Viability of a terrace covered with porous concrete paving blocks for coffee bean drying

The success of the coffee activity depends on the beans drying process since it influences the physical and chemical coffee quality, whose result can be good or bad quality beverages. In this sense, the type of terrace has considerable influence on the product’s final quality. Therefore, in this study, ground soil terraces and porous concrete paving blocks will be evaluated, and the experiment was conducted in the city of Cambuquira/MG. For this purpose, porous concrete and compressed earth blocks with dimensions of 50 cm x 50 cm x 10 cm were built, totaling 10 blocks of each type of terrace. The experimental design was in randomized blocks (RB), using cherry coffee, with 10 replications, with a total of 20 plots. For the evaluation of the water infiltration capacity in the porous concrete paving block, a cylinder of 30 cm in diameter was used placed in the center of the porous concrete block, and the lower edges rejoined with cement to guarantee the use of the internal area of the cylinder only. The drying process of coffee on a porous concrete paving block terrace provided better quality both in the beverage and in the reduction of the number of defects in the beans. In the city of Cambuquira, the potential for infiltration and storage of rainwater is 58.8 m3 year-1. Considering a 10-year lifespan, the construction of the porous concrete paving block terrace is economically viable concerning the ground soil terrace, providing gains of up to 15%.


Introduction
Brazil is a country that has favorable climatic conditions for the crop, providing planting from North to South, facing different climates, altitudes, soils, among others, making Brazilian producers achieve different quality standards and unique characteristics to their products.
The culture of coffee, since it was implanted in Brazil in the middle of the 17th century, has acquired considerable economic and social importance, becoming today the biggest exporter in the world scenario. In 2018, national production was approximately 58.04 million bags, representing 36 % of the international market. In the state of Minas Gerais, especially in the southern region, coffee culture is one of the principal activities developed on rural properties. In 2018, coffee production in the state reached about 30.7 million bags, corresponding to approximately 53 % of all national production (CONAB, 2018). 30.0 % to 65.0 % -depending on the maturation stage, to lose water to the environment through evaporation, aiming to achieve a suitable percentage of conservation, from 11.0 % to 12.5 % of humidity (BORÉM, 2008).
As Carvalho (1997) addresses in his study, the coffee quality depends on several factors and processes, such as crop management, pre-and post-harvest, which are essential to achieve a good characteristic for the beans.
According to the same author, artificial drying in terraces is the most used process by producers because it has a lower implantation cost compared to mechanical dryers, but coffee is exposed to climatic factors.
According to the study presented by the authors Santos and Reinato (2017) and Reinato (2006), terraces of asphalt mud and earth present mostly inferior beverages, such as Rio and Riada, whereas the cement and suspended terraces presented coffee beverages with superior qualities, mostly hard drink.
The suspended terrace has an installation price higher than the others, around R$ 38.54 per square meter, and lower durability, whereas the reinforced concrete has a price of R$ 22.30 per square meter, also presenting higher durability. The ground soil terrace has a low starting price of around R$ 2.70 per square meter, but as shown above, it has very low quality, when compared with the others, according to the study presented by Santos (2017).
In the patio made of porous concrete blocks, due to the rainwater infiltration process, it is expected that the humidity on the surface will be reduced and quickly dispersed to the environment, not being transferred to the grain, providing a product of better quality. The possibility of covering the patio for coffee drying combined with the rainwater infiltration for use on the property makes it interesting to use this material in the patio building.
Nowadays, the occurrence of long periods of drought, which are increasingly frequent, reinforces the need to capture and store water. When it comes to the rural environment, water has several usages, such as irrigation, cleaning the property, maintaining herds, and others.
The planet has undergone significant changes in the climate. Salati, Santos, and Nobres (2004) claim that "global warming will soon promote more extreme climate scenarios, with droughts, floods, and heatwaves becoming more frequent". Water is an essential natural resource for sustaining life and the environment. In this sense, all actions aimed at capturing and storing water in rural properties are extremely necessary and important.
In most of the coffee-producing rural properties, large areas are reserved for the drying process, the terraces for coffee drying. These areas are idle most of the time, and they are used only during the coffee harvest period. They could be used in other ways, such as rainwater infiltration, as long as it has been designed for this function. Therefore, there is the possibility of building these terraces with porous concrete paving blocks, which, besides removing moisture from coffee beans, will promote the rainwater infiltration that can be stored and used for non-potable purposes, such as cleaning the yard, corral, coffee washing, and even for irrigation, thus saving drinking water.
Rainwater harvesting occurs by the water infiltration through the pores of the porous concrete being collected by drainpipes and conducted to a storage reservoir. To increase the efficiency of the drainage system and avoid significant losses to the soil, the use of a waterproof plastic blanket is recommended.
Porous or permeable concrete has emerged as a solution in the United States of America in urban drainage, allowing water to infiltrate, reducing runoff. This fact occurs because the concrete presents interconnected empty spaces, as mentioned by Polastre and Silva (2006). Its durability varies from 20 to 40 years, depending on constant repair maintenance, since it is common to block the empty spaces by earth particles and chemical elements dispersed in the environment, such as sulfates, besides its natural degradation (POLASTRE; SILVA, 2006).
Regarding the load-bearing capacity, porous concrete has a lower resistance than conventional concrete, with variations between 3 MPa and 30 MPa depending on the material used. Reinforced concrete has a resistance that can reach up to 60 MPa (ACI -522, 2010).
The concrete permeability varies according to the density of the mixture. The larger the void spaces, the higher the absorption (KIM; LEE, 2010). In this context, tests carried out by Federal University of Rio Grande do Sul -UFRS researchers presented a result of permeability of 0.3 cm s -1 for 1:3 and 0.5cm s -1 for 1:4, demonstrating that the porous concrete permeability is sufficient to capture rainwater since absorption can reach up to 5 mm/s according to the test above (IBRACON, 2014).
Based on the above considerations, this study aims to analyze the feasibility of implementing a terrace for drying natural coffee, using porous concrete blocks as a covering and its influence on the final quality of the coffee drink. The potential for rainwater infiltration and the costs of implementing the terrace covered with porous blocks were also evaluated.

