Effect of sulfate on the properties of self compacting concrete 2

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308

(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME

270

EFFECT OF SULFATE ON THE PROPERTIES OF SELF

COMPACTING CONCRETE REINFORCED BY STEEL FIBER

Abbas S. Al-Ameeri1, Rawaa H. Issa

2

1(Civil, Engineering/ University of Babylon, Babylon City, Iraq) 2(Civil, Engineering/University of Babylon, Al-Najaf Al-Ashraf, Iraq)

ABSTRACT The Internal sulfate attack is considered as very important problem of concrete manufacture in Iraq and Middle East countries. Sulfate drastically influence the properties of concrete. This experimental study is aimed at investigating the effect of internal sulfates on fresh and some of the hardened properties of self compacting concrete (SCC) made from locally available materials and reinforced by steel fibers. Tests were conducted on fifteen mixes, three varied steel fiber contents (0, 0.75 and1.5) (%by Vol.) with five SO3 levels (3.9 ,5, 6, 7 and 8) (% by wt. of cement). The last four SO3 levels are outside the limits of the Iraqi specifications (IQS NO.45/1984). The results indicated that sulfate passively influenced the fresh and hardened properties of the plain and the reinforced SCC. However, regarding the effect on the hardened properties, the SCC reinforced with steel fiber showed similar to better sulfate resistance over plain SCC, the resistance enhanced with increasing steel fiber content. The results of the present study refer to that there might be a possibility of using reinforced SCC with unacceptable SO3 (with regard to Iraqi specifications) if high steel fiber content and long curing period are employed and if the SO3 is limited to 6 (% by wt. of cement).

Keywords: Self compacting concrete, Steel fiber, Steel fiber reinforced concrete, Steel fiber reinforced self compacting concrete, Sulfate attack, Internal sulfate attack.

1. INTRODUCTION Self compacting concrete (SCC) is a concrete which has the ability to flow by its own weight and achieve good compaction without external vibration. In addition, SCC has good resistance to segregation and bleeding because of its cohesive properties [1]. SCC, like any other concrete, is known to be brittle and can easily crack under low levels of tensile force. This inherent shortcoming, which limits the application of this material, can be overcome by

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the inclusion of fibers. The steel fiber is the most common fiber type in the building industry. The mechanical properties of SCC reinforced with steel fibers have been the pivot of numerous research programs, whereas its durability has not been investigated to the same extent. One of the durability problems which may encounter the concrete during its service life is the internal sulfate attack; internal sulfate attack is the major culprit of causing the deterioration to concretes in middle east countries, particularly in Iraq. Internal sulfate attack results from the reaction between sulfates in concrete ingredients ( water , cement , sand , gravel ) and cement paste, which had calcium aluminates, and water to form high calcium sulfoaluminate (ettringite). One of the main sources of internal sulfates that cause damage of concrete structures is the sand used. In the central and southern regions of Iraq, most sands are contaminated with sulfates mainly in the form of gypsum. About 95% of the sulfates in sand are in the form of calcium sulfates [2]. Gypsum is also normally added to cement to retard early hydration, prevent quickset and increase the efficiency of clinker grinding. The total sulfate in concrete may, therefore, be high enough to cause internal sulfate attack. This may lead to deterioration and possibly cracking and failure of concrete structure[3]. Therefore, an attempt has been made to study the behavior of self compacting concrete reinforced by steel fiber in the fresh and in the hardened state, in case of exposure to internal sulfate attack. To shed some light on the potential of the exposure to this kind of problem in such a concrete is highly requisite, it may illustrate to what extent internal sulfates can affect the properties of this type of concrete and to what extent can this concrete resist the sulfate attack. 2. Materials Used

2.1 Cement Ordinary Portland cement, which has specific gravity of 3.15 and the SO3 of 2.51, was used in this investigation. It is conforming to IQS:5 -1984 2.2 Coarse aggregate

Rounded shape aggregate of size of 10 mm was used and it has the following properties: Specific gravity of 2.61 and the SO3 of 0.04 2.3 Fine aggregate

Natural sand conforming to zone III of IQS: 45 – 1984 was used and its properties are found as follows: Specific gravity 2.56 and the SO3 of 0.37 2.4 Water &Super-plasticizer The drinking tap water has been used for both mixing and curing of concrete. A chemical admixture based on modified polycarboxylic ether, which is known commercially (Glenium 51) was used in producing SCC as a superplasticizer admixture.

2.5 Lime stone powder (LSP) This material was used to increase the amount of powder (cement + filler). It has SO3 of 1.9 and its specific gravity was 2.7.



272

2.6 Gypsum

Gypsum was added to the fine aggregate to obtain the required SO3 content in concrete. The added gypsum was natural gypsum rock .It was crushed and ground by hammer to obtain nearly the same gradation set of fine aggregate used in the mixes. This gypsum was used as a partial replacement by weight of fine aggregate with limited percentages. The following equation has been used to control the SO3 contents in the used sand:

( )N

SRw

%37.0−= …………. (1)

Where: � : the weight of natural gypsum needed to be added to fine aggregate. � : the percentage of SO3 desired in fine aggregate. � : the weight of fine aggregate in mix. N: the percentage of SO3 in the used natural gypsum (34.9%). 2.7 Fibers

In this work, type of steel fiber having geometry of cylindrical with hooked ends was used. The characteristics of the steel fiber ; length, diameter ,tensile strength, specific gravity were 30mm , 0.5 mm,1100 MPa and 7000 Kg/m3 respectively. 3. METHODOLOGY In order to cover a broad range of SO3 levels ( 3.9 which is within the limits of Iraqi specifications[4] and, 5,6,7and 8 which are outside the limits)% by weight of cement in concrete, a total of fifteen mixes were made. The mixture was designed according to [5]. Adding gypsum as a partial replacement of sand was the adopted procedure to obtain the required SO3 level in concrete. Fibers were added in quantities ranging from 0 to 1.5 % by volume of the total mixture. Moist curing was adopted , the curing time was for four ages (7, 28, 90 and 180) days. Table (1) shows the proportions of reference plain mixture.

Table (1) Proportions of reference plain mixture

Cement

(kg/m3)

Sand

(kg/m3)

Gravel

(kg/m3)

LSP

(kg/m3)

SP

(L/m3)

w/c w/p

425 870 600 129.2 3.35 0.52 0.4

4.FRESH CONCRETE TESTS The fresh properties of plain SCC and SCC reinforced by steel fiber were tested by the procedures of (European Guidelines for self compacting concrete). In this work three tests were used slump flow test, L-box test and V-funnel test.

