Synergistic Effects of Graphene Nanoplatelets and Metakaolin on the Properties of
Cementitious Composites Graphene nanoplatelets (GNPs) and metakaolin are two innovative
additives that have individually shown promise in enhancing cementitious composites. This
research investigates the potential synergistic effects when both materials are incorporated
together into cementitious composites. By examining their combined impact on mechanical
properties, this study aims to identify optimal combination ratios that maximize mechanical
performance for structural mortar applications.
Objectives
1. To design and produce nine concrete mixes with varying MK replacement levels
(0%, 10%, 20%) and GNP dosages (0%, 0.05% and 0.01% by binder mass), including
control, MK-only, GNP-only and combined MK–GNP mixes.
2. To evaluate the influence of MK and GNPs on fresh concrete properties by
measuring slump and fresh density for all mixes.
3. To determine the effect of MK, GNPs and their combination on mechanical
performance by testing compressive strength and splitting tensile strength at 7 and 28
days.
4. To assess potential synergistic behaviour by comparing the performance of
combined MK–GNP mixes with that of MK-only, GNP-only and control mixes.
5. To provide recommendations on optimal MK and GNP dosages for structural
concrete based on strength enhancement, workability and practical feasibility.
Experimental methodology
1 Materials and mix proportions Ordinary Portland cement (CEM I 42.5N) used as the
primary binder. Metakaolin (MK) employed as a supplementary cementitious material,
replacing 0%, 10% and 20% of the cement by mass. Graphene nanoplatelets (GNPs) were
added at a dosage of0%, 0.05% and 0.1% by mass of total binder (cement + MK). Natural
aggregates conforming to the grading requirements for structural concrete were used, with a
constant water–binder ratio of 0.45 for all mixes. A polycarboxylate-based superplasticizer was
used to maintain workability, particularly in mixes containing MK and GNPs.
Six concrete mixes were prepared: a control mix without MK or GNP (C), two mixes with MK
only (MK10 and MK20), one mix with GNP (G0.05, G0.01), and two mixes combining MK
and GNP (MK10-G0.05, MK10-G0.01 and MK20-G0.05, MK20-G0.01). The mix proportions
were kept constant in terms of aggregate and water–binder ratio, with only the binder
composition varying between mixes.
2 Dispersion of graphene nanoplatelets and mixing procedure to improve dispersion, GNPs
were first mixed with a portion of the mixing water and the required dosage of superplasticizer
using a high-shear mixer (or ultrasonic bath where available) for a fixed time of 5 minutes. The
dry materials (cement, MK and aggregates) were mixed in a pan mixer for 2–3 minutes.
Approximately 70–80% of the remaining mixing water was then added and mixing continued
for a further 2 minutes. Finally, the GNP–water–superplasticizer
suspension was slowly introduced while mixing, and the concrete was mixed for an additional
3 minutes until a visually homogeneous mixture was obtained. The same mixing sequence and
times were applied to all batches to ensure consistency.
3 Fresh concrete tests Immediately after mixing, slump was measured in accordance with the
relevant standard (e.g. BS EN 12350-2) to assess workability. Fresh density was determined
using a calibrated container following BS EN 12350-6. These tests were performed for each
mix to evaluate the influence of MK and GNPs on the fresh properties of the concrete.
4 Specimen preparation and curing for each mix, concrete was cast into cube moulds for
compressive strength testing and cylinder moulds for splitting tensile strength testing,
following BS EN 12390. The specimens were compacted using a vibrating table to minimise
entrapped air. After casting, the specimens were covered to prevent moisture loss and
demoulded after 24 hours. All specimens were then cured in water at 20 ± 2∘ Cuntil the
designated test ages of 7 and 28 days.
For each mix and each test age, three cubes were prepared for compressive strength testing and
three cylinders for splitting tensile strength testing, giving a total of six specimens per mix per
age. In total, 72 specimens were tested across all mixes and ages, providing sufficient data to
calculate mean values and standard deviations for statistical analysis.
5 Hardened concrete tests Compressive strength tests were carried out on cube specimens at
7 and 28 days in accordance with BS EN 12390-3. Splitting tensile strength tests were
performed on cylinder specimens at the same ages following BS EN 12390-6. The load was
applied using a calibrated testing machine at a controlled rate specified in the standards. For
each mix and age, the average strength and standard deviation were calculated from three
specimens.
Suggested mix matrix (minimum):
1. C: Control (0% MK, 0% GNP)
2. MK10: 10% MK, 0% GNP
3. MK20: 20% MK, 0% GNP
4. G0.05: 0% MK, 0.05% GNP
5. G0.10: 0% MK, 0.10% GNP
6. MK10-G0.05: 10% MK + 0.05% GNP
7. MK10-G0.10: 10% MK + 0.10% GNP
8. MK20-G0.05: 20% MK + 0.05% GNP
9. MK20-G0.01: 20% MK + 0.01% GNP
Total specimen count

