Showing papers on "Pervious concrete published in 2009"

Temperature Behavior of Pervious Concrete Systems

Abstract: To achieve the permitted stormwater effluent limits required by the Clean Water Act, many best management practices (BMPs) are being utilized to reduce the overall stormwater volume and provide initial pretreatment and pollutant removal. One such BMP is use of portland cement pervious concrete (PCPC), which allows stormwater to pass through the pavement into an aggregate base below to infiltrate. Until now, the temperature response of the entire system (concrete, aggregate base, and natural soil) was not known. Since PCPC is an infiltration-based BMP, once a frost line forms under the base the infiltrating capacity is reduced or eliminated. PCPC also is recommended for use in warmer climates as a cooler pavement alternative to conventional concrete or asphalt. To quantify the temperature behavior of a pervious concrete system, a fully monitored parking lot—composed of half traditional concrete and half PCPC—was constructed at Iowa State University as part of the Iowa Pervious Concrete Stormwater Project. ...

Stereology- and Morphology-Based Pore Structure Descriptors of Enhanced Porosity (Pervious) Concretes

Abstract: In the structural and functional performance of enhanced porosity concrete (EPC) (or pervious concrete) and other macroporous materials, porosity, pore sizes and their distribution, connectivity, and specific surface area and other pore structure features play dominant roles. Analysis of such EPC features is dealt with in this paper using mathematical morphology and stereological techniques. Similar porosity values for the studied mixtures were provided by a morphological method based on two-point correlation and stereological methods based on area and line fractions. Lower porosity was shown by single-sized aggregate EPC mixtures than blended aggregate mixtures. Smaller pore sizes are found to result from higher proportions of smaller sized aggregates in the mixture. There is definition of an effective pore diameter based on a critical size based on opening granulometric density function, a two-point correlation based characteristic size, and pore size distribution of equivalent diameters. The pore sizes of the blended aggregate mixtures lie in between those of mixtures in which single-sized aggregates make up the blend. Good correspondence is seen between the inverse of the specific surface areas of pores and the effective pore diameter and correlation lengths, whereas there is linear relation of the mean free spacing between pores and these quantities. There is comparison of stereology-based three-dimensional pore distribution density indicating preconnectivity and a hydraulic connectivity factor for permeability, and the latter is shown to be a more sensitive parameter through which EPC specimens made with different size aggregates can be distinguished.

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

Abstract: To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0–135.0 MPa and 5 void ratios between 15%–35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm (Nos. 7, 6 and 5 according to JIS A 5001) were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

Evaluation of Pervious Concrete Workability Using Gyratory Compaction

Abstract: Portland cement pervious concrete (PCPC) is increasingly used across the United States, and this has prompted various entities to begin the process of developing standardized test techniques. A major issue with placing PCPC is the inconsistencies in concrete workability between mixtures developed in the laboratory and in the field. It is therefore urgent to properly determine workability of pervious concrete and to ensure that the designed concrete mixtures are suitable for particular compaction methods and field conditions. This paper describes a new test method for characterizing PCPC workability—the gyratory compaction test method. A modified Superpave gyratory compactor (SGC) is employed in the present study. Two PCPC workability parameters are defined from the gyration compaction curve: (1) workability energy index, which describes initial concrete workability and (2) compaction densification index, which describes the resistance of the tested mixture to further compaction. The effects of binder content and water-to-cement ratio as well as effect of concrete mixing time on PCPC workability are studied. Based on the test results, values of the workability parameters for concrete with various degrees of workability are specified.

Field and Laboratory Evaluation of Pervious Concrete Pavements

Abstract: Portland cement pervious concrete (PCPC) is a material of increasing interest for parking lots and other applications. PCPC typically consists of coarse aggregates, portland cement, water, and various admixtures. Similar materials are used for cement-stabilized drainage layers in highway and airport pavements. In this research, in-service PCPC pavements were inspected in the field, and cores were removed in order to investigate properties in the laboratory. Field evaluation methods included visual inspection, two surface drainage measurements, and an indirect-transmission ultrasonic pulse velocity (UPV) test. Laboratory testing methods included void ratio, unit weight, compressive strength, splitting tensile strength, hydraulic conductivity, and direct-transmission UPV. Because it is compacted on the surface with screeds or rollers, PCPC generally has higher strength, lower void ratio, and lower permeability at the surface than at the bottom. Therefore, the properties of the tops and bottoms of core sampl...

