Self-Leveling Mortars Produced with Different Types of Cement: Physical–Mechanical Properties and Carbon Emissions

Abstract

Self-leveling mortars are a product that stands out in the market for optimizing production. Greater speed of application is achieved due to its high fluidity, and the ability to level without segregation. This paper approaches self-leveling mortars formulated with different types of cement and additions and evaluates these material’s effect on the rheological behavior, physical–mechanical characteristics, and environmental aspects of this type of mortar. The results indicate that rheological aspects can be achieved regardless of the type of cement and addition. With proper proportioning, the normative requirements in terms of mechanical properties are met. When using lower-fineness cement, the risk of cracking and the demand for water and chemicals increases. Mineral additions contributed to the mortars’ cohesion and reduced shrinkage in mixtures with contents of up to 25% metakaolin and 15% silica fume. Regarding the decarbonization process, opting for cement with pozzolanic additions becomes a favorable solution as it presents a reduction in CO₂ emissions of around 170 kg per m³ of mortar produced.

1. Introduction

The use of self-leveling mortar (SLM) in floor covering systems has been gaining prominence in the construction sector, as it is a material with specific characteristics in the fresh state that guarantees total horizontality and self-adhesiveness and in the hardened state conditions that ensure its resistance [1,2,3,4]. This type of system seeks to rationalize and systematize construction work by speeding up the execution of services, building multiple floors quickly, and producing large horizontal areas for industrial processes by combining raw materials and application processes [5,6]. SLMs are an alternative to the conventional flooring system, which uses a dry mortar between 15 and 100 mm thickness. This increases the self-weight of buildings and favors the appearance of pathological manifestations such as cracks, undulations, and unevenness [5,7,8].

The optimized combination of hydraulic binders, fine aggregates, mineral additions, chemical additives, and water favors the formulation of a mortar with high fluidity, pumpability, and homogeneity (resistance to segregation) in the fresh state [9] that is, an SLM. These mortars also have differences in the hardened state, standing out for the design of floor covering with greater initial strength, rapid setting time, and good volumetric stability [10].

However, some studies have reported that drying shrinkage is one of the causes of the appearance of cracks in this type of system [2,5,11,12] since the excess of fine particles present in their combinations leads to a greater demand for water when no chemical additive is used, generating a greater variation in volume due to the loss of water that produces tensile stresses, which cause the mortar to shrink and consequently, generates cracks [13,14,15]. The use of high initial strength cement also favors the appearance of cracks due to its characteristics such as rapid post-hydration hardening, high fineness (an advantage, considering that SLMs require a high fines content in their composition), and accelerated strength gain [16,17]. In addition, due to the higher clinker content in its composition, this type of cement is the most emissive cement in Brazil, with emissions ranging from 736 to 823 kg·CO₂/t [18].

To mitigate the shrinkage that occurs in this type of material, researchers have investigated the use of waste from different production processes, such as seashells [19], grounded slate from quarrying waste [20] porcelain tile waste [17] and recycled concrete aggregate [16]. Some types of waste are applied as a substitute for Portland cement and may minimize binder consumption [21], which is also desirable from an environmental point of view since cement is the most emissive material in SLM composition.

SLMs are commonly produced with approximate 1:2 (cement: sand) mass ratios [17,22,23]. This requires applying this material in small layers to meet the dematerialization of construction, cost optimization, and re-emissions reduction associated with its use, which requires optimized and planned construction processes.

The literature does not discuss the effect of the type of cement combined with mineral additions on the behavior of SLMs and their production. Nor do the discussions address aspects relating to the type of cement and CO₂ emissions. In this context, this research proposes the use of four types of Portland cement (CPI, CPII E, CPIV, and CPV ARI) with combinations of mineral additions (silica fume and metakaolin), assessing their effect on the physical–mechanical properties and carbon emissions, verifying that even if the materials are altered, the SLMs would meet the control parameters presented by existing methodologies.

High early-strength Portland cement is expected in this type of technology, as it facilitates the delivery of the subfloor in a short period. However, the rapid hydration reaction makes the material susceptible to shrinkage, causing cracks that can affect the material’s strength. In this context, employing cement with a slower initial hydration rate or mineral additions as secondary raw materials can help control shrinkage. Therefore, this research evaluates the effect of cement type on self-leveling mortars’ behavior. It investigates whether the proportioning of materials with cement of different hydration reaction rates impacts environmental indicators, shrinkage processes, and the fluidity parameters required in this type of technology. Additionally, it examines the effect of incorporating different mineral additions during this process.

