## 2 Influential Factors on the Performance of GSP
### Raw Materials and Admixtures
#### 2.2.3 High-Fluidity Cement Mortar  
High-fluidity cement mortar (HCM) is a specialized grouting material which can penetrate OMA due to its high fluidity to construct a fibrous-like network structure inside the asphalt mattress. Strength and shrinkage rate are the two main factors of HCM controlling the performance of GSP. Therefore, to investigate their effects, various formulas of raw materials and different additives are compared, as shown in Table 7.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Author** & **Asphalt Types** & **Test** & **Test Condition** & **Strength [Mpa]** & **Modulus [Mpa]** \\ \hline \multirow{4}{*}{Setyawan [46]} & 50-pen straight run asphalt & \multirow{2}{*}{Indirect Tensile Strength} & \multirow{2}{*}{20 \({}^{\circ}\)C} & 259.65 & 953.71 \\  & 7\%SBS-Modified Asphalt & & & 155.82 & 331.44 \\ \multirow{4}{*}{} & 100-pen straight run asphalt & & & 125.26 & 548.68 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Optimal binder and low temperature performance of OMA.  
The water-cement ratio is the critical factor affecting both fluidity and strength of cement mortar. The fluidity of HCM is positively associated with the water-cement ratio and negatively related to the sand-cement ratio [65]. However, an excess water-cement ratio or a short sand-cement ratio will lead to high dry shrinkage [60; 61]. In addition, with the increase of water-cement ratio, the bleeding rate of HCM shows an upward trend, which may cause void-blocking and slurry leakage [66; 67]. Therefore, [PERSON] et al., recommends that the water-cement ratio should be less than or equal to 0.55 for HCM, while [PERSON] et al., advises a ratio scope of 0.4-0.6 [45; 66]. Additionally, 10-14 s is a recommended range for HCM fluidity [45; 49; 67].  
The additive type is another factor in determining the performance of HCM. Super-plasticizer and fly ash are commonly used to increase fluidity of HCM and minimize residual void after grouting. Some studies indicates that silica fume, mineral powder, and ultrafine sand also have good effects on fluidity [43; 64; 68; 69]. Expansion agent UEA can reduce the shrinkage of HCM and furtherly enhance the anti-cracking ability of following GSP [60; 61; 62; 63; 70]. However, the strength of cement mortar is inevitably underestimated by fluidity improving in the methods above. Therefore, to achieve the balance design between fluidity and strength, a range of strength value is proposed as 10-30 Mpa, and furtherly narrowed to 20-25 Mpa for HCM [45; 49]. Although other factors such as the shrinkage and flexural strength of HCM have important effects on the low-temperature performance of GSP, their values are not considered as parameters by recent studies comprehensively.  
[PERSON] et al., used ABAQUS software to simulate the shrinkage and expansion of cement mortar in GSP to estimate the inner stresses [71]. Index values of the deformation were calculated and determined to protect GSP from cracking that is caused by stress concentration of shrinkage, as shown in Table 8.  
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline