The construction sector is facing growing challenges to reduce greenhouse gas emissions by adopting

environmentally sustainable construction materials with lower carbon footprints. Among the emerging solutions,

carbon dioxide (CO₂)-adsorbing concrete has attracted considerable attention because of its ability to capture

experimentally evaluates the potential of developing sustainable concrete blocks with enhanced CO₂ adsorption

capacity through the partial replacement of conventional materials with natural zeolite and Dunite. Concrete

replacement levels reduce workability and compressive strength, primarily due to increased pore volume and

weaker cementitious bonding within the concrete matrix. Overall, the results indicate that a balanced

combination of zeolite and Dunite can produce sustainable concrete blocks with enhanced carbon capture

potential and acceptable structural performance. The outcomes of this research provide valuable insights into

the development of eco-friendly construction materials that can contribute to carbon mitigation efforts while

supporting the long-term sustainability of the built environment.

Keywords: Sustainable concrete, Carbon sequestration, Zeolite, Dunite

Concrete is increasingly being engineered to perform multiple functions beyond providing structural strength,

with growing emphasis on improving its environmental performance. One of the most promising developments

Natural zeolite, in particular, has been extensively studied because of its highly porous alumina silicate

framework, large specific surface area, and pozzolanic characteristics. Earlier research has demonstrated that

replacing a portion of cement with zeolite can improve long-term compressive strength, refine the internal pore

structure, and enhance durability through the formation of additional calcium silicate hydrate (C–S–H) gel.

Nevertheless, higher replacement levels often result in reduced workability and lower early-age strength due to

the material's greater water absorption capacity. More recently, zeolite has also been recognised as a suitable

candidate for improving the CO₂ adsorption behaviour of cementitious materials.

Magnesium-bearing silicate minerals, particularly Dunite, have also attracted attention because of their ability

to permanently store carbon dioxide through mineral carbonation reactions. Most published studies have

concentrated on the carbonation characteristics of Dunite and its application in carbon capture and storage

mixtures with varying replacement levels were prepared and evaluated for workability, density, water

absorption, compressive strength, and CO₂ adsorption capacity to determine an optimum mix capable of

balancing structural performance with carbon sequestration efficiency. The findings are expected to provide a

better understanding of the combined influence of zeolite and Dunite and support the development of

environmentally sustainable cementitious materials with enhanced carbon capture capability.

Ordinary Portland Cement (OPC) 53 grade conforming to IS 12269 was used as the primary cementitious binder

throughout the study. Natural river sand meeting the requirements of Zone II as specified in IS 383 was used as

the fine aggregate, while crushed granite coarse aggregate with a nominal maximum size of 20 mm, conforming

atmospheric CO₂. Dunite, a magnesium-rich silicate mineral predominantly composed of olivine, was included

because of its potential to chemically sequester CO₂ through mineral carbonation while also contributing to the

refinement of the concrete microstructure. The physical characteristics of all constituent materials used in this

investigation are presented in Table 1.

The control concrete mix of M30 grade was designed in accordance with IS 10262:2019. Zeolite was used as a

partial replacement for cement at levels of 10%, 15%, and 20%, whereas Dunite was incorporated as a partial

replacement for fine aggregate at 10%, 15%, and 20%. Along with the control mix, seven modified mixtures

(10Z–10D, 10Z–15D, 15Z–10D, 15Z–15D, 15Z–20D, 20Z–15D, and 20Z–20D) were prepared to examine the

combined effect of these mineral admixtures on the fresh, physical, mechanical, and CO₂ adsorption properties

of concrete. The replacement percentages were selected based on the optimum ranges reported in earlier studies,

while the water-to-binder ratio, aggregate proportions, and mixing procedure were kept identical for all mixes

to ensure a uniform basis for comparison.

performance of each concrete mixture. The mould used for specimen preparation and the concrete block after

demoulding are shown in Figure 1.

After Demoulding at 24 hours, the specimens were cured in potable water under laboratory ambient conditions

(27 ± 2°C) until the specified testing ages of 7, 14, 21, and 28 days. At the end of the curing period, the specimens

were removed from the curing tank, surface moisture was wiped off, and they were allowed to reach a saturated

surface-dry (SSD) condition under laboratory ambient conditions before weighing and testing. This procedure

was adopted to minimize the effect of free surface water on the measured specimen mass and to ensure consistent

comparison among all concrete mixtures.

The workability of the concrete mixtures was evaluated using the slump cone test, and the corresponding results

are presented in Table 2. A gradual reduction in workability was observed with increasing replacement levels of

zeolite and Dunite. The control mixture recorded a true slump of 85 mm, while the slump reduced to 65 mm for

the mixture containing 20% zeolite and 20% Dunite. This decrease is mainly attributed to the porous structure

and high water absorption capacity of zeolite, which increases the water demand, along with the angular shape

of finely ground Dunite particles that increases internal friction within the concrete matrix. Despite the reduction

in slump, all mixtures exhibited a true slump, indicating adequate cohesion and workability for concrete block

casting.

The compressive strength results are presented in Table 3 and Figure 4. The concrete mixture containing 10%

4. The experimental results suggest that the combined incorporation of zeolite and Dunite is an effective

approach for producing sustainable concrete with enhanced environmental performance while retaining

satisfactory engineering properties.

5. Overall, the findings indicate that the mixture containing 10% zeolite and 10% Dunite offers the most

naturally occurring minerals in the development of environmentally sustainable concrete.

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