materials Article Analysis of the Physicochemical and Mineralogical Properties of the Materials Used in the Preparation of Recoblocks María Neftalí Rojas-Valencia 1, *, José Alberto Lopez-López 1 , Denise Yeazul Fernández-Rojas 1 , José Manuel Gómez-Soberón 2 and Mabel Vaca-Mier 3 1 Institute of Engineering, Coordination of Environmental Engineering, National Autonomous University of Mexico, Av. Universidad, 3000 Mexico City, Mexico; JLopezLo@iingen.unam.mx (J.A.L.-L.); yakult2007@hotmail.com (D.Y.F.-R.) 2 Department of Architecture Technology, Barcelona School of Building Construction, Polytechnic University of Catalonia, Av. Doctor Marañón 44-50, 08028 Barcelona, Spain; josemanuel.gomez@upc.edu 3 Department of Energy, Metropolitan Autonomous University- Azcapotzalco, 180 San Pablo Ave, 02200 Mexico City, Mexico; mvm@azc.uam.mx * Correspondence: mrojasv@iingen.unam.mx; Tel.: +52-55-5600-8663  Received: 19 July 2020; Accepted: 9 August 2020; Published: 17 August 2020  Abstract: The construction sector generates 14,000 t/d of construction waste in Mexico City, these materials do not have real applications and end up accumulating in landfills. This work, the objective of which was to analyze the physicochemical and mineralogical properties of soil and construction waste used in the manufacture of Recoblocks, is divided in five stages. First, the excavation material was submitted to field tests. Physical and chemical tests were then carried out on construction waste. Subsequently, the optimal mixture for making Recoblocks was determined. Next, Recoblocks were evaluated and compared with blocks made with water only, without mucilage of Opuntia ficus, and finally a feasibility study was performed. The X-ray diffraction study showed the presence of plagioclase, minerals that improve bending resistance, hardness, durability, as well as resistance to stress in a material. Compared to blocks manufactured without mucilage, the use of Opuntia ficus mucilage increased the compressive strength of the material by 59%, as well as the erodibility. Recoblocks are an environmentally friendly option because they are based on recycled materials, dried under the sun, which eliminates the use of brick oven. The production cost per unit is just USD 0.19, so it is a viable option as a building material. Keywords: excavation material; mucilage; construction waste 1. Introduction For centuries, the construction industry has consumed a significant amount of natural resources; actually, it is one of the main waste generators. It is estimated that more than 10 billion tons of construction and demolition waste are generated in the world [1]. China reported 600 million tons of construction waste in 2017, representing 30% to 40% of the total amount of urban garbage [2]. The European Union estimated that 820 million tons of construction and demolition waste were generated, corresponding to 25–30% of all waste produced in Europe [3,4]. In America, Canada produced more than 9 million tons in 2015 [5]. In total, 548 million tons of construction waste were produced in the U.S.A. at the same year [6]. In Brazil the estimated production of construction waste were more than 70 million tons per year [5]. In Mexico, 6,111,000 tons of construction and demolition waste were generated per year in the period from 2006 to 2012, the latest year for which data are available [7]. Materials 2020, 13, 3626; doi:10.3390/ma13163626 www.mdpi.com/journal/materials Materials 2020, 13, 3626 2 of 17 Excavation material, concrete and brick are the main components of this type of waste (43%, 24% and 23%, respectively). As observed in various parts of the world, these wastes have a great recycling potential in the place where they are generated, leading to a reduction of the consumption of natural materials [8–10]. In recent years, it has been shown that recycled materials are increasingly well accepted by consumers in our countries and throughout the world [11,12]. Properly processed the construction and demolition waste, rise to good quality products, for which a market of great potential has emerged. Local prices, the availability and demand of natural aggregates, as well as the economic situation of the country and the development of the construction industry, are important factors that influence the competitiveness and acceptance of recycled aggregates [10,12,13]. In Brazil, this type of recycling began many years ago; however, its development has been slow, in contrast to the situation in the European Union, where about 70% of construction waste should be recycled by 2020 [9]. In countries such as the Netherlands, Belgium, Switzerland and Austria, this goal has already been reached. There is a high potential for recycling and material recovery of construction wastes, which so far is under exploited, the level of recycling varies significantly from 10 to 90% [14]. Waste generation in Mexico increased from 30,733,000 tons in 2010, to 42,102,800 in 2012. For 2019, in Mexico City, 14,000 tons of construction and demolition wastes were generated every day [15,16]. Some of the most important uses to reutilize the construction and demolition waste in the construction industry are in hydraulic bases, cycle’s lanes bases and in the foundation fillings which are the places where you need a large volume of material, strategy that is also benefited by the lower prices of the same. The Mexico City Norm [16] indicates multiple uses that have already been tested in different locations in Mexico City [17]. The recycled aggregates easily comply with the standards to be used as road sub-bases [4,18], as construction materials in new buildings and structures or as concrete filler