Revista Română de Materiale / Romanian Journal of Materials 2023, 53(1), 23 - 32 23

ASSESSMENT OF SOME MECHANICAL PROPERTIES FOR CONCRETE

BASED ON ALUM SLUDGE AND METAKAOLIN

HADEL OBAIDI1, AHLAM ABDUL-RHEEM FARHAN1, TAHA H. ABOOD AL-SAADI2

1
Department of Water Resources Techniques, Institute of Technology/ Baghdad, Middle Technical University, Iraq
2
Fuel and Energy Techniques Engineering Department, Technical Engineering College-Baghdad/ Baghdad, Middle Technical University, Iraq

Since concrete is a consistently reliable building material, its importance to all nations' economies cannot be overstated.
However, the cement and concrete industries continue to generate massive amounts of waste which results in the emission of
carbon dioxide which is one of the environmental issues. Therefore, reducing the amount of cement is important by partially
replacing one of the waste materials. In this research; two municipal materials were used as alternatives for cement. It is
considered available in quantities with appropriate price as compared to other mineral materials. In addition, this research was
interest given to assess the strengths and durable behaviour of concrete production with these addition materials. The amount of
metakaolin used is (1-15) wt% and alum (1-5) wt% of cement. The central composite design (CCD) method was used in conjunction
with the response surface method to design concrete mixtures for this research and to analyse the results obtained from laboratory
tests. An empirical model was given for compressive strength, bulk density and splitting tensile strength. All concrete specimens
were cured after 7 and 28 days. The best results were found when metakaolin was used between (1-3) wt% and alum sludge
between (1.6-3) wt% as mixed materials to produce concrete and as a partial replacement of cement.

Keywords: Metakaolin; Alum sludge; Concrete; Minitab software; Compressive strength; Splitting tensile strength; Durability

1. Introduction energy use and CO2 emissions [8, 9 and 10]. From
the literature review, it has been found that
The industry of construction is growing fast metakaolin negatively influences the workability of
around the world. The huge growth in construction concrete which decreases with increasing the
is driving an increase in the demand for building replacement percentage of metakaolin until 15%
materials. Concrete is one of importance of the due to its high fineness. It has also been found that
building materials used in the industrial countries. the strength of metakaolin has been remarkably
Even though cement, aggregates, and water are all increased when replacing the cement with
integral constituents that must be used in the metakaolin from 10 to 15% compared to the poor
creation of concrete, the energy needed to produce effect of replacement ratios from 15 to 20% [11-15].
cement makes it expensive and harmful to the Therefore, the utilization of metakaolin as a
environment. Too much of a challenge has been supplementary cementitious material is considered
faced by the researchers to find varying alternatives beneficial in terms of environmental, technical and
or supplementary construction materials. These economic issues. Another alternative construction
may be characterized by cheaper, recycled and material in terms of reducing environmental impact
environmentally friendly materials to manufacture and saving costs is alum sludge. This material is a
concrete that is more durable, the life cycle of good final waste generated from the plant for drinking
strength that affects the cost of long-lasting it [1-4]. water treatment and is not considered a natural
Metakaolin is one of the alternative building pozzolanic material. Because of differences in
materials that is frequently used as a mineral source water and chemical composition from one
admixture to assist concrete to have better plant to the next, alum sludge is classified as a by-
properties, produce at a lower cost, and emit less product material [16-18].
CO2 due to the creation of the cement that is used Over the last decades, the waste water
in its production [5, 6 and 7]. It is a natural treatment plant has increased and had a negative
pozzolainc material [8]. The main advantages of this effect on the environment. Sludge is one of the main
material include its capacity to increase concrete wastes that are difficult to dispose of in an
strength and its high efficiency when used as a environmentally friendly manner and produces a lot
partial replacement for cement [5]. All experimental of pollution [19,20]. Much research has been done
testing indicated that mortar's sulphate resistance on the use of alum sludge in concrete to reduce the
had increased by around 30% and that concrete's harmful effects of this sludge on the environment. As
compressive strength had increased by about 50%. a result, it will lead to less cement being used while
Additionally, there has been a 40% reduction in still producing concrete with acceptable durability.


