APPLICATION OF SILICA FUME AND FLY ASH IN SELF CONSOLIDATING CONCRETE; A CASE STUDY

Transcription

1 APPLICATION OF SILICA FUME AND FLY ASH IN SELF CONSOLIDATING CONCRETE; A CASE STUDY Ali Pourzarabi 1, Mohammad Shekarchi 2 and Nicolas Ali Libre 3 1 Graduate Research Assistant, Department of Civil and Environmental Engineering, Politecnico di Milano, ali.pourzarabi@mail.polimi.it 2 Professor, Construction Materials Institute, School of Civil Engineering, University of Tehran, shekarch@ut.ac.ir 3 Visiting Scholar and Adjunct Professor, Department of Civil and Architectural Engineering, Missouri University of Science and Technology, libren@mst.edu ABSTRACT In this paper a case study investigation is presented and discussed which regards the application of self-consolidating concrete (SCC) in a severe environmental condition. The conventional concrete (CC) which was used in the project prior to the SCC, had serious problems which was mainly due to the poor compaction. The wall elements which concrete is cast into are 3m in height and 0.3m in width with high congestion of reinforcement and in some places with huge openings which makes it almost impossible to sufficiently vibrate and compact concrete. To overcome this problem the mix design was optimized which led to two SCCs which were proposed to be used instead. In both mix designs, cement was partially replaced with supplementary cementitious materials (fly ash and silica fume) to enhance the fresh and hardened properties of SCCs. The results obtained from compressive strength, absorption, electrical resistivity and rapid chloride penetration tests show that mix designs incorporating silica fume have a better performance in comparison to those with fly ash, while in terms of the fresh properties both mix designs fall into acceptable limits. After being cast into wall elements, the SCC shows considerable superiority relative to the CC used previously in the job-site, as it completely fills the formwork and leads to smoother surfaces. Keywords: Self-Consolidating Concrete; Silica Fume; Fly Ash; Wall Element; Fresh Properties; Hardened Properties Ali Pourzarabi, MSc., Politecnico di Milano, Piazza Leonardo da Vinci Milan, Italy ali.pourzarabi@mail.polimi.it Tel:

2 1. INTRODUCTION Self-Consolidating Concrete (SCC) being known as a relatively new technology in concrete industry, is increasingly being used and is quickly finding its place as a new material. SCC is able to flow and consolidate under its own weight, to fill the formwork even in the presence of highly congested reinforcement and can also be pumped easily [1]. Moreover, SCC can significantly enhance the working environment by the reduced noise generation due to the elimination of the vibration process, reducing the workmanship, the faster construction and higher quality finished surfaces. This type of concrete is characterized by three properties of filling ability, passing ability and segregation resistance. In order to achieve a SCC of high fluidity and to prevent the segregation and bleeding during transportation and placing, the formulators have employed a high portland cement (PC) content and used superplasticizer and viscosity modifying admixtures [2]. Moreover, to produce a SCC with good passing ability, the interparticle friction of aggregates should be considered. To provide an easy flow for the SCC, higher paste volume is required to cover the aggregate particles leading to their easy movement relative to each other. Therefore, self-consolidating concrete (SCC) must have sufficient paste volume and proper paste rheology to ensure the required characteristics [3]. A high powder content of kg/m 3 is often needed [4] to provide enough paste volume. If the powder content is only provided by cement, it notably increases the price and also has detrimental environmental effects. This, in turn, creates the opportunity of using waste and recycled materials which makes SCC a sustainable material. To counteract the problems associated with higher content of cement required to produce SCC, application of by-products such as Fly Ash (FA) and Silica Fume (SF) has been implemented to be used as a replacement for cement which is both economically beneficial and prevents the environmental pollution. These materials can improve workability with reduced cement content [5,6]. Besides, the pores between aggregates are filled and impermeable concrete can be produced. Therefore, the durability of concrete is also increased [5,6]. Soneby [7] reported that application of FA lessened the requirement of superplasticizer to reach the desired slump flow. It also improves the rheological properties and reduces the risk of cracking of concrete due to heat of hydration leading to a more durable concrete [7]. Turkel and Altuntas have also reported the enhancement of transition zone in mixtures incorporating SF [8] which causes the betterment of hardened properties. ACI committee 237 has also reported that the addition of SF to SCC mixtures can increase the segregation stability of SCC [9]. The Case study presented here is regarding the application of a SCC mix design. Two mix designs have been adjusted and proposed to be used in the project which incorporated FA and SF. The one incorporating SF was chosen to be used in the field. 2. PROJECT DESCRIPTION The job-site is in Assaluyeh, South Pars Phase 12, in south of Iran. Phase 12 field is the south eastern bloc of the South Pars Gas Field. The location of the project is in the proximity of the Persian Gulf which is one the richest in chloride content. The structures are substations with walls 3 m in height and 30 cm in width. By taking into account the concrete cover and the rebars, a 15 cm space is left for casting and vibrating the concrete within he wall thickness. There are openings in different areas of the wall elements up to 5 m in length, which makes it hard to vibrate the concrete beneath the openings when considering the overall geometry of the walls. Due to the problems described, the quality of the CC used in the project was not satisfying due the poor compaction given, and to eliminate this problem, a SCC mix design was proposed to be used instead. The general layout of the structures is shown in Figure 1.

