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Vol. 9. Issue 1.
Pages 847-856 (January - February 2020)
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Vol. 9. Issue 1.
Pages 847-856 (January - February 2020)
Original Article
DOI: 10.1016/j.jmrt.2019.11.024
Open Access
Effect of limestone powder substitution on mechanical properties and durability of slender precast components of structural mortar
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Alessandra Tolentino Souza
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alessandratsouza@gmail.com

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, Thiago Ferreira Barbosa, Lucas Andrade Riccio, White Jose dos Santos
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white.santos@demc.ufmg.br

Corresponding authors.
Department of Materials Engineering and Construction. Federal University of Minas Gerais. Antônio Carlos Avenue. 6627 – Pampulha - Class 3320 - UFMG’s Engineering Building ZIP Code: 31.270-901, Belo Horizonte, Minas Gerais, Brazil
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Tables (5)
Table 1. Fine aggregate characterization.
Table 2. Chemical composition of materials used.
Table 3. Materials mass proportions.
Table 4. Experimental program.
Table 5. Result of properties at maximum substitution content.
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Abstract

The use of structural mortars on slender components is already widely spread. However, due to the current demand, the high consumption of cement is the primarily responsible for carbon emissions and for cost increase. The objective of this research is to study the effect of partial substitution (0 %, 9 %, 16 %, 23 % and 30 %) of cement by limestone powder focusing on slender precast structures, natural sand, Portland Cement CP-V, limestone powder and a polycarboxylate superplasticizer were used. It measured mini-cone slump flow test, mass density at fresh and hardened state, water absorption index, porosity, modulus of elasticity, compressive strength and electrical resistivity. It is noticed that the substitution content significantly influences the properties also the durability parameters are more affected than mechanical properties. The restrictive property was the water absorption index, allowing the cement substitution by limestone powder up to 11 % to maintain mortar properties according to standards.

Keywords:
Limestone powder addition
Partial substitution
Durability
Structural mortar.
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1Introduction

Civil construction demands a profusion of products and raw materials, which extraction and management generate environmental impacts, such as erosion, siltation of water bodies, ground water and water source contamination [1]. Therefore the industries are progressively using and reusing materials that are more efficient and that can be used sustainably [2,3].

In this line of work, there is the structural mortar that is characterized as high compressive resistance, also known as micro concrete [4,5] high performance micro concrete [6] or high-performance mortar [7]. As presented in NBR 11,173 [8], it consists on a mortar compound of minimum of 25MPa of compressive resistance, which has steel meshes. They are pieces of small thickness, made of mortar and reinforcement, of limited opening steel mesh throughout the cross-section. Structural mortars require strict control over its execution because of the mesh application, small piece thickness and covers [9]. They need qualified work force [10] and control at mix design and materials proportions [1]. Among its properties, it is possible to highlight the fluidity and workability at fresh state, and compressive strength and elasticity modulus at hardened state [10]. Because of these qualities the self-compacting mortar spreads going through the small spaces between the steel meshes reducing porosity and defects in the concrete and mortar structures [11–13].

Structural mortars can be used in thin-walled [14], reinforced concrete shells [15] and thin reinforced concrete roofing [16]. Their thickness can vary from 5 to 8cm and because of this the reinforcement corrosion must be analyzed carefully due to the thin cover thickness [13–16]. Generally the slender precast structures is dictated by the fire resistance rating requirements. And the reinforcement is determined by wind load, earthquake or the fire stability load of 0,5kPa associated to ductility factor [14,15].

Most studies on prefabricated thin slabs are related to size dimensioning and little is studied about the associated building materials [13–16]. Due to the relation between the environmental issues and the high demand of environmental friendly products, researches are being made focusing on improving the results obtained by this product, whether to reduce costs, attenuate environmental impacts or even improve interesting features for its application [17]. To achieve these results, mineral additions are used, such as limestone powder addition, micro silica, fly ash, Nano silica and Nano titanium [12,13]. Limestone addition is characterized as an inert material; inert or inactive additions are type I and generally are used to enhance viscosity of self-compacting concrete [18].

