Influence of Laminated Expanded Clay Proportion on Mortar Properties

Abstract

Mortar is widely used in civil construction. The inclusion of expanded clay as a lightweight aggregate reduces the density of mortar, enabling lighter structural elements and potentially lowering material and energy requirements during construction. This research aims to produce lightweight mortars by partially replacing fine aggregate with proportions of expanded clay. Six mortar formulations were prepared with varying proportions of expanded clay. The constituent materials of the mixtures and the mortars were characterized according to regulatory prescriptions. The results indicated that the increase in the replacement of fine aggregate with expanded clay reduced the consistency and density of the mass in the fresh state. No significant differences were observed in water absorption by immersion among the mortars in the hardened state. Regarding mechanical tests, most mortars’ tensile strength in bending remained stable. On the other hand, compressive strength decreased. The tensile adhesion was also reduced with the incorporation of expanded clay. After exposure to sodium sulfate solution, all tensile strength results in bending improved. The coefficient of the constructive quality indicated that the ideal replacement formulation is 20% expanded clay. These mortars represent a viable technical alternative, complying with current standards and contributing more efficiently and sustainably to civil construction.

1. Introduction

The construction industry is critical in Brazil, significantly influencing the country’s economic and social development. The growing demand for housing, infrastructure, and commercial enterprises drives the use of mortars in various applications. However, despite being widely used, traditional mortars are considered fragile materials, susceptible to cracking, and have poor thermal and acoustic insulation [1]. Thus, proposals have emerged for incorporating new materials, such as lightweight expanded clay aggregates, which can improve their quality and performance, making them more effective [2].

Expanded clay, being a low-density material compared to conventional aggregates, reduces the demand for more robust foundations and structural elements, thus reducing the number of materials used. Additionally, this aggregate significantly contributes to thermal and acoustic insulation, thereby increasing the energy efficiency of the mortar [3]. The application of expanded clay optimizes construction processes and minimizes the environmental footprint, promoting more responsible practices in the sector. Although clay is an industrial resource, the fact that the final product is recyclable and reusable in various applications strengthens the cycle of material reuse, aligning with the principles of the circular economy. The incorporation of expanded clay in cementitious matrices, therefore, not only improves the technical properties of mortars but can also contribute to environmental sustainability.

Meeting the Sustainable Development Goals (SDGs), this practice contributes to the transition of the construction sector towards more sustainable models, favoring the achievement of SDG 7 (Affordable and Clean Energy), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action). Several authors, including Ruiperez et al. [4], Gunduz and Kalkan [5], Salgueiro et al. [1], Fontes et al. [2], Ortega et al. [6], and Becker et al. [3], have conducted investigations on the application of expanded clay in mortar formulations. Becker et al. [3] replaced sand with expanded clay in lightweight mortars, resulting in higher viscosity (from 221 mm to 283 mm) and a notable increase in flexural tensile strength, especially with 5% replacement. However, this reduced the mixture’s density, promoting lower compressive strength. The microstructural analysis showed better adhesion due to the reduction in the transition zone caused by the expanded clay.

Fontes et al. [2] addressed the mechanical and thermal analysis of coating mortars with partial aggregate replacement by expanded clay. Replacing 20% of the sand with clay slightly increased the compressive strength of the mixture. A more substantial increase occurred in the flexural tensile strength with the incorporation of 50% expanded clay in the mortar. The water absorption and the void index also showed increases corresponding to the proportion increase, while the mass density was reduced. These changes in the studied properties were attributed to the high porosity of this type of aggregate.

Although expanded clay offers several advantages, its use in coating mortars has not been extensively explored and remains largely unknown. Research on this material is constantly evolving, with discoveries emerging every day. An important aspect to be investigated is the adhesion resistance of these mortars, which can contribute to improvements in coating performance and make these mortars a viable and widely adopted alternative in civil construction. From this perspective, this study aims to evaluate the physical, mechanical, and durability properties of lightweight mortars with partial replacement of fine aggregate by different proportions of laminated expanded clay.

