Effect of phosphogypsum and water-retaining in the stabilization and durability of stabilized mortars

2.2.1 Fluidity loss over time

A mini-cone test evaluated the loss of fluidity of the pastes over time at times of 0, 24, and 48 h. The procedure used a small cone, whose dimensions are 60 mm high, 20 mm upper diameter, and 40 mm lower diameter. It was filled with the paste, and after complete filling, the cone was removed. The paste flowed over a glass plate, where two orthogonal measurements of the diameter were obtained after 1 min of the cone removal, and the result was the mean between measurements.

2.2.2 Hydration heat

To analyze the hydration kinetics, that is, the release of the heat of hydration from the pastes, measurements were performed using an eight-channel Tam Air AB isothermal calorimeter (TA Instruments), with a computerized data acquisition system, with a mean reading frequency every 30 s during the period in which the test was monitored. The test was performed with ≥10 g sample for all compositions addressed in Table 2. Throughout the test period and data acquisition, the temperature of the equipment was kept constant at 21°C.

2.2.3 Rheometry test

To evaluate the rheological parameters of the pastes, the rotational rheometry test was performed using a Thermo Scientific rheometer, model Hake Mars III, with a maximum torque of 200 N mm and a maximum rotation speed of 1,500 rpm. This test aimed to determine the variations in the apparent viscosity of the pastes over time. The samples were evaluated at 0, 24, and 48 h. The geometry used was a 35 mm serrated plate-plate, with a gap of 1 mm.

The following flow test routine was followed: a pre-shear lasting 60 s at a rate of 100 s⁻¹ was applied, then the cycle began, which was composed of two ramps, the first being the upward curve (acceleration) with a shear rate of 0.1–100 s⁻¹ and then the downward curve (deceleration) in which it started from the same point 100 s⁻¹ and returned to 0.1 s⁻¹.

The model adopted for the calculation was the Herschel–Bulkley model, according to equation (1).

where τ is the shear stress, τ _o is the dynamic initial yield stress, k is the plastic viscosity, γ ̇ is the shear rate, and η is the behavior index.

2.2.4 Mixing time

To analyze the start and end of setting times of the mixtures, the Vicat needle method was used, according to NBR 16607 [17]. Only pastes 3, 4, and 5 presented in Table 3 were produced, with an HSA content of 1.2% in the cement mass, to represent the mortars better. This happened because pastes 1 and 2 were mixtures only with cement, PG, and water, without admixtures.

For this test, the objective was to obtain the time of setting of the mortars for later stripping in Sections 2.3 and 2.4. Stabilization was conducted for the longest period, also the most critical, 72 h.

The pastes were placed in truncated conical molds with an internal diameter of a base greater than 80 ± 5 mm, a base smaller than 70 ± 5 mm, and a height of 40 ± 0.2 mm, provided with rigid, flat, and glass base plates, which is non-absorbent. For measurements, a Vicat device with a Vicat needle was used.

2.3.1 Workability parameters

The workability parameters were evaluated over 0, 24, 48, and 72 h. The consistency index test determined the spreading of mortars according to NBR 13276 [19]. The test consisted of measuring the spreading diameter of mortar contained in a volume of a truncated cone after 30 times the table rises and falls in 30 seconds evenly. The standard mold was filled with mortar in 3 layers of approximately equal heights, where 15, 10, and 5 blows were applied with a socket in each layer. Thirty drops were applied from the same height as the table, forcing the mortar to spread over the surface. The spread index was the average of three diameter measurements of the mortar spread over the surface of the screed.

As for the mass density and entrained air content in the mortar mixtures, NBR 13278 [20] was used. The test consisted of filling a cylindrical container in 3 layers, with 20 strokes in each layer. Afterwards, the container was dropped from an approximate height of 3 cm, in order to remove the voids between the mortar and the container wall. Finally, it was weighed and the mass of the mold with the mortar was recorded.