Partial substitution of cement by limestone powder, as studied by Nepomuceno, Oliveira and Lopes [13], presented 20 %, 40 % and 60 % substitution, showed that it can enhances rheological properties of cohesion, avoiding particles segregation [13]. Varhen [15], on his study, approaches the substitutions of fines, cement and filler, for 2 %, 60 % and 80 % by limestone, and the study highlights the positive effects on cohesion of self-compacting concrete. However, it also highlights the viscosity increase, which could have a negative effect when pumping the concrete. This type of substitution has been positive on inhibiting the temperature rise and preventing hydraulic retraction cracks [13], it provides lower hydraulic retraction indexes when compared to mixtures without addition [18]. It is important to highlight the cost reduction at materials acquisition and the environmental benefits attached to the lower consumption of Portland cement [18]. As for the mechanical properties, it is found that limestone powder content above 15 % does not participate in hydration reactions, resulting in a non-densified matrix, due to the increased pore size, lower compressive strength and tensile strength [19,20].

Therefore, the objective of this research is to evaluate the effects of partial substitution of cement by limestone powder, paying attention to durability characteristics and to mechanical resistance of structural mortar focusing on slender precast structures.

2Materials and experimental program2.1Materials

This study used Portland Cement CPV-ARI, because it is widely used in structural mortar precast industry and because it has a small addition (5 % of limestone powder), allowing a better evaluation of the influence of his substitution, Its characteristics are presented in Table 1, Fig. 1 and 2. Limestone powder passing in Mesh 100 (opening 0150mm) characteristics are in Figure 1, 2 and Table 1. The water used was from a public water supply, in accordance with NBR 15900-1 [21]. Fine aggregate from natural quartz were used, its characterization followed ABNT NM 248 [22], and the results are in Table 1 and Fig. 3.

Table 1.

Fine aggregate characterization.

  Cement  Limestone Powder  Aggregate 
D10 (μm)  1.2  1.3  100 
D50 (μm)  12  2.5  400 
D90 (μm)  50  27  1100 
Dmax (mm)  –  –  2.4 
FM  –  –  2.222 
ɣr (kg/dm³)  3.060  2.674  2.591 
ɣu (kg/dm³)  –  –  1.496 
SSA (m²/g)  9.63  10.16  – 
Porosity (%)  0.930  0.900  – 
Dp (nm)  0.008  0.003  – 

FM - Fineness Module; ɣr – Specific gravity; ɣu – Bulk Density; SSA - Specific Surface Area; Dp - Pore Diameter.

Fig. 1.

Particle size (Limestone powder and cement).

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Fig. 2.

Limestone powder (a) and cement (b) at SEM (scanning electron microscopy).

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Fig. 3.

Particle size distribution of sand.

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Table 2 shows the chemical composition of cement and limestone powder. Mortar composition also has polycarboxylate superplasticizer described as a liquid admixture of normal cure, indicated for pre-cast industry, high initial strength concretes, high performance concretes and self-compacting concretes.

Table 2.

Chemical composition of materials used.

Material  SiO2  Al2O3  Fe2O3  CaO  MgO  TiO2  P2O5  Na2K2MnO  LOI 
CPV-ARI  21.3  4.26  2.36  65.4  2.68  0.27  0.22  0.16  0.88  2.21  5.62 
Limestonepowder  5.79  1.44  0.69  55.7  0.53  0.07  0.16  <0.1  0.19  34.66  35.39 
2.2Experimental program

The percentages of limestone powder substitution were related to cement’s mass, being them, 0 %, 9 %, 16 %, 23 % and 30 %, generating materials proportions expressed in Table 3.

Table 3.

Materials mass proportions.

