ENGINEERING CHARACTERISTICS OF VOLCANIC ROCK AGGREGATES OF RWANDA

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 7, Issue 3, May–June 2016, pp. 81–90, Article ID: IJCIET_07_03_008
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ENGINEERING CHARACTERISTICS OF
VOLCANIC ROCK AGGREGATES OF
RWANDA
Mutabaruka Jean De Dieu
Civil Engineering Department, Jain University, Bangalore, India
Dr. M.R. Pranesh
Civil Engineering Department, Jain University, Bangalore, India
Prof. Umaru Galba Wali
Civil Engineering Department, University of Rwanda
ABSTRACT
Applicability of the volcanic rock aggregates in the construction industry
are still in the stage of exploration of finding best building materials. Usage of
volcanic rock as an aggregate could prove one global identity of Rwanda in
Infrastructure engineering as the place has abundance of rich volcanic rocks
especially in the north-western part. This paper investigates the engineering
behavior of volcanic rock aggregates with respect to performance standards
e.g. compressive strength, point load test, and permeability analysis. Tested on
International Standards of ASTM D4630-96(2008) and UNIEN 1926:2006,
the outcome of the study is compared with one of the recent work on similar
direction [19] to find volcanic rock aggregates from Rwanda could be suitably
use in construction industry.
Key word: ASTM, PLT, UCS
Cite this Article: Mutabaruka Jean De Dieu, Dr. M.R. Pranesh and Prof.
Umaru Galba Wali, Engineering Characteristics of Volcanic Rock Aggregates
of Rwanda, International Journal of Civil Engineering and Technology, 7(3),
2016, pp. 81–90.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3
1. INTRODUCTION
The areas of infrastructure engineering and building materials have encountered a
revolutionary change most recently by encouraging massive innovation in building
materials. It is also well known that owing to better logistic services, availability of
building materials in any part of the world is not a bigger issue. A closer look into the

Mutabaruka Jean De Dieu, Dr. M.R. Pranesh and Prof. Umaru Galba Wali
economy of the majority of the places in Rwanda shows its growing pace of
improvement in construction industry in last 5 years [1].
With availability of huge amount of volcanic rock in north-western part of
Rwanda, the local industry has already started using the volcanic rocks in the form of
building materials [2]; Basic engineering characteristics are not documented for
Rwanda volcanic rocks. At present, construction industry of Rwanda has already
started using pyroclastics, tuffs, and ignimbrites as the main building materials. This
paper discusses about investigation carried out on volcanic rock aggregates of north-
west Rwanda and assesses its engineering characteristics with respect to its
applicability as building materials for various types of construction of structures.
2. PREVIOUS STUDIES
This section discusses about the studies that are carried out in past for the considering
natural composites e.g. volcanic rock as aggregates in building materials. Investigation
show that such forms of studies started archiving since last decade. Most recently
Kishore et al. [3] have presented a study for exploring the feasibility of basalt
aggregates in concrete mixtures. Using normal laboratory test and slump test analysis,
the authors have calculated the compressive strength of the mixture. Zou and Zboon
[4] have investigated the case study of volcanic rocks from Jordan.
The study was mainly inclined to understand the possible effect of mixing
volcanic rock aggregates on cement mortar. The outcome of the study has witnessed a
significant enhancement in flexural strength. Medeiros et al. [5] have investigated the
geological properties of Azoream rock with respective to alkali and silica as it
adversely effects the building materials. Usage of advance computing and
optimization method on volcanic rock in order to compute compressive strength was
found in the work of Ozbek et al. [6]. Mathew et al. [7] have presented a comparative
analysis on the eligibility of volcanic rocks as concrete mixtures using workability,
compressive strength, and bulk density. Zhu et al. [8] have investigated the essential
properties of natural rocks found in Alban hill using density, porosity, and stress
mainly. Similar form of the study was also conducted by Wedekind et al. [9]
considering geological location of Mexico. Aydin et al. [10] have investigated the
possible effect of volcanic rock aggregates when mixed with concrete materials to
find better compressive and tensile strength. Yasar et al. [11] and Gennaro et al. [12]
have carried out a study to investigate the effect of rocks from volcanic site in
industrial utility in Turkey and Bologna (Italy) respectively. Chemical analysis was
carried out to investigate the volcanic rock properties.
After reviewing the above studies, it can be stated that there is some considerable
research work has been carried out on the suitability of volcanic rocks to be used as
coarse aggregates. All the above studies produce result with different impressions of
compressive strength. Moreover, places like Rwanda was never researched before
whereas in reality there lies an abundance of volcanic rocks in the north-western
region of Rwanda. This fact has motivated to carry out the research in this direction of
investigating the engineering behavior of volcanic rock aggregates in north-western
part of Rwanda. The aggregate production and availability is also there in Jamaica
[13] as well as in Island [14] from commercial market viewpoint.

