Transactions Template


 

  

JOURNAL OF ENGINEERING RESEARCH AND TECHNOLOGY, VOLUME 5, ISSUE 3, SEPTEMBER  2018 

 

  

34  

 

Influence of Internal Curing on the Mechanical Properties of 

Normal Strength Concrete 

Mamoun A. Alqedra 

Associate Professor of Structural Engineering, Faculty of Engineering, Islamic University of Gaza, Palestine. 

Abstract— 

The current study investigated the influence of internal curing on the mechanical properties of normal concrete produced at 

the Islamic University of Gaza (IUG) laboratories. Due to high absorption capacity of the local broken pottery fragments, 

crushed pottery material was utilized in this study as the internal water storage source. The specific gravity and the absorp-

tion capacity of the crushed pottery (CP) sieves were identified to ensure the suitability of such material. The current study 

investigated the partial replacement of 0%, 10%, 15%, 20% and 25% of fine aggregates with CP material. Slump tests were 

carried out for the CP samples to obtain the effect of various contents on the workability of the mixes. The CP specimens 

were also prepared to obtain the mechanical properties, including the compressive strength and flexural strength. The com-

pressive strength of the samples was obtained at ages of 7, 14 and 28 days. The optimum CP content was identified and ap-

plied to study the flexural strength. The results of the experiments showed that the use of the locally available crushed pot-

tery as an internal curing material was effective in curing the concrete samples. The partial replacement of the natural fine 

aggregates with various contents of CP was also positive for the slump values. Further, the application of CP material was 

successful in improving the early compressive strength and flexural strength. A slight improvement in the 28-days strength 

results was revealed with the increasing content of CP. The slump and strength results indicated that 20% partial replacement 

of fine aggregates with CP material was the optimum. 

Index Terms— Internal curing, crushed pottery, compressive strength, flexural strength. 

I INTRODUCTION

Concrete curing is the term given to the procedures used for 

promoting the hydration of the cement, and consists of a 

control of temperature and of moisture movement from and 

into the concrete [1]. Curing allows continuous hydration of 

cement and consequently continuous gain of the strength.  

Proper curing of concrete structures is significant to meet the 

concrete performance and durability requirements. In con-

ventional curing this is achieved by external curing applied 

after mixing, placing and finishing. Curing of concrete 

maintains satisfactory moisture content in concrete during its 

early stages in order to develop the desired properties. How-

ever, effective curing is not always practically achieved in 

many cases. Therefore, the need to develop more effective 

curing agents attracted several researchers [2-5]  

Self-curing or internal curing (IC) is a technique that can be 

used to provide additional internal moisture inside concrete 

in order to enhance hydration of cement and reduce self-

desiccation. Internal curing is a mean of maintaining mois-

ture or supplying an internal water source for concrete that 

promotes more cement hydration. Self-curing concrete is a 

special concrete that would overcome insufficient curing due 

to human negligence. Further, such concrete would help in 

case of scarcity of water in arid areas, inaccessibility of 

structures in difficult terrains and in areas where the pres-

ence of fluorides in water will badly affect the characteris-

tics of concrete [6-8]. 

Among the methods available for internal curing are the use 

of saturated porous lightweight aggregate (LWA), use of 

polyethylene glycol which reduces the evaporation of water 

from the surface of concrete and helps in water retention. 

Further, application of superabsorbent polymers is utilized 

as an internal curing method, which could absorb and retain 

extremely large amounts of a liquid relative to their own 

mass [8, 9]. 

Bentur, et al. [10] studied concrete with replacement of 25% 

of the normal weight aggregates with saturated lightweight 

aggregate. They indicated that this concrete exhibited no 

autogenous shrinkage, whereas the normal-weight concrete 

with the same matrix exhibited large shrinkage. The results 

showed that such concrete was very effective in eliminating 

the autogenous shrinkage and restrained stresses of the nor-

mal-weight concrete. 