2.3.2 Water exudation

Water exudation was measured following the methodology of RILEM MR-6 [21]. Spillway glass beakers with a volume of 600 mL were used. With the spoon, 500 mL of mortar was placed in each beaker without consolidating the material. After filling the 500 mL mark, the trapped air was removed. Then, the cup was covered with plastic film for 15 min.

Water exudation was measured at 15 min, 30 min, 1 h, 2 h, 4 h, 24 h, 48 h, and 72 h. The exuded water was removed from the surface with a graduated pipette.

2.3.3 Dynamic modulus of elasticity

The dynamic modulus of elasticity was performed on the equipment of Sonelastic da ATCP Engenharia, and it was a non-destructive test of the modulus of elasticity from natural frequencies acquired through the impulse excitation technique, based on ASTM E 1876 [22]. Because it is not destructive, the modulus was evaluated at the ages of 28 and 42 days of cure.

The test consisted of placing the specimen lying down and then positioning the acoustic sensor of the equipment, by means of a rod, a small impact was caused at the end of the prismatic specimen (40 mm × 40 mm × 160 mm), which was captured by the equipment sensor, where there is an acoustic pickup at the midpoint of its length.

The signal obtained went through an Fast Fourier Transform (FFT) processing to obtain the peaks of natural frequencies of vibration, this frequency depends on the mass, geometry, and dimensions of the specimens. From these frequency peaks, the modulus of elasticity was calculated. The vibration mode used in this test was longitudinal vibration, which allows the calculation of the modulus of elasticity using a Poisson ratio of 0.33 ± 0.01. The equipment consists of pickups, supports, and pulsator, connected to a computer that has the software installed to monitor the test results. The test was repeated three times on each specimen.

2.3.4 Mechanical strengths: compressive and tensile

For the mechanical tests of compressive strength and flexural tensile strength, NBR 13279 [23] was followed. The mortars were submitted to rupture at the age of 42 days, using a two-module Solotest press, with Module 1 for flexion with a load capacity of 2.0 kgf and Module 2 for compression with a load capacity of 2,200 kgf.

2.3.5 Statistical analysis

Statistical analysis was performed to verify the influence of PG and additives on cementitious pastes for the apparent viscosity property and also, HPMC and HSA on the mechanical properties (compressive and tensile strength) and durability (module) of mortars stabilized with PG, and assessing whether the control factors caused significant effects on the measured response variables.

The statistical treatment performed on the results of this research was done through the application of the factorial ANOVA analysis of variance method. This analysis is proposed with statistical significance with 95% confidence, using the STATISTICA 8.0 software, which seeks to assess whether the control factors cause significant effects on the measured response variable.

3.1.1 Fluidity loss over time

The openings of the pastes at the time of 0 h can be seen in Figure 1. When the cement was replaced by PG (1:1), the reduction in fluidity caused by the binder in 64.32% was evident due to the greater need of water for PG, proving to be a porous material. When adding the HSA, an increase of 16.96% in the opening was noticed compared to Paste 2, which can be attributed to the function of this admixture to avoid the loss of workability of the mixture in the fresh state, increasing its fluidity. When adding the HPMC at 0.15%, there was a reduction of 8.73% in the opening compared to Paste 3, but when the addition was increased to 0.20%, there was an increase of 28.62% in the opening compared to Paste 4. Paste 5 was the mixture with less reduction in fluidity in relation to the mixture of cement and water, indicating that the addition of HPMC in this percentage contributed to the increase in fluidity.

Figure 1

Effect of adding PG and admixtures on fluidity over time.

The study of fluidity over time was investigated for pastes 3, 4, and 5, as the pastes 1 and 2 without HSA hardened on the same day. HPMC pastes contributed to the maintenance of fluidity over time. Paste 5 with 0.20% HPMC was the one that obtained the greatest opening in 48 h with 55.10 mm, and Paste 4 was the one that reduced the percentage of fluidity over time, 13.03% in 48 h. The effect of HPMC to avoid water loss during stabilization, improving workability, and contributing to the maintenance of fluidity is evident, when compared to Paste 3 without HPMC.