for reconstruction of hydraulic structures [19]. Such use of concrete waste will reduce the volume of extracted natural resources, decrease the load on landfills, and minimize the logistics costs for the transportation of waste and natural resources [8,20,21]. Concretes made with construction and demolition waste have reached compressive strength 30% greater than concrete manufactured with conventional aggregates [22]. Regarding the prefabricated as dividing blocks, curbs and tubes, authors such as [23,24] have studied these products finding results similar to conventional prefabricated with replacement rates between 40% and 60% [25]. As road base and sub-base materials, the results have been very good when mixed with cement to achieve adequate stabilization [26]. The feasibility of using concrete waste for the manufacture of cold asphalt mixtures without altering the mechanical properties has also been evaluated [27], better behaviors have been observed under conditions of high humidity and temperature [28]. On the other hand, concrete waste has been used as raw material for the production of new products such as high quality coarse and fine aggregates [29], cement floor plates [30], coverage for municipal landfills [31], and fly ash for use as additives in high strength concrete [32], and even with the help of heat treatments for cement manufacturing [33]. It has also been possible to improve properties such as fire resistance and thermal and acoustic insulation [25]. There are few reports as regards its composition, so in this investigation complementary studies will be conducted to obtain additional data on this. To continue promoting the use of construction and demolition waste, this investigation analyzed the physicochemical and mineralogical properties of the materials used in the making of blocks for the construction industry, according to Mexican and European standards. 2. Materials and Methods The procedure followed in this work was divided into five stages. In Stage I, an analysis of the function of the materials used in the elaboration of Recoblocks (blocks manufactured with construction, excavation, logging and mucilage residues) was made. At the same time, a soil mixture Materials 2020, 13, 3626 3 of 17 (excavation material) from Toluca and Cuernavaca, Mexico was characterized to determine its essential physical aspects. The parameters and procedures used for the physical characterization of the excavation material and construction waste are shown in Table 1. Table 1. Characterization of excavation material. Physical Characteristics Procedure Granulometry [34]—Test method for particle size analysis in soils. Characterization of Fines (should pass [34]—Test method for particle size analysis in soils. through No. 200 mesh) Limits of Atterberg [35]—Test method for liquid limit, plastic limit and plasticity index. Density [36]—Test method for specific gravity of soils. Chemical Characteristics Content of Organic Matter [37]—Determination of the content of oxidizable organic matter in a Soil Content of Soluble Salts of a Soil [38]—Determination of the content of soluble salts of a soil. The characterization of construction waste (6.3 mm to fines, called all in one) was carried out in accordance with Table 2. The procedures followed for analyzing the excavation material were also used for determining waste granulometry and density, while the determination of chlorides, sulfates and total sulfur was performed in accordance with the Spanish standard [39] UNE-EN-1744-1-2013. Table 2. Characterization of construction waste (6.3 mm). Physical Characteristics Procedure Granulometry [34]—Test method for particle size analysis in soils. Density [36]—Test method for specific gravity of soils. Chemical Characteristics Chloride Content Soluble in Water by [39]—Tests to determine the chemical properties of aggregates (part 7). Volhard’s method Sulfate Content Soluble in Water [39]—Tests to determine the chemical properties of aggregates (part 10). Total Sulfur Content [39]—Tests to determine the chemical properties of aggregates (part 11). In this same stage, the Recoblocks were evaluated and the results were compared to the results obtained from blocks made without mucilage. The mucilage of cactus is made up of high molecular weight carbohydrates and contains mainly two organic natural polymers: amylase and amylopectin. The amylase is forming a helical chain that in solution has the ability to form films that when drying have high rigidity; while amylopectin, like any high molecular weight compound, has high viscosity but is highly soluble in water. Then, both carbohydrates combined and being in aqueous solution can form layers with different mechanical properties that offer cohesion characteristics and can be used to join materials [40]. The results obtained show that the cactus mucilage improves, in general, the characteristics of the compressed earth blocks due to the reduction of porosity related to a change in the permeability of the solid. The effect of Opuntia ficus mucilage on permeability appears to be due to an inhibition in the interaction between water and the solid that does not allow the liquid to rise due to capillarity. The results indicate that the use of Opuntia ficus mucilage in Recoblocks increased the compressive strength of the material by 59% compared to blocks that were manufactured without mucilage. The presence of the mucilage also improved the erosion resistance of the blocks in which water penetration is only half of the penetration of the blocks without mucilage. The above can be attributed to the impermeability provided by the presence of the cactus mucilage. These results have been