ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY &
ENVIRONMENT

AZOJETE September 2020. Vol. 16(3):569-578
Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.

Print ISSN: 1596-2490, Electronic ISSN: 2545-5818
www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 569

ORIGINAL RESEARCH ARTICLE

COMPARATIVE STUDY OF DURABILITY AND MICROSTRUCTURE
PROPERTIES OF CONCRETE MADE WITH DIFFERENT GRADES OF

NIGERIAN PORTLAND LIMESTONE CEMENT

C. A. Fapohunda*, B. I. Famodimu, B. C. Adigo and A. S. Jeje
Department of Civil Engineering, Federal University, Oye-Ekiti, Nigeria

*Corresponding author’s email address: christopher.fapohunda@fuoye.edu.ng

1.0 Introduction
Concrete industry in Nigeria has witnessed a large turn-out of research papers on the Portland
limestone cement concrete. However, most of these works focus on either strength
comparative analysis, or strength development investigations of concrete made from the
available grades of cement (Adewole et al., 2015; Joel and Mbapuun, 2016). Other studies such
as Ezeokonkwo and Anyanechi (2015) and Olonode et al. (2015) focused their attention on
ascertaining the quality of cement grades. The available grades of cement in Nigeria are grades
32.5 and 42. 5 (in the classes of N, representing ordinary early strength; R, representing high
early strength, and S, representing standard strength). Literatures documenting research works
on durability characteristics and microstructures of concrete produced with Portland limestone
cement are scarce. It is true that until recently, developments in cement and concrete
technology have concentrated on achieving higher strengths on the assumption that strong
concrete is durable (Neville, 2011). It is now known that, for many conditions of exposure of
concrete structures, both strength and durability have to be considered explicitly at the design
stage.

However, according to Hilal (2016), in order to achieve desirable strength and good durability
requirements to prevent concrete deterioration, reducing the capillary porosity and a
substantial reduction in the total porosity as well as reduction gel porosity are necessary. This
leads to changes in the C-S-H structure, from porous to more crystalline phase. It is
established that the microstructure of concrete (cementitious paste, pore structure, and
interfacial transition zone between the cement paste and the aggregate) has a significant role in
affecting the strength of concrete. Its effect on the durability of concrete is also overwhelming.
This is because microstructure describes the porosity, permeability, and pore size distribution

ARTICLE
INFORMATION

ABSTRACT
It is now becoming apparent that concrete should not only be strong but must
also be durable. It is also believed that understanding the microstructure of the
concrete will help produce strong and durable concrete, and thus enhance
innovativeness in concrete application. This paper compares the durability
performance and microstructure development of concrete produced with
Portland limestone cement (PLC) grades 32.5R and 42.5R. The durability
investigation was accomplished through coefficient of water absorption and
sorptivity measurements. The scanning electron microscopy (SEM) was used to
investigate the microstructure of the concrete samples. The results show that
concrete produced with cement grade 42.5R showed higher durability potential
than the ones produced with grade 32.5R using 28 days curing period. Similarly,
it was also observed that concrete specimens produced with 32.5R and with
water/cement ratio of 0.40 have better durability index at the later dayscuring of
90 days in comparison to grade 42.5R concrete specimens. It can be concluded
that concrete produced using grade 42.5R cement has potential for better
durability performance in relation to concrete produced with 32.5R.

© 2020 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

Submitted 14 April., 2020
Revised 11 July, 2020
Accepted 20 July, 2020

Keywords:
Durability,
Microstructure,
Portland limestone
cement,
Sorptivity,
Water absorption

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Fapohunda et al.: Comparative Study of Durability and Microstructure Properties of Concrete made with Different Grades of Nigerian
Portland Limestone Cement . AZOJETE,16(3):569-578. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 570

of concrete. Thus, when durability of concrete is considered, the quality of concrete within the
context of low permeability comes into the play. This is because, with the exception of
mechanical damage, all the adverse influences on durability involve the transport of fluids
through the concrete. Thus, durability of concrete is closely interwoven with the
microstructure of concrete. Proper understanding of this, is therefore, necessary to provide
design engineers with a greater knowledge of concrete behaviour, so that they can optimise the
use of the material aspects of concrete in their design. This is more so, when sustainability and
environmental issues are becoming important in structural concrete design and construction.