Sample  Cement  LimestonePowder  Sand  Water  Admixture 
1.00  0.00  2.120.450.015 
0.91  0.09  0.014 
0.84  0.16  0.013 
0.77  0.23  0.012 
0.70  0.30  0.011 

Materials mixture were done following the steps bellow:

  • a)

    Insertion of aggregate, cement and cement substitution on mortar mixer, They were mixed for 1min;

  • b)

    Adding 80 % of water content and then the mixture continues for 1 more minute in order to homogenize the mixture;

  • c)

    The second part of water containing 20 % of the remaining water was slowly added with the superplasticizer mixed in it. The mixture continued being blended for 5 more minutes;

  • d)

    After the last mixture procedure, the mortar rested for 2min and after this period, the samples were molded,

For water/fine ratio, or water/ (cement+limestone powder) ratio, the proportion adopted were 045 by mass. Nepomuceno [13] registered experiments with mortar with water/cement ratio around 0,60, obtaining compressive strength over 40MPa. Thus, this research has the intention to reach and to prove the standards determinations [8], with water/cement ratio over 045 (keeping the kneading water and reducing the cement content), and with this, reducing the production cost, which is generally associated to cement’s high cost.

The admixture content used on dosage was adjusted according to fluidity and cohesion of samples, because structural mortars need to fill the mesh obstructions, completely filling all gaps of the mold. This research used the parameters recommended to self-compacting structural mortars [8,11,13].

Mini-cone slump flow test and Mini v-funnel test were done to verify the fluidity. Mini-cone slump flow test experiment followed the recommendations of Rao [11] and Nepomuceno [13], they state that Gm, for self-compacting structural mortar must be between 5.3 and 5.9, and Dm must be between 251mm and 263mm, Mini v-funnel test is the determination of time (t – seconds) of mortar’s sample flow through a funnel structure, “V” shape. With flow time, it is possible to calculate Rm parameter. The range, that best achieve the desirable characteristics of flow and viscosity, is between 1.14 and 1.30 s−1[12].

The experiments were conducted to analyze the specified characteristics in Table 4, regarding durability and mechanical properties of slender precast components of structural mortar. Some experiments were done following standards and other experiments following technical and scientific researches as resistivity, last one listed in Table 4, according to the sources mentioned, the mechanical and durability aspects of structural mortar were evaluated, focusing on obtaining a self-compacting structural mortar [8].

Table 4.

Experimental program.

Experiments  Age(days)  Number ofSpecimens 
Specific mass at fresh state [26] 
Elasticity Modulus [24]  28 
Compressive strength [23]  28 
Specific mass at hardened state [27]  28 
Digital microscope images  28 
Porosity [26]  28 
Water absorption index [27]  28 
Eletric Resistivity [25]  28 
Mini-cone slump flow test [11,13] 
Mini v-funnel test [12] 

Cement and limestone powder were characterized: the particle size analysis was performed on a Sympatec laser diffraction particle size model Helos 12LA, computerized on the 50mm lens; Specific Surface Area (SSA) and porosity was evaluated in the fine fractions of the waste with Quantachrome Nova 1200e equipment, Quantachrome NovaWin software version 11.02. The adsorbate used was nitrogen (N2) on an analysis period of 24h for each sample. The specific surface area was calculated by the multipoint method in the BET adsorption isotherm, and the NLDFT method by the desorption isotherm to calculate porosity. The MalvernPanalytical X-ray fluorescence spectrometer, MagixFast from Geosol was used to determine the chemical composition of the samples, which were prepared by lithium tetraborate fusion. The Ignition loss was achieved by decomposing the samples by calcination in muffle furnace at 1000°C. Specific density was analysed on a Quantachrome, SPY-3, and helium gas pycnometer. The Quanta FEG 3D FEI Scanning Electron Microscope coupled to a DES no. Images were obtained with 5kV secondary electron detector and 10mm working distance. Dispersive Energy Spectroscopy (DES) analyses were performed with 15kV acceleration voltage and 10mm working distance with carbon metallization 15nm thick.