Characterization of the study area
The experiment was carried out in the city of Cambuquira, located in the south of the state of Minas Gerais, whose economy comes from agriculture, livestock, and tourism. According to the Köppen and Geiger classification, the climate is classified as Cwa, with an average temperature of 19.5 ºC and total annual precipitation of 1,470 mm (Climate-Data.org, 2012).

Construction of porous concrete paving blocks
In the construction of the porous concrete paving block, 270 liters of gravel number 1 were used in dry conditions mixed with 3.8 cans of 18 liters of cement, adding a quantity of 33 liters of water, masonry equipment (hoe, bucket, and a trowel).
Initially, the gravel was mixed with the cement until it was homogeneous, and then 33 liters of water were added, making a new mixture until a uniform mass with an appearance similar to the concrete used in civil construction was obtained. After that process, the obtained mass was transported in buckets and placed in frames of 50 cm x 50 cm x 10 cm totaling ten blocks, which were used in the experiment assembly.

Experiment Assembly and Conduction
For the experiment, cherry coffee was used. The experiment was carried out in a randomized block design (RBB) with 2 treatments and ten repetitions each, with a total of 20 plots. The treatments consisted of the disposition of cherry coffee in two types of terraces, ground soil and porous concrete, being distributed a 4 cm layer of cherry coffee.
The variables were subjected to analysis of variance, and the significant ones at the level of 5 % probability were subjected to the Tukey test. Statistical analyzes were performed using the Sisvar software (FERREIRA, 2011).

Evaluation of the presence of defects and the coffee drink quality
The classification of defects is made in a 300-gram sample of raw dry coffee beans, and it is counted in the sample for classification following the Normative Instruction n. o 8 from 2003, which has a rating scale of two to eight respectively and it will be separated according to the defects. Consequently, to rate the defect and remove the impurities and unusual matter present in the sample and then weight on a digital scale, the defect with higher gravity in the sample prevails as black partial black, sour, immature, and broken grain (BRASIL, 2003).
The conventional "coffee cupping" was carried out by an experienced taster, following the procedures required by the Ministry of Agriculture, Livestock and Supply. The analyzes were carried out at Cooperative of Coffee Growers in the Varginha Zone (Minasul), in the city of Cambuquira/MG.
According to normative n.° 8 of the Ministry of Agriculture, Livestock and Supply (BRASIL, 2003), there are currently seven quality scale of the coffee drink, which are Rio Zona, Rio, Riado, Hard, Just Soft, Strictly Soft, and Soft, the Strictly Soft being the one with the best characteristics and all the requirements for aroma and "soft" flavor.