Understanding the microstructure will enable innovativeness in the utilization of unfit, or weak
material, as complimentary material. While researchers in Nigeria have given prominence to
the study of mechanical properties of concrete produced with Nigerian Portland limestone
cement, little attention has been given to its durability and microstructure characteristics. Thus,
the aim of this investigation is to carry out comparative evaluation of concrete made with
cement grades 32.5 R and 42.5 R in relation to durability and microstructure. Specifically,
microstructural examinations using scanning electron microscopy (SEM) and water-based
durability investigations on concrete samples would be conducted. The choice of water-based
assessment of durability characteristics is informed by the observation made by the Institution
of Civil Engineers (ICE, 2019) that water could be responsible for deterioration in buildings and
other infrastructures.

2.0 Materials and Method
2.1 Materials and Mix Proportions
The following materials were used; cement, fine aggregate, coarse aggregate, and water. The
cement used was Portland limestone cement (PLC) classified as CEM II by NIS 444-1 (2014).
Two graces of cement, namely, 32.5 R and 42.5 R, being the only ones available in the Nigeria
market were used. River sand was used as the fine aggregate. The sand was obtained from river
FUOYE, a river flowing adjacent to the Ikole-Ekiti Campus of Federal University, Oye-Ekiti,
Nigeria. The sand was dried and all contaminants removed. The portion of the materials which
passes through sieve size 4.75 mm but retained in sieve size 2.36 mm was collected and stored.
An active quarry in Ikole town, where the Engineering Faculty of the University is situated,
served as the source of the coarse aggregate. In accordance to the stipulations of BS 8110
(1997), the maximum aggregate size was limited to 20 mm. Portable water, from the
University borehole, was used for this investigation. The concrete mix design method adopted
by BS EN 206 (2013), in combination with the recommendations by the Council for the
regulation of Engineering in Nigeria COREN (2017), were used to obtain the mix design. The
slump loss of between 30 – 60 mm for a target mean 28-day cube compressive strength for 25
N/mm2 was adopted for this investigation. The mix proportion is presented in Table 1.

Table 1: Mix Proportion for the Investigation
Grade W/C Ratio Mix

Designation
Cement
(kg/m3)

Sand
(kg/m3)

Gravel
(kg/m3)

Water
(kg/m3)

32.5 0.4 M14 343 686 1372 137
0.5 M15 343 686 1372 172
0.6 M16 343 686 1372 206

42.5 0.4 M24 343 686 1372 137
0.5 M25 343 686 1372 172
0.6 M26 343 686 1372 206

Concrete ingredients were batched by weight, thoroughly mixed, and cast into cube moulds
(100 x 100 x 100 mm). The cube specimens were demoulded after 24 hours and moist cured

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Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 569-578. ISSN 1596-2490; e-ISSN 2545-
5818; www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 571

until the day of testing at 28 and 90 days of curing. The specimens for microscopic investigation
were taking from the crushed 28-day samples.

2.2 Experimental Investigations
2.2.1 Characterization of Materials
In order to characterize the naturally-occurring materials used for this investigation, some
preliminary investigation was done to determine some of their properties. Physical properties
like: specific gravity, moisture content, water absorption, dry density, bulk density and sieve
analysis, were carried out on the aggregates. No preliminary investigation was performed on
the cement used. This is because the seal of the Standard Organization of Nigeria was
conspicuously displayed on the cement bags that were bought in the open market for this
investigation. This was considered a sufficient proof that it has been manufactured to conform
to NIS 444-1 (2014).

2.2.2 Durability Investigation
The durability assessment of the concrete samples was accomplished through two tests, namely:
(i) coefficient of water absorption test and (ii) sorptivity test.

2.2.2.1 Coefficient of Water Absorption Test
A measure suggested by Powers (1983), in which coefficient of water absorption is considered
as a measure of permeability of water was used for this investigation. This test measures the
rate of up take of water by dry concrete samples in a period of 1 hour. Concrete cube
specimens with dimensions 100 x100 x 100 mm were used for this test. The specimens were
cured and tested at 28 and 90 days. The concrete specimens were preconditioned by drying in
an oven at 105o C for three days until constant weight was reached and then allowed to cool
in a sealed container for three days. Since it is necessary that water flows in one direction only
in this test, the other sides of the concrete samples were coated silicone sealant. Then the
samples were kept partially immersed to a depth of 5 mm at one end in a vertical position,
while the rest of the sides were kept exposed to the laboratory air. This configuration to
assess the rate of water absorption is shown in Figure 1.