2. Materials and Methods

2.1. Portland Cement

The binder was Portland cement with high early strength (CP V-ARI). This was characterized according to its physical properties: fineness index—NBR 11579 [7]; normal paste consistency—NBR 16606 [8]; setting time—NBR 16607 [9]; real specific gravity—NBR 16605 [10], and Le Chatelier expandability—NBR 11582 [11]. The cement’s chemical composition was determined using the semi-quantitative X-ray fluorescence (XRF) technique. The analysis was carried out using Rigaku Primini EZScan equipment(Tokyo, Japan) under vacuum, using samples of approximately 10 g that were pressed into the shape of cylindrical bodies with a diameter of roughly 60 mm and a thickness of approximately 5 mm.

2.2. Aggregates

The fine aggregates were sand and laminated expanded clay (a variation in traditional expanded clay, in which the granules have a flatter or layered structure, instead of the conventional spherical or rounded shape, with dimensions of 0.1 to 2.5 mm), supplied by Cinexpan. The sand underwent a screening process, being submitted to a set of sieves (1.18 mm, 600 µm, 300 µm, and 150 µm). For characterization, the quantity retained in each specified sieve was used to obtain a greater degree of packing and reduce the voids between the grains. The laminated expanded clay was submitted to a 2.36 mm sieve to remove the larger grains. Then, both materials were oven-dried for 24 h at 105 ± 5 °C. After this procedure, the materials were stored in plastic containers with lids to protect against external factors.

The physical properties of sand and laminated expanded clay were characterized by the following tests: particle size composition—NBR 17054 [12]; unit mass—NBR 16972 [13]; true density and water absorption—NBR 16916 [14]. The chemical composition of the laminated expanded clay was also determined by the X-ray fluorescence (XRF) technique. The microstructural analysis was conducted using a Scanning Electron Microscope (SEM). This analysis utilized a JEOL microscope, model JSM-6510 LV Series Scanning Electron Microscope (JEOL, Tokyo, Japan). A particle-modifying additive (PowerMix VMA), supplied by MC-Bauchemie (MC, Scottsdale, AZ, USA), was used to ensure the workability of the mortars. This additive was applied to improve homogeneity and stability, optimizing the rheology of the mortars with laminated expanded clay.

2.3. Preparation of Formulations

The composition of the reference mortar was defined based on the dosages commonly used in practice at the construction site and employing NBR 7215 [15] with a ratio of 1:3 (Portland cement: sand) by mass and a water/cement ratio of 0.5. The percentage of additive used was 0.3% of the mass of cement. The reason for using this additive was the inadequate consistency of the reference mixture, which became excessively dry, and also due to the need to replace the sand with expanded clay in the other mixtures. Considering the reference ratio, the amounts of cement, water, and additive were kept constant, with only fine aggregate being replaced, at percentages of laminated expanded clay of 10%, 20%, 30%, 40%, and 50% (

Table 1. Formulations of mortars produced with different proportions of expanded clay, replacing traditional fine aggregate (sand).

Identification	C:A	Water	Adittive	Sand	Clay
	---------------------- Ratio --------------------			--------------- % ---------------
Ae0	1:3	0.5	0.3	100	0
Ae10	1:3	0.5	0.3	90	10
Ae20	1:3	0.5	0.3	80	20
Ae30	1:3	0.5	0.3	70	30
Ae40	1:3	0.5	0.3	60	40
Ae50	1:3	0.5	0.3	50	50

C:A = cement and fine aggregate ratio (weight: weight).

).

The mortars were produced in a standardized manner using a mechanical mixer, according to NBR 7215 [15], with the addition of expanded clay laminated later to the sand. Six formulations were molded, resulting in a total of 180 test specimens, with 30 specimens for each group. These samples were subjected to characterization tests (compressive strength, flexural tensile strength, tensile adhesion strength, durability, water absorption, real specific mass, and capillary absorption test), with six repetitions adopted for each test. Specifically for the tensile adhesion strength test, the mortars produced were applied to the walls of prototype houses with dimensions (1.0 m × 1.0 m × 1.2 m), where twelve samples were taken from each type of group (Figure 1).

