A Study On Hydration Recovery And Properties Of The Super-retarded Cement-based Materials With Sucrose

At present,a method had used by washing the waste plastic concrete from the commercial concrete mixing plant then reusing sand and gravel aggregate and wash water in our country.However,in foreign countries,it had achieved the reuse of cement unhydrated by incorporating two admixtures,one defined as hydration stopping admixture,while the second was hydration recovery additive.In order to reduce the waste caused by timely unused,we had developed a kind of mortar opening time regulator,which could effectively control the working time of wet-mixed mortar.This study tried using sucrose as hydration stopping admixture and mortar opening time regulator,and developed a kind of hydration recovery additive(HRA).Effects of HRA on hydration recovery and properties of the super-retarded cement-based material with sucrose were mainly studied.The results indicated that:(1)The addition of sucrose was help to improve the fluidity of fresh cement paste.With the increase of dosage,the improving effect was better.Adding HRA could also ameliorate the fluidity of cement,and with the adding of the amount of HRA,the fluidity enhanced.However,compared with sucrose,it had little improvement.(2)Incorporating sucrose showed an evident retarding effect on the fresh cement hydration,and the dosage was higher,the retarding effect was more obvious.While adding sucrose,the exothermic rate of cement paste decreased a little bit and the resistivity development was lagged.When the dosage was 0.20%,the exothermic peak of cement hydration appeared at as late as 64.4 hrs.(3)Both simultaneous and delayed incorporation of HRA could effectively alleviate the serious retarding effect of sucrose and the acceleration stage of cement hydration was advanced significantly.The starting time of the acceleration stage was shifted to 20 hrs in case that 2.0% HRA was added during mixing.If the addition was delayed to 24 hrs,the acceleration started in 2 hrs after incorporating HRA.(4)The flexural strength of the hardened cement-based materials was significantly improved by incorporating sucrose,but the compressive strength had a little impact.With increasing the dosage,the flexural strength was enhanced then decreased.The enhancement was most obvious when the dosage was 0.15%.The reason might be the growth of ettringite rapidly while adding sucrose in the cement-based material.(5)Both the flexural strength and compressive strength of the super-retarded cement-based material with sucrose showed a slight decrease if the HRA was incorporated.This was probably caused by the slight increase of the water cement ratio while incorporating the gel-like HRA in the cement-based material.(6)About reusing cement unhydrated in wash water,the dosage of wash water,placing time and sucrose content showed different effects on the mechanical properties of fresh cement mortar.It found that the dosage of wash water was the most important factor,but placing time caused a minimal impact on the strength of the fresh cement-based materials after 28 days.