Page 4 - ICJ Jan 2026

TECHNICAL PAPER

ERA FROM POZZOLANIC TO

SUPER POZZOLANIC MATERIALS:

THE SCIENCE BEHIND THE

INCLUSION OF NANO-SILICA IN

THE CEMENTITIOUS COMPOSITES B. B. DAS*

Abstract produce calcium silicate hydrate (C-S-H), the principal binding
phase, and calcium hydroxide (CH) [2-3] ,
Over the past decade, development in nanotechnology
has opened up avenues for the use of nano-additives in the 2C 3 S + 6H → C-S-H + 3CH (1)
field of construction. This nano-additives incorporation in
2C 2 S + 4H → C-S-H + CH (2)
concrete exhibit significant improvement in the properties and
performance, the problem of lower initial strength gain was These hydration reactions are strongly exothermic, and mixes
mitigated and “high performance concrete” could be produced richer in C 3 S content can elevate internal concrete temperatures
with a superior service life, owing to their reduced size from from ambient levels (≈25 °C) to 50-70 °C within the first
[4]
micro to nano-scale and hence the increased surface area, 24-48 hours, particularly in mass concrete . In large elements
surface energy, reactivity and surface morphology. Amongst such as dams and thick raft foundations, peak temperatures may
all the nano-additives, nano-silica is found to be the first nano reach 80-90 °C, and if cooling and restraint are insufficient, steep
[4]
product that replaced the micro silica or silica fume in concrete thermal gradients can induce early-age thermal cracking . As
and it is the most predominantly used nano particle amid all hydration continues, the developing matrix forms a multi-scale
other nano particles in cementitious system. In this regard, microstructure consisting of gel pores, capillary voids, crystalline
[5]
understanding the primitive concepts of cement and concrete deposits, and an interfacial transition zone around aggregates .
This evolving pore system influences permeability, stiffness,
at the level of nano i.e. hydrate phases of cement to figure and long-term durability, as the distribution and connectivity
out the mechanism of nano-particle addition in concrete. of pores regulate the movement of water, ions, and gases
Further, it requires understanding the potentiality of nano- within the hardened mass . Although conventional concretes
[6]
silica in making the concrete durable and environmentally possessed advantages such as straightforward mix proportions
sustainable. Considering this into consideration, a detailed and predictable strength gain, their relatively porous matrices
and comprehensive article is presented here describing the and higher permeability limited long-term durability. Typically,
chemistry that takes place with the inclusion of nano-silica in the ordinary concretes exhibit total porosity in the range of 10-25 %
cementitious system. and water permeability coefficients between 10 -10 ¹² m/s,
–10
–
depending on water-cement ratio and curing quality [7–9] . These
Keywords: Chemistry concrete; High performance; Nano-silica; characteristics make them more susceptible to moisture
Nanotechnology; Pozzolanic materials.
ingress, chloride penetration, and deterioration in aggressive
environments, prompting further advancement in material
1. INTRODUCTION design and performance expectations.
The transformation of construction and building materials began The shift towards high-performance concrete (HPC) was a
with the development of conventional concretes in the early gradual evolution from conventional concrete, beginning in
1900s, which provided compressive strengths in the range of the 1970s-1980s with advances in clinker quality, low w/c ratio
5-45 MPa and were adequate for the structural demands of that technology, and the introduction of superplasticizers [1,10] . The
[1]
period . Their performance was governed by the hydration of parallel rise in supplementary cementitious materials (SCM)
clinker phases, primarily tricalcium silicate (C 3 S) and dicalcium use, along with fly ash, ground granulated blast furnace slag,
silicate (C 2 S), which react with water (H denotes water, H 2 O) to (GGBS), silica fume, and rice husk ash, further enabled strengths

60 THE INDIAN CONCRETE JOURNAL | JANUARY 2026
* Corresponding author: B. B. Das, Email: bdas@nitk.edu.in