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20320140503015

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 132 MIX DESIGN FOR HIGH STRENGTH CONCRETE WITH PORTLAND CEMENT AND SILICA FUME Samir A. Al-Mashhadi Dalya Hekmat Hameed Asst. Prof. M.Sc. Student Babylon University Babylon University ABSTRACT The common method used to design mix with silica fume depends on similarity between projects requirements and make trail batches if there was a different. This study aims to build a design method for high strength silica fume concrete which covers a compressive strength (41-90) MPa, maximum aggregate size (14 to 25) mm, replacement level (5, 10, 15) % by wt. of cement and w/c+p (0.22-0.45) and make a trails mixtures to check its validation and modify it. This method based fixing cementitious material on (520) kg/m3 , it contains tables for select: maximum aggregate size, coarse aggregate content, w/c+p and silica fume replacement, air content, and initial dosage of SP to produce (50-75) mm slump. The materials content ranges in this method are: cement (442-494) kg/m3 , sand (444-784) kg/m3 , silica fume (26-78) kg/m3 , coarse aggregate (1067-1148) kg/m3 , water (114.4-234) kg/m3 , and SP (0.1-2.4) % by wt. of cement. Keywords: Silica Fume, Microsilica, High Strength Concrete, Mix Design of High Strength Concrete, Compressive Strength. 1. INTRODUCTION The term high strength concrete (HSC) is used to describe concretes that are made with carefully selected high quality ingredients, optimized mixture designs, and which are batched, mixed, placed, consolidated and cured to the highest industry standards ]1[ . The objective of any mixture proportioning method is to determine an appropriate and economical combination of concrete constituents that can be used for a first trial batch to produce a concrete that is close to that which can achieve a good balance between the various desired properties of the concrete at the lowest possible cost. A mixture proportioning method only provides a starting mix design that will have to be more or less modified to meet the desired concrete characteristics. In spite of the fact that mix INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132-150 © IAEME: www.iaeme.com/ijciet.asp Journal Impact Factor (2014): 7.9290 (Calculated by GISI) www.jifactor.com IJCIET ©IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 133 proportioning is still something of an art, it is unquestionable that some essential scientific principles can be used as a base for mix calculations ]2[ . Mix proportions for (HSC) are influenced by many factors, including specified performance properties, locally available materials, local experience, personal preferences, and cost ]3[ . Pozzolans such as silica fume (SF), fly ash, and metakaolin are introduced as supplementary cementitious materials. These admixtures play an important role as microfillers and help improve particle-packing density of cementitious system, rheological properties in fresh state, mechanical properties and durability. The American Concrete Institute ]4[ defines silica fume (SF) as “very fine non crystalline silica produced in electric arc furnaces as a by-product of the production of elemental silicon or alloys containing silicon”. SF was first sampled and characterized in the 1950s in Norway and formally adopted into design codes for concrete during the 1970s. Thereafter its use around the globe has been considerable. SF was first used in the UK in the early 1980s when major construction projects in the scrap, waste and marine industries commenced and concretes able to better resist these aggressive environments were required ]5[ . SF color varies from light to dark gray depending mainly on the carbon content. It is usually a gray colored powder, somewhat similar to Portland cement or some fly ashes containing at least 85% silicon dioxide. SF particles are spherical in shape and measure about 0.1 µm in diameter, i.e., they are about 100 to 150 times smaller than the average particle size of Portland cement. The specific surface area of silica fume is approximately (20000 – 30000) m2 /kg “as determined by the nitrogen adsorption method”. Silica fume is an extremely effective material for achieving very high strengths and significant decreases in permeability. Because of its chemical and physical composition, silica fume is highly effective for achieving high strength at both early and later ages ]6[ . It can be used as an admixture or a partial replacement for cement. There is no chart that can be used to drive the mixture ingredient to meet a specified level of performance for HSC with silica fume and most researchers interested on the effect of SF addition on the properties of fresh and hardened concrete and the best percentages for better results. The best approach to design a mix is to start with mixture proportions that have been used successfully on other projects with similar requirements ]4[ . Holland ]7[ put a procedure to select SF concrete mix proportion depending on concrete mixtures that are used in other projects, These procedures cannot consider as a method to design HSC with silica fume because most of starting mixes contain fly ash and slag. This study includes a proposal for silica fume high strength concrete mix design with specified concrete compressive strength. The proposed method is to cover the mix proportioning of concrete compressive strength in the range of (41-90) MPa, maximum aggregate size (MAS) of (14, 20 and 25) mm and silica fume replacement (5, 10, and 15) % by wt. of cement. 2. EXPERIMENTAL WORK 2.1 Material used HSC is obtained by selecting suitable materials, good quality control and proportioning. The material must be conforming to ACI committee 363R, 1997 ]8[ requirements. 2.1.1 Cement Ordinary Portland cement (type I) was used for making concrete. The chemical and physical properties of this cement are shown in tables, which comply with the Iraqi Standard Specification I.Q.S. No.5, 1984 ]9[ requirements.