Pervious Concrete Pavement: Integrated Laboratory and Field Study

Abstract: Pervious concrete pavement is an environmentally friendly, sustainable paving material for low-volume, low-speed applications. Pervious concrete has been used in warm climates extensively, but its use in freeze-thaw climates has been limited. The Centre for Pavement and Transportation Technology at the University of Waterloo and the Cement Association of Canada, Portland Cement Association, and local Canadian ready-mix producers have partnered to carry out a Canada-wide study to evaluate the performance of pervious concrete. Three test sections have been constructed to date with more planned for the future. The current test sections are located in southern Ontario and southern British Columbia. They are designed to represent all aspects of pervious concrete including but not limited to materials, design mixtures, structural design, potential applications, fresh and cured properties, permeability, environmental strain, filtration capabilities, and maintenance needs and options. A surface distress evaluatio...

VERDiCT: Viscosity Enhancers Reducing Diffusion in Concrete Technology

Abstract: Reinforced concrete structures are susceptible to attack by elements of the environment including chloride and sulfate ions. Past attempts at increasing service life have generally focused on limiting the ingress of these deleterious elements by producing less permeable concrete. Lower water-cementitious material ratios and the addition of fine pozzolans such as silica fume contribute to a denser cement paste matrix. Such mixtures are often classified as high-performance concretes. However, these mixture modifications also typically contribute to an increased temperature rise and increased autogenous shrinkage, both of which increase the concrete's propensity to undergo early-age cracking. Thus, attempts to produce less permeable concrete can be compromised by the existence of only a few through-depth cracks. This work describes a new means of increasing concrete service life that involves the use of carefully selected viscosity modifiers to substantially increase the viscosity of the concrete pore solution and slow down diffusion through the pore solution. Doubling the service life of a specific concrete may be possible by doubling the viscosity of its pore solution. This approach has been termed VERDiCT (viscosity enhancers reducing diffusion in concrete technology).

Previous concrete comprising a geopolymerized pozzolanic ash binder

Abstract: A process for making a pervious concrete comprising a geopolymerized pozzolanic ash. Generally, the process includes mixing a solid aggregate and a geopolymerized pozzolanic ash binder together to form a pervious concrete mixture. Some examples of suitable aggregates comprise recycled carpet, recycled cement, and aggregates of coal-combustion byproducts. The geopolymerized pozzolanic ash binder is made by combining a pozzolanic ash, such as fly ash, with a sufficient amount of an alkaline activator and water to initiate a geopolymerization reaction. The activator solution may contain an alkali metal hydroxide, carbonate, silicate, aluminate, or mixtures thereof. In some aspects, the final concrete forms a solid mass in the form of pavement or a pre-cast concrete shape. The solid mass of concrete may have a void content of between about 5% and about 35%.

Pervious Concrete: Compaction and Aggregate Gradation

Abstract: Pervious concrete is very different from traditional portland-cement concrete (PCC). Therefore, there are open questions regarding the suitability of the current standard concrete testing protocols as they may be applied to pervious concrete. There are unique features associated with pervious concrete that may require special testing considerations. This paper examines the compaction and consolidation of pervious concrete. This study presents cylindrical specimen preparation techniques that will produce laboratory specimens that are similar to the field pervious concrete slab. Additionally, a simple correlation is provided that allows concrete designers to estimate the porosity ofpervious concrete based on its aggregate bulk density when crushed limestone is used. This practical tool saves time when designing pervious concrete mixtures.

The Effect of Curing Regime on Pervious Concrete Abrasion Resistance

Abstract: The current method of curing pervious concrete is to cover with plastic for 7 days, although no studies have been performed to determine if that is sufficient or even required. This paper presents results of combinations of four different pervious concrete mixtures cured using six common curing methods. The surface abrasion of the concrete was tested using a rotary cutter device according to ASTM C944. The results show that the concrete abrasion resistance was improved with a majority surface-applied curing compounds; however the surfaces covered with plastic sheets produced the lowest abrasion levels. A majority of the curing regimes also produced higher flexural strength than the control concrete. There was no significant difference observed in the strength between curing under plastic sheets for 7 or 28 days. Of the surface-applied curing compounds, the best abrasion resistance and highest strength concrete was that applied with soybean oil. The best abrasion resistance and highest strength overall was the mixture containing fly ash and cured under plastic for 28 days.