2. Materials and Methods

2.1. Materials

This study used CP-I (Ordinary Portland Cement), CP II-E (Portland Cement Composed with Blast Furnace Slag), CP-IV (Pozzolanic Portland Cement), CP V-ARI (Portland Cement of High Initial Strength), silica fume (SF), and metakaolin (MK) according to the physical–chemical characteristics indicated in

Table 1. Chemical and physical characterization results of cement and additions.

Samples		SiO2	Al2O3	Fe2O3	CaO	MgO	SO3	Na2O	K2O	SrO	Others	Specific Mass (g/cm3)	BET Specific Area (m2/kg)
C1	CPI	1.50	4.90	2.10	75.5	10.0	4.40	0.40	0.50	0.20	0.31	3.17	3500
C2	CPII E	1.61	5.45	4.37	71.56	10.23	4.45	0.39	0.58	0.29	0.92	3.07	3000
C4	CPIV	27.2	14.60	3.2	46.30	2.80	4.00	0.05	0.17	0.04	1.22	2.95	8400
C5	CPV	1.50	4.24	4.64	68.79	10.77	6.95	0.97	1.34	0.51	0.23	3.06	5000
SF	Silica fume	95.75	1.01	0.06	0.73	-	1.73	-	-	0.73	0.93	2.26	22,000
MK	Metakaolin	52.54	34.0	2.10	0.36	2.42	0.38	0.41	-	3.38	10.56	2.56	19,100

. The main oxides, silica fume and metakaolin, comply with the chemical requirements of [24], making it a pozzolanic material. In physical terms, CP IV cement is the finest binder, and silica fume is the mineral addition with the largest surface area.

The study employed a variety of cement types, each with its unique properties and applications: CP-I (Ordinary Portland Cement), CP II-E (Portland Cement Composite with Blast Furnace Slag), CP-IV (Portland Pozzolanic Cement), and CP V-ARI (High Early Strength Portland Cement). These cements were used to formulate self-leveling mortars. Additionally, silica fume and metakaolin were adopted as secondary cementitious materials. As indicated in Table 1, these materials contain oxides at favorable levels to promote pozzolanic reactions. It is worth noting that these supplementary cementitious materials have a high surface area compared to cement and a lower specific mass. These factors can significantly influence the rheological aspects and productivity of the material.

The natural fine aggregate used was natural quartz sand extracted from the bed of the Tocantins River in Brazil, passed through a 0.60 mm mesh sieve, and characterized in terms of granulometry [25], water absorption [26], specific mass [27], and unit mass [28]. The results classified the sand as fine, with a low water absorption capacity (0.40%). The specific mass and unit mass were 2.4 g/cm³ and 1.59 g/cm³, respectively.

To guarantee fluidity in the mixture and reduce water consumption, the superplasticizer (SP) additive, consisting of an aqueous solution based on polycarboxylate polymers, was used, following the manufacturer’s recommendations (0.20% to 2.0% concerning the cement mass).

2.2. Methods

2.2.1. Self-Leveling Mortars (SLMs) Batching Study

The study was based on a mortar dosage method from the literature [29]. The authors used the dosage method for self-compacting concrete (SCC) [30], in which SCC concrete is obtained from the conventional concrete’s rheological alteration by incorporating chemical additives and mineral additions. In this way, the fluidity increased with the chemical additive, and segregation is corrected by adjusting the fines.

The materials ratio was kept fixed at 1:2 (cement: sand, by mass) and the water/cement ratio (w/c) at 0.50, according to previous studies [16,17] which indicates that the SLMs formulated in this proportion have the fluidity and cohesion required for the technology, with physical mechanical standards that meet current international standards [31,32].

The dosing study determined the optimum superplasticizer content. The response variable was the different mixtures’ average spread which, according to [32], should fall within the 250 to 260 mm range. In the study, the target value was 270 ± 10 mm due to the subsequent incorporation of SF and MK, which, due to their high fineness, tend to reduce the mixture’s consistency as the demand for water increases.

