PSI - Issue 41

Maria-Evangelia Stogia et al. / Procedia Structural Integrity 41 (2022) 744–751 Maria Evangelia Stogia et al. / Structural Integrity Procedia 00 (2019) 000–000

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four-point bending tests. The results obtained were then compared with respective ones from literature. The knowledge on the lime-based pastes allows for better understanding of the behaviour of the binder fraction required for the

production of the final mortar. 2. Experimental Procedure 2.1 Materials

Two different types of binder were used in the present investigation: the first one consists of natural hydraulic lime (NHL5 - Saint Astier ® Natural Hydraulic Limes) and metakaolin (MK) (Metacal ® 3000 - CALTRA Nederland B.V.) that will be referred hereafter as binary paste. Ternary binders were also prepared based on the same lime and meta kaolin and with the addition of cement (Aalborg White ® CEM I 52,5 N). The different mixtures were also compared with the paste consisted of 100 wt% lime. The proportions of binder, aggregates and water were selected in order to achieve optimum workability. The binary binders were prepared by mixing NHL5 and MK at different concentrations, i.e., 65 wt% and 35 wt%, 50 wt% and 50 wt%, and, finally, 80 wt% and 20 wt%, respectively. The ternary binders were prepared by mixing NHL5, MK and CEM I for different concentrations, namely (35 wt%, 35 wt%, 30 wt%), (40 wt%, 40 wt%, 20 wt%) and (47.5 wt%, 47.5 wt%, 5 wt%), respectively. The water to binder (W/B) ratio was set at 0.75 in all cases. The standard test method ASTM C305-06 was followed for all the specimens in the mixing procedure that was performed in a standard 5 L mixer made by TECHNOTEST ® . The amount of the building materials was placed into the mixing bowl with water. Initially, the mixer was set to rotate at low speed for 30 s. Then, its function was paused for 15 s to scrape down the paste that remained on the sides of the bowl. Finally, the mixer was rotated at medium speed for 90 s, according to the standard. Without excessive compaction or vibration, the paste was quickly put into the mold after mixing the components with bottled water of specific characteristics (VIKOS S.A. bottled water) according to the procedures described recently by Dimou et al. (2022). For each experimental set, six cylindrical and five prismatic specimens were prepared. The cylindrical specimens had a diameter of 30 mm and a height of 60 mm, while the prismatic specimens had dimensions of 80 mm in length, 20 mm in width, and 20 mm in height (Fig.1). After 48 h, all specimens were demolded and placed in water tanks at room temperature, where they were kept for 60 days when all the mechanical tests were carried out.

Table 1. Mix Recipes for the Pastes

Proportions of the mixing components (wt %)

Name

L100-M0-C0

L80-M20-C0

L65-M35-C0

L50-M50-C0

L47.5-M47.5-C5

L40-M40-C20

L35-M35-C30

Materials

NHL5 (L)

100

80

65

50

47.5

40

35

Metakaolin (M)

0

20

35

50

47.5

40

35

Cement (C)

0

0

0

0

5

20

30

Fig.1. Prismatic specimen after fracture in 4-point bending test