Rheological evaluation of rendering mortars by the squeeze flow method based on particle packing and water content of the mixture

Avaliação do comportamento reológico de argamassas de revestimento por meio do método do Squeeze-Flow com base no empacotamento de partículas e o teor de água da mistura

Abstract

Mortars’ workability results from other properties, such as consistency, plasticity, cohesion, water retention, exudation, initial adhesion and density. A workable mortar distributes itself in application, doesn’t segregate during transport, and remains plastic during the application time. This property depends on several application factors, together with the constituent materials. Therefore, this study aims to assess the influence of the formulation, aggregate type and water content on rheological behavior of rendering mortars, combined with particle packing studies. For this purpose, three usual mortar formulations were chosen. The minimum water content was calculated through the concepts of particle packing and the squeeze flow test. As a result, the influence of each constituent on the workability of the mortar was determined, together with the formulations optimized by the aggregate type. The water content analysis revealed the wet packing density and minimum value required for the formation of the water film around the particles.

Keywords:
Rendering mortars; Rheology; Particle packing

Resumo

A trabalhabilidade das argamassas resulta de outras propriedades, como consistência, plasticidade, coesão, retenção de água, exsudação, adesão inicial e densidade. Uma argamassa trabalhável distribui-se durante a aplicação, não segrega durante o transporte e permanece plástica durante o tempo de aplicação. Esta propriedade depende de vários fatores de aplicação, juntamente com os materiais constituintes. Portanto, este estudo tem como objetivo avaliar a influência da formulação, do tipo de agregado e do teor de água no comportamento reológico de argamassas de reboco, aliado a estudos de empacotamento de partículas. Para tanto, foram escolhidas três formulações de argamassas usuais. O teor mínimo de água foi calculado através dos conceitos de empacotamento de partículas e teste de squeeze flow. Como resultado, foi determinada a influência de cada constituinte na trabalhabilidade da argamassa, juntamente com as formulações otimizadas pelo tipo de agregado. A análise do teor de água revelou a densidade de empacotamento úmido e o valor mínimo necessário para a formação do filme de água ao redor das partículas.

Palavras-chave:
Argamassas de revestimento; Reologia; Empacotamento de partículas

Introduction

Workability is one of the most important properties in fresh mortars, resulting from the interaction of other important properties such as consistency, plasticity, water retention and exudation, internal cohesion, thixotropy, adhesion, specific mass, and consistency retention (Rilem, 1982; Oates, 1998; ASTM, 2004). Furthermore, it directly influences properties in the hardened state, such as porosity, mechanical resistance and adhesion, important parameters that promote greater durability and comfort in buildings (Cardoso; John; Pileggi, 2009). Workability had as its main proposal in the past, which was the ease of the worker in working with the mortar in its application (Rilem, 1982). Soon, the characterization of mortars was developed by single-point type tests, such as the flow table and dropping-ball tests, which ended up not considering the extreme shear requests that the material requires in practice (Hoppe Filho; Cincotto; Pileggi, 2007). These test methods do not effectively measure workability, but their results can be considered as indicative values of this property (Silva et al., 2016). This lack of parameters in the analysis of mortar workability led bricklayers to adjust the consistency of the material on-site, based on their experience and/or a visual assessment of the material at the time of application.

Over time the concept of workability improved since mortars cannot be evaluated simply for their intrinsic properties, but also according to their rheological behavior (Cardoso; John; Pileggi, 2009). In this context, the squeeze-flow technique, which aids in the analysis of the rheological behavior of mortars, has become increasingly popular. Thus, with the output data from the squeeze flow test, it is already possible to numerically develop the maximum deformations of the mortar in its plastic state (∆def.), which facilitates the comparison between the curves resulting from this test (Martins, 2021).

Since mortar is a material that presents multiphase and concentrated heterogeneous suspensions of particles (micro and macroscopic), this difference in the flow between the solid and liquid phases tends to be directly impacted by the characteristics of the materials that will be used (Cardoso et al., 2014; Collomb; Chaari; Chaouche, 2004). Moreover, the chemical composition and morphology (specific area and volume of microspores) also impact the viscosity of mortars. Any type of variation in these inputs can trigger an increase in water content (Carasek et al., 2016), or even in paste content for the same rheological behavior (Arizzi et al., 2012; Sébaibi; Dheilly; Quéneudec, 2004).

By adjusting workability simple mortars (composed of a binder), for example, require less water than mixed mortars, which generally have lime in their composition (larger specific area) (Apostolopoulou et al., 2019; Cho et al., 2017), which - due to their size of particles - necessarily demand more water (Haach; Vasconcelos; Lourenço, 2011; Casali et al., 2018). Mortars containing aggregates with a fineness modulus of up to 1.8 require more water than those containing coarser aggregates with a fineness modulus above this value; however, when lime is added to this formulation with coarse aggregate, this statement can be changed, because there is a packing of the fine lime particles with the coarse aggregate particles, and even a greater incorporation of air, which can cause a change in the fineness modulus (Giordani; Masuero, 2019; Caraseket al., 2016).