3 Figure 1. General layout of the substations. 3. PRELIMINARY INVESTIGATION The first step was to identify the problem and to visit the sections in which the concrete was supposed to be cast into. There were severe honeycombs in some parts of the walls which were a remarkable threat to the structures in terms of durability. This problem was mostly observed beneath the openings and in columns intersecting the wall (Figure 2). In some areas complete exposure of the rebars was observed as the concrete had failed to fill the forms completely due to the problems associated with vibration process and as the consequence of the insufficient compaction reached. The concreting process was time consuming, nevertheless, not a satisfactory result was obtained. Figure 2. Honeycombs in the walls and columns.

4 Based on the observations done in the site, some properties for the target SCC which could fully fill the formwork without signs of instability was considered. According to experience and based on observations, a SCC which could readily fill the form without any need to mechanical compaction required a slump flow of cm. Moreover, the concrete was placed into the walls by being dropped from top of the sections which meant that the SCC had to experience a dropping height of 3 m, therefore, sufficient cohesiveness should be provided to prevent the segregation of the aggregates from the paste in order to secure homogenous properties along the height of the walls. The other target properties were also assessed based on previous experience which is presented in table 1. Initial Slump flow (cm) Table1. Assumed acceptance criteria. J-ring Slump-J (cm) * Height (cm) ** V-funnel (sec) L-box U-box (cm) SSI *** (%) <10 < <0.7 <10 <45% * The difference between the free flow in the slump flow test and confined flow in the J-ring test ** The difference between the height of the concrete in inside and outside of the J-ring test *** Static Segregation Index 4. EXPERIMENTAL PROGRAM In this phase of the project, effort was made to adjust a SCC mix design which could comply with the targeted properties determined according to the visual observations made in the field. To this end, trial mixes were made to reach satisfactory properties both in the fresh and hardened state and also in terms of durability. After making the trial batches, two mix designs were chosen to be proposed for the project both of which could provide the expected properties. The experimental phase is described as follows: 4.1. Materials A Type 2 Kangan cement similar to ASTM C 150 Type 2 cement was used to make the SCC mixtures. In addition, a class F fly ash, Silica fume and polycarboxylic-based superplasticizer was employed in all the mixtures. Crushed local aggregate was used for fine aggregate, fine gravel ( mm) and coarse gravel ( mm) aggregates. Particle size distribution (obtained using sieve analysis) of aggregates is presented in Figure 3. The dashed lines are the size range given by ASTM C33 [10]. Specific gravity and water absorption of the fine aggregates were 2.5 and 2.1%, those of fine gravel were 2.68 and 2% and these values for the coarse gravel aggregate were 1.5 and 2.88%, respectively. Fine gravel Sand Coarse gravel Figure 3. Aggregate distribution.