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 134 Table (1): The chemical and physical properties of cement and silica fume Physical properties Cement Silica Fume# Specific surface (m2 /kg) 310* 25000** Specific gravity 3.15 2.2 Chemical Composition (%) CaO 62.20 1.3 SiO2 20.39 95.68 Al2O3 4.55 0.5 Fe2O3 3.81 - MgO 2.36 0.43 SO3 1.97 0.31 L.O.I 2.41 1.55 # Physical properties of silica fume are according to manufacturer. * Blain fineness ** Determined by nitrogen absorption method 2.1.2 Silica Fume The SF used was German production in a powder form, SiO2 content of 95.68%. Detailed physical properties and chemical composition are also given in Table 1. 2.1.3 Superplasticizrer To produce HSC with silica fume a high range water reducer was used. It was based on polycarboxylic ether and had the trade mark “Glenium 51”. It is a light brown color with 1.1 relative density. 2.1.4 Aggregate The coarse aggregate used was crushed granite with three maximum size (25, 20, 14 ) mm with specific gravity = 2.65, absorption = 0.6% and dry rodded unit weight (1530, 1537, 1546) for maximum size (25, 20, 14) respectively. Fine aggregate used was natural sand with specific gravity = 2.64, fineness modulus = 2.82, sulfate content = 0.3 and absorption = 1.4%. 2.2 Test Program Test program consists of fabricating and testing (10 ×10) cm cube compressive strength test specimens. Different variables were investigated, these variables are: 1- Six compressive strength ranges (41-90) MPa. 2- Maximum aggregate size (14, 20, and 25) mm. 3- Percentage of SF replacement (5, 10, and 15) % by weight of cement. 2.3 Mix design for high strength concrete After studying SF as a construction material, its effect on hardened and fresh properties of concrete, and its reactions inside concrete through the previous studies and mixtures which they were done to know the effect of this material on some properties of concrete, steps have been developed
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 135 for the design of concrete mix based on the data and recommendations mentioned in previous studies. These steps were checked to know the validity of them by fabricating trail mixtures and make necessary adjustments to the proposed design method. The principle of this method was fixing the cementitious material and slump in some way to control the amount of variables. About forty five trail mixes were done to investigate the required compressive strength and slump. In this study, three replacement ratios for the SF (5, 10, 15) % by weight of cement were used. Appointed a replacement ratio of 15% for the high, 10% for the medium and 5% for the relatively low compressive strength. It was decided to keep the SF content at not more than 15% by weight of cement so that the resulting concrete mixes would not be too expensive to produce. 2.4 Work Procedures Trails on mixtures selected from previous studies were done to obtain the required compressive strength and workability. According to that a mixture with proportion (C:F.A:C.A = 1:1.28:2.2) by weight was chosen as a starting mixture. A slump (50-75) mm was chosen as an initial slump in this study which is found suitable for mixing and vibrating the specimens [12]. The cementitious material is fixed on (520 kg/m3 ) ]12[ . This proportion used for:- 2.4.1 Determine initial superplasticizer dosage About forty five mixes are done to determine the suitable initial dosages for all blends to keep the slump constant. Because of high water demand of SF due to high surface area it can’t depend on mixing water to attain the required slump. So an initial dosage of superplasticizer is added to facilitate mixing, casting, and vibrating of samples. When no plasticizer is used, it has been suggested that an additional 1 litre/m3 of water should be used for every 1 kg/m3 of SF addition to maintain constant level of fluidity ]24[ . In this case the additional water leads to decrease compressive strength therefore, a high-range water reducing admixture should always be considered as a necessary ingredient in high-strength silica fume concrete. 2.4.2 Determine w/c+p to give the required strength Thirty trail mixes with different (w/c+p, maximum size of aggregate, and SF replacement) were making to ensure the relationship between each one of them and the resulted compressive strength. Two sets of mixtures were done to determine the suitable w/c+p for a required strength range. Tables (2) and (3) show the description of mixes and proportion of HSC used in first set which was the estimated one. After production the mixes above and depending on the obtained results, a new set were done with adjustment in w/c+p to ensuring the required compressive strength and trying to put it in the safe side. Tables (4) and (5) show the description of mixes and proportion of HSC used in second set. These two sets also helped to give the relationship between maximum sizes of aggregate and compressive strength which were used to check and modify the estimated one. Results obtained from the above-mentioned mixtures used in making the necessary adjustments to some pre-design estimation steps. To complete amendment on the pre-set design method, a new set of nine mixes were done to investigate if the table (4-3-3) in ACI committee 211.4R which was used to know the recommended volume of coarse aggregate per unit volume of high strength concrete with fly ash is applicable in this design method ]12[ .
