RELATION BETWEEN THE WORKABILITY AND STRENGTH OF SELF-COMPACTING CONCRETE

RELATION BETWEEN THE WORKABILITY AND STRENGTH OF SELF-COMPACTING CONCRETE M Mazloom*, Shahid Rajaee University, Iran A Ranjbar, Shahid Rajaee University, Iran 35 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25-27 August 21, Singapore Article Online Id: 13538 The online version of this article can be found at: http://cipremier.com/13538 This article is brought to you with the support of Singapore Concrete Institute www.scinst.org.sg All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information www.cipremier.com

35 th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 27 August 21, Singapore RELATION BETWEEN THE WORKABILITY AND STRENGTH OF SELF-COMPACTING CONCRETE M Mazloom*, Shahid Rajaee University, Iran A Ranjbar, Shahid Rajaee University, Iran Abstract This paper presents the results of an experimental research on the workability and compressive strength of self-compacting concrete. The work focused on concrete mixes having water/binder ratios of.35 and.45, which contained constant total binder contents of 5 kg/m 3 and 4 kg/m 3, respectively. The concrete mixes contained four different dosages of a superplasticizer based on carboxylic with and without silica fume. The percentage of silica fume that replaced cement in this research was 1%. The workability tests utilized in this research were the slump flow, V-funnel, L-box, and J-ring, which can be used to evaluate the passing ability of self-compacting concrete. Based upon the experimental results, there are some linear relationships between compressive strength and each of the workability tests executed here. Keywords: concrete, self-compacting, workability, superplasticizer, silica fume. 1. Introduction With the preface of the new generation of superplasticizers, self-compacting concrete has been industrialized. This type of concrete having advanced viscosity and workability properties can easily fill the molds without the necessity of using vibrators [1-4]. High volume of mineral powder is a necessity for a proper self-compacting concrete design. It is worth adding that Ho et al. have investigated the use of quarry dust in self-compacting concrete [5]. Moreover, the influence of limestone powder on selfcompacting concrete is investigated recently [6]. For this purpose, natural or artificial mineral additives such as limestone powder, fly ash, silica fume and blast furnace slag can be used too. In this study, the effects of replacing 1% of cement by silica fume on fresh and hardened properties of standard and self - compacting concrete have been investigated. It is worth noting that extensive investigations on the workability of self-compacting concrete have been made recently [7-9]. Kayat et al. reported that the L-box, U-box, and J-ring tests can be used to evaluate the passing ability of self-compacting concrete and, to a certain extent, the deformability and resistance to segregation [7]. When combined with the slump flow test, the L-box test is very suitable for the quality control of on-site self-compacting concrete [1]. It is worth noting that Bui et al. have introduced a rapid testing method for segregation resistance of self-compacting concrete [11]. It is apparent that workability depends on a number of interacting factors such as water content, aggregate type and grading, aggregate to cement ratio, kind and dosage of superplasticizers, and the fineness of cement. The main factors on self-compacting concrete are the water and superplasticizer contents of the mix since by simply adding them the interparticle lubrication is increased. In this

