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TECHNICAL PAPER

Table 3: Extent of utilization of manufactured coarse aggregate

SL. TYPE OF AGGREGATE MAXIMUM UTILIZATION AS A PERCENTAGE OF TOTAL MASS OF
NO. COARSE AGGREGATE
PLAIN CONCRETE, REINFORCED CONCRETE, LEAN CONCRETE (LESS THAN
PERCENT PERCENT M15 GRADE), PERCENT
a) Processed Air cooled Blast Furnace slag (ACBFS) aggregate 50 25 100
b) Processed Electric arc furnace slag (EAFs) aggregate 100 100 100
c) Processed Conarc slag aggregate 100 100 100
d) Recycled concrete aggregate (RCA) 40 40 (upto M30 grade) 100

Table 4: Extent of utilization of manufactured fine aggregate

SL. TYPE OF AGGREGATE MAXIMUM UTILIZATION AS A PERCENTAGE OF TOTAL MASS OF
NO. FINE AGGREGATE
PLAIN CONCRETE, REINFORCED CONCRETE, LEAN CONCRETE (LESS THAN
PERCENT PERCENT M15 GRADE), PERCENT
a) Processed Air cooled Blast Furnace slag (ACBFS) aggregate 100 100 100
b) Processed Granulated Blast Furnace slag (GBFS) aggregate 100 100 (up to M60 grade) 100
c) Processed Electric arc furnace slag (EAFs) aggregate 100 100 100
d) Processed Conarc slag aggregate 100 100 100
e) Processed Copper slag aggregate 40 35 50
f) Recycled concrete aggregate (RCA) 25 20 (upto M25) 100
g) Bottom ash from Thermal Power Plants 50 50* / 25** 50
* For concrete made with OPC
** For concrete made with PPC or OPC with fly ash, PSC or OPC with GGBS, and composite cement.

and stress block parameters for high-strength concrete (HSC), traditional deemed-to-satisfy approach toward a performance-
recognizing that the current code provisions are insufficient based, service-life-oriented methodology, where deterioration
beyond M55. Experimental research at NCCBM has shown that mechanisms like carbonation and chloride-induced corrosion
HSC exhibits a more linear and steeper ascending stress-strain are explicitly modelled. The revised framework is aligned with
curve (Figure 3) with a significantly reduced ultimate strain, ISO 16204 and fib Model Code principles, intending to use
unlike the constant 0.0035 strain value presently used in IS: 456. quantifiable durability limit states rebar depassivation, cracking
due to corrosion, and cover spalling to ensure that the initiation
Consequently, revised values of the strength reduction factor plus propagation period of corrosion exceeds the design service
(K) and lever arm factor (k 2 ) which reduce progressively with life. For carbonation, ingress is expressed as a square-root-of-
increasing concrete grade-are being proposed to prevent time model to determine when the carbonation depth equals
overestimation of flexural strength and compression capacity. the concrete cover, while chloride ingress is evaluated using
Typical values being recommended for higher grades are K Fick’s second law, where chloride concentration at reinforcement
in the range of 0.25-0.31 and k 2 between 0.33-0.36, compared depth ( , ) chloride concentration at reinforcement depth
to existing IS: 456 values of 0.36 and 0.42 [32-33] . The proposed ( , ) ( , ) is compared with the critical chloride threshold
revisions will enable more realistic modelling of flexural required to trigger corrosion. The apparent diffusion coefficient
behaviour, reduce neutral axis depth for balanced sections, D app decreases over time due to ageing, enabling prediction of
and enhance ductility and safety margins in structural design chloride penetration and cover design [16,25] . Under the upcoming
involving high-strength concrete, particularly in high-rise, IS: 456 revisions, concrete cover, material specifications, crack
prestressed and seismic-resistant structures. These inclusions control and quality control parameters are expected to be
aim to align IS: 456 with global design practices such as determined based on these predictive durability models,
Eurocode-2 and ACI, ensuring reliability and performance-based supporting a rational and reliability-based service life design
design using modern high-strength concrete.
rather than prescriptive minimum values.
3.14 Limit state of durability design for
resistance against corrosion 4. CONTRIBUTIONS TO INDIAN STANDARDS
Durability-based limit state design for resistance against Research outputs have led to the revisions of several BIS
corrosion proposed in the revision of IS: 456 shifts from the standards including IS: 456, IS: 383, IS: 9103, IS: 1199, IS:

THE INDIAN CONCRETE JOURNAL | JANUARY 2026 91