Autor corespondent/Corresponding author,
E-mail: hadel.obaidi@gmail.com
24 Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete
based on alum sludge and metakaolin

Previous research, for example, demonstrated that  Alum sludge was obtained from Unity Water
the amount of sludge used in the concrete mixture Station in Iraq. It was dried under the sunshine
affects the strength and stiffness of the concrete [19- for 3 days, after that manually milled by using
21]. Another study has shown that the sludge was a steel hammer. Then, the powder dried in
subjected to heat treatment to reduce the harmful electric oven at 120°C for 3 hrs. Consequently,
materials and obtain the best concrete results [21]. removed any impurities particles from this
Sometime, it can use the sludge as partial powder by using sieving technique (No.200). It
replacement of sand or cement that depends on is noteworthy, the sieved alum sludge powder
particles size of them. The previous study showed was treated with 70% alcohol in order to
acceptable results for both replacements in different murder the harmful bacteria. Finally, the wet
percentages [20]. Many researchers have examined alum sludge powder dried at 120°C for 1 hr.
how to use the sludge in the production of building The resulted powder (off white color) has 2.34
and construction materials, for example, the as specific gravity. Table 4 represents the
production of brick, artificial aggregate, cement, and chemical compositions of resulted alum sludge
ceramics [22-26]. powder.
Some researchers have experimented with
Table 1
varying amounts of alum sludge as a partial Gradation of sand
replacement for cement to produce concrete with Iraqi specification
(2.5-15) % cement by weight. They found that the Opening size of sieve limits I.O.S.45/1984
Passing %
addition of it was between 6 to 7.5 % and improved (mm) Grading zone (2)
the strength of concrete after 7 and 28 curing days [28]
10 100 100
[4, 16 and 27]. From the literature, a lot of research 4.75 92.39 100-90
has shown reusing the sludge as a supplementary 2.36 75.21 100-75
material for cement in concrete but very limited 1.18 59.24 90-55
research has shown the use of metakaolin and alum 0.6 46.19 50-35
sludge together in it. 0.3 10.16 30-8
0.15 0.07 10-0
In this research, an attempt has been made
to produce a concrete mixture from alum sludge and
Table 2
metakaolin as cement partials in different Gradation of gravel
percentages and examine the main properties of Iraqi specification limits
concrete. This technique is beneficial to the Opening size of Passing
I.O.S.45/1984 (5/14 mm)
sieve (mm) %
environment by decreasing the waste that is [28]
disposed in landfills and it is also useful from the 20 100 100
14 94.5 100-90
economic perspective by producing concrete with
10 57.34 85-50
acceptable strength and durability. 5 0 10-0

2.Materials and Methods Table 3

2.1 The Materials Used Chemical Properties of metakaolin
 Ordinary Portland cement type 1 was used in Particles Content %
this study, produced by United Cement SiO2 51.77
Company, known in the local market as Al2O3 35.50
Fe2O3 3.29
Tasulujah Bazian.
CaO 0.50
 Fine aggregate (sand) and coarse aggregate MgO 0.10
(gravel) were used in this study with specific SO3 0.06
gravities of 2.5 and 2.65 respectively. The Na2O 0.09
maximum size of the used gravel is 10 mm. The K2O 0.58
gradation of sand and gravel was shown in L.O.I. 5.45
Tables 1 and 2. Table 4
 The superplasticizer used in this study was a Chemical Properties of alum sludge
high-performance superplasticizer based on
polycarboxylic polymer, known as PC200, Particles Content %
produced by Don Construction Products Ltd. SiO2 39.14
 Tap water was used throughout this work in Al2O3 13.80
mixing concrete without any additives. Fe2O3 8.06
CaO 16.3
 Iraqi metakaoline powder (off white color)
MgO 2.68
obtained after thermal treatment at
SO3 0.23
temperature 700°C for 1hr [27]. The specific
Na2O 0.33
gravity of this powder was 2.32, as shown in
K2O 2.02
Table 3, which illustrates the chemical
L.O.I. 17.40
composition of used metakaolin powder.
Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete 25
based on alum sludge and metakaolin