research, the water contents of the mixes having the same water to binder ratios were constant and the dosages of the superlasticizer were.4%,.8%, 1.2%, and 1.6% of the weight of cement. Moreover, to achieve optimum conditions for minimum voids, or with maximum density with no segregation, the influence of the aggregate type and grading has to be considered. In this study, the quality and grading of the aggregates in all the mixtures were the same. In other words, the main objective of this research was to find the effect of the dosages of superplacticizers on the fresh and hardened properties of the mixes. 2. Materials and mix proportions This part of the paper presents the specifications of the mixes used for obtaining the workability and compressive strength of self-compacting concrete. The cementitious materials used were ordinary Portland cement (OPC) and silica fume (SF). Natural river sand and quartzite crushed gravel with a nominal maximum size of 14 mm were used as the aggregates. The control mixes were cast using OPC, while the other mixes were prepared by replacing 1% of the cement with silica fume on mass-for-mass basis. The water/binder ratios were.35 and.45 respectively. The effect of water to cement ratio on the properties of self-compacting concrete is studied recently [12]. The same mix proportions were used for the concrete mixes with the dosages of.4%,.8%, 1.2%, and 1.6% of a kind of carboxylic based superplasticizer. It is worth noting that the effects of superplasticizers on the mechanical strength of mortars have been studied recently [13]. Also, the application of carboxylic based superplasticizers in self-compacting concrete is investigated recently [14]. The effects of chemical admixtures and mineral additives on self-compacting concrete are studied too [15]. It is worth noting that Su and Miao have introduced a method for the mix design of flowing concrete [16]. The details of the mix proportions of the present research are given in Table 1. As a result of using different dosages of the superplasticizer, the fresh properties of the mixes were quite different. Table 1: Mix proportions of concrete containing different water to cementitious materials ratios Mix components Concrete Mixes W/C=.35 W/C=.45 OPC SF1 OPC SF1 Cement (kg/m 3 ) 5 45 4 36 Silica Fume - 5-4 Gravel (kg/m 3 ) 867 867 833 833 Sand (kg/m 3 ) 668 668 722 722 Water (kg/m 3 ) 175 175 18 18 Rock Flour (kg/m 3 ) 155 155 15 15 Superplasticizer (kg/m 3 ) 2 to 8 2 to 8 1.6 to 6.4 1.6 to 6.4 3. Workability and compressive strength The strict definition of workability is the amount of useful internal work necessary to produce full compaction. The useful internal work is a physical property of concrete and is the work or energy required to overcome the internal friction between the individual particles of the mixture. Because of the very high workability of self-compacting concrete, it needs no external vibration and can spread into place, fill the framework and encapsulate reinforcement without any bleeding or segregation. In other words, to ensure that reinforcement can be encapsulated and that the framework can be filled completely, a favorable workability is essential for self-compacting concrete. Moreover, aggregate particles in selfcompacting concrete are required to have uniform distribution in the specimen and the minimum segregation risk should be maintained during the process of transportation and placement. Because the strength of concrete is adversely and significantly affected by the presence of voids in the compacted mass, it is vital to achieve a maximum possible density [17]. This requires a sufficient workability or virtually full compaction. It is obvious that the presence of voids in concrete reduces the density and greatly reduces the strength, which means the presence of 5 percent of voids can lower the strength by as much as 3 percent [17]. This research compares the compressive strengths of selfcompacting and standard concrete mixtures having the same ingredients. It is worth noting that the hardened mechanical properties of self-compacting concrete have been reviewed recently [18].

4. Results and discussion In this part of the paper, the experimental results of self-compacting and standard concrete mixes on compressive strength and workability are discussed. The workability tests performed in this research were ordinary slump, slump flow, J-ring, L-box and V-funnel. 4.1 Workability of fresh concrete There is no acceptable test, which can directly measure the workability as defined earlier. The following methods give a measure of workability indirectly. In fact, these methods have found universal acceptance and their values are because of their simplicity and their ability to detect the variations in the uniformity of a mix. To better evaluate the workability of self-compacting concrete, both dynamic and static stability tests are usually required [7, 8]. Dynamic stability is concerned with the properties of self-compacting concrete during the process of mixing, transportation, and casting, while static stability deals with the properties of self-compacting concrete during the period from casting to initial set. This research concentrates on dynamic stability tests as follows. It should be noted that computational modeling of concrete flow has been overviewed recently [19]. Slump flow test Since the slump test is not suitable for the analysis of the fluidity of self-compacting concrete, the slump flow test is adopted. The testing apparatus consists of a normal slump cone and a steel plate with the dimensions of 9 9 mm. With this apparatus, the time for self-compacting concrete to spread to 5 mm in diameter, T 5, and the final slump flow diameters in the two orthogonal directions can be measured. According to EFNARC [2], for class 1 self-compacting concrete, the slump flow diameter is 55-65 mm and T 5 2 s; for class 2 self-compacting concrete the slump flow diameter is 6-75 mm and T 5 2 s; for class 3 self-compacting concrete the slump flow diameter is 76-85 mm, but no specification for T 5 is given. It is worth noting that the slump flow test is recently modeled using artificial neural networks [21]. The results of slump flow tests are presented in Table 2. V-funnel test The apparatus for V-funnel test is described by Wu et al. [1]. With this apparatus, the total time for self-compacting concrete to flow through the V-funnel, can be measured. The V-funnel flow test is to evaluate the fluidity of self-compacting concrete to change its path and to pass through a constrict area. According to EFNARC [2], for class 1 self-compacting concrete, T v is smaller than 8 s and for class 2 self-compacting concrete T v is 9-25 s. The measured values of T v are shown in Table 2. L-Box test The L-box test is used to evaluate the fluidity of self-compacting concrete and its ability to pass through steel bars [22]. The L-box consists of a chimney section and a channel section as described by Wu et al. [1]. With the L-box, the height of concrete in chimney, h 1, the height of concrete in the channel section, h 2, and the time for self-compacting concrete to reach 4 mm from three steel bars, T 4, can be measured. According to EFNARC [2], when the ratio of h 2 to h 1 is larger than.8, selfcompacting concrete has good passing ability. However, no specification for T 4 is given in EFNARC or other codes. In most previous studies on self-compacting concrete, T 4 is used to estimate the flow velocity of self-compacting concrete. The measured values of h 2 /h 1 are shown in Table 2. J-Ring test This test involves the slump cone being placed inside a 3 mm diameter steel ring, which is attached to vertical reinforcing bars at appropriate spacing [23]. The number of bars has to be adjusted depending on the maximum size of aggregates in the self-compacting concrete mix. The difference of the height of the mix before and after the bars is measured in this test. It is clear that as the workability of the mix is higher, the result of this test is lower. The results of J-ring tests can be observed in Table 2. Effect of silica fume on workability As described earlier, all of the results of workability tests on self-compacting concrete are shown in Table 2. This table includes the results of the slump tests of the standard concrete mixes too. It can be

