A Study on Partial Replacement of Cement with Rice Husk Ash and Bamboo Biochar in M25 Grade Concrete

Concrete is the cornerstone of modern infrastructure, yet its primary component, cement, is responsible for substantial CO? emissions. In pursuit of greener construction methods, this research examines the viability of using RHA and Bamboo Biochar (both agricultural byproducts) as supplementary cementitious materials. These alternatives not only minimize environmental degradation but also enhance concrete’s mechanical properties. Rice Husk Ash (RHA) and Bamboo Biochar have emerged as promising materials. RHA is a by- product obtained from the combustion of rice husks, commonly used as fuel in power or industrial plants. It contains a high amount of amorphous silica (SiO?), typically around 85–90%, which makes it a highly reactive pozzolanic material. When used as a partial replacement for cement, RHA enhances concrete’s compressive strength, durability, and resistance to chemical attack, while also reducing cost and environmental impact. Similarly, Bamboo Biochar, derived from the pyrolysis of bamboo waste, is gaining attention as an eco-friendly additive in concrete. It is lightweight, highly porous, and rich in carbon, offering multiple benefits such as improved internal curing, better insulation, enhanced durability, and reduced shrinkage. Bamboo biochar also contributes to carbon sequestration and waste management, making it a sustainable alternative. Incorporating RHA and Bamboo Biochar in concrete not only helps in reducing the consumption of cement and natural resources but also leads to improved mechanical and durability properties of concrete. These innovations support the development of greener construction practices that align with global sustainability goals.

LITERATUREREVIEW:

James and Rao (1986) emphasized that the chemical composition, silica content, and particle size of RHA are key factors influencing its reactivity and suitability for concrete. Ganesan et al. (2005) and Rodriguez de Sensale (2006) investigated the mechanical and durability characteristics of RHA-blended concrete. Their findings revealed that partial replacement of cement with RHA enhances compressive strength, impermeability, and overall performance of the concrete mix.

Kang-Hao Tan et al. (2021) presents a review on the use BC particles as an additive or cement replacement in cementitious composites over the last few decades. It comprehensively reviews and discusses the physicochemical properties of BC, as well as the influence of BC on the hydration kinetics, workability, physical properties, mechanical properties, and durability of mortar or concrete. The replacement of cement with 1%–3% BC, in weight, decreases the permeability and increases the mechanism strength of cementitious composites.

Shravan Muthukrishnan, Souradeep Gupta

And Harn Wei Kua (2019) investigated thermal treatment of RHA (TRHA) to produce ash with improved physical and chemical properties, which can then be used to reduce cement content in mortar by 20% (by weight). Furthermore, combination of rice husk biochar (RHB) and RHA, where RHB is used to replace 10% and 40% by weight of RHA,is used to improve mechanical and durability properties of RHA-RHB mortar. The performance was compared with control (without RHA) and mortar containing RHA produced under controlled laboratory condition (Lab RHA). Experimental results showed that addition of TRHA increased the strength of mortar by 20% and 34% at early stage (after 7days) and matured age (after 120days) compared to mortar with RHA respectively.

Sajjadi et al. (2019) emphasized the enhanced performance of chemically activated biochars, particularly those treated with alkaline agents such as potassium hydroxide (KOH) and sodium hydroxide (NaOH). Notably, NaOH is considered more environmentally friendly and cost-effective than KOH, and it requires lower concentrations to activate biochar efficiently. The activation of biochar significantly enhances its CO? sorption capacity.

Tan et al. (2014) identified 32% NaOH as the optimal concentration to maximize CO? uptake. Activated biochars develop improved pore structures and increased surface reactivity, which are essential for effective CO? capture when used in composite materials like concrete.

Anwar, Miyagawa, and Gaweesh (2001) explore the replacement of RHA at 0%, 20%, and 40% levels inconcrete. For 20% replacement, compressive and Tensile strength increased significantly, where as for 40% replacement, strength was decreased. Resistance to chloride ion penetration and porosity also improved with RHA concrete, thus enhancing durability. This study shows that RHA can be used for improving mechanical properties as well as durability and is a promising material for sustainable concrete applications.