Table 5
Codes used in the CCD for factors (independent variables) and their real experimental values

Metakaolin (W %) Alum sludge (W %)

Coded Level
X1 X2
-1.414 1 1
-1 3.050 1.586
0 3 8
1 12.95 4.414
1.414 15 5
Table 6
Coded levels utilized with their real values of metakaoline and alum sludge
Coded Variables Real Variables
Alum sludge
Mix No. Metakaolin
X1 X2 w%
w%
1 -1 -1 3.050 1.586
2 1 -1 12.95 1.586
3 -1 1 3.050 4.414
4 1 1 12.95 4.414
5 -1.414 0 1 3
6 1.414 0 15 3
7 0 -1.414 8 1
8 0 1.414 8 5
9 0 0 8 3
10 0 0 8 3
11 0 0 8 3
12 0 0 8 3
13 0 0 8 3

Table 7
The concrete mixes based on 1m3

Alum
Mix Cement Sand Gravel Metakaolin Water SP
Sludge W/C
No. Kg/m3 Kg/m3 Kg/m3 % L/m3 L/m3
%
R 485 820 748 0 0
1 484.95 820 748 3.050 1.586
2 484.85 820 748 12.95 1.586
3 484.92 820 748 3.050 4.414
4 484.82 820 748 12.95 4.414
5 484.96 820 748 1 3
6 484.82 820 748 15 3
182.4 4.365 0.37
7 484.91 820 748 8 1
8 484.87 820 748 8 5
9 484.98 820 748 8 3
10 484.98 820 748 8 3
11 484.98 820 748 8 3
12 484.98 820 748 8 3
13 484.98 820 748 8 3

2.2 Methods Y = b0 + b1 x1 + b2 x2 + b11x12 + b12x1x2 + b22x22 (1)

The experimental design includes statistical Where Y is the predicted response, X1
design experiments, estimation of coefficients and X2 are coded levels of the variables
through a mathematical model with predicted (metakaolin and alum sludge) % and (b0, b1, b2, b11,
response, and statistical analysis. Moreover, it can b12 …) are regression coefficients.
obtain the largest amount of information from a The equation for each property
small number of experiments. In this study, Central (compressive strength, bulk density and splitting
Composite Design (CCD) was used. Two factors tensile strength) is created to obtain three
were chosen as independent variables, (wt. % of responses Y1, Y2 and Y3 respectively. Thirteen
metakaolin and alum sludge additions). The experimental runs are required to use CCD of two
dependent output response variables are independent variables with five different levels of
compressive strength, bulk density and splitting each variable designated by the codes (-1.414, -1,
tensile strength. All responses were fitted to a 0, 1 and 1.414). The selected factors with the actual
second quadratic model as shown in Eq. 1, and the and coded levels according to the design are
model's adequacy was confirmed using analysis of represented in Tables 5 and 6. The data was
variance (ANOVA). analyzed using Minitab V16 (Minitab Inc., PA, and
USA) statistical and graphical software.
26 Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete
based on alum sludge and metakaolin