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 136 Table (2): description of mixes in first set Group Symbol description A1 A11 Mix with w/c+p = 0.25, MAS = 14mm, and SF replacement = 15% A12 Mix with w/c+p = 0.27, MAS = 14mm, and SF replacement = 15% A13 Mix with w/c+p = 0.25, MAS = 20mm, and SF replacement = 15% B1 B11 Mix with w/c+p = 0.35, MAS = 20mm, and SF replacement = 10% B12 Mix with w/c+p = 0.37, MAS = 20mm and SF replacement = 10% B13 Mix with w/c+p = 0.35, MAS = 25mm and SF replacement = 10% C1 C11 Mix with w/c+p = 0.45, MAS = 20mm and SF replacement = 5%. C12 Mix with w/c+p = 0.47, MAS = 20mm and SF replacement = 5%. C13 Mix with w/c+p = 0.45, MAS = 25mm and SF replacement = 5%. Table (3): proportion of first set mixtures Mix symbol Cement kg/m3 SF kg/m3 Sand kg/m3 Gravel kg/m3 water kg/m3 HRWR liter/m3 HRWR % wt of cementit- ious w/c+p A11 442 78 665.6 1144 130.0 10.30 1.8 0.25 A12 442 78 665.6 1144 140.4 8.58 1.5 0.27 A13 442 78 665.6 1144 130.0 10.30 1.8 0.25 B11 468 52 665.6 1144 182.8 2.29 0.4 0.35 B12 468 52 665.6 1144 192.4 1.72 0.3 0.37 B13 468 52 665.6 1144 182.8 2.29 0.4 0.35 C11 494 26 665.6 1144 234.0 0.57 0.1 0.45 C12 494 26 665.6 1144 244.4 - - 0.47 C13 494 26 665.6 1144 234.0 0.57 0.1 0.45
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 137 Table (4): description of mixes in second set Group Symbol description A2 A21 Mix with w/c+p = 0.22, MAS = 14mm, and SF replacement = 15% A22 Mix with w/c+p = 0.25, MAS = 14mm, and SF replacement = 15% A23 Mix with w/c+p = 0.22, MAS = 20mm, and SF replacement = 15% B2 B21 Mix with w/c+p = 0.32, MAS = 20mm, and SF replacement = 10% B22 Mix with w/c+p = 0.35, MAS = 20mm and SF replacement = 10% B23 Mix with w/c+p = 0.32, MAS = 25mm and SF replacement = 10% C2 C21 Mix with w/c+p = 0.42, MAS = 20mm and SF replacement = 5%. C22 Mix with w/c+p = 0.45, MAS = 20mm and SF replacement = 5%. C23 Mix with w/c+p = 0.42, MAS = 25mm and SF replacement = 5%. Table (5): proportion of second set mixtures Mix symbol Cement kg/m3 SF kg/m3 Sand kg/m3 Gravel kg/m3 water kg/m3 HRWR liter/m3 HRWR % wt of cementi -tious w/c+p A21 442 78 665.6 1144 114.4 12.58 2.2 0.22 A22 442 78 665.6 1144 130.0 10.30 1.8 0.25 A23 442 78 665.6 1144 114.4 12.58 2.2 0.22 B21 468 52 665.6 1144 166.4 3.43 0.6 0.32 B22 468 52 665.6 1144 182.0 2.29 0.4 0.35 B23 468 52 665.6 1144 166.4 3.43 0.6 0.32 C21 494 26 665.6 1144 218.4 1.14 0.2 0.42 C22 494 26 665.6 1144 234.0 0.57 0.1 0.45 C23 494 26 665.6 1144 218.4 1.14 0.2 0.42 These nine mixes differ from previous mixtures whither they designed by using the adjustment steps from the previous work with inclusion table (4-3-3) in ACI committee 211.4R for selecting volume of coarse aggregate and table (6-3-3) in ACI committee 211.1R for choosing air content reduced by one percent ]12[ . Tables (6) and (7) show the description of these nine mixes and proportions of them respectively.
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 138 Table (6): description of mixes used in checking coarse aggregate content and air content Group Symbol description CA CA1 Mix with w/c+p = 0.22, MAS = 14mm, and SF replacement =15% CA2 Mix with w/c+p = 0.25, MAS = 14mm, and SF replacement =15% CA3 Mix with w/c+p = 0.22, MAS = 20mm, and SF replacement =15% CB CB1 Mix with w/c+p =0.32, MAS = 20mm, and SF replacement =10% CB2 Mix with w/c+p=0.35, MAS = 20mm and SF replacement =10% CB3 Mix with w/c+p=0.32, MAS = 25mm and SF replacement =10% CC CC1 Mix with w/c+p=0.42, MAS = 20mm and SF replacement =5%. CC2 Mix with w/c+p=0.45, MAS = 20mm and SF replacement =5%. CC3 Mix with w/c+p=0.42, MAS = 25mm and SF replacement =5%. Table (7): proportion of mixes used in checking coarse aggregate content and air content Mix symbol Cement kg/m3 SF kg/m3 Sand kg/m3 Gravel kg/m3 water kg/m3 HRWR liter/m3 HRWR % wt of cementi- tious w/c+p CA1 442 78 784 1067 114.4 13.73 2.4 0.22 CA2 442 78 689 1067 130.0 10.87 1.9 0.25 CA3 442 78 743 1114 114.4 12.58 2.2 0.22 CB1 468 52 612.5 1114 166.4 2.86 0.5 0.32 CB2 468 52 570 1114 182.0 2.29 0.4 0.35 CB3 468 52 591.4 1148 166.4 2.86 0.5 0.32 CC1 494 26 485 1114 218.4 1.14 0.2 0.42 CC2 494 26 444 1114 234.0 0.57 0.1 0.45 CC3 494 26 462 1148 218.4 1.14 0.2 0.42 2.5 Mixing Procedures The laboratory mixing procedure used in this study was outlined by Holland ]7[ , 2005 and SF association. The concrete ingredients are mixed in a pan type mixer with 0.1 m3 capacity. Added SF with the coarse aggregate and some of the water. Batching SF alone or first can result in head packing or balling in the mixer. Mix SF, coarse aggregates, and water for 1½ minutes. The procedure is stated in the following: 1- Add the Portland cement. Mix for an additional 1 ½ minutes. 2- Add the fine aggregate and use the remaining water to wash in any chemical admixtures added at the end of the batching sequence. Mix for 5 minutes, rest for 3 minutes, and mix for 5 minutes.