Previous studies showed that the minimum superplasticizer content for this materials’ ratio was 0.30%. These studies showed that the minimum superplasticizer content for the proportion of this material was 0.30%. This value changed depending on the type of cement, with maximum contents of 0.35%, 0.40%, 0.5%, and 1% for CP II-E, CP I, CP V-ARI, and CP IV, respectively.

The mixtures were then homogenized with this content, from which the initial parameters were measured. Then, 0.05% portions of the additive were added to the mixture, with the optimum superplasticizer content being the value that resulted in a spread greater than the range recommended by [32].

After establishing the superplasticizer content, the optimum content of mineral additions was studied, adding 5% portions to the reference mixture until the target level was obtained. Cohesion and fluidity were assessed using the visual parameters cited by [33] as shown in Figure 1, which considers non-uniform and/or segregated edges inadequate, as shown in the figures. Based on these tests, 8 mortars were produced in this study (

Table 2. Material consumption in kg per m³ of self-leveling mortars produced in the study.

Silica Fume
Mixtures	Cement	Sand	Water	SP	SF/MK
C1.SF15	582.50	1165.01	291.25	2.16	87.38
C2.SF15	579.09	1158.18	289.54	1.97	86.86
C4.SF05	589.84	1179.69	294.92	7.37	29.49
C5.SF10	586.27	1172.54	293.13	2.93	58.63
Metakaolin
C1.MK25	571.91	1143.82	285.95	2.12	142.98
C2.MK25	568.30	1136.61	284.15	1.93	142.08
C4.MK05	590.87	1181.73	295.43	7.39	29.54
C5.MK10	588.11	1176.23	294.06	2.94	58.81

Note: Cn1.n2n3: (Cn1) mixtures by type of Portland cement, (n2) addition type and (n3) addition percentage. C1: CPI, C2: CPII E, C4: CPIV, C5: CPV, SF: silica fume, MK: metakaolin.

).

Table 3. Fines’ adjustment.

Addition	Cement Type	Exp. Adjustment	Cement	Sand	w/c	Additive (%)	Addition (%)	Edges (U/D)	Segregation (CS/SS)
SF	C1	1	1	2	0.5	0.40	5	U	CS
		2	1	2	0.5	0.40	10	U	CS
		3	1	2	0.5	0.40	15	U	SS
	C2	1	1	2	0.5	0.35	5	D	CS
		2	1	2	0.5	0.35	10	U	CS
		3	1	2	0.5	0.35	15	U	SS
	C4	1	1	2	0.5	1.25	5	U	SS
	C5	1	1	2	0.5	0.50	5	U	CS
		2	1	2	0.5	0.50	10	U	SS
MK	C1	1	1	2	0.5	0.40	5	U	CS
		2	1	2	0.5	0.40	10	U	CS
		3	1	2	0.5	0.40	15	U	CS
		4	1	2	0.5	0.40	20	U	CS
		5	1	2	0.5	0.40	25	U	SS
	C2	1	1	2	0.5	0.35	5	D	CS
		2	1	2	0.5	0.35	10	D	CS
		3	1	2	0.5	0.35	15	U	CS
		4	1	2	0.5	0.35	20	U	CS
		5	1	2	0.5	0.35	25	U	SS
	C4	1	1	2	0.5	1.25	5	U	SS
	C5	1	1	2	0.5	0.50	5	U	CS
		2	1	2	0.5	0.50	10	U	SS

U = uniform, D = non-uniform, CS = with segregation, and SS = without segregation.

shows the fines (silica fume and metakaolin) adjustment results. The mineral additions were added gradually to correct segregation and ensure the mixtures’ cohesion.

2.2.2. Mortars Production

After establishing the optimum proportioning of materials for self-leveling mortar production, the mixing order was set, as shown in Figure 2. The materials were added in batches at a slow speed by the mechanical mixer to disperse the materials and ensure the mixtures’ homogeneity.

At the end of each mixing, the average spreading and flow time tests were carried out to check whether the mortars met the self-adhesiveness criteria established by [31,32,33]. In addition to the fresh state tests, the mass density and the incorporated air content [34], curing time, and flow retention by C1708 standard [31] were evaluated. The method adapted from [35] was used to determine the exudation rate, which adjusts the Brazilian standard normative concrete test [35] to the mortar’s peculiarities. The axial compressive strength and flexural tensile strength [36] and the dimensional variation [37] were evaluated in the hardened state.

