This document investigates using coffee husk ash as a partial replacement for cement in concrete with a grade of C25. The objectives were to determine the workability and strength properties of concrete mixes containing different percentages of coffee husk ash. Testing showed that as the percentage of coffee husk ash increased, workability and compressive strength decreased while tensile strength initially increased up to 20% replacement before decreasing. The bulk density also decreased with higher coffee husk ash content. The conclusion was that a 5% replacement of cement with coffee husk ash provided benefits to strength without significantly impacting workability.

1. INVESTIGATING EFFECTS OF
COFFEE HUSK ASH AS PARTIAL REPLACEMENT OF
CEMENT IN CONCRETE GRADE C25
BY
PETER S ATEKA
111/05567
PROJECT SUPERVISOR: PROFESSOR GEORGE THUMBI

2. Introduction
• Cost of building materials; especially pozzolanic cement,
environmental pollution and global warming are the major challenges
of the world today.
• Rise husks, coffee husks and sugarcane baggasse ashes have
pozzolanic properties.
• Research was aimed at reducing the cost of building materials e.g
cement, and environmental pollution by replacing cement with coffee
husk ash in concrete.

3. Problem statement
• Cost of building materials and environmental pollution is affecting
every one. Therefore there is a need to research on alternatives of
building materials that are cost effective and environmental friendly.

4. Problem justification
• Rising cost of concrete production has impaired the construction
industry, a study on the alternative materials (like coffee husk ash) to
replace cement justifies the research.
• Recycling wastes would help in the protection of environment and
lowering of construction cost.

5. Objective
Main objective
• The main objective of this research is to investigate the effect of coffee
husk ash as partial replacement of Portland cement in concrete C25.
Specific objectives
• To determine workability of normal concrete mix and that replaced
with CHA.
• To evaluate the effect of concrete mix ratio on compression strength,
tensile strength and bulk densities of concrete cubes with different
percentages of coffee husk ash.

6. Literature review
• Concrete - mixture of cement, water, fine and coarse aggregates in
which water and cement have hardened by chemical reaction to form
a binder. Also included are admixtures (G.D Taylor and B.J Smith,
1986).
• concrete class C25 means that it has a characteristic cube crushing
strength of 25N/mm2( W.H. Mosley et al., 1999).
• Cement-material with adhesive and cohesive properties which makes
it capable of binding mineral particles into a compact whole. Most
important cements are Portland cements. (G.D Taylor and B.J Smith,
1986).
• Aggregates - fine aggregates and coarse aggregate (David Otieno
Kotieng’, 2015).

7. literature review
• CHA produced by burning coffee husk between 6000C and 7000C
temperatures for two hours contains 90-95% silica, 1-3% Potassium
Oxide and <5% unburnt carbon under controlled burning condition in
industrial furnace. (Lee- Kuo Lin and Yi-Shu- Hsu, 2013 ).
• CHA cement improves workability and stability, impermeability and
durability by strengthening transition zone, modifying the pore
structure, blocking the large voids in the hydrated cement paste
through Pozzolanic reaction.

8. Methodology
Involved collection of research materials, preparation and laboratory test
1.Materials
• Ordinary Portland cement, Fine aggregates and crushed coarse, aggregate,
Water, Coffee husk ash
2.Sieve analysis of aggregate, batching of concrete material, mixing
proportion and casting of samples
Laboratory test
1. workability-slump and compacting factor test
2. Compressive strength test
3. Tensile strength test
4. Density of hardened concrete

9. Result, analysis and discussion
Slump test
0
10
20
30
40
50
60
70
0 5 10 15 20 25
slump(mm)
CHA percentages replacement
SLUMP
SLUMP
As the replacement of
cement with coffee husk
ash increases, the
workability of the
concrete is decreasing
due to the absorption of
the water by the coffee
husk ash.

10. Compaction factor test
0.85
0.86
0.87
0.88
0.89
0.9
0.91
0.92
0 5 10 15 20 25 30
COMPACTIONFACTOR
CHA % REPLACEMENT
Compacting Factor values
The high demand for
water as the CHA
content increases is
due to increased
amount of silica in
the mixture.

11. Compression strength
0
5
10
15
20
25
30
35
0 5 10 15 20 25
COMPRESSIVESTRENGHT
CHA REPLACEMENT %
Compressive Strength (N/mm2) 7 days
Compressive Strength (N/mm2) 14 days
Compressive Strength (N/mm2) 28 days
The results of the
compressive strength of
concrete cubes show that the
compressive strengths
reduced as the percentage
CHA increased

12. Tensile strength for each mix
0 0 0 0 0 0
2.56
2.7 2.73 2.76
3.2 3.16
0
0.5
1
1.5
2
2.5
3
3.5
0% CHA 5%CHA 10%CHA 15%CHA 20%CHA 25%CHA
tensilestrength
percentage
Average value (N) fc (N/mm2) The analysis of the tensile
strengths at 28 days of curing
showed that the concrete made
from CHA gain strength from
2.56 N/mm2(control
experiment) to 3.2
N/mm2(20% replacement of
cement with CHA). The
tensile strength then generally
decreased at 25% replacement
of cement with coffee husk).

13. Bulk density
The results of the bulk
densities show that the bulk
density reduces as the
percentage CHA increases.
This could be attributed to
the increase in voids in the
concrete cubes as the
percentage CHA increases.
However, the bulk densities
increase as the number of
days of curing increase as
the concrete cubes become
denser.
2.05
2.1
2.15
2.2
2.25
2.3
2.35
2.4
2.45
0 5 10 15 20 25
bulkdensityg/cm3
CHA replacement %
BulkDensity(g/cm3) 7 days
BulkDensity(g/cm3) 14 days
BulkDensity(g/cm3) 28 days
Figure 4.7: Effect of CHA content on Bulk Density of Concrete at different curing age

14. Conclusion
• Concrete becomes less workable as the CHA percentage increases
• The compressive strength increased with curing period and decreases with
increased amount of CHA.
• Tensile strength was gained at 28th day.
• Only 5% CHA substitution is adequate to enjoy maximum benefit of strength gain.
Recommendation
• Research on flexural behaviour of lightweight concrete made with this material
should be carried out.
• Research on durability of concrete cubes made with CHA should be carried out.

15. References
• A.M. Neville, Properties of Concrete: Fourth and Final Edition, Pearson Education Limited,
Essex, 2002.
• International journal of Engineering and Applied Sciences 20012-2015 EAAS & ARF
www.eaas.journal.org
• K.S. Tan, M.F. M. Zain, K.M. Yusof, M. Safiuddin, T.Y. Chang and K.S. Lee”, Influence of
quarry dust and silica fume on the properties of high performances concrete”, Proceeding
of the Second International Conference on Advances in Strategic
Technologies,Bangi,Selangor,Malaysia.pp.1563-1572,2000.
• Materials in construction by G.B Taylor and B.J Smith 5th edition (1985)
• M. Safiuddin, M.F.M. Zain, M.F. Mahmud and R.S, Naidu,” Effect of quarry dust and
mineral admixtures on the strength and elasticity of concrete”, Proceedings of the
Conference Technology, Kota Kinabalu,Sabah,Malaysia.pp,68-80,2001.
• R.S .Naidu, M.F.M Zain and K.S. Tan,” Strength and elasticity of concrete incorporating
quarry dust and mineral admixtures”, Proceedings of the 3rd International Conference on
Advance in Strategic Technologies, Kuala Lumpur,Malaysia,pp.1179-1184,2003

16. Thank you for your time