2.4. Mortar Characterization

The mortars were characterized in their fresh state using the consistency index—NBR 13276 [16] and mass density—NBR 13278 [17]. In the hardened state, the water absorption and specific mass tests were performed—NBR 9778 [18]; tensile strength tests in flexure and compression—NBR 13279 [19]; determination of absorption by capillarity—NBR 9779 [20]; potential adhesion strength to traction—NBR 13528-2 [21]. The durability test was performed after a 28-day curing period in water immersion, following the suggestions of NBR 13583 [22]. Six prismatic specimens were immersed in a sodium sulfate solution (100 g of solute to 1 L of distilled water) for twenty-one days. After the end of the immersion period, the test specimens were subjected to flexural tensile strength tests, following the NBR 13279 [19].

Additionally, the coefficient of the constructive quality (CCQ) was estimated. The CCQ definition is the ideal percentage of replacement of coarse aggregate by lightweight aggregate in volume.

2.5. Data Processing and Analysis

To assess the experimental results, the normality of the data was verified, and then statistical analysis was performed using the analysis of variance (ANOVA) method using the Paleontological Statistics (PAST) software (v4.05), adopting a probability of significance less than or equal to 5% (p value ≤ 0.05), followed by the Scott Knott mean comparison test. To analyze the ideal proportion of expanded clay in mortars, the coefficient of the constructive quality (CCQ) was used, which correlates with the apparent density and mechanical resistance of the mortars.

3. Results

3.1. Characterization of Raw Materials

The results of the physical characterization tests of Portland cement CP V-ARI, sand and laminated expanded clay are available in

Table 2. Characterization results of Portland cement CP V-ARI used to produce mortars with the incorporation of sand and laminated expanded clay in different proportions.

Characteristics	Results	Regulatory Requirements *
Fineness Index (%)	0.82	≤6.0
Normal Consistency (% water)	30.30	-
Start of Setting (min)	160.00	≥60
Specific mass (g cm−3)	3.18	-
Le Chatelier Expansibility (mm)	4.00	≤5.0
Specific Surface Area (cm2 g−1)	4186	-

* NBR 16697 [23].

and

Table 3. Results of characterization tests on fine aggregates (sand and laminated expanded clay) used to produce mortars.

Characteristics	Sand	Expanded Clay
Fineness modulus	2.24	2.96
Maximum diameter (mm)	2.36	2.36
Specific mass (g cm−3)	2.50	1.43
Water absorption (%)	0.50	5.13
Unit mass in loose state (kg m−3)	1593	936
Unit mass in compacted state (kg m−3)	1688	943

. The granulometric curves of these aggregates are illustrated in Figure 2.

The chemical composition of the laminated expanded clay used to manufacture mortars is shown in

Table 4. Chemical composition of laminated expanded clay used to produce mortars.

Chemical Compound	Percentage (%)
SiO2	59.13
Al2O3	18.63
FeO3	8.48
K2O	5.31
MgO	3.56
CaO	1.98
TiO2	0.82
Na2O	0.58
P2O5	0.36
SO3	0.11
WO3	0.11
BaO	0.10
MnO	0.09
ZrO2	0.03
Cl	0.02
Cr2O3	0.02
ZnO	0.02
SrO	0.01
Y2O3	0.01
NiO	0.01
Calcination loss	0.62

. The images obtained using a Scanning Electron Microscope (SEM) are shown in Figure 3.

3.2. Characterization of Mortars in the Fresh State

3.2.1. Consistency Index

The results demonstrated a significant difference between the means of the consistency indices (Figure 4). It was found that all formulations with laminated expanded clay percentages showed a reduction in the consistency index compared to the reference composition. This drop in the consistency index can be attributed to the high porosity of expanded clay, which promotes water absorption and reduces the workability of the material.

3.2.2. Fresh Mass Density

The results showed a significant difference in the mass density averages between the different formulations evaluated (20%, 30%, 40%, and 50%), with a continuous reduction in density as expanded clay was incorporated (Figure 5). These decreases were expected due to the physical properties of expanded clay, which has a porous structure that retains more air, thereby increasing the volume of the mixture without adding proportional weight.