tested in the Engineering Institute laboratory and in other national and international laboratories. Other researchers have found that compressed earth blocks significantly increase dry and wet compressive strength up to 61.5 ± 4.6% [41]. In Stage II, X-ray fluorescence and X-ray diffraction studies were conducted on the excavation material and construction waste. Materials 2020, 13, 3626 4 of 17 2.1. X-ray Fluorescence Spectrometry X-ray fluorescence is a technique that allows the identification of chemical elements from the emission of secondary or fluorescent X-rays from a sample that has been exposed to the irradiation of primary X-rays [42]. The different energy states that are unique to each atom allow to determine the elementary composition of a sample with an intensity graph, where each element is identified by a distribution of characteristic energy peaks [43]. For the present work, an analysis of major elements in a molten sample was performed with a sequential X-ray spectrometer (Siemens SRS 3000, USA), using a 10% dry sample concentration. The calcination loss was determined by heating 1 g of the sample at 950 ◦ C for two hours and calculating the mass difference. 2.2. X-ray Diffraction of Excavation Material and Construction Waste X-ray diffraction is a technique that identifies the minerals present in a sample from the X-rays diffracted by the crystals. Since each crystalline structure is unique for each mineral, this implies that diffracted X-rays are also specific for each mineral, permitting to determine the presence of certain minerals in a spectrum [43]. An X-ray diffraction analysis was made to determine the mineralogical composition of the samples using a double-load aluminum sample holder, as well as an EMPYREAN diffractometer (Malvern, United Kingdom) equipped with a Ni filter, fine copper pipe lamp, graphite monochromator and PIXcel3D detector. The measurement was performed in a 2θ angular range from 5◦ to 80◦ with a “stepscan” of 0.003◦ and an integration time of 4 s per step. The samples were previously crushed and homogenized with a mortar and sifted through a 200 mesh (<75 microns). Stage III of the project consisted of determining the optimal mixture for making Recoblocks. After performing field tests to determine the characteristics of the excavation material, and based on previous studies [15,44,45], preliminary material mixtures were proposed in order to observe their behavior and determine the optimal conditions for making Recoblocks. Excavation materials obtained from Toluca, State of Mexico and Tlayacapan, Morelos, with a granulometry of 6.3 mm to fines, were mixed with virgin soil in a 60 to 40 ratio. Starting from an optimal mixture obtained from the design of experiments, the optimal mixture for the production of Recoblocks was made up of 66% excavation material (soil mixture), 30% construction waste 6.3 mm and 4% felling waste. In addition, water-mucilage material (3:1) equivalent to 20% of the dry weight of the mixture was added for moistening purposes. To carry out the test, the materials were weighed (with an industrial mixer Tecnoadobe brand, and then dry-mixed for five minutes). For the mixture was added approximately 1.5 L of mucilage, the criterion for this quantity is set until the mixture is moist and moldable by hand, and small Recoblocks were molded, and dried during 48 h. After drying, each block was submitted to compression to determine its resistance. 2.3. Description of the Statistical Design of the Experiment The experimental design for the present investigation was of one factor with two random levels, because its purpose was to evaluate the influence of mucilage on Recoblock compared to blocks made without mucilage. To determine the number of experimental units, the two proposed levels were considered: Recoblock and mucilage-free block. Based on the applicable regulations, five repetitions were made for each response variable: compressive strength, maximum initial water absorption, compressive strength after exposure in the weathering chamber, and erodibility. Thus, multiplying five repetitions by four response variables, by two levels, a total of 40 experimental units was obtained. because its purpose was to evaluate the influence of mucilage on Recoblock compared to blocks made without mucilage. To determine the number of experimental units, the two proposed levels were considered: Recoblock and mucilage-free block. Based on the applicable regulations, five repetitions were made for each response variable: compressive strength, maximum initial water absorption, compressive Materials 2020, 13, 3626 5 of 17 strength after exposure in the weathering chamber, and erodibility. Thus, multiplying five repetitions by four response variables, by two levels, a total of 40 experimental units was obtained. The result of the experiment for each of the variables was analyzed with the software GraphPad Prism 6,6,performing performing thethe unpaired unpaired two-tailed two-tailed T-analysis T-analysis of theofproposed the proposed levels levels for eachfor each of the of the response response variables. variables. The following hypotheses were considered: Hypothesis Hypothesis 0 (H0). 0 (H0). ThereThere is no is no difference difference between between treatments. treatments. Hypothesis Hypothesis The treatments 1 (H1). 1 (H1). are different The treatments from each are different from other. each other. 2.3.1. Block Making Procedure 2.3.1. Block Making Procedure The fresh block was weighed and dried in the shade at temperature ambient for 3 days to avoid The fresh cracking. Then,block it waswas weighed placed insideand thedried dryerinand theits shade at temperature weight ambient was monitored, for 3chart see flow daysintoFigure avoid cracking. Then, it was placed inside the dryer and its weight was monitored, see flow chart in Figure 1. 