Study On Autogenous Shrinkage And Crack Resistance Of Alkali-activated Slag Ceramsite Concrete

Alkali-activated slag concrete(AASC)has the advantages of low hydration heat,high strength,good durability and environmental friendship by recycling wastes,etc.However,AASC often cracks due to shrinkage,which seriously harms the safety and service of structures.Subsequently,it restricts the popularization and application of AASC.Ceramsite has the properties of water absorption and desorption,and it can improve the performance of AASC.The purpose of this paper is to research the autogenous shrinkage and crack resistant performance of alkali-activated slag ceramsite concrete(AASCC).Firstly,the water absorption and desorption properties of ceramsite in both water and AASCC were tested by using the volumetric flask test and self-made U-shaped tube test devices.The interfacial transition zone and pore structure of AASCC were tested by SEM and nitrogen adsorption method respectively.Then,a self-made hanged corrugated pipe device was used to study the autogenous shrinkage of AASCC,and the crack resistance performance of AASCC was evaluated by partly-restrained shrinkage ring without clapboard.Finally,combined the autogenous shrinkage and crack resistance performance,the tensile creep of AASCC was further studied.The main results are as follows:1.For the concrete with the same replacement rate of pre-wetted ceramsite,AASCC has denser pore structure compared to OPCC,and the percentage of pores whose diameter is under 50 nm of AASCC was 30%larger than that of OPCC.So autogenous shrinkage of AASCC,which is caused by water loss in the process of hydration products,is larger than that of OPCC.Autogenous shrinkage of AASCC at the first day exceeds the 80%of the autogenous shrinkage of AASCC at the age of 14 d.2.For the concrete with the same replacement rate of pre-wetted ceramsite,the greater autogenous shrinkage of AASCC leads to larger tensile stress.The hydration products of AASCC are amorphous and gelatinous,which has low crystallinity,but the hydration products of OPCC is crystal,such as Ca(OH)2,which is interlocking in the hardened cement paste,and the emergence and development of micro cracks is delayed.Therefore,the crack resistance of AASCC is worse than that of OPCC.3.For the concrete with the same replacement rate of pre-wetted ceramsite,AASCC has lower strength of hardened cement paste and bigger tensile stress that caused by autogenous shrinkage.So the tensile creep of AASCC is larger than that of OPCC.However,the growth rate decreases with the increase of curing age.The tensile creep of AASCC at the first day exceeds the 80%of the tensile creep at the age of 14d.4.For the concrete with the same types of cement,with the increase of the replacement rate of pre-wetted ceramsite,the water absorption stage become shorter,and the total water volume of desorption increases.Therefore,more water is provided for the hydration process of AASCC,the capillary pressure of AASCC is improved and the surface tension is reduced.Autogenous shrinkages of AASCC in 1 d and 14 d decrease with the increase of the replacement rate of pre-wetted ceramsite.The strength of interfacial transition zone is improved with the increase of replacement rate of pre-wetted ceramsite,crack resistance of AASCC becomes better and tensile creep decreases with the increase of replacement rate of pre-wetted ceramsite.