  8. 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 139 3- Add the fine aggregate and use the remaining water to wash in any chemical admixtures added at the end of the batching sequence. Mix for 5 minutes, rest for 3 minutes, and mix for 5 minutes. 2.6 Casting and Curing of Test Specimens The molds used were cleaned, assembled and oiled. The concrete was cast in molds in three layers; each layer compacted by using vibrating table for adequate time to remove any entrapped air. The concrete surfaces were leveled by trowel, and the specimens were covered with nylon sheets to prevent evaporation of water for 24 hours. In the second day the specimens were demolded and put in water for curing at temperature (21-27) o C to the day of testing after 28 day. 2.7 Testing Fresh and Harden Concrete a- Slump test This test is used to determine the workability of concrete mixture according to ASTM 143-05 by using standard slump cone. Slump maintained constant at rang (50-75) mm for each mix. b- Test the relation between slump and superplasticizer dosage Four mixes were used to determine the optimum dosage of superplasticizer in which there is no increase in slump when increasing the dosage of superplasticizer. The proportions of mixtures used for this purpose are shown in table (8). Table (8): proportion of mixes for determine optimum dosage of SP Mix No. cement kg/m3 SF kg/m3 Sand kg/m3 Gravel kg/m3 * Water kg/m3 SP % wt of cement 1 468 52 665.6 1144 156 2 2 468 52 665.6 1144 156 4 3 468 52 665.6 1144 156 6 4 468 52 665.6 1144 156 8 *MAS = 14 mm c- Compressive strength test (10×10) cm cubes were cast and tested to determine the compressive strength of hardened concrete at age of testing (28 days). The tests were made by a compression testing machine according to the BS 1881: Part 116, 1989. The machine which is used in the tests is one of the electronic type of 2000 kN capacity. The average of three specimens was recorded for each mix. 3 RESULTS AND DISCUSSIONS 3.1 Initial dosage of superplasticizer Table (9) shows the initial dosage of superplasticizer which was necessary for mixes containing different levels of SF to have a constant slump of (50-75) mm, measured according to ASTM 143-05. It can be observed that the mixes incorporating higher SF content and lower w/c+p tended to require higher dosages of superplasticizer like mixes CA1 and A21 which had maximum dosage of SP.
  9. 9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 140 Table (9): initial dosage of SP obtained from this study Mix Symbol Dosage of SP% wt. of cementitious materials Mix Symbol Dosage of SP% wt. of cementitious materials Mix Symbol Dosage of SP% wt. of cementitious materials A11 1.8 A21 2.2 CA1 2.4 A12 1.5 A22 1.8 CA2 1.9 A13 1.8 A23 2.2 CA3 2.2 B11 0.4 B21 0.6 CB1 0.5 B12 0.3 B22 0.4 CB2 0.4 B13 0.4 B23 0.6 CB3 0.5 C11 0.1 C21 0.2 CC1 0.2 C12 - C22 0.1 CC2 0.1 C13 0.1 C23 0.2 CC3 0.2 Mix C12 didn’t need an initial dosage of superplasticizer because it had a sufficient amount of water (w/c+p = 0.47) to obtain (50-75) mm slump. Generally the dosage range of SP in this work was (0.1-2.4) % wt. of cementitious materials. The higher demand of superplasticizer with the concrete containing SF can be attributed to the very fine particle size of silica fume that causes some of the superplasticizer being adsorbed on its surface ]6[ , ]15[ , ]16[ . It is worth adding that mixes incorporating more SF were more cohesive due to the large increase in surface area which gives a corresponding increase in internal surface forces and less segregation and bleeding this is in agreement with the findings of Khatri and Sirivivatnanon ]16[ , Sobolev and Batrakov ]17[ , Bhikshma et al ]18[ and Nacer .]19[ The effect of condensed SF on the rheology of fresh mortar is generally viewed as a ‘‘stabilizing effect.’’ In other words, the addition of very fine particles to concrete tends to reduce segregation and bleeding tendencies. Without SF, the finest particles in mortar are those of Portland cement. Since the sand particles are bigger than the cement particles, the latter act as stabilizers by reducing the dimensions of channels through which bleed water rises to the surface of mortar. When very fine particles of SF are added to the mortar, the size of flow channels further reduced because these fine particles are able to adjust their positions to occupy the empty spaces between cement particles ]20[ . 3.2 Relation between slump and superplasticizer dosage This relation obtained by making four trail mixtures with fixing all variables except SP dosage which is increased gradually to the optimum dosage. It gives an indication about the suitable estimation dosage to achieve the required slump because the effect of SP is different from type to another. Also it helps to know the dosage after which excess additions of SP lead to segregation and thus the selected dosage will be on the safe side. Table (10) and figure (1) show the results obtained from this study.