3.1.2 Hydration heat

The results of evaluating the hydration kinetics by isothermal calorimetry of the pastes are shown in Figure 2. The measurement time of 360 h is not usual in the literature for the evaluation of cement pastes, but as this study evaluated the influence of additives for the subsequent production of stabilized mortar, the use of HSA and HPMC caused an inactive period in the pastes 3, 4, and 5, delaying hydration, hence the long test period analyzed. The prolonged time in the cement hydration delay, due to the percentage of HSA used, reflected in the low mechanical performance of the 72 h stabilized mortars (Section 3.2.4).

Figure 2

Heat flow for 360 h.

The sample only with cement (Paste 1) showed a set start in the first initial hours (up to 5 h) and a maximum heat flow of 4.89 mW/g. When PG replaced the cement, there was a delay in the start of setting (for more than 20 h) and a reduction in the maximum heat flow peak, reaching 2.16 mW/g. In the presence of HSA, the start time of setting was extended to 230 h, and with the addition of HPMC in 0.15%, it extended up to 240 h. Still, with 0.20% HPMC, the longest time for the resumption of cement hydration was obtained, with 285 h. The contribution of PG and HPMC in prolonging the hydration reactions of Portland cement with HSA is evident.

This behavior of PG was also observed in the study by Costa et al. [14], the start times of setting were longer as the PG content increased, the induction period increased from 40 min with 5% to 3 h with 10% PG. The higher PG content favored the dissolution of tricalcium silicate in the system and the formation of hydrated calcium silicate (C–S–H).

Regarding HSA, Ma et al. [5] reported that incorporating sodium gluconate significantly alters the hydration kinetics of Portland cement. Sodium gluconate prolongs the induction period and delays the reaction of C₃S. With only 0.1% sodium gluconate, the start of setting was prolonged for more than 10 h. Still, the increase in the dosage of this admixture significantly decreased the maximum peak heat released.

The behavior of HPMC is justified by Pourchez et al. [24], where the methoxyl content is the main parameter in relation to the delay induced by HPMC. The delay time increases with the decrease in methoxyl content. In contrast, the molecular weight and hydroxypropyl content have little impact on the delay in cement hydration.

3.1.3 Rheometry test

At first, the flow curves of the pastes were analyzed considering the ascending and descending cycles. From this, it was chosen to work with the descending cycles, which presented consistent and repeatable rheological parameters, with greater regularities in the results, since in the first ramp (ascending), the mixture was still in the process of homogenization and adherence to the plate, and in some cases, depending on the viscosity of the paste, it presents irregular behavior in the first ramp.

Figure 3 shows the flow curves performed for the rheology test, where it can be observed that for the downward cycle (deceleration), the reduction in the shear rate implied decreases in stresses. However, this behavior did not follow a linear correlation, opting for the use of the Herschel–Bulkley model in order to obtain the most accurate yield stress and viscosity values.

Figure 3

Example of rheology test flow curves analyzed from the ascending and descending cycle.

From the downward curves, the rheological parameters of the pastes were obtained over the stabilization time. Due to their hardening, the pastes without HSA were evaluated only at 0 h. The fluid behavior index is presented in Table 5. The initial dynamic yield stress (τ _o) and the apparent viscosity (η) are shown in Table 6. Based on the fluid behavior index, the cementitious pastes present pseudoplastic behavior (n < 1), except for Paste 5 in 24 and 48 h and Paste 4 in 48 h, where over the stabilization time, they presented dilating behavior (n > 1).