Hence, in the quest to better understand this variation of inputs that make up the mortar, some concepts of particle packaging were included, which, in addition to being used to reduce the environmental impacts in terms of CO₂ emissions in cement production (Campos; Klein; Marques, 2020), assists in the rheological properties of mortars, which are directly associated with the distribution of particle sizes (Castro; Pandolfelli, 2009).

Particle packing methods allow the optimization of the granular material of cement mortars, reducing the void spaces and, therefore, improving its compressive strength (Karadumpa; Pancharathi, 2022). In the fresh state of the materials, the influence on the particle packing studies also acts on the particle size distribution that promotes the packing which, together with the fluid, defines the rheological properties of the material during the mixing process and in its fresh state (Li; Kwan, 2014).

Therefore, the objective of the research is to numerically quantify the rheological behavior of mortars (Martins, 2021) with variations in the characteristics of aggregates and formulations. Furthermore, after the analysis, it is possible to compare among the proposed formulations the influence of each material used on the rheological behavior of the mortars. This method numerically calculates the maximum deformation in the plastic state of mortars by means of compression tests (∆def). Thus, one can visualize the effect of these variables (formulation and aggregates) on the water content, which is directly related to the workability of all formulations. The coating mortars, when produced in works, present a complexity in the adjustment of water, which is often developed empirically, and directly affects its application.

Material and methods

The following items describe the characterization of the materials as well as the experimental program developed for this study.

Characterization of materials

To produce the selected coating mortars, Portland cement CP II F 32 was used, with a specific mass of 3.08g/cm³ and specific surface of 3,720 cm²/g and characteristics according to NBR 16697 (ABNT, 2018) and NBR 16372 (ABNT, 2015). This cement is similar to type II cement of C150M-19 (ASTM, 2019). Hydraulic lime was also used, with a specific mass of 2.45g/cm³ and specific surface of 6.230 cm²/g and characteristics as described in the NBR 7175 standard (ABNT, 2003a) NBR 16372 (ABNT, 2015), similar to the recommendations given by the C141M-14 standard (ASTM, 2014). Three different types of fine aggregates were used, two natural sands with a fineness modulus equal to 1.87 and 2.69 (NS1.87and NS2.69) and an artificial sand with a fineness modulus equal to 2.04 (CS2.04). Figure 1 shows the granulometric curve of all materials used. Table 1 displays the characterization of the aggregates used.

Figure 1 demonstrates that the D50 diameter of the materials used is equivalent to 23.12 µm for cement and 16.39 µm for lime. For aggregates, the D50 is equal to 413 µm for NS1.87, 613 µm for NS2.69 and 423 µm for CS2.04. It should be noted that the natural sand used originates from alluvial deposits, and the artificial sand from fine-grained sandstone, interdigitated with mudstone, silite and shale, classified based on Geological and mineral resources map of the state of Paraná (Besser; Brumatti; Spsila, 2021). Furthermore, artificial sand differs from natural sand, especially when it comes to the process of obtaining and processing which includes: the dismantling of the rock through scarification and the spiral classification that culminates in the surface wear of the particles and subsequently in the process of separating the granulometric ranges.

The morphology of the particles was determined using the CAMSIZER XT, which is an optical-electronic device that measures particle size and shape through dynamic image analysis. This method is regulated by the ISO 13322-2/06 standard (ISO, 2006). The material passes through an area where it is hit by an LED light and two cameras that capture the images, which are processed by the equipment's software. The data obtained are combined through algorithms, generating accurate information with excellent reproducibility (Hawlitschek, 2000). The result of the test determines aspects related to the morphology of the particles, where the most used are the sphericity (SPHT3) and the aspect ratio (b/l), according to Equations 1 and 2. The aspect ratio (b/l) is easy to interpret, since the smaller the b/l values, the more elongated the particles will be. The sphericity parameter represents the angularity of the particle, that is, the irregularity of its projected perimeter. Therefore, the closer to 1, the more uniform the surface will be and the closer to 0, the more irregular (Hawlitschek, 2000).

