Expanding agents are used in civil construction to achieve the purpose of reducing cracks. In the process of water research, it is usually required to add concrete expansion agents, retarders, and micro-expansion. For concrete admixtures with a very large mass, a slight expansion agent used together with other additives may cause side effects, so make sure the test is passed before use. Micro-expansion swelling is currently used in more varieties and the quality is uneven. Through experiments, we have found that the more commonly used one is UEA-H. The water curing and air curing are respectively 28d and 14d. 0.045% and 0.011%, in line with the building materials industry standard (JC478-92 14d), 0.04% in water and air 28d is maintained within an appropriate range, and UEA-H 60d 0.018%.
Control the concrete pouring temperature
According to technical specifications, rational use of layering should be used when pouring large-volume concrete, and the temperature should be kept constant before the concrete is mixed outside. The temperature is low and the concrete pouring temperature should not exceed 28°C. In summer, if the mold temperature is too high and there is less available water for mixing, it can not only cover the coarse aggregate, but also prevent the sun from shining to lower the indoor temperature. In the process of concrete pouring, the temperature of concrete cement hydration heat and the maximum temperature are the main factors entering the mold temperature and affecting the concrete hydration heat. Specifications: Design requirements within the temperature range. There are no special requirements during design. The temperature rise should not exceed 25°C. It is recommended to limit ΔT to 30℃. According to our experience, ΔT is 28℃ without surface cracks. The thickness of the castable floor is 1.0 to 2.5 million, and the actual maximum temperature usually occurs on the 3rd day of concrete formation.
Pay attention to the operating procedures of concrete construction in addition to following the "Concrete Construction and Acceptance" Implementation, we should also pay attention to:
1) Control of slump Concrete pumping is easy and generally requires a larger work site, which is usually solved by a mixing plant mixed with superplasticizer. The construction unit shall specify concrete slump and value requirements in the order contract. The general control of slump is 120±20 mm.
2) A large amount of bleeding and concrete vibration may occur during the pouring process To bleed water, it is best to use a uniform formwork close to the foot of the concrete slope, so that the direction can be changed from the far end of the concrete pouring to the back, where the raw materials are processed in a sump, and then a flexible shaft is used.
Strengthen the maintenance of concrete
Plastic film covering and rice watering straw bag covering are important components used to prevent cracks in the basement of high-rise buildings. This The purpose of this is to control the temperature and prevent cracks on the surface. It can make full use of the early strength of the concrete temperature stress to produce σmax %216t tensile strength Rf, which can prevent the occurrence of cracks. On the other hand, in humid environments, to prevent shrinkage cracks on the concrete surface due to dehydration, soil and water conservation should be maintained for no less than 14 days.
Do a good job of temperature measurement
The working temperature of the concrete base determines the heat of hydration of concrete. By adjusting specific measures to control the maximum temperature difference in the center, the surface temperature will not exceed the critical temperature crack.
Summary
The cracking of the basement concrete floor has a great impact on the stress and durability of the floor. Low-heat cement is used to mix concrete and reduce cement Dosage, adding fly ash, taking reasonable insulation and moisturizing measures, adding a slip layer, and rationally setting anti-cracking steel bars are effective methods to prevent cracking of the concrete floor. </p
微信扫一扫打赏
