Multicriteria analysis of the components of ecological paving stones made from plastic and glass waste, and granular reinforcements

Abstract

The use of plastic waste as a resource in construction applications is an opportunity for environmental protection,
conservation of natural resources and reduction of pollution. Unfortunately, they don’t always withstand the
stresses to which they are subjected, leading to subsidence and collapsing. An analysis of the causes using the
Pareto curve shows that 74.47 % of the causes of this collapse are due to poorly formulated mixes and poor
choice of raw materials for the composite. The compressive test carried out on the first sample of pavers studied
showed a maximum compressive strength value of 4.6 MPa, which is below the standard requirements. As a
result, the pavers were considered unsuitable for use on a T5 road. Through the use of the SUPERDECISION
software, we were able to identify two favourable constituent materials - glass/glass waste and gravel - for the
production of composite paving stones. By adding low-density plastic waste, collected, cleaned and crushed in
the form of aggregates, we obtain a compressive strength of 7 MPa with gravel and 8 MPa with glass waste. These
values are below the recommendations of the NF EN 1339 standard (Rc ≥ 20 MPa) for T5 traffic. The best
composition for ecological paving is therefore (PET/PP/PEBD) + sand + glass (50/12.5/37.5). Analyzing these
results shows that the raw materials used for ecological paving should be adapted to the loads.

Full text

Open Ceramics 18 (2024) 100604
Available online 8 May 2024
2666-5395/© 2024 Published by Elsevier Ltd on behalf of European Ceramic Society. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Multicriteria analysis of the components of ecological paving stones made
from plastic and glass waste, and granular reinforcements
Etienne Malbila
a
,
b
,
*
, Anicet Georges Lienou Koungwe
c
, David Y.K. Toguyeni
d
a
Ecole Sup´
erieure d’Ing´
enierie (ESI)-Universit´
e de Fada N’Gourma, Fada N’Gourma, Burkina Faso
b
Laboratoire d’Energies Thermiques Renouvelables (LETRE), Universit´
e Joseph KI-ZERBO, Ouagadougou, Burkina Faso
c
Ecole Sup´
erieure des Travaux Publics de Ouagadougou (ESTPO), Burkina Faso
d
Ecole Polytechnique de Ouagadougou (EPO), Ouagadougou, Burkina Faso
ARTICLE INFO
Handling Editor: Dr P Colombo
Keywords:
Multicriteria analysis
Material properties
Ecological paving stones
Waste recycling
Environment
ABSTRACT
The use of plastic waste as a resource in construction applications is an opportunity for environmental protection,
conservation of natural resources and reduction of pollution. Unfortunately, they don’t always withstand the
stresses to which they are subjected, leading to subsidence and collapsing. An analysis of the causes using the
Pareto curve shows that 74.47 % of the causes of this collapse are due to poorly formulated mixes and poor
choice of raw materials for the composite. The compressive test carried out on the rst sample of pavers studied
showed a maximum compressive strength value of 4.6 MPa, which is below the standard requirements. As a
result, the pavers were considered unsuitable for use on a T5 road. Through the use of the SUPERDECISION
software, we were able to identify two favourable constituent materials - glass/glass waste and gravel - for the
production of composite paving stones. By adding low-density plastic waste, collected, cleaned and crushed in
the form of aggregates, we obtain a compressive strength of 7 MPa with gravel and 8 MPa with glass waste. These
values are below the recommendations of the NF EN 1339 standard (Rc ≥20 MPa) for T5 trafc. The best
composition for ecological paving is therefore (PET/PP/PEBD) +sand +glass (50/12.5/37.5). Analyzing these
results shows that the raw materials used for ecological paving should be adapted to the loads.
1. Introduction
Plastic waste is thrown back into nature by its users and ends up in
our streets, gutters and drains, causing numerous oods. Plastics were
originally designed to be used as a tough and durable materials [1].
Plastic waste is a phenomenon that affects public health, the quality of
the environment and the economy in Burkina Faso and in sub-Saharan
Africa in general. In fact, the majority of products purchased are pack-
aged in plastic bags, which are discarded daily in nature, posing a major
challenge [2]. Plastic waste has been increasingly the focus interest [3]
and many initiatives have therefore been launched. Unfortunately, they
have not met expectations and some are not sustainable. However,
plastic waste is a real problem for the development and management of
our environment [2] due to the scale of the amount of waste dumped
into nature by the population.
Recycling and recovery plastic waste are therefore one of the most
promising ways to manage it [3] and prevent its proliferation. The cir-
cular economy is based on the ideal of zero waste, considering that
everything can be recycled, transformed or reused. This activity is in full
development but is problematic, mainly due mainly due to the
complexity of this material and the craft practices developed at local
level [3].
The current challenge is to reduce the pollution caused by dis-
charging waste into the environment, particularly plastic packaging, by
seeing it less as a nuisance and more as a job and income resource. One
way forward is to use these plastics as binders in the manufacture of
construction material such as concrete, pavers. So that they can replace
cement in the manufacture of new building materials, as they are less
expensive and their recycling improves the environment [4–6].
The recycled PET is used in the production of concrete for sustainable
development [7,8]. The authors observed a good result in terms of
reducing the weight of the concrete and in terms of sound insulation,
even if the aggregates (PET) not reduce signicantly the compressive
strength [7]. A combination of materials such as lateritic gravel, con-
crete, crushed stone and, more recently, recycled materials are
commonly used to construct roads around the world. The development
* Corresponding author. Ecole Sup´
erieure d’Ing´
enierie (ESI)-Universit´
e de Fada N’Gourma, Fada N’Gourma, Burkina Faso.
E-mail address: t.emalbila@gmail.com (E. Malbila).
Contents lists available at ScienceDirect
Open Ceramics
journal homepage: www.sciencedirect.com/journal/open-ceramics
https://doi.org/10.1016/j.oceram.2024.100604
Received 20 December 2023; Received in revised form 5 May 2024; Accepted 7 May 2024

