M25 Concrete with Sugarcane Bagasse Ash and Quarry Dust from the Mandya Belt: Strength, Cost per m³ and Embodied CO₂

Karnataka's sugar belt around Mandya, Mysuru and Belagavi burns bagasse in factory boilers for cogeneration and is left with large heaps of sugarcane bagasse ash (SCBA). A few kilometres away, stone-crushing units around Bengaluru and Ramanagara produce quarry dust that is often dumped. Both materials have been studied as partial replacements in concrete, but most student reports stop at "strength increased up to 10% replacement". This project goes further: it designs an M25 mix to IS 10262:2019, replaces cement with processed bagasse ash and river or manufactured sand with quarry dust, and reports strength, workability, cost per cubic metre and embodied CO₂ for every mix.

The experimental programme has two series. Series A replaces OPC 53 with 0, 5, 10, 15 and 20% sieved and recalcined bagasse ash. Series B takes the best Series A mix and replaces fine aggregate with 0, 25, 50 and 75% quarry dust. Each mix is tested for slump, 7- and 28-day compressive strength (IS 516), 28-day split tensile strength (both to IS 516 Part 1/Sec 1:2021) and water absorption. Results are analysed in Excel with one-way ANOVA and regression, and every mix gets a cost from the Karnataka PWD Schedule of Rates and a cradle-to-gate CO₂ estimate.

The project is written for VTU 2022 scheme Major Project Phase-II (BCV786) by a team of four, building on the literature survey and trial batches done in Phase-I (BCV685).

Abstract

The study evaluates M25 grade concrete in which ordinary Portland cement is partially replaced by sugarcane bagasse ash (0–20%) and fine aggregate by quarry dust (0–75%). Mixes are proportioned to IS 10262:2019 and tested for workability, compressive strength at 7 and 28 days, split tensile strength and water absorption. An optimum combination is identified using strength criteria and ANOVA, and each mix is compared on material cost per cubic metre and embodied carbon. The work shows whether two local wastes can produce structural-grade concrete that is cheaper and lower in carbon without compromising IS 456 durability requirements.

Introduction

Cement production is one of the largest industrial sources of carbon dioxide, and river sand mining is restricted in Karnataka, pushing builders to manufactured sand. Supplementary cementitious materials such as fly ash and slag are standard practice, but they are not available everywhere at low cost. Bagasse ash is a silica-rich residue available near sugar factories; when finely ground and burnt to low unburnt carbon, it shows pozzolanic activity. Quarry dust is the fine fraction of stone crushing, cheaper than processed manufactured sand.

Literature gap

Published work reports strength gains up to about 10–15% bagasse-ash replacement, but results vary widely because ash quality varies with boiler temperature and processing. Few studies (a) characterise the ash before use, (b) combine it with quarry dust in a designed M25 mix to the 2019 revision of IS 10262, or (c) report cost and carbon alongside strength. This project addresses all three.

Proposed work

• Characterise the ash (fineness, specific gravity, loss on ignition) and the quarry dust (grading, fines content).
• Design the control mix and 9 replacement mixes.
• Cast and test 90+ specimens; identify the optimum.
• Build a cost-and-carbon table and a recommendation for low-rise construction.

Feasibility

• Technical: the department concrete lab has a CTM, moulds and curing tank; ash is collected from a sugar factory near Mandya with a letter from the HOD.
• Economic: materials cost about ₹15,000–20,000, shared by the team.
• Schedule: 28-day curing fits within the 14-week Phase-II semester if casting finishes by week 6.

Builders around Mysuru and Mandya face rising cement prices and restricted river sand, while sugar factories and crushers in the same districts have waste fines with no use. Bagasse ash and quarry dust have been proposed as partial replacements, but small contractors and site engineers do not trust them because published results are inconsistent and rarely include the information they care about: whether the mix still meets M25 at 28 days with normal workability, what it costs per cubic metre compared with a standard mix, and how much carbon it saves. The problem addressed in this project is to determine the optimum replacement levels of cement by processed sugarcane bagasse ash and of fine aggregate by quarry dust in an IS 10262:2019 M25 mix, and to compare each mix on strength, workability, cost and embodied CO₂.

The study is limited to M25 grade concrete with OPC 53, 20 mm crushed coarse aggregate and moderate exposure as defined in IS 456. Bagasse ash comes from one sugar factory and quarry dust from one crusher; results may differ for other sources. Tests are mechanical and basic durability (water absorption); long-term durability such as chloride penetration and carbonation, and structural member testing, are outside scope and listed as future work.

Research design

Experimental laboratory study with two sequential series, followed by statistical, cost and carbon analysis. The work is split across VTU's two project phases.

Phase-I (BCV685, Semester 6) — completed before this report

• Literature survey of 25+ papers on bagasse ash and quarry dust.
• Collection and processing of ash: sun-drying, sieving through 300 µm then 90 µm, recalcination at about 600–700 °C to reduce unburnt carbon, and grinding.
• Material tests: cement (consistency, setting time, soundness, IS 4031); aggregates (specific gravity, water absorption, sieve analysis to IS 383:2016 zones); ash (specific gravity, fineness by 45 µm wet sieve, loss on ignition); quarry dust (grading and material finer than 75 µm).
• Trial mix of the control M25 and Phase-I report.

Mix design (IS 10262:2019)

• Target mean strength: f'ck = fck + 1.65 s = 25 + 1.65 × 4 = 31.6 MPa (compared with fck + X = 30.5 MPa; the higher value governs).
• Water-cement ratio from the code's strength relationship for OPC 53, checked against the IS 456 limit of 0.50 for moderate exposure.
• Water content for 20 mm aggregate adjusted for 75–100 mm slump; minimum cementitious content 300 kg/m³ (IS 456 Table 5) maintained.
• Coarse aggregate volume from the code table for the sand zone, then batch quantities per m³.

Phase-II (BCV786, Semester 7) — experimental programme

Specimens per mix: 6 cubes (3 at 7 d, 3 at 28 d), 3 cylinders (split tensile, 28 d), 3 cubes (water absorption). Total ≈ 96 specimens.

Tests

Slump (IS 1199 Part 2), compressive and split tensile strength (IS 516 Part 1/Sec 1:2021), water absorption (oven-dry and saturated mass).

Analysis

• One-way ANOVA (α = 0.05) on 28-day strength across Series A, then Series B; Tukey-style pairwise comparison in Excel.
• Polynomial regression of strength on replacement level to locate the optimum.
• Cost: materials per m³ × Karnataka PWD Schedule of Rates; ash and dust costed at transport plus processing.
• Carbon: kg CO₂/m³ = Σ (mass × emission factor) using published cradle-to-gate factors for OPC, aggregates and transport distance; processing energy for ash recalcination included.

Timeline (Phase-II, 14 weeks)