PSI - Issue 64

Hernán Xargay et al. / Procedia Structural Integrity 64 (2024) 1790–1797 Hernán Xargay / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Materials and Methods The subject of this research was a normal-strength mortar composed of normal-strength Portland cement, namely CPN40, two distinct sand types and water. The fine aggregates incorporated were derived from both natural siliceous river sand and crushed granitic rock sand. The mixture proportioning is provided in Table 1. It can be derived that the corresponding water to cement ratio was w/b=0.49.

Table 1. Mixture proportioning of mortar. Component

Weight [kg/m 3 ]

Water

288 590 971 416

Cement (CPN40) Natural River sand Crushed rock sand

Mortar batches were prepared in a laboratory-grade mortar mixer. Various specimens as prisms (40 mm x 40 mm x 160 mm) and cylinders (50 mm x 100 mm) were casted. These samples were demolded after a period of 24 hours and cured for 28 days submerged in water and maintained at a temperature of 20 °C. Afterwards, the specimens were stored in laboratory conditions to ensure moisture and mechanical strength stabilizations. The experimental design incorporated six different thermal treatment levels, set at 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, and 600 °C, alongside a control group maintained at 20 °C (ambient temperature). An electric furnace with a maximum operational temperature of 1200 °C was used. The thermal treatment involved a heating phase with a uniform temperature increase at a rate of 10 °C/min until reaching the targeted peak temperature, which was then sustained for three hours. Following this period, the electric furnace was switched off to allow the specimens to slowly cooling down within, thus minimizing the risk of thermal shock. The entire thermal treatment process spanned 24 hours. Notably, all samples maintained their integrity and only the specimens subjected to 600 °C exhibited visible surface thermal cracking upon removal. The flexural behavior was evaluated through three-points bending tests (TPB) as depicted in Fig. 1 (a). For each temperature group, four beam specimens were tested. The span between the supports was 100 mm and the vertical load was applied at a displacement rate of 0.005 mm/sec until failure (Fig. 1 (b)). Applied force was measured by a 100 kN capacity load cell placed in a Shimadzu brand testing machine. The bending strength ([MPa]) was computed using equation (1), where [mm] is the cross-sectional width of the beam, [N] represents the peak load and l [mm] is the span between supports. (1)

(a)

(b)

Fig. 1. (a) Experimental setup in three-points bending tests and (b) fractured specimen after a test.

Flexural tests were continuously monitored by AE technique. To achieve this, an AE monitoring system Physical Acoustic Corporation (PAC) brand PCI-2 board with two channels, was employed. This system was equipped with two sensors with a resonant frequency of 150 kHz and preamplifiers. The sensors were symmetrically positioned at