PSI - Issue 10

I. Karatasios et al. / Procedia Structural Integrity 10 (2018) 211–218

214

I. Karatasios et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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dolomite. The presence of clay phases and iron oxides attribute the yellowish variation of stone shades from off white to pale yellow.

3.2. Mechanical properties of stones

In the case of the Marl stones from Piraeus, all samples were characterized as soft rocks. Their mechanical and physical properties are presented in Table 2. The stone fragments were grouped according to their texture, mineralogy (type and amount of clay content) and strength, on three categories: soft marls, marly sandstones and marly limestones. However, one of the main issues that arises when attempting to classify different types of Marls according to their mechanical performance and strength is the difficulty of integrating their behavior in common rules. Besides their similarities in petrographic and lithological characteristics, mineralogical and chemical composition, their structural and mechanical behavior are mostly depended on microstructural characteristics that sedimentation process and geo logical parameters have resulted on each different layer (stratum). Therefore, the different stones were categorized according to their compressive strength values, following the Bieniawski (1989) system and were grouped to: very low strength (Strength Cat. 1, 2), moderate (Strength Cat. 4) and high (Strength Cat. 7).

Table 2. Mechanical and physical properties of different natural stone types (n=3) . 3-point flexural bending strength Compressive strength Open porosity Water Absorption Coefficient

Strength Category

2 sec 0.5 )

Stone Code ST σ f (MPa)

ST σ c (MPa)

%

A (g/ m

7 (high)

ST01 ST02 ST03 ST04 ST05 ST06 ST07 ST08

12.0

62.1 32.8 29.0 18.9 14.6 46.5 16.3 5.7

8.5

31.5 38.8

4 (moderate) 4 (moderate) 2 (very low) 1 (very low) 2 (very low) 4 (moderate)

1.8 5.5 4.0 3.8 5.4 7.6 nd

12.9 17.7 21.2 21.9 19.4 10.9 25.2

181.8 136.3

83.6 92.8 54.4

2 (very low)

357.6

3.3. Repair mixtures for joining natural stone fragments without reinforcement

According to the mechanical properties of mortar mixtures that are presented in Table 3 and the stone-groups formed, the following combinations were tested for evaluating the adhesion ability of the mortar mixtures:  for high strength stones a mix of white cement with pozzolan (RM1) was tested, in order to slightly reduce the strengths of pure cement,  for moderate strength stones two types of repair mixtures were tested: a) high hydraulicity natural hydraulic lime (NHL5) with metakaolin (RM3) and b) a ternary mix of white cement, lime and metakaolin (RM6), and finally,  for low strength stones two types of repair mixtures were tested: a) high hydraulicity natural hydraulic lime (NHL5) (RM2) and b) a lime-pozzolan mixture (RM4, RM5) were tested. In order to minimize the factors that could affect the comparison of the experimental results, the surface morphology of the stone substrates before the application of the joining mortar (Courard et al. (2014); Sadowski and Mathia (2016)) were flattened and grinded with a P360 grinding paper. After the application of mortar joins, all specimens were kept in a curing chamber at the same curing conditions (T= 20 ± 2 °C , RH % ≥ 95 %). During the four-point flexural bending test, the above compositions failed at the stone interface without damaging it. It is noted that RM3 (NHL5 cement mortar) exhibits a small difficulty in adhesion to the surface of the stone compared to cement and lime, so if chosen, it should be used with extreme care.