Regulation On Shrinkage Of High And Ultra-High Strength Concrete

High and ultra-high strength concrete with a compressive strength of 100 MPa or even high is known for high durability and improved frost resistance.However,these improvements are valid only in thestructures without cracks.Compared with normal strength concrete,high and ultra-high strength concrete normally has a larger shrinkage and higher temperature rise due to larger amount of cement and lower water to cement ratio.Considering shrinkage of concrete and temperature changes are the two major mechanisms leading to the formation of cracks,this article will focus on the early shrinkage,temperature field and fracture properties of high and ultra-high strength concrete.In the research,three series of high and ultra-high strength concretes with and without internal cuirng are designed with a compressive strength of 100 MPa,120MPa and 130 MPa.The shrinkage and internal relative humidity of these concretes are investigated.The results show that the development of both shrinkage and internal humidity follow a two stage pattern.The introduction of internal curing can significantly decrease autogenous shrinkage of high and ultra-high strength concretes and delay their reduction of internal relative humidiy.Concrete-steel ring tests are used to evaluate the shrinkage induced cracking performance of high and ultra-high strength concretes.It is concluded that concrete rings without internal curing are all cracked under drying,while the cracking performance of internally cured concretes are greatly improved.Based on the results of Concretes under sealed condition,the creep and stress relaxation of high and ultra-high strength concretes with and without internal curing are discussed.The results of bending tests show that the use of internal curing materials,especially pre-saturated lightweight aggregate,will lead to negative impacts on cracking,tensile strength and fracture parameters of high and ultra-high strength concretes.The introduction of steel has little effects on cracking and tensile strength of high and ultrahigh strength concrete,but it can greatly improve the brittle behavior of plain concrete.In order to study the temperature field of high and ultra-high strength concrete,a numerical model considering is developed.Meanwhile,temperature measurement tests on concrete slab are conducted as well to verify the temperature model.The effect of hydration heat of cement,solar radiation and atmospheric temperature changes are taken into consideration in the model.Related cement hydration parameters are obtained from adiabatic temperature rise tests.Based on the model calculations,the effects of compressive strength,internal curing,casting time and seasons on the temperature field in pavements and columns are discussed.This model can be used for temperature control and optimization of high and ultra-high strength concrete pavements and columns.