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Alexandria Engineering Journal (2014) xxx, xxx-xxx
FACULTY OF ENGINEERING ALEXANDRIA UNIVERSITY
Alexandria University Alexandria Engineering Journal
www.elsevier.com/locate/aej www.sciencedirect.com
ORIGINAL ARTICLE
Behavior of self-compacting fiber reinforced concrete containing cement kiln dust
Mohamed I. Abukhashaba *, Mostafa A. Mostafa, Ihab A. Adam
National Water Research Center, Construction Research Institute, Egypt Received 25 December 2013; revised 3 March 2014; accepted 12 March 2014
KEYWORDS
Self-Compacting Fiber Reinforced Concrete (SCFRC);
Cement Kiln Dust (CKD); Polypropylene fiber (PPF)
Abstract Self-Compacting-Concrete, SCC containing Cement-Kiln-Dust, CKD may offer several environmental, economic and technical benefits. The use of fibers extends its possibilities since fibers arrest cracks and retard their propagation. An investigation was performed to examine the effect of reinforcing SCC with Polypropylene fiber, PPF, on its stress strain characteristics as well as fresh and mechanical properties. Six mixtures with water-binder ratio (w/b) of 0.45 were conducted. The variables were fiber content, Cf and fiber length, Lf. Lf of 20, 40 and 60 mm and Cf of 0.005, 0.010, and 0.015 kN/m3 were examined. Slump flow and L-box were performed to assess PPF influence on workability. A comparison was carried out among the behavior of SCFRC mixtures in terms of fc, /.-development, tensile strength and shrinkage. It was found that SCC-shrink-age was reduced using PPF and fc of SCFRC was significantly affected by Cf and Lf. The higher the Cf, the higher the obtained fc and improved by 15.3-25.6% using various Cf. Strength development C28/C7 decreased from 1.29 to 1.14, 1.09, and 1.12 using PPF of 0.005, 0.010, and 0.015 kN/m3. PPF and CKD could be successfully used in SCC production in spite of its slightly negative effect on workability and a higher dosage of superplasticizer is required to achieve similar flow properties. The results show that shrinkage of SCC was reduced due to PPF inclusion.
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1. Introduction
* Corresponding author. Tel.: +20 1061104316; fax: +20 242188508. E-mail addresses: mmikhashaba@yahoo.com, c.ronaldo4141@yahoo. com (M.I. Abukhashaba).
Peer review under responsibility of Faculty of Engineering, Alexandria University.
Self-Compacting Concrete (SCC) mixtures are divided into three types; admixture type (it is produced using viscosity modifying agent, VMA), combination type (it is produced using fly ash and VMA), and powder type (it is produced using fly ash and super plasticizer) [1]. SCC or Self-Consolidating Concrete in USA, is a segregation-free concrete although it has a high flowability such that it can be placed to completely fill any area of the formwork without any compaction effort. So it was defined as a concrete that exhibits a high deformabi-lity and a good resistance to segregation. This kind of concrete is of great interest and has gained wide use especially in the
1110-0168 © 2014 Production and hosting by Elsevier B.V. on behalf of Faculty of Engineering, Alexandria University. http://dx.doi.Org/10.1016/j.aej.2014.03.006
case of difficult casting conditions such as heavily reinforced sections without undergoing any significant segregation or bleeding [1,2]. All possible SCC reported definitions include an essential requirement for the fresh mix; an ability to flow under its own weight and fill the formwork completely, producing a dense and uniform material without any need for compaction [1-4]. Therefore, it seems to be very promising for concrete construction. The main characteristic of SCC is the higher cement matrix aggregate ratio with respect to an ordinary concrete. In other words, the volume of cement matrix - responsible for the mobility of the concrete mixture must be increased in order to push the aggregate under the gravity action or under the pressure of a pumping system. On the other hand, the volume of the aggregate, in particular the coarse aggregate, must be reduced in terms of both volume and maximum size, to improve the mobility and the segregation-resistance of the fresh mixture. SCC is a sensitive mix, strongly dependent on the composition and the characteristics of its constituents. It has to possess the incompatible properties of high flowability together with high segregation resistance. This balance is made possible by the dispersing effect of high-range water-reducing admixture (superplasticizer) used for powder type combined with cohesiveness produced by a high concentration of fine particles in additional filler material [5].
The use of SCC with its improving production techniques is increasing every day in concrete industry. However, mix design methods and testing procedures are still developing. Mix design criteria are mostly focused on the type and mixture proportions of the constituents. Adjustment of the water/cement ratio and superplasticizer dosage is one of the main key properties in proportioning of SCC mixtures [6]. The compressive strength is best described by the water-to-cementitious materials, w/cm ratio and the porosity relationship. When fully compacted, the concrete strength was taken to be inversely proportional to the w/cm ratio [7]. It was reported that at similar w/cm ratios, the compressive strength of SCC was comparable or higher than normally vibrated concrete, NVC [8]. Moreover, it was also reported that, as the volume fraction of aggregate was increased, the modulus of elasticity was increased [9]. Since the aggregate volume fraction is typically lower compared to NVC, it is then expected that the elastic modulus of SCC would be lower than NVC having the same strength. Due to the usage of mineral and chemical admixtures in the concrete mixtures, an increase in the tensile strength of the SCC could be observed, compared to that of NVC [5]. However, the tensile strength of SCC may be safely assumed to be the same as the one for NVC for a given concrete strength class [10].