9 mixes

2 ages (7 and 28 days)

Tests: compressive + flexural only

3 specimens per mix per age per test
Per mix per age:

Compressive: 3

Flexural: 3

Total per mix per age: 6
For 8 mixes and 2 ages:

Total specimens
9 mixes × 2 ages × 6 specimens = 108 specimens
Mix design matrix
Mix ID
C
MK10
MK20
G0.05
G0.01
MK10-G0.05
MK10-G0.01
MK20-G0.05
MK20-G0.01
MK (% of cement)
0
10
20
0
0
10
10
20
20
GNP (% of binder)
0
0
0
0.05
0.01
0.05
0.01
0.05
0.01
Purpose
Control
MK effect only
Higher MK level
GNP effect only
GNP
Combined, moderate MK + GNP
Combined, moderate MK + GNP
Combined, higher MK + GNP
Combined, higher MK + GNP
Summary Timeline (6 May – 27 July 2026)
Phase
Planning
Approvals
Dates
&
Trial Mix
Main Casting –
Batch 1
Demoulding
–
Batch 1
6–18 May 2026
19–25 May 2026
27 May 2026
28 May 2026
Main Casting
2 June 2026
– Batch 2
Demoulding –
3 June 2026
Batch 2
Activities
Finalise mix design, safety notes, confirm materials, book casting
& testing slots.
Conduct trial batch (control + MK+GNP mix), check GNP
dispersion, slump, SP dosage, finalise procedure.
Cast C, MK10, MK20; perform slump & fresh density; cast cubes
& cylinders.
Demould after 24 hours; transfer to curing tank.
Cast G0.05, MK10-G0.05, MK20-G0.05; slump & fresh
density; cast cubes & cylinders.
Demould after 24 hours; transfer to curing tank.
7-Day Tests
28-Day Tests
Data Analysis
Dissertation
Writing
3 June 2026
Compressive strength (3 cubes/mix) + splitting tensile
(Batch 1) 9 June
(3 cylinders/mix).
2026 (Batch 2)
24 June 2026
(Batch 1) 30
Compressive strength + splitting tensile for all mixes.
June
2026
(Batch 2)
Process results, calculate means & SDs, plot graphs,
1–13 July 2026
identify synergy trends.
Complete
methodology,
results,
discussion,
14–27 July 2026
conclusions; final editing & formatting.
Risk Assessment Summary for Graphene Nanoplatelets (GNPs)
Hazard Identification

Nanoparticle inhalation risk: GNPs are extremely fine powders that can become
airborne and enter the respiratory system.

Skin and eye irritation: Direct contact may cause irritation.

Environmental contamination: Nanoparticles can disperse easily if spilled.

Agglomeration risk: Poor dispersion can lead to inconsistent mechanical properties and
unsafe mixing behaviour.
Risk Level (Before Controls): Medium–High
Control Measures
1. Personal Protective Equipment (PPE)

Laboratory coat (fully buttoned)

Nitrile gloves

Safety goggles

FFP3 dust mask or respirator (mandatory when handling dry GNP powder)
2. Handling Procedures

Handle GNPs inside a fume cupboard or designated low-airflow mixing booth.

Avoid opening GNP containers near fans, open windows, or busy walkways.
3. Spill and Waste Management

Clean spills using wet wiping — never sweep or blow.

Dispose of GNP-contaminated materials in sealed bags labelled “nanomaterial waste”.
Risk Level (After Controls): Low