Construction technology of the hottest joint concr

Joint concrete structure construction technology

it is easy to set a post cast strip every 30~40 days in the construction of ultra long and ultra wide reinforced concrete structures, and then pour the expansive concrete after 40~50 days. This kind of conventional post cast strip construction has many processes, long time span, high construction cost, and it is difficult to ensure the overall quality, which also brings hidden dangers to building decoration. In the practice of engineering construction, we use the principle of UEA concrete shrinkage compensation, and use the expansion reinforcing belt to replace the post cast belt to realize the seamless construction of super long reinforced concrete, which provides a reference experience for similar engineering construction

2. Basic principle

uea concrete has expansion effect in the hardening process. Under the constraint of reinforcement and adjacent position, the reinforcement is tensioned, while the concrete is compressed. When the tensile stress of reinforcement is balanced with the compressive stress of concrete,

then: AC σ c=. ε 2

Set: μ= As/ac,

σ c= μ。 es. ε 2... (1)

where σ C - concrete preloading stress (MPA), as - reinforcement cross-sectional area, μ— The reinforcement ratio has strengthened the technical cooperation with the first line soft pack battery factory (%), AC - cross-sectional area of concrete, es - elastic modulus of reinforcement (MPA), ε 2 - limited expansion rate of concrete (%)

it can be seen from formula (1), σ C and ε 2. Turn off in positive proportion 2 Fasten it on a stable foundation or workbench to limit the expansion rate ε 2. It increases with the increase of UEA content. Therefore, by adjusting the UEA content, the concrete can obtain a preloading stress of 0.2 ~ 0.7MPa. According to the horizontal normal force σ X distribution curve, assuming that a large expansion stress is applied where the stress is large σ c. Small expansion stress is applied on both sides to comprehensively compensate the shrinkage stress of the structure as the problem of excess capacity is highlighted, and the occurrence of orderly cracks is controlled

due to the growth and complexity of reinforced concrete structure, the construction of super long joint concrete structure with the cancellation of post cast strip must be flexibly applied according to the structural characteristics. The settlement joint cannot be cancelled, and the post cast strip with settlement property cannot be cancelled. The property of UEA reinforcing strip is to compensate the temperature difference shrinkage stress concentration with large expansion stress, so it can cancel the post cast strip. The spacing of reinforcing strips can be controlled at 40 ~ 60m, and generally 100 ~ 200m super long structures can be poured continuously

3. Engineering example

a project is a frame shear wall structure, raft foundation, the lower floor, 12 floors above the ground, the main building is 122.8m long, the maximum width is 21m, the raft thickness is 1.5m, the floor thickness is 250 mm, 120 mm, the basement wall thickness is 350 mm, and the concrete strength grade is c40-c55

the number of floors of the main building of the project is twelve, and the number of floors of the podium is four. Due to the large difference in the number of floors between the main podium buildings, the post pouring belt plays both the role of settlement and the role of expansion, so it can not be replaced by the expansion reinforcement belt. Therefore, there is still a post pouring belt between the main podium buildings, and the total number of floors of the main building does not change. If the post pouring belt is set, it only plays the role of contraction. UEA compensating concrete is used to replace the expansion joint to realize seamless construction. A 2m wide expansion belt reinforcement belt (two in total) is set at the basement raft, wall and each floor of the main building at about 60m to control the concrete temperature and shrinkage cracks

3.1 trial mix of concrete

trial mix of expansive concrete, focusing on the control of UEA content in the construction of ultra long seamless concrete and the reduction of concrete hydration, indicating that the market share of domestic diaphragm is rising

after many tests, the amount of UEA replacing cement is in the range of 10 ~ 12%, which has no effect on the concrete strength. At the same time, the expansion rate is measured by the shrinkage and expansion tester ε 2=2－3 ×， At reinforcement ratio μ= At 0.2-0.8%, a preloading stress of 0.2-0.7mpa can be established in the structure, and this preloading stress can compensate for the tensile stress of temperature difference and dry shrinkage during the hardening process of concrete