5. HARDENED CONCRETE TESTS The mechanical properties studied are compressive strength, splitting tensile strength, flexural strength and static modulus of elasticity. Furthermore, the non-destructive test methods, length change test, ultra-sonic pulse velocity test and Schmidt hammer test are used. The

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976

(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March

compressive strength test was performed in accordance with IQS:348cube specimens. The splitting tensile strength test was carried out according to IQS:283[7] using Ø100 × 200 mm cylinder specimens. The test procedure given in IQS:291was used to determine the flexural strength using 100 × 100 × 400 mm prisms. The stamodulus of elasticity was performed according to IQS:370Ø150×300 mm. According to IQS:54used to measure the changing in length due to sulfate action. The UPV antests were conducted according to IQS:300 6. Results of Tests 6.1 Fresh Concrete Properties 6.1.1 Slump Flow Test Table (2) and Fig. (1) show the results of slump flow tests . The vthe maximum spread (slump flow final diameter), while the values of T50 represent the time required for the concrete flow to reach a circle with 50 cm diameter. The results of the slump flow range between (486-750) mm, the results ofshown in Fig. (2). The results indicate that increasing sulfate decrease the slump flow diameter and increase the time required to reach the diameter of 50 cm (T50), This can be accounted for, during very early stages of hydration, ettringite forms in relatively increased quantities with increased sulfates content, as a result, relatively large amount of water would be consumed for the reaction forming ettringite, beside, the roughness of gypsum particles could be reason. Therefore, concrete mixtures tending to be cohesive value might be increased causing the reduced flowability. Significant decrease in slump flow diameter and increase in T50 have been observed with incoradding steel fibers increases the resistance to flow and reduces the flowability due to increasing the interlocking and friction between fibers and aggregate

Fig.(1): Slump flow diameter D (mm

6.1.2 L-Box Test The L-Box with 2 bars was used in this study to assessmixes. The Blocking Ratios results (BR=H

plotted in Fig. (3). The results of the BR ranged between

0

100

200

300

400

500

600

700

800

3.9 5 6 7 8

Slu

mp

flo

w d

iam

ete

r(m

m)

Total SO3 (% by wt. of cement)


6316(Online) Volume 4, Issue 2, March - April (2013), © IAEM

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compressive strength test was performed in accordance with IQS:348-1992 [6]

. The splitting tensile strength test was carried out according to IQS:283using Ø100 × 200 mm cylinder specimens. The test procedure given in IQS:291

was used to determine the flexural strength using 100 × 100 × 400 mm prisms. The stamodulus of elasticity was performed according to IQS:370-1993 [9] by using test cylinders of Ø150×300 mm. According to IQS:54-1989 [10] prisms of (75×75×285) mm of concrete was used to measure the changing in length due to sulfate action. The UPV and Schmidt hammer tests were conducted according to IQS:300-1993 [11] and IQS:325-1993 [12] respectively.

Table (2) and Fig. (1) show the results of slump flow tests . The values of (D) represent the maximum spread (slump flow final diameter), while the values of T50 represent the time required for the concrete flow to reach a circle with 50 cm diameter. The results of the slump

750) mm, the results of T50 cm range between (2.1shown in Fig. (2). The results indicate that increasing sulfate decrease the slump flow diameter and increase the time required to reach the diameter of 50 cm (T50), This can be accounted for,

ages of hydration, ettringite forms in relatively increased quantities with increased sulfates content, as a result, relatively large amount of water would be consumed for the reaction forming ettringite, beside, the roughness of gypsum particles could be reason. Therefore, concrete mixtures tending to be cohesive [13]. Accordingly, the yield stress value might be increased causing the reduced flowability. Significant decrease in slump flow diameter and increase in T50 have been observed with incorporating steel fibers in SCC mixes, adding steel fibers increases the resistance to flow and reduces the flowability due to increasing the interlocking and friction between fibers and aggregate [14].

Fig.(1): Slump flow diameter D (mm) Fig.(2):Time required to reach a circle

with50dia

Box with 2 bars was used in this study to assess the passing ability of the mixes. The Blocking Ratios results (BR=H2/H1) of the tests are summarized in Table (2) &

The results of the BR ranged between (0.58-1). According to

Vf%=0

Vf%=0.75

Vf%=1.5

0

1

2

3

4

5

6

3.9 5 6 7 8

T5

0(s

ec)



April (2013), © IAEME

[6] using 150 mm . The splitting tensile strength test was carried out according to IQS:283-1995

using Ø100 × 200 mm cylinder specimens. The test procedure given in IQS:291-1991 [8]

was used to determine the flexural strength using 100 × 100 × 400 mm prisms. The static by using test cylinders of

prisms of (75×75×285) mm of concrete was d Schmidt hammer

respectively.

alues of (D) represent the maximum spread (slump flow final diameter), while the values of T50 represent the time required for the concrete flow to reach a circle with 50 cm diameter. The results of the slump

cm range between (2.1-5.7) seconds as shown in Fig. (2). The results indicate that increasing sulfate decrease the slump flow diameter and increase the time required to reach the diameter of 50 cm (T50), This can be accounted for,

ages of hydration, ettringite forms in relatively increased quantities with increased sulfates content, as a result, relatively large amount of water would be consumed for the reaction forming ettringite, beside, the roughness of gypsum particles could be another

. Accordingly, the yield stress value might be increased causing the reduced flowability. Significant decrease in slump flow

porating steel fibers in SCC mixes, adding steel fibers increases the resistance to flow and reduces the flowability due to increasing

Fig.(2):Time required to reach a circle

the passing ability of the ) of the tests are summarized in Table (2) &

1). According to [5], a

8

Vf%=0

Vf%=0.75

Vf%=1.5



blocking ratio (H2/H1) of more than or equal to 0.

mixtures had a good passing ability with BR had BR less than 0.8.The results show that the BR decreased with increasing sulfates in concrete. This decrease is likely due to increased yield stress and viscosity with the increasing in sulfates.

Fig.(3): Blocking Ratios for L 6.1.3 V-Funnel Test The V-funnel test is used to assess the viscosity and filling ability of selfconcrete [5] . Table (2) shows the results of V(6.57-12.3). It is clear from the results that the Vincreasing SO3 content in the mixes, confirming that raising sulfate contentviscosity of the mixtures. V-Funnel flow time also increased by incorporating steel fibers in mixes. Similar behavior was observed in the T50 testcontent, the more the flow-time increased. This can be ascricontent leads to increase the friction between the fibers and aggregates and the friction of the fibers with each other which could extend the required time to empty the V

Fig.(4): V

0

2

4

6

8

10

12

14

Tv

(se

c)

0

0.2

0.4

0.6

0.8

1

1.2

BR



274

blocking ratio (H2/H1) of more than or equal to 0.8 represents good passing ability. All

mixtures had a good passing ability with BR ≥ 0.8 except the mixtures (S4F3 and S5F3) had BR less than 0.8.The results show that the BR decreased with increasing sulfates in

se is likely due to increased yield stress and viscosity with the

Fig.(3): Blocking Ratios for L-box tests

funnel test is used to assess the viscosity and filling ability of selfTable (2) shows the results of V-funnel test. The Tv values ranged between

