Researches On The Formation And Action Mechanism Of Interfacial Transition Zone In Light Aggregate High Strength Concrete

Lightweight aggregate concrete has characters such as high specific strength,temperature preservation,heat insulation,shock resistance and many other advantages,conform to the development trend of high performance and functional of modern concrete engineering.Lightweight aggregate concrete has a wide application prospect in large-span bridges and high buildings structure engineering.In the high strength concrete using prewetted lightweight aggregate,the hydration of interfacial transition zone is more sufficient than that of the matrix due to internal curing of water released from lightweight aggregate,and interfacial transition zone structure cladding lightweight aggregate with better performance is formed.the interface area is no longer the weak link of light aggregate concrete,which improves the performance of the light aggregate high strength concrete.If we can propose a further optimization of method to improve performance interface area from the mesoscopic and micro angle,which will significantly improve the performance of the light aggregate high strength concrete.This paper is based on Youth Science Fund Project“conformation mechanism and the effect of arch shell structure for lightweight aggregate high strength concrete on mechanical properties and medium transfer performance”.Several influence factors,including water absorption of ceramsite,water-cement ratio and bonding component,on the interfacial micro-hardness and microstructure were investigated by the testing techniques such as micro-hardness、SEM、²⁹Si NMR and XRD.Based on the studied results,the performance of light aggregate concrete such as Mechanical properties and durability were reviewed,the following conclusions are obtained:（1）when the water absorption of ceramsite increased,the MCL of C-S-H gel and the hydration degree of the cement paste in interfacial area increased,and the micro-hardness of interface area also enlarged.A weak interfacial area（about 40μm）could be observed surrounding ceramsite in the lightweight concrete using Gravel type shale rock ceramsite with water absorption of 3.7%,while the enhancement layer could be observed around Spherical shale and high titanium heavy slag lightweight aggregate with water absorption of 6.4% and 12%,the width is about 80μm and100μm,respectively.（2）Along with the increase of water cement ratio,the micro-hardness of paste inthe matrix and interfacial area decreased,while the MCL of C-S-H gel and the hydration degree of the cement paste in interfacial area increased.And when the water cement ratio were 0.26,0.3 and 0.3,compared with the matrix the growth of cement hydration degree of interfacial area were 7.95%,6.04% and 7.95%,respectively.the function of internal curing was more obvious under the condition of low water cement ratio.（3）With the increase of the admixture,microhardness in interface area reduced at the age of 14 d,the microhardness increases remarkably near the interface at90 d,while the MCL and degree of polymerization of C-S-H gel and the hydration degree of the cement paste in interfacial area increased.（4）Interface area shape and microstructure are important affecting factors for mechanical and medium permeation properties of lightweight aggregate high strength concrete.Although spherical shale light aggregate strength is lower than the gravel type shale lightweight aggregate,the interface zone structure is formed in arch shell style,because of porous structure and special form of interface area,which evenly disperse compressive stress,prevent migration of the harmful ion in wool stoma,improve the mechanics and durability performance of lightweight aggregate concrete.