Monitoring And Analysis Of Crack Resistance Of Large-volume Reinforced Concrete Structures

With the rapid development of China’s economy,mass concrete is widely used in engineering.However,deforms will be generated in its internal structure due to its heat of hydration and drying shrinkage and other factors,which will make the large volume concrete appear inconsistent with the deformation of the surface and excessive overall shrinkage as well as other problems,and then produce greater stresses under the action of internal and external constraints.If no effective measures are taken,deep cracks or even penetration cracks may appear.Therefore,it is of great importance to reduce the stress in the mass concrete and prevent the concrete from cracking.In the construction of large volume concrete by alternative bay construction method,the connecting bin blocks are constrained by the adjacent bin blocks,hence they are more prone to cracking.In this paper,the effects of anti-cracking measures for large volume reinforced concrete connecting bin blocks of a project are analyzed by using the methods of test,finite element simulation and field measurement,and thus anti-cracking measures are proposed in the actual project with good effect,which can provide reference for similar projects.(1)In accordance with the hydration temperature rise data of different cementitious materials,fly ash and mineral powder were used to replace part of the cement to test the doublemixed concrete,and the compressive strength as well as adiabatic temperature rise tests were carried out on the concrete with different ratios.According to the principle of ensuring the strength of concrete while reducing the adiabatic temperature rise,the most suitable concrete ratio was selected by comparing the test data.(2)Before the construction,the finite element model of large volume reinforced concrete joint bin block is established.The temperature values and stress values of the joint bin block itself and those values of the subsequent casting of the upper bin block are simulated.Based on the results of comparing the maximum tensile stress in the simulation results with the tensile strength at the same age,the crack prevention effect of the construction measures was evaluated for the safety of the connected bin blocks under different construction schemes.The results show that the construction measures to reduce constraints play a better role in reducing the tensile stress of concrete and preventing cracking.(3)Set temperature,strain and zero stress strain sensors according to the finite element results to monitor the temperature and strain data of concrete after construction.By comparing the simulated and measured temperature data,the simulated stress value is modified.By improving the existing method,the stress data are calculated from the strain and zero stress strain data,and the reliability is verified by comparing with the stress simulation values.The results show that the measured stress is close to the simulated value,so the measured stress calculation method can be considered reliable.The results show that the measured calculated stresses are close to the simulated values,consequently,the measured stress calculation method could be considered reliable.After that,the change law of temperature and stress in practice are analyzed based on the temperature and stress data.(4)The effect of temperature control measures and reinforcement measures on the crack prevention is evaluated by simulating and comparing the temperature and stress of mass concrete under different temperature control measures and the effect of different reinforcement on the stress and crack development of mass concrete.The results manifest that the measures to control the rate of temperature drop and the magnitude of temperature peak play a preferable role in reducing the tensile stress of concrete and preventing cracking.While reinforcement measures have little effect on bearing stress before cracking of concrete,but they can effectively inhibit the development of cracks after cracking.Larger diameter reinforcement contributes more to the inhibition of cracking,only with limited enhancement.