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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Fig.3. Flow table tests results

Fig. 4. Preparation of one cylindrical specimen (left) and one prismatic (right) respectively. M35-C0 seems to be similar at approximately 6 MPa. At 28 days of curing the value of average compressive strength of the binary pastes is about 5.5 MPa, which is in accordance with the specifications of the material, the number 5 in NHL5 indicates a minimum strength of 5 MPa at 28 days, while the maximum strength can reach 15 MPa. As the MK content increases the compressive strength also increases which is in accordance with the findings of Aggelakopoulou et al. (2011), who noticed that the final compressive strength increased with the ratio of MK/lime. As expected, the compressive strength of the ternary paste is higher, about 1.5 - 2 times to the compressive strength of the binary paste. Similarly to the flexural tests, the obvious difference is attributed to the cement. It is positive that the compressive strength in the ternary pastes has not been affected vastly by the presence of cement, which exhibits compressive strength in between 6 and 11 MPa. There is significant change between the binary and the ternary binders, since adding cement in the L35-M35-C30 paste increases by 40 % the compressive strength of the L65-M35-C0 paste as well as adding cement in the L40-M40-C20 paste increases by 60 % the compressive strength of the L50-M50-C0 paste. Α much higher increase of the compressive strength would indicate great incompatibility to the original materials of Monuments of Cultural Heritage concerning the mechanical properties. This trend is in line with the findings of Qian et al. (2019), who concluded that higher strength improvement can be achieved by the blended cement with higher metakaolin replacement. This is because more aluminate is available in the cement with higher content of metakaolin. Aluminate can also react with CaCO 3 to produce more ettringite and AFm phases, as shown in Eqs.(2), leading to denser microstructure and more improvement of the strength of the mortar. Similar trend was also observed by Antoni et al. (2012). They found that limestone addition is more effective in the blended cement mortar with higher metakaolin replacement. Wianglor et al. (2017) also proved that the compressive strength of alkali-activated metakaolin cement increased with the increase of cement content. 3(CaO) 3 (Al 2 O 3 ) . CaSO 4 . 12H 2 O + 2CaCO 3 + 18H 2 O→ →2(CaO) 3 (Al 2 O 3 ) . CaCO 3 . 11H 2 O + (CaO) 3 (Al 2 0 3 ) . 3CaSO 4 . 32H 2 O (2) According to Abdelli et al. (2017), the incorporation of metakaolin causes substantial pozzolanic activity at a very young age between 14 and 28 days. It begins to react with the free lime produced by the hydration of cement following