I have used class D or Class D Modified grout:
D
Approximate Percent Fine to Total Aggregate
Gravel 35 Stone 39
Maximum Free Water by W/C Ratio (lb/lb)0.44
28-Day Compressive Strength(psi)4,000
Slump (inches) 3-5
Minimum Cement Factor (lb/yd3) 639
Air Content(%) 6 ± 2
D Mod
Approximate Percent Fine to Total Aggregate
Gravel 35 Stone 39
Maximum Free Water by W/C Ratio (lb/lb)0.42
28-Day Compressive Strength(psi)5,000
Slump (inches) 3-5
Minimum Cement Factor (lb/yd3) 733
Air Content(%) 6 ± 2