2.1. Raw material

The investigated clay comes from the region of el Zulia, municipality of Norte de Santander; that area has traditionally been an important construction materials production place; it belongs to the Guayabo formation of reddish and plastic texture.

2.2. Equipment used

The equipment used for the development of this research are: a brand powder diffractometer Bruker D8 Advance model, a X-ray fluorescence Axios Panalytica, a laboratory extruder with empty model New Wave Metal Souza Ltda. with rectangular mold laboratory hammer mill brand Servitech model CT-058, two stoves, the first brand Gabrielli Stainless steel with natural ventilation from a range of 0 °C to 300 °C and the second Dies with electric resistance heating, vibrating screen brand Gabrielli, ASTM mesh sieve set 10 (2000 μm), 30 (600 μm), 60 (250 μm), 80 (180 μm), 100 (150 μm) and 120 (125 μm), plasticity equipment of Pfefferkorn, a brand muffle furnace Gabrielli, digital scale mark 1500 g capacity OHAUS adventurer 0.01 g sensitivity , thermobalance Ohaus MB45 and sensitivity 0.0001 g, hydrometer 152 H and Mitutoyo digital caliper brand and sensitivity 0.01 mm. Figure 1, shows some equipment used.

Figure 1  Equipment needed for the development of research 

2.3. Methods

Raw material for different characterization tests outlined above by international standards 4113-1 NTC, NTC 4113-2, ASTM D422-63, ASTM C323-56, ASTM C324-01 and ASTM C325-81 were prepared.

Sample preparation

The collected in situ sample was tested according to the 4113-1 NTC and 4113-2 NTC procedures, the moisture content was determined and then the drying process was performed at 110±5 °C. After drying the sample, pre-grinding was performed to a size of 10 mm [4]. Then it was crushed in a hammer mill to a size not exceeding 2 mm, in order to obtain a homogeneous and uniform particle size. It was then sieved to a ASTM 10 mesh being prepared for analysis of physical characterization. An outline of the analyses is shown in Figure 2.

Figure 2  Analysis performed in research 

Mineralogical and chemical testing

Determining the chemical composition: The chemical composition was determined by X-ray fluorescence (XRF) according to ASTM standard C323-56, obtaining the percentage of oxides present as shown in Table 1.

Table 1 Chemical analysis of raw 

Determination of the mineralogical composition : The mineralogical composition of the samples was performed by X-ray diffraction (XRD) under working conditions of 0º to 40º degrees 2. Diagrams have been obtained corresponding to the oriented samples, oriented with glycerine and calcined at 550 °C. The diffractogram is shown in Figure 3.

Technological analysis

Sieve analysis by hydrometer 152 H: It was performed on 50 g of sample.

Figure 3 X-ray diffractograms of MI 

Plasticity: the dry milled sample was used to determine the plasticity index using the Pfefferkorn method ⁵. The result is shown in Table 2.

Table 2 Results of plasticity index 

Sieve analysis by dry sieving: the particle size was determined using a representative sample of 100 g, the assay was performed using dry-sieve opening mesh ASTM 10 (2000 μm), 30 (600 μm), 60 (250 μm), 80 (180 μm), 100 (150 μm) and 120 (125 μm) and collector, the results can be seen in Figure 4.

Figure 4  Particle size analysis screening for dry 

Bigot curve

To perform the Bigot curve analysis, test tubes were formed, initially the material was wetted and left to stand for 12 h to homogenize the clay mass. Subsequently, the forming process, which is performed by extrusion, obtaining rectangular specimens of dimensions 11 cm ×1 cm × 4 cm (Figure 5) was started. The drying process was conducted at three temperatures 30±5 ºC; 60±5 °C and 80±5 °C.

Figure 5  Specimens shaped extrusion 

3.1. Study Physical - Chemical

As detailed in Figure 3, from the oriented sample it is observed that the major peaks are associated with kaolinite (K) and illite (I), this matches most clays found in the eastern region of North Santander; Quartz also has contributions (Q) with a principal line at 3.34 Å. The diffraction characteristics of the kaolinitic minerals are present in the diffractogram 7.14; 4.24; 3.57; 2.38 Å; There are also diffractions illite: 4.97; 4.47; 2.45 Å, and it can be precised that the existing carbonate is calcite, which occurs in diffraction 2.28 Å (6(.