5 4.2. Mix proportions 9 trial batches (25 liter of volume) were made using FA to obtain a mix proportion which could best satisfy the required properties assumed for the concrete (table 2). To this end, the slump flow and j- ring test were done on the trial mixtures to roughly assess their fresh properties. In case the mixtures properties could marginally meet the requirements, the rest of the fresh state tests were done on 75 liter final batches to thoroughly examine the fresh properties of the mixture. Two series of FA trial batches were made. In the first series, the cementitious material was fixed at 450 kg/m 3 while in the second series, 500 kg/m 3 of cementitious materials was used, 20% of the cement being replaced by FA. The FAC9 mixture performed well and hence was made in 75 liters batch for thorough examination. A 75 liters batch containing 7% SF as cement replacement was also made and tested which could satisfy the requirements. This mixture was labeled as SFC and its mixture proportions are given in table 3. Based on experience, these amounts were the optimum amount of usage for these mineral admixtures as higher amounts of FA could compromise the mechanical properties and higher SF content could remarkably increase the yield stress of the fresh concrete leading to an increase in SP demand. Water to cementitous materials (w/cm) ratio was varied between 0.36 and The aggregates were so proportioned to result the best fresh properties. To this end, the amount of fine aggregate, fine gravel aggregate and coarse gravel aggregate were varied between 65 to 75, 0 to 10 and 20 to 35% of the total weight of aggregates respectively. The optimum ratio was selected so that the best passing ability was reached while enough flowability was secured. The SP dosage was chosen to give a slump flow of 65±2 cm Mix procedure First, the aggregates were placed in the mixer. The cementitious materials were added and mixing resumed for 2 min so that a uniform mixture of solid material was obtained. Then half of the water was added while the mixer was mixing. Afterwards, the other half of water mixed with SP was added to the mixture. Mixing resumed for 3 minutes after the whole water and SP was added and then the workability tests were done Testing methods Fresh concrete test methods Slump flow, V-funnel, L-box J-ring, U-box and column segregation tests were performed on fresh self-consolidating concretes to measure its flowability. The slump flow test was conducted according to ASTM C1611 [11] which measures two perpendicular diameters of the spread concrete after the Abram cone is lifted. The J-ring test carried out complying with ASTM C1621 [12] consists of the measurement of spread diameter of SCC mixture in slump flow test when the Abram cone is placed in the center of the J-ring apparatus and then the result is compared to the free flow in slump flow test. The V-funnel test [13] measures the time required for concrete to flow through a V-shaped container bottom gate filled with concrete. In the L-box test [14] the concrete is poured in the vertical section of an L-shaped container and after the concrete flows in the horizontal section, the ratio of the height of concrete at the end of the horizontal section to the height of the concrete in the beginning of the horizontal section is calculated as the blocking ratio. The U-box test [15] consists of a U-shaped container in which the concrete is poured in the right section and after the concrete flows to the left section, the difference in height of the concrete in two sections is reported as the filling height. To evaluate the static stability of the SCC mixtures, the column segregation test was done according to ASTM 1610 [16]. During this test, a column of 660 mm in height divided into three parts, and 220 mm diameter is filled with concrete and left undisturbed for 15 min. Then the concrete in the top and bottom parts is extracted and washed on a 4.75mm sieve. The weight of the aggregate remained on the sieve is used to calculate the Static Segregation Index (SSI) as follows: =2 ( ) 100 (1) ( )

6 Trial batch label. Table 2. FA trial batches First series Second series FAC1 FAC2 FAC3 FAC4 FAC5 FAC6 FAC7 FAC8 FAC9 Cement (kg/m 3 ) Fly Ash (kg/m 3 ) Fine aggregate Fine gravel Coarse gravel (%) * (Kg/m 3 ) (%) * (Kg/m 3 ) (%) * (Kg/m 3 ) w/cm (%) SP (% by weight of cement) J-ring Slump flow (cm) Slump-J (cm) ** Height (cm) *** * by percent of total weight of aggregate ** the difference between the free flow in the slump flow test and confined flow in the J-ring test *** the difference between the height of the concrete in inside and outside of the J-ring test Batch label Cement (kg/m3) Silica Fume (kg/m3) Table 3. SFC mix proportions Fine aggregate Coarse Gravel W/C (%) * (kg/m 3 ) (%) * (kg/m 3 ) (%) SP (% by weight of cement) SFC * by percent of total weight of aggregate Where CA T and CA B refer to the weight of aggregates on the 4.75mm sieve, corresponding to the top and bottom sections of the cylinder respectively Hardened concrete test methods At 7 and 28 days of ages, three mm cylinder specimens of each concrete mixture were tested for compressive strength with a 2000 kn hydraulic press and a loading rate of 0.5 N/mm 2 /s. Water absorption test was done complying with ASTM C 642 [17] on cube specimens with dimensions of mm in 28 days of age. The test was carried out after the samples were oven-dried for 48 hr. The absorption of each specimen was measured by calculating the increase in mass after the samples were immersed in water for 30 min. Water permeability test was done to determine the depth of penetration of water in cylindrical concrete samples according to BS EN 12390[18] after 28 days of curing. Pressure was applied on samples so that the water could penetrate into the concrete. Then the specimens were split from the middle and the greatest depth the water could penetrate was measured in mm. The Rapid Chloride Ion Permeability Test (RCPT) was conducted according to ASTM C 1202 [19]. Three specimens 100 mm in diameter and 50 mm in height drilled form cylindrical samples were tested to assess the total charge passed through the specimens in 6h.