2.3 Mix proportions and specimen’s 3.Results and Discussion

preparation 3.1 Bulk density results
The percentage of partial replacement for Figure 1 illustrates the effect of curing time
metakaolin and alum sludge used was within the of studied mixes on the bulk density of concrete.
range of (1-15) % and (1–5) % of the weight of From the results, it can be shown that the addition
cement respectively as shown in Table 7. The ratios of metakaolin and alum sludge leads to a reduction
of replacement for metakaolin and alum sludge were in density for all curing times compared to the
dependent on several studies that proved that these reference mix (R).
ratios were the best when used to produce the Although the metakaolin and alum sludge
concrete [27, 29-31]. replacement percentages were small in comparison
Two types of specimens have been used in to the cement for mixes (1, 3 and 5), they contained
this study. The bulk density, durability and the the percentages of metakaolin and alum sludge
compressive strength were assessed for cubic (3.0503:1.5858) and 4.0503:4.414) (1:3)
specimens of 100x100x100 mm3, while the splitting respectively. It can be seen that the resultant
tensile strength was assessed for the cylindrical density of them was the best, see Table 7.
specimen’s of100 x 200 mm3. In contrast to what can be seen from the
All mixtures were done using manual mixing bulk densities of concrete results for mixes 2, 4 and
as followed the American specification (ASTM C- 6 containing metakaolin and alum sludge (12.95:
192-02) [32] until having a homogenous 1.586), 12.95: 4.414), and 15:3, respectively, it can
mixture. The alum sludge and metakaolin were be observed from the figure that the density has
added to the mix as a partial replacement of the been dramatically decreased compared to other
weight of cement. After thoroughly mixing all mixes. In addition, the values of concrete density for
materials, the first part of the mixing water was mixes (7, 8) were close and better than the density
added to the mixture continuous mixing; thereafter, values for mixes (9-13).
the superplasticizer was added. Finally, the second 3.2 Compressive strength results
part of water was added. All mixtures have been Figure 2 shows the effect of curing time on
casted in the molds and compacted by vibrating the compressive strength of all mixes studied. It is
machines for 1 minute. Consequently, the noted that there is an acceptable increase in the
specimens were de-molded and cured in water at compressive strength of the mixtures containing
room temperature up to 7 and 28 days. metakaolin and alum sludge for the mixes (1, 5) that
contained (metakaloin: alum sludge) (3.050:1.586)
2.4 Specimens testing (1:3) respectively. In contrast to the behaviour of
The bulk density of the hardened concrete mixes (4, 6) that contained (metakaloin: alum
cubic was determined by American specification sludge) (12.95: 4.414) (15:3), where there was a
(ASTM C652-13) [33]. The compressive strength significant decrease in compressive strength with
test was carried out using E.L.E. international- the progression of the curing time. The values of the
2007/UK/A.D.R.-2000- standard machine- compressive strengths of mix (1 and 5) were (44.70
instrument. It was performed according to B.S. and 43.74) MPa respectively, while the values of the
1881: Part 116 (1989) [34]. Splitting tensile strength strengths of mix (4 and 6) were (2.13 and 2.10) MPa
test was followed the American specification (ASTM respectively after 28 days.
C496-06) [35]. This behaviour can be explained by the fact
Durability test was performed according to that the use of metakaolin and alum sludge with
(ASTM C 666, 2003) [36]. The type of durability test high percentages has a reverse reaction that leads
was freezing and thawing test. This test carried out to a greatly reduced in compressive strength
by putting the cubes specimens from each concrete values. Unlike what happened when using low
mix in the fridge freezer at temperature of (-17±1) °C percentages of these materials with cement where
for about 7 hours. These specimens were taken out good resistance can be obtained, both of them have
of freezer and were placed in water at temperature acceptable properties to improve the strength of the
(+17±1) °C for about 19 hours. This procedure of concrete.
freezing and thawing was repeated for 8 cycles. To The strengths of the metakaolin and alum
find out how these specimens would behave under sludge-containing mixes (2, 3 and 7) were
these conditions, ultrasonic pulse velocity tests 12.95:1.586, 3.050:4.414, and 8:1, respectively,
were performed on them both before and after almost identical in terms of compressive strength,
freezing and thawing. This test was carried out in where the slightly increase about (22.05, 27.82, and
accordance with British standards (BS: 1881 part 23.92) MPa, respectively. In addition, mixes 8 to 13
203:1986) [37]. The ultrasonic device was designed had approximately the same trend and slightly
to operate at a frequency of 55 kHz. increased in the compressive strength values which
ranged from 13.07 to 17.67 MPa after 28 days.
Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete 27
based on alum sludge and metakaolin