Engineering Characteristics of Volcanic Rock Aggregates of Rwanda
Table 1 Properties of Rocks studied by other Researchers
Sl.No. Author Country Properties
1
Gennaro et al.
[12]
Italy
i) water absorption coefficients (1.4 vs. 5.5% after
24 h,
ii) Compressive strength of the particles (2.9 vs. 0.6
MPa).
2 Yasar et al. [11] Turkey
i) uniaxial compressive strength (UCS) of 62-505
kg/cm2
, ii) hardness (SH) of 11-45, abrasion (A) of
24.60-154.30 cm3/50cm2
, iii) water absorption
(WA) of 5.92-32.49%,
iv) specific gravity (γ) of 2.30-2.71 gr/cm3,v)
density (D) of 1.33-2.13 gr/cm3 and porosity (P) of
12.37-37.81
3
Wedekind et al.
[9]
Mexico
Compressive strength attains a value of 50.83
N/mm2
.
4 Zhu et al. [8] Alban hill porosities (21.9%
5 Ozbek et al. [6]
Tomarza,
Yavuzeli
SiO2 of rocks 48.69% to 70.56%
6
Medeiros et al.
[5]
Santa
Maria
Island
SiO2 < 50%
7
Zou and Zboon
[4]
Jordan
appropriate ratio of blended aggregate is 50%,
flexural strength of 2% on 300kf/cm2
Hence, it can be seen that different authors have discussed different technique on
volcanic aggregates. Table 2 highlights the most common properties and their values.
Table 2 Properties of Volcanic Aggregates [15]
Properties Finer aggregates Course Aggregates
Colour Reddish Black
Hardness (MOHS Scale) 5–5.5 5–5.5
Specific gravity (g/cm3) 2.68 2.74
Bulk density 1107 572
Water absorption (%) 5.05 22.16
Open pores (%) 11.14 21.44
Closed pores (%) 47.09 57.21
Fullness ratio (%) 41.77 21.35
Real porosity (%) 58.23 78.65
Waste material (%) 3.29 4.10
Saturation degree (%) 8.61 28.18
Sulphur analysis (%) 0.35 0.41
Structural spoiling (C) 840 855
Melting point (C) 980 1010
Sound transmission loss (dB) 45-52 45-56

Table 3 Modulus of elasticity of some common rocks [16]
Types of Rocks Name of Rocks
Young’s Modulus of
Elasticity (E) Kg/cm2
. 105
Igneous Rocks
Basalt 2.0 – 10.0
Diabase 3.0 – 9.0
Gabbro 6.0 – 11.0
Granite 2.6 – 7.0
Syemite 6.0 – 8.0
Sedimentary Rocks
Dolomite 2.0 – 4.4
Limestone 1.0 – 8.0
Shale 0.8 – 3.0
Sandstone 0.5 – 8.6
Metamorphic Rocks
Gneiss 2.6 – 6.0
Marble 6.0 – 9.0
Quartzite 2.6 – 10.2
Schist 4.1 -7.2
3. VOLCANIC ROCK AGGREGATES AT RWANDA
The proposed study investigates volcanic rock aggregates found in north-western part
of Rwanda. Normally, such forms of the rocks are fine grained and possess the glassy
texture. Availability of the other natural rocks as well as phenocrysts also exists in the
volcanic rocks. There is also presence of robust and rough minerals densely locked
with each other. One of the volcanic rocks is basalt created from lava that has contents
of silica and their surface consists of various holes of varied diameters. One of the
biggest uncertainties in using volcanic rock as prime aggregates in building materials
is its formation. The quality of the volcanic rock aggregates are difficult to be
predicted owing to discontinuities that are entailed from generation to generations.
Therefore, although volcanic rock aggregates ensure workability but at the same time
it doesn’t guarantee much about its usage as building materials. There are 3 different
volcanoes in Rwanda i.e. Mount Kalisimbi, Muhabura, Mount Bisoke. The geological
properties of the volcanic rocks are quite equivalent to its neighboring location
Uganda. Although, some of the volcanic rocks found in Rwanda have alkaline
properties but they usually don’t have much traces of phosphates. Some of the existing
literatures have already investigated about alkaline properties of volcanic stones, but
there was no such investigation being carried out for volcanic rock aggregates found
in Rwanda. It was also not explored, if such volcanic rocks have any utility as
building materials.
The proposed study considers the volcanic rocks found in the north west of
Rwanda. This study mainly focuses on investigating the compressive strength and
permeability for considering volcanic rocks as aggregates.
4. MATERIALS AND METHODS
The proposed study uses the performance factor of compressive strength as well as
permeability to evaluate applicability of volcanic aggregates extracted from Rwanda.
Around 30 samples of aggregates were investigated with seven days of curing
duration. The volcanic rock specimen were kept in the cast and performed
investigation of six types of samples, which are all maintained with 20-30o
C. A