1. Figure 1. Block Block making making procedure. 2.3.2. Equipment 2.3.2. Equipment Used Used in in the the Making Making of of Recoblocks Recoblocks As mentioned As mentionedearlier, a block earlier, molding a block machine molding and a solar machine anddryer are necessary a solar for manufacturing dryer are necessary for Recoblocks. They are described below: manufacturing Recoblocks. They are described below: 2.3.3. Block Molding Machine The Tecnoadobe TA-100 block molding machine is a manual machine for manufacturing compacted earth blocks. According to the technical data sheet, the gross weight of the equipment is 180 kg and its operation requires 3.50 m × 1.50 m of floor space and 2.50 m of ceiling height. It is made of high quality steel and covered with two-tone baked electrostatic paint. 2.3.3. Block Molding Machine The Tecnoadobe TA-100 block molding machine is a manual machine for manufacturing compacted earth blocks. According to the technical data sheet, the gross weight of the equipment is Materials 2020, 13, 3626 6 of 17 180 kg and its operation requires 3.50 m × 1.50 m of floor space and 2.50 m of ceiling height. It is made of high quality steel and covered with two-tone baked electrostatic paint. Based Basedononthe themold, mold,the theblock blockisis3030cm cmlong long× ×1515cm cmwide wide× ×1010cm cmhigh. high.With Withthis thismachine, machine,anan average average productivity productivityofof550 550blocks blocksper per day can day canbebeachieved, achieved,according accordingtotothe themanufacturer. manufacturer.Figure Figure2 2 shows the block molding machine. shows the block molding machine. Figure 2. Recoblock molding machine. 2.3.4. Solar Drier Figure 2. Recoblock molding machine. Regarding 2.3.4. Solar Drier the solar dryer, it work with a new design which was constructed from recycled elements such Materials 2020, 13, xas a metal FOR sheet, mirror sheet, support. In order to achieve better sunlight capture, PEER REVIEW 7 of 18 Regarding a metal the solar sheet with dryer, a moving it work mirror with sheet wasaused, new as design can bewhich was seen in constructed Figure 3. from recycled elements such as a metal sheet, mirror sheet, support. In order to achieve better sunlight capture, a metal sheet with a moving mirror sheet was used, as can be seen in Figure 3. Figure 3. Solar dryer for Recoblocks. Figure 3. Solar dryer for Recoblocks. 2.4. Recoblocks Evaluation After 28 days, Recoblocks were submitted to a series of tests as shown in Table 3. Materials 2020, 13, 3626 7 of 17 2.4. Recoblocks Evaluation After 28 days, Recoblocks were submitted to a series of tests as shown in Table 3. Table 3. Recoblocks evaluation tests. Performed Tests Procedure Determination of Dimensions [46] Determination of the Dimensions of Blocks Apparent Dry Density [47] Determination of net and gross dry density Compressive Strength [48] Resistance to compression of blocks Initial Maximum Water Absorption [49] Determination of abortion of water Accelerated Weathering Test Accelerated weathering chamber Erodibility [50] Standards New Zealand The first four tests were based on the method described by Aguilar et al., 2017 [44]. The remaining two tests are described in detail below. 2.5. Accelerated Weathering Test With the purpose of simulating weathering conditions, the Recoblocks were introduced in an accelerated weathering chamber Figure 4 (accelerated weathering chamber. Brand: The Q Panel Co. Model QUV (Cleveland, USA). The chamber worked with the following operating conditions: 4 h of exposure to UV light at 60 ◦ C, 4 h of condensation at 50 ◦ C. A UV-B lamp was used and rotated every 400 h.2020, 13, x FOR PEER REVIEW Materials 8 of 18 (a) (b) Figure Figure 4. Accelerated 4. Accelerated weathering weathering chamber chamber Q-LAB, Q-LAB, model model QUV.QUV. (a) QUV (a) QUV Chamber Chamber with with programmable controller, (b) Placement programmable controller,of(b) the sample under Placement of thestudy, sampleinside underthestudy, QUV inside accelerated weathering the QUV tester. accelerated weathering tester. In the chamber, a 12-min cycle is equivalent to a day under the chosen weather conditions. 2.6. Erodibility(168 h) are equivalent to a year under normal weather conditions in Mexico City. 840 cycles It is 2.6. well known that land-based building materials tend to lose strength and stability when they Erodibility are in contact with water for prolonged periods of time [51]. Therefore, in several studies, spray It is well known that land-based building materials tend to lose strength and stability when they erosion test is used to evaluate the durability of earth blocks [52,53]. are in contact with water for prolonged periods of time [51]. Therefore, in several studies, spray erosion On the other hand, pursuant to New Zealand standard NZS-4297-1998 [50], erodibility is test is used to evaluate the durability of earth blocks [52,53]. established as an additional test for land-based building materials. The test consists of spraying water On the other hand, pursuant to New Zealand standard NZS-4297-1998 [50], erodibility is on one of the faces of a block for an hour or until water penetrates through the specimen. Each 15 established as an additional test for land-based building materials. The test consists of spraying water min, the test is interrupted to check the depth of erosion caused by water in the block. on one of the faces of a block for an hour or until water penetrates through the specimen. Each 15 min, The maximum