  10. 10. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 141 Table (10): Results of slump test for mixtures includes *maximum aggregate size = 14 mm The results show an increased in slump with the increased of SP dosage this status may be analyzed as follows. When water is added to cement, the grains are not uniformly dispersed throughout the water but tend to form into small lumps or flocs due to van der Waals’ forces, electrostatic interactions between the opposite charges and surface chemical interactions between the hydrating particles. These flocs trap water within them causing the mix to be less mobile and fluid. In the presence of a superplasticizer, deflocculation or dispersion of cement particles occurs due to adsorption and electrostatic repulsion. This process does not allow the formation of entrapped water and discourangessurface interaction of the particles ]21[ , ]22[ . Fig. (1): Relation between SP dosage and slump 3.3 Compressive Strength results of silica fume high strength Concrete After putting hypothetic procedures for making silica fume high strength concrete, it was starting to make trail batches for each putting step to ensure it. The first set of mixtures used to ensure if a suggestion w/c+p are given strength ranges which selected for a certain MAS and level of SF replacement. Table (11) shows the results of compressive strength obtained from these mixtures and the ranges which are supposed to be within. The value of strength for all mixtures is average of three cubes (10 × 10) cm. Mix No. cement kg/m3 SF kg/m3 Sand kg/m3 Gravel kg/m3 * Water kg/m3 SP % wt. of cementitious materials Slump mm 1 468 52 665.6 1144 156 2 80 2 468 52 665.6 1144 156 4 130 3 468 52 665.6 1144 156 6 200 4 468 52 665.6 1144 156 8 segregation
  11. 11. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 142 Table (11): compressive strength results of first set Mix symbol w/cm Compressive strength (MPa) Range of strength (MPa) A11 0.25 81 80-85 A12 0.27 73 75-79 A13 0.25 76 75-79 B11 0.35 70 68-74 B12 0.37 61 61-67 B13 0.35 59 61-67 C11 0.45 52 50-60 C12 0.47 42 41-49 C13 0.45 46 41-49 All mixtures in the first set satisfy compressive strength range except (B13 and A12). Maximum strength is (81) MPa obtained from mixture (A11) due to the high replacement of SF, low w/c+p and small MAS, while minimum strength (42) MPa obtained from mixture (C12) due to low level of SF, high w/c+p and large MAS. It is obvious that the value of strength for most success mixtures is near to lower value of strength range. For this reason and to provide more safety when designing with making all mixes check the required strength range, it suggested re-casting the previous set of mixtures but with lower w/c+p. Table (12) shows the results of compressive strength obtained from second set mixtures and the ranges which are supposed to be within. Table (11): compressive strength result of second set Mix symbol w/cm Compressive strength (MPa) Range of strength (MPa) A21 0.22 88 80-85 A22 0.25 81 75-79 A23 0.22 79 75-79 B21 0.32 73 68-74 B22 0.35 70 61-67 B23 0.32 69 61-67 C21 0.42 56 50-60 C22 0.45 52 41-49 C23 0.42 49 41-49 Results show that all values of compressive strength were higher than first set and more than the put strength range. This belong to lower w/c+p which inversely proportional with strength. The higher strength allow amendment to the values of these ranges and makes it higher. Maximum strength reached to (88) MPa in mix (A21) and minimum strength was (49) MPa in mix (C23). Mixes (A22 and A23) have the same range of strength and give strength within it although the two mixes having different MAS this attributed to the effect of reducing w/c+p ratio for large MAS. This leads to reduce the effect of MAS on strength between two mixes. The same for mixes (B22 , B23) and (C22 , C 23).
  12. 12. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 143 Table (12) shows the results of strength obtained from mixtures which designed by following steps developed from results of previous mixes. Tables of air content and volume of coarse aggregate mentioned above were within the steps .]12[ The advantage of such mixes is to know if tables content of the air and coarse aggregate suitable for use in concrete mix design steps developed. Table (12): results of strength for the designed mixes Mix symbol w/cm Compressive strength (MPa) Designed Range of strength (MPa) CA1 0.22 87 80-85 CA2 0.25 82 75-79 CA3 0.22 78 75-79 CB1 0.32 74 68-74 CB2 0.35 68 61-67 CB3 0.32 66 61-67 CC1 0.42 57 50-60 CC2 0.45 53 41-49 CC3 0.42 52 41-49 The results of these mixtures are virtually identical to the results of mixtures in the second set, which means that the tables of content of air and coarse aggregate can be applied. Also it proved that it is possible to make a change to the pre-set ranges of strength. It is clear that SF enhanced compressive strength; the presence of SF in the Portland cement mixes causes considerable reduction in the volume of large pores at all ages and is therefore instrumental in enhancing the compressive strength. Also, the pozzolanic reaction of SF reduces the CH content, which leads to increase the strength. SF changes the orientation of CH crystals in the zone, resulting in less micro cracking at the transition zone ]23[ . 3.4 Procedures of mix design resulted from this study The results obtained from experimental work can be summarized and arranged into steps which can be easily followed to get the suitable proportion for mixtures according to required compressive strength. The slump value will be fixed on (50-75) mm, this value attained with initial dosage of superplasticizer because without superplasticizer concrete is difficult to consolidate due to the effect of SF. Cementitious materials will fix on (520) kg/m3 within limits of cement content for high strength concrete. step1. Calculate the required compressive strength Required compressive strength determined from below equation [8]: fcr ˊ = …………. (1) step2. Select maximum size of aggregate Depending on required strength table (13) shows the suitable sizes of aggregate for strength ranges. It should be noted that the ACI committee 318M, 2005 recommendation to determine maximum size of aggregate are valid.