Compressive strength test followed NBR 7215 [23] recommendations, it was evaluated with 28 days on 5×10cm samples with the aid of EMIC press, which has a load application of 0.5MPa and 10 Kgf of precision. Dynamic Elasticity Modulus (Ed) were measured with forced resonance, according to ASTM C 215 [24], with MKII Erudite equipment, samples had 10cm diameter and 20cm height.

The direct current of electrical resistivity test was measured by Santos [25] method, It was generated for each sample by an applied potential difference between two electrodes positioned on the surface of saturated samples. The equipment used for this experiment were digital function generator FG- 8102 of Politerm from Laboratory of materials characterization of civil construction and Mechanics of UFMG.

For the remaining experiments, samples (10×20) cm², cured by 28 days, were used. Specific mass were measured according to NBR 12,278 [26], water absorption index and porosity, both according to NBR 9778 [27] and capillary absorption according to NBR 15,259 [28]. These properties were obtained measuring the amount of water that penetrates the sample, using a weight balance with 0.01g precision. Digital microscope with 1000x magnification were used to analyze superficial images of the mortars with limestone substitution to better evaluate the matrix behavior and the association of aggregates with composites. The images were taken from the ruptured section of porosity and water absorption samples after these tests. The images chosen for each mixture were the most representative regarding the pore distribution and shape.

3Results and discussions

The intention of this research was to evaluate self-compacting structural mortars (SCM) studding its durability characteristics and mechanical properties [8]. Measurements and experiments were made to evaluate if the cement substitution by limestone powder influences the properties. Samples should behave between the follow parameters:

  • -

    Specific mass at fresh state must be greater than or equal to 1.800g/m³;

  • -

    Water absorption index must not overcome 8 %, when determined according to NBR 9778 [27];

  • -

    The characteristic compressive strength must be greater than 25MPa.

3.1Compressive strength and modulus of elasticity

Cement replacement by limestone powder decreased the compressive strength, not only by increasing porosity but also by decreasing hydration products, as limestone is an inert material (Fig. 4). However, it is possible to see in Fig. 4 that all mixtures achieved results above 40MPa [12,13]. Compressive strength reduced by 33.71 % on 30 % limestone addition. It was a significant reduction, although it is a lesser important property for a structural mortar as water absorption. As the cement is replaced by limestone powder, the matrix showed irregular particle size distribution, which explain the increased cohesion of the compound impairing workability, grain to grain rolling, and packaging, resulting in more voids and lower compactness [29]. And that is possible because the limestone powder diameter is smaller (Fig. 1 and 2) and the specific surface area is larger (Table 1) than on cement.

Fig. 4.

Compressive strength (fc), water/cement ratio (w/c) and Agent content reduction (%Ad) versus percentage of substitution.

(0.24MB).

In addition, admixture content suffers a reduction, reaching 26.67 % on 30 % of limestone powder replacement, due to the smaller specific area (Table 1) of the limestone in relation to the cement, reducing the water consumption for the same plasticity. Similarly, the cement/ water ratio suffered an expressive increase from 0.45 to 0.64, an increase of 42.86 %. This increase is explained because of the settlement of water/fine ratio established at the beginning of the study. It also increased the void, left by anhydrate water, increasing porosity (21.93 %) and reducing compressive strength up to 33.71 %.

It is important to notice that Nepomuceno [13] obtained similar results of compressive strength for self-compacting mortars, around 50MPa with water/cement ratio between 0.45 and 0.55. Poggiali [30] registered mortars with water/cement ratio of 0.50, using 10 % of cement substitution for sugarcane ash, obtaining compressive strength around 45MPa. Therefore, this research obtained higher values using an inert material, with lower cement consumption and higher water/cement ratio. This increase is justified by the adjustment of cement particles and limestone powder adjustment (Fig. 1 and 2). It is noteworthy that results could be optimized by maintaining water/cement ratio and using a more efficient proportion of high-performance water reducing admixtures [31].

