Preventive measures of sand from cement mortar floor


Release time:

2021-02-22

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Causes and prevention of sand on the ground of cement mortar building
 
Cement mortar surface layer is common in construction projects, especially the resettlement project, new rural construction project, dilapidated house renovation project, affordable housing, low rent housing and other livelihood projects are widely used. This kind of ground structure is simple in structure, strong and wear-resistant, and low in cost. However, due to improper construction, it is easy to cause three common quality problems: cracks, hollowing, and sand, which affect the quality of perception and normal use. Residents hate it deeply and reflect strongly. Therefore, attention must be paid to and serious management.
 
Cause analysis of sand:
1. The water cement ratio of cement mortar mixture is too large, that is, the consistency of mortar is too large. The water-cement ratio is inversely proportional to the strength of cement mortar, and the strength of mortar decreases when the water-cement ratio increases. If the construction of water consumption is too much, will greatly reduce the strength of the mortar; at the same time, the construction will also cause the mortar bleeding, further reduce the surface strength of the ground, after the completion of the walk wear, will be ash.
2, the process arrangement is not appropriate. Do not understand the principle of cement hardening, calendering process arrangement is improper, and the bottom is too dry or too wet, resulting in ground calendering time too early or too late. The calendering is too early, the hydration of cement has just begun, the gel has not yet been fully formed, and there is still a lot of free water. Although calendering is carried out, a layer of water will float on the surface, which is unfavorable to the strength and abrasion resistance of the mortar in the opposite layer. If the calendering is too late, the cement has hardened, which is not only difficult to operate, but also cannot eliminate the capillary holes and wiping marks on the surface of the surface, it will also greatly reduce the strength and wear resistance of the surface mortar.
3. The surface layer is not properly maintained. After the completion of the cement floor, if not curing or curing days is not enough, in a dry environment, the surface moisture evaporates rapidly, the hydration of cement will be affected, slow down the hardening speed, serious even stop hardening, resulting in cement mortar dehydration and affect the strength and wear resistance. In addition, if the ground is watered and maintained in less than 24 hours after wiping, due to the "tender" surface of the ground, it will also lead to large-scale peeling, exposed sand particles and sand after use.
4, the finished product protection is not effective. The cement floor has not yet reached sufficient strength on the premature use or the next process of construction, so that the surface of the ground is subject to friction and other effects, easy to lead to the ground from the sand. This is especially true at low temperatures.
5, raw materials do not meet the requirements. First, the cement strength grade is low, or with expired, damp caking cement, the cement activity is poor, affecting the ground surface strength and wear resistance; Second, the sand particle size is too fine, the water demand during mixing is large, the water cement ratio is increased, and the strength is reduced. Excessive mud content in sand will also affect the bonding force between cement and sand, which is easy to cause sand on the ground.
 
Precautions for sand lifting
1. Strictly control the water-cement ratio. The consistency of cement mortar used for the ground surface layer shall not be greater than 35mm, and the slump of concrete and fine stone concrete shall not be greater than 30mm. The cushion shall be fully wet, and the cement slurry shall be evenly brushed and leveled with the ash. The concrete surface layer shall be vibrated, and the fine stone concrete shall be rolled by rollers or beaten with wooden trowel to make the surface flushed to ensure the strength and compactness of the surface layer.
2, master the surface lamination time. Cement surface calendering is generally not less than three times. The first pass shall be carried out after the surface course is laid. First, rub it evenly with a wooden trowel to make the surface material uniform, compact, and smooth, so that there is no water layer on the surface. The second calendering shall be completed after the initial setting of the cement and before the final setting (generally, it is advisable for the above people to have slight footprints but not obvious subsidence), and the surface shall be compacted and leveled. The third calendering is mainly to eliminate smearing marks and occlude fine pores, and further compact and smooth the surface (time should be controlled when the master does not show footprints or has unobvious footprints). It is advisable to avoid calendering after the final setting of cement.
3, cement ground after calender, should be depending on the temperature, generally in a day and night after sprinkling water conservation, or with grass curtain, sawdust cover after sprinkling water conservation. If conditions permit, yellow mud or lime paste can be used to store water for curing after the sill is made at the door. The use of ordinary Portland cement ground, curing time of not less than 7 days and nights; with slag Portland cement ground, curing time should not be less than 10 days and nights.
4, reasonable arrangement of construction flow, to avoid the person too early. Cement floor should be arranged as far as possible in the wall, ceiling painting and other decorative works after completion, to avoid pollution and damage to the opposite layer. If the construction must be arranged before other decoration works, effective protective measures should be taken, such as laying reed mats, straw curtains, linoleum, etc., and the maintenance period of 7-10 days and nights should be ensured.
5. Portland cement and ordinary Portland cement with high early strength should be adopted, and the strength grade should not be lower than 32.5. Expired or damp-caking cement shall not be used. The sand should be coarse and medium sand, and the silt content should not be greater than 3%. The particle size of fine stone and crushed stone used for the surface layer shall not be greater than 15mm, nor shall it be greater than 2/3 of the thickness of the surface layer, and the silt content shall not be greater than 2%.
 

Key words:

Self-leveling cement ground