Open Ceramics 18 (2024) 100604
2
of new road construction materials, such as ecological paver, appears to
be one of the solutions to eliminate plastic waste [9]. Unfortunately,
some of these roads collapsed after only a short period of use, with
visible damage as shown in Fig. 1 making it virtually unusable.
To manufacture ecological paving stones using plastic waste, the
waste is sorted and shaped, aggregates are prepared, and the mixture is
baked and melted at 260 ◦C. The resulting material is then molded,
compacted, cooled, and demolded [5]. The shaping stages are illustrated
in the Fig. 2 below.
The aim of this study is to identify the main causes of damage to
paved roads and to propose a material solution to signicantly improve
the physical and mechanical properties of ecological pavements.
2. Materials and methods
2.1. Raw materials
The main materials used in this study are presented in Fig. 3 and
consist of:
- on the one hand, plastic waste (PEDB, PET and PP) collected from
street and household bins and sand;
- on the other hand, gravel and glass waste, identied through the use
of the SUPERDECISION application.
2.2. Study framework
The present study comprises three main steps: collecting road and
raw material data, analyzing the causes of road damage, and charac-
terizing the pavement sample. The complete study framework is illus-
trated in Fig. 4 below.
The analysis of these causes is based on two methods: the Ishikawa’s
diagram and Pareto law, as shown in Fig. 5. The causes of road damage
are classied into ve families, named M1 to M5.
The Pareto diagram was used to rank the different causes identied
from the Ishikawa diagram, allowing us to identify the 20 % of causes
that we need to prioritize in order to reduce 80 % of the causes of
pavement damage. The present study compared the compressive
strength and water absorption rate of the 10 ×10 ×15 cm paving stones
from two companies. The compressive strength test was conducted using
a hydraulic press, and the value was obtained by applying formula 1:
Rc=
F
S(1)
With
- Rc: compressive strength in MPa;
- F: Applied load in N;
- S: contact surface of the sample in mm
2
.
The water absorption test was carried out following the procedure of
the standard NBN B 15–215: 1989 and the rate is determined by the
following formula 2:
Abs =
mw−md
md
x100 (2)
With
- m
w
: the wet mass in g
- m
d
: the dry mass in g
- Abs: the water absorption percentage
in %
Through multi-criteria analysis, we were able to condently choose
between several solutions. For this purpose, we have used the SUPER-
DECISION analysis grid software. This software includes various criteria
with coefcients indicating their relative weights and is based on two
methods: the Analytic Hierarchy Process (AHP) and the Analytic
Network Process (ANP). To select a suitable composite material to
enhance the ecological cobblestone formulation, we applied this method
to the present study.
The life cycle analysis of plastic waste-based paving is carried out
according to the ISO 14040 and 14044 standards. The ratio of green-
house gas is determined and the synoptic is shown in Fig. 6 [10].
To achieve this, we followed the Gabi and Open LCA methodologies,
which contain a database of different processes. We used the TRACI 2.1
method and the US-Canadian 2008 standard, which can be found in
various software packages, to inventory and calculate our data.
3. Results
3.1. Analysis of the causes of damage to plastic waste paving stones paved
road
Fig. 7 present the categories of causes and their contents which are
found on the paved road.
The Ishikawa diagram below is applied to a 1700 m
2
paved road. It
shows that the most common causes of collapse are follows:
- the raw material
- the environment.
For each of the two (02) causes, a skilled worker would know how to
use a good production method with the appropriate equipment to pro-
duce ecological paving blocks.
3.2. Ranking of causes of damage to paved roads
Once the causes have been identied, the next step is to prioritize
them. This was done using the Pareto chart. To do this, we determined
the frequencies and used the cumulative frequencies to show the rela-
tionship between 80 % of the effect resulting from 20 % of the causes,
after assigning weights to each cause identied in the Ishikawa chart.
These causes are classied from 1 to 5 according to their importance in
Table 1. With these values, we were able to plot the Pareto curve, as
Fig. 1. Presentation of the damage to a paved road-1) Slump, 2) Removal of material 3) Fading 4) Failure 5) Stripping.
E. Malbila et al.

