Issue 60

A. Taibi et alii, Frattura ed Integrità Strutturale, 60 (2022) 416-437; DOI: 10.3221/IGF-ESIS.60.29

not the case in practicality, the impact of the geometry of the aggregate in the model is minimal to the study we are going to be focusing on. Fig. 2 shows the ( 10×10) cm² and (20×20) cm² sample meshes.

(10*10) cm 2

(20*20) cm 2

Figure 4: Mesoscopic mesh for the two samples. The behaviours of the two samples are firstly simulated under hydration to investigate the initial state after hydration. The size of mesh is related to the smallest considered aggregate. In this investigation, quadrangle elements (QUA4) of 0.4mm size were used to model aggregates and mortar, whereas a number of 536 segment elements (2-node line) were used to mesh the cooling pipes. Fig. 5 shows an example of the pipe cooling meshing. Parameters for pipe cooling listed in Tab. 4 were adopted from [39]. For aggregate cooling system, Tab. 5 shows the initial temperatures for aggregate cooling. Tab. 6 gives the other parameters used in the simulations.

Characteristics of the cooling pipe system The coefficient of convective heat transfer on the pipe loop, W / (m 2 °C)

Values

282

Speed, m/s

0.5

Water temperatures in the pipes, K The density of water, kg / m 3

293

1000

Specific heat capacity, kJ/ (kg °C)

1.12

Thermal conductivity, w / (m °C)

0.64

Pipe radius, m

0.003

The duration of cooling

172hrs

Ambient temperature, K

293

Table 4: Model parameters for the cooling pipes.

Type

Initial Temperature (K)

Aggregates

283

Cement paste 293 Table 5: Initial temperatures for aggregate cooling method.

424