Because lime-fly ash soil is formed by rolling when it is close to or slightly larger than the optimum water content, if it is not cured in time after forming, the surface of lime-fly ash soil is prone to crack. If this kind of crack does not interact with soil, the degree of crack is slight and the depth is shallow, but if it is superimposed with the above three situations, it will produce deeper, wider and larger cracks. Another main reason is that lime and fly ash contain highly chemically active substances, such as calcium dioxide, which will have a series of physical and chemical reactions. When the reaction occurs, it is necessary to absorb water molecules to form crystals and become crystal particles, and at the same time, it is necessary to evaporate some water during the exothermic reaction. The initial reaction is fast, and if it is not replenished in time, it is easy to cause shrinkage cracks. Therefore, the curing of lime-fly ash soil after molding is very important, generally at least seven days. If the upper layer cannot be covered in time and it is difficult to spray water for a long time, the method of covering soil can be adopted to ensure the slow evaporation of water in lime-fly ash soil and avoid the increase of cracks.

To sum up, most of the three common quality problems mentioned above are related to water content, and controlling water content is a key to the success of lime-fly ash soil. Therefore, as a construction worker, the water content of lime-fly ash soil must be strictly controlled. At the transition stage of spring and summer, the water content is slightly higher than the optimal water content by 2-3%. If it often rains in rainy season or summer and autumn, it is best to control the construction water content at the best water content. At the same time, we should pay special attention to the detection method of water content. There may be a big deviation in determining the water content of lime-fly ash soil by loss on ignition method. This is because the fly ash in lime fly ash soil contains combustible substance coal, and some substances in the fly ash burn when the ignition loss is reduced, and the total weight becomes lighter. If this part of the loss on ignition is regarded as water content, the water content must be low and inaccurate. This situation has also happened in some construction units. The measured results show that the water content of lime-fly ash soil is slightly greater than or close to the optimal water content, but it is difficult to form when rolling, and even serious peeling occurs. From the mixing uniformity and rolling machinery and equipment, the crux of the problem can not be found. Later, it was accidentally discovered that the waterwheel failed because of too much running water, which not only did not peel off, but also turned blue and shiny after rolling, indicating that the water content was still small, and then it was inferred that the water content measurement was inaccurate, thus finding the reason for the loss on ignition of fly ash. It is faster to determine water content by loss on ignition, and this method can also be used. However, before using this test method, several groups of comparative tests must be carried out by drying method and loss on ignition to determine the loss on ignition of fly ash with the same road section and the same gradation. In this way, the actual water content can be obtained by subtracting the measured loss on ignition from the loss on ignition, so as to guide the construction.

It is worth mentioning that special attention should be paid to the evaporation loss of water on the surface of lime-fly ash soil during leveling. Therefore, lime-fly ash soil is required to be slightly higher than 1 ~ 2 cm when feeding, and it shall be leveled forward by grader. With the increase of the remaining lime-fly ash soil, the construction workers can transport it with the help of loaders, which can achieve two purposes. One is to remove the thin layer patch; The second is to slow down the evaporation of water on the surface of lime-fly ash soil. This process is very critical and needs to be strictly mastered by on-site construction personnel to get twice the result with half the effort.

There is not much technical problem in lime-fly ash soil construction, but if it is not mastered well, it may bring the above quality problems. Therefore, we should constantly explore and master certain construction skills in order to form a complete set of construction methods, avoid detours, transform science and technology into productivity, and better serve the construction personnel.