Study On Crack Control Technology Of Concrete Structure

With the rapid development of China's economy,the investment in infrastructure is increasing,large and extra large projects are increasing,and concrete structures can be seen everywhere.However,due to the characteristics of concrete materials,as well as the good and bad of the design and construction units,there are always more or less quality problems in buildings.Among them,the problem of concrete cracking is a very important factor affecting the quality of buildings.Because the concrete cracking will cause the leakage of buildings,especially the underground space and marine concrete structure,after the concrete cracking,the corrosive ions will corrode the steel bars in the concrete through the crack channel,resulting in the rust of the steel bars,which will greatly reduce the safety and durability of the building.The problem of concrete cracks has always been an important topic for many scholars and engineering units,and many achievements have been made.This mainly includes two aspects:taking technical measures in the construction and strictly controlling the quality of each component in the concrete material to control the concrete cracking.There are many kinds of concrete cracks,such as cracks caused by uneven settlement of foundation,cracks caused by load,cracks caused by concrete shrinkage,cracks caused by external constraints of concrete and temperature cracks,etc.This paper mainly focuses on how to reduce the external constraint stress of concrete,make concrete deformation subject to as little constraint as possible,and finally control the tensile stress on itself within the range of ultimate tensile strength to reduce the risk of cracking.Therefore,for the new and old concrete pouring,the concept of mortar buffer layer is introduced.By laying mortar buffer layer on the new and old concrete pouring interface to reduce the restraint stress,setting the material and process parameters of the mortar buffer layer,the reduction rate of the constraint stress can reach more than 50%,and the number of cracks can be reduced by more than 50%.The main research contents of this paper are as follows:1 Add redispersible latex powder and emulsified asphalt and other polymers into ordinary mortar to form polymer cement mortar.Through the modification effect of polymer on mortar,develop a polymer mortar with low elastic modulus and good performance.2 On the basis of obtaining polymer mortar with good performance,the influence of technological parameters of mortar buffer layer on interface mechanical properties was studied,in which the thickness of mortar buffer layer was 0cm,3cm and 5cm respectively,and the age of interval between old and new concrete was 7d,14 d and 28 d respectively.3 Based on the polymer mortar with good performance,the influence of mortar buffer layer on the interface durability was studied,the interface types are HNB(Once formed concrete)?SJ0(The concrete is formed in two steps,no mortar layer at the interface)?SJ3(The concrete is formed in two steps,and the thickness of mortar layer at the interface is 3cm)and SJ5(The concrete is formed in two steps,and the thickness of mortar layer at the interface is 5cm).4 Study the influence of mortar buffer thickness on concrete restraint degree.5 Study the influence of interval time between mortar buffer layer and new concrete on concrete restraint degree.6 Study the influence of age of separation between old and new concrete on concrete restraint.The test results of polymer mortar show that the compressive strength and flexural strength of mortar decrease gradually with the increase of redispersible latex powder and emulsified asphalt.However,the flexural strength of mortar decreases more slowly than the compressive strength,that is,with the increase of polymer content,the compressive flexural ratio of mortar decreases,the brittleness of mortar decreases,toughness increases,and crack resistance improves.Because the polymer used belongs to a kind of polymer compound,it can fill the holes in the mortar,thus changing the distribution and size of the holes in the mortar,reducing the dry shrinkage of the mortar.As for the influence of mortar buffer layer on the interface mechanical properties and durability,the test results show that,when the thickness of the mortar buffer layer is 5cm,the failure surface of the whole concrete specimen is located in the weakest mortar layer,and the flexural strength of the concrete is the lowest;when the thickness of the mortar buffer layer is 3cm,the failure surface of the specimen is located in the concrete layer,and the flexural strength of the concrete specimen is equivalent to that of the concrete specimen without the mortar buffer layer,which basically has no adverse effect on the mechanical properties of the concrete specimen.As the thickness of the mortar buffer layer increases,the electric flux value of the concrete interface increases gradually,because the mortar material has a lower compactness than the concrete material,thus the anti-erosion property is poor.In order to ensure that the durability of the concrete interface has no adverse impact,the thickness of the mortar buffer layer must be strictly controlled.As for the influence of mortar buffer layer on the restraint degree of concrete,the test results show that,the mortar buffer layer is laid at the interface between the new and old concrete,which is beneficial to reduce the external restraint stress of the new concrete and avoid the excessive restraint tensile stress inside the new concrete when it shrinks and deforms.When the thickness of the mortar buffer layer is 3cm,the interval time between the mortar buffer layer and the new concrete is 6h,and the interval age between the new and old concrete is 14 d,the new concrete is the least restrained,the shrinkage deformation of 28 d is 171.2 micro strains,which is 84% of the shrinkage deformation of the concrete in the free state.At this time,the constraint degree of newly poured concrete is 0.16.The research results of this paper have important practical value in engineering,and put forward technical measures to reduce the constraint degree of concrete,so as to achieve the purpose of controlling concrete cracks,and further improve the control system of concrete cracks in construction projects,providing reference for similar projects in the future.