Mechanical And Self-healing Properties Of Thermally Damaged Cement Paste Modified By Calcium Carbonate Whisker And Fly Ash

Nowadays,sustainability and multifunction of cementitious composites are two new demands of developing infrastructures.In this paper,calcium carbonate whisker?CW?and fly ash?FA?are incorporated to partially replace cement to manufacture sustainable cement paste with high temperature resistance and self-healing abilities based on mix designs and experimental optimization.The mechanical and physicochemical changes and microstructure of this sustainable cement paste are systematically investigated and studied.The results can be found as follows:?1?The roles of CW were revealed based on analysis of microstructure and physico-mechanical changes of cement paste induced by high temperature.CW demonstrates both micro-fiber and filler effects.Below 600°C,its micro-fiber effect can restrain the cracking induced by elevated temperatures,and further reduce the deterioration of strengths.In addition,it's favorable to facilitate the generation and development of calcium silicate hydrate?C-S-H?by acting as a nucleation site when transformed to calcite CW at around400°C.?2?The effects of FA on microstructure and physico-mechanical properties of CW modified cement paste?CWMCP?before and after high temperature were investigated.Below400°C,the pozzolanic effect of FA can be activated by hydrothermal condition induced by combined effect of temperature and water vapor.Thus,more calcium hydroxide?Ca?OH?2?can be consumed and additional C-S-H can be generated to improve the strengths.Above 800°C,FA involves in sintering process and accelerate the formation of ceramic phases,and further to reduce the deterioration on microstructure and residual strengths.?3?The effects of water re-curing on the microstructure and physico-mechanical properties of thermally damaged cement paste were studied.The mechanical and physicochemical deterioration can be healed by post-fire water re-curing.FA is favorable to facilitate the self-healing process of thermally damaged cement paste through its pozzolanic effect.?4?The microstructure and compressive strength changes of FA and CW modified cement paste?FA-CWMCP?at ambient temperature,after high temperature exposure and after re-curing were analyzed.FA and CW have combined effect both at heating and self-healing processes,which means FA can supply aluminates for hydration of CW,and CW can supply Ca²⁺solution for hydration of FA at the same time.Therefore,FA-CWMCP has high temperature resistance and self-healing abilities as well as sustainability.