Fig. 1- Effect of curing time on the bulk density of concrete

Fig. 2- Effect of curing time on the compressive strength of concrete

Fig. 3 - Effect of curing time on the splitting tensile strength of concrete

3.3 Splitting tensile strength results At 28 days, the tensile strengths of mixes (2
As demonstrated in Fig. 3, the behavior of and 7) were approximately 3.21 and 3.98 MPa
concrete's tensile strength for all mixes was about respectively. When compared to the strength
the same as that of its compressive strength. results for mixes from (8 to13), the lowest values at
It is clear that the effects of the metakaolin 28 days dropped between 2.51 and 2.47 MPa.
and alum sludge additions on strength resulted in
mixes (1, 3, and 5) having acceptable strengths of 3.4 Analysis of variance (ANOVA)
around (4.54, 3.78, and 5.90) MPa at 28 days Table 8 illustrates the experimental results
respectively. While mixtures (4, 6) had significantly for all mixes studied by using variance analysis
decreased in tensile strength at 28 days, by around (ANOVA). Consequently, Tables (11, 12 and 13)
(0.47 and 0.40) MPa, respectively. present the findings. The experimental results are
used to build the regression model equations
28 Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete
based on alum sludge and metakaolin

Table 8
The matrix design along with the experimental results
Independent variables
Responses(dependent variables)
Coded Real
Exp. Y1
Meta Alum Y3
No. Y1 Predict Y2 Y2 Y3
X1 X2 Kaolin wt% Predict
Exp. ed Exp. Predicted Exp.
w% ed
1 -1 -1 3.050 1.586 44.77 42.206 2355 2355.306 4.54 4.851
2 1 -1 12.95 1.586 18.86 14.477 2344 2330.547 3.21 2.735
3 -1 1 3.050 4.414 27.82 29.651 2350 2363.953 3.78 4.455
4 1 1 12.95 4.414 2.13 2.138 2293 2293.194 0.47 0.360
5 -1.414 0 1 3 43.74 43.728 2377 2367.021 5.9 5.248
6 1.414 0 15 3 2.1 4.666 2290 2299.479 0.4 0.857
7 0 -1.414 8 1 24.46 28.841 2339 2348.399 3.98 4.128
8 0 1.414 8 5 13.07 11.237 2338 2328.101 2.52 2.169
9 0 0 8 3 15.27 16.399 2273 2281.600 1.77 1.606
10 0 0 8 3 17.67 16.399 2286 2281.600 1.47 1.606
11 0 0 8 3 15.73 16.399 2279 2281.600 1.65 1.606
12 0 0 8 3 16.22 16.399 2290 2281.600 1.55 1.606
13 0 0 8 3 17.1 16.399 2280 2281.600 1.59 1.606

Table 9
Analysis of variance for compressive strength Y1

Source DF Adj SS Adj MS F-Value P-Value

Metakaolin X1 1 1525.85 1525.85 171.97 0.000
Alum X2 1 309.88 309.88 34.93 0.001
X1X1 1 105.76 105.76 11.92 0.011
X2X2 1 23.05 23.05 2.60 0.151
X1X2 1 0.01 0.01 0.00 0.972
Pure Error 4 3.88 0.97
Total 12 2015.79

Table 10
Analysis of variance for bulk density Y2

Source DF Adj SS Adj MS F-Value P-Value

Metakaolin X1 1 4561.9 4561.87 34.53 0.001
Alum X2 1 412.0 412.05 3.12 0.121
X1X1 1 4639.5 4639.52 35.12 0.001
X2X2 1 5581.3 5581.26 42.25 0.000
X1X2 1 529.0 529.00 4.00 0.085
Pure Error 4 173.2 43.30
Total 12 15474.9

