Accident cause analysis and treatment method of th

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Accident cause analysis and treatment methods of cement mortar surface

common cement mortar surface engineering quality accidents in construction include: ash rising, hollowing, cracking, cracks, inverted flashing, etc. The reasons mainly include raw materials and construction, which should be handled according to the actual situation

I. analyze and propose treatment methods in detail

(I) causes of ash raising

causes: cement grade is low, or expired damp caked cement is used; Sand particle size is too fine; The water cement ratio is too large; The silt content of sand is too large; Calendering too early or too late; Curing too early or not; Cement mortar is frozen; Bear the load when it does not reach sufficient strength

treatment methods: (1) dust in a small area, and use a stone grinder to water grind the dust; (2) For large-scale ash lifting, remove the floating sand of the ash lifting part with a steel wire brush, water it to wet, and then use cement: 107 glue: water = 1:0 25:0 is much higher than the bone of human body 35 mortar is used as the bottom layer, and the surface layer is coated after the initial setting and before the final setting of the bottom layer. The ratio of cement to mortar is cement: 107 glue: water = 1:0.2:0.45. The surface layer is usually brushed for 2 ~ 3 times, and the next layer must be brushed when the previous layer is dry. Finally, carry out maintenance. (3) The cement ground with serious ash shall be renovated, that is, the surface course shall be removed completely, roughened and wetted, then brushed with a layer of plain cement slurry with a water cement ratio of 0.4 ~ 0.5 (mixed with an appropriate amount of 107 glue), and then paved with 1:2 (volume ratio) cement mortar, and the slurry shall be brushed with the pavement

(II) hollowing

causes: the cushion surface is not cleaned up, and there is floating ash or other dirt; The cushion surface is not watered enough and is too dry; There is ponding on the cushion surface, which makes the water cement ratio suddenly increase; The cement slurry has been air dried and hardened

treatment methods: (1) generally, there is no need to repair empty drums with an area of less than 0.1m2 at the corners of the room and no cracks; During local renovation, the hollowing part shall be chiseled away and chiseled into the well bonded layer for 30 ~ 50mm. 1 ~ 2D before repair, the surface layer shall be washed and wetted. When repairing, first brush a layer of plain cement slurry with a water cement ratio of 0.4 ~ 0.5 at the bottom and around. If the surface layer is thick, repair it in several times, and the thickness of each time should not be greater than 20mm; After final setting, use wet sand or wet straw bags for curing. (2) For large-area hollowing, the whole surface course shall be chiseled, the bottom course shall be chiseled, and a new surface course shall be paved

(III) cracking

causes: low cement strength and poor stability; The sand is too fine, the mortar is mixed unevenly, and the water cement ratio is too large; The bottom layer is dry and not fully wet before paving; The temperature is too high, the wind and sun are blowing, and the watering and maintenance are not timely; The area is too large and no dividing joint is set; Insufficient strength of base course; The construction load is too large

treatment method: because the causes of ground cracking are complex, the causes of cracks should be investigated before treatment, and then treatment. If the crack is fine, there is no hollowing phenomenon, and there is no liquid flowing, it can not be handled generally. When the cracks are large, cement slurry (107 glue slurry) can be used for sealing (or batch embedding) treatment. If the cracks are caused by structural changes, they should be treated in combination with the structural conditions

(IV) cracks along the width of the floor

causes: cracks caused by negative bending moments at the slab end; The reserved reinforcement in the slab is not firmly anchored; Longitudinal temperature contraction of floor slab

treatment method: if the cracks appear to be fine, they are generally not repaired when there is no leakage requirement on the floor. If it is expected that the main crack is wide and there are anti-seepage requirements during short-term or weak stable operation, it needs to be repaired; A groove with a width of about 10mm and a depth of about 20mm can be cut at the crack, and then filled with mastic. The gap shall be cleaned before patching. It can also be filled with fine aggregate concrete not lower than grade C20, and set up a new composite material named pocan af4130 jointly developed by Langsheng, a steel special chemical company, and hailahook group company in Germany. The composite material is the shell material ribs of one battery management unit (BMU) and two cell detection units (CMU)

(V) cracks along the length of the floor

causes: the floor is not carefully maintained and is loaded too early; The stiffness of the floor is poor, resulting in elastic deformation under load

treatment methods: (1) if the number of cracks is small, and the cracks are fine, and there is no anti-seepage requirement for the floor, it can not be repaired. (2) If the number of cracks is small and the cracks are fine, but the floor has leakage requirements, it should be repaired. It is necessary to chisel out the cracks in the slab joints, so that the joint surface is in a slope shape, with a slope of H/b = 1:1 ~ 1:2, and clean it up, wash it with water, and repair it when the saturated surface is dry. When repairing, first brush a layer of pure cement slurry in the slab joint, and then pour fine aggregate concrete. 1/2 of the first pouring and tamping slab joint depth. Wait for water absorption for the second time. If the slab joint is narrow, pour 20 ~ 30mm with 1:2 ~ 1:2.5 cement mortar first, and then pour C20 fine aggregate concrete to 10mm away from the slab surface after tamping. Tamp and flatten it, but do not polish it. Cure it for 2 ~ 3D. No one is allowed to walk on it during the curing period. When repairing the surface course, first apply pure cement slurry on the plate surface and the joint, and then mix and fill with the same material as the surface course. When calendering, pay attention to pressing the joints on both sides until they are dense, and cover them with wet sand or wet straw bags for curing after final setting

(3) if there are many cracks in the room, all the surface courses should be chiseled out, and chiseled into the slab joints for 10 ~ 20mm. A layer of reinforced concrete pouring layer with a thickness of not less than 30mm should be poured on it, and a layer of two-way reinforcement sheets should be equipped inside( Ф 4 @ 150 ~ 200mm) pour and vibrate fine aggregate concrete of not less than grade C20, trowel as you tamp, and cure as required

(VI) inverted flashing on the ground with floor drain

causes: the ground of balcony, corridor and bathroom should generally be 20 ~ 50mm lower than the indoor ground, but it may not meet the requirements due to neglect in design or inaccurate ground elevation during construction

treatment method: the surface course shall be chiseled off completely, and then the floor drain shall be taken as the center, the reinforcement shall be made around according to a certain slope, the slope shall be found, and the trowel shall be used to level it after plastering. Before installing the floor drain, check whether the elevation of the floor drain is accurate. During installation, it is better to place the floor drain lower than the elevation

II. Conclusion

for these quality accidents of cement mortar surface, we can only start from the two major aspects of raw materials and construction care, strictly control the quality, and improve the measurement method of construction fineness displacement, which covers a wide range, and these quality accidents can be completely avoided and eliminated

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