Sanding phenomenon cause analysis
- Water-cement ratio improperly configured
The water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25, the water-cement ratio is 0.2-0.25. If too much water is used during construction, it will greatly reduce the strength of surface mortar; at the same time, the construction will also cause mortar secretion of water, further reducing the surface strength of the ground, and after completion, it will be dusty after walking around and wear.
- Improper maintenance
After the cement is mixed with water, it enters the hardening stage through initial and final setting. However, the beginning of cement hardening is not the end of hydration, but continues to deepen into the cement particles. The strength of the cement mortar increases as the hydration process continues.
The hydration of cement can only take place in a humid environment. After the cement floor is completed, if there is no maintenance or the number of days of maintenance is not enough, the surface moisture in the dry environment will evaporate quickly, which will affect the hydration of cement, slow down the hardening speed, or even stop hardening in serious cases, resulting in cement mortar dehydration and affect the strength and anti-wear ability.
In addition, if the ground is wiped after less than 24h to water maintenance, due to the ground surface is tender, it will lead to a large area of rubber skin, sand exposed, sand after use.
- Improper protection of fresh concrete
The finished surface of the construction is frozen or rained on, which will also cause the phenomenon of sanding.
- Poor concrete and easy
Concrete that falls down too much (> 200mm) and has poor cohesion/water retention, and surface water secretion is serious is easy to sand.
- Materials do not meet the requirements
1).low cement strength level, or use expired cement, moisture caking cement, the cement activity is poor, which affects the strength and abrasion resistance of the ground surface layer.
2). The sand particle size is too fine, which requires large amount of water when mixing, thus the water-cement ratio is increased and the strength is reduced. The test shows that the strength of the mortar mixed with fine sand is 25%-35% lower than the mortar mixed with coarse and medium sand with the same proportion of mortar test pieces; the sand containing too much mud will also affect the cement and sand adhesion, easily cause sand on the ground.
How to prevent sanding
- Strict control of water-cement ratio
The consistency of the cement mortar used for the ground surface layer should not be greater than 35mm (standard cone sink), with concrete and fine stone concrete ground slump should not be greater than 30mm, the pad layer should be fully moistened beforehand, the cement slurry should be evenly coated, the distance between the punch bars should not be too large, it is best to control the 1.2m or so, with the paving ash with a short bar scraped flat. Concrete surface layer should be vibrated with plate vibrator, fine stone concrete should be rolled with roller or beaten with wooden trowel to make the surface pulp, to ensure the hardness and density of the surface layer.
- Master the calendering time of the surface layer.
Concrete floor is generally calendered in no less than three coats. The first time should be done immediately after the surface layer is laid. First, use a wooden spatula evenly rubbed once, so that the surface material evenly, close, smooth smoothing, to the surface does not appear water layer is appropriate. The second time calendering should be completed after the initial setting of cement, before the final setting (generally when the upper man has a slight footprints but not obviously sagging is appropriate), the surface will be compacted, pressed flat. Third time calendering is mainly to eliminate smear marks and occlusion of fine pores, and further surface compaction, pressure smooth (time should be mastered in the upper people do not appear footprints or footprints are obvious appropriate), but do not final set in the cement pressure after light.
- Do not close the light in the secretion
The long scraper must be used at the beginning of lightening, otherwise the water will be pressed into the concrete surface. Do not use beating board, otherwise it will lead to the surface of the slurry too much, resulting in sand.
- Fill water to collect light is forbidden, and start curing immediately after collecting light.
Ensure that the temperature of concrete pouring is >10c. During winter construction, pay attention to measure the temperature of the concrete on site and adjust the initial setting time.
How to fix a sanding floor
- Concrete floor used as bedding
Remove sanding loose layer by shot blasting or mechanical milling.
If the surface layer is epoxy flooring, in addition to the physical methods such as shot blasting treatment, should discuss with the material supplier, using high penetration epoxy primer for reinforcement treatment.
It is not recommended to use liquid hardener for reinforcement treatment and then do epoxy top layer, unless the liquid hardener manufacturer can provide pulling test data (>1.5mpa) to prove its adhesion with epoxy top layer.
- Concrete floor used as top layer
➤ Slight gritting (gritted porous layer <2mm) treated with liquid hardener and/or abrasive polish.
➤ Moderate gritting (2 – 5 mm of grit crust) Treat with an acrylic, epoxy or polyurethane concrete sealant.
➤ Heavy gritting (gritty layer >5 mm) Mill and apply a polymeric mortar layer or resin flooring.
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