Kamal, et al. [11], in their first stage of the study, investigat-

ed the effect of internal curing agents on the main properties 

of normal-strength and high-strength self-compacted con-

crete. The internal curing agents included chemical curing 

agents and Light Expanded Clay Aggregates ―LECA‖ as 

internal reservoirs. Results indicated that curing agents re-



Mamoun A. Alqedra / Influence of Internal Curing on the Mechanical Properties of Normal Strength Concrete  (2018)  

  

35  

duced the water evaporation from concrete, and increased 

the water retention capacity with sufficient hardened con-

crete properties. 

Shen, et al. [12] utilized internal curing (IC) with up to 50 % 

prewetted lightweight aggregates (LWAs) to enhance the 

early-age behavior of high performance concrete. This was 

included temperature, shrinkage, creep deformation and 

stress for low cracking potential. They indicated that inter- 

nally cured concrete with prewetted clay LWAs is more ro-

bust for construction at early ages. 

Wu, et al. [13] investigated the replacement of normal ag-

gregates by several proportions of waste recycled brick ag-

gregate (RBA) as an internal curing material in concrete. 

The results demonstrate that RBA has a great potential for 

internal curing purpose in recycled aggregate concrete. 

Kevern and Nowasell [14] obtained the effect of replacing 

small fraction of normal fine aggregates in concrete with 

prewetted lightweight aggregates. This study concluded that 

the results of the concrete strength, degree of hydration, 

shrinkage, and freeze–thaw testing showed substantial im-

provements over the control mixture. Therefore, the study 

strongly recommended applying internal curing as a routine 

curing for concrete. 

Lee, et al. [15] investigated the potential of utilizing recy-

cled aggregates (RA) as an internal curing agent for an alkali 

activated slag (AAS) system compared with using artificial 

lightweight aggregates. They indicated that RA could reduce 

the autogenous shrinkage of an AAS system without a de-

crease in compressive strength. Further, the addition of RA 

did not increase degree of hydration for AAS mortar. This 

resulted from the dilution effect of the alkali activator, which 

was caused by the additional water supplied from internal 

curing materials. 

In high performance concrete, high self-desiccation and high 

temperature rise occur due to the low water-to-cement would 

increase the cracking potential of concrete at early age. 

Therefore, Shen, et al. [16] studied experimentally the effect 

of using pre-wetted lightweight aggregates (LWAs) on the 

tensile creep and cracking potential of high performance 

concrete at early age under adiabatic condition. They 

showed that using pre-wetted LWAs to internally cure con-

crete reduced the autogenous shrinkage, tensile 

creep/shrinkage as compared with the corresponding values 

of normal concrete.  

Mousa, et al. [17]  investigated the mechanical properties of 

concrete having replaced pre-soaked lightweight aggregate 

with several ratios of sand (0%, 10%, 15% and 20%). They 

indicated that the optimum ratio of pre-soaked lightweight 

aggregate was 15%, which showed improved mechanical 

properties. Mousa, et al. [18] indicated also that replacing 

20% of pre-soaked lightweight aggregate with sand was 

effective for improving permeability and mass loss, but ad-

versely affects the sorptivity and volumetric water absorp-

tion of the tested concrete samples. 

The aim of the current study is to investigate the influence of 

internal curing on the mechanical properties of normal con-

crete produced at IUG laboratories. Crushed pottery material 

was utilized as an internal water storage source. Several con-

tents of crushed pottery were added to concrete mixes in 

partial replacement of fine aggregates to obtain its effect on 

the mechanical properties.  

II MARTIALS AND EXPERIMENTAL PROGRAM. 

A. Material Properties 

Crushed pottery (CP) was utilized as an internal source of 

water to perform the internal curing process. The crushed 

pottery introduced to the mix as a partial replacement of fine 

aggregates in several percent. The specific gravity and the 

absorption capacity of the crushed pottery were tested in 

accordance to ASTM D6473 [19] and ASTM C642 [20], 

respectively. 