observed that the standard mixes incorporating silica fume content tended to have lower workability. This finding is obvious in the self-compacting mixes as well. The reason for decreasing the workability of the mixes can be attributed to the very fine particle size of silica fume that causes some of the superplasticizer being adsorbed on its surface [24]. It is worth adding that mixes incorporating silica fume were more cohesive and this is in agreement with the findings of Khatri and Sirivivatnanon [24]. 4.2 Compressive strength For concrete stored in water, the development of compressive strength with age is shown in Table 3. It is clear that the compressive strength development of concrete mixtures containing different dosages of the utilized superplasticizer were quite different. According to Tables 2 and 3, it can be said that as the workability of the mixes improved, the compressive strength of the self-compacting concrete mixes decreased. This may be because of wider spread of the air bobbles in the mixtures as a result of higher dosages of the superplasticizer. According to Figs. 1 to 4, there were linear relationships between the test results on workability and the 28-day compressive strengths of self-compacting mixes. It means the relation between the compressive strength and workability is linear when the mix proportions are constant; therefore, the compressive strength of each mix containing a new dosage of superplasticizer can be estimated from its workability tests. However, the comparison between the mixes containing silica fume and the similar ones without silica fume shows the first group had lower workability and higher compressive strength. The reason for this phenomenon can be the pozzolanic activities of silica fume. Table 2: Workability of the concrete mixes Concrete Mixes Superplasticiz er Dosage W/c=.3 5 W/c=.4 5 OP C SF1 OP C SF1 Slump Flow (mm) Workability Tests Self-Compacting Concrete V- Funnel (second) L-Box (ratio) J-Ring (mm) Standar d Concret e Slump (mm).4% 46 --- --- --- 238.8% 73 6.5.86 12 --- 1.2% 785 5.4.9 6.3 --- 1.6% 825 4.8.95 4 ---.4% 41 --- --- --- 215.8% 55 8.62 14.5 --- 1.2% 67 6.2.82 8 --- 1.6% 78 5.3.9 5.5 ---.4% 41 --- --- --- 216.8% 73 4.88 14 --- 1.2% 81 3.6.96 6.5 --- 1.6% 83 3.3.98 4.2 ---.4% 32 --- --- --- 185.8% 53 4.8.57 17 --- 1.2% 76 4.2.86 12 --- 1.6% 77 3.8.9 11 ---