$\mathrm{Sphericity}\left(\mathrm{SPHT}3\right)=\frac{4\mathit{*\pi *particle\; area}}{{\mathit{particle\; perimeter}}^2}$ Eq. 1

$\mathrm{Aspect\; ratio}\left(\frac{\mathrm{b}}{\mathrm{l}}\right)=\frac{\mathit{x\_min}}{\mathit{Fe\_max}}$ Eq. 2

Figure 1
Particle size distribution of the used materials

Table 1
Properties and characteristics of the aggregates

Parameters	Standards	NS1.87	NS2.69	CS2.04
Specific gravity (g/cm³)	NBR NM 52 (ABNT, 2009)	2.51	2.63	2.53
Bulk density (g/cm³)	NBR NM 45 (ABNT, 2006)	1.55	1.57	1.45
Voids Index (%)	NBR NM 45 (ABNT, 2006)	37.9	40.30	42.37
Material finer than 150µm (%)	-	3.64	3.44	13.18
Material finer than 75µm (%)	NBR NM 46 (ABNT, 2003b)	1.16	1.33	3.86
Fineness Module (-)	NBR NM 248 (ABNT, 2003c)	1.87	2.69	2.04
Maximum aggregate size (mm)	NBR NM 248 (ABNT, 2003c)	1.18	4.75	4.75
Absorption (%)	NBR NM 30 (ABNT, 2000)	0.90	0.01	1.27

The equations can be expressed by analyzing the different parameters related to the size of the particles, where x_min (b) is the smallest value among the maximum diameters and Fe_max (l) is the greatest distance between two parallel lines that touch the particle.

Images were captured using a ProScope HR digital microscope with a 50x lens, Aptina imager and 1280x1024 resolution. Figure 2 shows the images of aggregates NS1.87, NS2.69 and CS2.04, classified according to grain size, that is, material retained on sieves #1.2 mm, 0.6 mm, 0.3 mm and 0.15 mm. The results obtained for sphericity and aspect ratio are shown in Table 2.

When analyzing the data obtained from the CAMSIZER XT and through the analysis of images captured by the microscope, the NS1.87 aggregate can be considered the most uniform aggregate of the other tests (SPH3). The b/l ratio shows that the NS2.69 aggregate is more elongated than the others. A Figure 3 shows a sphericity by particle size range.

It can be observed that the AN1.87 sample results in greater sphericity than the others aggregates in most sieves. At particle size fraction #0.21mm, AN1.87 has 0.906 of sphericity, this value being the closest to the perfect sphere (Hawlitschek, 2000). However, among the thicker fractions (#0.21mm and #1.7mm), although the aggregate AN1.87 presented a lower sphericity, yet it was much higher than the other aggregates, reaching 10.5% higher than AN2.69 sand in fraction #1.4mm.

Method

The experimental program that makes up the present study is presented in Figure 4.

Three mortar formulations were used for the experimental evaluation, based on their use in Brazilian works and bibliographical references (ABNT, 1982; Hawlitschek, 2000; BSI, 1992; Gomes; Neves, 2002). The formulations used were: 1:1:6, 1:2:6, and 1:2:9, (cement: lime: aggregates, by volume). For each formulation, three types of fine aggregates (NS1.87, NS2.69, and CS2.04) were used, as presented in Figure 2, totaling 9 formulations produced in the experimental study.

The experimental method proposed by Wong and Kwan (2008) was used to determine the packing density of the granular and the minimum water content set for each studied mortar. This method establishes the packing density for fine materials in the presence of water, as this alters the surface energy of particles and the agglomeration condition of fine materials. The test consists of producing mortars with different volumes of water in their composition and determining the apparent density of each mixture produced. From the apparent density, the void ratio and solids concentration of the mixtures can be calculated, according to Equations 3 to 5, with the packing density being equivalent to the maximum solids’ concentration found. In this study, the water to dry materials (w/dm) ratio, determined by the minimal water, ranged between 0.08 and 0.23, by weight, with a variation of 0.03, depending on the mortar produced. These values are equivalent to w/dm ratio variation of 0.20 to 0.59, by volume, for aggregates NS1.87 and CS2.04; and 0.21 to 0.61, by volume, for aggregates NS_2.69. The metallic container used for the apparent density determination had a volume of 399.2 cm³, and the mixtures were compacted and they were molded in two layers, and for each layer the metal cup was subjected to 30 drops. with a compacting rod prior to the determination of apparent density.

$V_S=\frac{M}{{\rho }_w\times u_w+{\rho }_a\times R_a+{\rho }_b\times R_b+{\rho }_c\times R_c}$ Eq. 3

$u=\frac{(V-V_S)}{V_S}$ Eq. 4

$\mathrm{\Phi }=\frac{V_S}{V}$ Eq. 5

Where:

V_S is the solids’ volume in the mortar;

M is the mass of mortar that occupies the mold used in the test;

ρ_w is the density of the water;

ρ_a, ρ_b and ρ_c are the densities of the solids a, b and c;

u_w is the water/dry material ratio (in volume);

R_a, R_b, and R_c is the volumetric ratio between materials a, b, and c and the total solids;

V is the volume of the mold used in the test; and

u is the void ratio and Φ is the solids concentration of mortar.

