Project Overview

This laboratory study assessed eggshell powder (ESP) and charcoal ash (CA) as partial replacements for cement in M25 concrete. ESP was tested at 5%, 10% and 15%; charcoal ash was combined at 0%, 2.5%, 5% and 7.5%. The research measured slump, compressive strength at 7 and 28 days, and water absorption to identify a practical waste-based mix.

RESEARCH PROBLEM

Cement is costly and carbon-intensive.

Concrete depends heavily on ordinary Portland cement, whose production creates substantial carbon emissions and adds to construction costs. Eggshells and charcoal ash are abundant waste streams in Uganda, yet are frequently discarded. This study examines whether they can safely reduce cement demand in concrete.

OBJECTIVES

Research Objectives

Main Objective

Investigate eggshell powder and charcoal ash as partial cement replacements in concrete.

Workability

Assess how the replacement materials affect concrete slump and fresh-mix handling.

Compressive Strength

Determine strength development at 7 and 28 days for each mix.

Water Absorption

Evaluate the effect of replacement levels on absorption and durability behaviour.

MATERIALS

Materials Used

Portland Cement

The conventional binder partially replaced by the investigated waste materials.

Eggshell Powder

Calcium-rich powder produced from waste eggshells and used at 5–15% replacement.

Charcoal Ash

Locally available ash assessed for its potential pozzolanic contribution.

Concrete Constituents

Fine aggregate, coarse aggregate and clean water for M25 concrete production.

METHODOLOGY

Research Methodology

The work was conducted at the IUEA Civil Engineering Laboratory using controlled M25 concrete mixes and recognised testing standards.

Material Preparation

Eggshells and charcoal ash were processed and assessed for physical properties.

Mix Proportions

Eleven mixes combined 0–15% ESP with 0–7.5% charcoal ash.

Cube Casting

M25 concrete specimens were prepared consistently for each test mix.

Curing

Concrete cubes were cured before 7- and 28-day strength assessment.

Laboratory Testing

Slump, compressive strength and water absorption were measured.

Results Review

Mix performance was compared against conventional M25 control concrete.

LABORATORY TESTS

Experimental Tests

Slump Cone Test

Compressive Strength

Water Absorption

KEY FINDINGS

Research Results

Eggshell powder showed promise at low content, while the tested ESP-and-charcoal-ash combinations required further optimisation.

5% ESP

Most practical replacement level identified

24.24 MPa

28-day strength for the 5% ESP-only mix

26.85 MPa

28-day strength of the control mix

~90%

Control strength retained by the 5% ESP mix

115 mm

Slump recorded for the 5% ESP-only mix

10.56 MPa

Lowest 28-day strength, at 5% ESP + 7.5% CA

CONCLUSIONS

Major Findings

Eggshell Powder Is Viable

At 5% replacement, ESP produced near-control strength with acceptable workability and lower water absorption.

Charcoal Ash Needs Optimisation

The tested ESP-and-CA combinations consistently reduced strength and gave variable workability.

Local Circular Value

Waste eggshell has a practical role in low-impact, non-critical concrete applications in Uganda.

RECOMMENDATIONS

Next Steps

Use 5% eggshell powder for suitable non-critical concrete applications.

Optimise charcoal ash processing, including controlled calcination.

Test strength development beyond 28 days.

Assess durability, tensile strength and cost benefits in future work.