PSI - Issue 70

Sreegovind M. et al. / Procedia Structural Integrity 70 (2025) 556–563

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on the bearing surface of a Universal Testing Machine (UTM), ensuring no eccentricity in placement as shown in fig.3. The average of three specimens of each mix is used to determine the compressive strength. 3.2 Thermal conductivity The thermal conductivity of the mortar mixes is conducted by casting mortar slabs of size 450 × 300 × 20 mm. The mortar specimens are placed in a hot guard apparatus, as shown in fig. 4, conforming to ASTM C177 (2019). The process involves placing the test material between two plates, one hot and one cold, and allowing heat to flow from one side to the other. A guard plate is used to prevent heat loss, so that all the heat flows through the test material, resulting in an accurate reading.

Fig. 3. Compressive strength test

Fig. 4. Thermal conductivity test

4. Results and discussion 4.1Compressive strength

Compressive strength is the ability of mortar to resist loads which tends to compress it. The result obtained after testing normal mortar (CM) and mortar with replacements (CM5, CM10, CM15) is given in Fig. 5. The compressive strength keeps reducing with increase in mass proportion of expanded vermiculite. By 5% replacement (CM-5), the strength is reduced by 38.62%. By 10% (CM-10) and 15% (CM-15) replacements there is a reduction of 54.05% and 60.99% respectively. Expanded vermiculite is a porous material, which leads to increase in voids within the mortar mix. The higher the amount of voids present, the lesser will be the strength. The compressive strength of CM, CM-5 and CM-10 is above 7.5 MPa, so all the mixes, except CM 15, satisfy the minimum compressive strength requirements as suggested by the code provisions of IS 2250- 1981. 4.2 Thermal conductivity This test is very essential to find the heat transfer in buildings and helps to understand the difference in heat flow of different materials. The thermal conductivity result obtained after testing normal mortar (CM) and mortar with replacements (CM5, CM10, CM15) is given in Fig. 6. Compared to CM, for 5% replacement (CM-5) the thermal conductivity reduces by 61.41%. By 10% (CM-10) and 15% (CM-15) replacements there is a reduction of 67.86% and 68.52% respectively. The thermal conductivity reduces with increase in mass proportion of expanded vermiculite. Expanded vermiculite has a very porous structure, which produces more air pockets into the mortar mix when added. As a result of poor heat conductivity of air, the mortar's overall thermal conductivity falls.