12.3). It is clear from the results that the V-funnel flow time increased with the content in the mixes, confirming that raising sulfate content

Funnel flow time also increased by incorporating steel fibers in Similar behavior was observed in the T50 test. Besides, the higher the steel fiber

time increased. This can be ascribed to, the increasing in fiber content leads to increase the friction between the fibers and aggregates and the friction of the fibers with each other which could extend the required time to empty the V-funnel

Fig.(4): V-funnel flow time Tv (sec)

3.9 5 6 7 8


Vf%=0

Vf%=0.75

Vf%=1.5

3.9 5 6 7 8


Vf%=0

Vf%=0.75

Vf%=1.5



8 represents good passing ability. All

0.8 except the mixtures (S4F3 and S5F3) had BR less than 0.8.The results show that the BR decreased with increasing sulfates in

se is likely due to increased yield stress and viscosity with the

funnel test is used to assess the viscosity and filling ability of self-compacting values ranged between

funnel flow time increased with the content in the mixes, confirming that raising sulfate content increases

Funnel flow time also increased by incorporating steel fibers in . Besides, the higher the steel fiber

bed to, the increasing in fiber content leads to increase the friction between the fibers and aggregates and the friction of the

funnel



275

Table (2) Results of fresh concrete tests

Mix SO3 (%by

wt. of

cement)

Steel Fiber

(% by Vol.)

D (mm) T50 (Sec) Blocking Ratio

(BR)

Tv (sec)

S1F1 3.9

0 750 2.1 1 6.57

S1F2 0.75 681 2.95 0.95 7.68

S1F3 1.5 584 4.25 0.84 9.23

S2F1

5

0 745 2.18 1 6.69

S2F2 0.75 675 3.1 0.93 7.86

S2F3 1.5 573 4.53 0.82 9.46

S3F1

6

0 729 2.35 0.98 6.8

S3F2 0.75 658 3.37 0.91 8.27

S3F3 1.5 555 5 0.79 10.27

S4F1

7

0 699 2.55 0.96 7.22

S4F2 0.75 625 3.71 0.88 8.9

S4F3 1.5 518 5.7 0.71 11.53

S5F1

8

0 685 2.73 0.93 7.51

S5F2 0.75 595 4.12 0.83 9.36

S5F3 1.5 486 N.a* 0. 58 12.3

*N.a: not applicable

6.2 Hardened Concrete properties 6.2.1 Compressive Strength Table (3) and Fig.(5) refer to that there is an optimum SO3 content at which the compressive strength is maximum. The data in table (5) indicate that the optimum SO3 content for these mixes is about (5) (% by wt. of cement), beyond this optimum value the compressive strength decreased with the increase of sulfates content for all SCCs the plain and the reinforced ones, at all ages of test. at age of 180 days, the percentages of change (increase or decrease) in compressive strength for SCCs having 5 %, 6 % ,7% and 8 % SO3 content in concrete, were (4.36%, -10.89%,-25.66% and -36.14%) relative to corresponding reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the percentages of change were (5.10%, -5.92%,-23.02% and -33.39%) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were (4.66%, -3.39%,-19.49% and -29.26%) relative to their corresponding reference SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively. Adding steel fibers decreased compressive strength at low sulfate contents at (3.9 and 5)%. while, at high sulfate contents(6,7 and 8)% the compressive strength was increased by adding steel fibers. at age180 days, the percentages of change in compressive strength for SCCs having 3.9%,5%,6%,7% and 8% percent SO3 content in SCC reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.), were (-2.97%, -2.28%, 2.44%, 0.48%, 1.21%) and (-6.53%, -6.26%, 1.33%, 1.23%, 3.53%) respectively relative to corresponding plain SCC. The improvement in strength refer to the control of cracking and the mode of failure by means of post cracking ductility as indicated by

AL-Musawee [14].While, the decrease in strength refer to entraining air with incorporating steel

fibers [15]. Moreover, the steel fiber indirectly would contribute to the increment of strength through delaying the deterioration due to the sulfate action while, the corresponding plain SCC continue to deteriorate, therefore, there would be a definite difference between plain and reinforced SCC.



Fig.(5):Effect of increasing SO

days (b) 28 days (c) 90 days (d) 180 days

6.2.2 Splitting Tensile Strength Table (3) shows the average of the results of splitting tensile strength test at 7, 28, 90 and 180 days gained from cylinders. Table (3) and Fig.(6), show the optimthe splitting tensile strength is maximum. Further increase in SOstrength. at age of 180 days, the percentages of change in splitting tensile strength for SCCs having 5 %, 6 % ,7 and 8 % SO-33.33%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the percentages of change were (3.05%, 1.5 (% by Vol.) the percentages of change were (8.97%,their corresponding SCCs reinforced with 0.75 and 1.5 (%by Vol.)that both the plain and the reinforced SCC suffered reduction in splitting tensile strenincreased SO3 beyond the optimum value. However, in general, the reinforced SCC showed better performance than SCC. This reduction can be ascribed to, with high sulfates contents and continued exposure to water, more ettringite would be formed, coincreased, inducing high tensile stresses and causing decrease in ultimate strength. The existence of steel fibers restricts the expansion and hence, delays the failure process. The SCC reinforced with steel fibers and contained 6 tolerable limits. By contrast to the compressive strength, the results of the splitting tensile strength tests, indicated in Table (3), clearly showed the benefit of steel fibers. Splitting indicated significant increase in strength due to the inclusion of steel fibers. The percent of

15

20

25

30

35

40

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Fcu

(MP

a)


25

30

35

40

45

50

55

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Fcu

(M

Pa

)


c



276

Fig.(5):Effect of increasing SO3 content in concrete on compressive strengt


Table (3) shows the average of the results of splitting tensile strength test at 7, 28, 90 and 180 days gained from cylinders. Table (3) and Fig.(6), show the optimum SO3 content at which the splitting tensile strength is maximum. Further increase in SO3 content caused decreasing in strength. at age of 180 days, the percentages of change in splitting tensile strength for SCCs having 5 %, 6 % ,7 and 8 % SO3 content in concrete ,were (4.95%, -12.90%, 33.33%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the

percentages of change were (3.05%, -10.00%,-31.3%and -36.49%) and for SCC reinforced with ercentages of change were (8.97%,-2.21%,-23.72% and -31.86%) relative to

their corresponding SCCs reinforced with 0.75 and 1.5 (%by Vol.) respectively. It can be seen, that both the plain and the reinforced SCC suffered reduction in splitting tensile stren

beyond the optimum value. However, in general, the reinforced SCC showed better performance than SCC. This reduction can be ascribed to, with high sulfates contents and continued exposure to water, more ettringite would be formed, consequently the expansion increased, inducing high tensile stresses and causing decrease in ultimate strength. The existence of steel fibers restricts the expansion and hence, delays the failure process. The SCC reinforced with steel fibers and contained 6 % (by wt. of cement) suffered losses at later ages within a