As shown in Figure 5, the materials were mixed in a mortar according to the method recommendations (Wong; Kwan, 2008). The method calls for the initial addition of 100% water to the mixture. In the current study, it was decided to add only 80% of the water at first, followed by the remainder of the other materials.

Figure 2
Images of aggregates NS1.87, NS2.69 e CS2.04

Table 2
Results of aggregate morphology

Aggregate	SPH3	b/l
NS1.87	0.875	0.740
NS2.69	0.827	0.690
CS2.04	0.828	0.718

Figure 3
Average sphericity by particle size range

Figure 4
Research flowchart

Figure 5
Mixing procedure

During the test to determine the packing density, the minimum volume of water necessary to produce a homogeneous mixture is obtained (Wong; Kwan, 2008), which is equivalent to the maximum concentration of solids (or packing density) obtained for the mortars with different water contents. From this minimum volume, the amount of water in the mortars was gradually increased to promote the fluidity of mixtures. The mortars were then characterized regarding rheological behavior using the squeeze-flow test,based on the analysis of three samples (ABNT, 2010). The mortars were prepared as prescribed by NBR 13276 (ABNT, 2016).

The squeeze-flow test consists of measuring the effort required to compress a suspension (in the present study, a volume of fresh mortar) between two parallel plates. The fundamental principle of this method is based on the fact that when the ratio of the sample's diameter (D) to thickness (h) is high (D/h >> 5), the effective deformation of the material compressed between the plates occurs by radial shear. Lower ratios lead to the appearance of compressive stresses (Cardoso; Pileggi; John, 2005). The test for rheological evaluation through squeeze-flow, for all mortars in this research, was performed in the EMIC (DL 10000 NO 10225 NS 358) press using a 2 kN load cell, with a displacement speed of 1 mm/s, with a data acquisition rate of 10 points per second, as the lowest speed prescribed by the NBR 15839 standard (ABNT, 2010), and which could allow a more detailed analysis of spot readings.

Figure 6 shows the standard graph obtained by the squeeze-flow test. It appears that the stress versus strain curve obtained as a result can be divided into three distinct stages. In stage I there is a small displacement, which shows the elastic deformation of the material; stage II represents a larger displacement showing plastic deformation or viscous flow, and stage III refers to a small displacement and strain hardening, influenced by the approximation of the aggregates and the friction formed by them (Cardoso; Pileggi; John, 2005). For cement-based materials, such as coating mortars, the squeeze-flow test is analogous to the conditions presented in the mortar application process on site. It is desirable, in terms of workability, that a mortar remains in stage II during a large part of the test, presenting high deformations associated with low applied loads, which is desirable in practice, as it allows the mortar application processes, facilitating the spreading of the mortar on the substrate, without demanding great efforts on the part of the construction worker.

From the squeeze-flow tests, it was possible to determine the stage change points, both from the elastic to the plastic stage (EDmax) and from the plastic stage to the imbrication (PDmax). The Yield Limit (EDmax), also called elastic limit stress, or yield stress, is the maximum stress that the material supports even in the elastic regime of deformation. If there is still some increase in tension, the material no longer follows Hooke's law and begins to suffer plastic deformation (definitive deformation). EDmax is calculated mathematically using the Excel software, from a straight line, starting from zero and reaching the straight line that best represents this behavior, seeking the best fit, where the coefficient of determination R² will be as close to 1 as possible for the obtained series (Cardoso; John; Pileggi, 2009).

Figure 6
Curve typically obtained in the squeeze-flow test

When comparing the curves resulting from the squeeze flow test, elaborated through Excel software, for the rheological analysis of the mortars, the greater the deformation variation (∆def) (Equation 6),the more extensive the plastic state (stage II), the better the application performance of the coating mortars. The ability to deform, then, indicates when a mortar can be spread more easily, especially if this is associated with a low force, indicating in practice a lower effort required by the worker (Martins, 2021).

$∆\mathit{def.}={\mathit{PD}}_{\mathit{max}}-{\mathit{ED}}_{\mathit{max}}$ Eq. 6

The determination of the transition point from the plastic regime to the imbrication (PDmax) was determined according to Cardoso, John and Pileggi (2009), where it is known that in the third stage, there is a significant increase in the load necessary to obtain deformations. This behavior is represented by an exponential curve, where we sought to determine, through Excel software, the mathematical equation of an exponential curve with the best mathematical fit, that is, coefficient of determination R² as close to 1 as possible. Thus, the starting point of this exponential curve will correspond to the point that characterizes the beginning of the PDmax embedding stage.