The crushed pottery (CP) was obtained from several facto-

ries that deal with such damaged material, as shown in Fig-

ure 1. The CP was crushed and dried at 105 C
0
 for 24 hours 

and the absorption capacities of various sizes of CP are pre-

sented in Table 1.  

 

Figure 1. Crushed pottery (CP) 

The absorption values of CP was compared with light 

weight aggregates (LWA) used by Dayalan and Buellah [21]. 

The absorption of the 2.36 to 0.6mm CP sizes ranges be-

tween 10.82% to 12.2%, respectively, which compares well 

with that of LWA (10.03%) indicated by Dayalan and Buel-

lah [21]. Therefore, an equal combination of CP sizes of 

2.36, 1.18 and 0.6 mm was made for the internal curing pro-

cess. The experiments showed that the specific gravity of the 

CP is 2.52. 

Table 1. Absorption results of crushed pottery (CP) 

CP particle size 

(mm) 

Absorption capacity, % 

(ASTM D6473-15) 

2.36 11.1 

1.18 12.2 

0.6 10.82 

0.425 7.23 

0.3 6.14 

0.15 4.61 

0.075 4.46 



Mamoun A. Alqedra / Influence of Internal Curing on the Mechanical Properties of Normal Strength Concrete  (2018)  

  

36  

Ordinary Portland Cement II AM 42.5 N was used in this 

study; the specific gravity of the cement was taken as 3.15. 

The fineness of the cement particles was 4200 cm
2
/g; the 

initial and final setting time were 1.5 and 6.5 hours, respec-

tively, based on ASTM C191 [22]. 

The maximum size of the coarse aggregate (CA) was 20 

mm. The average specific gravity and absorption of the 

coarse aggregates were 2.61 and 2.1 %, respectively. The 

grading of coarse aggregates is shown in Table 2. 

Sand was applied as fine aggregate (FA) and the specific 

gravity and absorption of the fine aggregates obtained in 

accordance to ASTM D6473 and ASTM C642 were 2.41 

and 0.9%, respectively. The grading of the fine aggregate is 

presented in Table 3. 

Table 2. Grading for coarse aggregate 

Sieve opening, mm Passing, % 

19.00 100 

12.50 90 

9.50 45 

4.75 0 

Table 3. Grading for fine aggregate 

Sieve opening Percent passing 

No. 16 100 

No. 30 76 

No. 50 10 

No. 100 4 

B. Experimental Program 

The current study investigated partial replacement of fine 

aggregates with four contents of the CP. These CP contents 

included 0%, 10%, 15%, 20% and 25%. The mix design of 

the concrete samples was carried out based on ACI 211 [23]. 

The results of the mix design proportions is included in Ta-

ble 4. 

Table 4. Mix proportions for 1m
3
 concrete 

proportions 
CP samples 

0% 10% 15% 20% 25% 

w/c ratio 0.43 

Cement, kg 442 

CA, kg  1073 

FA, kg 795 716 676 636 597 

CP, kg 0 80 120 159 199 

The 150 mm-cube samples were kept in a dry place with 

room temperature of 25 °C. These samples were maintained 

in this place until the day of testing. 

The fracture of various CP cube samples revealed well dis-

tribution of CP particles in the concrete matrix, as shown in 

Figure 2. This well distrubtuion ensures that the internal 

curing process covers the complete concrete matrix. 

Slump tests were carried out for the CP samples according to 

ASTM C143 [24] to obtain the effect of various CP contents 

on the workability of the mixes. The CP specimens were 

tested to obtain the mechanical properties; namely the com-

pressive strength and flexural strength according to ASTM 

C39 [25] and ASTM C78 [26]. The compressive strength of 

the samples was obtained at ages of 7, 14 and 28 days for 

w/c of 0.43. Afterwards, the optimum CP content mix was 

applied to study the flexural strength. Finally, the long-term 

compressive strength was also studied at age of 90 days. 

