity.The maximum heat transfer capacity of the test piece for heating was 238.8±4.1 W, and for cooling was −116.65±7.99W. The maximum humidification capacity was 3.42±0.34g•kg −1 , and the dehumidification was -9.04 ± 0.9 g•kg −1 .Porous concrete with vegetal layer showed a passive dehumidification capacity of − 4.57 ± 0.22 g•kg −1 without the need for other energy sources.The energy-free dehumidification capacity of porous concrete with vegetal layer shows the tendency of the vegetation layer to neutralize extreme atmospheric conditions.Experimental results showed that there is a new scope of green infrastructure, demonstrating the ability of porous concrete with a vegetal layer to control environmental conditions.Also, porous concrete with vegetal layer can be applied to the hydroponic growth of plants.

4.
Conclusions The use of porous concrete reinforced with polymers can potentially contribute to the research objective of reducing pollution and waste in the construction industry.Porous concrete allows for water to infiltrate the surface, which can help to reduce stormwater runoff and prevent flooding.This can help to protect nearby bodies of water from pollution and reduce the demand for traditional drainage systems.Additionally, reinforcing the porous concrete with polymers can increase its durability and strength, which can reduce the need for frequent repairs or replacements.This can help to reduce the amount of materials that are wasted during construction and minimize the environmental impact of construction activities.Polymer-modified porous concrete is becoming increasingly popular in construction due to its improved properties and sustainability.The addition of different types of polymers to the pervious concrete mix can significantly enhance its mechanical properties, including its compressive strength, permeability, and total void ratio.Polymer-modified porous concrete has a higher compressive, tensile, and flexural strength compared to traditional porous concrete due to the presence of the polymer.The polymer optimizes the adhesion, flexibility, and workability of the concrete, which can contribute to the overall durability of the structure.Synthetic fibers, steel fibers, glass fibers, and natural fibers are commonly used and have been tested for reinforcing pervious concrete.These fiber types have been extensively studied and applied to enhance the mechanical properties and performance of pervious concrete in various applications.Extensive research and testing have been conducted on the performance of these fiber types in pervious concrete, considering factors such as fiber dosage, length, and distribution.The selection of the most suitable fiber type depends on the specific project requirements, desired performance objectives, and environmental considerations.The aim of reducing noise caused by traffic and activity in residential areas and city centers is an important research objective, as excessive noise can have negative effects on human health and wellbeing.Using recycled aggregates from waste from demolished concrete structures to prepare new concrete can contribute to this objective in several ways.However, it's important to note that the use of polymers may have its own environmental impact, depending on the type and source of the polymer.Therefore, it's important for researchers to carefully consider the environmental implications of any new materials or processes being developed, and to ensure that they are truly environmentally friendly and sustainable.