Autogenous shrinkage, eaut depends on the concrete mixture design and hydration process and not on the surrounding environment. For NVC, eaut was found relatively small with typical values of 40 i at early ages and 100-150 i in the long-term [7-11]. Nowadays with the use of high-range water reducers, low w/cm ratio, higher cement contents, and the use of some supplementary cementing materials SCMs, the structure of the paste has drastically changed. Drying shrinkage is the contraction due to moisture migration from concrete to the environment and the water is not consumed by the cement reaction as for eaut. Time is the most important factor influencing drying shrinkage. As time under drying increased, more water was withdrawn from capillaries causing more shrinkage [12,13]. The shape of the aggregate and spacing among
aggregate particles also play a role in shrinkage restraining and generation of internal stresses [14]. A larger maximum size of aggregate (MSA) provided a higher restraining effect for shrinkage [15]. It was generally agreed that the effect of cement and water contents on drying shrinkage was indirect [16]. Those effects are mainly linked to the fact that they change the total volume of cement paste, and therefore, change the proportion of the aggregate and its restraining effect [7-16]. Extending the period of wet curing, the shrinkage on subsequent drying exposure got diminished [17]. This is obvious due to the progress of hydration in concrete that is kept wet. The effect of hydration occurs simultaneously in two different ways: elastic modulus of concrete increases, and moisture diffusivity decreases as long as concrete remains wet. It was concluded that water curing for a period up to 6 days after demolding has resulted in a reduced shrinkage of the concrete [18]. Today, self-compacting mortars are preferred for repair purposes due to the application easiness and mechanical advantages [19]. An experimental and numerical study on mechanical properties of SCC and the corresponding properties of NVC was outlined. The examined water-binder ratio (w/b) varied between 0.24 and 0.80. Four different stresses to strength levels were studied. Parallel studies were performed on strength (fc) and relative humidity (RH). The elastic modulus, creep and shrinkage of SCC did not differ significantly from the corresponding properties of NVC [20].
The efficiency of the SCC can be further increased by introduction of fibers like steel fibers and glass fibers, further enhances their toughness, tensile strength, resistance to crack propagation thereby further enhancing the durability properties [21-24]. A study on the fresh and mechanical properties of SCFRC incorporating high-volume fly ash that does not meet the fineness requirements of ASTM C618 was presented. Two different types of steel fibers were used, and the effect of fiber inclusion on the workability of hybrid fiber reinforced self-compacting concrete was studied. The effects of fibers were quantified based on the fiber volume, length, and its aspect ratios. It was concluded that in addition to the above-mentioned quantifiable three properties, other properties of fibers such as shape and surface roughness are also found to be important
[21]. A polycarboxylic-based superplasticizer was used in combination with a VMA. In mixtures containing fly ash, 50% of cement by weight was replaced with fly ash. Two different types of steel fibers were used in combination, keeping the total fiber content constant at 0.060 kN/m3. The results indicated that high-volume coarse fly ash can be used to produce SCFRC, even though there is some reduction in the concrete strength because of the use of high-volume coarse fly ash
[22]. In order to produce thin precast elements, a SCC was prepared. When manufacturing these elements, homogenously dispersed steel fibers instead of ordinary steel-reinforcing mesh were added to the concrete mixture at a dosage of 10% by mass of cement. Compression and flexure tests were carried out to assess the safety of these thin concrete elements [23]. An investigation was performed to compare the properties of SCC with/without steel fibers. The slump flow, a fiber funnel and the J-ring test were used to evaluate the fresh concrete characteristics. The effect of the coarse aggregate content, the content and type of steel fibers on the workability of SCC were discussed [24]. The behavior of standard grade hybrid SCFRC which is made with a combination of steel and glass fibers in suitable proportion was conducted [25]. It was
observed that the confinement of the concrete has increased the 28 days strength from 12.39% to 28.2% for different percentages of confinements and the corresponding strain at peak stress increases with increase in confinement percentages.
Limestone powder has been the traditional material used in controlling the segregation potential and deformability of fresh SCC. The utilization of alternative materials, such as quarry dust, for SCC applications was dealt with [26]. The by-pass CKD adversely affects the mechanical properties of the mortars containing Ordinary Portland Cement, OPC especially at the high value of substitution. The substitution of OPC with CKD up to 6% has no clear effect on the compressive strength of the hardened mortar. However, it improves the physico-mechanical properties as well as chemical properties of the slag cement; this is because it acts as an activator for slag cement hydration [27]. CKD was added to concrete and mortar mixtures to study its effect on the strength and on the ability of the cover zone to absorb water, an important factor in the deterioration process [28]. The sorptivity and the initial surface absorption tests (ISAT) of mortars were used to measure the absorption characteristics for different mortar samples containing CKD. It was found that substitution of cement with CKD does not lead to strength gain for all samples studied and proper addition of CKD has no negative effects on strength properties. It is also shown that mortars prepared using suitable amounts of CKD have better absorption characteristics. However, above certain limits, the water absorption of the mortar increased with increasing CKD contents and decreasing mortar strengths [28]. SCC improves the efficiency at the construction sites, enhances the working conditions and the quality and the appearance of concrete. With fibers inclusion, it bridge cracks and retard their propagation. They contribute to an increased energy absorption compared with plain concrete [29].
