# Mechanical Characterisation and Shrinkage of Thermoactivated Recycled Cement Concrete
## 2 Experimental Programme  
### Materials  
For this study, CEM I 42.5R, crushed limestone coarse aggregate and natural siliceous sand were selected to produce concrete. Tables 1 and 2 present the main properties of these constituents. The origin paste (OP) was produced with a w/b of 0.55, having reached an average 28 days compressive strength of about 41 MPa. After production, the OP was cured in a controlled environment at 95% relative humidity (RH) up to 7 days and then kept under laboratory environmental conditions for over 90 days. After curing, the OP was subjected to several crushing, grinding and milling processes, in order to decrease their average grain size. First, the OP was reduced into approximately 7 cm particles by means of two jaw crushers with distinct jaw openings. Afterwards, the OP ran twice through a roller mill, leading to particle sizes smaller than 2 mm, and then was further ground in a horizontal steel ball mill for about 2 h. Finally, the fine OP particles were passed through a 250 um sieve. The thermal activation of the waste cement paste was accomplished in a rotary tube furnace from _Thermolab Scientific Equipments_. The waste material was heated at 10 \({}^{\circ}\)C/min, up to 150 \({}^{\circ}\)C, where it remained for 1 h, followed by heating at 10 \({}^{\circ}\)C/min until the treatment temperature of 650 \({}^{\circ}\)C, where it remained for 3 h. Afterwards, the binder was cooled inside the oven until ambient temperature. The main phase composition of the binders was analysed by means of x-ray diffraction (XRD) and thermogravimetric (TG) analyses. For the XRD analysis, the samples were scanned at a 5-60 \({}^{\circ}\)C 2\(\theta\) range, with a step size of 0.03\({}^{\circ}\) and a step time of 100 s, using a _PANalytical X'Pert Pro_ diffractometer with CuK\(\alpha\) radiation. The TG analysis was performed using a _PC LUXX Thermoblance_ with a heating ratio of 10 \({}^{\circ}\)C/min, from ambient temperature to 950 \({}^{\circ}\)C. The degree of hydration and the calcium hydroxide (CH) content were determined according the procedure described in [PERSON] et al. [9]. The obtained recycled cement paste (RCP), with rehydration capacity, was mainly composed of \(\alpha\)\({}_{\mathrm{{}^{\mathrm{H}}}}\)-C\({}_{2}\)S and CaO, as well as traces of calcite (Figure 1). Moreover, the XRD and TG analyses demonstrated that the thermal treatment at 650 \({}^{\circ}\)C enabled the decomposition of the hydration products of the non-treated hydrated cement paste (NT)--namely, calcium silicate hydrates (C-S-H) and CH--without \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameter** & **Standard** & \multicolumn{3}{c}{**Sand**} & \multicolumn{3}{c}{**Crushed Limestone**} \\ \cline{3-6}  & & **Fine Sand** & **Coarse Sand** & **Fine Gravel** & **Coarse Gravel 1** & **Coarse Gravel 2** \\ \hline \begin{tabular}{c} Over-dried particle \\ density (kg/m\({}^{3}\)) \\ Water absorption at \\ 24 h (\%) \\ Loose bulk density \\ (kg/m\({}^{3}\)) \\ Granulometric fraction \\ (d\({}_{\mathrm{i}}\)/D\({}_{\mathrm{i}}\)) \\ \end{tabular} & EN 1097-6 [23] & 2598 & 2599 & 2669 & 2683 & 2650 \\ \hline \begin{tabular}{c} 24 h (\%) \\ Loose bulk density \\ (kg/m\({}^{3}\)) \\ Granulometric fraction \\ (d\({}_{\mathrm{i}}\)/D\({}_{\mathrm{i}}\)) \\ \end{tabular} & EN 1097-3 [24] & 0.15 & 0.26 & 0.39 & 0.31 & 0.46 \\ \
\begin{tabular}{c} Lowse bulk density \\ (kg/m\({}^{3}\)) \\ \end{tabular} & EN 1097-3 [24] & 1588 & 1606 & 1424 & 1420 & 1462 \\
\begin{tabular}{c} Granulometric fraction \\ (d\({}_{\mathrm{i}}\)/D\({}_{\mathrm{i}}\)) \\ \end{tabular} & EN 12,620 [25] & 0/1 & 0/2 & 2/8 & 4/11.2 & 11.2/20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of the natural aggregates. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Standard** & **OPC** & **NT** & **RCP** & **RCC** & **CF** \\ \hline \