Dynamic modulus of elasticity (Fig. 5) is an important property for slender structures, because larger the dynamic modulus of elasticity is, greater the structure’s difficulty in absorbing deformation. Slender precast components of structural mortar with lower water/cement ratio generally have a higher elasticity modulus due to less pores quantity [32,33]. The results of the five samples (Fig. 7) showed that elasticity modulus varies between 27.32–31.62GPa, varying up to 13.71 % in relation to the reference sample. This is supported by literature [34], which states that smallest elasticity modulus is associated with the increase of incorporated air, in other words, with higher porosity results and lower values of mechanical properties.

Fig. 5.

Elasticity modulus (Ed) results versus percentage of substitution.

(0.1MB).
3.2Specific mass

NBR 11173 [8] does not specify whether the specific mass analyzed should be at fresh or hardened state, because of that, both situations were analyzed as seen in Fig. 6. The bibliography [8] indicates that the lowest limit parameter for this property is 1.89g/cm³ for slender precast components of structural mortar. All mixtures meet the specified conditions for specific mass, whether fresh or hardened, so it is not a parameter for delimitation for these mortars.

Fig. 6.

Specific mass at fresh state (ɣf) and Specific mass at hardened state (ɣh) results versus percentage of substitution.

(0.18MB).

Increasing the specific mass at fresh state is generally associated with increasing content of water reducing agent [31], however it is possible to observe by correlating Fig. 6 and Fig. 4 that the largest admixture reduction generated a reduction on specific mass, thus, the most important parameter in this study is the increased water/cement ratio, increasing porosity and reducing specific mass at hardened state. In fresh state, the presence of admixture is more intense on mortars rich in cement, which generated mortar densification [31] increasing specific mass.

It can be seen in Fig. 6 that the specific mass at hardened state’s behavior is similar, Variation up to 2.87 % for specific mass at fresh state and up to 8.82 % for specific mass at hardened state, which shows how the two properties are closely linked to air content incorporated during mixture procedure and with pores generated by water that didn't hydrate. The water outflow at hardening of samples favored density drop of all mixtures [35], being an average decrease of 6 %, decreasing the range of hardened density results compared to specific mass at fresh state.

3.3Water absorption by immersion, porosity and digital microscope image

With the results, expressed on Fig. 7, it is possible to observe that as the percentage of limestone powder replacement increases, it also increases the voids in the mixture, increasing the water absorption by immersion of the material, which can be harmful to the structural mortar’s durability. A substitution of up to 30 % of cement generated an increase of up to 25.53 % on water absorption by immersion. According to NBR 11173 [8], the water absorption index of the slender precast components on structural mortars should not be higher than 8 %, as this condition guarantees steel mesh protection in slender reinforced structures. Up to 9 % (sample’s results) and around 15 % (curve approximation) are an adequate replacement of cement by limestone, attending the upper limit of 8 % of water absorption.

Fig. 7.

Open porosity (P) and water absorption index (Ai) results versus percentage of substitution.

(0.2MB).

Porosity results (Fig. 7) show that with the increase of water/cement ratio there is an amount of water added in the mixture, which after the cement hydration reaction becomes pores, because it is vaporized, thus, increasing the mortar’s porosity. It is noticeable that greater the replacement of cement by limestone powder, greater the porosity of the material. Samples with substitutions of cement up to 30 % had porosity increase up to 21.93 %, a significant value for the material’s durability. According to Neville and Brooks [29], it can be considered as porosity parameter, for high initial resistance mortars with compressive strength higher than 40MPa, an average value of 12 %. None of the substitution got higher values, proving to be a durable material, even with the increased water absorption. This result is corroborated by Fig. 8 and 9, which show that capillary water absorption index has a direct relationship with porosity and its interconnection. Greater the probability of interaction between the pores, greater will be the permeability of the mixture [30]. The low degree of permeability is important in protecting the meshes against water percolation and aggressive agents that may compromise the durability of the system [30].

Fig. 8.

Capillary absorption results versus time.