7 5. RESULTS AND DISCUSSION 5.1. FA trial batches According to table 1, mixture FAC1 has a very poor passing ability with 6.8 cm difference in height of concrete inside and outside of the j-ring and 22 cm difference between the confined and free flow in J-ring apparatus and the slump flow test respectively. Not enough paste is provided in this mixture in order to lubricate the relative movement of aggregate particles and hence, the paste does not have the capacity to retain the aggregates within itself while moving. In the second and third mixtures, FAC2 and FAC3, the aggregate proportions have been modified to 70% by mass of whole aggregate for sand, 20% for coarse gravel and 10% for fine gravel. The results show that although decreasing the gravel aggregate volume has enhanced the passing ability, it is not in the acceptable range yet. In the FAC3 mixture, the w/cm ratio is increased by 2% which has slightly increased the flow of the mixture in the same SP demand compared to FAC2 while hindering the passing ability as the confined flow has declined by 3 cm in FAC3. Due to the increase in total water in FAC3, the cohesion of the mixture is reversely affected which in turn decreases the ability of the paste to carry the coarse and fine aggregates. In FAC4, the fine gravel portion of the aggregates is excluded with 75% sand and 25% coarse gravel by mass of the total aggregate, comprising the solid skeleton. To reach the same slump flow as FAC2 and FAC3, the SP demand is increased by 0.4%. The higher the sand volume, the higher the specific surface area of the aggregates which leads to more water required for covering the surface of the aggregates which in turn lowers the amount of free water available in the mixture. The result would be a reduction in flowability of the mixture or in the other words, higher SP dosage would be needed to ensure the same flowability. Based on the results obtained from the second series of the trial mixtures, FAC5 mixture exhibits high flowability while a moderate passing ability has been provided. The free flow is 72 cm with the confined flow being 65 cm which results in a 7 cm difference which is within the acceptance limit of 10 cm. In FAC6, although the total weight of coarse aggregates is reduced by 5% compared to FAC5, the passing ability is noticeably reduced. In FAC7 mixture, the fine gravel is excluded. Comparing FAC7 to FAC5 and FAC6, it is seen that the flowability of the former is lower that the two other mixtures. Using 1% of SP has resulted the slump flow of 65 cm while in FAC5 and FAC6 higher flowabilities was reached with the same or lower SP dosages. This, again, could be attributed to the increase in surface area of the aggregates when sand content is increased which leads to lower amount of free water contributing in flowability of the mixture or in the other word, the coarser the aggregates, the higher the flowability. Considering passing ability, FAC7 has the lowest difference in height between inside and outside of the j-ring showing the good ability of the mortar to hold the aggregates in dynamic state while passing through narrow spacing. The fine content in sand provides higher cohesion by increasing the interparticle attractions [20] which enhances the ability of mixture to stay homogenous while passing through obstacles. On the other hand, the highest difference between the free and confined flow is related to FAC7. Higher viscosity of this mixture makes it sticky and hence hindering its easy flow. It is worth noting that a proper proportioning of the sand and coarse aggregates can result a moderate viscosity and at the same time a desirable flowability. Hence exclusion of fine gravel and adding to the amount of coarse gravel could enhance the flowability. To further study this, FAC8 and FAC9 mixtures were made. As is evident, both mixtures show the same level of workability with almost equal flow in the J-ring test while the difference in height of the concrete between inside and outside of the apparatus is higher for the FAC8 mixture. Due to its better passing ability compared to FAC8, FAC9 was made in 75 liter batch (FAC) to be compared with the SFC mixture made. By comparing the first and second series of the trial mixes, it could be concluded that increasing the cementitous material from 450 kg/m 3 to 500 kg/m 3 has incredibly enhanced the passing ability of the mixtures while lowering the SP demand in the same flowability level. According to table 1, both of the measurements done in the J-ring test has generally improved for the second series and also higher flowabilities has been reached in lower SP dosage. As the fine content of the mixture is increased, the paste gets more cohesive leading to an enhanced ability in carrying the aggregates which results in a better passing ability. Moreover, as the paste volume increases, the thickness of the paste layer

8 surrounding the aggregates is increases. The result would be the smoother flow of aggregates relative to each resulting a better flowability A comparison between SFC and FAC Fresh Properties To evaluate the fresh properties of the proposed mix designs of FAC and SFC, SCC flowability tests were undertaken. The tests done were Slump flow test, J-ring test- V-funnel test, L-box test, U-box test and column segregation test. The results of these tests are manifested in table 4. Batch label slump flow (cm) Table 4. Flowability test results J-ring Difference in height (cm) Slump-J (cm) V-funnel (sec) L-box U-box (cm) Column segregation (%) FAC SFC Filling Ability Slump flow and L-box tests were undertaken to examine the filling ability of the mix designs. The obtained results represent the good filling ability of both of the mix designs. The initial slump flow of FAC was measured to be 68 cm when 0.5% superplasticizer was used by weight of cement; while, adding 0.9% superplasticizer to the SFC mix resulted in the slump flow of 64 which indicated the higher SP demand of the latter. This is due to the spherical shape of the fly ash particles which play a lubricating effect on the surface of the solid particles, enhancing the flow behavior of the fluid material. Furthermore, although lower amount of cement has been replaced by SF when compared to FA replacement level, the very fine particles of SF due to high specific surface area, absorb a very large amount of water, lowering the free water available in the mix design which help the mix to flow which leads to higher amount of SP to reach the same fluidity level. Figure 4 shows the slump flow test for both mixtures. The results obtained from the L-box test also show the good filling ability of the mixtures with the blocking ratio of 0.7 and 0.78 for FAC and SFC respectively, with SFC being slightly better than FAC in the L-box test. The EFNARC determines the blocking ratio of higher that 0.8 as the acceptance criteria [21] while Hwang et al. determines 0.7 as the minimum blocking ratio criteria [22]. a) SFC b) FAC Figure 4. Slump flow test