2.3. CO₂ Emissions

To assess the CO₂ emissions related to SLM production and use, materials consumption, CO₂ emissions associated with them, and the mortar application thickness were considered. CO₂ emissions estimate was obtained by adding the emissions of each material (

Table 4. CO₂ emissions associated with the SLM materials production.

Variables		Data (kgCO2/kg)	Reference
Eclinker		0.834	WBCSD [38]
% clinker	CP I 1	90–95%	NBR 16697 [39]
	CP II 1,2	46–89%
	CP IV 1,2	40–80%
	CP V 1,3	85–95%
Esand		0.03	Taveres and Bragança [40]
ESF		0.014	Norchem [41]
EMK		0.279	Díaz et al. [42]
Ead		1.065	Ma et al. [43]
Eenergy		0.108 kWh/kg	WBCSD [38]
FEenergy		0.08 kgCO2/kwh	MCTI [44]

¹ Sulfate content, estimated at 5%. ² Limestone filler and Flay Ash. ³ Limestone filler.

) multiplied by the respective consumption in the mortar proportioning (Table 2), according to Equation (1).

$${CO}_{2_{SLM}}=\sum E_c\ast C_c+E_{sand}\ast C_{sand}+E_{SF}\ast C_{SF}+E_{MK}\ast C_{MK}+E_{Ad}\ast C_{Ad}$$

(1)

where ${CO}_{2_{SLM}}$ is SLM total emissions (kgCO₂/m³). $E_c$, $E_{sand}$,$E_{Ad},$ $E_{SF}$, $E_{MK}$ is cement, sand, admixture, silica fume and metakaolin emissions in kg·CO₂/kg, respectively. $C_c$, $C_{sand}$, $C_{Ad},C_{SF},C_{MK}$ is cement, sand, admixture, silica fume, and metakaolin consumption in kg/m³, respectively.

Portland cement emission is determined based on Equation (2), using the clinker percentages shown in Table 5.

$$E_c=\left(E_{\mathit{clinker}}·{{\%}_{\mathit{clinker}}}_{\mathit{cem}}\right)+\left(E_{\mathit{energy}}·{FE}_{\mathit{energy}}\right)$$

(2)

where:

• $E_c$ = Total emissions of cement (kgCO₂/kg);
• $E_{clinker}$ = Clinker production emissions (kgCO₂/kg);
• ${{\%}_{\mathit{clinker}}}_{\mathit{cem}}$ = Clinker percentage of cement used.
• $E_{energy}$ = Emission from electric energy used in the process (kWh/kg);
• $F{E}_{energy}$ = Electric energy emission factor (kgCO₂/kg).

Table 5. Self-adhesiveness parameters results.

Mixtures	EFNARC Parameters (2002)		Martins’ Parameters (2009)
	Average Spreading: 240 to 260 mm	Flow Time: 7 to 11 s	Edges	Segregation
C1.SF15	257	7.56	U	SS
C2.SF15	252	7.65	U	SS
C4.SF05	259	7.30	U	SS
C5.SF10	248	8.60	U	SS
C1.MK25	242	8.77	U	SS
C2.MK25	244	8.68	U	SS
C4.MK05	259	7.35	U	SS
C5.MK10	248	8.58	U	SS

Note: Cn1.n2n3: (Cn1) mixtures by type of Portland cement, (n2) addition type, and (n3) addition percentage. C1: CPI, C2: CPII E, C4: CPIV, C5: CPV, SF: silica fume, MK: metakaolin.

Table 5. Self-adhesiveness parameters results.

Mixtures	EFNARC Parameters (2002)		Martins’ Parameters (2009)
	Average Spreading: 240 to 260 mm	Flow Time: 7 to 11 s	Edges	Segregation
C1.SF15	257	7.56	U	SS
C2.SF15	252	7.65	U	SS
C4.SF05	259	7.30	U	SS
C5.SF10	248	8.60	U	SS
C1.MK25	242	8.77	U	SS
C2.MK25	244	8.68	U	SS
C4.MK05	259	7.35	U	SS
C5.MK10	248	8.58	U	SS

Note: Cn1.n2n3: (Cn1) mixtures by type of Portland cement, (n2) addition type, and (n3) addition percentage. C1: CPI, C2: CPII E, C4: CPIV, C5: CPV, SF: silica fume, MK: metakaolin.