Note: Each curve corresponds to a content (0 %, 9 %, 16 %, 23 % and 30 %) of cement replacement by limestone powder,

(0.17MB).

It is observed in Fig. 9 that mixtures with higher content of limestone powder addition have larger amount of pores with smaller diameter allowing interconnection between the pores, increasing water absorption by immersion, capillarity and porosity. Samples with 16 %, 23 % and 30 % substitution have smaller and irregular shaped pores around the larger pores, while reference mixture and 9 % of substitution samples, the pores have a bigger diameter and they are spherical. Some water reducing agent have the side effect of incorporating air [1,36], and in this study it is possible to see the generation of spherical pores, as in Fig. 9. Irregular pores are usually from particle size mismatch (Fig. 1 and 2), in other words, the aggregate, limestone powder addition and cement ratio generated voids because of the lack of some particle sizes to fill these pores [37,38].

Fig. 9.

Digital microscope for each percentage of substitution.

(0.99MB).

The larger specific surface area of limestone particles demanded more water and as the amount of water was the same, the cement hydration was compromised (excess of water), thus the paste did not wrapped the aggregates well due to the formation of water slides around it, and it also emerged many pores because of the excess of water [38]. According to Tutikian [14] and Peng [37], refinement of pores structure, seen in Fig. 9, is a consequence of the filler effect caused by limestone powder. In general, the images verify the water absorption and porosity results, since few intercommunicated pores were found. However, mixtures with higher substitutions create pore connection, which increase porosity and water absorption, thus reducing the durability of reinforced mortars [39,40].

Thus, its notice that the elasticity modulus (Fig. 5) was less influenced by the substitution than other properties; such as compressive strength (Fig. 4), porosity (Fig. 7,9) and water absorption (Fig. 7), which showed similar behavior (gain in compressive strength, is inversely proportional to porosity increase, and also the increase in water absorption is directly proportional to porosity increase, but all properties presented linear behavior as the percentage of substitution increases).

3.4Electrical resistivity and capillary filtration coefficient

Electrical resistivity results were very satisfactory as it is an important parameter for corrosion assessment of reinforced concrete structures (Fig. 10). Whiting [41] described that the very high probability of corrosion range corresponds to resistivity less than 5 kΩ.cm, high corrosion range is 5–10 KΩ.cm, moderated to low corrosion range is 10–20 KΩ.cm, and low corrosion range is above 20 kΩ.cm, for Santos [20], resistivity is related to fluid permeability, ion diffusivity through the material pores and cement paste hydration. Lubeck [42] states that resistivity is highly sensitive to several factors related to concrete composition, such as water/cement ratio, consumption and type of cement, type of aggregate mineral additions and admixtures, as they promote changes in size and pore distribution, internal humidity and pH, among other factors. Therefore, the increase in pores caused by the growth of water/cement ratio, and saturation of specimen before the experiment makes easier to electricity be conducted through the saturated pores, thus reducing electrical resistivity. However, as shown in Fig. 10, all mortars proportions obtained results in low corrosion ranges, above 20 kΩ.cm, with low corrosion tendency.

Fig. 10.

Electrical resistivity (R) and Capillarity coefficient results versus percentage of substitution.

(0.18MB).

Mehta [43] demonstrated that resistivity is an important parameter to evaluate corrosion in reinforced concrete structures as it is often caused due to alkalinity (carbonation), with alkalis influence on porosity percolation or significant amount of Chloride’s ion penetration. In this work, it is noticeable the influence of pore permeability, defined by capillary coefficient (Fig. 10), which shows that the samples with lower permeability (9 % and 15 % substitutions by limestone) show greater resistivity, even higher than reference sample, demonstrating that at this percentages the structural mortar mix tends to be more durable. It is evident that the substitution content identified in item 3.3 (15 %) proves to be a good option for the electrical resistivity parameter as well.

