The need of present time is stronger buildings, industrial or common utility buildings, such as Malls, Railway stations, hospitals, offices, bridges etc. For this, there is need of long durable, tough and stable concrete, which could stand under normal and seismic conditions. Tough railway bridges are required for bullet trains to pass without any damage. Railway tunnels, sea-links, coastal roads, bridges and multistorey buildings, are the need of the hour. The question comes, is the normal cement called OPC is sufficient to take care of such requirements or better combination of cements and sand mixtures is required?IntroductionA good stable building structure can be made with a good quality of cement+sand+water system. Its quality can be enhanced by keeping the density of admixture higher (varies from 30 in normal buildings to bridges etc to 80). Further enhancement in the properties of various cements admixtures is made by adding several additives which give additional strength, waterproofing, flexibility etc. These are called construction chemicals.However, if the strength of the concrete structure is needed to be enhanced to 2000MPa and its durability to 100 years plus, then there are special kinds of concrete structures, called Ultra-High-Performance Concrete (UHPC). It offers huge advantages like extreme strength (4-10 times compared to the standard concrete), superior durability, very low permeability to water/chemicals, high ductility (acts like metal), abrasion resistance, and potential for thinner, lighter structures, leading to longer service life, reduced maintenance, and better sustainability in bridges, buildings, and infrastructure [1].Let us first begin with two basic kinds of cements OPC and PPC. OPC is best for projects needing high early strength and fast setting (foundations, columns, quick builds). PPC is superior for long-term durability, moisture resistance, and better finishing (plastering, coastal areas, general housing), offering cost-effectiveness and lower heat during hydration, making it ideal for most modern residential buildings,Portland pozzolana cement (PPC) is a mixed hydraulic cementitious material made by grinding silicate cement clinker with pozzolanic materials: fly ash, volcanic ash or calcined clay and gypsum. The amount of pozzolanic mixed materials is greater than 20% and less than 40% by mass. Ordinary Portland Cement (OPC) is the world's most common hydraulic cement, a fine grey powder made from limestone, clay, and gypsum, forming the base for concrete, mortar, and plaster, known for its strength, durability, and versatility in general construction, from homes to massive infrastructure, classified by strength (33, 43, 53 grades) based on its compressive strength after 28 days. PPC achieves an initial strength equivalent to OPC 33 but gives better long term strength. Now when we talk about the composition of UHPC, it contains random reinforcing steel fibers of more than 2% (by volume), whose tensile strength exceeds 2000 MPa, and ranges from 10 mm to 20 mm in length and 0.1 mm to 0.25 mm in diameter. UHPC is broadly defined as a cementitious composite material that has enhanced strength, durability, and free from environmental degradation. Table 1 gives the composition of a typical UHPC [2]Some UHPC mix designs can even achieve 50,000 psi, matching that of steel. It also has strong resistance to environmental degradation. Also, it is impervious to water, and strong enough to have negligible surface damage. It is completely waterproof and is even highly resistant to gases due to its fine pore structure. It has a very long service life. Its 100+ year lifespan means that structures made with UHPC require minimal maintenance and fewer repairs over time. Compared to conventional concrete, UHPC is also more resistant to environmental factors.Applications of UHPCUHPC mix designs exhibit three important properties of concrete mixes: the flowing and passing abilities of self-consolidating concrete (SCC), second, the superior strength and long-term performance of high-performance concrete (HPC), and third, the increased ductility and post-cracking strength of fiber reinforced concrete (FRC). Such concrete mix results in a self-consolidating ultra-high-performance fiber-reinforced concrete (UHPFRC), presented to the construction industry as UHPC [2]To-date, UHPC mixes are used in the fabrication of multiple bridge projects within the US.  It includes the fabrication of full UHPC bridges, construction of shear connectors and panel joints, pier jacketing. and deck overlays. Approximately 200 bridge construction projects used UHPC admixtures from 2006 to 2018 in US.   