# MSWI Bottom Ash Application to Resist Sulfate Attack on Concrete
## Materials and Methods
### Experimental Methods  
#### 2.3.1 Mechanical Property Measurements  
The specimen preparation and strength tests of the mortar were conducted in accordance with GB/T 17671-199 [25]. The well-stirred mixtures of cement, BA, sand, and water were put into a mold (\(40\times 40\times 160\) mm) fixed on a vibrating table; after vibrating 120 times, the mixtures together with the mold were stored in a curing room (maintained at \(20\pm 2\)\({}^{\circ}\)C and no less than 95% RH). Then, form stripping was carried out. After 28 days of curing in standard conditions, the flexural and compressive strengths of the mortar were determined using a bending and compression tester.  
The activity index of BA was determined with reference to GB T1596-2017 [27]. According to this standard, the compressive strengths of mortar with 30% and without fly ash were tested under a water-to-binder ratio of 0.5. Here, the activity index is defined as the compressive strength of the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Cement Mortar** & **Cement Concrete** \\ \hline Cement (kg/m\({}^{3}\)) & 450 & 330 \\ Water (kg/m\({}^{3}\)) & 225 & 130 \\ Natural sand (kg/m\({}^{3}\)) & 1350 & 614 \\ Crushed stone (kg/m\({}^{3}\)) & — & 1248 \\ Water-cement ratio (W/C) & 0.5 & 0.4 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Mix proportions of materials in the mortar and concrete.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **Cement** & **BA** & **Material** & **Cement** & **BA** & **Cement/BA** & **Designation** \\  & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & & \\ \hline Cement mortar & 405 & 45 & Cement concrete & 297 & 33 & 90:10 & C90 BA10 \\  & 382.5 & 67.5 & 280.5 & 49.5 & 85:15 & C85 BA15 \\  & 360 & 90 & 264 & 66 & 80:20 & C80 BA20 \\  & 337.5 & 112.5 & 247.5 & 82.5 & 75:25 & C75 BA25 \\  & 315 & 135 & 231 & 99 & 70:30 & C70 BA30 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Cemertitious material combination scheme for mortar and concrete.  
mortar with BA divided by the compressive strength of the mortar without BA, and it can be calculated as follows:  
\[H=\frac{R}{R_{0}}\times 100 \tag{1}\]  
where \(H\) is the activity index (%); \(R\) is the compressive strength of mortar with BA at 28 days of curing (MPa); and \(R_{0}\) is the compressive strength of mortar without BA at 28 days of curing (MPa).  
The concrete specimens were prepared and cured according to GB/T 50081-2002 [28]. All the materials were accurately weighed and put into the mixing pan. After stirring, specimens \(100\times 100\)\(\times\)\(100\) mm in size were manufactured by the vibration molding method. Next, all specimens were left to stand for 24 h at a temperature of \(20\pm 5\)\({}^{\circ}\)C. In order to evaluate the strength property of the concrete, the specimens were cured in a curing room (maintained at \(20\pm 2\)\({}^{\circ}\)C and no less than 95% RH). After 28 days of curing, the compressive strength of the concrete was determined using a WAW-B Electro-hydraulic universal testing machine.  
For durability tests, specimens \(100\times 100\times 100\) mm in size were divided into two series. The first one was cured under standard curing conditions. The second one was firstly cured at T = \(20\pm 2\)\({}^{\circ}\)C and RH \(\geq\) 95% for 28 days and then totally immersed in a solution containing 10% sodium sulfate for 60 days; the solutions were renewed monthly. The sulfate damage was evaluated mechanically by determining the compressive strength loss of the specimens using the following equation:  
\[\textit{Strength loss}\ (\%)=\frac{R_{1}-R_{2}}{R_{1}}\times 100 \tag{2}\]  
where \(R_{1}\) is the compressive strength of concrete specimens under standard curing conditions (MPa) and \(R_{2}\) is the compressive strength of concrete specimens in sulfate solutions (MPa).