Figure 4(a–c) shows the shear stress results by the shear rate of the pastes over time. Analyzing at 0 h, it is assumed that the shear stress increased significantly when cement was replaced by PG (Paste 2). The hydrated compounds of Portland cement, such as C–S–H, contributed to the interlocking of the dihydrate crystals produced in the mixture with calcium sulfate, thereby leading to a denser and closed structure, even avoiding complete dissolution in water. They require higher initial yield stress to be applied for the paste to flow, increasing the yield stress by the shear rate and consequently the apparent viscosity, causing a reduction in paste fluidity. Another factor that may have contributed is the combined effect of the size and shape of the PG particles, the coarser and irregular particles may facilitate the formation of a stable cluster structure, increasing the solid friction between the particles and requiring a greater shear force to destroy [25].

Figure 4

Shear stress vs shear rate over time. (a) 0 h; (b) 24 h; (c) 48 h. Mixture 1: Ref.100%C; Mixture 2: 50%C.50%PG; Mixture 3: 50%PG.0.5%HSA; Mixture 4: 50%PG.0.5%HSA.0.15%HPMC; Mixture 5: 50%PG.0.5%HSA.0.20%HPMC.

When the HSA was added, the stresses decreased. Tan et al. [26] reported that increasing the dosage of HSA (sodium gluconate base) reduced the yield stress, demonstrating that this admixture has a plasticizing effect on the cement paste. The plasticizing effect increases with the increase in dosage, above 0.1%.

Over time, the shear stresses increased for Pastes 3, 4, and 5 compared to 0 h. In 48 h, Paste 4 with 0.15% HPMC was the one with the highest shear stress and a greater increase in yield stress (Table 6) among the pastes studied.

Pastes could be classified as non-Newtonian fluids because viscosities varied with shear rate and time. Figure 5(a–c) shows the apparent viscosity versus the shear rate over time. All pastes obtained an increase in viscosity from 0 to 24 h. From 24 to 48 h, only pastes with the addition of cellulose ether (HPMC) had an increase in the viscosity. Paste 4 with 0.15% HPMC was the one with the highest viscosity values at the shear rate in 48 h, implying a reduction in fluidity. Paste 5 with an addition content of 0.20% HPMC had lower viscosity and greater ease of flow than that with the addition of 0.15% HPMC.

Figure 5

Apparent viscosity versus shear rate over time. (a) 0 h; (b) 24 h; and (c) 48 h.

The paste with HSA showed a reduction in viscosity by the shear rate in 48 h, indicating greater ease of flow than in the stabilization time of 24 h, showing a trend similar to the shear stress observed in Figure 4(c).

Both in shear stress and viscosity by shear rate, the addition of 0.15% HPMC obtained the largest increments in these parameters than the addition of 0.20% HPMC. According to Ma et al. [27], cement particles can be adsorbed on an HPMC molecule by combining superficial Ca²⁺ and ether groups. Still, various HPMC molecules may also connect a cement particle, resulting in the viscosity-increasing effect. Another aspect is that ether groups and hydroxyl groups can polarize water molecules to form hydrogen bonds, and this can fix water molecules within the molecular structure of HPMC. These hydrogen bonds can crosslink several HPMC molecules, called free water combination, also resulting in the viscosity-increasing effect. These two effects may explain the reason for the increase in yield stress, apparent viscosity, and shear rate stress when adding HPMC to the pastes.

According to the ANOVA statistical analysis, Figure 6 shows the effect of the stabilization time on the apparent viscosity of pastes 3, 4, and 5 and in Table 7, the analysis of variance for this property is presented. Statistically analyzing the results, it is verified with 95% confidence that Paste 5 did not show significant differences between the apparent viscosity variations over the 48 h. For Paste 4, from 24 to 48 h, the difference was not significant, and the same did not occur for 0 h. Paste 3, on the other hand, had a significant difference in all stabilization times. Pastes 3, 4, and 5 at 0 h did not show significant differences between them. At 24 h, differences in apparent viscosity were significant for all pastes. In 48 h, only for the pastes with HPMC (4 and 5) there were no significant differences compared to each other. If compared with Paste 3, the difference was statistically different.

