Page 6 - ICJ Jan 2026

TECHNICAL PAPER

3. FUNDAMENTAL RESEARCH arc furnace (EAF) slag and CONARC slag (Figure 1) were both
CONTRIBUTIONS shown to be viable for complete replacement of natural fine
and coarse aggregates while maintaining satisfactory fresh,
3.1 Alternate Aggregates hardened, and durability properties of concrete. Ferrochrome
slag demonstrated application‑specific potential, wherein
Research on alternate aggregates included systematic water‑cooled slag could replace up to 60 % of natural fine
evaluation of C&D waste, ferrochrome slag, EAF slag, LD/ aggregates, and air-cooled slag could replace up to 60 % of
BOF slag, Conarc slag, bottom ash [10-11] , blast furnace slag and natural coarse aggregates . Copper slag was found suitable
[12]
copper slag. Studies established fundamental relationships
between mineralogical composition, microstructure, surface for replacing natural fine aggregates up to 50 % without
[11]
roughness, and interfacial transition zone (ITZ) behaviour. The compromising performance . Additionally, the use of recycled
[2]
research work has led to the revision of IS: 383 . The current concrete aggregates derived from construction and demolition
revision will now be published in two parts-Part 1 catering to (C&D) waste was found feasible up to 40 % in reinforced
specifications of aggregates for use in concrete and Part 2 cement concrete of M30 grade, marking a significant step
catering to specifications of fine aggregates for use in masonry toward enhancing resource efficiency and sustainability in the
[7, 20, 22]
and plaster. Extensive research conducted by the National construction sector . Further to establish correspondence
Council for Cement and Building Materials (NCCBM) has with the specification standard. i.e., IS: 383, the standards
demonstrated the potential of various industrial by-products on testing of aggregates, i.e., IS: 2386 and the standard on
and recycled materials as sustainable alternatives to natural methods of sampling of aggregates, i.e., IS: 2430 are also
aggregates in concrete [7, 9-12, 18-22] . currently under revision.

NCCBM has undertaken systematic investigations on alternative 3.2 Low‑carbon cement systems and
aggregates derived from industrial by-products and C&D waste cementitious materials
to reduce dependence on natural aggregates. The studies
covered over 150 concrete mixes across strength grades The group developed multiple low-carbon binders including
M20-M60, with durability exposure extending up to years. composite cement, Portland limestone cement (PLC), High
Bottom ash was found suitable as a fine aggregate replacement Volume fly ash cement, PSC blended with granulated blast
up to 50 % in OPC-based concretes, maintaining compressive furnace slag (GFS) and LD slag, and fly ash‑limestone composite
strength above 95 % of control mixes and chloride diffusion cements. Research focused on hydration kinetics, particle
[9]
–12
coefficients below 12 × 10 m²/s . Granulated and air-cooled packing, synergistic effects of multi‑mineral fillers, and durability
blast furnace slag enabled 100 % replacement of natural sand in sulfate, carbonation, and chloride environments. For the
and up to 50 % replacement of coarse aggregates, achieving formulation of new standards for low carbon cement extensive
compressive strengths exceeding 60 MPa. Processed EAF study has been carried out in terms of its durability under various
and CONARC slags demonstrated stable volumetric behavior, aggressive environment (Figure 2).
permitting full replacement of natural aggregates under defined To address carbon intensity in cement production, NCCBM
limits. Recycled concrete aggregates from C&D waste were conducted extensive research on blended and low-clinker
validated for 40 % replacement in M30 concrete [8-10] . These binders, including Portland limestone cement, high-volume
findings directly informed the expansion and restructuring of fly ash cement, and fly ash‑slag composites. More than 120
IS: 383, along with revisions to IS: 2386 and IS: 2430, enabling concrete mixtures were evaluated, with clinker substitution levels
performance-based acceptance of alternative aggregates.
ranging from 30 to 60 %. Long-term carbonation and chloride
Bottom ash, constituting approximately 20 % of ash generated in exposure long term studies showed that optimized composite
thermal power plants, was found suitable for partial replacement binders achieved carbonation depths comparable to OPC and
of fine aggregates, and the corresponding recommendations
have been incorporated into the revised IS: 383 [9-10] . Studies
on granulated blast furnace slag (GBFS) revealed that it can
effectively replace natural fine aggregates up to 100 % for
producing concrete of grades up to M60 . Similarly, air-cooled
[11]
blast furnace slag (ACBFS) exhibited favorable characteristics,
enabling complete (100 %) replacement of natural sand .
[10]
Investigations on basic oxygen furnace (BOF/LD) slag
established its suitability as fine aggregate in reinforced cement
concrete, provided that appropriate weathering treatments
are applied to reduce free lime and magnesia content. Electric Figure 1: EAF slag and conarc slag aggregates

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