permeability testing is performed at normal room temperature using standard ASTM
D4630-96(2008) [17].
5. RESULT AND DISCUSSION
The proposed study considers experimental mode of research methodology. The study
mainly intends to perform analysis of compressive strength and permeability factor.
The proposed study considers measurement of the volcanic aggregate samples in
multiple directions in compliant of UNIEN 1926:2006 standard, which is later
narrowed down using average value of it. Table 4 discusses the compressive strength
(MPa) of volcanic aggregates and is expressed in terms of the recent discussion of
engineering behavior of rocks discussed by Bell [18]
Table 4 Compressive Strength of volcanic aggregates Samples
Samples Compressive Strength (Mpa) Bell Classification [18]
S1 125 High Strength
S4 354 Very High Strength
Table 4 discusses about classification of rocks discussed by Bell in 2013 [18],
which states that the compressive strength of rock is stated to be Very High Strength if
it is more than 224 Mpa. Similarly, compressive strength is stated as High Strength for
values between 112-224 Mpa. The numerical values in Table 4 show majority of the
volcanic aggregate samples to have compressive strength more than 224 Mpa.
Different compressive strength of volcanic aggregates is due to the different places of
location of samples collected. The maximum value is recorded for S4 sample and
lower value is found for S1 sample. Therefore, the samples with 224 Mpa or more
compressive strength can be deployed for cladding as well as for structural load in
engineering construction of a building. Such forms of volcanic aggregates could also
be morphed with pebble in order to generate better pavements and platforms in the
building constructions. The volcanic aggregates samples are taken from the north-
western part of Rwanda. 10 unique samples are highlighted in Table 1 Some of the
samples highlighted the vitrophyric in its texture composition with presence of
variable quantity of quartz, fragments of rock, volcanic glasses, chalcedony,
pyroxene, biotite, plagioclase etc. Some of the fragments of the rock are also found in
the form of pumice stone and rhyolite.
The study also uses Point Load Test (PLT) in order to further investigate the
compressive strength which includes positioning the volcanic aggregate sample in
between two pointed structures until the sample breaks down. We apply the following
expression to perform PLT,