Figure 1: Set up for the measurement of Coefficient of water absorption and sorptivity of
Concrete specimens (adaptation from Ganesan et al., 2008).

The quantity of water absorbed during the first 60 min by the concrete samples was calculated.
Coefficient of water absorption values of concrete specimens after 28 and 90 days of moisture
curing were determined using the Equation 1 as suggested by Ganesan et al., 2008.

�� � � �
�
�� � �

�
(1)

2.2.2.2 Sorptivity Test
According to Neville (2011), sorptivity is a material property which characterizes the tendency
of a porous material to absorb and transmit water by capillarity. For the sorptivity test, the
configuration, cube specimens and sample preparation used for coefficient of absorption as

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Fapohunda et al.: Comparative Study of Durability and Microstructure Properties of Concrete made with Different Grades of Nigerian
Portland Limestone Cement . AZOJETE,16(3):569-578. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 572

shown in Figure 1, were also used. The difference is that, in this case, the tests were conducted
at selected times 0, 2, 4, 8, 10, 20, 30, 60, 90 and 120 minutes. At the selected times, the
samples were removed from the water, excess water blotted off with a damp paper towel and
then the sample was weighed. The samples were then replaced in the water for the selected
time period. Then the gain in mass per unit area over the density of water was plotted versus
the square root of the elapsed time. The cumulative water absorption (per unit area of the
inflow surface) is believed to increase as the square root of elapsed time (t). The slope of the
line of best fit of these points was taken as the sorptivity value. The sorptivity values of blended
concrete specimens after 28 and 90 days of moisture curing were calculated by the following
formula (Equation 2) suggested by Stanish et al. (1997).

� � �
��

(2)

2.2.3 Microstructural Investigations
In order to carry out microstructural investigation of the concrete samples, a JEOL Scanning
electron microscopy (SEM) equipment with energy dispersive spectrometry capabilities shown
in Figure 2, was used. The equipment model comes with energy dispersive spectrometer
(EDX), and allows high resolution identification of elements and compounds present in
prepared 2-D cross-sections of aggregate samples to be obtained. The SEM studies were
conducted on broken samples of concrete samples cured for 28 days in order to investigate
their morphological structures. The samples were collected from the innermost core of the
concrete cubes after crushing. Each of the samples are then prepared into appropriate size that
fit into the specimen chamber of the SEM equipment. Samples were then freeze-dried, cut and
polished and examined on the backscattered electron (BSE) mode of the SEM equipment. The
range of scale used in SEM analysis was 5μm with the resolution of x 10000.

Figure 2: The SEM Equipment used for Microstructural Investigation of Samples

3.0 Results and Discussion
3.1 Materials Characterization
Some of the properties of the aggregates are shown in Table 2.
Table 2: Some Physical Properties of the Aggregates

Sand Gravel
Specific Gravity 2.63 2.67
Bulk Density (kg/m3) 1666.67 1641.67
Water Absorption (%) 2.00 2.00
Moisture Content (%) 0.00 0.00
Coefficient of curvature (Cc) 0.88 0.98
Coefficient of uniformity (Cu) 3.00 2.43

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Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 569-578. ISSN 1596-2490; e-ISSN 2545-
5818; www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 573

It was observed that the specific gravities of the sand and gravel are in the range of 2.63 and
2.67 respectively. Specific gravities of natural aggregate according to Gambhir (2013) should be
between 2.5 and 2.8. Thus, both the sand and gravel used in this investigation can be
considered as natural aggregate. Additionally, the densities of the aggregate ranged from 1280
to 1920 kg/m3; for water absorption, it is 0 to 8% and the moisture content is 0 – 2% for sand
and 0 - 10% for gravel. All these vales obtained for density, water absorption and the moisture
content of both the sand and gravel fell between the ranges used in normal concrete (ACI,
1999). Also, the coefficient of curvature for both are close to 1, thus indicating that both are
well-graded, while the coefficient of uniformity of less than or equal to 4 recorded for both
sand and gravel suggest that both are uniformly graded (Iowa, 2020). Overall conclusion of all
of these is that the materials are good for concrete production.