As stated above, SCC is a relatively new type of concrete with high flowability, segregation resistance, and improved performance. However the basic property of weakness in tension remains. To offer very attractive economical and technical benefits, SCC can be further extended when combined with FRC. The concept of fiber reinforcement in SCC was then needed to improve its strength, toughness, resistance to cracking thereby further improving its durability and enhancement of energy. Various fibers such as steel, and glass, were tried by many researchers and results have been encouraged since some enhancement in the performance characteristics of the SCC was reported. Therefore, the current study is aimed to investigate the characteristics behavior of SCC with fiber addition and its confinement effect. Polypropylene fiber, PPF is investigated as reinforcements for SCFRC.
2. Research significance and purpose
Research investigations on various aspects of SCC have been reported worldwide. However, there is an obvious paucity of information when reinforcing with fibers especially polypropylene fibers. Moreover, the cement plants generate large quantities of cement kiln dust, CKD, during the manufacture of the cement clinker constituting a great source of air pollution. To overcome this problem, CKD is introduced to be used as a partial replacement of cement. Thus, there is a great need to evaluate the mechanical and physical properties as well as
time-dependant properties (shrinkage) of SCFRC containing CKD. Therefore, the current investigation is conducted to clarify that SCFRC combines the benefits of SCC in the fresh state and shows an improved performance in the hardened state due to the addition of the fibers and, therefore new fields of application such as lining can be explored. The main purpose of this research is to examine the effects of fiber inclusion on the overall behavior of SCFRC.
3. Experimental program
SCC mixtures presented in this paper is a powder type (it is produced using super plasticizer and CKD as a fine material instead of fly ash or lime stone powder or Blast Furnace Slag). CKD was also used as a partial replacement of cement. The main examined parameters include fiber content, Cf and fiber length, Lf. Slump flow time and diameter, L-box were performed to assess the fresh properties of the concrete. Mechanical properties were determined in terms of compressive strength, fc, and tensile strength in terms of splitting and flexure strength. Drying shrinkage as a time-dependent property was also measured, fc was measured on cubes (150 x 150 x 150 mm) according to the Egyptian Code of Practice, ECP [30]. Splitting strength was measured on cylinders (150 x 300 mm) according to ASTM C496, while the flexure strength was examined according ASTM C78. Shrinkage strains were measured on prismatic specimens of 100 x 100 mm cross section and having 400 mm length. It is assumed that if the length of the specimen is much larger than the cross-sectional dimensions, the shrinkage takes place only in the length direction.
3.1. Materials
The materials that were involved in the experimental work were selected from local sources in Egypt. Ordinary Portland cement (CEM I 42.5N) was used. It is produced according to the Egyptian standards 4756/1-2007. The CKD was used in producing all SCFRC mixtures. The properties of chemical composition of CKD are shown in Table 1, while the physical and chemical properties of the used PPF are listed in Table 2. Fine aggregate used was locally available natural siliceous sand with a fineness modulus of 2.34 and specific gravity of 2.64 confirming to ECP [30]. The grain size distribution of the fine aggregate is shown in Fig. 1. The natural siliceous gravel with a nominal maximum size of 20 mm and specific gravity of 2.50 was used as coarse aggregate, and its grain size distribution confirming to the ECP is shown in Fig. 2. Grain size distribution test was performed in accordance with the ASTM-D422 test method. The specific gravity of CKD is 3.12, which is equivalent to that of cement. Superplasticizer, (BVS) was used, and it is a superplasticizer and high range water reducer without retarding effect for concrete.
3.2. Mix proportioning
Durable concrete mixtures with a w/c ratio of 0.45 and S/A ratio of 0.50 were designed to investigate the effect of the examined variables on the behavior of SCC (Table 3). The composition of an ordinary SCFRCs with CKD as a partial
Table 1 Properties of chemical composition of CKD.
Oxides SiO2 AI2O3 Fe2O3 CaO MgO SO3 Na2O K2O CL" F.L LOI
% 11.40 5.40 2.48 56.49 1.03 1.53 0.11 0.83 0.86 3.9 15.97
Table 2 Physical and chemical properties of PPF. Property
Length, mm 20
Nominal diameter of fiber, im 75
Water absorption, % 0
Specific weight, kN/m3 9.0
Melting degree, °C 162
Combustibility degree, °C 600
Acids, alkaline and salts resistance, % 100
£ 60 Oß
1 / / / f [ 1
1 1 f 1 1 1 1
1 1 _______ / / f
____ / 1 / L j 1 / I
—■— Sand — — Lower Limit ~ ~ Upper Limit
♦ T 1 / ' ÍÁ / /
0.01 0.1 1 10 100 Seive Diameter (mm)
Figure 1 Grain size distribution of fine aggregate.
60 -■
20 -■
■ Gravel — — Lower Limit ~ ~ Upper Limit Tr*— 1/ f
____________, if
/ 1 _________J. j
1 1 1 ________1 /
if / /
0.1 1 10 100 1000 Seive Diameter (mm)
Figure 2 Grain size distribution of coarse aggregate.
replacement of cement with 20% (0.80 kN/m3) as fine mineral addition, was manufactured with cement content of 3.20 kN/m3 and at a given amount of mixing water (1.80 kN/m3). The maximum nominal size of the coarse aggregate was 20 mm. Among the three different concepts of designing and producing SCC, it was produced using SP of 2.4% of Cm. SCC in its fresh state requires high fluidity and segregation resistance ability. Therefore, many trial batches are often
required to generate the data that enable to identify optimum mix proportions of the specific used raw materials. The effect of Cf of (0.0, 0.005, 0.010, and 0.015 kN/m3) and Lf of (20, 40, and 60 mm) on the behavior of FRSCC mixture was examined. Three specimens were tested for each case.