Water infiltration evaluation in porous concrete paving blocks and the potential for rainwater infiltration
To carry out the infiltration test on porous concrete paving blocks, the methodology described in NBR 16416 -Permeable Concrete Pavements (ABNT, 2015) was used.
To start the infiltration test, the porous concrete blocks were pre-wetted, pouring 3.6 liters of water into the cylinder, and registering the time taken for all the water to infiltrate. For pre-wetting times of less than 30 seconds, 18 liters of water were used to perform the test, and the time was measured again. For times higher than 30 seconds in the pre-wetting stage, the amount of water required for the test was 3.6 liters. For both the pre-wetting stage and the performance of the test, it was sought to maintain a constant flow of water inside the cylinder so that a blade between 10 mm and 15 mm was maintained during the procedure. To simulate the impact of moisture present in the porous concrete paving blocks in the infiltration process, a 20 mm rain was simulated by applying 5 liters of water over each block; after 24 hours, the infiltration test was carried out.
The infiltration test was carried out on all porous concrete paving blocks. For this purpose, a cylinder of 30 cm in diameter with a height of 50 cm was placed in the center of each porous concrete paving block, and the lower edges rejoined with cement to guarantee the use of the internal area of the cylinder only. It was calculated the time that every volume of water took to completely infiltrate the block's surface, allowing the calculation of the block's permeability.
The following equation used by Gonçalves and Bandeira (2017) was applied in this study: (1) At which: K: is the infiltration rate given in mm h -1 m: infiltrated water mass, expressed in kg d: internal diameter of the cylinder, expressed in mm t: time taken by the water to infiltrate, expressed in seconds C: SI unit conversion factor, with a value of 4,583,666,000 To evaluate the potential rainwater infiltration in the study area, the average annual precipitation was calculated based on a historical series of daily precipitation between 1988 and 2018, from the weather station known as Fazenda Juca Casimiro, code 02145008, located in the city of Cambuquira, under the responsibility of IGAM-MG, coordinates S 21° 52 '27.12'' and W 45 ° 15' 29.88 '' and altitude of 875 m. Table 1 shows the cost of producing the porous concrete paving blocks. The cost of implementation for the porous concrete paving blocks 10 cm high in the patio building was equivalent to R$ 42.24 per m² in the year 2019. When compared to the costs of setting up a ground soil terrace, this amount is approximately 11 times higher. According to Santos and Reinato (2017), who evaluated several types of terraces, they concluded that the cost of implementing the ground soil terrace at that time was R$ 2.70 per m², equivalent to 6.4 % of the cost of implementing the terrace with porous blocks. In 2019, it would be a value of approximately R$ 3.73 per m², and this value will be considered in the following calculations.

Results and discussions
Although the implantation cost is very high concerning the ground soil terrace, it has the advantage of the possibility of rainwater infiltration, contributing to the environmental sustainability of this resource. Table 2 shows the statistical results of coffee beans quality and defects for the two types of drying terraces. Averages followed by the same letter, on the line, do not differ statistically through the Tukey test, at 5 % probability.

Classification of beverage quality and analysis of physical coffee bean defects
Source: Authors' elaboration (2019).
As shown in Table 2, the ground soil terrace provides lower quality in the coffee drink, as a result of several factors interaction such as the undesirable fermentation process during the drying process. Similar results were also observed by Santos and Reinato (2017).
The best drink was obtained when the coffee beans were dried on the porous concrete paving terrace, a fact that may encourage the implementation of this type of terrace by coffee producers.
Most of the ground soil terrace provided coffee with Riado or Rio drink, that is, grade 2 to 3, except one sample classified as Duro, grade 4. Coffee dried on the porous concrete block terrace produced, in its majority, hard drink coffees, with grade 4, except for two samples that presented drink type Riado, grade 3 and Soft, grade 5.
Most of the dried coffee on a ground soil terrace generated drink of low appreciation value from customers, on average 2.8b and, consequently, a lower market value, concluding that the coffee beans dried on a porous concrete block terrace produced a better quality drink, presenting a statistically better result, an average of 4.0a. Similar results were obtained by Reinato (2006) concerning ground soil terrace, where he concluded that that is the least viable for the drying process.
Regarding the defects found, according to Table 2, the result provided by the classification in relation to the defects of each sample was given by the 'type' that varies from 2 to 8, being classified as 2 the ones of least defects, and as 8 the one of highest number of defects (CARVALHO, 1997).
Coffee beans dried on a ground soil terrace had defects ranging from 5 to 7, with an average of 5.9a. On the other hand, the ones dried on a porous concrete block patio presented defects between 3 and 4, with an average of 3.4b.
Based on these results, it can be concluded that the ground soil terrace has a higher number of defects than the porous concrete block terrace. According to Reinato (2006), the fact that the ground soil terrace has higher numbers of defects is due to the sanitary, higher incidence of fungi and bacteria that deteriorate the quality of the coffee bean, issues that came up at the time of drying, favoring the appearance of burnt and dark grains. Therefore, it is evident that the ground soil terrace does not favor the final quality of the product, generating a devaluation in the price. In this sense, the porous concrete block terrace compared to the ground soil terrace showed better results statically. However, even presenting the best results, the porous concrete block terrace did not obtain the best score for such classification, which is type 2. This may be due to the number of broken grains, due to the terrace that has a rougher surface than the other ones.