Next application is Bridge Beam Repair due to the improved fatigue resistance of UHPC and UHPC shear connectors. UHPC proprietary mixes are used to repair the corroded steel girders ends negatively impacted by expansion joints located above the girders due to water leakage. UHPC treatment of steel girder ends are successfully replacing the conventional treatment methods of corroded steel elements.Another application in bridges is Bridge deck overlays where UHPC is currently used in pouring bridge deck overlays to improve the conditions of bridge decks. There is a high demand for effective and durable rehabilitation of bridge decks being deteriorated under the increased vehicle number, increased vehicle loading, freeze-thaw cycles, deck cracking, delamination of concrete cover, and corrosion of reinforcing steel. Traditionally, normal concrete overlays, latex-modified concrete, and special asphalt mixes with polymer-based materials were used which are now replaced by UHPC overlays. They have advantages due to the possibility of using slim 2.5–5.0 cm thick overlays, with superior bond to existing concrete. The very low permeability and superior strength characteristics of UHPC provide sufficient strengthening required, in addition to protection from ingress of contaminators as chemical attacks and de-icing salts [2]. Another important application of UHPC is in Bridge piles which supports bridge load. Traditionally, piles are fabricated using steel sections, precast or cast-in-place concrete where many failures were noted such as limited capacity, pile failure during installation, and deterioration of piles due to environmental attacks The use of UHPC mixes in fabricating piles has substantially improved the piles capacity and long-term performance. UHPC mixes, with high strength, are easily driven with minimal to no damage. The very low permeability of UHPC mixes results in improved resistance to environmental attacks.  Accelerated Bridge Construction (ABC) Applications: using Prefabricated Bridge Elements and Systems (PBES) technique where UHPC mixes are used in pouring different bridge elements to be used in expedited bridge construction. The use of UHPC in ABC technique enabled bridge design engineer to design innovative bridge sections with geometrical dimensions that results in significantUHPC in IndiaUHPC is a new class of concrete that has been developed in recent decades for its exceptional properties of strength and durability, first developed in 1990 in France. It is now manufactured in India by several companies. Dramix® steel fibers [3] provide a homogeneous reinforcing network across the entire concrete cross-section. This leads to increased post-crack strength and ductility throughout the entire floor. These are also known as Steel fiber reinforced concrete (SFRC) uses steel fibers for reinforcement. The fibers are added to the concrete at the ready-mix plant or on the jobsite. The concrete is poured with the reinforcement inside. In contrast to traditional reinforcement (rebar/mesh), steel fibers are relatively short (Fig.1), discontinuous elements that are evenly distributed throughout the concrete floor. As such, the fibers become part of the concrete matrix, turning it into a strong, ductile composite material.Fig. 1 Showing traditional wire/rod reinforcement compared to Steel fiber reinforcement (3). UHPC India Pvt. Ltd. is an other company who is making UHPC concrete since 2020. The ingredients of the concrete are shown in Fig. 2 with steel fiber details: Steel Fibers: 2% by volume and size 0.2 mm (d) x 13 mm (L). It could achieve a tensile strength ~ 2800 MPaFig. 2 Showing UHPC composition and its mechanical properties The company claims an elastic modulus of concrete as 50,000 MPa with a maintenance free durability of 100 years and there is 50% reduction in the weight of structural elements and the concrete is ultra high wear and impact resistance with cost just 10-15 times that of conventional concrete. They have already done several structure in Pan-India, Mumbai- GCC Namaste building, a Bungalow Project in Tirupati, Andhra Pradesh, and is being planned to be used in several upcoming bridges (2). Other projects done in India using UHPC concrete are : Palkhi Marg (NH-965), Maharashtra: Features India's first 100-meter span UHPFRC bridge, allowing for longer spans with fewer piers, as seen in the Chandani Chowk and Mumbai Pune Expressway missing link. Sole River Bridge, Latur, Maharashtra: The first UHPC bridge in India, significantly reducing substructure work due to lighter, longer-span girders. Samruddhi Mahamarg (Mumbai-Nagpur Expressway): UHPC girders are being used for various bridges, notes Morth and Indian Infrastructure Magazine. Rob (Railway Over Bridge) Strengthening: UHPC is used for strengthening existing ROBs, such as one near Saphale for the Dedicated Freight Corridor. Conclusion Thus, the future of long lasting, tough and stable buildings is Ultra-High-Performance Concrete mix which is picking up fast in world as well as in several projects in India. Presence of steel in fibers help to change the durability and its flexibility which results in a concrete structure much superior than the conventional OPC mix. References: [1] https://www.uhpcsolutions.com/blog/what-is-ultra-high-performing-concrete [2] A.K. Akhnoukh and C. Buckhalter, Construction Materials 15 (2021) [3] https://construction.bekaert.com [4] https://uhpcindia.com About the author: Prof. A. S. Khanna, former IIT Bombay professor with 27 years of service, has guided 27 PhDs and authored over 350 papers. Chairman of SSPC India, he also leads a NABL-accredited coatings laboratory and is a fellow of leading global institutions.