3.3. Characterization of Mortars in the Hardened State

3.3.1. Real Specific Mass

The results indicated that adding expanded clay reduced the actual specific mass of the mortars compared to the reference formulation (Figure 6). The lower density and greater porosity of expanded clay contain more air in its structure and less solid material per occupied volume. The lack of significant differences between the 20–30% and 40–50% expanded clay formulations indicates that, after a specific limit, the increase in the amount of expanded clay does not promote a significant reduction in the specific mass, due to the decrease in the effective interaction between the expanded clay particles and the cementitious matrix.

3.3.2. Water Absorption

Regarding the water absorption test, there was no significant difference between the mortars containing different percentages of expanded clay and the reference mortar (Figure 7). This result can be explained by the fact that, although more porous materials were incorporated, greater particle packing may have occurred, thus balancing the porosity issue.

3.3.3. Water Absorption by Capillarity

Water absorption by capillarity increased for each mortar type (Figure 8). Over time and with the increase in the proportion of expanded clay, it was observed that mortars reduced water absorption by capillarity. This effect can be attributed to the greater porosity of expanded clay, which reduces the speed of water percolation, resulting in lower capillary absorption.

3.3.4. Compressive and Tensile Strengths in Bending

A significant reduction was identified between the averages of the compressive strength test of the mortars with the addition of expanded clay (Figure 9). The incorporation of 10, 20, and 30% expanded clay was insufficient to generate significant variations in strength between the samples, as the cementitious matrix continued to play a predominant role in load transfer, ensuring stable mechanical performance. On the other hand, after the replacement of 40%, a saturation in the strength reduction effect was observed, attributed to forming a more fragile matrix, with a greater number of voids and less mechanical interaction between the particles.

The flexural tensile strength test results indicated a significant difference between the averages of the mortars with 30% and 40% laminated expanded clay compared to the reference (Figure 10). This increase in strength can be attributed to the contribution of expanded clay, which, in adequate quantities, can improve the distribution of stresses in the cementitious matrix, resulting in better performance under flexural stresses. It should also be noted that, due to the wide variation in the grain sizes of laminated expanded clay, some mixtures may contain more fine particles, which allows for more efficient filling of voids without compromising the flexural tensile strength, as occurred in the formulations with 10, 20, and 50%.

3.3.5. Tensile Strength of Adhesion

The tensile bond strength of mortars with expanded clay decreased with increasing percentage of expanded clay. The formulation with 50% expanded clay did not achieve adhesion to the substrate (Figure 11). Due to this porosity, the transition zone between the cement paste and expanded clay tends to be more fragile, creating discontinuities and microcracks. In addition, the increase in the mixture’s total porosity reduces the effective contact area for adhesion.

3.3.6. Durability

After exposing the mortars to sodium sulfate for 21 days (Figure 12), the flexural tensile strength test showed an increase in all formulations relative to the strengths obtained before exposure. Exposure of the mortar to sodium sulfate solutions may have triggered chemical reactions between sulfate ions and cement paste compounds, such as calcium hydroxide, leading to the formation of ettringite.

3.3.7. Coefficient of the Constructive Quality (CCQ)

The results of the mortar averages showed that for the calculation of the constructive quality coefficient, the formulations with the addition of 10%, 20%, and 30% expanded clay did not present a significant difference compared to the reference (Figure 13). It is the ideal proportion for replacing fine aggregate with expanded clay for lightweight mortars.