3.2 Coefficient of Water Absorption
The results of the coefficient of water absorption are presented in Table 3.
Table 3: Coefficient of Water Absorption for the Concrete Specimens

Water/Cement Ratios Ka (m2/s) x 10-8

28 days 90 days
32.5R 42.5R 32.5R 42.5R

0.40 5.2 x 10-9 2.01 x 10-10 2.5 x 10-9 3.73 x 10-9
0.50 7.72 x 10-9 7.72 x 10-10 1.9 x 10-9 2.78 x 10-10
0.60 7.72 x 10-9 2.78 x 10-10 4.9 x 10-9 1.51 x 10-10

At 28 days, the values of coefficient of water absorption obtained for cement grade of 42.5R
were lower than that of grade 32.5R at all the water/cement ratios. Since coefficient of water
absorption is a measure of permeability, it can be said that concrete specimens produced with
cement grade of 42.5R are less permeable in comparison to concrete produced with cement
grade 32.5R. This can be due to the fact that, at the early ages, more C-S-H gel are produced
by concrete with cement grade 42.5R, which has a densifying effect. However, at 90 days curing
period, concrete specimens produced with grade 32.5R cement displayed low permeability at
water/cement ratio of 0.40 than that of concrete produced with grade 42.5R cement. At the
water/cement ratios of 0.50 and 0.60, the concrete specimens produced with grade 42.5R
cement have smaller values of coefficient of water absorption, hence low permeability.
Furthermore, it can be seen from Table 3 that the observed values of coefficient of water
absorption reduced with curing age. This suggested that prolonged curing of concrete samples
resulted in more production of C-S-H gel with pore-refining effects leading to reduction in
permeable voids.

3.3 Sorptivity
Sorptivity test measures the rate of absorption of water by capillary suction of unsaturated
concrete placed in contact with water; no head of water exists (Hall, 1989; Dias, 2000 and
Neville, 2011). The results of the sorptivity investigation are presented in Table 4.
Table 4: Sorptivity for the Concrete Specimens (10-2 mm/s1/2)
Water/Cement Ratio 28 days 90 days

32.5R 42.5R 32.5R 42.5R
0.40 0.048 0.097 0.073 0.058
0.50 0.034 0.026 0.032 0.018
0.60 0.032 0.022 0.031 0.015

At 28 days of curing, with the exception of concrete samples with water/cement ratio of 0.40,
the values rate of absorption of water obtained for grade 42.5 R specimens were lower than
that of grade 32.5 specimens. Also, the values of the rate of absorption of water reduced with
water/cement ratio for all the concrete specimens. This is ostensibly due to higher water

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Fapohunda et al.: Comparative Study of Durability and Microstructure Properties of Concrete made with Different Grades of Nigerian
Portland Limestone Cement . AZOJETE,16(3):569-578. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 574

content in concrete samples at higher water/cement ratios. At 90 days of curing, the values of
the rate of water absorption for concrete samples produced with grade 42.5R were lower than
that produced with grade 32.5 R specimens at all the water/cement ratios. Furthermore, the
sorptivity values at 90 days reduced with water/cement ratios for all the specimens, due to
higher water content at higher water/cement ratios. It also ought to be observed that sorpitivy
at 90 days were lower than sorptivity values at 28 days for all the specimens. It is known that
prolong curing results in the densification of the concrete matrix, thus inhibiting the rate of
water absorption by the specimens.

