浅谈外墙水泥砂浆开裂的原因及防治翻译

Prevention

A cement mortar for cracks

1, the selection of raw materials and ingredients misconduct. ① some construction units in the construction of buildings in the beam, column selection, such as better cement and aggregate, that mistakes do not have to consider when painting the structural safety problems is the use of low-grade cement and fine aggregate, cement mortar lead to the contraction and getting cracking. ② cement mortar in the preparation of simple incorporation gypsum or lime powder, although workability improved, but dropped mortar strength, shear force and adhesive strength also will be dropped, from the shell easily (hollowing) cracking.

2, Construction Technology improper or not regulatory requirements Construction ① mortar whitewash of the distribution grid points unreasonable or embedded too deep and undermine the integrity of the external walls of the ground floor. ② walls勾缝Department mortar strength not enough, not enough thickness, density uneven, mortar mixing or using artificial uneven mixing. ③ mortar, painting master improper construction process, conservation officers (grassroots handled wet or too dry) under - or over-watering will cause surface loss or shrinkage. ④ not grasp different wall materials such as red brick, hollow clay brick, concrete hollow block, aerated concrete block of material, wood, different methods of operation should be used to whitewash. ⑤ masonry wall during mortar strength poor bonding of not enough, not dense, full, the aggregate masonry or masonry difference arising from the wrong-way joints and Air Gap, blind joints caused cracks. ⑥ operators usually work with the left hand of bricks, in the right hand of the brick上抹cement mortar so easy for the left hand gripping parts of the brick with cement mortar, paste space-time caused drum leakage.

3, structural deformation caused cracks in the wall: the foundation uneven settlement horizontal wall

space too large, brick wall stress concentration at corner without reinforcement, doors and windows too big hole, deformation crack improperly installed due to other reasons而使wall strength, stiffness and stability arising from insufficient structural deformation cracks, leading to cracking of the mortar .

4, temperature and humidity changes in the factors ① temperature changes lead to expansion or contraction of construction materials, but different materials have different stress and deformation temperature coefficient. Thermal expansion interface in a temperature stress, once the temperature stress greater than the tensile strength of cement mortar, will allow material relative displacement, resulting in a mortar cracks. Most of the external walls of cement mortar exposed to the sun, mortar layer temperature may greatly exceed temperature, and even higher than the outdoor temperature doubled with the addition of bright sunshine duration in the sweltering heat and the cold of winter temperature changes, the larger the thermal stress generated temperature of the external walls of cement mortar shrinkage cracks, although temperatures should be the crack of the relatively small, but so will constantly repeated crack the expansion. ② exposed external walls in cement mortar in the air a long time, often due to changes in humidity expansion or contraction. Humidity deformation of cement mortar for the water content changes and the rate of shrinkage. The deformation caused by the humidity in the expansion of its shrinking value of the 1 / 9, cement mortar shrinkage rate is a drop of reverse curve, the initial rapid shrinkage, a long time will gradually slowed down, this contraction is irreversible. The contraction caused by changes in humidity is a wet and dry cycle of irreversible process. When the contraction stress greater than the tensile strength of mortar, the mortar cracks inevitable.

To summarize the above, the external walls of cement mortar cracks to various reasons, in addition to the construction, ratio, choice of materials, wall and so on standardized, improved, from its cement mortar can take effective control measures to improve the quality of external walls.

Second, the prevention cracks

1, silicone waterproof mortar

Silicone is the main component methyl alcohol silicon sodium, it contains polarity factor - OH, easy to generate hydrogen bonds, and further polycondensation reaction of the branched molecules and mesh with methyl silicone resin cement hydration reaction, it's packing a mortar microporous and毛细孔, an increase of the density of mortar and impermeability. As a result of these methyl silicone resin polymer plastic polymer has higher strength, we can reduce shrinkage cracks in the mortar, reduce shrinkage stress and improve the crack resistance of mortar. In addition because of its decentralized stress and prevent stress concentration, improving the interface effect mortar and plastic. Comprehensive improvement mortar tensile properties.