By contrast to the compressive strength, the results of the splitting tensile strength tests, indicated in Table (3), clearly showed the benefit of steel fibers. Splitting tensile strength indicated significant increase in strength due to the inclusion of steel fibers. The percent of

Vf%=0

Vf%=0.75

Vf%=1.5

20

25

30

35

40

45

50

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Fcu

(MP

a)


Vf%=0

Vf%=0.75

Vf%=1.5

30

35

40

45

50

55

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Fcu

(M

Pa

)


d



content in concrete on compressive strength at (a) 7

Table (3) shows the average of the results of splitting tensile strength test at 7, 28, 90 and content at which

content caused decreasing in strength. at age of 180 days, the percentages of change in splitting tensile strength for SCCs

12.90%, -26.88% and 33.33%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the

36.49%) and for SCC reinforced with 31.86%) relative to

respectively. It can be seen, that both the plain and the reinforced SCC suffered reduction in splitting tensile strength with

beyond the optimum value. However, in general, the reinforced SCC showed better performance than SCC. This reduction can be ascribed to, with high sulfates contents and

nsequently the expansion increased, inducing high tensile stresses and causing decrease in ultimate strength. The existence of steel fibers restricts the expansion and hence, delays the failure process. The SCC reinforced

% (by wt. of cement) suffered losses at later ages within a

By contrast to the compressive strength, the results of the splitting tensile strength tests, tensile strength

indicated significant increase in strength due to the inclusion of steel fibers. The percent of

Vf%=0

Vf%=0.75

Vf%=1.5

Vf%=0

Vf%=0.75

Vf%=1.5



increase in splitting tensile strength was found to be increase with the increase in steel fibers content for all mixes. at age180 days, the peSCCs having 3.9%, 5%, 6%, 7% and 8% SOfiber contents (% by Vol.) were (40.86%, 38.32%, 45.56%, 32.35% and 34.19%) and (55.9%,61.89%,75.06%, 62.65% and 59.35%) respectively relative to corresponding plain SCC.



6.2.3 Flexural Strength The flexural strength results for the plain and the reinforced SCC mixes are listed in Table (3). The optimum SO3 content at which the flexural strength is maximum has been recognized, Fig.(7). The flexural strength decreased with increasing SOoptimum value. at age of 180 days, the percentages of change in flexural strength for SCCs having 5 % 6 % ,7 and 8 % SO36.17%) relative to reference SCC. While, for SCC reinforcedpercentages of change were (4.97%,with 1.5 (% by Vol.) the percentages of change were (3.91%,relative to their corresponding SCC reinforced with 0.75 a The fine voids developed over the aggregate surface represent structural breaks in the continuity and are, at the same time, an opportunity for the accumulation of ettringite,

aaaa

1.5

2.5

3.5

4.5

5.5

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

ft (

MP

a)


2.5

3.5

4.5

5.5

6.5

7.5

8.5

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

ft (

MP

a)


c



277

increase in splitting tensile strength was found to be increase with the increase in steel fibers at age180 days, the percentages of increase in splitting tensile strength for

SCCs having 3.9%, 5%, 6%, 7% and 8% SO3 content in SCC reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) were (40.86%, 38.32%, 45.56%, 32.35% and 34.19%) and

% and 59.35%) respectively relative to corresponding plain SCC.

Fig.(6):Effect of increasing SO3 content in concrete on splitting tensile strength at (a) 7


The flexural strength results for the plain and the reinforced SCC mixes are listed in content at which the flexural strength is maximum has been

recognized, Fig.(7). The flexural strength decreased with increasing SO3 content beyond the at age of 180 days, the percentages of change in flexural strength for SCCs

having 5 % 6 % ,7 and 8 % SO3 content in concrete ,were (15.60%,-7.80%,-36.17%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the percentages of change were (4.97%,-7.18%,-25.97% and -38.12%) and for SCC reinforced with 1.5 (% by Vol.) the percentages of change were (3.91%,-7.24%,-23.11% and relative to their corresponding SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively.

The fine voids developed over the aggregate surface represent structural breaks in the continuity and are, at the same time, an opportunity for the accumulation of ettringite,

bbbb

Vf%=0

Vf%=0.75

Vf%=1.5

1.5

2.5

3.5

4.5

5.5

6.5

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

ft (

MP

a)


Vf%=0

Vf%=0.75

Vf%=1.5

2.5

3.5

4.5

5.5

6.5

7.5

8.5

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

ft (

MP

a)


d



increase in splitting tensile strength was found to be increase with the increase in steel fibers rcentages of increase in splitting tensile strength for

content in SCC reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) were (40.86%, 38.32%, 45.56%, 32.35% and 34.19%) and

% and 59.35%) respectively relative to corresponding plain SCC.

content in concrete on splitting tensile strength at (a) 7

The flexural strength results for the plain and the reinforced SCC mixes are listed in content at which the flexural strength is maximum has been

ent beyond the at age of 180 days, the percentages of change in flexural strength for SCCs

-24.65% and -with 0.75 (%by Vol.) the

38.12%) and for SCC reinforced 23.11% and -32.47%)

respectively. The fine voids developed over the aggregate surface represent structural breaks in the

continuity and are, at the same time, an opportunity for the accumulation of ettringite,

Vf%=0

Vf%=0.75

Vf%=1.5

Vf%=0

Vf%=0.75

Vf%=1.5



ettringite forms in voids and microcpaste [16]. It has been observed by many researchersthat the ettringite crystals are usually present in cracks, voids, and transition zone at the aggregate-binder interface, if concrete is submitted to expansion due to ettringite, fact which leads to an additional stress on the aggregateBeside, ettringite formed in microcracks, due to expansion pressure will widen thesemicrocracks. These processes will result in debonding of aggregates/matrix under low applied stresses, giving rise to prompt failure. The presence of steel fibers will delay these whole processes by restricting the widening and arresting any new microcracnegative effect of sulfates on concrete. Concrete mixes reinforced with steel fibers showed significant improvement in flexural strength at all ages relative to their corresponding plain concretes.percentages of increase for SCCs having 3.9%,5%,6%,7% and 8% SOreinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) , were (60.46%, 45.71%, 61.54%, 57.65% and 55.56%) and (117.91%, 95.86%, 119.23%, 122.35% and 130.56%) respectively relative to corresponding plain SCC. This is mainly due to the increase in crack resistance of the composite and to the ability of fibers to resist forces after the concrete matrix has failed. The SCC reinforced with 1.5 % steel fiber and contain 6% (by wt. ofsuffered losses within tolerable limits.


