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TECHNICAL PAPER

creep, shrinkage, fracture energy, micro cracking patterns, and risk of cracking, and enhanced reliability in performance based
rate-dependent behavior [28-33] . Experimental work was supported specifications. By embedding this coefficient into analytical
by advanced characterization, including SEM-EDS, TGA-DTG, and design frameworks, researchers and practitioners can more
MIP, etc. NCCBM’s research on HPC and UHPC focused on effectively bridge the gap between experimental observations
mechanical behavior, creep, shrinkage, and durability under and predictive models, addressing key uncertainties in long term
Indian conditions. Experimental programs included compressive performance of UHPC components.
strengths from 60 to 150 MPa, with creep and shrinkage A major advancement is the adoption of a hybrid creep
monitoring extending up to 365 days. UHPC mixes incorporating modelling framework, combining creep coefficients for
steel fibres achieved tensile strengths exceeding 8 MPa and conventional structures in line with fib Model Code 2010
exhibited post-cracking ductility with fracture energy values practice for precision-based and long-life design. The model
more than five times that of conventional concrete. Durability expresses creep as φ(t, t₀) = φ₀ · β(t, t₀), where φ₀ accounts for
indicators such as water permeability and chloride diffusion were humidity, member size, concrete strength and age at loading,
an order of magnitude lower than OPC concretes. Mechanistic while β(t, t₀) governs time evolution, improving the accuracy
insights into creep of blended cements informed revisions to of long‑term deflection and prestress loss predictions for
creep models included in IS: 456 (under revision) [29-30] . IS: 456 advanced concrete systems. Research work of NCCBM on fire
(under revision) introduces HPC defined through engineered behaviour of HPC shows that elevated temperatures significantly
characteristics such as reduced permeability, abrasion and reduce strength and stiffness. Dense matrices are prone to
erosion resistance, shrinkage control, and enhanced ductility, explosive spalling, which can be mitigated by polypropylene
moving beyond strength‑based classification. Provisions for fibres that provide vapour release paths. Thermal gradients and
UHPC and ultra‑high‑performance fibre‑reinforced concrete microcracking further compromise post‑fire performance. Heat
(UHFRC) enable the adoption of advanced composites with of hydration, thermal diffusivity, and conductivity govern the
[31]
superior tensile capacity, crack control, and impact resistance . material’s response, emphasizing the need for performance-
Steel‑fibre‑reinforced concrete gains formal recognition, with based evaluation. In the IS: 456 under revision methods to
performance classification based on residual tensile strengths improve the fire resistance of high strength concrete has been
and post-cracking behaviour determined through standardized included based on limited research done and guidance taken
testing aligned with IS: 516-1 (2021) and EN 14651. Design from European standard EN-1992.
treatment of SFRC predominantly as a strain-softening material
ensures structural safety consistent with fib Model Code 2010 3.4 Geopolymer concrete
practice. Special provisions for high-strength concrete (HSC) Geopolymer concrete (GPC), an emerging class of alkali-
address explosive spalling risks during fire exposure, suggesting activated, low-carbon binders, offers a sustainable alternative
the use of polypropylene fibres for concrete grades above M60. to ordinary Portland cement (OPC) by utilizing industrial by-
M60 [32-33] . UHPC represents an advancement over conventional products such as fly ash and GGBS and significantly reducing
and HPC due to its exceptional mechanical strength, durability, CO 2 emissions. Laboratory and field studies covered over 80
and dense microstructure, enabling more efficient, long lasting mixes with compressive strengths ranging from 30 to 80 MPa,
structural systems with reduced member sizes and enhanced using fly ash‑slag based alkali‑activated systems. Durability tests
service life. However, UHPC’s low water to binder ratio and demonstrated chloride diffusion coefficients below 8 × 10 m²/s
–12
dense matrix, while beneficial for strength, result in higher and excellent resistance to sulfate attack. Full-scale precast
autogenous shrinkage and complex creep behaviour, which can elements and ready‑mix trials confirmed consistency, workability
induce internal tensile stresses, microcracking, and serviceability retention, and early-age strength development suitable for
issues if not accurately predicted and managed. Conventional precast applications. Based on these validated datasets,
creep and shrinkage prediction models (e.g., B3, B4) [29-30] tend to geopolymer concrete was standardized in IS: 17452, providing
overestimate or misrepresent time dependent strains in UHPC mix design guidance, material specifications, and acceptance
because they do not fully capture mechanisms such as self criteria. For structural applications, despite strong laboratory
desiccation, chemical shrinkage, pore humidity reduction, and evidence of its mechanical and durability performance, its
the influence of diverse admixtures and microstructural features widespread adoption has been limited by the lack of field‑
inherent to UHPC. The development of a specific coefficient scale validation and standardized guidelines. NCCBM’s study
calibrated for UHPC in mix optimisation research provides a addresses that gap by developing an M35-grade reinforced
more accurate representation of its time dependent deformation geopolymer concrete (RGC) mix suitable for ready-mix
characteristics by incorporating parameters directly linked to production, evaluating its mechanical and durability properties,
microstructure, binder interactions, and early age behaviour. and constructing and load-testing a full-scale demonstration
Such a coefficient improves predictive accuracy for shrinkage structure [34-36] . Activated using sodium hydroxide and sodium
and creep strains, enabling better structural design, reduced silicate, the developed mix achieved high workability,

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