Likewise, in this diagram 4, Å line between position 20 to 21 Ɵ appears, when analysing glycol is still listed as line 4 Å but it has taken a bit to a position 21 , it has run completely and has decreased after calcinated at 550 °C for two hours which suggests, without any doubt, the presence of kaolinitic.

It may indicate a significant presence of free silica because the intensity peak of quartz and the high molar ratio SiO₂/Al₂O₃ (2, 7, 8(. According to the results of chemical analysis, which is shown in Table 1, K₂O content of samples reaches a value of 1.63%, a fact that suggests the existence of micaceous minerals in relatively high proportions, although the existence of other layered minerals cannot be ruled out. The Fe₂O₃ content seems to indicate the presence of free iron oxides and the low content of alkali oxides and

alkaline gives the possibility to the clay to generate the glass phase at relatively high temperatures, which is a property of semirefractory, corroborating the data obtained in XRD analysis [2, 9-11].

3.2. Technological study

In the results in Figure 6, it is observed that in the distribution of fractions it is predominant the clay material with a percentage of 68.93%, this is the reason for its high plasticity as shown in Table 2, followed by fraction silty fine-medium 27.73%, it can be concluded that this fraction also helps the development of plasticity; finally, the sand fraction is 3.34% and it is associated with spherical particles with a diameter greater than 2 mm indicating that generally is silty clay samples. The clay fraction is associated with very fine clay minerals that are primarily responsible for the plasticity of the same; so its grain size is suitable for all kinds of ceramic applications.

As shown, this plasticity index 28.3%; This index corresponds to the amount of water needed to reach the clay a plastic consistency, enabling extrusion molding. For practical purposes, it should be above 10%, so they are suitable for the production of structural products, common manufacturing in the region. Besides, above this percentage it will not be at risk of problems during forming material, as may be inappropriate size or cracks in raw parts.

Figure 6 Sample fractions textural 

In cases where the clay has to be mixed with raw materials with coarser particle size materials such as sands or degreasing chamotte or cooked, to decrease the plasticity and improve the compactness thereof, these materials should not exceed 30% by weight, in order to avoid without moldability material becomes as shown in Figure 4 [12, 13].

3.3. Bigot curve

It was performed to observe the behaviour of the material in the drying step, mainly by determining the rate of shrinkage of the sample at different selected temperatures and relating the drying losses with shrinkage percentage dry the shaped specimens (Figure 7). Critical parameters such as relative humidity, air temperature, drying rate but mainly contraction speed, may cause, if not working to optimum values, the formation of internal defects, which are undetectable during the drying cycle but quite problematic in the cooking process ¹⁴. The results obtained for contraction rates in different drying cycles were investigated 0.027%/min to 30 °C, 0,037%/min to 60 °C and 0,036%/ min to 80 °C. The studies performed show a similar behaviour, but concluded that the best performance is obtained at room temperature 30±5 °C, because the speed of contraction is this lower temperature which will have a high risk of breakage during the process ¹⁵.

Figure 7 Bigot curve 

3.4. Gresification diagram

The Gresification diagram allows the determination of the firing temperature and the temperature range, looking forward to annulling the open porosity and the shrinkage remains constant indicating that it generates products of high mechanical strength by the low porosity of the material [16, 17].

In Figure 8, the curve gresification diagram details that the clay has no significant changes to 1050 °C, however above this temperature, an increase occurs in linear shrinkage and a decrease in water absorption, so the sample above 1050 °C and below 1100 °C generates stability in their crystalline components, a minor vitreous phase leads to a decrease in the deformation of the work piece and reduce the chances of defects in them.

This performance at high temperatures is associated with the mechanism of sintering, which densifies the sample and reduces the porosity, this reduction brings benefits such as an excellent vitrification and increased mechanical strength of the product, fundamental characteristics for the production of structural materials. This can be explained by the influence of the kaolinite structure and low content of alkali oxides and alkaline causing a refractory behaviour characteristics observed in Figure 3 and Table 1.

Figure 8 Gresification diagram sample