28 days (c) 90 days (d) 180 days

2

4

6

8

10

12

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

fr (

MP

a)

Total SO3(% by wt. of cement)

aaaa

cccc

1

3

5

7

9

11

13

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

fr (

MP

a)




278

ettringite forms in voids and microcracks requires less surface energy than forming in bulk . It has been observed by many researchers [16], [17], [18] in damaged concretes,

that the ettringite crystals are usually present in cracks, voids, and transition zone at the er interface, if concrete is submitted to expansion due to ettringite, fact which

leads to an additional stress on the aggregate-matrix interface and hence to microcracks. Beside, ettringite formed in microcracks, due to expansion pressure will widen these

These processes will result in debonding of aggregates/matrix under low applied stresses, giving rise to prompt failure. The presence of steel fibers will delay these whole processes by restricting the widening and arresting any new microcracks. Thus, reducing the negative effect of sulfates on concrete.

Concrete mixes reinforced with steel fibers showed significant improvement in flexural strength at all ages relative to their corresponding plain concretes. at age180 days, the

ges of increase for SCCs having 3.9%,5%,6%,7% and 8% SO3 content in SCC reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) , were (60.46%, 45.71%, 61.54%, 57.65% and 55.56%) and (117.91%, 95.86%, 119.23%, 122.35% and 130.56%)

ive to corresponding plain SCC. This is mainly due to the increase in crack resistance of the composite and to the ability of fibers to resist forces after the concrete matrix has failed. The SCC reinforced with 1.5 % steel fiber and contain 6% (by wt. ofsuffered losses within tolerable limits.

Fig.(7):Effect of increasing SO3 content in concrete on flexural strength at (a) 7 days (b)


8

Vf%=0

Vf%=0.75

Vf%=1.5

bbbb

dddd

2

4

6

8

10

12

14

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

fr (

MP

a)


1

3

5

7

9

11

13

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

fr (

MP

a)


8

Vf%=0

Vf%=0.75

Vf%=1.5



racks requires less surface energy than forming in bulk in damaged concretes,

that the ettringite crystals are usually present in cracks, voids, and transition zone at the er interface, if concrete is submitted to expansion due to ettringite, fact which

matrix interface and hence to microcracks. Beside, ettringite formed in microcracks, due to expansion pressure will widen these

These processes will result in debonding of aggregates/matrix under low applied stresses, giving rise to prompt failure. The presence of steel fibers will delay these whole

ks. Thus, reducing the

Concrete mixes reinforced with steel fibers showed significant improvement in at age180 days, the

content in SCC reinforced with 0.75 and 1.5 steel fiber contents (% by Vol.) , were (60.46%, 45.71%, 61.54%, 57.65% and 55.56%) and (117.91%, 95.86%, 119.23%, 122.35% and 130.56%)

ive to corresponding plain SCC. This is mainly due to the increase in crack resistance of the composite and to the ability of fibers to resist forces after the concrete matrix has failed. The SCC reinforced with 1.5 % steel fiber and contain 6% (by wt. of cement)

content in concrete on flexural strength at (a) 7 days (b)

Vf%=0

Vf%=0.75

Vf%=1.5

Vf%=0

Vf%=0.75

Vf%=1.5



6.2.4 Modulus of Elasticity The static modulus of elasticity for all mixes is experimentally determined at ages 28 and 90 days, the results of this test are listed in Table (3). Fig.(8), show the optimum SO3

presence of sulfates up to the optimum value of compressive strength means that more densification of material occurs. Therefore, the modulus of elasticity of concrete also increases. Further increase in SO3 content above the optimum, resulted in specimens due to the decrease in modulus of elasticity of the matrix caused by the degeneration of the interfacial bond strength between bulk cement paste and aggregate.percentages of change in elastic modulus for SCCs having 5 % 6 % ,7 and 8 % SOconcrete ,were (6.03%,-16.36%,-28.22% and reinforced with 0.75 (%by Vol.) the percentages of change were (13.14%,33.60%) and for SCC reinforced with 1.5 (% by Vol.) the percentages of change were (12.96%,5.69%, -19.96% and -32.30%) relative to their corresponding reference SCC reinforced with 0.75 and 1.5 (%by Vol.) respectively. Steel fibers demonstrated similar impact oon compressive strength. However, the increments ,if any, due to incorporating steel fibers were insignificant. at age 90 days, the percentages of change in elastic modulus for SCCs having 3.9%,5%,6%,7% and 8% SO3 content in SCC rein(% by Vol.) , were (-7.01%, -0.78%, 1.65%, 0.92% and 0.81%) and (2.39% and 1.51%) respectively relative to corresponding plain SCC.


6.2.5 Length Change Concrete prisms (75×75×285) mm were tested to determine the length change (expansion) of concrete at ages of 3,7,14,28, 56, 90 and 180 days. From fig.(9) ,it is quitthat expansion increased with age and with increasing sulfates content in concrete for both plain and reinforced SCC, more ettringite formation can be anticipated since more sulfates will be available for the reaction forming ettringite. The expacrack enlargement. Ettringite deposited in rims surrounding aggregate grains, and ettringite deposited in cracks considered as contributing to the overall expansion, through crack development and propagation by ettcompared to the energy needed for the formation of new cracks in concretetransformation of monosulfate to ettringite is well known to cause 2.3 times increase in volume and thus represents another source for expansioncontent of 5% had little propensity to expand among the increased SO

aaaa

15

17

19

21

23

25

27

29

3.5 4 4.5 5 5.5 6 6.5 7 7.

Ec

(GP

a)




279

lasticity for all mixes is experimentally determined at ages 28 and 90 days, the results of this test are listed in Table (3). The results listed in Table (3) and plotted in

3 content at which the modulus of elasticity is maxipresence of sulfates up to the optimum value of compressive strength means that more densification of material occurs. Therefore, the modulus of elasticity of concrete also increases. Further increase in SO3 content above the optimum, resulted in decrease in elastic modulus of specimens due to the decrease in modulus of elasticity of the matrix caused by the degeneration of the interfacial bond strength between bulk cement paste and aggregate. at age of 90 days, the

modulus for SCCs having 5 % 6 % ,7 and 8 % SO28.22% and -38.76%) relative to reference SCC. While, for SCC

reinforced with 0.75 (%by Vol.) the percentages of change were (13.14%,-8.57%,-and for SCC reinforced with 1.5 (% by Vol.) the percentages of change were (12.96%,

32.30%) relative to their corresponding reference SCC reinforced with 0.75 respectively. Steel fibers demonstrated similar impact on elastic modulus as

on compressive strength. However, the increments ,if any, due to incorporating steel fibers were at age 90 days, the percentages of change in elastic modulus for SCCs having

content in SCC reinforced with 0.75 and 1.5 steel fiber contents 0.78%, 1.65%, 0.92% and 0.81%) and (-8.18%, -2.17%, 3.54%,

2.39% and 1.51%) respectively relative to corresponding plain SCC.

