Ceramic Tile Powder For Ultra-high Performance Concrete And It's Modification Mechanism

Sanitary and floor ceramic tile powders have been widely used as admixtures to produce ordinary and high performance concrete and assign better mechanical properties and permeability if an appropriate amount of ceramic tile powder added,However,there is little literature focused on the effects of ceramic tile powder on the performances of Ultra-high performance concrete?UHPC?.In order to fill the gap in the existing literature,the aim of this thesis is to investigate the feasibility of the ceramic floor tile powder for Ultra-high performance concrete.UHPC is a cement-based materials and has excellent performances which has gaining widely attention from the whole society.Since the engineering application of UHPC still limit because of its high costs,complex technological processes,autogenous shrinkage and the lack of standards,so the focus of this thesis is on the performances of UHPC that cured under ambient environment.The effects of ceramic tile powder on the on the mechanical,chemical and microstructural properties under constant content of silica fume and water have been studied.The results are following:The development of the compressive strength of UHPC before 7d indicated that the ceramic tile powder shows no obvious reactivity before 7d.The development of the compressive strength between 7 to 28 d curing age shows that the reactivity of ceramic tile powder gaining its ground after 7d.The mix with 35% ceramic tile powder by weight has no obvious increase in compressive strength after 28 d,However,the compressive strength of mixes with 10% silica fume by weight still increasing,and with the increasing of the content of ceramic tile powder,the development of the early age compressive strength getting slower,the 60 d compressive strength also decreasing but in a small degree.These results mean that only a fraction of ceramic tile powder has pozzolanic reactivity and the part of the ceramic tile powder with pozzolanic reactivity was almost depleted before 28 d curing age.The influence of ceramic tile powder on the early age compressive strength development is stronger than that of late age when silica fume was added.Hydration degree test results showed that mixes with admixture have higher hydration degree at 7d and 28 d curing age than that of no admixture,which indicated that the SiO₂ in ceramic tile powder has pozzolanic reactivity and reacted with hydrated cement increasing the hydration degree of cement.Microstructure test with SEM showed that at 7d curing age the mix with 35% CTP by weight reduced the width of ITZ by about a half of trial test,Mixes with 10% silica fume and10% or 25% CTP has a ITZ width of about 10% of that of the trail test.The ITZ of all mixes closed when cured 28 days under ambient temperature.Part of CTP that has no pozzolanic reactivity filled in the gaps between big particles and part of CTP with pozzolanic reactivity reacted and the hydrates fill in the pores and ITZ resulting the width decrease of ITZ and density increase of hardened concrete.The CTP with pozzolanic reactivity was virtually depleted about at 28 d curing age.Ca/Si is a measurement of the relative rate between Ca and Si of C-S-H gel.The lower the rate,the higher the mechanical properties of C-S-H gel,and the higher the mechanical properties of C-S-H gel,the higher the compressive strength of hardened concretes.In this experiment,the Ca/Si of mixes with admixtures are lower than that of no admixtures,which implied that like silica fume,the CTP also participated in the second hydration and led to the decrease of Ca/Si.The Ca/Si of mixes with silica fume and CTP is the lowest among all tests,the silica fume and CTP may have “synergy effect”.The content of Ca?OH?₂ of hardened concrete with same W/C could be used to represent the second hydration degree of cement.The higher the degree of hydration,the more the consumed Ca?OH?₂,and the less the residual of Ca?OH?₂.In this experiment,the mixes with admixtures have lower content of residual of Ca?OH?₂ which mean higher degree of hydration.The CTP participated in the second hydration.However,the mixes with silica fume and CTP got higher degree of hydration because the residual of Ca?OH?₂ is the lowest among all of tests,which showed that 10% silica fume by weight has been completely depleted and the CTP with pozzolanic reactivity also take part in the second hydration process.