Open Ceramics 18 (2024) 100604
3
shown in Fig. 8.
From this graph it can be seen that the raw materials account for
74.47 % of the causes of the paved road. However, from Table 1 we can
see that the problem related to the formulation, with a weight of 25, is
very signicant compared to the others. It is therefore one of the prob-
lems to which we will turn our attention.
3.3. Comparative study of the enterprises initial paving stones
This comparative studied is carried out on sand and plastic waste
based paving stone at four different proportion of sand/plastic waste
such as 50/50, 40/60, 65/35 and 60/40.
Fig. 9 below shows the results of compressive strength and water
absorption rate of these four types of plastic waste-based pavers.
The compressive strength test showed that the highest value is
Fig. 2. The process of manufacturing the paving stones using plastic wastes.
Fig. 3. Presentation of raw material a) PET bottles b) PP bags and c) Sand 0/5.
Fig. 4. Study framework.
E. Malbila et al.

Open Ceramics 18 (2024) 100604
4
achieved with the 50/50 composition and the lowest with the 35/65
composition. The water absorption rate of the different samples was in
the range of 2.5 %–5.8 %.
3.4. Multicriteria analysis of the manufactured paving stones
A multicriteria analysis allowed us to choose between several alter-
natives by breaking down an analysis grid into several criteria, each
weighted by a coefcient. In the present study, it’s used to select a
suitable composite material for improving the paving stones formula.
Five principal criteria to be considered during the material choice are
identied: price, strength, availability, recyclability, density and tem-
perature of use.
For the application, we used SUPERDECISION, a decision support
software that implements the analytical hierarchy process (AHP) and the
analytical network process (ANP). These criteria are combined in a
matrix to efciently rank options and predict outcomes. Then, Fig. 10
below shows the rank by weight of each criteria considered when
selecting materials.
The main information presented in Fig. 10 is the relation by weight
between the criteria and the predicted ranking for the choice. This graph
clearly demonstrates the signicance of each criterion in relation to the
others. So, based on the analysis, it seems that our composite material
should possess a high mechanical strength and operating temperature.
Table 2 and Fig. 11 below display the priorities resulting from the
analysis of the proposed criteria and alternatives.
The multi-criteria analysis showed that mechanical strength and
operating temperature were the main priorities in terms of criteria.
Fig. 5. Synoptic of the Ishikawa diagram.
Fig. 6. Synoptic of the paving stones life cycle analysis.
Fig. 7. Ishikawa diagram showing causes of deteriorating paved roads.
Tableau 1
Weigh of the categories of causes.
N◦Categories of causes Decreasing
weigh
% of weigh Cumulated
weigh
M1 Raw material 70 71,43 71,43
M2 Environment 14 14,29 85,72
M3 Material 8 8,16 93,62
M4 Workforce 3 3,06 96,81
M5 Method 3 3,06 100
TOTAL 98 100
E. Malbila et al.