Fig.(8):Effect of increasing SO3 content in concrete on modulus of elasticity at (a) 28

days (b) 90 days

Concrete prisms (75×75×285) mm were tested to determine the length change (expansion) of concrete at ages of 3,7,14,28, 56, 90 and 180 days. From fig.(9) ,it is quitthat expansion increased with age and with increasing sulfates content in concrete for both plain and reinforced SCC, more ettringite formation can be anticipated since more sulfates will be available for the reaction forming ettringite. The expansion can be a direct consequence of the crack enlargement. Ettringite deposited in rims surrounding aggregate grains, and ettringite deposited in cracks considered as contributing to the overall expansion, through crack development and propagation by ettringite swelling or crystal growth, much less energy is needed compared to the energy needed for the formation of new cracks in concrete [18]

transformation of monosulfate to ettringite is well known to cause 2.3 times increase in volume thus represents another source for expansion [19]. It can be noticed that the mixtures of SO

content of 5% had little propensity to expand among the increased SO3 contents of mixtures, this

bbbb

18

20

22

24

26

28

30

32

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

Ec

(GP

a)

Total SO3(% by wt. of cement).5 8

(% by wt. of cement)

Vf%=0

Vf%=0.75

Vf%=1.5



lasticity for all mixes is experimentally determined at ages 28 and The results listed in Table (3) and plotted in

content at which the modulus of elasticity is maximum. The presence of sulfates up to the optimum value of compressive strength means that more densification of material occurs. Therefore, the modulus of elasticity of concrete also increases.

decrease in elastic modulus of specimens due to the decrease in modulus of elasticity of the matrix caused by the degeneration

at age of 90 days, the modulus for SCCs having 5 % 6 % ,7 and 8 % SO3 content in

38.76%) relative to reference SCC. While, for SCC -22.10% and -

and for SCC reinforced with 1.5 (% by Vol.) the percentages of change were (12.96%,-32.30%) relative to their corresponding reference SCC reinforced with 0.75

n elastic modulus as on compressive strength. However, the increments ,if any, due to incorporating steel fibers were

at age 90 days, the percentages of change in elastic modulus for SCCs having forced with 0.75 and 1.5 steel fiber contents

2.17%, 3.54%,

oncrete on modulus of elasticity at (a) 28

Concrete prisms (75×75×285) mm were tested to determine the length change (expansion) of concrete at ages of 3,7,14,28, 56, 90 and 180 days. From fig.(9) ,it is quite evident that expansion increased with age and with increasing sulfates content in concrete for both plain and reinforced SCC, more ettringite formation can be anticipated since more sulfates will be

nsion can be a direct consequence of the crack enlargement. Ettringite deposited in rims surrounding aggregate grains, and ettringite deposited in cracks considered as contributing to the overall expansion, through crack

ringite swelling or crystal growth, much less energy is needed [18]. As well, the

transformation of monosulfate to ettringite is well known to cause 2.3 times increase in volume . It can be noticed that the mixtures of SO3

contents of mixtures, this

Vf%=0

Vf%=0.75

Vf%=1.5



content was defined earlier as the optimum SOreally close to the expansion values of the reference mixes with SOcrucial role in this test by reducing expansion. Steel fibers provided internal restraint to concrete expansion by bridging the micro-cracks and restraining further propagation of those cracks. As a result, the expansion related stresses will be reduced and by this way, the steel fibers mitigate the effect of sulfates on concrete.It was noticed at high expansion values there stistrength with progressing age. The last mix despite its high expansion at later ages showed relatively some gain in strength. The occurrence of relatively slow expansion in concrete at later ages may not lead to concrete deterioration

Fig.(9): Effect of steel fibers content on expansion for SO

aaaa

cccc

100

150

200

250

300

350

400

0 50 100 150 200

Ex

pa

nsi

on

*1

0-6

Age (Days)

0

50

100

150

200

250

0 50 100 150 200

Ex

pa

nsi

on

*1

0-6

Age (Days)

Ex

pa

nsi

on

*1

0-6



280

content was defined earlier as the optimum SO3 content. In fact, the values of this content were really close to the expansion values of the reference mixes with SO3 =3.9%. steel fiber played a crucial role in this test by reducing expansion. Steel fibers provided internal restraint to concrete

cracks and restraining further propagation of those cracks. As a result, the expansion related stresses will be reduced and by this way, the steel fibers mitigate the

It was noticed at high expansion values there still a development in strength with progressing age. The last mix despite its high expansion at later ages showed relatively some gain in strength. The occurrence of relatively slow expansion in concrete at later ages may not lead to concrete deterioration [20].

Fig.(9): Effect of steel fibers content on expansion for SO3(a)3.9 (b)5 (c)6 (d)7 (e) 8 (% by

wt. of cement))))

bbbb

dddd

eeee

50

100

150

200

250

0 50 100 150 200

Ex

pa

nsi

on

*1

0-6

Age (Days)

200

Vf%=0

Vf%=0.75

Vf%=1.5

150

200

250

300

350

400

450

500

0 50 100 150 200

Ex

pa

nsi

on

*1

0-6

Age (Days)

200

Vf%=0

Vf%=0.75

Vf%=1.5

250

350

450

550

650

750

0 100 200

Age (Days)

Vf%=0

Vf%=0.75

Vf%=1.5



the values of this content were steel fiber played a

crucial role in this test by reducing expansion. Steel fibers provided internal restraint to concrete cracks and restraining further propagation of those cracks. As a

result, the expansion related stresses will be reduced and by this way, the steel fibers mitigate the ll a development in

strength with progressing age. The last mix despite its high expansion at later ages showed relatively some gain in strength. The occurrence of relatively slow expansion in concrete at later

(a)3.9 (b)5 (c)6 (d)7 (e) 8 (% by

Vf%=0

Vf%=0.75

Vf%=1.5

200

Vf%=0

Vf%=0.75

Vf%=1.5



6.2.6 Ultrasonic pulse velocity Ultrasonic pulse velocity UPV test was used to evaluate the effects concrete. The values of ultrasonic pulse velocity for the various types of concrete at (7, 28, 90 and 180 days) are presented in Table (3).content at which the velocity is maximum, beyond tincrease in sulfates content as shown in Fig(10). change in pulse velocity for SCCs having 5 %, 6 %, 7% and 8 % SOwere (2.98%, -1.03%,-4.93% and reinforced with 0.75 (%by Vol.), the percentages of change were (2.35%, and -11.48%) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were(2.55%, -0.58%, -4.86% and reinforced with 0.75 and 1.5 (%by Vol.)disrupting effect of sulfates on the microstructure of concrete. Introducing steel fibers negatively affected the ultrasonic pulse velocity. This might be attributed to the increase of the amount of entrapped air voids due to incorporation of fibers into the mixes. besides, the fibers inside cube were randomly oriented, when the wave pass through the fibers the wave maybe deflected to other directions rather than pass straight forward to the end of the cube.