High SRI Systems For Cementitious Applications

Abstract: High SRI cementitious systems comprising integral concrete coloring admixtures, toppings, dry-shake hardeners, and other cementitious systems are provided. The high-SRI cementitious systems comprise one or more IR reflective pigments and other components to make-up the cementitious system, depending on the application. The high-SRI cementitious systems of the invention may be in the form of mixtures which increase the total solar reflectivity (TSR or albedo) and the Solar Reflectance Index (SRI) of concrete. The high-SRI cementitious systems may be toppings mixed with water for application to existing concrete surfaces, dry-shake hardeners for application to freshly-placed plastic concrete, or the IR reflective pigments may be mixed into integrally colored concrete in various forms, such as conventional cast-in-place concrete, lightweight concrete, pervious concrete and concrete building panels, pavers or masonry units. The topping and dry-shake hardener formulations of the invention may further comprise one or more of cementitious binder(s), graded aggregates, super-plasticizers, one or more pigments selected for improving infrared reflectivity and color composition, and/or optionally other additives, such as dry redispersible polymers or fillers to provide decorative and LEED compliant, highly durable (sustainable) concrete hardscapes and other decorative concrete.

Pervious Concrete and Mitigation of the Urban Heat Island Effect

Abstract: Paved surfaces are large contributors to the urban heat island effect as they absorb and store energy during the day. There are many alternative pavements which are being considered for their environmental benefits with respect to stormwater runoff control. One of these is pervious concrete. Due to the potential insulating capability of its void structure it is theorized that pervious concrete will aid in abetting the urban heat island, although studies have shown that pervious concrete has a high surface temperature. This study compared pervious concrete of two different porosities to traditional concrete and traditional asphalt pavements. It was found that the surface temperature of the pervious concrete was higher than traditional concrete and could be adequately modeled based on a combination of solar reflectance, the lower mass at the surface and additional surface area caused by its unique void structure. It was found that the base temperature under the pervious concrete pavements remained similar to ‘cooler’ surface applications such as soil and lighter concrete, even with the higher surface temperatures, verifying the insulating capability of the pervious concrete during the daytime heating cycle. The rate of heat transfer for pervious concrete with 23% total porosity was found to be approximately 59% of the rate through traditional concrete for similar circumstances. Using pervious concrete instead of impervious pavement surfaces appears to be a viable method of not increasing urban heat island impacts while also benefiting from its stormwater management characteristics.

Laboratory Sample Preparation Techniques for Pervious Concrete

Abstract: With the current environmental and climatic trends that have been observed and studied there has been increasing pressure on different industries and the public at large, to become more environmentally conscious. Interest has risen regarding the use of pervious concrete as an environmentally friendly pavement option, since it allows water to infiltrate directly into the ground water and reduces the need for a stormwater management system. Pervious concrete is in use in the United States, however, research is currently being conducted to determine whether pervious concrete is suitable for use in cold weather climates. A challenge related to pervious concrete is creating laboratory samples that adequately relate to in-situ conditions. The work outlined in this paper has involved evaluating five methods of pervious concrete sample preparation. The methods included various amounts of rodding and Proctor Hammer blows. Testing of the prepared samples included fresh testing, permeability, air void content and compressive strength. Compressive strength samples were produced for use with either end grinding or sulfur capping as the end preparation method. Pervious concrete has different characteristics than conventional concrete therefore conventional sampling and preparation techniques may not be adequate for pervious concrete. An appropriate sample compaction method should produce a consistent and reliable sample. The method should also produce a sample that replicates the characteristics of pervious concrete in the field. Samples that were placed in two layers with each layer receiving ten blows from the Proctor Hammer proved to be the most to field placed samples and also had the lowest standard deviations. Overall the paper presents a comprehensive evaluation of five test procedures for laboratory preparation of pervious concrete samples.