Open Ceramics 18 (2024) 100604
5
Regarding alternatives, glass ber was the most suitable material, fol-
lowed by gravel. Glass can be blown, molded, tempered, formed, and
even 3D printed depending on the desired outcome. After collecting the
glass bottles, we crushed them using grinders and recovered only the
particles that passed through the 106
μ
m sieve. Samples were created
using various mass ratios while maintaining a consistent percentage of
plastic and varying the percentage of sand by adding either gravel or
glass-ber. The compositions of these composite materials dened in the
experiment are given in Table 3. Additionally, Low density plastic
(PEHD) was added to the plastic mixture. The results obtained from the
compressive strength are respectively presented in Fig. 12 below.
From Fig. 12, it noted that the Composite 4, made from plastic waste,
sand, and glass waste, demonstrated the highest compressive strength
among all four composites. It’s outperformed composites 1, 2, and 3,
which were made from plastic waste, sand, and gravel.
From the results in Table 4 and Fig. 11, the highest compressive
strength is achieved by mixing of 50 % plastic waste, 37.5 % glass ber,
and 12.5 % sand.
3.5. Life cycle analysis of ecological paving stones
Fig. 13 shows the results of ecological paving stones analysis.
The evaluation of greenhouse gas emissions during the life cycle of
paving stones reveals that carbon monoxide (CO) has the highest pro-
duction rate, while carbon dioxide (CO
2
) has the lowest. CO is called the
unnoticed poisons and silent killer of 21st century and its effect of
inhaling CO can cause of hypoxic injury, neurological break and even
death [11]. To reduced theses effects, catalytic conversion of carbon
monoxide (CO) is one of the most important process for human health
protection [11]. Despite this, it is not ideal to prioritize CO
2
emissions
due to the environmental issues caused by their increase, particularly
from human activities [12]. The strategies to reduce CO
2
in the building
sector are enforcing standards and policy, conducting impact assess-
ment, adopting low carbon technology, and restricting energy utiliza-
tion [10].
4. Analysis
The initial studied paver sample did not meet the standard
Fig. 8. Pareto’s diagram of causes of paved road damage.
Fig. 9. Properties of plastic waste based paving stones: compressive strength and water asborption rate.
E. Malbila et al.