Figure 6

ANOVA: Effect of stabilization times on the apparent viscosity of pastes.

For all the stabilization times analyzed, a reduction in viscosity is noticed when HPMC is added by 0.15% compared to Paste 3 only with AEH, this reduction is even more accentuated when the addition is increased to 0.20%, evidencing the positive effect of HPMC on AEH dispersion. The beneficial effect of the 0.20% addition percentage is visible, which contributed to the reduction in the apparent viscosity compared to other pastes and improved fluidity, facilitating the flow of the pastes over time.

3.1.4 Mixing time

Analyzing Figure 7, it can be seen that as the HPMC was added, there was an increase in the times of setting, contributing to the delay in the hydration of the cement. Another factor that contributed to the high times of setting found in this study was the use of PG, which consists mainly of calcium sulfate, which regulates cement setting. Upon contact with C₃A, calcium sulfate forms very fine crystals of ettringite, which create a protective membrane around the cement particles. This membrane hinders its contact with water, thus slowing its hydrolysis process and the consequent formation of hydrated aluminate because while there are sulfate ions, ettringite is formed slowly [28].

Figure 7

Start and end of setting of mixtures.

Another factor that interfered, decreasing the cementitious materials’ hardening speed, was the impurities contained in the PG. According to Costa et al. [14], phosphorus-soluble impurities can delay the time of setting and decrease the water/binder ratio.

3.2.1 Consistency index

The results of the consistency index loss rates over time of the mortars are presented in Table 8. The reference mortar of 48 h was the one that presented the most pronounced reduction in fluidity among the samples, 1.507 mm/h, at the end of the stabilization. The mixtures with 0.15 and 0.20% HPMC exhibited the lowest losses in fluidity, 1.061 and 1.166 mm/h, respectively. The same occurred for the 72 h mortars at the end of the stabilization period. The reference mixture obtained a higher fluidity loss rate with 1.102 and the mixtures with HPMC (0.15 and 0.20%), smaller reductions in fluidity, with a rate of 0.897 and 0.808 mm/h, respectively. The lower consistency index loss rates achieved with the mixtures containing HPMC at the end of the stabilization periods are attributed to the water retention effect of the HPMC, which preserved the water inside the mortar during the time it remained open, granting it workability, without major fluidity losses.

The consistency index over time of the stabilized mortars is shown in Figure 8. The reference mortars (without HPMC) of 48 and 72 h, in the initial period of 0 h, obtained a greater spread than the other mixtures due to the increase in the workability provided by the HSA. With the addition of HPMC there was a reduction in spreading from 10.33 to 0.15% and 10.79 to 0.20% compared to the reference for the 48 h mortars. In 72 h, the decrease in spreading was from 5.32 to 0.15% and 9.82 to 0.20%. This reduction in fluidity occurred due to the increase in viscosity caused by HPMC, which is related to the adsorption of cement particles and the fixing of free water by forming the hydrogen bond [27]. However, these decreases were not detrimental to the system, as they obeyed the consistency index parameter of 270 ± 10 mm.

Figure 8

Consistency index over time of stabilized mortars. (a) 48 h; (b) 72 h.

At the end of the stabilization, it is clear that all the compositions were able to keep the mortars in a fresh state for up to 48 and 72 h, with a consistency index greater than 180 mm, a criterion used to consider the stabilized mortar usable.

3.2.2 Mass density and entrained air content

The mass densities of the mortars increased over the stabilization time, as can be seen in Table 9. Over time, this increase in densities occurred due to the loss of entrained air in the mixtures (Figure 9), causing decreases in spreading rates and consequently reducing fluidity.

Figure 9

Evaluation of entrained air content over time for mortars. (a) 48 h; (b) 72 h.