aaaa

cccc

3.6

3.8

4

4.2

4.4

4.6

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

UP

V (

Km

/se

c)


3.4

3.6

3.8

4

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

UP

V (

Km

/se

c)




281

Ultrasonic pulse velocity Ultrasonic pulse velocity UPV test was used to evaluate the effects of sulfates on

concrete. The values of ultrasonic pulse velocity for the various types of concrete at (7, 28, 90 and 180 days) are presented in Table (3). The results indicated that there is an optimum SOcontent at which the velocity is maximum, beyond that value, the velocity decreased with the increase in sulfates content as shown in Fig(10). at age of 180 days, the percentages of change in pulse velocity for SCCs having 5 %, 6 %, 7% and 8 % SO3 content in concrete,

4.93% and -10.88%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.), the percentages of change were (2.35%, -0.88%,

%) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were4.86% and -9.72%) relative to their corresponding reference SCC

reinforced with 0.75 and 1.5 (%by Vol.) respectively. The decrease in UPV is due to the disrupting effect of sulfates on the microstructure of concrete. Introducing steel fibers

ltrasonic pulse velocity. This might be attributed to the increase of the amount of entrapped air voids due to incorporation of fibers into the mixes. besides, the fibers inside cube were randomly oriented, when the wave pass through the fibers the wave

aybe deflected to other directions rather than pass straight forward to the end of the cube.

Fig.(10):Effect of increasing SO3 content in concrete on pulse velocity at (a) 7 days (b)


bbbb

dddd

Vf%=0

Vf%=0.75

Vf%=1.5

3.8

4

4.2

4.4

4.6

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

UP

V (

Km

/se

c)


3.4

3.6

3.8

4

4.2

4.4

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

UP

V (

Km

/se

c)


Vf%=0

Vf%=0.75

Vf%=1.5



of sulfates on concrete. The values of ultrasonic pulse velocity for the various types of concrete at (7, 28, 90

The results indicated that there is an optimum SO3 hat value, the velocity decreased with the at age of 180 days, the percentages of

content in concrete, relative to reference SCC. While, for SCC

0.88%, -4.91% %) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were

relative to their corresponding reference SCC The decrease in UPV is due to the

disrupting effect of sulfates on the microstructure of concrete. Introducing steel fibers ltrasonic pulse velocity. This might be attributed to the increase of

the amount of entrapped air voids due to incorporation of fibers into the mixes. besides, the fibers inside cube were randomly oriented, when the wave pass through the fibers the wave

aybe deflected to other directions rather than pass straight forward to the end of the cube.

content in concrete on pulse velocity at (a) 7 days (b)

Vf%=0

Vf%=0.7

5Vf%=1.5

Vf%=0

Vf%=0.75

Vf%=1.5



6.2.7 Rebound Number The surface hardness of the 150 mm concrete cubes was assessed by the, "Schmidt rebound hammer test". The rebound number results of plain and the reinforced SCC with different percentages of SO3 content in concrete at the ages ofare presented in Table (3). maximum, referring to densification effect due to ettringite formation at the plastic stage. Beyond the optimum value, the rebound number decreasshown in Fig (11). at age of 180 days, the percentages of change in rebound number for SCCs having 5 %, 6 % ,7% and 8 % SO19.23%) relative to reference SCC. While,percentages of change were (1.07%, 1.5 (% by Vol.), the percentages of change were (6.48%,their corresponding reference SCC reinforced with 0.75 and 1.5 (%by Vol.)decrease is ascribed to the detrimental action of sulfates which causes the weakness of surface. Incorporating steel fiber in SCC, decreased the rebound number for all specimens due to the entrained air increase which gave rise to increasing in porosity of the surface.


(a) 7 days (b) 28 days (c) 90 days (d) 180 days

aaaa

cccc

21

23

25

27

29

31

33

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

R.N


22

24

26

28

30

32

34

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

R.N




282

The surface hardness of the 150 mm concrete cubes was assessed by the, "Schmidt rebound hammer test". The rebound number results of plain and the reinforced SCC with

content in concrete at the ages of 7,28,90 and 180 days There is an optimum SO3 at which the rebound number is

maximum, referring to densification effect due to ettringite formation at the plastic stage. Beyond the optimum value, the rebound number decreased with increased SO

at age of 180 days, the percentages of change in rebound number for SCCs having 5 %, 6 % ,7% and 8 % SO3 content in concrete , were (1.44%, -9.86%,19.23%) relative to reference SCC. While, for SCC reinforced with 0.75 (%by Vol.) the

centages of change were (1.07%, -9.66%, -14.72%, -17.15%) and for SCC reinforced with 1.5 (% by Vol.), the percentages of change were (6.48%,-5.93%, -9.17%,-11.77%) relative to

CC reinforced with 0.75 and 1.5 (%by Vol.) respectively. decrease is ascribed to the detrimental action of sulfates which causes the weakness of

Incorporating steel fiber in SCC, decreased the rebound number for all specimens ined air increase which gave rise to increasing in porosity of the surface.

Fig.(11):Effect of increasing SO3 content in concrete on rebound number at

7 days (b) 28 days (c) 90 days (d) 180 days

bbbb

dddd

22

24

26

28

30

32

34

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

R.N


8

Vf%=0

Vf%=0.75

Vf%=1.5

25

27

29

31

33

35

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

R.N


8

Vf%=0

Vf%=0.75

Vf%=1.5



The surface hardness of the 150 mm concrete cubes was assessed by the, "Schmidt rebound hammer test". The rebound number results of plain and the reinforced SCC with

7,28,90 and 180 days at which the rebound number is

maximum, referring to densification effect due to ettringite formation at the plastic stage. ed with increased SO3 content as

at age of 180 days, the percentages of change in rebound number for SCCs 9.86%,-15.62%,-

for SCC reinforced with 0.75 (%by Vol.) the 17.15%) and for SCC reinforced with

11.77%) relative to respectively. This

decrease is ascribed to the detrimental action of sulfates which causes the weakness of Incorporating steel fiber in SCC, decreased the rebound number for all specimens

ined air increase which gave rise to increasing in porosity of the surface.

content in concrete on rebound number at

Vf%=0

Vf%=0.75

Vf%=1.5

Vf%=0

Vf%=0.75

Vf%=1.5



283

Table (3) Results of hardened concrete tests

Mix

Compressive strength (MPa) Tensile strength test (MPa) Flexural strength test (MPa)