Mixture Design of Pavement Surface Course Considering the Performance of Skid Resistance and Disaster Proof in Road Tunnels

Abstract: Incidents may arise in road tunnels, in particular at the tunnel entrance and exit. Investigation conducted in the road tunnels in the provinces of Guizhou and Yunnan in China showed that the concrete pavement surface skid resistance decreased rapidly inside the tunnels and was significantly different from that outside the tunnels. Pavement surface skid resistance is one of the most important factors that affect travel safety, in particular wet weather skidding accidents. Countermeasures are necessary to enhance the skid resistance on concrete pavements in tunnels. The writers made an effort to investigate possible pavement surfaces to provide long-lasting skid resistance, including porous concrete surface and open graded friction course (OGFC) surface. Porous concrete was paved directly on the regular concrete pavement and OGFC was paved on the existing surface of concrete pavement to provide sufficient skid resistance. Accelerated abrasion devices have been developed to evaluate the skid resistances of the porous concrete and OGFC, respectively. Regular asphalt materials will burn easily and emit toxic gas in fire, which may reduce the survival rate for tunnel users involved in fire accidents. Fire-retardant asphalt has been developed to reduce the tendency of asphalt materials to burn and reduce emission.

Test Methods for Characterizing Air Void Systems in Portland Cement Pervious Concrete

Abstract: Portland cement pervious concrete is becoming a common tool for stormwater management across the United States. The air void system in pervious concrete is particularly important because of its effect on stormwater infiltration, concrete strength, and long-term durability. However, currently the concrete industry lacks standardized testing techniques for characterizing air void systems in pervious concrete. In this paper a series of air system characterization tests performed during a field placement of pervious concrete is detailed, and the test results are compared. Fresh pervious concrete samples from two delivered mixtures were evaluated using pressure, volumetric, Chace, and air void analyzer air test methods. The hardened concrete samples were tested for water-permeable void content, water permeability, air voids (using ASTM Standard C457 method), and freeze-thaw durability (using ASTM Standard C666A method). Based on the results of the study, determination of air systems for the freeze-thaw protection of pervious concrete is proposed.

Nano photocatalysis porous concrete product and preparation method thereof

Abstract: The invention provides a nano photocatalysis porous concrete product and a preparation method thereof. The nano photocatalysis porous concrete product is prepared by the method comprising the following steps: curing press formed porous concrete for 1 to 7 days, then soaking the porous concrete in nano TiO2 dispersion liquid of which the mass concentration is between 2 and 10 percent for 1 to 5 minutes, and taking out the cured porous concrete to obtain the nano photocatalysis porous concrete product. The nano photocatalysis porous concrete product has the following main advantages: (1) compared with dense concrete, the nano photocatalysis porous concrete product has a larger contact area between the nano photocatalysis porous concrete product and polluted gas or liquid, has high photocatalysis efficiency, and can be applied to air purification treatment or water treatment; and (2) compared with P25, the nano photocatalysis porous concrete product adopts the P25 doped with nano titanium dioxide powder to have higher photocatalysis Nox degradation efficiency.

High-strength fiber pervious concrete road pavement brick and preparation method thereof

Abstract: The invention relates to a high-strength fiber pervious concrete pavement brick and a preparation method thereof. The high-strength fiber pervious concrete pavement brick is formed by stirring, distributing, extruding materials such as single-sized aggregate (quartz sand, broken stones), P.O42.5 cement, modified polypropylene fiber as a reinforcing material, an air-entraining hardening accelerator, and water. The aggregate gradation has no continuity, a large quantity of connecting pores exist in a structure, so the pervious concrete pavement brick is a porous concrete product with a large quantity of non-closed pores inside. During the rain or when water is accumulated on a road surface, the water can successfully permeate into the underground or is temporarily stored in a pervious subgrade along the perforative 'paths' in the pervious concrete pavement brick and then is further drained.