  13. 13. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 144 Table (13): select maximum size of aggregate Required Concrete Strength fcr (MPa) Maximum Size of Aggregate (mm) 90 - 75 14 - 20 74 - 60 20 - 25 59 - 41 20 - 25 step3. Select optimum coarse aggregate content Optimum coarse aggregate selection is relating to the maximum size of aggregate as shown in table (14). The amount of coarse aggregate per m3 can be determined according to the elect value by the following equation: Weight of coarse aggregate = (coarse aggregate factor x DRUW) ........ (2) Table (14): volume of coarse aggregate *Volumes are based on aggregates in oven-dry rodded condition as described in ASTM C29 for unit weight of aggregates. step4. Select water to cementitious ratio and silica fume replacement Depending on the required compressive strength and maximum size of aggregate, w/c+p can be chosen form table (15). This table also gives the percentage replacement of silica fume for each range of compressive strength. Table (15): Select w/c+p and SF replacement *fcr (MPa) 28 day SF (% by weight of cementitious materials) Maximum size of aggregate (mm) 14 20 25 90 - 83 15 0.22 - - 82 - 75 0.25 0.22 - 74 - 67 10 - 0.32 - 66 - 60 - 0.35 0.32 59 - 52 5 - 0.42 - 51 - 41 - 0.45 0.42 *fcr ′ = fc ′ +1400 step5. Calculate content of water and cementitious material As mentioned previously the amount of cementitious material is fixed on (520) kg/m3 . So, after chosen w/c+p and silica fume replacement in step 4, water content can be determine by multiply w/c+p by 520. While silica fume content per m3 calculated by multiplying the selected Optimum coarse aggregate contents for nominal maximum sizes of aggregates to be used with sand with fineness modulus of 2.5 to 3.2 Nominal maximum size, mm 14 20 25 Fractional volume* of oven dry rodded coarse aggregate 0.69 0.725 0.75
  14. 14. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 145 percentage replacement by 520. The result of 520 minus silica fume content will be equal the cement content per m3 . step6. Select volume of entrained air required Table (16) shows the volume of air entrained for each maximum size used throughout the study. Table (16): Air content of silica fume concrete Nominal maximum aggregate size Entrapped Air content % mm 14 1.38 20 0.92 25 0.5 step7. Calculate sand content After determining the weights per m3 of coarse aggregate, the cement, silica fume, water, and the percentage of air content, the sand content can be calculated to produce m3 , using the absolute volume method. step8. Estimate initial dosage of superplasticizer To produce high strength concrete with silica fume, using of HRWR is unavoidable. So table (17) gives estimation for dosage of HRWR to achieve an initial slump between 50 to 75 mm. Table (17): Initial dosage of HRWR w/c+p 0.22 0.25 0.32 0.35 0.42 0.45 SP(% by wt. of cement) 2.2 1.9 0.5 0.4 0.2 0.1 # These dosages may be changed due to the type of SP step9. Making trail mixtures Trail mixtures are necessary to ensure that all proportion used in concrete production give the required properties such as slump and compressive strength. The weights of sand, coarse aggregate, and water must be adjusted to correct for the moisture condition of the aggregates used. These mixes are essential to chemical admixture dosage to know the exact dosage for a required slump. 3.5 Examples for silica fume high strength concrete mix design Design a silica fume high strength concrete mix to cast bridge girders. Compressive strength for this concrete was 73 MPa in 28-day. specific gravity = 2.65, absorption = 0.6% and oven dry rodedd unit weight of coarse aggregate = (1546, 1537, 1530) kg/m3 for MAS (14, 20, 25) mm respectively. Natural sand was used conforming to ASTM C33 with fineness modulus = 2.83, specific gravity depending on oven-dry weight of fine aggregate = 2.64, absorption = 1.4% and oven dry rodedd unit weight = 1680 kg/m3 . Specific gravity for silica fume = 2.2 and for cement = 3.15, moisture content = (0.4, 0.3) % for sand and coarse aggregate respectively. (This example will repeated for compressive strength = 73 , 56 , 45 MPa)
  15. 15. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 146 Example 1 for 73 MPa Example 2 for 56 MPa Example 3 for 45 MPa Solution:- Slump fixed on (50-75) mm as initial slump for all examples. step 1:- Determine required compressive strength: ( fcrˊ) for Ex1 = = 13333 psi ≈ 92 MPa ( fcrˊ) for Ex2 = = 10580 psi ≈ 73 MPa ( fcrˊ) for Ex3 = = 8857 psi ≈ 61 MPa step 2:- From table (13) choose maximum size of aggregate (MAS) depending on required compressive strength:- MAS for Ex1 = 14 or 25 mm MAS for Ex2 = 20 or 25 mm MAS for Ex3 = 20 or 25 mm step 3:- Optimum coarse aggregate content for maximum aggregate size from table (14): (14 mm) = 0.69 m3 /m3 concrete. (20 mm) = 0.725 m3 /m3 concrete. (25 mm) = 0.75 m3 /m3 concrete. So weight of coarse aggregate per m3 according to Eq. (2): 0.69 × 1546 = 1067 kg/m3 for (MAS = 14 mm) 0.725 × 1537 = 1114 kg/m3 for (MAS = 20 mm) 0.75 × 1530 = 1148 kg/m3 for (MAS = 25 mm) step 4:- Although the required compressive strength of laboratory trail mixtures is (92, 73, 61) MPa the value of strength to be used in table (15) to select w/c+p will be:- 92 × 0.9 = 83 MPa for Ex1 73 × 0.9 = 66 MPa for Ex2 61 × 0.9 = 55 MPa for Ex3 So the value of w/c+p for three cases will be: 0.22, SF replacement = 15% by wt. of cement and MAS=14mm for Ex1 0.35 (for economical reason), SF replacement = 10% by wt. of cement and MAS= 20mm for Ex2 0.42, SF replacement = 5% by wt. of cement and MAS= 20mm for Ex3 step 5:- Cementitious material content = 520 kg/m3 for all mixtures. Weight of water = Cementitious material content × w/c+p = 114.4 kg/m3 for Ex1 = 182 kg/m3 for Ex2 = 218.4 kg/m3 for Ex3 Weight of silica fume = 0.15 × 520 = 78 kg/m3 for Ex1 = 0.1 × 520 = 52 kg/m3 for Ex2 = 0.05 × 520 = 26 kg/m3 for Ex3 Weight of cement = Cementitious material content – SF content = 442 kg/m3 for Ex1
  16. 16. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 147 = 468 kg/m3 for Ex2 = 494 kg/m3 for Ex3 step 6:- From table (16) the value of air content = 1.38% for Ex1 = 0.92% for Ex2 = 0.92% for Ex3 step 7:- Calculate weight of sand per m3 :Volumes of each material used per m3 without sand are determine as below: Volume of cement = = 0.14 m3 Volume of silica fume = = 0.035 m3 Volume of coarse aggregate = = 0.4 m3 Volume of water = = 0.114 m3 Volume of air content = = 0.0138 m3 Sum of volumes = 0.703 m3 Volume of sand per m3 = 1 – 0.713 = 0.297 m3 Weight of sand = 1000 × 2.64 × 0.297 = 784 kg/m3 for Ex1 Using the same way, weight of sand = 570 kg/m3 for Ex2 = 485 kg/m3 for Ex3 step 8:- Estimation dosage of SP is chosen from table (17):- 2.2 % by wt. of cementitious materials for Ex1= 12.58 L/m3 0.4% by wt. of cementitious materials for Ex2= 2.29 L/m3 0.2% by wt. of cementitious materials for Ex3= 1.14 L/m3 step 9:- Adjust water content: Weight of sand (wet) = wt. of dry sand × (1+ moisture content) = 784 × ( 1 + 0.004 ) = 787 kg/m3 Weight of coarse aggregate (wet) = wt. of dry coarse agg. × (1+ moisture content) = 1067 × (1 + 0.003) = 1070 kg/m3 Adjustment wt. of water = wt. of water – wt. of dry sand(moisture – absorption)for sand – dry wt. of gravel (moisture – absorption)for gravel = 114.4 – 784 (0.004 – 0.014) – 1067(0.003 – 0.006) = 125 kg/m3 for Ex1 = 193 kg/m3 for Ex2 = 227 kg/m3 for Ex3 step 10:- Make trail mixes to adjust superplasticizer content to obtain the required slump and required strength. Hint:- In case of not satisfying required compressive strength reduce w/c+p by 0.02 and retry trail mixes 0.2 % by wt. of cementitious materials from SP can increase slump 1 cm Table (18) shows the proportions of the mixtures per m3 for the pervious examples and compressive strength resulted from them.
  17. 17. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 148 Table (18): Proportions of mixtures for all examples Material Ex1 Ex2 Ex3 Cement (kg) 442 468 494 Silica fume(kg) 78 52 26 Sand, dry (kg) 784 570 485 Gravel, dry(kg) 1067 1114 1114 Water(kg) 114.4 182 218.4 HRWR % (wt. of cement) 2.2 0.4 0.2 Comp. strength 7 days(MPa) 64 46 39 Comp. strength 28 days(MPa) 90 67 58 4. CONCLUSIONS In this work, it was aimed to propose a mix proportioning method for the design of silica fume high strength concrete with compressive strength in the range of (41-90) MPa. The only method developed for this proposes depends on a mixture previously used in other project and makes necessary adjustment on it. From the results of the experimental work obtained in this work, the following conclusions are withdrawn:- 1- It is necessary to use superplasticizer when introducing SF to concrete in order to keep the water ratio at acceptable levels and obtain reasonable and maintainable workability. 2- Superplasticizer dosages increased with increasing SF replacement level by weight of cement. 3- Fresh concrete mixtures with SF are cohesive and therefore less prone to segregation and show no bleeding due to the high surface area of SF. 4- The resulted mix design has no table to select water content because SF needs high water demand which offset with compressive strength. So HRWR was used to obtain the required workability. 5- Table (4-3-3) in ACI committee 211.4R which was used for select volume of coarse aggregate for high strength concrete with fly as was valid to use with high strength silica fume concrete. 6- The resulted mix design method gives wide ranges to select compressive strength and w/c+p. 7- For different (MAS) the resulting compressive strength would be in the same range by increasing w/c+p. This effect gives an economical benefit. 8- Table (6-3-3) in ACI committee 211.1R for choosing air content reduced by one percent for silica fume concrete with compressive strength over (35) MPa was valid and right with resulted mix design. 9- High range of compressive strength conjugated with high replacement level of silica fume and low content of cement and vice versa.