7

days

28

days

90

days

180

days

7

days

28

days

90

days

180

days

7

days

28

days

90

days

180

days

S1F1 34 43.25 49 50.5 3.385 3.95 4.35 4.65 4.5 5.1 5.4 5.64

S1F2 34.91 44.4 48 49 4.65 5.015 6.44 6.55 7.2 8.25 9 9.05

S1F3 33.1 42 46.57 47.2 5 5.54 7.19 7.25 11 11.7 12.15 12.29

S2F1 35.4 46.65 51.75 52.7 3.55 4.1 4.6 4.88 4.8 5.6 6 6.52

S2F2 33.5 45.11 50.9 51.5 5 5.54 6.72 6.75 7.46 8.7 9.3 9.5

S2F3 34.16 43.6 48.19 49.4 5.21 5.9 7.7 7.9 11.3 11.96 12.45 12.77

S3F1 29 37.1 42.5 45 2.45 3 3.87 4.05 3.9 4.48 4.9 5.2

S3F2 30 38.5 42 46.1 3.4 3.77 5.78 5.895 6.2 7.3 8.22 8.4

S3F3 31 41 44.7 45.6 3.76 4.1 6.83 7.09 9.6 10.37 11.3 11.4

S4F1 23 29.84 34.5 37.54 2 2.39 3 3.4 3 3.55 4 4.25

S4F2 25 31.7 34.67 37.72 2.85 3.124 4.1 4.5 5.09 5.59 6.4 6.7

S4F3 25.5 32.22 35.05 38 3.29 3.69 4.94 5.53 8 8.9 9.1 9.45

S5F1 20.3 24.5 29.74 32.25 1.75 1.96 2.85 3.1 2.7 2.95 3.4 3.6

S5F2 21.33 25 30.12 32.64 2.54 2.9 3.99 4.16 4.2 4.6 5.3 5.6

S5F3 22 26.1 31.65 33.39 3.06 3.232 4.7 4.94 6.9 7.2 8.17 8.3



284

Continuous

Mix Modulus of

elasticity (GPa) U.P.V (Km/sec) Rebound number test

28

days

90

days

7

days

28

days

90

days

180

days

7

days

28

days

90

days

180

days

S1F1 28.2 30.37 3.88 4.23 4.35 4.365 30.6 31.6 32.5 33.28

S1F2 27.2 28.24 3.84 4.21 4.33 4.338 29.78 30.84 31.2 31.66

S1F3 27 27.89 3.82 4.2 4.31 4.32 28.33 29.13 29.3 29.58

S2F1 29.6 32.2 3.92 4.33 4.47 4.495 31.7 32.5 33.2 33.76

S2F2 29.38 31.95 3.87 4.29 4.44 4.44 30.7 31.45 31.6 32

S2F3 29.25 31.5 3.835 4.26 4.4 4.43 29.47 30.8 31 31.5

S3F1 24.2 25.4 3.77 4.15 4.28 4.32 26.9 27.9 28.73 30

S3F2 24.44 25.82 3.74 4.115 4.23 4.3 26.1 27 28 28.6

S3F3 25.72 26.3 3.72 4.095 4.22 4.295 25.25 26 26.77 27.83

S4F1 20.25 21.8 3.64 3.99 4.108 4.15 24.57 25.7 26.54 28.08

S4F2 20.64 22 3.6 3.97 4.094 4.125 23.61 25 25.6 27

S4F3 21.2 22.32 3.6 3.94 4.075 4.11 23 24.5 25.9 26.87

S5F1 17 18.6 3.5 3.63 3.77 3.89 23.75 24.25 25.3 26.88

S5F2 17.55 18.75 3.49 3.615 3.74 3.84 22.88 23.6 24.8 26.23

S5F3 18 18.88 3.5 3.6 3.75 3.9 22.45 23 24.5 26.1



285

7. CONCLUSIONS

1. Overall, slump flow diameter (flowability) and L-Box blocking ratios (passing ability) decrease with the increase in sulfates content in concrete with respect to mixtures having the reference SO3, similarly, with the increase in steel fiber content of the concrete mixtures with respect to plain mixtures. However, steel fibers affected the flow ability and passing ability more than the sulfates did.

2. Slump flow time and V-funnel flow time increase with the increase in the sulfates content in concrete with respect to mixtures having the reference SO3 and also with increase in steel fiber content of the concrete mixtures with respect to plain mixtures.

3. The effect of sulfates and steel fibers together on the fresh properties of the mixtures was greater than the effect of each one separately.

4. The optimum SO3 content, at which a higher mechanical properties and little tendency to the expanding were obtained, was at SO3 equal to 5 (% by weight of cement). Further increase in sulfates content in concrete after this optimum value showed a considerable reduction in mechanical properties; compressive strength, splitting tensile strength, flexural strength, static modulus of elasticity, U.P.V and rebound number, splitting tensile strength was more sensitive to sulfate attack than the other mechanical properties. Nonetheless, there was some recovering with advance in age at which the affected mixtures retrieve some of their lost strength.

5. Steel fibers decreased compressive strength at low sulfates and increased it at high sulfates contents and in the same manner the modulus of elasticity was. Overall, steel fibers had a marginal increments on both compressive strength and modulus of elasticity compared to the increments in the other mechanical properties.

6. For different SO3 contents in concrete, all steel fiber mixes demonstrated a higher splitting tensile strength and flexural strength relative to plain mixes at all curing ages. The tensile strength increased as the fiber content increased, however, the increments in flexural strength were higher than splitting tensile strength with more than 100% increments having been recorded.

7. Increased sulfates contents increased the expansion for all mixes with varied steel fiber contents. On the other hand, expansion of steel fiber mixes was less than plain mixes. The lowest expansion values were for the highest steel fiber content.

8. For different SO3 contents, pulse velocity and rebound number decreased with including steel fiber.

9. The highest steel fiber content 1.5 (% by Vol.) had, in general, best effect on hardened properties but the worst on fresh properties of SCC. As well, 0.75% steel fiber content was sufficient for achieving satisfying performance in fresh and hardened properties of SCC.

10. SFSCCs showed similar to better resistance to sulfate attack than plain SCCs, the resistance to sulfates enhanced with increasing fiber content.

11. Self compacting concrete containing SO3 of 6 (%by wt of cement) and reinforced with 1.5 steel fiber (% by Vol.) suffered losses in strength within tolerable limits in the later ages.



286

8. REFERENCES

1. Al-Rawi R.S., (1977),“Gypsum content of cements used in concrete cured by

accelerated methods”, Journal of Testing and Evaluation, Vol.5, No.3, pp. (231-237).

2. Al-Rawi R.S., ( 1985), “Internal sulfate attack in concrete related to gypsum

content of cement with pozzolan addition“, ACI-RILEM , Joint Symposium , Monterey, Mexico, pp. 543 .

3. Okamura H., and Ouchi M., (2003), “Self-Compacting Concrete”, Journal of Advanced Concrete Technology, Vol.1, No. 1, pp.(5-15).

4. Iraqi Specification, No.45/1984, “Aggregates from natural sources for concrete and

construction” Central Organization for Standardization &Quality Control COSQC, Baghdad, 2001.

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Effect of sulfate on the properties of self compacting concrete 2

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