3.3. Mixing procedure, casting, and curing
The concrete mixtures used in this study were laboratory produced with a rotating drum mixer 100 litre in capacity. Buttering of the mixer (disposal of the first mix) was always firstly conducted before the first intended batch. This is to eliminate the effect of the mixer-drum dryness/wetness condition. The following mixing procedure was followed for all SCC mixtures. Firstly, the total content of sand, fiber, cement, CKD, and gravel were dry mixed all together in the mixer for 1 min. Secondly, water was added and the mixing was continued for further 2 min. SP was then added and the mixing process was continued for further 2 min. Once the mixing time was completed, the rhe-ological tests (slump flow test, and L-box test) were performed in quick succession. The oiled steel moulds were then placed horizontally on the floor, and were filled into two and three layers. SCFRC was placed under its own weight without compaction. Immediately after casting, the top surface of the specimens was leveled. Then, all specimens were stored in laboratory atmosphere until demolding. The moulds were removed after 24 h and all specimens were cured in water until testing. Two hours before testing, shrinkage specimens were taken out from water to glue the gauge points.
3.4. Testing procedure, set-up and instrumentation
Compression test was carried out at the ages of 7, 28, 56, and 90 days, while tensile strength in terms of both flexure and splitting test was conducted at ages 7, and 28 days. All these specimens were tested under the digital hydraulic universal testing machine UTM, of the Construction Research Institute, CRI, Egypt, which has a LVDT transducer for measuring the vertical induced displacement in addition to the applied load reading, and during the test it can be easily monitor the load displacement behavior of the tested specimen till failure occurs through the readout unit of the UTM. Finally, the test data results can be easily transferred to the PC connected to the UTM. Shrinkage test specimens were conducted in accordance with the recommendations provided [31,32]. At the intended day of the commencement of the test, specimens were taken out from water to dry and clean its surface from any external moisture or impurities. For each specimen, one pair of gauge points, with an effective gauge length of 200 mm, was glued on each surface of two opposite sides (excluding the casting surface and its opposite side as shown in Fig. 3a). A mechanical strain gauge with an accuracy of 0.001 mm and 300 mm gauge length was used to measure shrinkage strains as described in Fig. 3b. All shrinkage specimens were subjected to drying at age of 28-day. Shrinkage observations were then
Table 3 SCFRC mixtures proportions, (kN/m3).
Mix Cement Water Gravel Sand SP CKD PPF
Content Length
FSCC-0 FSCC-0.5 FSCC-1.0 FSCC-1.5 FSCC-1-4 FSCC-1-6 3.20 1.83 8.53 8.57 0.096 0.80 0.000 0.005 0.010 0.015 0.010 0.010 20 mm 40 mm 60 mm
(a) Specimen with 2 demic points. (b) Strain gauge device.
Figure 3 Shrinkage test for SCC mixtures.
monitored, and measurements were carried out at 1, 3, 7, 10, and 14 days, and every 14 days thereafter, after the starting of drying.
4. Results and discussion
4.1. Concrete workability
Three different contents of PPF as well as 3 fiber lengths were investigated in order to answer the question to what extent the workability of SCC is influenced. The slump flow test, and the L-box test as described in Fig. 4a and b, were carried out to evaluate the material characteristics of the fresh concrete.
The slump flow test was conducted to assess the flowability and flow rate of SCC in the absence of obstructions. The result of the slump flow is an indication of the filling ability of SCC. The slump flow is the mean of two measurements of the spread flow diameter at right angle to the nearest 10 mm. The slump
flow of SCC mixtures used in this study was found in adverse relation with fiber content; it was measured 745 mm for SCC mixture without fiber, while it ranged from 560 to 680 mm for SCFRC with fiber as illustrated in Table 4. The L-box test was used to assess the passing ability of SCC to flow through tight openings between reinforcing bars and other obstructions without segregation or blocking. The passing ability of SCC mixture was 0.91, while it ranged from 0.65 to 0.78 for SCFRC. Both the obtained results indicate that using PPF for reinforcing SCC mixtures reduces its workability by 9-19.5%; therefore a higher dosage of superplasticizer is needed.
4.2. Load-displacement; P-d behavior
The PS curves for all specimens tested in compression at ages 7, 28, 56, and 90 days are plotted in Figs. 5 and 6. By comparing load-displacement, (P-d) curves for SCC and SCFRC
(a) Slump flow test
(b) L-box test
Figure 4 Concrete workability tests for SCC mixtures.
Table 4 Fresh and hardened properties of the tested SCC mixtures.
