Physical, Thermal and Microstructural Characterization of Earth Mortars Stabilized with Incorporating Air Additive

Abstract:

In recent years, the search for non-conventional materials has intensified, aiming to reduce environmental impacts in the civil construction sector as a strategy for more sustainable development. Among these materials, earth mortars are a promising option, as they have technological, economic, and environmental advantages. Due to the absence of literary data on the use of air-incorporating additives (AEA) in earth mortars, the objective of this article is to verify the influence of the incorporation of AEA (0,10, 20, and 40% of the total volume of the mixture) in the mechanical properties (compression strength at 28 days), physical (total water absorption by immersion), thermal, and microstructural (scanning electron microscopy) of the referred mortars. The study was carried out in a stabilized earth mortar, with a 1:3 mass mix proportion (binder: aggregate). The raw materials used were constituted by binders (cement, hydrated lime, fly ash, metakaolinite), aggregates (sand, a coarse fraction of the soil), additives (AEA, calcium chloride, superplasticizer), and water. The water-binder material ratio (a / bm) was fixed at 0.65, and the consumption of binder and aggregate was 461.71 and 1385.12 kg, respectively, per m³ of the mixture. The tests demonstrated that the incorporation of the additive influenced the behavior under compression (strength and stiffness reduction), thermal performance (conductivity reduction), and physical behavior (absorption and voids index´s increases) compared to the mixture without AEA. From the analysis of the results, it was found that the incorporation of air in the mortars led to an increase in porosity, directly influencing the thermal insulation capacity, measured by thermal conductivity. Microstructure changes were observed through SEM images, corroborating the influence of the AEA. Under compression loads, the stiffness reduction decreases the risk of eventual cracking, however, the reduction in strength should be controlled to meet normative limits.

• Periodical: Construction Technologies and Architecture (Volume 1)
• Pages: 211-218
• DOI: https://doi.org/10.4028/www.scientific.net/CTA.1.211
• Online since: January 2022
• Authors: Rayane de Lima Moura Paiva*, Patrícia Brandão Sousa, Camila de Barros Lima Carreira, Adriana Paiva Souza Martins, Romildo Dias Toledo Filho
• Keywords: Air Incorporating Additive, Earth Mortars, Mechanical Behavior, Thermal Conductivity

References

[1] Brazilian Association of Technical Standards, 2005. Hardened mortar and concrete - Determination of absorption, voids and specific gravity: NBR 9778, Corrected Version 2:2009. Rio de Janeiro.

[2] Brazilian Association of Technical Standards, 2005. Mortars applied on walls and ceilings - Determination of the specific gravity and the air entrained content in the fresh stage: NBR 13278. Rio de Janeiro.

[3] Brazilian Association of Technical Standards, 2005. Mortars applied on walls and ceilings - Determination of the specific gravity in the hardened stage: NBR 13280. Rio de Janeiro.

[4] Brazilian Association of Technical Standards, 2005. Thermal Performance of Buildings. Methods of calculating thermal transmittance, thermal capacity, thermal delay and solar factor of building elements and components: NBR 15220. Rio de Janeiro.

DOI: 10.3403/30313347

[5] Brazilian Association of Technical Standards, 2016. Mortars applied on walls and ceilings - Determination of the consistence index: NBR 13276. Rio de Janeiro.

[6] Brazilian Association of Technical Standards, 2017. Concrete - Determination of static modulus of elasticity and deformation by compression: NBR 8522. Rio de Janeiro.

[7] Brazilian Association of Technical Standards, 2018. Concrete - Compression test of cylindrical specimens: NBR 5739. Rio de Janeiro.

[8] Brazilian Association of Technical Standards, 2020. Concrete - Determination of air content in fresh concrete - pressometric method: NBR 16887. Rio de Janeiro.

[9] Gomes, M.I., Faria, P., Gonçalves, T.D., 2018, Earth-based mortars for repair and protection of rammed earth walls. Stabilization with mineral binders and fibers. Journal of Cleaner Production 172, 2401-2414.

DOI: 10.1016/j.jclepro.2017.11.170

[10] IEA – International Energy Agency, 2019. Report: Perspectives for the Clean Energy Transition – The Critical Role of Buildings. https://webstore.iea.org/download/direct/2496 (accessed 12.08.2020).

[11] Melià, P., Ruggieri, G.,Sabbadini, S., Dotelli, G.,2014. Environmental impacts of natural and conventional building materials: a case study on earth plasters. Journal of Cleaner Production 80, 179-186.

DOI: 10.1016/j.jclepro.2014.05.073

[12] Mehta, P. K.; Monteiro, P. J. M., 2008. Concrete. Microstructure, Properties and Materials. 3rd ed. Sao Paulo. Ibracon - Brazilian Concrete.

[13] Resende, P. S. O., 2010. Effect of Incorporated Air in Coatings Mortars (Master's Dissertation). Federal University of Goiás, School of Civil Engineering, Goiânia, Brazil.

[14] Santos, T., Gomes, M.I., Silva, A.S., Ferraz, E., Faria, P., 2020. Comparison of mineralogical, mechanical and hygroscopic characteristic of earthen, gypsum and cement-based plasters. Construction and Building Materials 254. https://doi.org/10.1016/j.conbuildmat.2020.119222.

DOI: 10.1016/j.conbuildmat.2020.119222

[15] Souza, P. F. S., 2016 Characterization of earth and lime mortars for reworking stone masonry joints in Vale das Lobas. (Master's thesis), University of Nova Lisbon, Portugal.