 

 

 

 

Figure 2. Well distribution of Crushed pottery particles 

III. RESULTS AND ANALYSIS. 

It was observed that the CP samples showed wet appearance 

on the surfaces at the age of 3 days and at room temperature. 

This indicates that the CP particles started releasing its inter-

nal water to the mix and hence the internal curing continues 

well, as shown in Figure 3. This wet appearance remained 

for the first 7 days. Afterwards, this wet appearance disap-

peared gradually. This finding was not observed in the 0% 

CP samples. 

Crushed pottery 



Mamoun A. Alqedra / Influence of Internal Curing on the Mechanical Properties of Normal Strength Concrete  (2018)  

  

37  

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25

S
lu

m
p

, 
cm

  
  
 

CP contents, % 

 

Figure 3. Wet appreance on the CP samples compared with 

0% CP samples at 3 days age and room temperature. 

 

A. Slump 

Slump values of 3.3, 3.5, 3.7, 3.8 and 4.1cm for 0%, 10%, 

15%, 20% and 25% CP samples are presented in Figure 4. 

The results indicated that the partial replacement of the natu-

ral fine aggregates (sands) with various contents of CP was 

positive for the slump values. This would be attributed to a 

small portion of the internal water stored in CP particles is 

added to the free water of the mix, which in turn improves 

the workability. Such behavior of workability improvement 

needs more investigation and study. 

Figure 4. Slump values for CP samples 

B. Compressive Strength 
The compressive strengths of the CP samples were obtained 

at ages of 7, 14, 28 and 90 days. Figures 5 to 8 present the 

compressive strength of the CP samples at various ages. 

 

 
Figure 5. Compressive strength for CP samples at 7- days 

Figure five shows that increasing the CP content up to 20 % 

of the sand content resulted in improving the 7 days com-

pressive strength (early strength) up to 7.5%. Afterwards, 

any further increase in CP content (25%) showed a reduction 

in the early strength improvement.  

The 14 days strength of the CP samples, as shown in Fig-

ure 6, showed a similar improvement to that of the 7 days 

strength values. As the CP content increased to 20% re-

placement of sand the 14 days strength values improved by 

6.7%. A reduction in the 14 days strength was indicated be-

yond the 20% CP content (i.e. 25%). 

 
Figure 6. Compressive strength for CP samples at 14 days 

24

26

28

30

0 5 10 15 20 25

7
-d

a
y
s 

c
o

m
p

re
ss

iv
e
 s

tr
e
n
g
th

, 
M

P
a
 

CP contents, % 

26

28

30

32

0 5 10 15 20 25

1
4

-d
a
y
s 

c
o

m
p

re
ss

iv
e
 s

tr
e
n
g
th

, 

M
P

a
 

CP contents, % 

CP samples 

0% CP samples 



Mamoun A. Alqedra / Influence of Internal Curing on the Mechanical Properties of Normal Strength Concrete  (2018)  

  

38  

 
Figure 7. Compressive strength for CP samples at 28 days 

 

A slight improvement in the 28 days strength results was 

revealed as the CP contents increased, as shown in Figure 7. 

No significant improvement in the 28 days compressive 

strength beyond 20% CP content of sand replacement. 

The compressive strength results indicated that the use of CP 

as an internal curing material was effective in curing the 

concrete samples. This finding was confirmed by the fact 

that higher strength values are obtained in this study. This 

behavior can be attributed to the continuing process of ce-

ment hydration due to the availability of more internal rela-

tive humidity that is stored inside the CP particles. This con-

tinuation of cement hydration process ensures lower voids 

and pores, and greater bond between cement paste and ag-

gregate particles, as mentioned by several researches [27-

29]. 