depth is measured one hour after the start of the test. When water bores a hole the test is interrupted to check the depth of erosion caused by water in the block. through the specimen in less than an hour, the rate of erosion is obtained by dividing the thickness The maximum depth is measured one hour after the start of the test. When water bores a hole of the specimen by the time taken for full penetration to occur. The erodibility index is determined through the specimen in less than an hour, the rate of erosion is obtained by dividing the thickness according to Table 4. of the specimen by the time taken for full penetration to occur. The erodibility index is determined according to Table 4. Table 4. Erodibility indices. Parameter Criteria Rate of Erosion 0 ≤ D ≤ 20 1 20 ≤ D ≤ 50 2 Depth of Erosion D (mm/h) 50 ≤ D ≤ 90 3 Materials 2020, 13, 3626 8 of 17 Table 4. Erodibility indices. Parameter Criteria Rate of Erosion 0 ≤ D ≤ 20 1 20 ≤ D ≤ 50 2 Depth of Erosion D (mm/h) 50 ≤ D ≤ 90 3 90 ≤ D ≤ 120 4 2.7. Standards Applicable to Brick Making In Mexico the construction sector is regulated by the “Organismo Nacional de Normalización y Certificación de la Construcción y Edificación (ONNCCE)” (National Organization for Standardization and Certification of Construction and Building). However, it is important to mention that as regards the use of excavation material and construction waste as primary materials in the manufacture of bricks and blocks, no applicable standards were found for manufacturing and quality evaluation. Because of this, the following standard was considered for this investigation. NMX-C-441-ONNCCE-2013 [53] for non-structural construction parts is a standard that sets the limits of compressive strength and initial maximum water absorption. Table 5 shows compressive strength values. The average compressive strength for construction parts is based on 5 specimens. Table 5. Compressive strength values for Mexican standards. Average Compressive Individual Minimum Type of Piece Configuration Strength (kg/cm2 ) Compressive Strength (kg/cm2 ) Block Solid or Hollow 35 28 Extruded Brick Solid or Hollow 40 32 Artisanal Brick Solid 30 24 Rectangular Face 25 20 Lattice Piece Non-rectangular Face 25 20 Table 6 shows initial maximum water absorption values. Table 6. Initial maximum water absorption values for Mexican standards. Initial Absorption for Exterior Initial Absorption for Interior Type of Material Exposed Walls (g/min) Walls (g/min) Concrete 5 7.5 Extruded or Pressed Clay 5 7.5 2.8. Standards Applicable to Recoblocks Manufacture Internationally, standards for compressed earth blocks stabilized with lime or cement are available. It is important to mention that only the Spanish standard UNE-41410-2008, cited by Esteve, 2016 [54] “Compressed earth blocks for walls and partitions. Definitions, specifications and test methods” considers the stabilization of the material by natural elements. Table 7 summarizes the specifications for water absorption and compressive strength established in various international standards. Materials 2020, 13, 3626 9 of 17 Table 7. International specifications for compressed Earth block [55]. Country Initial Absorption Compressive Strength (kg/cm2 ) Spain No water absorption limits indicated 13.3–50.9 Kenya No water absorption limits indicated >20.4 Cb < 20 g/min, very low capillary absorption Colombia 10.2–50.9 Cb < 40 g/min, low capillary absorption Cb < 20 g/min, very low capillary absorption France 10.2–50.9 Cb < 40 g/min, low capillary absorption Brazil No water absorption limits indicated >20.4 At international level, Spanish Standard UNE-41410:2008 cited by Esteve, 2016 [54] “Compressed earth blocks for walls and partitions. Definitions, specifications and test methods”, establishes the characteristics that blocks must comply with and the tests to determine them. This standard defines a compressed earth block (CEB) like a “piece for masonry generally in the form of a rectangular parallelepiped shape, obtained by static or dynamic compression of wet earth, followed by immediate demolding, and which may contain stabilizers or additives to achieve or develop the particular characteristics of the product”. Finally, in Stage IV, the environmental benefits of the project were analyzed. 2.9. Benefits Economic of the Project An economic analysis of Recoblocks was performed in order to determine the benefits obtained by using recycled materials instead of natural materials. The initial investment and the unit cost of manufacturing Recoblocks were established in order to demonstrate the economic feasibility of this proposal, based on the current dynamic of artisanal brick manufacturers in Mexico. The estimates were based on the following assumptions: the manufacturer owns the land where blocks are produced, and its manufacturing capacity is 20,000 blocks per month. 