Durability Study Of High Ductility Recycled Micropowder Concrete (HDRPC)

The rapid development of urbanization has led to an increase in the amount of construction waste.In order to achieve green environmental protection and low-carbon sustainable development,construction solid waste can be recycled.At present,the application of construction waste is to prepare the construction waste into recycled coarse and fine aggregate for concrete,and a large amount of powder will be produced during the treatment of construction waste,which will cause serious environmental pollution.Therefore,this thesis takes the recycled powder as the raw material to prepare high ductility recycled powder concrete（HDRPC）.Recycled micro powder is grinded from waste concrete,which is different from ordinary concrete in mechanical properties and durability.Therefore,this thesis designs eight groups of mix proportions with water binder ratio（0.24,0.28,0.32）,recycled powder concrete content（0,25%,35%,45%）,single and compound fiber（1.9%BF,1.9%PVA,0.2%BF+1.7%PVA）as variables to study its mechanical properties and durability.In this thesis,the strength activity index of recycled powder concrete ash and fly ash were tested.Cement mortar was prepared by replacing cement with recycled powder concrete or fly ash with different quality.The compressive strength was measured to determine the strength activity index of the two materials.The results show that the strength activity index increases first and then decreases with the increase of the replacement rate of recycled powder concrete and fly ash;When the replacement rate of fly ash and recycled powder concrete is 30%,the strength activity index is higher than 70%,which meets the requirements of the specification.The effects of water binder ratio,single or double doped fiber and the substitution rate of recycled powder concrete on the mechanical properties of HDRPC were investigated.The results show that the increase of water binder ratio and the addition of recycled powder concrete have adverse effects on the mechanical properties of HDRPC;The effect of improving the mechanical properties of HDRPC with BF is better than that with PVA fiber;The flexural strength of recycled powder concrete mixed with fiber is higher than that of recycled micro powder concrete mixed with fiber,which reflects the good fiber mixing effect.The bending toughness of HDRPC was evaluated by ASTM C1018 standard.The results showed that the bending toughness index I_max increased first and then decreased with the increase of water binder ratio;The addition of recycled recycled powder concrete is beneficial to improve the bending toughness index I_max of HDRPC;The addition of basalt fiber is beneficial to improve the initial crack energy of HDRPC,and the addition of PVA fiber can improve the ductility of HDRPC.Combined with the characteristics of the two fibers,hybrid fiber can be used to improve the bending toughness of HDRPC.Study the impact of various variables on HDRPC durability.It is found that the water binder ratio has a great impact on the durability of HDRPC,and the increase of water binder ratio has an adverse impact on the impermeability,salt freezing resistance and carbonation resistance of HDRPC;The addition of recycled micro powder will reduce the frost resistance and carbonation resistance of HDRPC,but low content of recycled micro powder will help to improve the impermeability of HDRPC;The single addition of BF is better than that of PVA fiber in improving the impermeability and carbonation resistance of HDRPC,while the hybrid advantages of hybrid fiber recycled powder concrete in impermeability and carbonation resistance have not been reflected.The water seepage height and carbonation depth of hybrid system test block are between the two single addition systems;PVA fiber alone is better than BF alone in improving the frost resistance of HDRPC,and hybrid fiber is better than single fiber in improving the frost resistance of HDRPC.Fitting the initial crack bending load of HDRPC with the 28d carbonation depth,it was found that there was a negative correlation between them;According to the mechanical damage theory,the damage value of HDRPC under different freeze-thaw cycles is determined,and the freeze-thaw damage degradation model is established.According to the（GB/T50082-2009）,the maximum number of freeze-thaw cycles of each group is determined,and the freeze-thaw cycle life of HDRPC is predicted on this condition.