Further, the use of CP material for internal curing was suc-

cessful in improving the early strength of the samples. It can 

be concluded that the optimum partial replacement of fine 

aggregates by CP content is 20%. This optimum CP content 

was applied for the subsequent stages of the experimental 

program. This result agrees very well with the optimum con-

tent of light weight aggregates applied by [17] and [16], who 

obtained an optimum content between 15 to 20 %. 

The long-term effect of the internal curing of CP material on 

the compressive strength was also investigated using the 

optimum CP content (20%). The 0% and 20% CP content 

samples were kept in a dry place for 90 days in a room tem-

perature of 25 °C. Compressive strength at 7, 28 and 90 days 

of the 0% and 20% CP content samples are presented in Fig-

ure 8. 

 
Figure 8. Compressive strength of 0% and 20% CP samples 

at 7, 28 and 90 days 

The long-term compressive strength results presented in 

Figure 8 showed that the improvement in strength continues 

beyond the 28-days strength almost with the same rate as 

compared with the 0% CP samples. This finding can also be 

attributed to the continuation of the cement hydration for 

longer times.   

C. Flexural Strength  

Flexural strength of the 0% and 20% CP samples at 7 and 28 

days are indicated in Figure 9. The results revealed that there 

was an increase of 19.5% in the 28 days flexural strength of 

the 20% CP content sample as compared with that of the 0% 

CP content sample. This finding can be referred to the ob-

tained improvement of the compressive strength, which was 

in turn reflected positively on the flexural strength. 

V  CONCLUSIONS 

The current study investigated the influence of internal cur-

ing on the mechanical properties of normal concrete. 

Crushed pottery material was utilized as the internal water 

storage source. Having performed the experimental program 

and analyzed the results, the following conculsions were 

achieved: 

 
Figure 9. Flexural strength of 0% and 20% CP samples at 7 

and 28 days. 

32

34

36

38

0 5 10 15 20 25

2
8

-d
a
y
s 

c
o

m
p

re
ss

iv
e
 s

tr
e
n
g
th

, 
M

P
a
 

CP contents, % 

20

25

30

35

40

7 28 90 

C
o

m
p

re
ss

iv
e

 s
tr

e
n

g
th

, 
M

P
a 

CP samples age, days 

0% CP content

20% CP content

2.5

3

3.5

4

4.5

5

5.5

0 5 10 15 20

F
le

x
u
ra

l 
st

re
n
g
th

, 
M

P
a
 

CP content, % 

7-days Flexural Strength

28-days Flexural Strength



Mamoun A. Alqedra / Influence of Internal Curing on the Mechanical Properties of Normal Strength Concrete  (2018)  

  

39  

1- The use of the locally available crushed pottery as an 
internal curing material was effective in curing the 

concrete samples. 

2- The partial replacement of the natural fine aggregates 
(sands) with various contents of CP was positive for the 

slump values. The workability of the CP samples was 

higher than that of the control samples (0% CP). 

3- The use of CP material for internal curing was successful 
in improving the early strength of the concrete samples. 

There was an increase of 7.5% and 6.7% in the 7 days 

and 14-days strength for the 20% CP samples, 

respectively, as compared with the control samples. 

4- A slight improvement in the 28 days strength results 
were revealed as the CP contents increased. No 

significant improvement was obtained at the 28 days 

compressive strength beyond the 20% CP content of 

sand replacement. 

5- The slump and strength results indicated that the 
optimum partial replacement of fine aggregates by CP 

content as an internal curing material is 20%. 

6- The long-term compressive strength results showed that 
the improvement in strength continues after the 28 days 

strength with the same rate as compared with the 0% CP 

samples. 

7- The results indicated that there was an increase of 19.5% 
in the 28 days flexural strength of the 20% CP content 

sample as compared with that of the 0% CP content 

sample.  

ACKNOWLEDGMENT 

The author wish to thank Ahmed Jarad, Ibrahim Khalafallah, 

Mohammed Assaf and Mahmoud Abu-Mustafa for their 

assistance in conducting the experimental program. 

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