The scope used to estimate emissions was cradle-to-gate, and water emissions were not calculated due to the lack of Brazilian data. Emissions associated with transporting materials, mixing, and applying mortars must be assessed individually when using the material, as they are affected by the transportation distance, production process, and application thickness. The carbon index (CI) was determined according to Equation (3). The CI expresses the amount of CO₂ emitted per m³ of material to obtain one MPa, making it possible to assess the efficiency of the dosing process and the quality of the materials that make up the SLMs.

$$CI=\frac{C_{C{O}_2}}{fck}$$

(3)

where:

• CI = Carbon Index, at kg·m⁻³·MPa⁻¹;
• C_CO2 = CO₂ emissions associated with materials production that make up the SLM (cradle-to-gate scope). fck = compressive strength at 28 days.

3. Results and Discussions

3.1. Self-Adhesion Parameters, Curing Time, Exudation Rate, and Flow Retention

Table 6. Mortar curing time.

Mixtures	Curing Time (Min)
C1.SF15	15
C2.SF15	15
C4.SF05	10
C5.SF10	10
C1.MK25	20
C2.MK25	15
C4.MK05	15
C5.MK10	10

Note: Cn1.n2n3: (Cn1) mixtures by type of Portland cement, (n2) addition type, and (n3) addition percentage. C1: CPI, C2: CPII E, C4: CPIV, C5: CPV, SF: silica fume, MK: metakaolin.

shows SLM’s average spreading and flow time produced with different cement types and SF and MK levels added. All the mortars met the 250 mm ± 10 mm flow limit recommended by EFNARC [32]. They also met Martins’ visual parameters [33], maintaining the desired workability and stability without segregation.

Figure 3 presents the different SLM fluidity analyses based on the flow time results. For the effect of the type of cement on the mortars’ fluidity, it was seen that the SLMs with the finest cement (CP IV) were the most fluid. The mortars that combined cement and the addition of the lower surface area had the lowest fluidity.

Zhang et al. [45] state that fineness contributes to fluidity since finer materials have a greater thickness of water adsorbed on the grains, and this surface water makes the mixtures more fluid. However, the random movement of the particles during mixing agglomerates the fines, requiring dispersant additives to secure the fluidity needed for this technology. In this regard, Mehdipour et al. [46] commented that dispersant additives favor the mortars’ mobility by dispersing the flocculated grains, releasing the water from the trapped layer, and making the mixtures more fluid. For this reason, dispersants must be controlled, as they tend to increase the risk of exudation and product instability, requiring the mineral additions incorporation to control cohesion and guarantee stability and homogeneity [23,46]. A difference in the rheological behavior of mortars with silica fume (SF) and metakaolin (MK) was observed for the mineral additions in SLM production. The mortars with metakaolin required a higher material content to achieve the established self-adhesion parameters. As the MK surface area is smaller than that of SF, it was necessary to incorporate higher levels of MK to control fluidity and cohesion. Similar behavior has been observed in previous research [23,47], indicating a certain complexity in the SLM dosage, especially regarding the content of additives and additions, since small changes in these can modify the material’s rheological properties.

The self-leveling mortars under study had a curing time ranging from 10 to 20 min (Table 6). The results showed that mixtures with these binders quickly recovered their original leveling state. It was seen that this type of special mortar was sensitive to changes in materials, with reduced handling times. Knowledge of the working time is essential for planning the execution stages in practical applications. However, there are no normative recommendations for minimum curing times for SLM to date. Because of this, the curing time results of this study were compared with the literature, and it was noted that the results were similar to those of Oliveira et al. [16] who studied the effect of recycled aggregate on this characteristic and found average values between 15 and 25 min. Mendes et al. [48] analyzed the effect of marble and granite cutting waste and obtained curing times ranging between 15 and 20 min.

Cement with factory pozzolanic additions (CP IV and CP II E) containing up to 50 pozzolans and 34% fly ash, respectively, showed lower exudation values (Figure 4). The literature indicates that mixtures with exudation rates close to zero are favorable [48,49,50] since controlling exudation directly influences this composite’s durability. In this respect, only the SLMs produced with CP IV-type cement did not exude for the two additions.