3. Results and Discussions In this section, the theoretical results of the fusion of the mixtures are presented, showing the physical and compositional properties of the floors and the construction waste. The mechanical or durability properties are shown and finally the special characterizations such as X-ray diffraction or X-ray fluorescence. Table 8 shows the functions of the various materials used to make Recoblocks. Table 8. Functions of materials. Materials Functions (a) Excavation Material Binding material (b) Construction Waste Filler material (c) Wood Waste Prevention of crack formation during drying (d) Mucilage Opuntia ficus Formation of layers that increase material cohesion and permeability 3.1. Physical and Compositional Properties Table 9 shows the results of the characterization of excavation materials and construction waste that were used to make the mixture. With respect to granulometry, it is shown that the major minerals in the materials analyzed are Silts and Sand in the excavation materials, and 93% of sand in the construction materials. The granulometric curve (Figure 5) was constructed by plotting the wet track results, as well as the results of the hydrometer method for fine particles against the opening diameter of the meshes in the case of sieving and the particle diameter for the content of fines. Materials 2020, 13, 3626 10 of 17 Materials 2020, 13, x FOR PEER REVIEW 11 of 18 Table 9. Characteristics of the excavation material and construction waste. According Physicalto the results, 50% of the Characteristics material Excavation passes(Soil Material through No. 200Construction Mixture) mesh and thus, based Waste (6.3 mm on Fines) the Unified Soil Classification Granulometry System classification [55], the excavation Sand = 41%, Silts = 54%, Clays = 5% material can be considered Sand = 93%, Fines = 7% as a fine soil.Characteristics of Fines 50% of material passes through No. 200 mesh NA On theLimits otherofhand, Atterberg in Figure 5, the blackLLcurve = 34.9,represents IP = 11.4 the granulometry limitsNA established Density 2.74 2.66 in the Spanish standard UNE-41410:2008 Chemical Characteristics [55], where it is recommended that the soil used should contain atOrganic least 10% ofContent Matter clay material. 1.076% NA Content of soluble Considering salts in soilsize obtained using the hydrometer method, the excavation material the particle 0.559% 0.0010% < 0.01% Water soluble chloride content [54] from Toluca could Water soluble be considered sulfate content [54] essentially as silt. However, NA for a more precise classification, 0.0351% < 1%it was necessaryTotal to determine Sulfur Contentthe Atterberg limits which resulted [54] NA so the soil mixture could be considered 0.3285% < 1% sandy clay of low plasticity. NA = Not applicable, LL = Liquid limit, IP = Plastic limit. 100 90 Percentage that goes through (%) 80 70 Wet Wat VÍA 60 HÚMEDA Hydrometer HIDRÓME 50 TRO Slime LIMOS 40 Clays ARCILLAS 30 20 10 0 10.000 1.000 0.100 0.010 0.001 Average particle diameter (mm) Figure 5. Granulometric Figure curvecurve 5. Granulometric of theofToluca and Cuernavaca the Toluca excavation and Cuernavaca material excavation mixture. material mixture. The According to thecontent organic matter results,in 50% theofexcavation the material passes was material through No. which 1.076%, 200 mesh and thus, is below the based on the 2% limit Unified indicated in Soil Classification[55]. UNE-41410:2008 System Theclassification [55], theisexcavation excavation material thus suitable material can be blocks. for making considered This as a fine result soil. has noticed to be similar with the results obtained by Bisht and Neupane [56], which suggests On matter that organic the other hand, inwith increases Figure 5, the black the distance andcurve claims represents the granulometry that Organic limits established carbon level greater than 0.8% in the Spanish indicates standard good quality UNE-41410:2008 [55], where it is recommended that the soil used should contain soil. atThe least 10% of clay material. content of soluble salts present in the excavation material was 0.559%, which is below the Considering 2% limit indicated the particle size[55]. in UNE-41410:2008 obtained using the material The excavation hydrometer method, is thus suitablethe forexcavation material making blocks. from Tolucawith In conjunction could be from data considered essentially the literature as silt. However, [17,57–60] for athis indicated that more preciseisclassification, material appropriate it towas necessary to determine the manufacture bricks. the Atterberg limits which resulted so the soil mixture could be considered sandy clay of low plasticity. The organic matter content in the excavation material was 1.076%, which is below the 2% limit indicated in UNE-41410:2008 [55]. The excavation material is thus suitable for making blocks. This result has noticed to be similar with the results obtained by Bisht and Neupane [56], which suggests that organic matter increases with the distance and claims that Organic carbon level greater than 0.8% indicates good quality soil. Materials 2020, 13, 3626 11 of 17 The content of soluble salts present in the excavation material was 0.559%, which is below the 2% limit indicated in UNE-41410:2008 [55]. The excavation material is thus suitable for making blocks. In conjunction with data from the literature [17,57–60] indicated that this material is appropriate to the manufacture bricks. 3.2. X-ray Fluorescence Results of Excavation Material and Construction Waste From the qualitative point of view both samples have the same chemical composition, the major component being SiO2 with contents of 64% and 50% for excavation material and construction waste 6.3 mm fines all in one, respectively. The SiO2 content allows both materials to be classified as intermediate rocks that are mainly constituted by plagioclase, quartz, feldspars and pyroxene. Table 10 shows the results of the X-ray fluorescence analysis. Table 10. X-ray fluorescence of excavation material and construction waste. Component Unit Soil Mixture RC 6.3 mm SiO2 64.463 50.568 TiO2 0.808 0.733 Al2 O3 16.290 13.950 Fe2 O3 4.880 4.635 MnO 0.051 0.077 MgO 1.106 2.580 mass % CaO 3.968 12.503 Na2 O 3.384 2.307 K2 O 1.458 1.311 P2 O5 0.126 0.225 PXC 3.460 11.110 Total 99.994 99.999 The presence of Al2 O3 can be attributed to the ceramics found in both samples, while the greater presence of CaO in construction waste can be attributed to the mortar and