How to prevent ground mortar hollowing and cracking

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How to prevent ground mortar hollowing and cracking
1. good raw materials off
1. Cement: Portland cement or ordinary Portland cement with qualified stability reinspection shall be selected. Because the shrinkage rate of these two kinds of cement is small, the dry shrinkage rate of cement mortar in the hardening process is also small. But these two kinds of cement must not be mixed. At the same time, it is strictly prohibited to use expired, damp and caked cement. Because the cement stability is not qualified, the free calcium oxide, magnesium oxide in the condensation process of hydration is very slow, when the cement mortar or cement concrete in the hardening, the free material continues to hydrate, the solid volume increases by 2-2.5 times, will destroy the hardened structure and crack. Slag Portland cement, fly ash Portland cement and pozzolanic Portland cement with low early strength and poor wear resistance should not be used in ground engineering.
2. Sand: clean medium coarse sand with silt content less than 3%. Because with fine sand, mud sand mixing mortar in the hardening process of dry shrinkage, shrinkage value is relatively large, the ground is prone to shrinkage cracks.
2. clean up and wet the base.
1. Base layer: refers to the structural layer under the surface layer, including filling layer, isolation layer, leveling layer, cushion layer and foundation soil.
2, grass-roots treatment: the construction of the ground before the project must be carefully handled at the grass-roots level. Check the quality of the base, including material requirements, strength, thickness, surface flatness and slope, etc., must meet the design requirements. If there is any defect, it shall be corrected to be qualified first, and the construction can only be carried out after the acceptance visa, because the quality of the base layer directly affects the quality of the upper surface layer.
3. Clean up the grass-roots level: remove the garbage on the grass-roots level, scrape off the mud, mortar and free glass film on the cement grass-roots level adhered to the surface, and clean the dust and oil stains on the clean surface. Before construction, there shall be no water on the surface of the grass-roots level. This is the key to ensure the quality of ground engineering.
4, the grass-roots wet: the upper cement mortar or concrete structure layer of the bond is very important. In the dry floor of the grass-roots construction, dry grass-roots cement mortar or cement concrete layer in the moisture to absorb, affecting the cement to continue hydration and hardening, so that the grass-roots and the upper structural layer of the bond force is reduced; when the surface layer dry shrinkage and shrinkage, and the grass-roots produce separation and shelling and cracks. Should be 1-2 days before the surface construction in the clean base surface spray, drenching water to keep wet and dry, but there is no water, so that the base surface to dry saturation state. This is the key to make the surface layer and the next layer firmly, without hollowing and cracks.
5, laying pipeline: ground hidden laying pipeline should be laid in the grass-roots as far as possible. If some pipelines are exposed to the base surface, the surface layer mortar at that place is too thin, water loss is fast, and cracks are easy to occur. For example, when water and electricity embedded pipelines are slightly exposed to the base surface, a layer of steel wire mesh with a width of more than 500mm or steel wire mesh with a diameter of 4mm is laid along the middle of the cement mortar layer above the pipeline to prevent cracks.
3. master the construction environment temperature
The surface area of ground construction is large, and the best construction environment temperature is 5-35 degrees Celsius. If it is lower than 5 degrees Celsius, the doors and windows should be closed in time to prevent the early freezing of the ground surface from sand.
4. close the good combination layer
1. Binding layer: refers to the intermediate layer connecting the surface layer and the next structural layer.
2. Construction requirements: before the construction of the surface layer, a layer of cement slurry is applied to the base layer as the bonding layer, which can enhance the bonding strength between the surface layer and the base layer. However, the combined layer often plays a role in isolation due to improper construction.
(1) The cement slurry that is prematurely painted has hardened, and then the cement mortar surface layer is laid, which can only play a role in isolation. Therefore, the surface layer cement mortar can be laid only after a layer of qualified cement slurry must be removed and brushed again.
(2) It is not allowed to sprinkle dry cement after watering at the grass-roots level or sprinkle dry cement before watering (slurry sweeping method), because open water and cement slurry that has not been swept evenly play an isolation role, and the surface layer is prone to shelling and cracks.
(3) must be based on the degree of dryness and wetness of the grass-roots and climate conditions, the use of water and cement ratio of 0.4-0.5 cement slurry. The specified measurement of water and cement mixing evenly pure cement slurry in the construction of the base surface (do not leak coating), after about 30 minutes to lay the cement mortar surface.
5. Strictly Control the Mixing Ratio of Cement Mortar
1, the general ground cement mortar mix should be controlled within 0.4, the consistency should not be greater than 55mm. If the mix proportion of cement mortar in each plate is correct and the water consumption is accurate, the consistency, strength and shrinkage of mortar will be consistent.
2, such as random water to make the mortar water consumption is too large, the cement mortar after hardening water evaporation is too much, the volume shrinkage rate is also large, so that the ground surface layer strength is relatively reduced, not wear-resistant, but also easy to produce shrinkage and shrinkage cracks.
3. The test data show that the cement mortar mix ratio is the same, and its strength is related to the consistency (I. e. water consumption). If the consistency increases from 30mm to 70mm, the compressive strength will decrease by about 30%. Large bleeding during construction will reduce the strength, hardness and wear resistance of the ground surface.
6. master the ground surface layer compaction smearing off
Cement mortar, cement concrete surface plaster work is generally divided into three times.
1, the first cement mortar surface layer paved enough, with a scraping ruler to scrape flat, compaction; Generally, there are no construction joints in the room, and the surface flatness must be mastered. The cement mortar shall be polished and leveled with a trowel or a wooden trowel after receiving water. The sand holes, pits and footprints on the surface shall be polished and leveled.
2. The second smearing shall be calendered with iron trowel or smearing machine at the time of initial coagulation, I .e. when adults stand up and leave footprints about 5mm deep. Mainly remove surface bubbles. The plastered and calendered surface shall be free of defects such as smear marks, footprints and blisters.
3. The third calendering time is before the cement is finally set, that is, when there is no fingerprint mark on it with your finger. Use iron trowel to plaster and press for the third time. When plaster and press, use a little more force to smooth and calender the surface. The surface is free of sand holes and marks, and the capillary holes are further blocked. The operation of retreating from the inner wall to the doorway is the key to ensuring a smooth and smooth ground.
7. good cement mortar surface layer maintenance off
After the construction of the surface layer is completed, the doors and windows shall be closed in time for 24 hours and then cured by spraying water or drenching water for not less than 7 days. During the maintenance period, it is strictly forbidden to trample on the ground, and it is not allowed to carry out other types of work operations, stacking materials and other heavy objects on the ground. Do a good job of keeping warm at low temperature. Such as poor maintenance, early use or frozen, will cause cracks and ground sand.
To sum up, only from the construction of raw materials, construction process and later maintenance of several aspects, in order to ensure that the cement mortar floor will not appear from the ground from sand ash, ground cracks, ground air drum and other quality problems.

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