9 In this study, as mentioned before, the 0.7 blocking ratio has been selected as the acceptance criteria. Apart from the blocking ratio in L-box test, it is the quality of the flow which should be considered when conducting the test. Visual observations show the homogenous flow of the mixtures in the horizontal section of the apparatus, not being too fast, nor too slow. The slow flow of the SCC may be indicative of high viscosity which in practice may cause the air bubbles to get stuck in the concrete not being able to be released while, a fast flowing SCC in the L-box test could be a sign of the low cohesiveness of the mixture which can be incorporated with segregation when being cast in place. Passing Ability To determine the passing ability of the mix designs selected for the project,v-funnel, L-box, J-ring and U-box tests were carried out. The V-funnel test results show the good passing ability of both mixtures. The results show 7 and 8 seconds for FAC and SFC respectively to flow through the V- funnel. EFNARC has suggested the acceptance criteria for V-funnel time in the range of 6 to 12 secs. [21]. Longer times may be attributed to very high viscosity or the settlement of coarse aggregates accumulating above the opening in the bottom of the V-funnel hindering the flow of the SCC and shorter times indicate the lack of cohesiveness of the mixture. To obtain an acceptable result, the SCC should not be too stiff to increase the inter particle friction nor too fluid to lose the ability to retain the coarser aggregates within the mix preventing the accumulation of coarse materials above the bottom gate. A good mixture should provide sufficient viscosity to secure the smooth and homogenous flow of the SCC while being statically stable to eliminate the settlement of aggregates. The visual observation of the V-funnel test also showed the continuous flow of the SCC out of the V-funnel which indicates the homogenous dispersion of the aggregates in the mixtures. The L-box test was also used to determine the passing ability of the mixtures. The blocking ratios obtained were within the acceptance limit. Moreover, no accumulation of aggregates was observed behind the rebars. The J-ring test is a simple and easy test which can be conducted to examine the ability of SCC to resist blocking of aggregates and can be done both in laboratory and in-site. The results of the confined flow in the J-ring test was measured to be 9 and 11 cm lower than the free flow measured in the slump test for FAC and SFC respectively. According to ASTM 1621 [12], difference of lower than 2.5 cm between the free flow and confined flow of SCC shows a high passing ability for a SCC mixture. According to previous experience, a difference of lower than 10 cm could ensure a sufficient passing ability for the wall elements considered. The FAC was marginally superior to the other mixture in terms of passing ability measured in the J-ring test which could be attributed to the higher fluidity of this mixture due to the lubricating effect of FA particles. The mean difference in height between the concrete just inside the bars and that just outside the bars was measured to be 2.2 and 2.3 cm for FAC and SFC mixtures respectively. No information is provided by EFNARC regarding the acceptable range for this experiment but, previous experience shows that a difference in height less than 2.5 cm secures a good passing ability. Here, both mixtures fulfill this condition. The U-box test was also carried out to inspect the passing ability of the mixtures. The less the filling height, the better would be the passing ability of the SCC. A filling height lower than 3 cm indicates that the SCC has the properties required to secure passing ability [21]. U-box test is too strict to evaluate the fresh properties of SCC and failure in this test does not necessarily indicate the poor passing characteristic of a mixture [23]. The results obtained for the two mix designs in this test were 10 and 4 cm for FAC and SFC respectively. Due to the strict nature of this test, these results could be satisfying. To have a good performance in this test, the SCC should be stable enough to have the capacity to retain the aggregates in order to prevent their settlement and hence the blockage of the aggregates between the rebars. Furthermore, a moderate viscosity is required to ease the flow of the SCC by reducing the inter particle friction. The obtained results from this test show that both mixtures exhibit very good passing ability with SFC having a better performance in this test. This test also is an indicative for filling ability of SCC mixtures.