cement paste adhered to the bricks [57]. The result of components such as SiO2 , Fe2 O3 are similar as the ones presented by Kim, 2018 [58]. Talking about CaO and Na2 O the results obtained by excavation material and construction waste are higher than the ones presented by Kim, 2018 [58]. In addition to the above, the high contents of 2SiO2 , both in excavation material and construction waste (greater than 50%), fall within the range of 47% to 85% reported in other studies [59,60]. Table 11 shows the results of the X-ray diffraction analysis. These results agree well with the investigations of Bianchini et al 2005 [61], who analyzed different size fractions of recycled fine aggregates by X-ray fluorescence, and determined that there are high contents of calcium compounds in fractions larger than 1 mm. Table 11. X-ray diffraction analysis of excavation material and construction waste. Phases Unit Toluca Soil 6.3 (mm) Plagioclase (Na, Ca) (Si, Al)3 O8 80 68 Actinolite 11 16 Tridymite: SiO2 9 10 Mass % Phyllosilicates Traces - Plaster: CaSO4 2H2 O - 6 Total 100 100 3.3. X-Ray Diffraction of the Excavation Material and Construction Waste The most abundant minerals correspond to plagioclase that are considered primary aggregates within the tricyclic feldspars of Na and Ca. Actinolite and tridymite were identified in smaller amounts Materials 2020, 13, 3626 12 of 17 Materials 2020, 13, x FOR PEER REVIEW 13 of 18 as constituents of intermediate and basic igneous rocks. After feldspars, quartz is the most abundant Materials 2020, 13, x FOR PEER REVIEW 13 of 18 mineralTheinresults the earth’s of thecrust and tridymite chemical is considered microanalysis show thata polymorph of quartz the proportion (SiO of SiO in). all the samples 2 2 The tested The results is results similarof of tothe the chemical the composition chemical microanalysis show that of stone materials microanalysis show that the thatthe proportion abound in theof proportion SiO ofbanks in all all the SiO22 adjacent in thetosamples Mexico samples tested is similar City (dacite tested to andto is similar the composition andesite) of as reported the composition stone of [62]. materials that abound in the banks adjacent stone materials that abound in the banks adjacent to Mexico to Mexico City (dacite and andesite) As regards City (dacite as reported the excavation and andesite) [62]. material, as reported [62]. it is important to mention that phyllosilicates, minerals As associatedregards with the claysexcavation and relevant As regards the excavation material, material, for it is the it is important mechanical important to to mention behavior that that phyllosilicates, of Recoblocks, mention represent lessminerals phyllosilicates, than 1% minerals associated associated with of the mixture, clays and that and with clays relevant is torelevant for say, pure the forclay mechanical behavior represents less the mechanical behavior of than of Recoblocks, 1%Recoblocks, represent of the excavation represent less than material less than1% of1% of the the of mixture, mixture. the Thethat mixture, is tois above that say, to pure corresponds clay say, pure torepresents the result clay less than obtained represents less1%inthanof the the 1% excavation granulometric material of thethe curve ofmaterial of the excavation mixture. excavation of the The above material corresponds which indicates to the that result the obtained fines are silt in the without granulometric the presence curve of mixture. The above corresponds to the result obtained in the granulometric curve of the excavation of clays. the excavation material whichRegarding materialindicates that which indicates the fines the construction are waste that the silt without fines 6.3silt are mm the presence fines without allthe of clays. in one, the presence presence of clays.of plaster can be observed Regarding in a Regarding the smaller proportion construction that can bewaste related 6.3 to mm the fines CaO all content the construction waste 6.3 mm fines all in one, the presence in one, reportedthe inpresence the X-rayoffluorescence of plaster plaster can can[58]. be observed be observed Figures in a smaller in 6 anda smaller 7 showthat proportion proportion the can that diffractograms can be related to of be thethe related CaO to excavation the CaO content materialinand content reported reported in the construction the X-ray the X-ray fluorescencewaste,[58]. fluorescence 6 and[58]. respectively. Figures 7 show Figures 6 and 7 show of the diffractograms thethe diffractograms excavation material of the excavation material and and the construction the waste, construction waste, respectively. respectively. Figure 6. Diffractogram of the excavation material mixture. Figure Diffractogram of 6. Diffractogram Figure 6. of the the excavation excavation material material mixture. mixture. Figure7.7.Diffractogram Figure Diffractogramof ofthe theconstruction constructionwaste waste6.3 6.3mm mmfines finesall allininone. one. Figure 7. Diffractogram of the construction waste 6.3 mm fines all in one. According to the diffractograms, the phases found do not exhibit crystalline behavior because the diffraction According peaks to the are wide with low diffractograms, theintensities, which phases found doisnot typical of low exhibit crystalline crystalline or amorphous behavior because the diffraction peaks are wide with low intensities, which is typical of low crystalline or amorphous [63]. 