It is a homogeneous mixture of fine inorganic aggregates, cement, and water, used in construction with wide applications in masonry according to its dosage [10] . According to their cement: sand ratio, they are classified according to their use as shown in Table 1 .

Source: [11] .

Design

Dosages were designed by ASTM C 270-14 (American Society for Testing and Materials) [12] , which specifies that laboratory tests should be carried out in mass ratios. For the experimentation, the ratios 1:3, 1:4 and 1:5 were considered, using as fine aggregate, blue powder and Portland cement type GU by NTE INEN 2380 (Instituto Ecuatoriano de Normalización) [13] .

The amount of water required for the dosage was defined experimentally until the workability of the mixture was achieved, by standard NTE INEN 2518 [14] . Table 2 details the dosage for the mortar for the three ratios and additive concentrations from 0 to 2%. To confirm that the effect of the additive in the mixture is different from that of the cement, a sample with an additional 1.5% binder was added, as shown in Table 2 .

^aAddition of cement instead of additive.

It is a homogeneous mixture of binder, water, and fine and coarse aggregates. It is currently the most widely used material in the construction industry because of its durability, strength, impermeability, ease of production, and economy [11] .

Design

For the design of 1 m³ of concrete, the characterization of fine and coarse aggregates was carried out based on the ASTM C33 [15] , C128 [16] , C136 [17] , C 127 [18] , C 566 [19] , C 29 [20] , C 131 [21] , C 40 [22] , as shown in Table 3 and Table 4 .

As part of the characterization of the allophane, surface area analyses were carried out using the BET technique using a Chemisorption of MICROMETRICS analyzer, following ASTM E11 [23] and using three particle size fractions of 45, 106, and 425 μm, obtained by sieving. Before exposure to the inert gas, a degassing process was applied to the samples to eliminate any surface contaminant.

To complement the structural and morphological characterization of the nanomaterial two electron microscopy techniques were used: the scanning electron microscope, with a Tescan-MIRA 3 model, and the transmission electron microscope, with an FEI-Tecnai Spirit Twin (120 kV) model. These analyses were carried out on samples with the same physical separations used in the BET analysis. Subsequently, a frequency distribution study was performed based on sub-particle measurements observed in the TEM analysis and measured with the Fiji software, in order to identify their size.

Three samples were tested pure allophane and concrete with and without additives, for which it was necessary to reduce the particle size of each of the samples for subsequent sieving to ensure uniformity.

The X-ray diffractometer (XRD) Panalytical-Empyrean of the Laboratory of Characterization of Nanomaterials of the University of the Armed Forces (ESPE) was used.

The result of the interaction between the emitted X-rays and the sample structure gives us a diffractogram that, once interpreted, identifies the structure of crystalline materials and the short-range order of non-crystalline materials. [24] .

For the calculation of the average size of the nanocrystals, first, a peak fitting of the diffractogram was performed using the voigt function of the OriginLab 2024 software and the average crystallite size was determined using the Scherrer equation.

The Scherrer equation is used in crystallography to estimate the average size of crystals in a material [25] from the width of peaks in an X-ray diffraction pattern. The equation is expressed as follows:

$L=\frac{K\lambda }{\beta \cdot \cos \theta }$ (1)

Follow:

L = Crystallite size (nm);

K = Scherrer constant (depends on crystalline form);

λ = X-ray wavelength (Å);

β = FWHM (Full width at half maximum);

θ = Angular position of peaks (Bragg), half of 2-theta 2θ.

For the tests, 10 × 20 cm cylinders were made with the experimental design proposed in point 2.1.2.1, following the ASTM C39 [26] and ASTM C1231 [27] protocol at seven days of curing, using sieved allophane with physical separation of 106 μm. The experimentation was performed in triplicate. It is important to emphasize that the study was carried out only at early ages because previous research showed that the maximum peak of resistance concerning the standard was reached in this period [28] .

Cubes of 50 mm edge were tested according to ASTM D2938-950 [29] , following the experimental design presented in section 2.1.1.1, at the same age as the concrete tests, with allophane from the 425 μm physical separation sieve. They were tested in duplicate.

The 50 mm cubes were tested according to ASTM C1585 [30] , using allophane from the 425 μm sieve of physical separation; at 7 and 28 days of curing. The tests were performed in duplicate.

The results of the BET analysis revealed the presence of nanopores in the material, which was reflected in the high gas adsorption capacity at various pressures during the analysis, indicating an active surface and a significant porous structure.

These findings suggest that nanoporous admixture has the potential to improve the properties of construction materials, such as concrete and mortar, by providing a larger surface area for physicochemical interactions and a higher water-holding capacity [31] . The results obtained for the three types of admixture analyzed are shown in Table 5 .

The incorporation of nanopores into the masonry mix can offer a potential improvement by increasing its specific surface area [32] , which, in turn, increases its capacity to adsorb moisture from the surrounding air, causing the material to maintain a more stable relative humidity inside the structure.

On the other hand, nanopores can modify the capillary structure of the material, which would affect how water moves within it. In addition, they can make it more difficult for water to penetrate deeply [33] . Finally, they can act as water reservoirs during the preparation of the material mix, allowing the allophane to act as an internal curing agent, which would contribute to improving its durability and strength [34] .

The images obtained by SEM analysis reveal the surface morphology of the nanomaterial. Observing for the three types of samples an amorphous configuration without a defined crystalline structure, typical of aluminosilicates. The particles show an irregular and rough shape. There is no observable atomic ordering, as shown in columns (a), (b), and (c) of Figure 1 .