Mixa Flow Compressive strength, fc (N/mm2) fflx (N/mm2) fspt (N/mm2)
/ (mm) PA 7-D 28-D 56-D 90-D 7-D 28-D 7-D 28-D
FSCC-0 745 0.91 18.50 23.78 24.10 26.34 2.58 3.79 1.16 1.40
FSCC-0.5 680 0.75 21.34 24.27 27.79 31.59 3.32 4.15 1.28 1.43
FSCC-1.0 620 0.78 22.64 24.76 30.05 32.54 2.74 3.74 1.34 1.53
FSCC-1.5 560 0.65 23.00 25.77 30.28 31.12 2.56 3.48 1.29 1.43
FSCC-1-4 625 0.75 19.45 21.29 25.02 26.40 2.86 3.76 1.22 1.44
FSCC-1-6 600 0.70 17.22 20.76 20.83 26.17 2.84 3.48 1.12 1.45
a Values listed in the table is the average of 3 specs; flowability; PA: passing ability.
Figure 5 (a) P-d behavior for SCFRC with various fiber contents at 7-days. (b) P-d behavior for SCFRC with various Cf at 28-days. (c) PS behavior for SCFRC with various Cf at 56-days. (d) P-d behavior for various Cf at 90-days.
without/with fibers, the plotted figures demonstrate that all SCFRC mixtures have a better performance than the unrein-forced SCC mixture. With increasing the fiber content, the more PS behavior improvement gained and these observations can be noticed at all tested ages, as clearly noticed in Fig. 5a-d, for ages 7-days, 28-days, 46-days, and 90-days respectively. Moreover, one can easily observe the higher reached strain (displacement) at the maximum stress (load) which means that SCFRC mixtures are more ductile than SCC without fiber. The corresponding strain at peak stress increases with increase in confinement percentages induced by PPF inclusion, and it matches with the previous results [25]. Moreover, SCFRC mixtures seem to have a more linear and
steeper slope in the ascending portion of the curve that indicating a higher stiffness (i.e. young's modulus) practically at later ages.
Furthermore, when examining the effect of PPF length on the overall P-d behavior, there is no specific trend can be obtained especially for the examined fiber length of 60 mm which affects negatively to some extent the overall behavior (strength and stiffness) especially at the early ages even though it is more or less comparable with the unreinforced SCC at the age of90-days. For SCFRC having 40 mm length, it shows a slight behavior enhancement as well as the peak load reached before failure. However, since the fibers are rarely randomly oriented, SCFRC was found to be an inhomogeneous and this finding is
Figure 6 (a) P-5 behavior for SCFRC with various fiber lengths at 7-days. (b) P-5 behavior for SCFRC with various Lf at 28-days. (c) PS behavior for SCFRC with various Lf at 56-days. (d) PS behavior for various Lf at 90-days.
clarified in Fig. 7 which shows the PS results for 2 specimens from the same mixture, (FSCC-1-4) having PPF content of 0.010 kN/m3 with 40 mm length and tested at the same age of 56-days. This plot shows scattering in the results for the same mixture especially for the peak compression load, (495.15 and 630.86 kN) with a strength difference about 27.50%. Therefore, the focus on the orientation and the distribution of the fibers, PPF is needed, and different techniques should be applied to quantify 'orientation'. Fig. 6a-d, summarize these behavior changes on a quantitative basis by comparing the P-d behavior in an ordinary SCC and in the corresponding SCFRC having different lengths, 20, 40, and 60 mm keeping the fiber content constant (0.010 kN/m3) for all SCFRC mixtures. It can be also concluded that SCFRC reinforced with PPF of 20 mm length has the best behavior among all. Furthermore, the effects of fibers can be quantified based on the fiber volume, length, and aspect ratios of the fibers.
4.3. Compressive strength, fc
The average compressive strength; fc at various ages for all the investigated five SCFRC mixtures and the corresponding unreinforced SCC mixture are listed in Table 4. Moreover, the ultimate load can be monitored from Figs. 5 and 6, that present the influence of the examined PPF content as well as PPF length on the overall performance. It can be noticed that
the compressive strength was affected by the Cf as well as Lf. The increase in PPF content leads to an increase in the com-pressive strength values of SCC by 15.4%, 22.4%, and 24.3% at the age of 7 days, while it was increased to 2.1%, 4.1%, and 8.4% for 28-days, and increased again to be settled at 15.3%, 24.7%, and 25.6% for 56-days, and finally the improvement was found 19.9%, 23.5%, and 18.1% at age of 90-days when SCC was reinforced with PPF by 0.005, 0.010, and 0.015 kN/m3 respectively. It was observed that the
650 600 550 500 450 400 350 300 250 200 150 100 50 0
l-SCC -Î-4
.......FSCC -1-4
/ / / /
/ ! / .' /
0 2 4 6 S
Displacement, (mm)
Figure 7 Effect of fiber content, Cf on PS behavior at 56-days
confinement of the concrete due to PPF inclusion has increased the compressive strength from for different percentages of confinements and the obtained results match with that reported by Chandrasekhar et al. [25] which were stated in the range 12.4-28.2%. SCFRC-1 showed the highest compressive strength values among all tested mixtures especially at 90-days. However, there is no specific trend can be noticed for compressive strength as a function of fiber length. The obtained compressive strength results demonstrated that the PPF of length 20 mm has a highly significant positive effect since a strength was improved with 22.4%, 4.1%, 24.7%, and 23.5% at the ages 7, 28, 56, and 90 days respectively. The compressive strength of SCFRC mixture reinforced with PPF of 40 mm length is slightly higher than unreinforced SCC, the strength improvement ranges from 0.2% to 5.1%. SCFRC mixture that reinforced with PPF of 60 mm length, showed the lowest compressive strength values at all tested ages even lower than SCC without reinforcement at tested ages 7-days, 28-days, and 56-days, even though it is more or less comparable with unreinforced at age 90-days.