3.4. Mechanical or Durability Properties Twenty Recoblocks were prepared. In parallel, other 20 blocks without Opuntia ficus mucilage were made Materials for3626 2020, 13, comparison purposes. The results are shown in Table 12, while Figure 8 shows 13 ofthe 17 qualitative results. According to the diffractograms, the phases found do not exhibit crystalline behavior because the Table 12. Results of block evaluation. diffraction peaks are wide with low intensities, which is typical of low crystalline or amorphous phases Test Performed due to components formed Recoblocks in the hydration of concrete and ceramics that haveH 2O-Only been Blocks crushed [63]. Compressive Strength (kg/cm ) 2 25.0 15.7 3.4. Mechanical or Durability Initial Maximum Water Properties Absorption (g/min) 21 33 Erodibility (mm/h) 7.0 14.7 Twenty Recoblocks were prepared. In parallel, other 20 blocks without Opuntia ficus mucilage were made for comparison purposes. The results are shown in Table 12, while Figure 8 shows the Recoblocks qualitative results.showed a 59% greater compressive strength than blocks made without mucilage. Plagioclase improves resistance to bending and impacts, and increase compressive strength, adding hardness, durability and shine toTablea material. Thisoftype 12. Results ofevaluation. block feldspar is used in the ceramic and pottery industry [22]. Moreover,Test Performed only water blocks showed an Recoblocks H2 O-Only Blocks initial maximum water absorption 33 (g/min) lower 2 Compressive than Recoblocks Strength made with(kg/cm ) mucilage 21 (g/min). 25.0 15.7 Finally, in the erosion test, Recoblocks showed a Initial Maximum greater resistance to waterWater penetration 7 (mm/h), compared to the blocks made without mucilage, 21 33 Absorption (g/min) which exhibited a water penetration more than twice as high 14.7 (mm/h). Erodibility (mm/h) 7.0 14.7 (a) (b) (c) Figure 8.8.Qualitative Figure Qualitative results results of compressive of compressive strength strength (a), maximum (a), initial initial maximum absorption absorption (b) and (b) and erodibility erodibility (c), (c), respectively.respectively. Recoblocks 3.5. Economic showed a 59% greater compressive strength than blocks made without mucilage. Viability Plagioclase improves resistance to bending and impacts, and increase compressive strength, An analysis was carried out to demonstrate the economic viability of this project. The production adding hardness, durability and shine to a material. This type of feldspar is used in the ceramic and cost per unit was obtained taking into account the acquisition price of the equipment, as well as the pottery industry [22]. cost of patent, labor and maintenance of the equipment over 5 years. Moreover, only water blocks showed an initial maximum water absorption 33 (g/min) lower Recoblock production cost per unit was USD 0.19, and it is thus a viable building material for than Recoblocks made with mucilage 21 (g/min). Finally, in the erosion test, Recoblocks showed a interior walls. greater resistance to water penetration 7 (mm/h), compared to the blocks made without mucilage, which exhibited a water penetration more than twice as high 14.7 (mm/h). 3.5. Economic Viability An analysis was carried out to demonstrate the economic viability of this project. The production cost per unit was obtained taking into account the acquisition price of the equipment, as well as the cost of patent, labor and maintenance of the equipment over 5 years. Recoblock production cost per unit was USD 0.19, and it is thus a viable building material for interior walls. Materials 2020, 13, 3626 14 of 17 4. Conclusions After submitting construction waste to physical, chemical and mineralogical tests, it was determined that the content of sulfates, total sulfur and chlorides present in construction waste was 6.3 mm, which is below the limit established in the Spanish standard UNE-17441. The use of mucilage Opuntia ficus in Recoblocks increased the compressive strength of the material by 59% compared to blocks made without mucilage. The presence of mucilage also improved the erodibility of Recoblocks with a water penetration only half as high as in the case of blocks without mucilage (7 mm/h). The above can be attributed to the impermeability provided by the presence of mucilage Opuntia ficus. Internationally, the resistance of Recoblocks made with a mixture of soils and Opuntia ficus mucilage meets the minimum resistance levels established in Brazil, Colombia, Spain, France and Kenya. The samples analyzed contain different amounts of calcite, which may represent a potential alkaline reserve that serves to stabilize clay soils, so recycled aggregates should not be considered completely inert. 5. Suggestions It is recommended to use the hydrometer method to identify the presence of clay in the soil used. It is necessary to carry out an evaluation of the adhesion between pieces and mortar, as well as tests on walls built with Recoblocks. It is advisable to use Recoblocks for interior walls. If they are used for exterior walls, a conventional coating must be applied. At international level, it is necessary to develop standards that regulate the manufacture of construction materials with recycled aggregates. A Life Cycle Analysis (LCA) should be performed to show the environmental benefits derived from this construction material. Author Contributions: M.N.R.-V., J.M.G.-S. and J.A.L.-L. (research concept and design); J.A.L.-L. and M.N.R.-V. (data analysis and interpretation); M.N.R.-V. and J.M.G.-S. (writing of the article); D.Y.F.-R. and M.V.-M. (critical revision, correction of the article and editing). All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors express their gratitude to USI -II-UNAM and CONACYT. Conflicts of Interest: The authors declare no conflict of interest. References 1. Wang, J.; Wu, H.; Tam, V.W.; Zuo, J. 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