4. Discussion

4.1. Raw Materials

The average results of the characterization tests of Portland cement CP V-ARI (Table 2) met the minimum requirements stipulated by NBR 16697 [23]. The sand presented a particle size distribution with a uniformity coefficient (Cu) of 2.66, indicating uniformity, and a curvature coefficient (Cc) of 0.5, suggesting a tendency toward discontinuity in the curve. Regarding the fineness modulus, the sand presented a value of 2.24, within the optimal range, as defined by NBR 7211 [24]. The laminated expanded clay revealed a uniformity coefficient (Cu) of 5, indicating moderate uniformity. In contrast, its curvature coefficient (Cc) was recorded at 0.61, suggesting a tendency toward discontinuity in the curve, similar to sand. Regarding the fineness modulus, the expanded clay with a value of 2.96 is in the upper usable range. NBR 12655 [25] classifies as lightweight aggregate those with a specific mass value less than or equal to 2.0 g cm⁻³. The measured specific mass of sand was 2.50 gcm⁻³, while expanded clay, used as a substitute, had a specific mass of 1.43 g cm⁻³. This value aligns with the manufacturer’s technical data sheet [26], which indicates a density of 1.40 g cm⁻³. Similar results were observed in the studies by Rossignolo [27], Becker et al. [3], and Silva et al. [28].

Expanded clay recorded a compacted unit mass of 943 kg m⁻³. This characteristic qualifies it as a relatively light material as defined by NBR 7211 [24]. On the other hand, sand exhibits a higher unit mass, possibly due to the more rounded shape of its grains, which facilitates better filling of voids due to lower friction. The chemical composition of expanded clay found that the highest percentages were silicon dioxide—SiO₂ (59.13%) and aluminum trioxide—Al₂O₃ (18.63%) (Table 4). According to Becker et al. [3], these components form stronger chemical bonds within the structure of expanded clay, making it more resistant and capable of withstanding mechanical loads. Gunduz and Kalkan [5] also mention that aluminum dioxide is especially beneficial for the thermal stability of expanded clay, making it capable of withstanding temperature variations without disintegrating.

Scanning Electron Microscopy images of laminated expanded clay (Figure 3) reveal the mineral’s high rate of intralamellar voids. This characteristic favors its use as thermal insulation, due to the low thermal conductivity of the air present in these voids. In addition, the high void rate reduces the mortars’ specific mass and compressive strength [27].

4.2. Physical Characterization of Mortars

Moravia et al. [29] comment that expanded clay’s irregular and rough particles increase internal friction, making water percolation difficult, unlike sand. Additionally, the non-uniform particle size distribution of expanded clay generates more voids in the mortar, resulting in a drier, less cohesive mixture with lower workability.

Malaiskiene et al. [30] observed that replacing the aggregate with different percentages of expanded clay reduced the cementitious matrix’s consistency, affecting the workability of the mixtures. In turn, Becker et al. [3] used two types of expanded clay to replace the aggregate, with dimensions of 2.5 mm and 5 mm. This approach increased the consistency index of the mortars, which is likely attributed to the greater incorporation of air into the mixture due to the porous properties of expanded clay. The incorporated air acts as a lubricant, facilitating the movement of particles and increasing the fluidity of the mix.

According to Rossignolo [27], expanded clay tends to incorporate air bubbles during mixing due to its surface texture, contributing to an even more pronounced reduction in the density of the fresh mass.

The classification criteria for the mass density of mortars in the fresh state according to NBR 13281 are as follows [31]: the formulations with 10%, 20%, 30%, and 40% are in class DE2 (1600 < DE < 1800) and the formulation with 50% is in class DE1 (1200 < DE < 1400). Becker et al. [3], Fontes et al. [2], and Ruipérez et al. [4], when investigating the replacement of fine aggregate by expanded clay, observed a reduction in the mass density of the mixture as larger proportions of expanded clay were incorporated. This reduction is attributed to the porous and lightweight nature of expanded clay, which results from the exfoliation process during the material’s production. Density is a critical parameter in assessing the viability of these mixtures as lightweight mortars.

The classification criteria of the actual specific mass of mortars according to NBR 13281 [31], the reference formulations, 10%, 20%, and 30% of expanded clay addition are in class DE4, which indicates values above 1800 kg m⁻³, while the formulations with the incorporation of 40% and 50% expanded clay, fall into class DE3, where the density values are between 1600 and 1800 kg m⁻³. Becker et al. [3], Souto [32], Ruiperez et al. [4], and Ozkiliç et al. [33] demonstrated in their research that the partial replacement of fine aggregate by expanded clay in mortars results in significant reductions in the specific mass values. This reduction is directly associated with the greater porosity of the material, characterized by the presence of larger pores, which contribute to the decrease in this property. This effect is related to air retention in the structure of lightweight aggregates.