3.4 Microstructure of Concrete Specimens
The scanning electron microscopy (SEM) images of the concrete specimens at 28 days of curing
are shown in Figure 3. Microstructure is usually explained in terms of distribution of pores,
sizes of pores and interconnectivity of the pores. Figure 3 shows the images of the
microstructure of concrete produced with cement grades 32.5 R and 42.5R at the same
water/cement ratio. It could be observed that the microstructure of concrete produced with
grade 32.5R at 0.40 water/cement ratio consisted of big pores or voids in comparison to grade
42.5R concrete. This suggests that concrete produced with grade 32.5R are likely to be porous
and less durable than concrete produced with grade 42.5R. This observation is consistent with
the results of permeability measured through the rate of water absorption test as presented in
Table 3. This pattern can also be observed in the images of the microstructure of concrete
samples produced with water/cement ratio of 0.50 for both grades of cement. In particular, the
very large pores, from the images of concrete produced with grade 32.5R cement is very
glaring. There is also an evidence in the microstructure of weak interfacial zone (ITZ) between
the vicinity of aggregate and the hydrated products. This ITZ is the weakest region in concrete
due to its higher porosity resulting from the poor packing of cement particles (Mehta and
Monteiro, 2006). Although, the images of concrete samples produced with grade 42.5 R
cement and with water/cement ratio of 0.60, showed a microstructure consisting of large pores,
there is evidence that the pores are not connected. Figure 4 showed the EDX spectrum of the
samples from which the elemental counts presented in Table 5 was extracted for clarity.
Silicates and calcium are the constituents of the strength-forming products of hydration. Their
counts, through the EDX spectrum and the ratio of calcium to silicate are strength indicator.
From Table 5, the ratio

�
�

for concrete produced with 32.5R grade of cement increase
marginally with increase in water/cement ratio. However, for concrete produced with grade
42.5R cement, the ratio increases with water/cement ratio.

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Arid Zone Journal of Engineering, Technology and Environment, September, 2020; Vol. 16(3) 569-578. ISSN 1596-2490; e-ISSN 2545-
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Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 575

Figure 3: The SEM Micrograph of the Concrete Samples at 28 days of Curing

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Fapohunda et al.: Comparative Study of Durability and Microstructure Properties of Concrete made with Different Grades of Nigerian
Portland Limestone Cement . AZOJETE,16(3):569-578. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 576

Figure 4: EDX Spectrum of the Concrete samples at 28-day curing

Table 5: The C/S Ratio of the Mixes
Concrete Mix Mix Designation Ca (C) Si (S) �

�
32.5 M04 40.60 15.45 2.63

M05 35.50 25.50 1.39
M06 41.60 15.65 2.66

42.5 M04 40.50 23.50 1.72
M05 43.50 20.50 2.12
M06 44.50 20.50 2.17

According to Nazari et al. (2011), increasing ratio means increasing strength-forming activities.
This conclusion is consistent with the results of sorptivity presented in Table 4.

4. Conclusions and Recommendations
4.1 Conclusions
From the analysis of the results of this investigation, the following conclusions can be made.
The values of coefficient of water absorption obtained for concrete specimens produced with
grade 42.5 R are lower than specimens produced with cement grade 32.5 R at 28-day curing.
At 90 days curing age, concrete specimens produced with grade 32. 5R cement had lower
coefficient of water absorption at lower water/cement ratio of 0.40. The microstructure of
concrete produced with 32.5R are more porous than those produced with grade 42.5R cement
at 28-day curing .

4.2 Recommendations
The concrete specimens produced with cement grade 32.5R resulted in low durability,
especially at the structural age of 28 days curing. Since both of them are available in the Nigeria
market and both are equally widely used, the need to improve the durability performance of
concrete made with grade 32.5R cannot be overemphasized. The use of highly reactive
pozzolans like rice husk ash, that abounds in Nigeria (Joel, 2010, Oyekan and Kamiyo, 2011 and
Abalaka, 2013), should be given consideration by incorporating it into concrete mix with
cement grade 32.5R. Incorporating pozzolans in the concrete with 32.5R cement grade,
according to Büyüköztürk and Lau (2020) will improve the concrete durability performance by
strengthening the hydrated cement paste through the adding of mineral additives. This will help
in generating a crystalline C-S-H gel with lower gel porosity, compared to a conventional
amorphous C-S-H gel. Reduction in the porosity of the paste, which translate to low
permeability and improved durability, will result.

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Fapohunda et al.: Comparative Study of Durability and Microstructure Properties of Concrete made with Different Grades of Nigerian
Portland Limestone Cement . AZOJETE,16(3):569-578. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: christopher.fapohunda@fuoye.edu.ng 578

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