24/09/2020
"Look everywhere you can to cut a little bit from your expenses. It will all add up to a meaningful sum."
– Suze Orman
This week's topic is—
SELF-COMPACTING CONCRETE WITH RECYCLED AGGREGATE
One of the major challenges faced by civil engineering industry is to execute projects in harmony with the nature. In the recent years the demand for construction materials has grown so tremendously that the amount of construction and demolition waste is putting a huge pressure on the environment. This has encouraged the use of recycled coarse aggregate (RCA) in concrete which not only allows for more efficient life cycle of natural resources but also contributes to environmental protection leading to sustainable development.
Nowadays this RCA are used in the production of self-compacting concrete (SCC) in varying percentage replacements of natural coarse concrete from 0% to 100% with increment of 20% because the RCA reduces the quality of normal concrete (the RCAs are generally poorer quality than the normal coarse aggregates with greater water absorption and lower density), but on the other hand the price of SCC is higher than the normal concrete. So, if we use the RCA in making SCC the overall effective price reduces and “eco-friendly” developments could be reached.
1) For determining the fresh state properties of the SCC the Slump Flow, T-50 Slump Flow, V-Funnel, L Box tests were done and all the mixes showed horizontal slump flow without any bleeding at the periphery which indicates good deformability and segregation resistance.
2) For the investigation of the strength of the SCC the hardened concrete was kept for 3-7-28-90 days for compressive strength and 28 days for the tensile strength. In compressive strength it was found that the percentage of RCA and the strength of SCC are in inverse relation and it also revealed that the RCA mixes get high early strength. The tensile strength test also showed the same thing, the tensile strength of SCC decreases with the increment of the percentage of the RCA.
3) In the last the durability test (permeable voids and water absorption, resistance to acid attack, chloride pe*******on depth, alkalinity test) was done for the concrete. In the permeable voids and water absorption test it was found that the initial water absorption of RCA was 4.3 times higher than that of NCA and the maximum increase in permeable voids with increasing RCA was just 1.57 times that of mix with no RCA. This indicates the good and dense microstructure of concrete. In the resistance to acidity it was found that mix having high RCA content due to adhered mortar the cement content increases which subsequently results in increased alkalinity and reduced resistance to acids. For the chloride pe*******on depth, the concrete immersed in 5% Nacl solution in 90 days. The result indicates that chloride pe*******on depths of SSC increases as the RCA increases. The increase in porosity and capillary pores in recycled aggregate causing chloride ions to pe*****te easier into concrete. The results of alkalinity test shows that with increase in RCA in SCC the pH of cement increases which helps to form a passivating layer around reinforcing steel, protects it from possible corrosion and increases the service life of the concrete structures.
So, it can be concluded that there is a significant potential for growth of RCA as an appropriate and green solution for sustainable development in construction industry and moreover it is noticed that the mix accelerates the hydration process.
© ASHESH PAL
For more information regarding this, go through the reference link: https://www.hindawi.com/journals/amse/2016/2761294/
