PSI - Issue 10

I. Karatasios et al. / Procedia Structural Integrity 10 (2018) 211–218 I. Karatasios e tal. / Structural Integrity Procedia 00 (2018) 000 – 000

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efficient (C) and open porosity, were determined (n=3) according to the procedure described in EN 1936:1999. The cross sections were also examined under scanning electron microscope (FEI - Quanta Inspect) coupled with energy dispersive X-ray analyzer (SEM/EDX) (Alvarez de Buergo et al. (2004)). Both compressive and 3-point flexural bending strength were determined by loading three cubic (40x40x40 mm ) and three prismatic (40x40x160 mm) specimens (EN 1926 (2006)), normal to the planes of anisotropy (orientation of layers) of each different stone type.

2.2. Mortar mixtures

In order to select the most promising mixtures for joining the different stone fragments, six different mixtures were designed, aiming at different strength levels (Table 1). The cementing materials used in the mixtures were: Type I 52.5 R white cement, NHL5 hydraulic lime and, lime-metakaoline/lime-pozzolan mixed binders. Cement and NHL binders were further modified with metakaoline to adjust hydraulicity and the level of mechanical strength. Fine quartz sand (0/0.5 mm) was used in all mixtures for avoiding shrinkage and micro-cracking. The mechanical properties and the adhesion ability of mortar mixtures were tested after curing for 28 days, using three specimens for each experiment. Mortars mixtures were prepared in a planetary movement mixer, following the proportions described in Table 1, in accordance with EN-196-1. The w/c ratio was determined according to the demand of each mixture, in order to achieve mortars of the same consistence and a flow value between 15.5 - 16.0 cm (EN 1015-3 (1999)). Each mixture was cast into metal molds, producing three identical prisms with dimensions of 40 mm X 40 mm X 160 mm. All mixtures were cured at temperature of (20 ± 2) °C and re lative humidity of not less than 95 %. The mechanical (compressive and 3-point flexural bending strength) and physical properties (open porosity, capillary absorption coefficient) of all mixtures were studied after curing for 28 days in standard cubic and prism specimens. The study of both 3-point and 4-point flexural bending strength is aimed to provide a relation between the adhesive strength (4-point flexural bending) and the mechanical properties commonly studied in conservation mortars and stone building materials. Thus, to elucidate the role and contribution of each parameter on the effective design of conservation mortars for joining archaeological stone fragments without reinforcement.

Table 1. Mix proportions of initially designed mortar mixtures for joining stone fragments without reinforcement. Mixture Binder proportions (wt %) Aggregates (wt %) Cement (d<45 um) NHL5 (d<90 um) Lime (d<90 um) Pozzolan (d<75 um) Metakaolin (d<63 um) Quartz sand (0/0.5 mm)

w/c

c/aggr.

RM1 RM2 RM3 RM4 RM5 RM6

70

30

100 100 100 100 100 100

0.45 0.52 0.52 0.75 0.77 0.66

1:1 1:1 1:1 1:1 1:1 1:1

100

90

10 20

80 50 40

50

40

20

3. Results and discussion

3.1. Petrographic and mineralogical characteristics

All stone samples belong to the same geological formation of marly limestone, characterized by coherent calcitic matrix, mesoporous pore structure, presence of micro-fossils and discontinuities. The so called „ M arl of Piraeus‟ is a typical sedimentary marly limestone belonging to the Pliocene period of the Neogene. The lithology of the different marl layers varies, depending on parameters such as the ratio between calcite and clay content, the presence of dolomite and fossils, as well as the amount and gradation of clastic material. The main mineralogical phases identified in all samples tested include calcite (as dominant phase), quartz, illite, montmorillonite (in specimens 05 and 06) and