Open Ceramics 18 (2024) 100604
6
requirements for use as pavers on a roadway for trafc T5, as the
compressive test yielded a maximum strength value of 4.6 MPa. The
multi-criteria analysis has enabled us to condently identify glass or
glass waste and gravel as the materials to reinforce the formulation of
the pavers. The research found that glass or glass waste best met our
criteria in terms of the desired properties, followed by gravel.
Furthermore, the addition of glass waste increased the compressive
strength to 8 MPa, exceeding the results of 5.45 MPa reported in
Ref. [13]. Similar outcomes of 7 MPa were obtained with a composite
based on tropical wood sawdust coming from Benin and recycled
polystyrene (CBPo) by Ref. [14]. These results don’t meet the standard
as specied in NF EN 1339 for T5 trafc and are under the results of
previous research. The mix containing 27.45 % PET plastic, 57.84 % ne
sand with a particle size of less than 0.250
μ
m, and 14.70 % gravel
achieved a strength of 16.6 MPa, as reported in Ref. [5].The compressive
strength of a sand matrix obtained from a river, however, increases from
5.15 to 30.61 MPa by using low-density plastic waste as a binder when
the plastic content varies from 10 % to 30 % [4]. Moreover [2],
discovered that the optimal compression resistance was achieved with a
65/35 ratio of 6.5 kg of slag and 3.5 kg of plastic, resulting in an
impressive compressive strength of 50.52 MPa. Similar outcome was
observed by Ref. [15]. Finally, these results indicate that the compres-
sive strength of pavers are inuenced according to the type of compo-
sition and the rate of plastic waste.
The water absorption rate of manufactured pavers ranges from 2.5 %
to 5.8 %, meeting the minimum standards. The hydrophobic matrix of
the plastic waste is responsible for this low absorption rate. The results
are consistent with those found by Ref. [15] which observed absorption
rates ranging from 0.95 ±1.6 % to 46 ±0.1 % for the pavers. However,
the porosity decreases from 4.99 % to 1.21 % as the plastic content in-
creases from 25 % to 50 % [4].
It’s appeared that the paving stones best composition is obtained by
Plastic waste (PET/PP/PEBD) +sand +glass (with ratio at 50/12,5/
37,5). To improve the compressive strength, the reduction of plastic
waste in the composite can be explore to meet NF EN 1339 standard
requirement as achieved by previous studies.
5. Conclusion
Based on the investigation and experimental results, it is found that
plastic and glass waste are signicant environmental concerns. The
followings conclusions were drawn:
−74.47 % of the causes of degradation are due to improper mix design
and component selection;
- ensure the optimal choice of constituents and proper mixing of the
composite;
- adjust the selection of raw materials and use of ecological pavers to
their capacity to resist these loads;
- the glass ber and the chippings, are the most suitable materials for
the production of composite paving materials;
- chippings and glass waste increase compressive strength by 52.17 %
and 73.91 %, respectively;
- the optimal composition for ecological paving is PET/PP/PEBD +
sand +glass in a ratio of 50/12.5/37.5;
- the compressive strength of the pavers studied is below 20 MPa as
specied in NF EN 1339 for T5 trafc;
- according to the OpenLCA Life Cycle Analysis, CO has the highest gas
emission rate, while CO
2
has the lowest.
Fig. 10. Comparison of material choice criteria.
Table 2
Listing of the priorities.
N◦Name of Goal node Normalized by cluster Limiting
01 Price 0,02915 0,014573
02 Mechanical strength 0,42038 0,210191
03 Availability 0,09155 0,045773
04 Recycling 0,07907 0,039534
05 Density 0,04319 0,021596
06 Ambient Temperature 0,33667 0,168333
07 Glass ber 0,2725 0,136252
08 Clay 0,17331 0,086654
09 Gravel 0,2215 0,11075
10 Carbon ber 0,20909 0,104544
11 Aramine 0,1236 0,061799
Table 3
Description of new composite mixing.
Type of mix Plastic waste
(%)
Sand
(%)
Gravel
(%)
Glass Waste bers
(%)
Composite 1 50 0 50 0
Composite 2 50 25 25 0
Composite 3 50 37,5 12,5 0
Composite 4 50 12,5 0 37,5
E. Malbila et al.

Open Ceramics 18 (2024) 100604
7
By investigating a formulation that blends plastics waste (PET/PP/
PEBD) with aggregates (sand and gravel) and glass waste bers, it is
possible to improve the physical and mechanical properties of paving
stones.
Nomenclature
Abs Water absorption percentage in %
AHP Analytic Hierarchy Process
(continued on next column)
(continued)
ANP Analytic Network Process
LCA Life Cycle Analysis
Md Dry mass in g
Mw Wet mass in g
F Applied load in N
Rc Compressive strength in MPa;
S Contact surface of the sample in mm
2
PEBD Low density plastic
PET polyethylene terephthalate
PP Polypropylene
CRediT authorship contribution statement
Etienne Malbila: Writing – review & editing, Writing – original
draft, Validation, Software, Formal analysis, Conceptualization. Anicet
Georges Lienou Koungwe: Software, Methodology, Formal analysis.
David Y.K. Toguyeni: Formal analysis, review, Validation, Supervision.
Fig. 11. Value of the priorities as function of the criteria.
Fig. 12. Compressive strength of the new composite for paving stones.
Tableau 4
Comparison of paving stones compressive strength.
N◦Type of composite Compressive strength (Rc
in MPa)
1 Plastic waste (PET/PP) +sand (ratio at 50/50) 4,6
3 Plastic waste (PET/PP/PEBD) +sand +gravel
(ratio at 50/37,5/12,5)
7,0
4 Plastic waste (PET/PP/PEBD) +sand +glass
(ratio at 50/12,5/37,5)
8,0
E. Malbila et al.

Open Ceramics 18 (2024) 100604
8
Declaration of competing interest
The authors declare that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
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