Table 11
Analysis of variance for splitting tensile strength Y3
Source DF Adj SS Adj MS F-Value P-Value
Metakaolin X1 1 19.2817 19.2817 83.50 0.000
Alum X2 1 3.8388 3.8388 16.62 0.005
X1X1 1 3.6367 3.6367 15.75 0.005
X2X2 1 4.1374 4.1374 17.92 0.004
X1X2 1 0.9794 0.9794 4.24 0.078
Pure Error 4 0.0501 0.0125
Total 12 32.5955

(second-order polynomial) that relate the response. The p-values for the coefficients in regression
As a result, three equations for compressive analysis reflect whether these relationships are
strength, bulk density and splitting tensile strength statistically significant. A low p-value (<0.05)
have been obtained. indicates that they are statistically different from
zero at the 95% confidence level. Therefore,
Where coefficients' p-values (<0.05) are statistically
Y1: Compressive Strength (MPa), Y2: bulk significant. Tables (11, 12 and 13) provide the F and
density (kg/m3), Y3: Splitting Tensile Strength P values for all linear, quadratic and interaction
(MPa) effects of the parameters. The smaller the value
Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete 29
based on alum sludge and metakaolin

Table 12
Summary of the response regression analysis
Response R2 (% ) Adjusted R2 (%) Predicted R2 SD
s (%)
Y1 96.92 94.72 79.16 2.979
Y2 94.02 89.76 63.71 11.494
Y3 95.04 91.50 65.59 0.481

of P, the bigger the magnitude of F and thus the The contour plot shows the best limits for the
more significant the corresponding coefficient term. replacement percentages of metakaolin and alum
The coefficients for the linear effect of the factors sludge, which ranged up to 2% of metakaoline and
metakaolin (p=0) and alum sludge (p=0.001) for the up to 1.8% of alum sludge, which contributed good
compressive strength are significant, as shown in strength to the concrete.
Table 9. The interaction between the variables From Fig 5 it can be observed more
metakaolin and alum sludge was not significant clarification of the results. The bulk density was
(p=0.972).Moreover, the quadratic effect of increased with decreasing the replacement
metakaolin (p=0.011) is significant, whereas it is percentage of metakaolin and alum sludge.
less so for alum sludge. The contour plot shows the area that gives a
For bulk density Table 10, the coefficients of low density when the percentages of addition of
all the effects of the factors were significant except metakaolin are between 8 to 13 and the alum
for the linear effect of alum (p=0.121) and the sludge percentages are between 2.7 to 4. This
interaction between the variables kaolin and alum agrees with mixes 4, 6, and 9.
(p=0.085). While the results for splitting tensile Figure 6 presents the effect of the
strength were all significant, except for the replacement percentage of metakaolin and alum
interaction between the variables kaolin and alum sludge on the splitting tensile strength. It can be
(p=0.078), as shown in Table 11. seen that strength values reduced with increasing
The regression equations in uncoded units are given in the proportions of metakaolin and alum sludge as
in Eqs. (2), (3) and (4). shown in 3D surface plot. In the contour plot, it can
be observed that the area represented by the
1- Compressive strength (Y1) = 70.48 - 5.360 X1 smallest triangle at the bottom and top on the left of
- 9.92 X2 + 0.1591 X12 + 0.910 X22 + 0.008 X1X2 the figure showed the best results of replacement
……… (2) percentages of about 2.5% of metakaolin with 1.6%
of alum sludge, and 2% of metakaolin with 4.4% of
2- Bulk density (Y2) = 2490.9 - 16.76 X1 - 76.9 X2 alum sludge respectively.
+ 1.054 X12 + 14.16 X22 - 1.643 X1X2 …… (3)
3.6 Durability results
3- Splitting tensile strength (Y3) = 9.25 - 0.574 X1
- 2.238 X2 + 0.02951 X12 + 0.3856 X22 In this research, this test was used to
- 0.0707 X1X2 ………. (4) determine the durability of concrete after 4 and 8
cycles of freezing and thawing. From Fig. 7, it can
The ANOVA for the three properties be seen that the pulse velocity of mixes (1, 3 and 5)
showed that the second-order polynomial model is higher than mixes (4 and 6) before and after
Eqs. (2), (3), and (4) is highly significant and subjecting to cycles of freezing and thawing. The
adequate to represent the actual relationship results showed decline in pulse velocity after
between the response and variables, with high subjecting the samples to cyclic freezing and
coefficients of determination (R2 = 96.92 %, 94.02 thawing. Where the decline of pulse velocity was
%, 95.04 %) for Y1, Y2, and Y3, respectively, as increased with increasing the number of cycles
shown in Table 12. These results indicate that the compared that of no cycles. The decrease of
three properties could be described well by the ultrasonic pulse velocity of mix (2 and 7) at 4 and 8
predicted model. cycle was approximately similar to that mixes from
8 to 13.
3.5 Plots of the 3D response surface and This may be happened due to the shrinkage
contours and expansion phenomena that was subjected to
The three regression equations (2), (3), and the samples during cycles of freezing and thawing.
(4) are presented by 3D response surface and This caused the generation of stresses resulting
contour plots, as shown in Figs.4, 5 and 6. from changing the volume of water in their pores
It can be seen from Fig. 4 that there is a inside the specimens, leading to a negative effect
sharp decline in the compressive strength values on the pulse velocity. This deterioration was clear
with increasing ratios for the metakaolin additive, that can be observed especially on mix (4 and 6).
while there is a slight increase in the compressive
strength value for alum sludge.
30 Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete
based on alum sludge and metakaolin