Moravia [29] and Fontes et al. [2] investigated mortars containing expanded clay and observed increased water absorption due to its incorporation. This reference was attributed to the greater porosity of the internal surface of the expanded clay, which is related to the formation of gas bubbles during its manufacturing process. Vaiciene et al. [34] observed increased water absorption in cementitious matrices with expanded clay. According to the authors, this increase is attributed to the presence of elongated pores in the microstructure, which facilitates water penetration.

Borja [35] used two granulometries of expanded clay (5 mm and 15 mm) in a cementitious matrix and found that, when evaluating the formulations in isolation, there was an increase in water absorption by capillarity. However, this property was reduced when comparing the impact of expanded clay with the reference formulation. This behavior is attributed to the greater initial porosity caused by the presence of expanded clay in the mixtures. However, as the proportion of expanded clay increases, a reorganization occurs in the cementitious matrix, leading to an interconnection between the pores and a reduction in capillary absorption. Souto [32] mentions that increased water absorption by capillarity in mortars produced with lightweight aggregate occurs due to internal pores. This porosity facilitates water penetration, making the mortars more susceptible to absorption [33].

4.3. Mechanical Characterization of Mortars

Angelin [36] and Ruiperez et al. [4] comment that the reduction in compressive strength can be attributed to the porosity of the aggregate. Aggregates with a more porous structure tend to be less resistant. Following the classification criteria for the compressive strength of mortars expressed in NBR 13281 [31], the reference is classified in class AAE16 (16.0 < fa < 20.0 MPa), mortars with addition of 10%, 20% and 30% expanded clay were classified in class AAE12 (12.0 < fa < 16.0 MPa), and finally, mortars with 40% and 50% clay were classified as AAE8 (8.0 < fa < 12.0 MPa). This classification considers situations of use in structural masonry of buildings with coated walls, encompassing all formulations within the standard specifications.

Cintra [37], Koksal et al. [38], Xu et al. [39], Barros [40], and Silva et al. [28] also reported reductions in compressive strength. According to Angelin [36], the rupture of conventional mortar occurs due to the difference in the deformations of the cement paste and the aggregate. In contrast, in lightweight mortars, failure occurs due to the collapse of the paste and the formation of a fracture line that crosses the aggregate, making the material more fragile.

For flexural tensile strength of mortars according to NBR 13281 [31], all formulations fall into class R3, where 1.5 < Rf < 3.0 (MPa), which helps to specify their properties and appropriate uses. Fontes et al. [2] and Becker et al. [3] observed that flexural tensile strength remained unchanged in all mixes analyzed for producing mortars with expanded clay. This lack of variation can be explained by the fact that resistance to this type of stress depends more on the integrity of the cementitious matrix than on the density or the incorporated lightweight aggregates.

The classification criteria of tensile strength of adhesion for mortars proposed by NBR 13281 [31], values greater than 0.20 MPa are considered applicable. The reference mortar is used in the production of external coatings that apply ceramic tiles. Mortar with a 10% clay addition has the potential to produce both internal and external coatings for the application of ceramic tiles. Mortar with 20% clay may be suitable for making internal coatings for applying paint and/or texture, while mortars with 30% and 40% do not comply with the standard described. In turn, Becker et al. [3] used two types of expanded clay, with 2.5 mm and 5 mm dimensions, to produce mortars. The tests were conducted on the reference mix with 10% and 20% replacement of expanded clay. The results obtained showed an increase in resistance with the increment. This increase was attributed to the better packaging between the two types of clays used with different granulometries, which favored the cohesion between the components.