10 Static Stability To assess the resistance of the mixtures to static instability, the segregation column test was conducted. Based on previous experience, an SSI of less than 45% could secure the static stability of the mixtures. Both mixtures exhibited almost the same result in this test with SSI of FAC and SFC equal to 31 a 30.6% respectively and therefore, the minimum requirements was fulfilled. Static stability depends on yield stress and viscosity of mixtures. Zerbino et al. has shown the good correlation between slump flow and V-funnel test results with yield stress and viscosity of SCC mixtures respectively [24]. Accordingly, and based on the resemblance in results obtained from Slump flow and V-funnel tests for these two mixtures, the SSI achieved could be expected to be close for both mixtures and the results reconfirms it. To adjust SCC mixtures which could perform better in static state, higher viscosity was required which could be provided by using viscosity enhancing admixtures, but a higher viscosity could make some problems in application of this SCC in practice. Providing a higher viscosity, due to the 3 m height of the wall elements, which the concrete was supposed to be cast into, could result in the entrapment of air bubbles in the fresh concrete leading to honeycombs and therefore threatening the durability of the structures. Hence, providing the minimum viscosity which could yet, keep the stability of the mixture, was a proper strategy in this case. This is why no more effort was made to enhance the static stability of the mixtures. Generally speaking, the fresh properties of the mix designs adjusted for the project, were almost similar in terms of the three main properties considered for SCC; filling ability, passing ability and segregation resistance Hardened Properties The required cylinder compressive strength in 28 days is 30 MPa. Due to the environmental condition of the structures in the project, it is mandatory that the hardened concrete fulfills the requirements of the National Code of Practice for Concrete Durability in the Persian Gulf and the Sea of Oman [25]. In this code, exposure condition of structures is divided into 6 categories from normal condition to very severe (A to F) on the basis of which, some requirements are assessed for the structures in each condition. These features depend on permeability characteristic of concrete towards deleterious chemicals, most importantly chloride as the prime reason of damage to the structures in this region due to corrosion. The experiments done on hardened concrete to investigate its durability properties are water absorption, water permeability and rapid chloride permeability tests (RCPT). By taking into account the location of the structures, the National Durability Code categorizes them as "above-ground onshore facilities exposed to winds carrying chloride" which places them in the severe condition category. In the following, the result of compressive strength is presented and results from durability tests are compared to the allowable limits mentioned in the National Durability Code. Compressive strength Compressive strength test is done on cylindrical specimens in 7 and 28 days of age. The results are shown in Figure 5. As expected, SFC samples demonstrated higher strengths compared to FAC samples. Compressive strength of FAC samples were 35.1 and 38.4 MPa in 7 and 28 days respectively while, SFC compressive strength was higher for 14% and 20% in 7 and 28 days of age compared to corresponding FAC mixtures leading to 40.2 and 46.2 MPa of strength. These results clearly show the superiority of SF in enhancing the mechanical properties in comparison to FA. Water absorption, water permeability and rapid chloride ion permeability The water absorption results of concrete specimens are presented in Figure 6 (a). The allowable limit for this test mentioned in the National Durability Code is 3 percent of the mass of the dry specimen. As is seen, both mix designs fall into the allowable range with SFC having considerable lower water absorption. This is mainly due to the enhancement of the microstructure of the concrete made with SF replacement.

11 Figure 5. Compressive strength results Water permeability results are displayed in Figure 6 (b). The obtained results are 5 and 7.9 mm for SFC and FAC respectively, both of which are remarkably lower than the maximum depth of penetration determined in National Durability Code. The better durability characteristic of the mixture incorporating SF is again evident in this experiment. Rapid chloride ion permeability test was conducted on both SCC mixtures. The total charge passing in 6 h as a measure of the chloride permeability is presented in Figure 6 (c). The total charge passed is 923 for SFC sample and 1262 for FAC specimens. The formation of a less porous, denser microstructure is critical for reduced chloride ion permeability. According to ASTM 1202, the chloride ion permeability is subsumed as very low for SFC and low for FAC. As expected, the mixture containing SF has better hardened properties when compared to the one incorporating FA. While both mix designs have almost the same fresh properties the superiority of SFC in terms of hardened properties makes it a better choice to be used in practice. Moreover, the easier accessibility of SF in the region makes this mix design economically justifiable and more convenient for application in the project. Therefore among the two possible choices, the SFC was chosen to be cast in the wall elements. 6. CASTING THE CONCRETE Based on the mix design adjusted in laboratory, the concrete was fixed using the equipments in the site to reach the required fresh properties. Fluctuation in raw material gradations and moisture contents can have dramatic effect on the stability and fluidity of the concrete mix. The total water content consists of mixing water and water from the surface moisture of aggregates [26]. Due to the changes in water content of aggregates, especially fine aggregates, and the difficulties associated with measuring it in site, the concrete had to be adjusted for the required water. (a) (b)

