concrete is a kind of heterogeneous brittle material which is mixed with sand and gravel aggregate, cement, water and other additional materials. Concrete is one of the most widely used building structural materials at present. However, concrete cracks are common problems in building engineering. Due to a series of problems such as concrete construction, deformation and constraints, concrete cracks have become the most common engineering diseases in civil engineering, water conservancy, bridges, tunnels and other projects. There are many micro-pores, air pockets and micro-cracks in hardened concrete. It is precisely because these early concrete buildings and components usually work with cracks. Because of the existence and development of concrete cracks, the internal steel bars and other materials will usually corrode, which will reduce the bearing capacity, durability and impermeability of reinforced concrete materials, affect the appearance and service life of buildings, and seriously threaten people's lives and property.
II. Reasons for Concrete Cracks
There are many reasons for concrete cracks, mainly as follows:
(1) Cracks generated when the volume deformation caused by drying shrinkage is restrained during the hardening process of concrete cracks, sometimes the width of such cracks is very large, even running through the whole component.
(2) A large amount of hydration heat generated during the hydration of mass concrete cannot be dissipated, which leads to a large temperature difference between the inside and outside of the concrete, which makes the deformation of the concrete exceed the limit and causes cracks.
(3) Cracks caused by plastic collapse of concrete in thick members.
(4) when there are constraints, the volume expansion and contraction of concrete caused by thermal expansion and cold contraction, because of the constraints, internal temperature stress is generated. Due to the low tensile strength of concrete, it is easy to be cracked by the tensile stress caused by temperature, resulting in temperature cracks. Cracks caused by sun exposure are also the most common phenomenon in engineering.
(5) After the concrete is mixed with water, the alkaline substances in the cement react with the active silica in the active aggregate, and the precipitated colloidal alkali, silica gel, absorbs water from the surrounding medium and swells three times, thus causing cracks in the concrete.
(6) In hot and windy weather, the surface of concrete evaporates too quickly, resulting in too high hydration heat inside the concrete, which is still in a plastic state after several hours of concrete pouring, and it is easy to produce plastic shrinkage cracks.
(7) Cracks caused by overloading of members, such as internal force bending moment caused by uniformly distributed load or concentrated load exceeding the design, cracks perpendicular to the longitudinal axis of members, and oblique cracks caused by large shear force, which extend up and down.
(8) When the foundation of the structure has uneven subsidence, cracks may occur, and with the further development of subsidence, cracks will further expand.
(9) When the reinforced concrete is in an unfavorable environment, such as corrosive water, due to the limited thickness of the concrete protective layer, especially when the concrete has poor compactness, chloride ions in the environment and oxygen dissolved in water will make the steel bars in the concrete rust and generate iron oxide. The volume of iron oxide is much larger than that of the original metal, and the rust volume expands, squeezing the surrounding concrete and cracking the concrete.
Huatong brand cold joint sealant produced by Yantai Huatong Company is a new one-component oily cold joint sealant developed by Yantai Huatong Company with independent property rights, which is a national patent product. This product is a fast-curing oily material with excellent displacement resistance and waterproof performance. It absorbs moisture in the air, reacts and cures, has strong weather resistance, does not flow at high temperature, does not crack at low temperature, and can be constructed at 5℃ to -4℃. The product will not peel off after construction before and after rain, and it remains elastic. The color of cold joint sealant can be customized according to customers' needs to meet the needs of pavement crack treatment with various colors. It is mainly used for bonding and sealing cracks (joints) such as expansion joints, settlement joints, cutting joints and construction joints of cement or asphalt pavements, squares, airport runways, roofs and basements. According to the determination, each kilogram of cold joint sealant can pour 1-3 linear meters of cracks with common width, and the total cost of cold joint sealant per meter of materials and machines such as joint expansion, dust removal, glue pouring and glue application does not exceed that of 2 yuan.
construction technology
1. seam expanding
the hand-held small saw blade seam expanding machine independently developed by huatong company is small in size, light in weight, free in seam expanding activities, and can track any turning and seam expanding.
2. Dust removal
Huatong's new-style air blower dust remover is adopted, which can completely remove the loose concrete slag left in the joint after expanding the joint while ensuring the clean removal of floating dust.
3. Filling
For wide and deep cracks, foam strips or quartz sand can be filled in the cleaned cracks before pouring glue, and 25px space is reserved above for pouring glue.
4. Pouring glue
For cracks with a width of less than 3 mm, it is necessary to expand the joint before pouring glue. Generally, the width of the expanded joint is 4 to 8 mm, and the depth of the expanded joint is 3 to 6 mm. Cracks with a width greater than 3 mm shall be directly poured with special bags for joint pouring.
5. Open traffic
The surface drying time of joint sealant is less than half an hour. For cracks with a width less than 3cm, the traffic can be directly opened after the sealant is poured. For wider and deeper cracks, the surface can be protected by spreading isolation sand after the sealant is poured, or the traffic can be opened after 24 hours.
6. Storage and packaging
Store in a cool place away from fire sources. Packing: 4 kg/bag, 3 kg/barrel. Shelf life: 24 months in bags and 12 months in barrels.
Common repair materials for highway diseases: 1. Bitumen cold patch can be used for pit and groove repair, which can be directly repaired and opened to traffic; 2. Cold joint sealant can be used for cracks in cement pavement, which can be directly opened to traffic, and the cost per meter is not higher than that in 2 yuan. 3, the asphalt pavement cracks can use the joint tape, according to the crack direction tracking joint, after 2 months, it will be integrated with the original asphalt pavement, without jumping, which will not affect the snow removal in winter; 4. The broken surface of cement pavement can be repaired with quick patching material, 5 mm thin layer and opened to traffic for 2 hours; 5. Color cold patching materials can be used for paving or repairing potholes on small-area colored pavements. At the construction site, bags can be unpacked, paved and compacted, and then they can be opened to traffic.