Zhang et al. [45] studied the role of pozzolanic materials in cement mixtures’ fluidity. They observed that the water in the grains’ surface layer plays a major role in the mixture’s fluidity. This same study showed that the purer the cement, the lower the amount of water in the surface layer that aids fluidity and the greater the risk of exudation. Such behavior was observed in this study, as shown in Figure 4. The mixtures with silica fume showed a lower rate for the effect of the addition on the exudation rate. It is considered that silica fume addition promoted greater stability in cementitious matrices than the addition of metakaolin since, due to its fineness, it manages to correct the dispersing effect caused by the superplasticizer additive, controlling cohesion. It secures the necessary fluidity for the system from the water surface layer present in its grains. Another parameter assessed was flow retention, which evaluates the loss of workability of mortars over time, as shown in Figure 5 and Figure 6.

C 1708 standard [31] does not stipulate minimum or maximum requirements. Still, it highlights the need for the mortar to have a sufficient flow retention time to not compromise the material’s application and finish. For applicability, the loss of workability was measured by the consistency test, which measured 20 and 30 min after mixing. Figure 7 shows the risk of using these mortars after 20 min, which may lead to pumping failures and hose clogging, compromising the material finish.

For the effect of the cement type, the greatest fluidity losses were seen for mixtures with CP IV cement with a higher content of superplasticizing additive, which lost their efficiency over time. Kwan and Fung [51] stated that the particles’ surface area affects the additive’s efficiency, reducing the molecules’ adsorbed concentration on the cement grains’ surface, thus affecting the chemical additive’s action. Adjoudj et al. [52] state that the presence of fines modifies the paste volume, increasing it through the packing effect of the particles [53,54]. The larger the paste volume, the greater the plasticity and cohesion, and the higher the water volume. Initially, this water enhances fluidity by coating the solid particles and improving workability. However, it evaporates over time, leading to a more significant loss of fluidity.

3.2. Physical–Mechanical Properties Evaluation of Mortars

Figure 8 shows that the differences between the mass density of the silica fume and metakaolin mixtures did not vary much when the materials were changed. As the mixture, mixing procedure and w/c factor are fixed for all the formulations, the results for the density and incorporated air content tests follow the same trend with slight variations.

Figure 9 presents the results of self-leveling mortars’ mechanical properties formulated with different cement types and additions. They all met the minimum 20 MPa standard set by EFNARC [32] for compressive strength and 5 MPa for flexural tensile strength.

The simple compressive strength results ranged from 25.87 to 49.38 MPa, in line with those found in the literature [3,9,22]. Also, according to the NBR 12041 standard (ABNT, 2012), a mortar with more than 40 MPa strength has high mechanical strength self-leveling mortar for floors. The mixtures that fall into this category were C5.SF10, C5.MK10, C1.SF15, C1.MK25 and C4.MK05.

When the flexural strength of self-leveling mortars was evaluated, it was observed that the values did not exceed 12 MPa, with very similar values being found regardless of the type of addition incorporated. As there are no normative parameters for this property, the results were compared with those found in the literature, and it was found that the values range from 7 to 15 MPa [55,56,57].

3.3. Dimensional Variation Evaluation

Table 7. Mortar dimensional variation depending on the type of material.

Mixtures	Readings (mm)				Standard Deviation	Variation Coefficient
	ε0	ε1	ε7	ε28
C1.SA15	0.00	−0.22	−0.48	−0.67	0.23	0
C2.SA15	0.00	0.31	−0.12	−0.61	0.46	3
C4.SA05	0.00	−0.09	−0.5	−0.85	0.38	1
C5.SA10	0.00	−0.64	−0.97	−1.64	0.51	0
C1.MC25	0.00	−0.26	−0.73	−0.73	0.27	0
C2.MC25	0.00	−0.03	−0.68	−0.76	0.40	1
C4.MC05	0.00	−0.15	−0.82	−0.95	0.43	1
C5.MC10	0.00	−0.32	−1.28	−2.19	0.93	1

shows the average shrinkage values for each formulation tested, corresponding to days 1, 7, and 28, according to the NBR 15261 standard [37]. The results showed that the mixtures with the greatest displacement at 28 days were those with CPV ARI and CPIV, with more than 0.80 mm/m variations.