12 (c) Figure 6. Durability tests results, a) Water absorption test, b) Water penetration tets, c) RCPT To this end, all the ingredients including the superplasticizer dosage were chosen to be equal to what was achieved in the laboratory and the water was adjusted so that the slump flow of cm was reached. By this means, reaching to a slump flow equal or close to the targeted slump flow could indicate that the targeted w/cm ratio was fulfilled. However, the moisture content of fine materials was measured manually every morning and prior to the production of the concrete. Due to the inaccuracy of the measurement, the results were not reliable and were only used as a first assumption to calculate the required mixing water. After a few trial batches, the concrete was successfully adjusted to comply with the laboratory results Concreting the test wall To examine the suitability of the mix design for application in wall elements, a test wall was formed. It was 2 m in height and 30 cm width. The congestion of reinforcement in the test wall was approximately two times more than the real walls with a big opening in the middle and two columns on both side of the opening with the intention to simulate the worst case. Figure 7 shows the test wall layout. 3 m 3 of concrete was made to be cast into the test wall. The batching machine capacity was 0.5 m 3 and therefore 6 batches were made successively and then carried to the pilot wall by a truck mixer. The slump flow of the first, third and sixth batches were measured to be 62, 65 and 64 cm. After each slump flow measurement, water was adjusted for the next batches so that the final slump flow of the concrete would be cm. However, strict quality control was necessary in the beginning of the work until a consistent production could be achieved. The concrete was discharged in truck mixer mixing the concrete with a speed of 15 rpm. After 20 minutes of hauling time, the slump flow was measured to be 60 cm with the same opening in the J-ring test flow (confined flow) just before the concrete was cast. The concrete was placed by a bucket into the test section and no mechanical compaction was done. Figure 8 shows the wall one day after concreting and after the forms were removed. It is evident that the concrete has fully filled the form and that has compacted under its own weight. Although a considerable congestion of reinforcement existed in the pilot wall, the concrete has properly passed from the narrow spacing between the rebars, resulting in a smooth and dense surface without any signs of honeycombs or any deficiencies. The application of the SFC in the test wall confirmed the suitability of this mixture for casting in the structures of the project.

13 Figure 7. The test wall Figure 8. The test wall after removing the forms Concreting the wall elements After checking the concrete in the test wall and meeting the acceptance conditions, the concrete was adjusted for application in the structures. Concrete was pumped into the wall elements. Unlike the conventional concrete in which when being cast, a considerable number of workers were required for vibrating the concrete and moving the pump hose, utilizing SCC could reduce the number of workers required to the minimum of one. The concrete was released at 10 m distances and could flow horizontally for about 15 m. Final report of RILEM TC 188-CSC 'Casting of self-compacting concrete' suggests 5-8m distances along the formwork for the concrete to be discharged [26]. As mentioned in this report, it is beneficial to let the concrete flow horizontally to prevent the air bubbles to get trapped in the concrete. No vibration was done. Figure 9 shows the walls after the removal of the forms. As is seen, the concrete has fully filled under the openings which was a cumbersome in case of using the conventional concrete. No honeycomb is observed and the surface of the walls appears to be very smooth with a uniform color.

14 (a) (b) (c) Figure 9. Appearance of the walls after removal of the forms.(a): Columns intersecting the walls, concreting the columns was a major problem in the past while by using SCC this problem has been overcame (b): The SCC has fully filled under the openings with the length of 5 m ( The dark color seen is due to the curing compound used) (c): SCC has fully filled under the openings 30 cm above the ground. Vibrating the concrete beneath these openings is almost impossible when CC is used. 7. CONCLUSION In the paper presented, a case study investigation was carried out. Due to the problems associated with the consumption of the CC, application of SCC was proposed for wall elements 3 m in height and 30 cm in thickness. Trial batches were made using FA to reach a mix proportion which could ensure the proper fresh state properties. The results obtained could be summarized as follows: Increasing the cementitous materials from 450 kg/m 3 to 500 kg/m 3 has a marked influence on passing ability of the FA mixtures in the J-ring test.