4.3.1. Effect of fiber content on fc behavior as a function of time Fig. 8 shows the compressive strength, fc values and its developments with time at the ages 7-28-56-90 days for the three SCFRCs reinforced with 0.005, 0.010, and 0.015 kN/m3 in comparison with that of the unreinforced SCC mixture; ''FSCC-0 mixture''. At a given fiber length of 20 mm, all the three SCFRCs mixtures, have higher strength than the unrein-forced SCC one at both early and later ages. The strength gain at 7, 28, 56, 90 days, is (15.4%, 2.1%, 15.3%, and 19.9%), (22.4%, 4.1%, 24.7%, and 23.5%), (24.3%, 8.4%, 25.6%, and 18.1%) when SCFRC specimen reinforced with fiber content of 0.005, 0.010, and 0.015 kN/m3 respectively. With increasing the Cf used, fc is directly increased with time. The SCFRC mixture (FSCC-0.5) reinforced with Cf of 0.005 kN/m: has a linear trend, and the following relation Eq. (1) matches its behavior, while Eq. (2) describes the behavior of SCFRC mixture (FSCC-1.0) reinforced with Cf of 0.010 kN/m3. However, Eq. (3) can represent the behavior of unreinforced SCC mixture but with a smaller accuracy.
For FSCC-0.5 fc = 0.123d + 20.681, R2 = 0.9977 (1)
For FSCC-0 fc = —0.0012d2 + 0.1994d + 17.751 R2 = 0.8942 c (3)
where d is the age of the tested specimen in days.
4.3.2. Effect of fiber length on fc behavior as a function of time Figs. 9 and 15 show the fc values and its developments with time at the ages 7-28-56-90 days of the three SCFRCs mixtures reinforced with different PPF lengths of 20 mm, 40 mm, and 60 mm and all have the same fiber content of 0.010 kN/m3 compared with that of the unreinforced SCC mixture. For mixture (FSCC-1.0) reinforced with PPF having 20 mm as Lf, fc has a well improved performance with time at all ages, while fc for mixture reinforced with Lf of 40 mm was not significantly affected at all ages and more or less comparable with that of unreinforced mixture. However, fc for mixture reinforced with Lf of 60 mm was negatively affected at early ages.
4.3.3. Behavior of fc as a function of fiber content, Cf
The cube compressive strength fc as a function of fiber content (Cf) and Lf was kept constant of 20 mm is illustrated in Fig. 10. The measured fc values varied according the fiber PPF content used as clearly observed at all tested ages 7-28-56-90 days and the proportional relationship is found for all tested ages, which means that fc increases as the doze of fibers increases. (fc — Cf) relation is found approximately linear at the age 28-days, while it is found nonlinear at the remaining tested ages, (7, 56, 90 days). All these relations can be described as follows:
At age 7-days :fc = —24907Cf + 669.91Cf+18.523 R2 = 0.9985 (4) At age 28-days : fc = 129.16Cf + 23.678 R2 = 0.9621 (5)
For FSCC-1.0 fc = 0.1254d + 21.825, R2 = 0.9666
3 At age 56-days :fc = — 34626Cf + 935.86Cf+24.065 R2 = 0.9993 (6)
At age 90-days: fc = — 66749Cf + 1308Cf + 26.426 R2 = 0.992 (7) where Cf is the fiber content in (kN/m3).
4.3.4. Behavior of fc as a function offiber length, Lf
In contrary with (fc — Cf) relation, the compressive strength has an inverse relationship with all the investigated fiber
g 20.0
-«- FSCC-0
—■—FSCC-0.5 —*—F$CC-1.0
—x—FSCC-1.5
Age, (Days)
Figure 8 Effect of Cf on fc behavior with age.
g 20.0 |
J ' ------■
- FSCC-0 —*—FSCC-1-2 —»—PSCC-1-4
— • —FSCC-1-6
Age, (Days)
Figure 9 Effect of Lf on fc behavior with age.
35.0 30.0
¿^T-____ ---- ---- ----------
- 7-days — —28-days
—«—56-days ——90-days
0.000 0.005 0.010 0.015
Fiber Content, (KN/m3)
Figure 10 Cube compressive strength fc behavior as a function of Cf.
length. Whenever, the fiber length increases, fc decreases and the (f — Lf) relations were found linear for 7-days and 56-days tested specimens, while it was nonlinear for specimens tested at ages 28-days and 90-days. The following equations describe these relations. Fig. 11 illustrates these (fc — Lf) relations.
At age 7-days : fc = —0.1293Lf + 24.855 R2 = 0.9945
(8) (9) (10)
At age 28-days: f = 0.0031Lf - 0.3385Lf + 29.843 R2 = 1
At age 56-days : fc = -0.2197Lf + 33.942 R2 = 0.9994
At age 90-days :fc = 0.0064Lf - 0.649Lf+42.159 R2 = 1 (11) where Lf is the fiber length in (mm).