In the mortars stabilized for 48 h (Figure 9(a)), the mixtures with HPMC at 0.15 and 0.20% lost entrained air at the end of the stabilization compared to the reference mortar, at 9.09 and 13.63%, respectively. For mortars stabilized for 72 h (Figure 9(b)), the mixtures with HPMC obtained higher levels of entrained air at 72 h compared to the reference mixture. At 72 h, the air entrained in the 0.15% mixture was 2.52%, and for 0.20%, it was 3.58%, higher than the reference. Despite the reductions in the entrained air content during the entire stabilization period, all mixtures complied with the established parameter of entrained air content of 18 ± 2% at the end of 48 and 72 h. This was possible due to the use of the AEA. It preserved the plasticity and workability characteristics of the mortars for the time they remained open in the fresh state.

Comparing the results of this research with the stabilized cement mortars from the study by Guindani and Rocha [3], it can be seen that all mortars, both 48 and 72 h, reached the end of the stabilization period with higher levels of incorporated air to that of literature, where for Guindani and Rocha [3], it was 13% for the 48 h mortar and 15% for the 72 h mortar.

3.2.3 Water exudation

The exudation phenomenon occurred only for the reference mortars (Figure 10), without HPMC. It is possible to see the beneficial effect of the cellulose-based water-retaining agent, which ceased the exudation effect in mortars with 0.15 and 0.20% HPMC, conferring water retention to the material.

Figure 10

Water released by exudation in mortars for 48 and 72 h.

The process of coalescence and collapse of the bubbles that occur in mortars with the air entrainment can result in exudation, due to the reduction in the amount of bubbles and the approximation of the solid particles, with the refinement of the capillary porosity in the fresh state, which favors the upward movement of the water. The use of water-retaining agent (cellulose ether) in 0.15 and 0.20% increased the water retention and the viscosity of the material, which contributed to the stabilization of the entrained air bubbles, reducing the trend of movement of water and particles, reducing coalescence, and avoiding the occurrence of exudation.

The largest amount of water exuded for both the reference mortar of 48 and 72 h occurred at 4 h, with 7.72 and 8.35%, respectively. Afterward, there was a reduction in the release of water to the surface. At 24 h, the water released was 0.73% for the 48 h reference mortar and 0.41% for the 72 h, suggesting that the water was possibly absorbed back by the material since the beakers were closed with plastic film to prevent evaporation of the water.

Guindani and Rocha [3] produced stabilized mortars (w/c 1.25) with the same type of cement (CP II F-32) and the same chemical composition of HSA (sodium gluconate and sucrose) used in this research (w/c 1.30). The mixture with cement (without fines) showed water exudation with greater intensity in the first 10 h, close to 9% for the 48 h mortar and 10% for the 72 h stabilization. In 24 h, for the 48 h mortar, the exuded water was close to 8%, and for the 72 h mortar, close to 9%. Comparing these results with this research, where the reference mortar is composed of cement: PG (1:1), it is observed that the mortars exuded water in the initial hours as much as the cement of the study by Guindani and Rocha [3]. However, at 24 h, the PG mortars (48 and 72 h) had a much more significant reduction in water exudation than cement-only mortars, of 90.54 and 95.08% compared to the 4 h test time. For the cement mortars of 48 and 72 h, the reductions were 11.11 and 10.0%, respectively.

Despite exudation, the mortars with PG got to 48 h with a zero content of free water on the surface, that is, the sample consumed all the water during the hardening process. The same did not occur in the study of cement mortars. It indicates that PG needs more water than cement for complete hydration reactions of the mixtures to occur.

3.2.4 Compressive strength, flexural tensile strength, and modulus of elasticity

Table 10 shows the mechanical results of compressive and tensile strength at 42 days, as well as the results of modulus of elasticity at 28 and 42 days and standard deviation of these properties. In Tables 11, 12, 13 the analysis of variance (ANOVA) for the analyzed properties are given.