It is important to note that the increase in water volume occurred while it was possible to remove the ring used to mold the mortar specimen in the squeeze-flow test without spreading the sample on the test template. This is because the squeeze-flow technique is only valid when the material has sufficient yield strength to maintain its shape after demolding (Cardoso; John; Pileggi, 2009).

Two-way ANOVA analysis was applied in order to verify the existence of significant differences among the data obtained of the deformation variation (∆def) according to similar water to dry material ratio (w/dm), formulations and aggregate types, and the individual interaction of these two factors with w/dm. The analyzes were carried out only for data that contained the same w/dm for all treatments.

Results and discussion

The results obtained in this study are presented in this section.

Determination of the packing density of the granular set

Figures 7 to 9 and Table 3 show the solid concentration and void ratio results for the studied mortars. The increase in the water to dry material ratio (w/dm) leads to an increase in the void ratio related to the separation of solid particles effect caused by the addition of water content. The inverse occurs with the solid concentration, which decreases with the increase of w/dm ratio. Once the water content is lower, the distance between particles is reduced, also decreasing the proportion of voids. This process occurs until the critical point is reached, with maximum solids and minimum voids point. In the sequence, in case of further decrease in the w/dm ratio, there will be no available water in the mixture leading to a collapse in water-particles bridges, which will consequently move apart, decreasing the concentration of solids and increasing the voids ratio (Li; Kwan, 2014; Klein, 2012; Hermann et al., 2016).

Figure 7
Solid’s concentration and voids ratio obtained for NS1.87mortars

Figure 8
Solid’s concentration and voids ratio obtained for NS2.69 mortars

Figure 9
Solid’s concentration and voids ratio obtained for CS2.04 mortars

Table 3
Summary of packaging densities of formulations

Formulation	NS1.87		NS2.69		CS2.04
	w/dm	Packing density (-)	w/dm	Packing density (-)	w/dm	Packing density (-)
1:1:6	0.17	0.703	0.17	0.684	0.17	0.666
1:2:6	0.17	0.700	0.17	0.683	0.17	0.666
1:2:9	0.17	0.693	0.14	0.685	0.17	0.662

When analyzing the results shown in Figures 7 to 9, the inverse relationship between the solid concentration (ɸ) and the void ratio (υ) can be seen for all the analyzed formulations (Wong; Kwan, 2008). For the set of grains represented by the 1:1:6 formulation, for the NS1.87 aggregate, the maximum packing density equal to 0.703 corresponds to a void ratio equal to 0.422, and these parameters were found in the ratio of w/dm of 0.17. This w/dm ratio of 0.17 means that the surfaces of the particles are completely surrounded by water and connected to each other by a water bridge at the points of contact between particles. When this d/dm ratio decreases, there is not enough water in the mixture, resulting in the breaking of contact between particles, with a new spacing, decreasing the solids concentration and increasing the voids ratio of the mixture. Consequently, when this ratio increases, there is a greater distance between the particles, filled by water, increasing the void ratio and a decrease in the solids concentration (Li; Kwan, 2014; Wong; Kwan, 2008; Klein, 2012).

It is observed that there is a difference in the packing density values when the characteristics of the aggregates used are changed. The NS1.87 natural aggregate had the highest packing density compared to the other aggregates, which may be explained by the result of the morphology where it was characterized as the most spherical and less angular aggregate than the other aggregates (Ulsen et al., 2013). Formulations with NS1.87 showed mean values 2.6% higher than the means of NS2.69 and 5% higher than CS2.04. The greater the deviation from a spherical shape and the more angular the particles, the lower the packing density of a distribution, because the irregular surfaces of particles, combined with a greater number of edges in the grains, cause friction between particles (Castro; Pandolfelli, 2009).

Regarding the minimum water obtained, it is observed that for the mixes developed with NS1.87 and CS2.04 the minimum w/dm ratio was 0.17 and for the formulations produced with NS2.69 it was 0.14. For AN2.69, the averages between the formulations 1:2:6, 1:2:9 and 1:0.6:6 have an absolute difference of 0.2%, making it difficult to classify. It is also noteworthy that the amount of binders may have influenced the packing density, that is, when the amount of binder (in volume) increases, there is a tendency towards a decrease in packing density values. Therefore, the binders, which have the smallest grains in the composition, are susceptible to agglomerations, whether due to the contact of this material with water due to the force of interparticle attraction such as van der Waals forces, electrostatic forces between positions of sites with opposite charges and great interaction, or bonds that involve the molecules of water or hydrates (Aitcin et al., 1994). This agglomeration is easily seen in the particles' thin, permanent or not, influences the microstructure of the material, which can be either in the rheology of particle suspensions and their packaging itself (Castro; Pandolfelli, 2009). In this way, it is possible that formulations with a greater amount of cement and lime may have agglomerated.