15 The higher the cementitious materials, the higher the flowability in the same SP dosage. It seems that in the same cementitious materials content, excluding the fine gravel and replacing it with the coarse gravel leads to a better passing ability in a condition that enough paste is provided i.e. the second series with 500 kg/m 3 cementitious materials. Different Proportions of aggregates can largely affect the fresh properties and hence the best combination should be adopted. Two SCC mix designs were selected as the final mix design, the FAC and SFC. Fresh properties were tested to ensure that the mix designs meet acceptance criteria assumed for the concrete. Further, the compressive strength and durability properties of the mixtures were investigated to meet the National Code of Practice for Concrete Durability in the Persian Gulf and the Sea of Oman due to the proximity of the structures to rich-in-chloride waters of the Persian Gulf. While the fresh properties were almost similar for both mixtures, the mix design incorporating SF performed much better in terms of the hardened properties. The values obtained for compressive strength, water absorption, water penetration and RCPT were much higher for the SFC. Due to the superiority of the SFC and also due to the easier accessibility of SF in the region, the SFC was chosen to be cast into the structures. The concrete was then adjusted in the site using the available facilities in the site and was cast into the wall elements. Although the concrete was placed without any mechanical vibration, it fully filled the formwork without any signs of honeycombs. Moreover the finished surface had also a better and smoother appearance with a more uniform color. REFERENCES [1] Okamura, H., Ozawa, K., Ouchi, M. (2000). Self-Compacting concrete, Structural concrete, 1(1), 3-17 [2] Gesoglu, M., Ozbay, E. (2007). Effects of mineral admixtures on fresh and hardened properties of self-compacting concretes: binary, ternary and quaternary systems, Materials and Structures, 40(9), [3] Koehler, P. E., Fowler, D. W. (2008). Dust-of-fracture aggregate microfines in self-consolidating concrete, ACI Materials Journal, 105(2), [4] Poon, C.S., Ho, D.W.S. (2004). A feasibility study on the utilization of r- FA in SCC, Cement and Concrete Research, 34(12), [5] Ye G., Liu X., De Schutter, G., Poppe, A-M., Taerwe, L. (2007). Influence of limestone powder used as filler in SCC on Hydration and microstructure of cement pastes, Cement and concrete composites, 29(2), [6] Poppe, A-M., De Schutter, D. (2005), Cement hydration in the presence of high filler contents, Cement and concrete research, 35(12), [7] Sonebi, M. (2004). Medium strength self-compacting concrete containing fly ash: modeling using factorial experimental plans, Cement and Concrete Reseach, 34(7), [8] Turkel, S., Altuntas, Y. (2009). The effect of limestone powder, fly ash and silica fume on the properties of self-compacting repair mortars, Sadhana, 34 (2), [9] ACI Committee 237, (2007). Self-consolidating concrete (237R-07), American Concrete Institute, Farmington Hills, USA [10] ASTM C33-99, (1999). Standard specification for concrete aggregates, ASTM international, West Conshohocken [11] ASTM C1611/ C 1611 M-09b, (2009). Standard test method for slump-flow of self-consolidating concrete, ASTM international, West Conshohocken. [12] ASTM C1621/C1621 M-09b, (2009). Standard test method for passing ability of selfconsolidating concrete by J-ring, ASTM international, West Conshohocken. [13] Ozawa, K., Sakata, N., Okamura, H. (1995). Evaluation of self-compactibility of fresh concrete using the V-funnel test, Concrete library of JSCE, 25, [14] Petersson, O., Billberg, B., Van, B. K. (1986). A model for self-compacting concrete. In : Bartos PJM et al. (eds) Proceedings of International Rilem conference on production methods and workability of concrete, Chapman & Hall/E & FN Spon,

16 [15] BS EN , (2010) Testing fresh concrete part 12: self-compacting concrete, J-ring test, BSI Standards Publication. [16] ASTM C1610/ C 1610 M-10, (2010) Standard test method for static segregation of selfconsolidating concrete using column technique, ASTM international, West Conshohoken. [17] ASTM C , (1997). Standard Test Method for Density, Absorption, and Voids in Hardened Concrete, ASTM international, West Conshohoken. [18] BS EN , (2009). Testing hardened concrete. Depth of penetration of water under pressure, BSI Standards Publications. [19] ASTM C 1202, (1994). Standards test method for electrical indication of concrete's ability to resist chloride ion permeability, Annual book of ASTM standards, (4): [20] ACI committee 212, (2010). Chemical admixtures (212.3R-10), American Concrete Institute, Farmington Hills, USA. [21] EFNARC, (2002). Specifications and guidelines for self-compacting concrete, UK: EFNARC. [22] Hwang, S., Khayat, K.H., Bonneau, O. (2006). Performance-based specifications of selfconsolidating concrete used for structural applications, ACI Materials Journal, 108 (3), [23] Shekarchi, M., Libre, N. A., Mahoutian, Mohebi, A., Behradi Yekta, S. (2007). SCC Test Methods and Discussion of the Results of Fresh SCC Stability, Proceedings of 1st SCC Workshop, University of Tehran, Iran, [24] Zerbino, R., Barraga, B., Garcia, T., Agullo, L., Gettu, R. (2009). Workability tests and rheological parameters in self-compacting concrete, Materials and structures, 42(7), [25] Ramezaanianpour, A.A., Pourkhorshidi, A., (2007). National Code of Practice For Concrete Durability In The Persian Gulf and the Sea of Oman (in Persian), Building and Housing Research Center, Iran. [26] Rilem TC 188-CSC, (2006). Casting of self-compacting concrete, Materials and structures, 39(10),