By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.Jul 18 2024An article published in Sustainability has explored the physical and mechanical properties and environmental aspects of self-leveling mortars prepared using different types of cement.
Exudation rate as a function of cement type and addition. Image Credit: https://www.mdpi.com/2071-1050/16/14/5898
Background
Self-leveling mortars (SLMs) are increasingly utilized in modern flooring systems, praised for their ability to automatically achieve perfect levelness and self-adhesion when wet. Their enhanced durability surpasses that of traditional flooring systems, which tend to rely on dry mortar. One of the primary advantages of SLMs is their high fluidity, which not only accelerates application but also ensures even leveling without the risk of segregation.
Typically, SLMs are formulated from a blend of cement and sand in approximately a 1:2 mass ratio and are applied in thin layers. This approach not only aids in dematerializing construction processes but also contributes to cost reduction. However, achieving these benefits requires careful optimization to minimize re-emissions during use.
Despite their growing use, the impact of different types of cement and the addition of mineral supplements on the physical and mechanical characteristics of SLMs and their associated CO2 emissions remain underexplored. This gap in knowledge led to the present study, which investigates the effects of four distinct types of Portland cement and two mineral additions on the overall performance and environmental impact of SLMs.
Methods
CP-I (ordinary Portland cement), CP II-E (Portland cement with blast furnace slag), CP-IV (pozzolanic Portland cement), and CP V-ARI (Portland cement with high initial strength) were used to formulate SLMs. In addition, silica fume (SF) and metakaolin (MK) were used as secondary cementitious materials (SCMs).
Locally sourced natural quartz sand (sieved through a 0.60 mm mesh) was used for preparing mortars. Furthermore, a superplasticizer (SP) based on polycarboxylate polymers was added (0.20-2.0 wt.% of cement) to the SLMs to ensure fluidity and reduce water consumption.
As per international standards, cement:sand and water:cement (w/c) ratios were fixed as 1:2 and 0.50, respectively. Alternatively, the SP content was varied as 0.35 %, 0.40 %, 0.5 %, and 1 % for CP II-E, CP-I, CP V-ARI, and CP-IV, respectively. Consequently, eight homogenized mortar mixtures were prepared using these proportions and 0.05 % additives.
The average spreading and flow time of the SLMs were studied in the fresh state. Attributes such as mass density, incorporated air content, curing time, and flow retention were evaluated through standard tests. Additionally, axial compressive strength, flexural tensile strength, and dimensional variation were examined after solidification.
Finally, CO2 emissions related to SLMs were evaluated by considering material consumption and mortar application thickness according to the cradle-to-gate scope. The carbon index (CI) calculated for each mortar composition revealed the efficiency and quality of the materials used.
Results and Discussion
The properties of SLMs varied significantly with the type of cement and SCMs. Notably, all mortar compositions met the standard 250 ± 10 mm flow limit and Martins’ visual parameters, ensuring sufficient workability and stability without segregation. While the SLM with the finest cement (CP-IV) was the most fluid, the mortars with a lower surface area additive had the lowest fluidity.
SF and MK influenced the rheology of mortars differently. The mortars with MK (a smaller surface area than SF) required a higher SP content to achieve the desired self-adhesion parameters such as fluidity and cohesion.
The prepared SLMs exhibited a curing time of 10 to 20 minutes and rapid recovery to their original leveling state upon adding SCMs. Additionally, the mortar comprising pozzolanic cement (CP-IV and CP II-E) demonstrated lower exudation values, which enhances the composite’s durability. Furthermore, the SLM with CP-IV cement did not exude after adding SF and MK. However, it exhibited maximum fluidity loss with a higher SP content.
All the formulated SLMs met the minimum standards of 20 MPa for compressive strength and 5 MPa for flexural tensile strength. Additionally, their flexural strength did not exceed 12 MPa, irrespective of the type of additive. Considering the average shrinkage values after 28 days, SLMs with CP V-ARI and CP-IV exhibited maximum displacement (> 0.80 mm/m variations) by adding SF and MK.
SLMs with pozzolanic cement (CP-IV and CP II-E), SF, and MK had lower CO2 emissions due to the lower cement clinker content. Among these, mortar comprising CP-IV and MK exhibited the best efficiency (5.8 kg·CO2/MPa). However, it is greater than the standard of 5 kg·CO2/MPa for an eco-efficient mortar.
Conclusion
The detailed investigation into self-leveling mortars that utilize various types of cement and supplementary cementitious materials identified cement surface area as the most influential factor affecting mortar performance. Mortars made with high-surface area cement were found to require more superplasticizers (SP) to attain desirable properties and tended to exhibit higher shrinkage rates.
The study also found that the self-adhesiveness and overall quality of the mortars—characterized by enhanced fluidity, uniformity, and absence of segregation—could be adjusted by fine-tuning the amount of SCMs used. For instance, using coarser cement generally resulted in denser mortars, necessitating adjustments with additional mineral and chemical additives to meet performance standards.
In terms of environmental impact, the study highlights several strategies to lower CO2 emissions associated with cementitious materials. These include reducing the total amount of cement used or opting for cements with a lower clinker content.
Furthermore, the authors advocate for the implementation of dematerialization strategies in construction processes as a means to further the goals of decarbonization. These findings suggest that careful material selection and formulation adjustments can significantly enhance both the functional and environmental performance of SLMs.
Journal Reference
Alves, B. M. O., Teixeira, M. da C., Bernardo, K. S. M., Cordeiro, L. de N. P., & Possan, E. (2024). Self-Leveling Mortars Produced with Different Types of Cement: Physical–Mechanical Properties and Carbon Emissions. Sustainability, 16(14), 5898. DOI: 10.3390/su16145898, https://www.mdpi.com/2071-1050/16/14/5898
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