It should be noted that the minimum water is not enough for adequate performance in mortars, considering that mortars do not vibrate like concrete and still require the ideal rheological behavior for their adhesion to the substrate and adherence in their hardened state.

Evaluation of the rheological behavior of mortars produced from excess water

The minimum amounts of water necessary for the production of a homogeneous mortar, according to the results obtained by the packing density test of the granular sets in the presence of water (Wong; Kwan, 2008) were used to produce mortars for the squeeze-flow test (Cardoso et al., 2014). From the minimum water, the amounts of water were extrapolated until it was not possible to carry out the squeeze flow test, that is, the volume of water was too high for the removal of the ring used to mold the mortar test specimen without the spread of the sample on the test jig (Wong; Kwan, 2008).

The graphs resulting from the test show the load versus deformation curves for the mortar developed with NS1.87 aggregate and are shown in Figures 10 to 12. Table 4 shows the stage change points PDmax and EDmax of the mortars also taken from the squeeze flow curves.

It is noted that for all tested formulations the addition of water resulted in an increase in ∆def, even if small. Statistical analysis of the data revealed significant difference (p<0.05/) among the experimental groups (Table 7). The high increase in fluidity in w/dw 0.26 seen in the 1:1:6 formulations can be explained by an excess of water in the mixture, which may have caused phase separation in the mortar. Following Cardoso, John and Pileggi (2009), phase separation occurs due to the multiphase nature of the mortar, making the occurrence of segregation quite common and which needs to be considered in the analysis of results.

Figure 10
Squeeze-flow tests for NS1.87 1:1:6

Figure 11
Squeeze-flow tests for NS1.87 1:2:6

Figure 12
Squeeze-flow tests for NS1.87 1:2:9

Table 4
Change of stage - EDmax and PDmax for mortars produced with NS1.87

Formulation	w/dw	EDmax		PDmax		(def (mm)
		Def. (mm)	Load (N)	Def. (mm)	Load (N)
1:1:6	0.17	0.006	0.068	1.101	1.287	1.100
1:1:6	0.20	0.022	0.135	1.001	5.487	0.980
1:1:6	0.23	0.006	0.068	1.035	10.364	1.030
1:1:6	0.26	0.015	0.135	2.201	6.909	2.190
1:2:6	0.17	0.022	0.203	1.551	40.508	1.530
1:2:6	0.20	0.031	0.135	1.385	9.619	1.350
1:2:6	0.23	0.031	0.135	2.051	40.575	2.020
1:2:6	0.26	0.022	0.271	2.535	270.410	2.510
1:2:9	0.17	0.015	0.135	1.035	10.229	1.020
1:2:9	0.20	0.010	0.145	1.101	10.161	1.090
1:2:9	0.23	0.015	0.135	1.635	20.863	1.620
1:2:9	0.26	0.005	0.068	2.017	2.303	2.010

The impact of granulometry with little continuity, lack of fines (pulverulent material of 1.16%) and a low fineness modulus (FM of 1.87) may have been one of the causes that negatively impacted the fluidity and lack of cohesion of all formulations developed with the NS1,87 (Carasek et al., 2016). This lack of fluidity and cohesion described above can be seen at the stage change points, where the ∆def of most mortars in this set was between 0.98mm and 2,510mm of deformation and a maximum load of 270.41. Furthermore, this little deformable behavior was observed even with the increase in water content.

The 1:2:6 formulation showed the highest values of ∆def, for all w/dw ratios. This proportion was the one that presented a greater volume of lime, which may have been the cause of this slightly more workable behavior than the other formulations. Another observation to be mentioned is regarding the ∆def between the w/dw ratio of 0.17 and 0.20, which was very similar in all tested formulations and can be explained by some factors such as the lack of fines in the mixture.

Figures 13 to 15 and Table 5 show the results of the squeeze-flow test and the inflection points, respectively, of the mortars developed with NS2.69.

Figure 13
Squeeze-flow tests for NS2.69 1:1:6

Figure 14
Squeeze-flow tests for NS2.69 1:2:6

Figure 15
Squeeze-flow tests for NS2.69 1:2:9

Table 5
Change of stage - EDmax and PDmax for mortars produced with NS2.69

Formulation	w/dw	EDmax		PDmax		(def (mm)
		Def. (mm)	Load (N)	Def. (mm)	Load (N)
1:1:6	0.17	0.006	1.490	1.045	5.284	1.040
1:1:6	0.20	0.002	1.897	1.491	9.822	1.490
1:1:6	0.23	0.003	1.829	2.179	49.991	2.180
1:1:6	0.26	0.003	1.694	2.246	12.261	2.240
1:2:6	0.17	0.005	1.490	0.858	1.694	0.850
1:2:6	0.20	0.009	0.948	1.807	19.238	1.800
1:2:6	0.23	0.006	1.084	3.612	72.345	3.610
1:2:6	0.26	0.002	1.152	3.028	39.966	3.030
1:2:9	0.14	0.003	1.490	1.445	15.648	1.440
1:2:9	0.17	0.003	1.490	1.545	7.587	1.540
1:2:9	0.20	0.006	1.355	3.679	51.075	3.670
1:2:9	0.23	0.006	1.523	3.895	45.182	3.890