(a) (b)

Fig. 4- (a) 3D response surface and (b) contour plots of compressive strength (Y1) between alum sludge and metakaolin

(a) (b)
Fig.5- (a) 3D response surface and (b) contour plots of bulk density (Y2) between alum sludge and metakaolin

(a)
(b)

Fig. 6 - (a) 3D response surface and (b) contour plots of splitting tensile strength (Y3) between alum sludge and metakaolin
Hadel Obaidi, Ahlam Abdul-Rheem Farhan, Taha H. Abood Al-Saadi / Assessment of some mechanical properties for concrete 31
based on alum sludge and metakaolin

Fig. 7 - Effect of durability cycles on pulse velocity of concrete

4. Conclusions [3] Mandlik, A. D and Karale, S. A., 2018. Sludge Use in

Concrete as a Replacement of Cement. International Journal
for Research in Engineering Application & Management
Overall, the results of the laboratory experiments (IJREAM), 3, pp 22-27.
can be concluded as follows: [4] Breesem, KH. M., Faris, G. F and Abdel-Magid, I. M., 2014.
1- When increasing the replacement Behavior of Self-Compacting Concrete Using Different
Sludge and Waste Materials. A General Overview. 2, pp 151-
percentages of cement, the addition of alum sludge
155.
and metakaolin combined for the production of [5] Aiswarya, S., Prince Arulraj, G and Dilip C., 2013.A review on
concrete had a detrimental impact. use of metakaolin in concrete.
[6] Haider, M. O., Hamid, R., Abudullah, S.R.S., Tan Kofli, N. and
2- The best mixes based on the overall results Mohd R. T., 2013.Physical and Mechanical Properties of
tests were mixes (1, 3, and 5), which contained the High Performance Concrete with Alum Sludge as Partial
Cement Replacement.
percentages of metakaolin and alum sludge [7] Vasudevan, G., 2019, November. Effect of Alum Sludge and
(3.0503:1.5858), (3.0503:4.414), and (1:3), Metakaolin as a Partial Replacement Cement Adding
respectively. While the poorest mixes given the Superplastizer. In IOP Conference Series: Materials Science
worst result were mix (4, 6) that contained the and Engineering (Vol. 692, No. 1, p. 012013). IOP
Publishing.
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