3.5Optimal percentage of substitution

All properties were influenced by cement replacement and because of this the incorporation of limestone powder should be done with caution. Because of the parameters expressed at the beginning of this chapter, it is clear that the limiting property is water absorption by immersion, having an upper limit of 8 % [8]. The others limitations: Compressive strength (25MPa) and specific mass (1.8g/cm³) were lower than the values found in this research, thus, the water absorption by immersion (Ai) equation found by linear regression (Excel trend line - Equation 1) was used to define the maximum percentage of substitution (t), being 16.29 % of cement substitution. Since the standard deviation of water absorption results were around 5 % and considering a reliability of 95 %. When using Equation 2, the maximum substitution value should be around 11 %.

Ai=6.531t + 6.936 (1)

Mixed mortars must meet a mix design condition given by equation 2 [1]:

Fd = Fk ± t(a/z)(n-1),s (2)

Where: Fd corresponds to the mix design limit of certain properties of the mortar;

Fk corresponds to the characteristic limit of a certain property of the mortar;

t(a/z)(n-1) corresponds to a tabulated value (Distribution t) for a significance level of 5 % (95 % confidence) and degree of freedom (n-1);

s” is the standard deviation of the sample evaluated by linear regression of each property as a function of the constituents’ materials; and

“n” stands for number of samples.

With the value of maximum percentage replacement, it is possible to find the values of other properties by the equations found and represented in each Figure, as shown in Table 5, proving that properties with up to this value of substitution (11 %) meet all properties’ requirements (Table 5), generating a suitable structural mortar mix for slender structures.

Table 5.

Result of properties at maximum substitution content.

Sample  Obtaining Form  Value found  Limit 
Water aborption (%)  Ai=6.531t+6.936  7.25  ≤ 8 
Compressive strength (MPa)  fc=−76.66t+66.971  58.54  ≥ 25 
Modulus of elasticity (GPa)  Ed=−14.552t+31.971  30.37  – 
Specific mass at fresh state (g/cm³)  ɣf=−0.7083t+2.4005  2.323  ≥ 1.800
Specific mass at hardened state (g/cm³)  ɣe=−0.2232t+2.1075  2.083 
Porosity (%)  P=11.846t+14.702  16.01  – 
Electrical resistivity (kΩ.cm)  Linear interpolation  ≈ 50  – 
Capillary coefficient (g/cm²)  Linear interpolation  ≈ 30  – 
4Conclusions

This research aimed to present the behavior of structural mortar when cement is partially replaced by an inert smaller material paying attention to durability characteristics and to mechanic resistance of slender precast structures. Given this we can list the following conclusions:

  • -

    Water absorption by immersion and porosity increased about 23 % compared to reference mixture due to the excess of water and grain adjustment of components of mixtures samples;

  • -

    Compressive strength dropped more than 30 % due to hydration products reduction and increased porosity in matrix and in aggregate/paste transition zone;

  • -

    Elasticity modulus, with the increased percentage of substitution, varied by a maximum of 13 % and specific masses by a maximum of 8 % compared to reference sample, without substitution. Being more preponderant in those properties the voids left by water evaporation and water reducing agent reduction;

  • -

    Electrical resistivity had its behavior associated with pore permeability, in other words, closer to capillary filtration absorption and capillary filtration coefficient, demonstrating that up to 11 % substitution the structural mortar mix would not show corrosion or degradation.

It was concluded that even using a water/cement ratio greater than 0.45, water absorption index, porosity, elasticity modulus, electrical resistivity and specific mass provided adequate results. Within the standards, proving that slender precast components of structural mortar mix could be more durable. Axial compressive strength was compromised with the increased cement replacement, but despite that, it remained higher than 40MPa, allowing a mixture proportion that could replace a portion of cement up to 11 %. The limiting property of slender precast components of structural mortar mix with cement replacement by limestone powder was water absorption index, showing that durability parameters may be more relevant than just controlling mechanical strength.

Conflict of interest

None.

Acknowledgements

Acknowledgements to UFMG, CAPPES, FAPEMIG, and CNPQ support.

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