4.4. Maturity of concrete
A comparison in the development of compressive strength values with time was carried out to examine whether PPF acts as an accelerator or a retarder. The effect of PPF content as well as fiber length on the maturity of SCFRC could be traced through the rate of strength gain. Fig. 12 shows C28/C7 ratio
for all the tested series in terms of fiber content, and C56/C7 ratio and C90/C7 ratio are also shown in Fig. 12. Moreover, strength development is plotted also against fiber length in Fig. 13 for all the tested series. Results show that the strength development for unreinforced SCC mixture, (FSCC-0) was 1.29 for C28/C7, while it became 1.14, 1.09, and 1.12 after reinforcing with Cf of 0.005, 0.010, and 0.015 kN/m3 for specimens FSCC-0.5, FSCC-1.0, and FSCC-1.5 respectively. The obtained values are fewer than the normal ranges for normal vibrated concrete, NVC, which means the higher strength gain for the examined SCFRC due to the effect of the used PPF. The ratios for C56/C7 and C90/C7 were found identical for reinforced and unreinforced SCC mixtures and in the range 1.30-1.33 and 1.42-1.48 respectively. It can be concluded that the tested SCFRC mixtures with its different constitutions not only did not show a pronounced negative effect on the maturity of concrete but also lead to higher strength gain.
4.5. Modulus of rupture
4.5.1. Flexure strength
The P-d curves for all specimens tested in flexure at ages 7, 28 days are plotted in Figs. 14 and 15. Moreover, the ultimate flexure strength is plotted as a function of the used fiber content in Fig. 16, while it is plotted in terms of fiber length in Fig. 17. From all these results, a significant enhancement in the overall behavior and all the tested SCFRC mixture have more ductile behavior than the unreinforced SCC due to the fiber inclusion. Moreover, an improvement in the flexure strength 28.7%, 9.50% at ages 7-days, 28-days was gained when reinforcing SCC with PPF of 0.005 kN/m3. However, there is no strength enhancement after 28-days for the rest of specimens reinforced with 0.010, 0.015 kN/m3 even it gained 6.2% at the age 7-days. This result may be due to the bad distribution of the fiber as it was randomly distributed.
4.5.2. Splitting strength
The P-d curves for all specimens tested in splitting at ages 7, 28 days are plotted in Figs. 18 and 19, while, the ultimate splitting strength is plotted as a function of the used fiber content in Fig. 20, while it is plotted in terms of fiber length in Fig. 21. From all plotted curves, a significant enhancement in the
£ 20.0
—•— 7-days
—■—28-days --56-days
—x—90-days i i
20 40 60
Fiber Length, (mm)
Figure 11 Cube compressive strength fc behavior as a function of L
Fiber Content, (KN/m3; Figure 12 Effect of Cf on strength gain.
SÉ js
Vl s a t
\ '— --- y
— C28/C7
—»— C90/C7
0 20 40 60 80
Fiber Length, (mm)
Figure 13 Effect of Lf on strength gain.
overall P-d behavior and all the tested SCFRC mixture have better ductile behavior than the unreinforced SCC due to the fiber inclusion. Moreover, an improvement in the splitting strength estimated by 10.3%, 15.50%, and 11.2% at age 7-days, and 2.1%, 9.3%, and 2.1% at age 28-days was gained when reinforcing SCC with PPF of 0.005, 0.010, 0.015 kN/m3 respectively. A strength enhancement became 5.2% after
(a) 8.0
•a S
11 \ / / / i
t i / / / / i i
i / y'/ 1
t /\7
- - fscoo ]
f / //> i \ -FSCC|-1 -2
•- - -FScdl-6
0.5 1 1.5 2 2.5 Displacement, (mm)
(b) 10.0
3 -J 4.0
A ---FSCC-0
i 1 / / -FSCC-1-2
' i / / -FSCC-1-4
! /¡ \
* / * ; // y
// 's / / \ S i -S 1
0 1 2 3 4 5
Displacement, (mm)
Figure 15 (a) Effect of Lf on flexure P-d behavior at 7-days. (b) Effect of Lf on flexure P-d behavior at 28-days.
f , . 4 "I _ — 1
»- 7-days
—■—28-days
Figure 14 (a) Effect of Cf on flexure P-d behavior at 7-days. (b) Effect of Cf on flexure P-d behavior at 28-days.
Fiber Content, (KN/m3) Figure 16 Flexure strength behavior as a function of Cf.
7-days and 2.9% after 28-days when changing the PPF length to be 40 mm instead of 20 mm with the same fiber content.
Since the fibers are rarely randomly oriented, SCFRC was sometimes found to be an inhomogeneous material. The preferred orientation of the fibers can be considered as a benefit or, the opposite as an intrinsic weakness of SCFRC, and this
vF 1-5
-- ------ __
—•— 7-days
—■—28-days
Fiber Length, (mm) Figure 17 Flexure strength fflx behavior as a function of Lf.
Figure 18 (a) Effect of Cf on splitting P-5 behavior at 7-days. (b) Effect of Cf on splitting P-5 behavior at 28-days.
fact is the key for explaining the obtained results. Comparing all the obtained results of the different mechanical SCC with PPF, one can notice the optimum PPF content for improving the compressive strength, fc is different from that for enhancing the concrete tensile strength, ft and no contradiction is found among them since PPF was randomly distributed and
Figure 19 (a) Effect of Lf on splitting P-5 behavior at 7-days. (b) Effect of Lf on splitting P-5 behavior at 28-days.
in all cases it becomes useful for fc specimens since it provides some kind of confinement. However for splitting and flexure specimens, its effect is very sensitive since it is mainly dependent on its orientation especially if it is distributed in the right path to resist the occurred tensile stresses.