Permeability analysis of the porous concrete block
The infiltration test was carried out on all the porous concrete paving blocks used, showing the capacity of water infiltration that passes through the blocks per unit of time.
The results showed that the water infiltration capacity of the porous concrete paving blocks varied from 3,637.8 mm h -1 to 3,960.0 mm h -1 , with an average value of 3,842.8 mm h -1 representing a potential volume of rainwater infiltration equal to 3,842.8 l / m² h -1 .
The result above demonstrates the excellent permeability of the porous concrete block obtained with a 1:3 line, a cemented part for three parts of number 1 gravel, this line and line 1:4 are the most recommended when the objective is the infiltration of water, according to Kim and Lee (2010).

Rainwater infiltration potential by the porous concrete paving block terrace in the city of Cambuquira -MG
Based on the historical series of the meteorological station precipitation known as Fazenda Juca Casimiro, in the city of Cambuquira/MG, the average annual precipitation for the municipality was 1,470.0 mm.
According to Araújo, Tucci and Goldefum (2000), the effective infiltration of water that crosses the porous concrete block through the drainage system is 40 % if the drains are placed on the ground, that is, without the blanket plastic. The remaining 60 % is lost due to evaporation, percolation in the soil, and the non-infiltration of the drainage system.
In this way, considering that a plastic blanket was not used below the porous concrete terrace, of the total precipitated annually, 1,470.0 mm, it would be possible to infiltrate 588 mm year -1 . Considering a terrace for drying coffee with an area of 100 m², it would be possible to capture and store 58.8 m³ year -1 . This volume would be used for non-potable purposes, requiring no treatment, reducing the consumption of drinking water for less noble purposes.

Analysis of the economic feasibility of implementing a porous concrete block paving terrace
Considering a distribution of 50 liters of cherry coffee per square meter of the terrace and one bag of coffee corresponds to 500 liters, 10 m² of the terrace would be needed for each bag of coffee beans. For the analysis of the porous concrete paving blocks terrace implementing feasibility, the costs for the porous concrete blocks production, the drainage system, and a reservoir with a water storage capacity of 20 m³ were considered. The quotations for coffee bags type 4 hard drink and type 6 Riada drink were obtained from the Coffee Growers Cooperative of the Varginha Zone (Minasul), in November 2019, representing the Southern region of the State of Minas Gerais. The average values found were, respectively, R$ 505.00 and R$ 418.00 for bags of coffee type 4 hard drink and type 6 Riada drink. In this way, it was possible to evaluate the expected gain per square meter in each type of terrace for drying coffee.
In the ground soil terrace, the predominant type of drink was the Riada drink, which provides an approximate yield of R$ 41.80 m², whereas the dried coffee in the porous concrete block paving terrace generates gains of R$ 50.50 m², that is, a profit of R$ 8.70 m² concerning coffee dried on a ground soil terrace.
For a 100 m² terrace, R$ 4,224.00 would be spent for the implementation of the porous concrete block terrace, plus R$ 600.00 for the drainage system, and R $1,000.00 for the acquisition of a polyethylene reservoir to store infiltrated water, with a capacity of 20 m³, totaling an implementation cost of R$ 5,824.00. For the ground soil terrace, the costs would be R$ 373.00.
Considering a useful life of 10 years, since the necessary maintenance is carried out, the costs of patios implementation would be paid in the first, for the ground soil terrace and from the second year onwards, for the porous concrete block paving terrace, that is, for the rest of the useful life period, the producer would have 100 % profit. For the ground soil terrace, the gain in the period of its useful life is R$ 41,427.00. As for the porous concrete block terrace, the gain is equal to R$ 44,676.00, a profit of approximately 8 % compared to ground soil terrace, equivalent to R$ 3,249.00.
Based on the potential for water infiltration by the porous concrete paving block terrace for the city of Cambuquira equal to 58.8 m³ year -1 and considering a value of R$ 5.00 per m³ of treated water, which would be used for non-potable purposes (environmentally incorrect) that will no longer be paid, the profit concerning the volume raised would be R$ 2,940.00 in 10 years, totaling in the end a profit for the porous concrete paving block terrace of R$ 47,616.00, corresponding to R$ 6,189.00 above the profit provided by the ground soil terrace, approximately 15 %.

Conclusion
The cherry coffee drying process on a porous concrete block terrace provided better quality for both drinking and reducing the number of defects in the beans.
The construction of the porous concrete block terrace is economically viable compared to the ground soil terrace.
A potential for rainwater infiltration in the porous concrete block area of approximately 3.8 m³/ m².h -1 was identified. In the city of Cambuquira/MG, the volume with the potential to be infiltrated and stored is around 58.8 m³ year -1 .