2
d
FL
PLT 
eq (1)
The above equation measures the point load value considering LF as identified
load that results in failure and diameter of the sample. However, we will apply
multiple format of the above equation in order to evaluate the PLT of major sample,
blocks of sample (as well as samples with uneven sizes) using 4LF/πd2
and LF/(π/4).d2
respectively. We also interpret the variable d as average thickness of the volcanic
sample. The next part of the investigation was to check for size of the core volcanic
specimen to be 50 mm in diameter for identifying if the values require to be corrected
in terms of sizes. The outcome of the PLT is highlighted in Table 5.
Table 5 Summary of PLT on considered volcanic samples
Samples Load(N) Width(mm) Thickness(mm) d2
(mm) d(mm) PLV(Mpa)
S1 500 55 19 770.6176 27.76 0.64883
S2 3500 35 29 1156.68 34.01 3.025901
S3 6500 37 12 372.1041 19.29 17.46823
S4 9500 41 10 731.1616 27.04 12.99302
S5 12500 29 22 1073.218 32.76 11.64722
S6 15500 37 19 961.6201 31.01 16.11863
S7 11000 28 16 703.8409 26.53 15.62853
S8 7900 24 21 729.5401 27.01 10.82874
S9 10240 31 19 788.4864 28.08 12.98691
S10 14000 42 27 1160.765 34.07 12.06101
Table 5 shows that Point Load Value (PLV) which lies between 0.64 to 17.46
Mpa. The numerical outcomes show enhanced value of PLV, which goes well with
the compressive strength of the volcanic samples considered for the proposed study.
Simples S1 and S2 show low values because the different places of location
6. COMPARATIVE PERFORMANCE ANALYSIS
In order to perform comparative analysis, we choose to consider the work done by
Isik et al. [19], who have investigated the applicability of using Ahlat stone as a
volcanic aggregate in using building materials. Hence, in order to perform
comparative analysis, we consider taking the 6 different forms of volcanic aggregates
on different ratio of cement, silica fume, water, and water-binder ratio.

Table 6 Comparative Analysis of Compressive Strength
#
Volcanic
Stones
Silica Fume Cement Water W/B Existing Proposed
H1 1040 192 768 272 0.35 61.89 87.65
H2 888 216 864 304 0.35 50.74 99.15
H3 1352 144 576 200 0.35 51.57 121.88
H4 1410 200 792 280 0.35 57.54 175.98
H5 1390 176 704 248 0.35 69.14 174.98
H6 1425 132 528 184 0.35 34.54 187.22
The outcome highlighted in Fig.1 is accomplished by usual curing process for
seven days maintaining the temperature of the aggregates to be within 20-30o
C.
During the experiments, we retrain the sizes of the aggregates approximately
equivalent to 50x20 mm. Hence, the outcome proves the applicability of the proposed
volcanic aggregates in building materials.
Figure 1 Comparative Performance Analysis of Compressive Strength
The proposed system also explores the water permeability using Darcy’s
coefficient of permeability for both existing and proposed system.

Table 7 Comparative Analysis of Permeability
# W/B A/B % Replacement
Existing
m/s
Proposed
m/s
S1 0.395 2.1 1 1156.04 2073.7
S2 0.4025 2.3 1.4 908.78 1770.1
S3 0.4025 2.3 2 988.01 1146.5
S4 0.405 2.15 2.7 552.33 877.6
S5 0.42 2.4 3 763.16 1004.3
S6 0.3825 2.1 4 633.20 653.6
S7 0.39 2.3 3.2 350.21 900.4
S8 0.3975 2.3 2 1015.55 1275.1
S9 0.405 2.15 2.7 876.54 1067.3
S10 0.41 2.4 3 922.17 1120.5
The proposed system also offers enhanced water permeability showing that
volcanic aggregates of north-western part of Rwanda is highly applicable on
constructing building materials for modern infrastructure engineering.
Figure 2 Comparative Performance Analysis of Permeability
7. CONCLUSION
With the rise of population, there is a dynamic growth in urbanization that leads to a
bit of unbalanced or trade-off in present requirement of infrastructure and services
provided by construction industry. Although, bigger giants of construction industry
are still in exploration of best building materials that doesn’t’t only provide safety but
also comes with cost effectiveness. Hence, this paper presents a discussion where
volcanic rocks are highlighted to have possible contribution in building materials. The
existing literatures have been reviewed. Volcanic rocks have higher compressive
strength; however, much is not explored for Rwanda, which has some of rich
availability of volcanic rocks. It is found that samples of Rwanda have very high
compressive strength and better permeability, which is one of the essential
characteristics of building materials. Also compared our study outcomes with one
recently executed research using Ahlat stone, which is also a type of volcanic rocks.
The outcome shows proposed system to excel better performance compared to
WaterPermeability
Unique No. of Specimen
Existing…
Proposed…

existing system. It is suggested that Volcanic Rock aggregates of Rwanda possess
higher potentials. Hence it is a suitable material as an aggregate.
ACKNOWLEDGEMENTS
The Authors would like to thank the University of Rwanda and Jain University for the
opportunities and all facilities given to the researchers from the beginning, up to the
end of this research work.
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