ITZ in Recycled Aggregate Concrete presentation
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This document discusses interfacial transition zones (ITZs) in recycled aggregate concrete (RAC). It explains that RAC contains two types of ITZs - old ITZ between original aggregate and old cement paste, and new ITZ between recycled coarse aggregate and new cement paste. The document investigates the mechanical properties of these ITZs using nanoindentation testing. The results show that a two-stage mixing approach leads to a stronger and denser new ITZ compared to normal mixing, by reducing porosity and calcium hydroxide crystals. In conclusion, a two-stage mixing approach improves the microstructure and mechanical properties of new ITZs in RAC.
ITZ in Recycled Aggregate Concrete presentation
- 1. INTERFICIAL TRANSITION ZONES IN RECYCLED AGGREATE CONCRETE Using different mixing approaches and techniques
- 2. INTRODUCTION RAC or Recycled Aggregate Concrete is one of the most important use of waste concrete and is being used throughout the world . It is manufactured by using previously prepared concrete as aggregate with fresh cement matrix. It is sustainable and environment friendly as it recycles the concrete which would have been discarded as waste and had to be dumped off. It reduces the construction cost and when used properly gives similar performance as virgin aggregate concrete.
- 3. INTRODUCTION (cont.) Some advantages of using RAC are: Keeping concrete debris out of landfills saves landfill space. Using recycled material as gravel reduces the need for gravel mining. Recycling one ton of cement could save 1,360 gallons (5.14 m3) water, 900 kg of CO2. Using recycled concrete as the base material for roadways reduces the pollution involved in trucking material.
- 4. INTRODUCTION(cont.) The strength of RAC greatly depends on the micro structural interfaces present in it. There are two interfaces in RAC: 1. Old interfacialTransition Zone(Old ITZ):It is the zone formed between natural aggregate and old cement matrix. 2. New InterfacialTransition Zone(New ITZ):It is the zone formed between Recycled Coarse Aggregate(RCA) and new cement matrix. The study of interfaces is important as they are a prime source of internal micro cracks which greatly affect the strength and durability of concrete.
- 5. SOME TERMS AND DEFENITIONS NORMAL MIXING APPROACH(NMA) It is traditional mixing approach in which all the ingredients are mixed all together. It has been used for a long time and is effective for the production of virgin aggregate concrete. TWO STAGE MIXINGAPPROACH(TSMA) In this method, the RCA is firstly mixed with cement paste, which is followed by adding sand to the mixture, thus making a two stage mixing. The two-stage mixing can help to form a layer of cement slurry on the surface of RCA to fill up the initial damage such as micro-cracks and voids, leading to an improved interfacial zone at the pre-mix stage.
- 6. TSMA VS. NMA 0 10 20 30 40 50 60 7 Days 28 Days 90 Days NAC(NMA) RAC(NMA) RAC(TSMA)
- 7. SCANNING ELECTRON MICROSCOPY(SEM) It is a type of microscopy which uses electron produce an detailed image of any 3-D body. It uses an electron gun to produce a beam of electrons which hit the surface and then get to the detectors which forms a detailed, magnified, digital image of the specimen. With SEM technique, one can identify the phase distribution, such as C–S–H or CH, in concrete.
- 8. ATOMIC FORCE MICROSCOPY(AFM) It is a very high-resolution type of scanning probe microscopy, with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit. It is another increasingly popular tool for studying cement-based materials which is often used to assess concrete surface roughness.
- 9. NANOINDENTATION METHOD Nanoindentation is a variety of indentation hardness tests applied to small volumes. In nanoindentation small loads and tip sizes are used, so the indentation area may only be a few square micrometres or even nanometres.This presents problems in determining the hardness, as the contact area is not easily found. Instead, an indenter with a geometry known to high precision (Berkovich tip) is employed. This helps to find out theYoung’s modulus for points very near to each other thus giving an accurate picture about the variation of strength of material .
- 10. For the present study the indendation scheme followed is as shown in figure: For Old ITZ: For New ITZ:
- 11. RESEARCH SCOPE AND ADVANTAGES This research mainly focuses on studying two properties of ITZs: the elastic modulus and the thickness. Knowing the elastic modulus distribution within ITZs can help to improve our knowledge of the failure mechanism and cracking progresses in RAC. And knowing the thickness can help to develop methodologies to improve the quality of RAC by minimizing the ITZ volume. This study presents two gaps in the current understanding of RAC behavior by: 1. Obtaining a more accurate understanding of local mechanical properties on nanoscales for ITZs in RAC 2. Revealing the differences in nanoscale mechanical properties between old and new ITZs in RAC
- 12. CONCLUSIONS For the old ITZ, the indentation modulus increases as the distance from original aggregate surface increases. For the new ITZ with TSMA, there is no obvious trend indicating that the indentation modulus increases or decreases with the increasing distance from the old paste matrix surface, while in the new ITZ with NMA the modulus distribution appears to decrease significantly from the old paste matrix surface. It indicates that theTSMA can effectively reduce the size and effect of water layers and CH crystals formed around the RCA. Therefore, the amount of porosity is reduced and the enhanced hydration provides a source for production of C–S–H. It is observed that the volume fractions of porosity and CH phases in the new ITZ withTSMA are relatively lower than those of the old ITZ and new ITZ with NMA, which can explain the improvement in RAC compressive strength.
- 13. CONCLUSIONS (cont.) For the new ITZ withTSMA, the cement slurry permeates into the porous old paste matrix and fills up the voids and cracks, which improve the microstructure of the new ITZ.However, for the new ITZ with NMA, there is a significantly loose microstructure that contains a large volume of porosity and CH crystals. It is interesting to note that there is a stronger and denser zone existing in the vicinity of the new ITZ in RAC.The EDX analysis exhibits that the dense zone with high indentation modulus is most likely the calcium carbonate crystals which covers the surface of RCA
- 15. GRID NANOINDENTATION Old ITZ New ITZ
- 16. 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Natural aggregate Old ITZ Old Paste matrix Old Paste matrix New ITZ New Paste matrix Contour map of modulus in GPa (old ITZ) Contour map of modulus in GPa (new ITZ) X (um) X (um) Y(um) Y(um)
- 17. 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Contour map of hardness in GPa (old ITZ) Contour map of hardness in GPa (new ITZ) X (um) X (um) Y(um) Y(um) Natural aggregate Old ITZ Old Paste matrix Old Paste matrix New ITZ New Paste matrix
- 18. Perpendicular to old ITZ, at old paste matrix side Perpendicular to new ITZ, at new paste matrix side SEM images of old ITZ and new ITZ in RAC at 90 days.