4.6. Free drying shrinkage
The development of drying shrinkage strain with time for the tested mixtures is presented in Figs. 22 and 23. It is clear that, the shrinkage behavior of SCFRC mixtures for all testes series is lower than that of SCC mixture without reinforcement. Therefore, shrinkage strain values of SCFRC mixtures reinforced with PPF are lower than that of unreinforced SCC mixture. The use of fibers extends the possibilities of SCC since fibers bridge cracks, retard their propagation, and improve several concrete characteristics. Additionally, it can be noticed that, incorporation of PPF with higher percentage results in a reduction in shrinkage strain values. Among all, the unrein-forced SCC mixture (FSCC-0) showed the highest shrinkage strain values at all tested ages. Fig. 22 clearly demonstrates the significant effect of PPF content in reducing the drying shrinkage strain. However, using the PPF of various lengths for reinforcing SCFRC with the same quantity leads to improvement in the shrinkage behavior. On the other hand,
0.000 0.005 0.010 0.015
Fiber Content, (KN/m-*)
Figure 20 fspi Behavior as a function of Cf.
■•:•■«••■ FSCC-0.0 —■— FSCC-1.0-2
"^fi^-FSCC-1.0-4 —FSCC-1.0-6
50 100
Time (Days)
Figure 23 Effect of Lf on drying shrinkage of SCFRC mixtures.
5. Conclusion
Fiber Length,
Figure 21 fspl Behavior as a function of Lf.
,<y" m
...o..... ......
••••©■•• FSCC-0.0 —•— FSCC-0.5
—•— FSCC-1.5
Time (Days)
Figure 22 Effect of Cf on drying shrinkage of SCFRC mixtures.
using PPF of 60 mm to reinforce SCC resulted in a well not defined behavior especially at later ages. However, it showed a more or less comparable shrinkage behavior with that of unre-inforced SCC. In other words, at later ages, the shrinkage of SCFRC did not differ significantly from the corresponding properties of SCC as shown in Fig. 23.
Beside unreinforced SCC concrete (slump flow about 745 mm), 5 SCFRC mixtures reinforced with PPF and all containing CKD, (0.80 kN/m3) as fine materials have been studied with the same w/cm (0.45), the same S/A ratio (0.50), and cement content (3.20 kN/m3). The results of the present work indicate that:
1. After designing the parameters of mix proportions of self-compacting fiber reinforced concrete; SCFRC containing CKD and PPF, a SCC with good workability, high mechanical properties, and improved time dependent properties was developed. The PPF inclusion affect the workability of SCFRC, results showed that both the flowability and passing ability measurements indicated that SCFRC workability was slightly reduced, and a higher percentage of superplasticizer is needed.
2. The compressive strength, fc of SCFRC is significantly affected by PPF particularly, its fiber content; Cf. The higher the Cf ratio, the higher the obtained fc. The influence of Cf on the fc of SCC is diminished when varying the fiber length; Lf especially for the examined Lf of 60 mm. This is maybe due to the concrete inhomogeneity as a result of the fibers bad distribution that is rarely randomly oriented. In this situation, the preferred fibers orientation can be considered as the opposite as an intrinsic weakness of SCFRC.
3. The mechanical behavior of the SCFRC is attractive due to the inclusion of fibers and has a great significant effect on enhancing the fc of the SCC. fc was found in the range 15.4-24.3% at the age of 7-days, while it was 2.1-8.4% for 28-days, 15.3-25.6% for 56-days, and finally 18.1-23.5%, and at the age of 90-days using various Cf.
4. Drying shrinkage was measured in order to evaluate the contribution of PPF in counteracting the high concrete strains due to a low aggregate-cement ratio. All the tested PPF contents showed a significant effect all time on the whole shrinkage behavior, which was improved since SCC without reinforcement showed a higher shrinkage strain values than all SCFRCs. The higher the applied PPF content ratio, the lower the obtained strain values resulting from drying shrinkage. This is due to the use of fibers bridges cracks, retards their propagation, and finally improves concrete characteristics.
5. The tested SCFRC mixtures with its different constitutions did not show a pronounced negative effect on the maturity of concrete, and leads to a higher strength gain as well. The strength development for unreinforced SCC mixture was 1.29 for C28/C7, while it decreased to 1.14, 1.09, and 1.12 after reinforcing with 0.005, 0.010, and 0.015 kN/m3. The ratios for C56/C7 and C90/C7 were found in the range 1.30-1.33 and 1.42-1.48 respectively.
6. Using the CKD, beside PPF in the production of SCC mixtures, extends their technical and environmental benefit since it minimizes air pollution resulting from CKD. However, due to its shape and particle size distribution, mixes with CKD required a higher dosage of superplasticizer to achieve similar flow properties.
7. Research results demonstrated that applications with SCFRC mixtures containing both CKD and PPF can be economical, offer the final concrete products with interesting characteristics and can introduce innovative solutions for specific applications such as canals lining.
8. The focus on the orientation and the distribution of the PPF in SCC mixes still needs further investigation. Different techniques should be looked for to be examined and applied to quantify orientation.
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