# Frost Resistance of Coal Gangue Aggregate Concrete Modified by Steel Fiber and Slag Powder
## 2 Materials and Methods
### Materials
#### 2.2.2.3 Mixing Process  
The preparation of CGAC specimens was conducted according to Chinese code GB/T 50081-2002 [37]. The mixing procedures were as follows:  
* Mix the fine and coarse aggregate (dry-condition) for 30 s;
* Add steel fibers (HESF, USF, or CPSF) and mix them for 30 s;
* Add cement and mix for 30 s;
* Add the mixing water with superplasticizer into the dry mixture and mix them well for 3 min (with slag powder) or 5 min (with steel fiber).  
Finally, the mixture was poured into molds and vibrated for 20 s. After 24 h of curing, the concrete samples were demolded and put in a chamber with a temperature of (\(20\pm 2\)) \({}^{\circ}\)C and relative humidity above 95%.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Component (kg/m3)**} & \multicolumn{3}{c}{**Fiber Volume Fraction (\%)**} \\ \cline{2-10}
**Mixture** & & \multicolumn{3}{c}{**Coarse Coal**} & \multicolumn{1}{c}{**Fine Coal**} & \multicolumn{1}{c}{**CPSF**} & \multicolumn{1}{c}{**USF**} & \multicolumn{1}{c}{**HESF**} & \multicolumn{1}{c}{**SP (\%)**} & \multicolumn{1}{c}{**Reducing Agent (\%)**} \\ \cline{3-10}
**ID** & **Water** & **Cement** & \multicolumn{1}{c}{**Gauge Cerassite**} & \multicolumn{1}{c}{**Gauge Cerassite**} & \multicolumn{1}{c}{**CPSF**} & \multicolumn{1}{c}{**USF**} & \multicolumn{1}{c}{**HESF**} & \multicolumn{1}{c}{**SP (\%)**} & \multicolumn{1}{c}{**Reducing Agent (\%)**} \\ \cline{3-10}
**U1** & **185** & **500** & **389.9** & **349.5** & **269.7** & **1.5** & & **0.6** \\
**U2** & **185** & **500** & **389.9** & **349.5** & **269.7** & **2.0** & & **0.6** \\
**H2** & **185** & **500** & **389.9** & **349.5** & **269.7** & & **0.5** & **0.6** \\
**H2** & **185** & **500** & **389.9** & **349.5** & **269.7** & & **1.0** & **0.6** \\
**H2** & **185** & **500** & **389.9** & **349.5** & **269.7** & & **1.5** & **0.6** \\
**SP1** & **185** & **500** & **389.9** & **349.5** & **269.7** & & **10** & **0.6** \\
**SP20** & **185** & **400** & **389.9** & **349.5** & **269.7** & & **20** & **0.6** \\
**SP30** & **185** & **350** & **389.9** & **349.5** & **269.7** & & **30** & **0.6** \\
**SP40** & **185** & **300** & **389.9** & **349.5** & **269.7** & & **40** & **0.6** \\ \hline \hline \end{tabular} Note: Each mixture was named based on the type of modified materials (R, CP, U, HE, SP = reference group, copper-plated steel fiber, undulated steel fiber, hooked-end and steel fiber, slag powder, respectively) and its dosage (0.25, 0.5, 0.75, 1, 1.5, 2 = 0.25%, 0.5%, 0.75%, 1%, 1.5%, 2%, etc., respectively).  
\end{table}
Table 6: Mixture proportions.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Fibers** & **Length** & **Diameter** & **Aspect** & **Density** & **Tensile Elastic** & **Tensile** & **Elongation** \\
**_1_ **(mm)** & **_d_ **(mm)** & **Ratio _l/d_ & **(g/cm3)** & **Modulus (GPa)** & **Strength** & **at Break** \\
**HESF** & **30** & **0.5** & **60** & **7.8** & **475** & **1457** & **2.6** \\
**USF** & **30** & **0.6** & **50** & **7.8** & **248** & **476** & **1.8** \\
**CPSF** & **13** & **0.2** & **65** & **7.8** & **854** & **3015** & **3.7** \\ \hline \hline \end{tabular}
\end{table}
Table 5: Physical properties of steel fibers.