A Lab Study of Photo-Catalytic Oxidation and Removal of Nitrogen Oxides in Vehicular Emissions and Its Fieldwork on Nanjing No. 3 Bridge of Yangtze River

Abstract: This paper reports the results of experiments (conducted on road surface materials) that may effectively reduce the concentration of nitrogen oxide (associated with vehicular traffic) in the air. The performances of Portland cement concrete and bituminous mixtures as carriers of nano-TiO2 for the removal of NO2 are compared. Portland cement concrete was found to be superior to bituminous materials because of its porous microstructure. In the absence of light, the porous concrete specimen adsorbs more NO2 and also forms a higher concentration field of NO2 around the specimen. Even after a significant surface weight loss per unit of area from abrasion, the photo-catalytic oxidation efficiency of the concrete that carried nano-TiO2 remained stable because the nano-TiO2 particles were fixed in the exterior pores and fissures due to permeation. The nano-TiO2 photo-catalyst composite that was placed on the concrete road of the north toll square was found to efficiently reduce the nitrogen oxide concentration and control the air quality in accordance with the China National Air Quality Standard Grade I.

Porous cement road surface made from polymer modified cement and a construction method thereof

Abstract: A porous concrete road surface structure made from polymer modified cement and a construction method thereof are disclosed. The structure successively comprises a bottom layer, a bonding layer, a porous concrete layer and a surface treatment layer. The bonding layer is located on the bottom layer, and the porous concrete layer on the bonding layer is prepared through paving, leveling and jolting a composition mixed from broken stone, sand and a slurry mixture of polymer modified cement. The addition of polymer promotes bonding of granular materials with the slurry mixture tightly, the use of the bonding layer makes the road surface structure and the bottom layer form an integral body, and the road surface structure has high strength, good crack resistance, water resistance, ageing resistance and corrosion resistance; the use of an intermittent or single graded of particles results in large pores, makes the road surface water-penetrating, decreases noise and amount of the polymer; and, the surface treatment can improve markedly surface properties and its use according to the application can make the porous concrete layer has rigid or flexible characteristic. The porous concrete road surface can be paved, leveled and jolted by paving machine or manual labor.

Development of pervious concrete

Abstract: In many developed countries, the use of pervious concrete for the construction of pavements, car parks and driveways is becoming popular. In order to develop material specification for pervious concrete, it is necessary to conduct testing to evaluate the performance of this new type of high-performance concrete. In addition, carbon dioxide emission from Portland cement production is significant and contributes to global warming which leads to undesirable climate change. Therefore, it is necessary minimise the use of Portland cement in pervious concrete mixes by partially replacing the cement with industrial by-product, such as fly ash and slag which have been used successfully as supplementary cementitious materials in structural concrete mixes. The pervious concrete is produced by using conventional cementitious materials, aggregates, and water. This concrete is tested for its properties, such as density, porosity, compressive strength, water permeability and drying shrinkage. The most important property of pervious concrete is its water permeability. Currently, there is no standard experimental procedure to determine to this property. A method was therefore developed to determine the water permeability. Fly ash is used as a supplementary cementitious material to partially replace Portland cement in pervious concrete mixes up to 50% by weight. To improve the acceptance of pervious concrete, it is necessary to improve the surface texture. Due to the rough surface texture and bigger void content, it may be difficult for pervious concrete for wide acceptance by the construction industry. Therefore, fine textured pervious mortar is produced using cementitious materials, aggregate and water, and its properties are investigated. New type of pervious pavement, a combination of pervious concrete and pervious mortar, is developed and its properties are studied. Pervious concrete having density around 1800 kg/m3 shows the following properties, porosity 0.32 to 0.36, 28-day compressive strength between 5.7 MPa and 10.1 MPa, water permeability between 9.2 mm/s and 17.3 mm/s, and 56-day drying shrinkage between 470 and 600 microstrain. The properties of pervious mortar having 0.35 water/cement ratio with hand compaction are as follows; density of 1690 kg/m3, porosity of 0.34, 28-day compressive strength of 5.8 MPa, water permeability 2.6 mm/s, and 56-day drying shrinkage of 490 microstrain. Combination of pervious concrete and pervious mortar is tested in density and water permeability. The density is around 1750 kg/m3, while the water permeability between 2.3 mm/s and 3.0 mm/s. Further investigation on the development of this system to have adequate water permeability, strength and durability is recommended.