For the analysis of the tests developed with the NS2.69, contrary to the one seen with the NS1.87, it is observed that in general, when there is an increase in the w/dm factor, the curves of the squeeze-flow results require less force and even so, reach greater displacements. That is, the mortars produced with NS2.69 begin to behave in a more plastic and deformable state than the curves developed with NS1.87. This greater plasticity can be seen in the behavior of mortars where the ∆def of most mortars is ≥2mm. Two-way ANOVA (Table 7) for NS2.69 aggregate showed a significant difference of ∆def with w/dm variation. Nevertheless, the variation of the formulation did not statistically have any effect on ∆def values.

For the 1:1:6 formulation, where there is a smaller amount of lime in its composition, the ∆def results were the lowest among the others presented. Lime is a thin material that provides better lubrication between the aggregate particles and thus reduces grain friction, improving workability and water retention capacity, decreasing modulus of elasticity, i.e., better absorbing stresses (Apostolopoulou et al., 2019; Cho et al., 2017; Hendrick, 2009). As for the 1:2:6 formulation with the amount of water in w/dm 0.23, it is possible to visualize a plastic and applicable mortar, since its ∆def was 3.61mm, the highest value presented, even compared to the formulation with w/dw of 0.26. At a w/dm content of 0.26, a noise was observed in the curve, which may have been caused by the separation of phases that excess water ends up causing in the mixture compressed by the squeeze-flow plates.

Unlike the other formulations, in 1:2:9 the minimum water acquired through the experimental method of Wong and Kwan (2008) was 0.14 and not 0.17 as the other formulations. However even with the reduced amount of water “strain hardening” or hardening of the material by deformation were not observed. For this formulation, higher values of ∆def were associated with water ratios of 0.20 and 0.23.

Finally, Figures 16 to 18 and Table 6 show the squeeze-flow results and the stage change points of mortars developed with artificial aggregate CS2.04.

Figure 16
Squeeze-flow tests for CS2.04 1:1:6

Figure 17
Squeeze-flow tests for CS2.04 1:2:6

Figure 18
Squeeze-flow tests for CS2.04 1:2:9

Table 6
Change of stage - EDmax and PDmax for mortars produced with CS2.04

Formulation	w/dw	EDmax		PDmax		(def (mm)
		Def. (mm)	Load (N)	Def. (mm)	Load (N)
1:1:6	0.17	0.008	0.135	0.932	2.506	0.924
1:1:6	0.20	0.017	0.203	1.828	42.133	1.811
1:1:6	0.23	0.013	0.203	1.381	9.483	1.368
1:1:6	0.26	0.004	0.068	3.515	35.630	3.511
1:1:6	0.29	0.015	0.271	3.618	25.673	3.603
1:2:6	0.17	0.001	0.068	2.468	86.163	2.467
1:2:6	0.20	0.031	0.135	2.685	39.627	2.653
1:2:6	0.23	0.006	0.068	3.501	66.248	3.496
1:2:6	0.26	0.003	0.068	4.401	7.113	4.398
1:2:9	0.17	0.022	0.135	1.701	118.750	1.679
1:2:9	0.20	0.010	0.068	2.251	97.137	2.242
1:2:9	0.23	0.022	0.135	2.518	104.590	2.496
1:2:9	0.26	0.003	0.068	2.535	46.604	2.532
1:2:9	0.29	0.054	0.339	2.835	18.289	2.781

The aggregate used for this last set of tests is a washed artificial aggregate CS2.04 where the minimum water obtained through the experimental method of Wong Kwan (2008) was w/dw of 0.17. Although the CS2.04 aggregate is artificial, its amount of fines (pulverulent material of 3.86%) is approximately three times higher compared to the natural aggregates of this research (pulverulent material of NS1.87 - 1.6% and NS2.69 - 1.33%). However, because CS2.04 is washed, this percentage of fines drops considerably compared to artificial aggregates without this type of treatment, which, according to C33 (ASTM, 2023), have a maximum content of 20% (Carasek et al., 2016; Ferreira et al., 2019). Note that in the tests developed with squeeze-flow, the curves are more deformable, where most of the mortars developed with CS2.04 obtained a greater range of deformations, with significant difference (Table 7), which did not occur in the mortars developed with natural aggregate.