Studies by [14,15] found that shrinkage in self-leveling systems is influenced by the high content of fine particles needed to achieve adequate fluidity. According to Bauer (2005) [58] high cement consumption increases the modulus of elasticity, making the materials more rigid and, consequently, less capable of deforming without breaking, generating a greater risk of cracking.

In this respect, the mixtures with CP IV and CP V-ARI cement showed displacement variations greater than 0.80 mm/m at 28 days with the addition of silica (1.64 and 0.85 mm/m) and with metakaolin (2.19 and 0.90 mm/m), respectively. This behavior was attributed to the chemical and physical parameters (Table 1) of the materials involved, which explain the high reactivity in the first few hours, causing stiffening and changes in the initial consistency due to the mixing water partial loss, which leads to greater variation and the appearance of cracks. The appearance of cracks is not desirable from the point of view of durability and useful life and, consequently, sustainability [59].

3.4. CO₂ Emissions

Mixtures with pozzolanic cement (CP II E and CP IV), silica fume, and metakaolin had lower CO₂ emissions (Figure 10), linked with the lower average amount of cement clinker. In the isolated analysis of mechanical properties (Figure 9), SLMs with CP II E (C2) and CIV (C4) performed less well than the others.

The deviation bar (Figure 10) indicates the maximum and minimum emissions for each mixture, which are related to the maximum and minimum clinker content allowed by Brazilian regulations for each cement type [39], as shown in Table 6. When analyzing the carbon index (CO₂ emissions per m³/mixture’s compressive strength), it was noted that the best efficiency was achieved for SLMs produced with CP IV cement with metakaolin (5.8 kg·CO₂/MPa) followed by mortar with silica fume (6.8 kg·CO₂/MPa). For concrete, this indicator should be less than 5 kg·CO₂/MPa for an eco-efficient mix [60]. There is no reference in the literature to this indicator for SLM.

When analyzing emissions from cementitious materials, cement is generally the most emissive item in the mixture. For this reason, choosing cement with lower clinker contents or reducing cement consumption in the mixture are the main strategies for significantly reducing emissions. In the first case, knowing the classes of cement available and their associated emissions is vital to selecting the lowest emitting material, provided it meets the necessary technical requirements. In the second case, optimized proportioning is needed, considering the replacement of Portland cement with fine materials, such as filers and pozzolanic additions, among others, and using superplasticizing additives. In addition, CO₂ emissions reduction (decarbonization) in construction is associated with dematerialization (material consumption reduction), which is directly related to the reduction of waste generation and incorporated losses and the optimized application in the material.

4. Conclusions

When analyzing the effect of the type of cement and mineral additions on the physical and mechanical behavior of self-leveling mortars, it was concluded that the cement surface area was the factor that most influenced the mortars’ performance. Cement with higher surface areas required more superplasticizing additives to achieve the target properties in the fresh state and had higher shrinkage rates.

For all the cement evaluated, achieving self-adhesiveness for mortars with high fluidity, uniformity, and no segregation depends on adjusting the content of mineral additions and additives. The number of adjustments with mineral additions was lower in mixtures with finer cement than in coarser cement. Coarser cements tend to produce more dense mortars, which must be corrected with higher mineral and chemical additive levels.

Mineral additions contributed to the physical and mechanical properties of self-leveling mortars, as well as to their cohesion and reduced shrinkage in mixtures containing up to 25% metakaolin and 15% silica.

The type of cement is directly related to SLM’s CO₂ emissions. Cement with a lower clinker content leads to mixtures with up to a 170 kg CO₂ reduction per m³ of material and is 34% less emissive. This advantage was maintained when evaluating the CI (carbon index), around 5.8 kg·CO₂/MPa for SLM produced with cement with the lowest clinker content (CP IV) and 11.4 CO₂/MPa for cement with the highest clinker content (CP I).

To reduce emissions from cement-based materials, it is necessary to reduce cement consumption or use cement with a lower clinker content. Cement is the most emissive component, making it imperative to use additions and admixtures. Reducing CO₂ emissions in the construction industry also depends on dematerialization, which should minimize waste and optimize the use of materials, considering life cycle aspects, especially the service life. Future studies should consider dematerialization solutions for global climate issues to achieve construction decarbonization.