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TECHNICAL PAPER

unsorted C&D wastes, which is one of the challenges for C&D dimensional stone wastes as precursors preserves the natural
[13]
waste management in India. A previous study shows that colour of the stone in the resulting geopolymer . Results show
thermal exposure of 700 °C produces the optimum aggregate that a higher ratio of dimensional stone waste in the precursor
characteristics, by weakening of adhered mortar, combustion increases the colour intensity, but reduces strength. The
[12]
of organic impurities and sintering of clay materials . The composition can be optimised to produce a naturally coloured
weakened adhered mortar is then removed by abrasion geopolymer . The naturally coloured geopolymer has been
[13]
and sieve segregation. The resulting aggregate satisfies all used to produce a coloured-layer in bi-layered bricks and other
codal provisions for high-quality aggregates, as stipulated in building materials .
[13]
[12]
IS: 383 (2016) . At 100 % substitution of natural aggregates,
the treated aggregate showed over 90 % mechanical strength . Key contributions: The study demonstrated the colour-retaining
[9]
The treatment also results in the generation of recycled fine properties of geopolymer. Multiple repetition with different
aggregates and recycled fine powder, which show higher stone wastes, precursor and activator concentrations confirms
strength than natural river sand and fly ash in mortars. the same.
Key contributions: Among the different studies, the introduction Limitations: The developed geopolymer, in many cases,
of surface irregularities during abrasion is considered a novel shows a significant reduction in strength, indicating reduced
contribution with potential for impact. The results prompt a new sustainability. Furthermore, both colour and strength significantly
direction for improving abrasive cleaning of adhered mortar, depend on the precursor, making the solution susceptible to
which is widely used in the observed literature. In the case of raw material availability. Further investigations are needed to
thermo-mechanical treatment, the previous study demonstrated develop a geopolymer design mix with consistent strength,
the suitability and industrial scalability of the solution for mixed colour and lower susceptibility to precursor changes.
recycled aggregates.
3.3.2 Cow dung as foaming agent
Limitations: The results on surface irregularities are based on
20 mm recycled concrete aggregates from the same batch. The Cow dung particles show a porous, irregular surface with a
efficiency of the modification may be influenced by arrangement hollow tube-like structure (Figure 6a), resulting in high moisture
and type of irregularities, rotation speed and duration, grade retention. When added to concrete with excess water, the
of parent concrete, degree of adhered mortar, and presence particles retain the moisture without disturbing the stability and
of particles other than concrete. Further investigations in this flowability of the fresh mix. On hardening, the excess water is
direction can show the overall viability of smooth and irregular taken up by the concrete, creating voids and imparting internal
surfaced abrasive treatment. curing. The voids are uniformly distributed throughout the
concrete matrix and recreate an action similar to a foaming or
3.3 Alternative materials with functional aerating agent (Figure 6b). Furthermore, the internal curing
applications action provides better strength than foam concrete at small
dosages of cow dung powder.
3.3.1 Naturally coloured geopolymer
Key contributions: The study demonstrated a first-of-its-kind
Dimensional stone wastes, like marble slurry, retain the colour of foaming agent based on moisture pockets, as compared to
their parent rocks. Preparation of geopolymer using GGBS and previously reported foaming agents. The results were validated

(a) Microstructure of cow dung particles (b) Effect of cow dung on concrete
Figure 6: High moisture retention of cow dung and its application for foaming action

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