For example, with reference under:

Cement

In the Sand

Silicone + water (1:8) 1 2.5 0.6

Before construction on the grass-roots level in the surface刷涂silicone + water (1:8) solution once again started painting.

2, polymer cement mortar

Mortar is a polymer organic polymer materials to replace part of cement, and cement and cementitious materials together as a mortar. A commonly used polyvinyl acetate polymer, ethylene copolymer emulsion, acrylic resin copolymer emulsion, such as styrene-butadiene rubber latex polymer. Blending a certain proportion of polymer can overcome ordinary mortar shrinkage, brittle, high bond strength is not common, can effectively raise mortar plastic deformation ability and bond strength, cracking results improved markedly. But polymer mortar should pay attention to the following questions: ① polymer content is, the higher the decline mortar compressive strength, but with a different polymer mortar strength of a certain difference. To polyvinyl acetate as an example, Xiaoqian Qian study shows that: Volume for the 10-15% of cement, water-cement ratio of 0.4 or so, polymer cement mortar compressive strength than not polymer mortar fell 30-40 percent, but the tensile strength and adhesive strength are improved, deformation modulus decreased more than 30%. ② in cement mortar, cement hydration needs humid conditions, and the need for polymer membrane drying pool water loss environment. Thus the conservation of polymer mortar to cement both must also ensure that adequate hydration polymer film, that is to damp early conservation, the late appropriately dry.

3, fiber cement mortar crack resistance

To cement mortar for the matrix, short of a non-continuous or continuous fiber for long fiber reinforced material composed of cement-based composite materials,

Known as fiber reinforced concrete (mortar).

Europe and the United States and other countries last century synthetic fibers for the medium-term study that the enhancement of cement mortar material. Some experiments show that, if the volume in concrete mixing for 0.1% -0.3% of the polypropylene fiber, the mortar will reduce 12-25% of plastic shrinkage, the first brother to the United States Hill Chemical Company production of Dura fiber (Durafiber) is a modification of the fascicular PP monofilament fiber, look for the white, soft touch slide in mortar scattered root was turned into a separate single-wire, monofilament uniform distribution in the post-mortar block, a three-dimensional chaos to the distribution of state support in plastic aggregate to prevent segregation, the mortar can bear the shrinkage and anti-stress and reduce cracks, but also in after mortar sclerosis, a stop block in the development of micro-cracks and reduce internal pore mortar cracks stress concentration coefficient matrix played improve tensile, shear. intensity of the role. Impermeability and improve mortar, durability, toughness and impact resistance increased capacity.

Blending when first joining Dura fiber cement, sand, water used by the added fiber, fiber mortar mixing time for the uniform distribution, the general 3-5 min, conservation requirements remain unchanged. Cost per square foot increased by only 1.5-2.0 yuan.

4, swelling materials cracking mortar

Expanders materials incorporation cement mortar and cement hydration have ettringite crystalline hydrates (C3A, 3CASO4, 32H2O) will produce micro-mortar internal expansion, resulting from the stress of surcharging effective compensation mud mortar own shrinkage and the tensile stress to prevent cracking. Research shows that in the conservation process, the moisture adequate or not, the decision expansive materials and cement hydration reaction produced expansive effect is good or bad. Expanders can significantly reduce the early contraction mortar, but also can significantly reduce the humid conditions of the late cement mortar shrinkage, but not reduced even under conditions of increasing drying shrinkage of cement mortar. Expansion materials and the use of composite materials superplasticizer, because the lower water-cement ratio, mortar of the early shrinkage of mortar reduce, but not very effective late, the latter part of the conservation crucial. We Lung Chak Habitat in an external wall construction materials used in expansion + superplasticizer common use, according to standardize construction moisturizing fully achieve conservation, pouring mortar observation after the good results of 2002, not a large-scale crack.