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knowledge

1. High Performance concrete

2. Introduction Several advancements have been made in concrete design, leading to improved: performance durability sustainability

3. Concrete technology developments Fig 1: development of technology in various phases

4. High performance concrete With the advent of super plasticizers, reduction in water and increase in workability made concretes with phenomenal improvement in strengths, proving it plausible to manufacture concrete of M60 and above. Mehta and Aïtcin used the term HPC for concrete mixtures possessing high workability, high durability, and high ultimate strength. T o achieve high-strength concrete it is imperative to improve the ITZ. A low w/c ratio and use of SPs and fine supplementary cementitious materials (SCMs) were reported to be effective ways to reduce the ITZ width and porosity.

5. Advent of superplasticizers The development of new chemical admixtures has revolutionized concrete design. Until the 1970s, prior to the development of superplasticizers (SPs), concretes with strengths greater than 40 MPa were considered high strength concretes (HSC). Water reducers are classified broadly into two categories: (1) normal and (2) high range. T he normal water reducers are also called plasticizers , while the high-range water reducers are called superplasticizers . Lignosulfonates are generally regarded as 1st-generation water reducers, while the sulfonated naphthalene formaldehyde condensates are 2nd-generation water reducers and polycarboxylic ether is a 3rd-generation water reducer.

6. Fig 2: Mechanism of water reducing admixture Steric effect of PCE Polycarboxylic ether-based water reducers are polymers with backbone and side chains. The backbone gets adsorbed on the surface of the cement grains, and the side chains cause dispersion of cement grains by steric hindrance .

7. Supplementary Cementitious Materials S CMs are those inputs which have moderate or no heat of hydration but do render hydrated mineralogy akin to that of OPC by availing lime released out of OPC-hydration. Most of the SCMs such as fly ash, Ground Granulated Blast furnace Slag (GGBS), silica fume, rice husk ash (RHA) are industrial byproducts, except metakaolin that is processed out of natural mineral. By addition of CCM not only lime and heat during OPC-hydration is reduced, but the surplus lime, which otherwise would have leached out, is converted to strength rendering hydrated mineralogy, contributing for pore refinement and micro-densification of concrete. The result is durability enhancement.

8. Fig 3 : Reaction of silica in pozzolana

9. Fig 10: Microstructural images of high performance concrete

10. Binary blending of SCMs The specific proportions of each SCM in the binary blend can vary depending on the desired concrete properties and local conditions. It is important to consider factors such as chemical interactions, particle size distribution, pozzolanic activity, and cementitious efficiency when designing binary blends of SCMs . Binary blends can capitalize on the individual benefits of the SCMs, such as improved workability, strength, durability, and reduced carbon footprint.

11. Fig 7: binary blend of FA in mix

12. Ternary blending Enhanced performance: Ternary blends can offer a wider range of performance benefits by incorporating two different SCMs, potentially providing superior strength, durability, workability, and sustainability characteristics. Synergistic effects: The combination of three SCMs can create synergistic effects, where the interaction between the materials leads to performance improvements beyond what each SCM can individually provide. Flexibility: Ternary blends allow for more flexibility in mix design, as the inclusion of an additional SCM can help compensate for limitations or deficiencies of the primary SCM. Increased complexity: Ternary blends introduce additional complexity to the mix design process, requiring careful consideration of the proportions and interactions between the three SCMs.

13. Fig 8: ternary blended concrete mixes T ernary blended concrete mixes made with micro-silica and fly ash has amended well-developed dense and impermeable microstructure .

14. Awareness on transition zone in modern concrete In concrete, surplus water laden with dissolved lime tends to settle around coarse aggregate due to differential densities. This zone between coarse aggregate and cement paste is called as transition zone which is the weak zone out of total concrete matrix and, one of the main causes for effecting durability. Higher the size of coarse aggregate greater is the transition (weak) zone. Due to this fact, aggregate size is confined to not more than 12 mm in HPC. Fig 9: Transition zone

15. References Aitkin, P. C., (2004). High Performance Concrete , 3 rd ed., E & FN Spon. Khitab , A., and Arshad, M.T. (2021). “Synergistic use of fly ash and silica fume to produce high strength self compacting cementitious composites.” Crystals , 11, 915-930. Liu, C., He, X., Deng, X., Wu, Y., Zheng, Z., Liu, J., and Hui, D. (2020). “Application of nanomaterials in ultra-high performance concrete: A review .” De Gruyter. , 9, 1427–1444. Zhdanok , S.A., Potapov, V.V., Polonina , E.N., and Leonovich S.N. (2016). “Modification of cement concrete by admixtures containing nanosized materials.” Journal of Engineering Physics and Thermophysics ., 93, 648-652. Kong, D., Du, X., Wei, S., Zhang, H., and Shah, S.P. (2017). “Influence of nano-silica agglomeration on microstructure and properties of the hardened cement-based materials .” Construction and building materials ., 37, 707-715 . Khaloo , A., Mobini , M.H., and Hosseini, P. (2016). “Influence of Different types of nano-silica particles on properties of high performance concrete.” Construction and building materials ., 113, 188-201. Shah, S.P., Hou, P., Gdoutus , M.S. (2015). “Nano-modification of cementitious material: toward a stronger and durable concrete.” Journal of Sustainable Cement- based Materials., 5, 1-22. Sohail, M.G., Kahraman , R., Nuaimi, N. (2021). “ Durability characteristics of high and ultra-high performance concretes .” Journal of Building Engineering , 33, 915-930. Wang, B., Jain, A., Soahil , M.G. (2017). “ Advancements in Concrete Mix Designs .” Journal of Materials in Civil Engineering, ASCE , 30, 3101-3120. Abhilash, P.P., Nayak, D.K., Sangoju , B., and Kumar, R. (2021). “ Effect of nano silica; a review .” Construction and Building Materials , 278, 1-19.