# The Effect of Curing Conditions on Selected Properties of Recycled Aggregate Concrete
## 2 Materials and Methods
### Methods
#### 2.2.6 Properties of Hardened Concretes  
Compressive strength tests were conducted on 100 mm cubic samples. After demolding, the samples were divided into three groups and subjected to three different conditions of hardening until the time of testing came: in a curing chamber at RH \(>\) 95% and 20 \({}^{\circ}\)C (wet conditions), in a sheltered space at RH 50-60% and 20 \({}^{\circ}\)C (dry conditions), and protected against drying (preventing \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Constituent** & **Unit** & **0\% RCA** & **50\% RCA** & **100\% RCA** \\ \hline Cement (CEM I or & & & & \\ CEM III) & (kg/m\({}^{3}\)) & 386 & 386 & 386 \\ Superplasticiser & (\% of CEM) & 0.2 & 0.2 & 0.2 \\ _uvc_ & (-) & 0.45 & 0.45 & 0.45 \\ Water & & 175 & 175 & 175 \\ W\({}_{\text{abs}}\)\({}^{*}\) & (kg/m\({}^{3}\)) & 0 & 11.5 & 23.0 \\ W (total) & & 175 & 186.5 & 198 \\ \hline Sand 0/2 mm & & 577 & 616 & 648 \\ Natural 2/4 mm & & 0 & 137 & 278 \\ Gravel 2/8 mm & & 636 & 316 & 0 \\ Gravel 8/16 mm & & 636 & 316 & 0 \\ \hline RCA 4/6 mm & & 0 & 93 & 184 \\ RCA 6/8 mm & & 0 & 79 & 157 \\ RCA 8/12 mm & & 0 & 139 & 278 \\ RCA 12/16 mm & & 0 & 101 & 202 \\ \hline \hline \end{tabular} w/c—water to cement ratio; W\({}_{\text{abs}}\)\({}^{*}\)—additional water needed as the result of RCA absorbability; W—total amount of water.  
\end{table} 
Table 4: Recipes for the RAC series. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Fraction** & **Mass of Aggregate (g)** & **Water Absorption** \\ \cline{2-3} (mm) & **Dry State** & **Wet State** & **(\%)** \\ \hline
4/6 & 400 & 411.3 & 2.8 \\
6/8 & 600 & 614.2 & 2.4 \\
8/12 & 800 & 823.6 & 3.0 \\
12/16 & 1200 & 1228 & 2.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Water absorption of recycled concrete aggregate (RCA). water evaporation) under foil at 20 \({}^{\circ}\)C (PEV conditions). The number of samples for each examined series of concrete was five. The obtained results were recalculated for the case of 150 mm cubic samples and these were analyzed further. The testing of compressive strength was carried out according to the European standard EN 12350-3:2009 [42]. The testing of sorption as a useful parameter for the assessment of concrete durability has been proposed in [43], among others, and alternatively in European standard EN 13057:2002 [44]. Sorption was conducted on 100 mm diameter cylindrical samples. The number of samples for each examined series of concrete was four. Each sample was dried at 50 \({}^{\circ}\)C for 5 days in the laboratory dryer. In the subsequent stage they were put onto a plastic mesh to allow for free water capillary sorption on the entire base surface without direct contact with the container bottom. The water level was equal to 1/5 of the sample height. Figure 2 shows the samples during the sorption test. Measurements were performed after 1, 5, 10, 20, 40, 60, and 75 min in order to evaluate the rate of sorption. Calculations of saturated water sorption (S) were done according to Formula (1) given below [43]:  
\[S=\left(\frac{\Delta M_{t}}{\sqrt{t}}\right)\left(\frac{d}{M_{sat}-M_{o}}\right) \tag{1}\]  
where \(S\) is sorptivity (mm/h\({}^{0.5}\)); \(\Delta M\)--change of mass with respect to dry mass (g); \(M_{sat}\)--saturated mass of concrete (g); \(M_{o}\)--dry mass of concrete (g); \(d\)--sample thickness (mm); \(t\)--period of absorption (h). At regular time intervals the mass of absorbed water was determined using a balance. Measurements were terminated after 75 min and the specimens were then vacuum-saturated and soaked in water in order to determine the effective porosity. Plotting the mass of water absorbed against the square root of time gives a linear relationship. The sorptivity of concrete can be calculated from the slope of the straight line plot. According to [33], the acceptable limit is \(<\)9 mm/h\({}^{0.5}\) (\(<\)6 mm/h\({}^{0.5}\) for laboratory conditions).