Research On Residual Properties After Exposure To Elevated Temperatures Of Sustainable Concrete Considering Wet Packing Density Theory

The 20^th National Congress of the Communist Party of China proposed the idea about respect for nature,conforming to nature and protection for nature,which emphasized the eco-friendly development.Concrete is a kind of manmade material whose main ingredients are gravel,sand,cement,water and chemical additives with the second-most consumption in the world nowadays.It could be noticed that the huge production of concrete comes with the huge energy consumption that the over-exploitation of raw materials of concrete would destroy the environment severely and this situation conflicts with the idea of eco-friendly economic development in China.However,the demand of engineering construction in China becomes more and more due to the purpose of“Build a moderately prosperous society in all respects and realize the First Centenary Plan”for China,a developing country.Therefore,in order to satisfy the huge demand of engineering construction and promote the idea of eco-friendly development simultaneously,to develop new eco-friendly construction materials and to apply them to the actual engineering construction is significant.Sustainable concrete is a new-type concrete whose natural raw materials are replaced by industrial wastes with outstanding properties such as workability,mechanical property,fire resistance,etc.Firstly,the Ordinary Portland Cement（OPC）can be replaced by fillers including Ground Granulated Blast Furnace Slag（GGBFS）,Fly Ash（FA）,Silica Fume（SF）,etc.Secondly,the natural aggregates can be replaced by granular wastes including Steel Slag（SS）,Iron Slag（IS）,etc.Along these materials,as a by-product in the steel making process,steel slag is considered as a potentially new-type eco-friendly construction material by researchers.As reported,China is always the country with the most steel production in the world but the stacking of raw steel in China is high and the utilization rate is low.In addition,fire is one of the most common disasters which would destroy the concrete-built construction seriously and irreversibly and thus,it is important to develop a sustainable concrete with excellent residual properties after exposure to elevated temperatures,so called post-fire behavior.To this end,this study uses fillers and steel slag coarse aggregate to replace OPC and granite gravel respectively and/or together to produce sustainable concrete and then investigates its post-fire behavior through a series of experiments and analyses.To be specific,this study firstly uses GGBFS,FA and SF to replace OPC partially,respectively and then finds out the filler with the best optimizing effect on the post-fire behavior of concrete after comparison.After that,a new-type sustainable concrete is to be produced,which contains the best filler mentioned above and steel slag coarse aggregate.This new-type steel slag concrete containing filler with superior post-fire behavior is to be produced in this study,after comprehending how fillers and steel slag coarse aggregate influence the post-fire behavior of concrete.Based on this,18 concrete mixes totally were designed and a series of experiments were conducted:wet packing density test,flowability test,compressive test,heating test,XRD analysis,mass loss calculation and surface change comparison,among which the experiments except for the first two ones were conducted after 28-day curing.The results showed that:（1）GGBFS was the filler enhancing post-fire behavior of concrete most among GGBFS,FA and SF:After replacing OPC with GGBFS partially,the compressive strength of concrete at ambient temperature was reduced slightly but the flowability and post-fire relative strength were improved effectively;（2）The compressive strength of concrete at ambient temperature was enhanced after adding steel slag while the flowability and post-fire relative strength decreased;（3）The compressive of steel slag concrete with GGBFS maintained a excellent level while the flowability and post-fire relative strength were enhanced.In conclusion,under the guidance of wet packing density theory,sustainable concrete containing steel slag and GGBFS with superior wet packing density,flowability,compressive strength at ambient temperature and post-fire relative strength was produced,after the post-fire behavior optimizing experiments.