Influence of Recycled Concrete Fine Powder on Durability of Cement Mortar

In this paper,the durability of cement mortar prepared with a recycled-concrete fine powder(RFP)was examined;including the analysis of a variety of aspects,such as the carbonization,sulfate attack and chloride ion erosion resistance.The results indicate that the influence of RFP on these three aspects is different.The carbonization depth after 30 days and the chloride diffusion coefficient of mortar containing 10%RFP decreased by 13.3%and 28.19%.With a further increase in the RFP content,interconnected pores formed between the RFP particles,leading to an acceleration of the penetration rate of CO_(2)and Cl^(−).When the RFP content was less than 50%,the corrosion resistance coefficient of the compressive strength of the mortar was 0.84-1.05 after 90 days of sulfate attack.But the expansion and cracking of the mortar was effectively alleviated due to decrease of the gypsum production.Scanning electron microscope(SEM)analysis has confirmed that 10%RFP contributes to the formation of a dense microstructure in the cement mortar.

Study on the Durability of Recycled Powder Concrete against Sulfate Attack under Partial Immersion Condition

In order to make full use of waste recycled fine powder(RFP)in concrete and achieve the goal of carbon neutrality in the concrete industry,the durability of sulfate resistance is an important aspect of evaluating the performance of recycled powder concrete(RPC).Therefore,the durability of RPC under partial sulfate immersion was studied to provide theoretical guidance for understanding the erosion mechanism of RPC.The compressive strength,mass loss,and microstructure change patterns of RPC under partial immersion of 5%Na2SO4 and MgSO4 solutions were analyzed by cubic compressive strength,mass loss rate,SEM-EDS,and XRD.The results showed that the surface crystalline matter of concrete in Na2SO4 solution was mainly white powders,and that of concrete in MgSO4 solution was mainly transparent paste,both of which had a little spalling on the outer surface of the concrete.The compressive strength and mass loss rate of concrete with 20%RFP was relatively good,indicating that concrete with 20%RFP had better durability against sulfate.The compressive strength of the lower part of the concrete partially immersed in Na2SO4 solution was higher than that of the upper part and the strength of the lower part of RPC-2 was 3.11%higher than the upper part at 180 d;The pattern was reversed in the MgSO4 solution,where the strength of the lower part of RPC-2 was 19.74%lower than the upper part at 180 d.Microscopic analysis showed that the hydration products of RPC were mainly gypsum and ettringite,while the RPC produced more hydration products with the promotion of magnesium ion in the MgSO4 solution.The higher the replacement rate of RFP,the more frequent the gypsum-type failures in the concrete.