Phatak and Kishor (2024) recently reviewed RHA- based cement substitution with a focus on the sustainable development of rice producer country India. India alone accounts for high RHA generation with 90% silica content and pozzolanic properties. Their findings showed RHA enhances concrete strength, durability, and environmental sustainability by reducing CO? emissions and addressing waste management challenges. They highlighted its effective use in various concretes, such as high- strength and self-compacting types, achieving performance comparable to traditional mixes. The study concluded that integrating RHA promotes resource conservation and supports sustainable construction practices.

MATERIALSANDMETHODS:

MATERIALS:

Cement: Cement is a material that has cohesive and adhesive properties in the presence of water. Such cements are called hydraulic cements. These consist primarily of silicates and aluminates of lime obtained from limestone and clay. Portland Pozzolana Cement (PPC) was used in design mix. The properties of cement are in compliance with the Indian standard organization. The specific gravity of cement is 3.15. The cement initial and final setting time are obtained as 60 minutes and 4 hours 45 minutes respectively and Fineness of cement is obtained as 3.98 %.

Coarse Aggregate: Coarse aggregates are materials passing through an IS sieve that is less than 75mm gauge and retained on 4.75mm IS sieve. The shape and texture of aggregate affects the properties of fresh concrete more than hardened concrete. Concrete is more workable when smooth and rounded aggregate is used is used instead of angular or elongated particle suspension. The nominal size of aggregate we used is 20 mm (As per IS: 2386- 1963). The specific gravity of coarse aggregate is 2.77.

Fine Aggregate: Fine Aggregates are material passing through an IS sieve that is less than 4.75 mm gauge. Fine aggregate form the filler matrix between the coarse aggregate. The most important function of the fine aggregate is to provide workability and uniformity in the mixture. The fine aggregate also helps the cement paste to hold the coarse aggregate. The fine aggregate we used falls under zone- II (As per IS: 383:1970) and the specific gravity of fine aggregate obtained was 2.50.

Rice Husk Ash: It is a by-product obtained from the controlled combustion of rice husks, rich in amorphous silica (~90%). It exhibits strong pozzolanic activity, enhancing concrete’s strength and durability. For this study, RHA was 0prepared by slowly burning rice husks in a tin chamber surrounded by bricks, ensuring limited oxygen supply to retain silica content. The ash was then cooled, sieved, and stored in airtight containers.

Bamboo Biochar: It is a carbon-rich, porous material produced by pyrolyzing bamboo waste in a low- oxygen environment. It improves internal curing, reduces shrinkage, and enhances thermal resistance. In this research, BB was prepared using the traditional pit method: dry bamboo was charred in a soil pit and smothered with wet cloth to control combustion. The cooled product was ground and sieved for use

METHODS:

Concretecubesof150mmx150mmx150mmwere cast with varying cement replacement (0%,4%,8%, 10%,12%,14%,16%&20%) using combined RHA and Bamboo Biochar. Awater-cement ratio of 0.46 was maintained. Tests conducted:

• Slump test(workability)
• Compressiontestat7and28days

RESULTS AND DISCUSSION: SLUMP TEST:

The results from the slump test shows that workability properties of concrete decreases with increasing % of biochar in the mix. The table below shows the slump test value for various % of replacements.

Table1: Slump test values

Fig1: Slump values v/s % mix

Compressive Strength:

The various types of cubes of different mixes were tested under compression testing machine (CTM)at 7 days & 28 days as recommended in IS code. The results obtained from all the experimental works carried under this study have been discussed below.

Comparison of Compressive Strength:

Fig 2: Compressive strength at7days

Fig3: Compressive strength at 28days

Fig4: Overall comparison of compressive strength at7 and 28days

Fig5: Comparison of compressive strength of different% replacement of cement with RHA and bamboo biochar (standard M25 concrete) at 7 and 28 days.

QUANTITY OF CEMENT SAVED:

Table2: Quantity of cement saved