Effect of methods of adding urea in culture media on sand solidification tests

The sand solidification technology can improve the mechanical properties of sands and is being widely applied in engineering. Adding urea to culture media can drastically accelerate the curing reaction. The influence of adding urea to culture media on sand solidification is studied. At first, three methods of adding urea are examined to investigate the effects of them on the growth characteristics and urease activity: that is, adding urea before sterilization, adding urea after sterilization and not adding urea. Different amounts of urea are then added to obtain the appropriate amounts of adding urea for subsequent experiments. Finally, the method of adding urea after sterilization, length of sand columns, injection speed of gelling solution and sizes of sand particles are investigated to observe the influences of different factors on the curing of sand. The results show that the method of adding urea to the culture media can increase urease activity, but it will slightly inhibit bacterial growth. The proper amounts of urea added are between 5 and 20 g/L. The method of adding urea after sterilization markedly increases the strength of the injecting path. However, a long injecting path leads to lower overall strength. The faster the injection speed, the higher overall strength the sand columns have. When 20 g/L of urea is added, the overall strengths of the solidified sand columns increase with larger sand particle size. Therefore, the method of adding urea to the culture media for sand solidification is suitable for coarse sand, which will act as a guide for the application of sand solidification technology.