Causes and prevention of sand on the ground of cement mortar building

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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 ground structure, simple structure, strong wear-resistant, low cost, but often due to improper construction, easyCausing cracks, hollowing, sand three common quality problems, affecting the quality of perception and normal use, residents deeply hate, reflect strong, so we must pay attention to, seriously control.
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 too much water, will greatly reduce the strength of the mortar; at the same time, the construction will also cause the mortar bleeding, further reduce the ground tableSurface strength, once the completion of walking wear, will be gray.
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 fully formed, and there is still more free water. Although the surface will swim after calendering.Floating a layer of water, the strength and wear resistance of the mortar on the opposite layer are unfavorable. If the calendering is too late and the cement has hardened, it will not only be difficult to operate, cannot eliminate the capillary holes and smear marks on the surface of the surface layer, but also disturb the hardened surface, which will greatly reduce the strength and wear resistance of the mortar on the surface layer.
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 the cement with expired and damp caking is used, which has poor activity and affects the strength and wear resistance of the ground surface layer. Second, the sand grain 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 cement.And the bond force of sand, easy to cause the ground from the sand.
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 with rollers.Press, or beat with a wooden trowel to make the surface floodplaste 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 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 slagPortland 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 it is necessary to arrange construction before other decoration works, effective protective measures should be taken, such as laying reed mats, straw curtains,Linoleum, etc., and should ensure a 7-10 day and night curing period.
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 course shall not be greater than 15mm, and shall not beMore than 2/3 of the thickness of the surface layer, the silt content should not be greater than 2%.
Treatment of ground sand
1, small area of sand. Use a grindstone to water and grind the sand part until a hard surface is exposed. It can also be repaired by the method of pure cement slurry cover. The operation sequence is: cleaning the base layer → fully rinsing and wetting → laying pure cement slurry (or spreading dry cement surface) 1-2mm → calendering 2-3 times → curing. such as surfaceNot smooth, but also water grinding again.
2, serious sand. Should be refurbished, the surface layer will be removed, rinse with water. Before laying the surface layer, the chiseled surface should be kept moist, and brush a water cement ratio of 0.4-0.5 plain cement slurry (can be mixed with appropriate amount of 108 glue) to enhance its bonding force, and then use 1: 2 cement mortar to lay anotherFor layer layer, the surface layer shall be laid with the brush slurry. After the surface layer is laid, calendered and cured.
3, a large area of sand. Available 108 glue mud repair, specific methods and precautions are as follows:
(1) Use a wire brush to remove the floating sand from the sand part and rinse it with clean water. If there are cracks or obvious dents on the ground, the putty made of cement mixed with a small amount of 108 glue is used to make up.
(2) with 108 glue and water (about twice the water) after stirring evenly, brush the surface of the ground, in order to enhance the 108 glue mud and the surface of the bond.
(3)108 glue mud should be applied in layers, each layer should be applied about 0.5mm thick, generally 3-4 times, with a total thickness of about 2mm. The mixing ratio of the bottom mortar can be cement: 108 glue: water = 1: 0.25: 0.35, which is evenly mixed and applied to the treated ground. The operation can be leveled with a scraper,The bottom layer is generally applied 1-2 times. The mixing ratio of surface layer glue can be cement: 108 glue: water = 1: 0.2: 0.45, which is generally applied 2-3 times. After smearing, the cement floor shall be maintained according to the maintenance method. After 2-3d, the smear marks shall be gently ground with a fine grinding wheel or oilstone, and then waxed once before use.

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