On the other hand, the images obtained in the TEM analysis ( Figure 2 ) show details of the additive at a nanometer scale, evidencing the presence of sub-particles forming conglomerates, found between 3.2 and 3.8 nm and showing a variable density, suggesting a heterogeneous composition. No defined crystalline structures are identified, confirming the amorphous nature of the material. Finally, no porosities were visualized in the samples which is far from the results obtained in the BET analysis, which showed a high surface area.

The non-crystalline nature of the additive could offer multiple advantages in the structural properties of building materials [35] . This structural complexity may result in greater flexibility in interaction with the components of the mixture, which would facilitate their uniform dispersion in the matrix of the building material. These allophane particles are prone to form highly porous micro aggregates [36] .

On the other hand, the characterization of the material allowed determining the presence of nanoparticles that form allophane conglomerates; their external diameter is between 3.2 and 3.8 nm from Fiji analysis, which coincides with previous characterization analyses that indicate that these nanoparticles have diameters between 3 and 5 nm [37] , as shown in Figure 3 .

In a nanoparticle size distribution with positive skew, most nanoparticles are small, but there are some that are much larger. This distribution has a longer tail to the right, indicating that although the average size is low, there are significantly larger nanoparticles that influence the skew.

It should be noted that the porosities described in the BET analysis are not perceptible with the microscopy techniques used, suggesting the presence of a nanoporous structure, which should be found in an estimated pore diameter of less than 1 nm [38] . This characteristic increases the adsorption capacity and the microstructure of the material, which would benefit both its physicochemical and mechanical properties.

Characterization by X-ray diffraction identifies the crystalline phase or phases present in the analyzed sample. The result of the refraction of the beam by a material that has an atomic arrangement in its crystal lattice [25] . The beams

diffract and form certain patterns called fingerprints [39] .

Applying Scherrer’s equation to characterize the crystallography of concrete, the value of the constant K = 0.89 for spherical and porous allophane particles was proposed [37] , yielded a crystallite size of 18.79 nm ( Table 6 ) and for the concrete with admixture a value of 19.79 nm ( Table 7 ), evidencing that there is an interaction by the admixture that is influencing the microstructure of the concrete.

The Scherrer Equation does not apply to allophane, since it does not have a defined crystalline structure. This is because it presents a predominant amorphous area between the peaks and along the diffractogram, according to the XRD study of [40] for quantitative analysis of materials.

The diffractogram ( Figure 4 ) shows reflections of amorphous characteristics because no clear diffraction pattern is found. But it presents three broad bands with intensities of strong, medium, and weak; similar to the allophane samples described in the research of [41] . However, there are some differences due to the impurities in the allophane used in that experiment.

For the diffractograms obtained from the concrete standard sample ( Figure 5 ) and the additized concrete ( Figure 6 ), modifications are observed in some peaks that suggest changes in the crystalline structure.

It may be that the admixture used in the concrete promotes more significant crystalline growth or less crystalline deformation than the standard concrete.

Due to the specific nature of the admixture, allophane being an andosol, a consequence of weathering processes under acidic conditions in humid climates [37] and supergene processes such as tephra-disturbed soils and leached layers, appears as an aggregate of hollow nanospheres [42] , its pores (0.35 - 0.5 nm) and coarse surface area, give it a high adsorption capacity [43] , giving it distinctive characteristics of volcanic soils such as water retention, which depends mainly on the texture and the presence or not of non-crystalline aluminosilicates [44] .

In this way, allophane participates as an internal curing agent, allowing nano-level interactions with the components that make up the concrete. Rheological properties (viscosity/time/resistances) and hydration properties (nucleation and crystalline growth) are crucial during the setting process because of their effects on the final appearance and the strength and durability of the concrete [45] .

Figure 5 and Figure 6 , show that allophane influences the microstructure of concrete, which in turn affects the size and distribution of crystallites and, therefore, could promote a better dispersion of cementitious materials, resulting in a more homogeneous microstructure with larger crystals in the concrete with admixture.

The addition of allophane to concrete results in an increase in compressive strength, as seen in, with the largest increase being 9.4% for the additive concentration of 0.13%, in relation to ( Figure 7 ) its standard sample.

The resistance obtained in the standard samples differs from each other because the tests were carried out in different environmental conditions and times

of the year, which is why the parameter of analysis is the increase in resistance in each test.

Comparing these results with the difference in crystallite size of the sample with additive and the standard, it can be presumed that this effect is due to the nanotechnological influence of allophane in the crystalline structure of the material.

Figure 8 shows that the admixture, at any concentration, decreases the compressive strength, regardless of the cement: sand ratios, the maximum decrease for each ratio being 36.64% for 1:3, 41.15% for 1:4, and 28.78% for 1:5.

However, this compressive strength was evaluated at early ages; therefore, it is not conclusive at older ages. The lowest percentage decreases were found in the 1:5 ratio at low additive concentrations.

Figure 9 shows that, with one week of curing, the absorption behavior is unpredictable, being so, that the curves in the different ratios do not present a single optimum concentration, where the absorption of water by capillarity is prevented in the samples concerning the standard.

On the contrary, at the age of 28 days of curing, it is observed that in the 1:5 ratio, the concentration of 0.5% has the lowest absorption concerning the standard, thus being the dosage with the best-obtained results.

On the other hand, the implementation of a specimen with the presence of cement in substitution of the additive (1.5% C), in all cases presents higher absorption than the standard, which shows that the additive provides properties different from those of the binder powder used.