# Pathway to Carbon Neutrality in the Cement Industry: CO2
## 3 Materials and Methods
### Methods
#### 3.2.1 Thermogravimetric Analysis  
The carbonation potential of recycled aggregates was assessed by TGA, using a SE-TARAM TGA92 simultaneous DTA-TGA thermal analyser and a HITACHI STA7200 apparatus. This test measures the mass loss of the samples while they are heated continuously from 25 to 1000 \({}^{\circ}\)C at a uniform rate of 10 \({}^{\circ}\)C min\({}^{-1}\), with an argon atmosphere (3 L/h). The test conditions used, namely heating rate and temperature range, as well as the type of gas and flow rate, are those commonly used for the study of cementitious materials [58].  
From the mass losses obtained during the test at different temperature ranges, it is possible to quantify the calcium hydroxide and calcite content of the sample and evaluate the degree of carbonation in cement-based materials. The calculation of the first derivative  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline \multirow{2}{*}{**Aggregate**} & \multicolumn{2}{l}{**Water Absorption (\%)**} & \multicolumn{2}{l}{**Particle Density (kg/m\({}^{3}\))**} \\ \cline{2-5}  & **Non-Carbonated** & **Carbonated** & **Non-Carbonated** & **Carbonated** \\ \hline Natural sand & 0.25 \(\pm\) 0.06 & - & 2627 \(\pm\) 5 & - \\ \hline MRA-RP1 & 7.05 \(\pm\) 0.44 & 3.63 \(\pm\) 0.23 & 2424 \(\pm\) 66 & 2556 \(\pm\) 48 \\ \hline MRA-RP2 & - & - & - & - \\ \hline MRA-RP3 & 6.89 \(\pm\) 0.91 & 3.90 \(\pm\) 0.88 & 2485 \(\pm\) 52 & 2570 \(\pm\) 40 \\ \hline RCA-IS & 7.18 \(\pm\) 0.20 & 4.87 \(\pm\) 0.20 & 2426 \(\pm\) 28 & 2640 \(\pm\) 264 \\ \hline RCA-RP2 & 3.81 \(\pm\) 0.54 & 2.45 \(\pm\) 0.13 & 2636 \(\pm\) 57 & 2694 \(\pm\) 44 \\ \hline RCA-RP1 & 5.58 \(\pm\) 1.18 & 2.48 \(\pm\) 0.36 & 2510 \(\pm\) 130 & 2514 \(\pm\) 12 \\ \hline RCA-IW & 5.01 \(\pm\) 0.28 & 3.25 \(\pm\) 0.34 & 2408 \(\pm\) 18 & 2553 \(\pm\) 5 \\ \hline CA-L & 4.74 \(\pm\) 0.16 & 0.46 \(\pm\) 0.04 & 2622 \(\pm\) 7 & 2670 \(\pm\) 9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: RA physical properties.  
of the mass loss curve (DTG) for this specific type of material, usually shows peaks in three different temperature ranges (Z1, Z2 and Z3) [10; 13]. Each range represents the mass loss due to certain compound's decomposition:  
* Z1, [20-400 \({}^{\circ}\)C]: temperature range that corresponds to release of moisture and dehydration of hydrated calcium silicate (C-S-H) and calcium aluminate hydrates (AFt and AFm phases);
* Z2, [400-500 \({}^{\circ}\)C]: temperature range that corresponds essentially to the dihydroxylation of portlandite (CH); allows to estimate the content of free portlandite, that can be used to estimate the carbonation potential of a cementitious material;
* Z3, [500-900 \({}^{\circ}\)C]: temperature range that corresponds to carbonates decarbonation, allowing to estimate CaCO\({}_{3}\) content.  
Due to the high heterogeneity of RAs, samples of about 100 g were separated using an automatic rotary sample splitter apparatus. Subsequently, each sample was crushed in a mechanical grinding device until fine powders with particle size <106 \(\upmu\)m were obtained.  
TGA was used to evaluate the amount of CaCO\({}_{3}\) formed and Ca(OH)\({}_{2}\) remaining. The maximum CO\({}_{2}\) uptake is determined by the difference between the calcium carbonate content of the noncarbonated samples (0 h) and the calcium carbonate content after the \"ideal\" carbonation period (Equations (10) and (11)).  
\[\Delta CaCO_{3}=\left(CaCO_{3\ final}-CaCO_{3 initial}\right) \tag{10}\]  
\[\%CO_{2}uptake=\Delta CaCO_{3}\times\frac{MM_{CO_{2}}}{MM_{CaCO_{3}}} \tag{11}\]  
CaCO\({}_{3 initial}\) is the CaCO\({}_{3}\) content of uncarbonated samples and the CaCO\({}_{3 final}\) corresponds to the maximum CaCO\({}_{3}\) content obtained after carbonation, being \(MM_{CO_{2}}\) and \(MM_{CaCO_{3}}\) the molecular weight of CO\({}_{2}\) and CaCO\({}_{3}\), respectively.