  18. 18. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 149 10- Fine/coarse aggregate ratio decrease with decreasing of strength due to the increased of w/c+p. 11- With silica fume it can produce high strength concrete even with high w/c+p (equal to 0.45). 12- It is possible to design a mix with silica fume by following procedures proposed in this study. 13- Mixing procedures of silica fume concrete need long time to break down the agglomeration and to disperse silica fume. 5. REFERENCES [1] Lwin, P. E., and Triandafilou, P. E., 2005, “High Performance Concrete Structural Designer’s Guide,” First Edition, Federal Highway Administration’s, March 2005, 128 pp. [2] Aïtcin, P.C., 1998, “High-Performance Concrete,” E & FN Spon, London and New York. [3] Russell, H. G., 2000, “High-performance concrete mix proportions,” Concrete products Magazine, issue. June, 2000. [4] ACI Committee 234.R, 2000, “Guide for the Use of Silica Fume in Concrete,” American Concrete Institute. [5] Dunster, A., 2009, “Silica fume in concrete,” BRE, Information Paper IP 5/09, 12 pp. [6] Mazloom, M., Ramezanianpour, A. A., Brooks, J. J., 2004, “Effect of silica fume on mechanical properties of high-strength concrete,” Cement & Concrete Composites, Elsevier, Vol. 26, pp. 347-357. [7] Holland, T. C., 2005, “Silica Fume User’s Manual,” first edition, Federal Highway Administration, Washington, 193 pp. [8] ACI committee 363R, 1997, “State of the Art Report on High-Strength Concrete,” American Concrete Institute. Detroit, Vol. 81, No.4. [9] Iraqi Specification, No.5/1984, “Portland Cement,” National Center for Construction Laboratories and Researches, Baghdad, 2001. [10] ACI committee 211.4R, 1998, “Guide for Selecting Proportions for High-Strength Concrete with Portland Cement and Fly Ash,” American Concrete Institute. Detroit. [11] ACI committee 211.1, 2002, “Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete,” American Concrete Institute. [12] Hameed, D. H., 2010, “ Mix Design for High Strength Concrete with Portland Cement and Silica Fume”, M.Sc. Thesis, University of Babylon. [13] ACI Committee 234.R, 2000, “Guide for the Use of Silica Fume in Concrete,” American Concrete Institute. [14] Khatri, R.P., Sirivivatnanon, V., 1995, “Effect of different supplementary cementitious materials on mechanical properties of high performance concrete,” Cement and Concrete research , Vol. 25, No.1, pp. 209– 220. [15] Chakraborty, A. K., Ray, I., Sengupta, B., 2001, “High Performance Concrete for Containment Structures,” 16th international Conference on Structural Mechanics in Reactor Technology, Washington DC. [16] Khatri, R.P., Sirivivatnanon, V., 1995, “Effect of different supplementary cementitious materials on mechanical properties of high performance concrete,” Cement and Concrete research , Vol. 25, No.1, pp. 209– 220. [17] Sobolev, K. G., and Batrakov, V. G., 2007, “Effect of a Polyethylhydrosiloxane Admixture on the Durability of Concrete with Supplementary Cementitious Materials,” Journal of Materials in Civil Engineering, ASCE, Vol. 19, pp. 809-819.
  19. 19. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online) Volume 5, Issue 3, March (2014), pp. 132- 150 © IAEME 150 [18] Bhikshma, V., Nitturkar, K. and Venkatesham, Y., 2009, “Investigations On Mechanical Properties of High Strength Silica Fume Concrete,” Asian Journal of Civil Engineering (building and housing), Vol. 10, No. 3, pp. 335-346. [19] Nacer, S., 2005, “Optimization of Silica Fume Content And Water to Enhance Performance Of Concrete,” M.Sc. Thesis, Southern Illinois University Carbondale. [20] Appa Rao, G., 2003, “Investigations on the performance of silica fume-incorporated cement pastes and mortars,” Cement and Concrete Research, Vol. 33, pp. 1765-1770. [21] Dransfeild, J., 2003, “Admixtures for concrete, mortar and grout,” advanced concrete technology set, part II, Elsevier, chapter 4, pp. 3-36. [22] Ramachandran, V. S., 1995, “Chemical admixtures-recent developments,” Concrete admixture handbook: properties, science, and technology,” second edition, Noyes publications, U.S.A, chapter four, pp. 137-176. [23] Larbi, J.A., Bijen J.M., 1990, “Orientation of calcium hydroxide at the Portland cement paste-aggregate interface in mortars in the presence of silica fume a contribution,” Cement and Concrete Research, Vol. 20, pp. 461–470. [24] Sellevold, E. J., 1984, “Review: Microsilica in Concrete,” Project Report No. 08037-EJS TJJ, Norwegian Building Research Institute, Oslo. [25] P.J.Patel, Mukesh A. Patel and Dr. H.S. Patel, “Effect of Coarse Aggregate Characteristics on Strength Properties of High Performance Concrete using Mineral and Chemical Admixtures”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 89 - 95, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [26] Asst. Prof. Mr. Samir A. Al-Mashhadi, Asst. Prof. Dr. Ghalib M. Habeeb and Abbas Kadhim Mushchil, “Control of Shrinkage Cracking in End Restrained Reinforced Concrete Walls”, International Journal of Civil Engineering & Technology (IJCIET), Volume 5, Issue 1, 2014, pp. 89 - 110, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [27] Dr. D. V. Prasada Rao and G. V. Sai Sireesha, “A Study on the Effect of Addition of Silica Fume on Strength Properties of Partially Used Recycled Coarse Aggregate Concrete”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4, Issue 6, 2013, pp. 193 - 201, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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