4.4. Durability and Coefficient of the Constructive Quality

This process fills the pores, temporarily increasing the cohesion and density of the matrix, thus improving its strength [41]. Following the classification criterion for flexural tensile strength of mortars according to NBR 13281 [31], all formulations fall into class R4, where flexural tensile strength values are greater than 3.0 MPa. For Ortega et al. [6], the improvement in the mechanical performance of the series studied over time occurs regardless of the type of binder or aggregate used. This can be attributed to the formation of solid phases, resulting from the continuous progress of clinker hydration, gradually reducing the porosity of the cementitious matrix [42].

The composite gains lightness at low expanded clay contents without significantly compromising mechanical strength. Larger replacements, however, can increase porosity, reducing the capacity to withstand loads [27]. Ozkiliç et al. [33] investigated cementitious matrices with different expanded clay contents, where they also addressed the coefficient of the constructive quality, concluding that the most effective replacement of expanded clay with natural aggregate occurred at a proportion of 20%. This solution provides an excellent balance between strength and lightness, desirable characteristics in several applications.

The formulations that replaced fine aggregate with expanded clay by 30%, 40%, and 50% exhibited unsatisfactory performance in terms of tensile bond strength. This was assessed according to the NBR 13281 [31] criteria, which set a minimum value of 0.20 MPa for mortars used as coatings. The mortars with 30% and 40% replacements fell below this limit, while the mortar with a 50% replacement did not adhere at all to the substrate, indicating a complete failure in the bond between the mortar and the base. This poor performance is attributed to the significant increase in porosity and the fragility of the transition zone between the cement paste and the expanded clay grains, which reduces internal cohesion and the effective contact area with the substrate.

This limitation is particularly important for applications that require excellent mechanical performance and durability, such as external coatings or those used in aggressive environments. In this research, only formulations containing up to 20% expanded clay met the regulatory requirements and demonstrated adequate adhesion, thus being considered technically viable. Proportions exceeding this limit, while reducing the density of the mortar, compromise safety and functionality in practical use. As a result, these higher proportions are restricted to non-structural applications or those that do not rely heavily on adhesion as the primary performance factor [2,3].

5. Conclusions

This research identified that the ideal percentage of replacement of fine aggregate by laminated expanded clay is 20%. This proportion results in a significant reduction in mortar density, which implies lower consumption of structural materials, greater ease of transportation, and application without compromising mechanical performance or adhesion to the substrate. The main innovation of the work is the integrated evaluation of the physical, mechanical, and durability properties of these mortars, with emphasis on the use of the coefficient of the constructive quality (CCQ) CQC) as an ideal performance criterion and the analysis of the effects of exposure to sulfate, an approach still little explored in the national literature.

The replacement of fine aggregate by expanded clay significantly impacted the consistency index, which decreased as the proportion of expanded clay increased and the mass density of the fresh mortars decreased. The actual specific mass of the mortars also reduced as the proportions of expanded clay increased. Regarding water absorption, there was no significant variation between the different formulations. However, absorption by capillarity decreased over time and with the incorporation of expanded clay. A reduction was observed in all mortars containing expanded clay for the compressive strength results. However, concerning flexural tensile strength, most mortars had no significant impairment with the addition of expanded clay, indicating that the ability to withstand flexural stresses was preserved. Regarding the potential tensile bond strength, the inclusion of expanded clay had a negative influence on this property. However, formulations with up to 20% expanded clay presented similar performance to the reference, even meeting the resistance value specified by the standard.

Regarding durability, all mortars demonstrated improvements in flexural tensile strength after exposure to the sodium sulfate solution, resulting in better performance in aggressive environments. Based on the results obtained, it was possible to determine the coefficient of the constructive quality, representing the ideal expanded clay content to replace the fine aggregate in the mortar composition partially. This replacement provided better performance by balancing the reduction in density with preserving mechanical properties. The formulation, composed of 80% natural sand and 20% expanded clay, meets the requirements established by NBR 13281 [31], which regulates mortars for laying and coating. Thus, these results indicate that 20% partial replacement of fine aggregate by expanded clay is a promising strategy for producing mortars, preserving their essential properties. This approach reduces the density of the elements that comprise the building, enabling the optimized dimensioning of the foundation structures.