The 48 h mortars with HPMC showed an increase in compressive strength compared to the reference, by 6.02%. These mortars also obtained increases in strengths when compared to 72 h mortars with 0.15 and 0.20% HPMC, at 31.01 and 51.28%, respectively. The increase in the stabilization time to 72 h and consequently the increase in the HSA content to 1.2% caused losses in the compressive strengths. These may have occurred due to the high dosage of HSA associated with the increased addition of HPMC, contributing to the reduction in the mechanical performance of the mixtures. Similar behavior was reported in other studies, where the increase in HSA dosage impaired mechanical performance in stabilized mortars [1,2,29]. Antoniazzi et al. [18] obtained lower strengths in pastes when they increased the HSA content to 1.5%. The high admixture dosage influenced the cement hydration process, delaying the properties in the hardened state due to the later formation of the hydrated compounds. This reinforces the behavioral trend found in this study.

In the study by Schackow et al. [2], the stabilized cement mortar with 0.80% HSA had a strength of 2.91 MPa, comparing it with the reference mortar with PG of 48 h (HSA: 0.85%) of this research, it is noticed that there was a 71.13% increase in compressive strength with PG. Other authors also report that the use of PG in mortars provided superior or similar strengths to the control mortar (cement). Islam et al. [30] obtained an increase in compressive strength of 1.96% with PG and 4.20% with treated PG, both in 5% replacement, compared to cement mortar. Degirmenci [31] achieved an improvement in compressive strength at 28 days, with 13.76 MPa for 50% replacement of treated PG (150°C for 2 h).

From the ANOVA of the results of the 48 h mortars, the HPMC content did not significantly influence the compressive strength values. In 72 h, when 0.15 and 0.20% HPMC were added, there were significant reductions in compressive strengths compared to the reference. The 0.20% addition content was not significant compared to that of 0.15% HPMC at 72 h.

The reference mortars of 48 and 72 h showed the same behavior of flexural tensile strength. When the HPMC was added in 0.15 and 0.20%, there were reductions in the strengths compared to the reference mortars. For 48 h, it was 5.02 and 6.53%, and for 72 h, it was 9.04 and 13.06%, respectively. This reduction in the values of 72 h mixtures is similar to the behavior observed in the compressive strength.

Through statistical analysis ANOVA, it was found that the decreases in flexural tensile strength were not significant when adding the HPMC, both for the 48 h mortar and the 72 h mortar. The combined effect of stabilization times, i.e., the increase in HSA dosage from 0.85 to 1.2%, did not significantly influence this property.

Regarding the modulus of elasticity, there was an increase in the values with HPMC compared to the reference for mortars stabilized for 48 h. At 28 days, there was an increase in the mixtures of 0.15 and 0.20% HPMC by 6.67 and 5.07% compared to the reference mixture. At 42 days, the increase was 7.11 and 5.88%, respectively. However, for mortars stabilized for 72 h, there are reductions in modulus values compared to the reference and HPMC increase. At 28 days, the reductions were 8.63 and 12.39% for 0.15 and 0.20% HPMC compared to the reference mixture. At 42 days, they were 6.11 and 12.74%, respectively.

All mortars showed increases in modulus values at the age of 42 days compared to 28 days. This may be related to the slow hydration of the stabilized mortar and, consequently, gain in the mechanical performance at a higher curing age.

At 28 days, based on the ANOVA of the results of the mortars stabilized for 48 h, it was found that the addition of HPMC did not significantly influence the values of modulus of elasticity. For 72 h mortars, there were decreases in modulus values when 0.15 and 0.20% HPMC were added, which were significant when compared to the reference, but not among them. At the curing age of 42 days, the addition of HPMC also did not significantly influence the moduli of elasticity of the mortars stabilized for 48 h. For 72 h mortars, the reduction by adding 0.15% HPMC had no significant influence, but with 0.20% HPMC, there was a significant decrease compared to the reference. Despite the reduction with 0.20% HPMC compared to the mixture with 0.15%, the percentage of HPMC did not significantly influence the modulus of elasticity when compared to each other.