Table 3: Development of compressive strength with age Concrete Mixes Superplasticizer Compressive strength (MPa) Dosage 7 Days 28 Days W/c=.35 OPC.4% 44 61.8% 4 58 1.2% 39 58 1.6% 35 56 SF1.4% 46 69.8% 42 62 1.2% 4 6 1.6% 38 58 W/c=.45 OPC.4% 32 47.8% 3 42 1.2% 3 4 1.6% 27 37 SF1.4% 34 48.8% 31 45 1.2% 3 46 1.6% 28 41 OPC; W/C=.35 8 6 4 2 y = -.119x + 66.597 R 2 =.971 3 6 9 Slump Flow (mm) SF1; W/C=.35 8 6 y = -.289x + 79.66 4 R 2 =.9215 2 3 6 9 Slump Flow (mm) OPC; W/C=.45 8 6 4 2 y = -.25x + 55.717 R 2 =.8993 3 6 9 Slump Flow (mm) SF1; W/C=.45 8 6 4 y = -.99x + 5.877 2 R 2 =.5166 3 6 9 Flump Flow (mm) Fig. 1: Compressive strength versus slump flow of the concrete mixtures

OPC; W/C=.35 SF1; W/C=.35 8 6 4 2 y = 1.314x + 51.592 R 2 =.593 3 6 9 V-Funnel (s) 8 6 4 2 y = 1.4286x + 5.714 R 2 =.9643 3 6 9 V-Funnel (s) OPC; W/C=.45 SF1; W/C=.45 8 8 6 4 2 y = 7.27x + 14.135 R 2 =.9616 6 4 2 y = 3.5526x + 28.842 R 2 =.4568 3 6 9 3 6 9 V-Funnel (s) V-Funnel (s) Fig. 2: Compressive strength versus V-funnel results of the concrete mixtures OPC; W/C=.35 SF1; W/C=.35 8 6 4 2 y = -22.951x + 78.66 R 2 =.833.4.8 1.2 L-Box (Ratio) 8 6 4 2 y = -13.462x + 7.5 R 2 =.9423.4.8 1.2 L-Box (Ratio) OPC; W/C=.45 SF1; W/C=.45 8 8 6 4 2 y = -42.857x + 79.952 R 2 =.812 6 4 2 y = -6.327x + 48.99 R 2 =.1851.4.8 1.2.4.8 1.2 L-Box (Ratio) L-Box (Ratio) Fig. 3: Compressive strength versus L-Box ratio of the concrete mixtures

OPC; W/C=.35 SF1; W/C=.35 8 6 4 2 y =.224x + 55.829 R 2 =.5212 6 12 18 J-Ring (mm) 8 6 y =.417x + 56.18 4 R 2 =.9382 2 6 12 18 J-Ring (mm) OPC; W/C=.45 SF1; W/C=.45 8 8 6 4 2 y =.4499x + 35.962 R 2 =.8395 6 4 2 y =.3871x + 38.839 R 2 =.2212 6 12 18 6 12 18 J-Ring (mm) J-Ring (mm) Fig. 4: Compressive strength versus J-ring results of the concrete mixtures 5. Conclusions From the results presented in this paper, using concrete containing different dosages of a kind of superplasticizer based on carboxylic, the main conclusions are: 1. In standard concrete mixes with constant ingredients and different dosages of the superplasticizer, the ones incorporating silica fume, tended to have lower workability. This finding was obvious in the self-compacting mixes too. 2. To improve the compressive strength of the concrete mixtures, utilizing the superplasticizer dosage that causes better dispersions of cementitious materials and also produce lower air bobbles in the mixes are suggested. Comparing the results of the mixes containing different dosages of the superplasticizer shows the effect of air bobbles is more important than the dispersions of the cementitious materials. 3. The effects of silica fume and the dosage of the superplasticizer were higher on improving the compressive strength when the w/c ratio was lower. 4. The relation between the compressive strength and workability of concrete mixes was linear when the w/c ratio and other mix proportions were constant. In other words, in this context, the compressive strength of a concrete mixture containing a new dosage of superplasticizer could be estimated from its workability tests. References [1] Okamura, H. and Ouchi, M. Self-compacting concrete: development, present use and future, Proceedings of the First International RILEM Symposioum, 1999, 3-14. [2] Jianxiong, C., Xincheng, P. and Yubin, H. A study of self-compacting HPC with superfine sand and pozzolanic additives, Proceedings of the First International RILEM Symposioum, 1999, 549-56. [3] Sari, M., Prat, E. and Labastire J.F. High strength self-compacting concrete-original solutions associating organic and inorganic admixtures, Cement and Concrete Research, 29, 1999, 813-818. [4] Felekoglu, B. Investigation on mechanical and physical properties of SCC, M.Sc. Thesis in Civil Engineering, Dokus Eylul University, Izmir, 23.

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