Physical, mineralogical and mechanical characterization of ready-mixed clay plaster

Abstract

The use of clay plasters with or without plant fibers (straw, hemp or other) inside buildings is currently showing considerable growth in many countries. Despite this development, there are very few data in the literature on the characteristics of clay plasters. This paper deals with the characterization of five ready-mixed clay plasters from French brickworks using the recent German standard. The work essentially consisted in measuring the flow of fresh clay plasters and their characteristics after hardening (shrinkage, and compressive, flexural and adhesive strength). The characterization of the samples showed that the granular characteristics were practically the same and that the main difference concerned the nature of the clayey minerals they contained: four samples were essentially composed of montmorillonite, chlorite and illite whereas one was only composed of kaolinite. Despite this difference, the flow of fresh clay plasters and their characteristics after hardening (shrinkage, compressive and flexural strength) were very similar and were comparable to the values given by the standard. However, the measurement of the adhesive strength led to two significant problems: the dispersion of the values was very high and the results were markedly different from the values given by the standard. For these reasons, it seems necessary to complete and adapt the procedure for measuring adhesive strength and it could be interesting to develop new tests for the measurement of this important characteristic, either in the laboratory or on building sites.

Earthen Plasters Based on Illitic Soils from Barrocal Region of Algarve: Contributions for Building Performance and Sustainability

“…The significantly low linear drying shrinkage of the assessed mortars (less than 1.5%) can be compared with five earth-based mortars characterized by Delinière et al [12], which were formulated with similar proportions of clayish earth and sand and presented higher drying shrinkage (between 1.5 and 2.5%) probably due to the different mineralogy of the clayish earths used, where illite is not the predominant clay mineral. Similar comparison can be made with the results obtained by Faria et al [14], which assessed a ready-mixed earth-based mortar with addition of oat straw fibers (shrinkage less than 1%), and Lima & Faria [15] which characterized six mortar specifically formulated with different additions of oat straw fibers and typha fiber wool (shrinkage also less than 1%).…”

“…Regarding adhesive strength the results obtained by Delinière et al [12], following DIN 18947 [11] test protocol, were highly dispersed and much lower than the limit values given by the class S-I of the standard (≥ 0.05 N/mm 2 ). This lead the researchers to test a modification of the protocol procedure, which mainly consist in previously wetting the support surface with a suspension (liquid mixture) of the clayish earth and water.…”

“…Regarding compressive and flexural strength, according to DIN 18947 [11], the five earth-based mortars characterized by Delinière et al [12] clearly achieved the class S-II for compressive strength (≥ 1.5 N/mm 2 ) and the class S-I for flexural strength (≥ 0.3 N/mm 2 ), while in the present study results were significantly lower, being the four assessed mortars just close to reach the minimum values defined for class S-I either for compressive and flexural strength. Considering that the mortars from both studies were formulated with similar proportions of clayish earth and sand, and apart from any contribution that may come for subtle differences of the used sands, the different results of mechanical resistance obtained may be justifiable by the different mineralogy of the clayish earths used on each study.…”

“…However, in Germany, the Deutsches Institut für Normung (DIN) recently released DIN 18947 [11], a national standard specifically devoted to earth-based mortars. Thenceforth that standard has been followed by several scientific studies regarding the assessment of mechanical and physical properties of this type of mortars [12,13,14,15].…”

Eco-Efficient Earthen Plasters: The Influence of the Addition of Natural Fibers

“…Thenceforth that standard has been followed by several scientific studies regarding the assessment of mechanical and physical properties of this type of mortars (Delinière, 2014;Faria et al, 2014;Lima and Faria, 2014).…”