Fuzzy set approach to condition assessments of novel sustainable pavements in the Canadian climate

Abstract: Since the use of pervious concrete pavement structures (PCPSs) is essentially still in the trial stage in Canada, long-term and quantitative pavement condition data are not available. The existing ...

Pervious concrete composition

Abstract: The invention relates to pervious concrete compositions containing hydraulic binder, filler and polymer, characterized in that the polymer present is a vinyl acetate-ethylene-copolymer having a glass transition temperature Tg of ≦20° C.

A model for reactive porous transport during re-wetting of hardened concrete

Abstract: A mathematical model is developed that captures the transport of liquid water in hardened concrete, as well as the chemical reactions that occur between the imbibed water and the residual calcium-silicate compounds residing in the porous concrete matrix. The main hypothesis in this model is that the reaction product—calcium-silicate hydrate gel—clogs the pores within the concrete, thereby hindering water transport. Numerical simulations are employed to determine the sensitivity of the model solution to changes in various physical parameters, and compare to experimental results available in the literature.

Experimental Study of Pervious Concrete on Parking Lot

Abstract: In order to resolve the runoff of rainwater resource, to prevent the spoliation of ecology, and to reduce the effect of heat island, the search for a suitable mix design of the pervious concrete for Taiwan is not a trivial issue. The main purpose of this study is to find the suitable pervious concrete mix for pavement engineering. The two experiments included in this study are: (1) test the suitable mix design of pervious concrete; and (2) test certification in the field construction of pervious concrete on parking lot. Pervious pavement composed of 8-in surface layer (pervious concrete) and a 4-in base layer (gravel) were made. The results showed that the compression strength of the two pervious concrete core specimens from test certification in the field construction (parking lot) exceeds the ordinary concrete structure specification (175 kg/sq cm). The field permeability test for the parking lot is about 1,000 ml/15 sec. The water penetration of the above pervious concrete is very good and no cracks were present on surface. Therefore, it is an environment-friendly material for pavement.

MnROAD Cell 64 Pervious Concrete: Third Year Performance Report

Abstract: This report evaluates the first year performance of the Pervious Concrete test cell #64 located in the parking lot on the south side of the MnROAD pole barn. Performance measures utilized for this report include examination of stress-strain response through loading from the 80 kip MnROAD truck and Falling Weight Deflectometer (FWD). The FWD deflection basins were compared to those obtained for normal concrete of similar thickness design. The second performance measure was the vibrating wire strain gauge sensor response. Elastic modulus values were computed from the sensor data. In addition, petrographic analyses of cores taken from the test pad and pavements were performed to determine the macroscopic and microscopic characteristics of pervious concrete pavement after the first year. Furthermore, a surface rating of the pavement was performed to corroborate petrographic and freeze-thaw data in order to ascertain the cause of any structural anomalies within the pervious concrete structure. Overall, the pervious concrete cell #64 is performing well after its first year. Normal sanding and salting operations do not appear to have impacted the pore structure within the pervious concrete to date. However, a more quantitative method of measuring flow through the cell and base materials is needed before a final conclusion can be made about the enduring ability of pervious concrete to pass water. Such a quantitative flow measurement method is currently under development. The structure of the pervious concrete cell #64 remains strong after a year of FWD/MnROAD truck loading and normal usage by vehicular movement over the driveway. Microcracking observed from petrographics does not appear to be worsening. Spalling and raveling conditions appear to have stabilized and are surficial in nature. This report concludes that pervious concrete is performing well in cell 64, and with continuous monitoring there will be greater confidence in more low volume applications.

Mix Design of Pervious Recycled Concrete

Abstract: Rules and parameters of mix design for pervious recycled concrete were proposed. Making use of proportioning mix method for stone matrix asphalt (SMA) and open graded friction course (OGFC), volume indexes including volume of voids( VV ), volume of cement paste ( VP ) as well as percent air voids in coarse aggregate(VCA ) can be seen as key parameters guiding for mix design. Mix design procedures for pervious recycled concrete were then put forward. Both compressive strength and water seepage velocity were put forward as verification indexes. A practical mix design example was given and the compressive strength and VV test result show that the new mixing design method for no-fines pervious recycled concrete or conventional pervious concrete is practical and feasible.