Research On Dynamic Mechanical Properties Of Green Cement-based Composites And Its Reinforcing Mechanism

With the rapid development of China’s economy,and the acceleration of industrialization and urbanization,the extensive use of cement-based materials has resulted in the reduction of natural sand and gravel as well as environmental damage（building waste,CO₂ emissions）.Therefore,the investigation of green ecological cement-based composite materials is one of the important directions for the sustainable development of the construction industry in the future.In the process of using green cement-based composites,the dynamic mechanical properties of the structure is a significant indicator,which is characterized by loss factor（damping）and storage modulus（deformation ability）.Improving the dynamic mechanical properties of the materials can not only reduce the vibration caused by dynamic loads,noise,etc.,but also reduce the damage to the structure caused by natural disasters.However,there are relatively few studies on its dynamic mechanical properties.For example,the study of the dynamic mechanical properties of alkali-activated materials is basically in a blank state.Therefore,two typical green composite materials,cement-based recycled composites and alkali-activated materials were investigated in this study and the dynamic mechanical properties were studied.The specific research content is as follows:（1）The effects of different dosage（0.05 wt%,0.10 wt%,0.20 wt%）graphene oxide（GO）on the macroscopic properties of cement-based recycled composites were studied.At the same time,the microscopic mechanism was analyzed by XRD,SEM and MIP techniques,and the enhancement mechanism of its dynamic mechanical properties was discussed.1.The results show that GO will reduce the fluidity of the cement-based recycled composites,but will increase its static mechanical properties（compressive and flexural strength）to a certain extent.2.The loss factor of the paste increases initially and then decreases with GO incorporation（0.1wt%turns occurs）,and the loss factor of the mortar increases with increasing GO content.The storage modulus of the paste and mortar increases with the increase of GO.3.Physical phase and electron microscope analysis results show that GO does not change the type of hydration product,but it promotes the formation of hydration products,improving the aggregate interface in the recycled mortar and its internal porosity structure.4.The dynamic mechanical properties of GO-cement-based recycled composites are related to the internal contact area,porosity,and inhomogeneous stress distribution within the cement matrix,but little change with temperature.（2）The effects of different recycled rubber（RCR）replacement rates（0%,20 vol.%,40 vol.%,60 vol.%）on the macroscopic properties of alkali-activated material（AASM）were investigated.Simultaneously,the microscopic mechanism of AASM was analyzed by XRD,SEM and MIP.1.The results show that RCR reduces AASM fluidity and static mechanical properties,and when the vibration frequency is 0.5Hz,the corresponding storage modulus and loss factor of AASM are the maximum.2.In addition,RCR effectively improves the AASM loss factor.When the RCR replacement rate exceeds 40 vol.%,the AASM’s storage modulus is increases largely.3.Microscopic tests show that the AASM has many organic-inorganic interfaces and the interfaces are not quite dense,resulting in the storage modulus of AASM decreases.Because RCR is an elastic material,it can significantly enhance the AASM’s loss factor.（3）This project takes the life cycle assessment（LCA）as the theoretical basis,and calculates the energy consumption（EE）,CO₂ emissions（ECO₂）and cost（Cost）of green cement-based composite materials,and finally calculates ecological and economic evaluation.1.The results show that at the same strength,recycled mortar using GO can reduce CO₂ emissions by 6.7%and consume less energy compared to ordinary mortar,but its cost increases（65.7%）.Although the GO cost is high,the amount of the unit volume is small.As the industry develops,the production cost will decrease,and the final unit cost will decrease.2.ECO₂ is negative when the replacement rate of RCR is 40 vol.%.Compared with the control mortar,when the replacement rate of RCR was 60 vol.%,the EE only increased by 0.11%and the cost can be negligible.Therefore,from the environmental point of view,GO-cement-based recycled composites and RCR-alkali-activated composites are all kinds of green cement-based composites.