Research On Processes And Properties Of Alkali-Activated Cement Based Ultra-High Performance Concrete

Ultra-High Performance concrete(UHPC)is a cement-based composite with excellent mechanical properties.Domestic and foreign scholars have carried out a wide range of researches on UHPC,and made substantial progresses in engineering applications.But there are also many deficiencies of current UHPC,such as the high hydration heat,high energy consumption,and high costs.Alkali-activated cement is a low-carbon sustainable cementitious materials.If the two materials can be combined together to produce alkali-activated cement based UHPC,it can not only reduce the cost but also have a very positive impact on our environment.The process development of alkali-activated cement based UHPCs and their mechanical properties,microscopic structure,engineering applications were investigated in this thesis,the main issues and conclusions of the research are presented as follows:1.The effects of mix proportions and curing systems on the mechanical properties of alkali-activated UHPC were studied.And compressive strength of alkali-activated cement based UHPC with tailored mix compositions and steam curing exceeds 160MPa and flexural strength exceeds 25MPa.The material cost is 8.6%lower than the ordinary UHPC of the same mechanical index.The energy consumption,natural resource consumption and CO2 emissions are only 1/10,1/9 and 1/20 of ordinary UHPC,there is also no pollutants emissions such as waste residue,SO2 and NOx,and its environmental performance is superior.2.The microscopic structure is analyzed by FESEM,EDS,XRD,and pore structure analyzer.Such microscopic investigations were useful to understanding the mechanisms which were responsible for the superior mechanical properties of alkali-activated cement based UHPC.Test results show that,the mechanical properties of alkali-activated cement based UHPC with steam curing are superior to that of alkali-activated cement based UHPC with standard curing.Compared with standard curing,the hydration products of alkali-activated cement based UHPC with steam curing have more preferred morphologies,high thermal stability,much compact,and smooth interface between hardened cement paste and aggregate.Meanwhile the alkali-activated cement based UHPC with steam curing has better pore structure distribution and more harmless pores.The mechanical properties of alkali-activated cement based UHPC with standard curing gradually improve with age.When standard curing age increases,the quantity of hydration products increases,and the microscopic structure becomes much compact.And with the contents of waterglass increasing,the quantity of hydration products increases,and the microscopic structure becomes much compact.3.The feasibility study of application of alkali-activated cement based UHPC in Bridge Engineering was carried out.Test results show that,the design structure meets the relevant specification requirements.In terms of economy,compared with C40 concrete,its structure can reduce the weight of 43.8%,the material costs increased by 44.3%.If consider the economic benefits of the savings of 60%of the construction period and the decrease in the quantity of lower structural engineering,its project cost will be close to C40 concrete.From the point of view of management,the alkali-activated cement based UHPC with excellent durability,and there is considerable feasibility of its saving in considerable maintenance,repair costs and environmental benefits.Finally,the construction technology of alkali-activated cement based UHPC bridge is given,which is different from ordinary concrete bridge.And it will lay the foundation for the engineering application of the new material.