The analysis referring to the 1:1:6 formulation, which results in less deformable mortars, was already expected due to the reduced amount of binder (∆def in the w/dw ratio of 0.17 in 0.924mm with the application of 2,506N of force). However, as water is added, the formulations become more deformable (Cardoso et al., 2014).

For the 1:2:6 formulation, where there is a greater amount of binder concerning the aggregate, it is possible to observe results referring to plasticity closer to the ideal mortar for application, except for the w/dm ratio of 0.26 where the squeeze-curve flow exhibits a noise that is characteristic of heterogeneity between phases and/or particle agglomeration when the mixture is compressed by the squeeze-flow plates. Nevertheless, for the 1:2:9 formulation, it is noted that, as expected, the addition of water causes an increase in deformations, but in smaller ranges compared to the 1:2:6 formulation, reaching a maximum of ∆def of 2,781 mm to a w/dm ratio of 0.26.

Based on this, assumptions related to mechanical properties are necessary, such as flexural tensile strength, modulus of elasticity, among others, to effectively indicate what is the ideal amount of water for this specific study.

Table 7
Two-way ANOVA results to ∆def with variation of w/dm and formulation

Aggregate type	Source of variation	Sum of squares	Degrees of freedom	Mean square	F	P-value	F-critical	Significance criteria (p<0.05)
NS1.87	w/dm	2.2504	3	0.7501	19.788	0.002	4.757	Significant
	Formulation	0.6195	2	0.3098	8.172	0.019	5.143	Significant
	Error	0.2275	6	0.0379
	Total	3.0974	11
NS2.69	w/dm	6.5469	2	3.2734	9.261	0.032	6.944	Significant
	Formulation	3.3045	2	1.6522	4.674	0.090	6.944	Not Significant
	Error	1.4139	4	0.3535
	Total	11.2652	8
CS2.04	w/dm	5.0532	3	1.6844	6.321	0.027	4.757	Significant
	Formulation	3.9555	2	1.9778	7.422	0.024	5.143	Significant
	Error	1.5989	6	0.2665
	Total	10.6077	11

Conclusions

After performing the tests and respective results analysis, the following conclusions can be made:

1. with the application of the wet particle packing method of Wong and Kwan (2008) it was possible to obtain the minimum w/dw ratios for all tested formulations. The NS2.69 aggregate was the one that obtained the best packing density result in individual results, that is, the packing of particles with this specific material resulted in a higher concentration of solids with a minimum of voids. As for the set of formulations, the NS1.87 aggregate was the one that obtained the highest packing densities;

2. when the formulations were analyzed, they all had very close results when applied to the packing model targeting the granular set. The impact visualized was greater when there was a change in the characteristics of the aggregates. Thus, the formulation that resulted in a better particle packing both for the NS1.87, aggregate, while in the CS2.04 was in 1:1:6 (ɸ=0.703 and 0.660 respectively);

3. in the analysis regarding the rheological behavior using the squeeze-flow test, it was possible to use a numerical comparison between the curves resulting from the test (Δdef). This coefficient helps in the analysis of the workability of mortars, where the higher this coefficient, the greater the worker’s ease in applying this material;

4. when assessing the Δdef, small variations were identified, even when there is variation in the type of formulation, which only for NS2.69 aggregate was identified a not significant difference. In contrast, a greater difference in the results of Δdef. was identified when there was a change in the types of aggregates. The formulations developed with the CS2.04 aggregate showed the highest Δdef, compared to the other formulations; and

5. as a suggestion for future research, the addition of chemical additives could be a material to be increased in this dosing flow in order to verify the indicated guidelines focusing on the workability of the mortars. The air-entraining additive, widely used in coating mortars, is an indicative material for this inclusion. The air-entraining additives help in the rheological properties of the mortars, and even optimize issues related to the application of the material in the substrate. Future work could analyze ideal water parameters through Ddef relating some of the mechanical properties of mortars, such as, for example, compressive strength, tensile strength in bending and/or modulus of elasticity. This correlation, together with some design assumptions for coating mortars, can adjust the amount of water needed for each type of formulation.

Acknowledgments

The authors would like to thank Votorantim Cimentos, which provided test equipment at its facilities, and Higher Education Personnel Improvement Coordination (CAPES) for the financial support. They also thank the Graduate Program in Civil Construction Engineering of the Federal University of Paraná (PPGECC/UFPR) for encouraging research and development in the field of civil construction.

This work was supported by the Higher Education Personnel Improvement Coordination (CAPES).

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Edited by

Editores:

Marcelo Henrique Farias de Medeiros e Eduardo Pereira

Publication Dates

• Publication in this collection
  07 Oct 2024
• Date of issue
  Jan-Dec 2024

History

• Received
  25 Aug 2023
• Accepted
  04 Jan 2024