# Crossover Effect in Cement-Based Materials: A Review
## 6 Effect of Cementitious Materials on COE Phenomenon Due to Different Initial Curing Temperatures  
### Blast Furnace Slag  
[PERSON] et al. [15] used Portland cement (OPC) with GGBFS in their investigation. They studied the effect of curing temperature on hydration process and the phenomenon of COE. Two blast-furnace cements, BFS40 and BFS80, were made by replacement of OPC with 40% and 80% slag by mass, respectively. They found that for all test mixtures (OPC, BFS40 and BFS80) compressive strength decreased when w/b ratio increased, as shown in Figure 5A-C, respectively. All w/b ratios had 20-60 \({}^{\circ}\)C increase in the water curing temperature, and loss in compressive strengths was observed in OPC and BFS40 pastes at 7-365 days. Moreover, compressive strengths at early ages are lower at lower water curing temperatures for all w/b ratios.  
Figure 5: _Cont._  
The losses in compressive strengths (COE %) and age of COE for OPC and BFS40 pastes were calculated from the original results provided by the researchers (Table 2). However, no COE was observed for BFS80 at all w/b ratios with 20-60 \({}^{\circ}\)C increase in water curing temperature up to 365 days.  
[PERSON] et al. [66] described the effect of increasing curing temperature from 20-60 \({}^{\circ}\)C on the long-term strength of OPC and two slag blended cement mortars (BFS30 and BFS50). They used 30% and 50% slag in replacement of OPC by mass. They found that the long-term strengths of slag cements are mostly greater than those of OPC for all replacement levels. Moreover, the long-term strengths of OPC and slag blended cement mortars were decreased with increasing curing temperature from 20-60 \({}^{\circ}\)C.  
Figure 6 shows the loss in compressive strengths at later ages in OPC and slag blended cement mortars with 20-60 \({}^{\circ}\)C increase in water curing temperature. These losses in compressive strengths of Portland cement and slag blended cement mortars were calculated from the actual data obtained by researchers (Table 3). From the results in Table 3, it can be concluded that the amount of COE increases with age and it will be higher at later ages.  
Figure 5: Compressive strength (MPa) at various water curing temperatures and ages for (**A**) OPC; (**B**) BF540; (**C**) BFS80 pastes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Paste Name** & **w/b Ratio** & **Age at Which COE Occurred** & **COE (\%)** \\ \hline  & & 28 & 7.2 \\  & 0.3 & 90 & 7.2 \\  & & 365 & 8.2 \\ \cline{2-3}  & & 7 & 7.6 \\ OPC paste & 0.4 & 28 & 17.3 \\  & & 90 & 18.3 \\  & & 365 & 18.3 \\ \cline{2-3}  & & 7 & 2.9 \\  & 0.5 & 28 & 11.5 \\  & & 90 & 14.4 \\  & & 365 & 12 \\ \hline  & 0.3 & 365 & 5.2 \\ \cline{2-3}  & & 28 & 0.1 \\ BFS40 & 0.4 & 90 & 9.8 \\  & & 365 & 5 \\ \cline{2-3}  & & 28 & 2.6 \\  & 0.5 & 90 & 3.9 \\  & & 365 & 10.2 \\ \hline BFS80 & \multicolumn{3}{c}{No COE was observed at all w/b ratios up to 365 days} \\ \hline \hline \end{tabular}
\end{table}
Table 2: COE records with 20–60 \({}^{\circ}\)C increase in water curing temperature at ages up to 365 days for ordinary Portland cement (OPC), BFS40 and BFS80 pastes.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Paste Name** & **\% Age Replacement** & **Age at Which COE Occurred** & **\% Age of COE** \\ \hline  & & 28 & 10.9 \\ OPC & 0 & 60 & 16.3 \\  & & 90 & 15.3 \\ \hline  & & 28 & 23.7 \\ BFS30 & 30 & 60 & 18.5 \\  & & 90 & 27.8 \\ \hline  & & 28 & 18.2 \\ BFS50 & 50 & 60 & 3.7 \\  & & 90 & 18.9 \\ \hline \hline \end{tabular}
\end{table}
Table 3: COE records with 20–60 \({}^{\circ}\)C increase in water curing temperature at ages up to 90 days for OPC and slag blended cement mortars.  
Figure 6: Compressive strength (MPa) at various water curing temperatures and ages for OPC and slag blended cement mortars (BFS30 and BFS50).