YIELD OF CONCRETE WITH MINERAL ADMIXTURE

Transcription

1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 4, April 2018, pp , Article ID: IJCIET_09_04_061 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed OF CONCRETE WITH MINERAL ADMIXTURE Shruthi. A P. G. Student, Department of Civil Engineering, Karunya Institute of Technology and Sciences, Coimbatore, Tamilnadu Prince Arulraj. G Dean, Engineering and Technology, Karunya Institute of Technology and Sciences, Coimbatore, Tamilnadu Jayalin.D Assistant professor, Department of Civil Engineering, Karunya Institute of Technology and Sciences, Coimbatore, Tamilnadu ABSTRACT The volume of fresh concrete from a known quantity of materials is called Concrete yield. When the concrete is added with mineral admixtures such as silica fume, fly ash etc., there will be some changes in yield. There are two types of yield namely Over-yield and Under-yield. There will always be a difference between the theoretical and actual yield. Details of yield of concrete with mineral admixtures are not available in the literature. An attempt has been made to determine the yield of concrete with the mineral admixture silica fume. Cubes and cylinders were cast with different replacement levels of cement with silica fume. Yield of M20, M30 and M40 concrete with silica fume at replacement levels of 5%,, and were found. The 28 th day compressive strength of concrete specimens was also found. It is found that as the replacement level increases, yield and the corresponding strength of concrete also increase upto replacement level for M30 & M40 concrete. In case of M20 concrete, the yield increases upto replacement level. However the strength decreases beyond the replacement level of. The yield was found to be maximum at replacement level for all grades of concrete. Keywords: yield of concrete, volume, silica fume, mineral admixture Cite this Article: Shruthi A, Prince Arulraj G and Jayalin D, Yield of Concrete with Mineral Admixture, International Journal of Civil Engineering and Technology, 9(4), 2018, pp editor@iaeme.com

2 Shruthi A, Prince Arulraj G and Jayalin D 1. INTRODUCTION Concrete yield is defined as the volume of freshly mixed and unhardened concrete in a given batch. It shall be determined from the summation of the masses of individual ingredients of concrete divided by the mass per unit volume of the ingredients of concrete. The American Society for Testing and Materials (ASTM) standard specification for Ready Mixed Concrete (ASTM 94) has prescribed the calculation of yield. The total mass of the batch is calculated either as the sum of the masses of all materials, including water, entering the batch or as the net mass of the concrete in the batch as delivered. The unit weight is determined in accordance with ASTM C 138 (Test method for Unit weight, Yield and Air Content). ASTM C 94 requires the unit weight to be an average of at least three measurements with each sample removed from the midpoint of a different truck and measured using a ½ cubic-foot container. Yield has two problems. When an ordered concrete is insufficient to fill the forms it is called as Under-yield condition. When concrete has too much air or aggregate within it or if the forms are not filled properly, it produces surplus amount and this condition is called as Over-yield. Silica fume is a fine powder which is rich in silicon oxide content produced as a byproduct of silicon metal and ferrosilicon alloys. This material gets discharged into the atmosphere. In order to keep the environment clean, this fine powder gets collected and it is treated as a waste material. Nowadays silica fume is added as a mineral admixture in concrete because of its pozzolanic action. The silica fume is largely silicon dioxide with small amounts of iron or other impurities. Silica fume particles are 100 times finer particles than cement. The word Microsilica to denote silica fume was coined by the American Association of State Highway and Transportation Officials (AASHTO). When silica fume is mixed with the Portland cement, some portion of silica fume will enhance the process of hydration, while the other portion act as microfiller. When water is mixed with portland cement, the process of hydration starts which produce two primary products, calcium silicate gel and calcium hydroxide. Calcium silicate gel acts as a glue which binds the aggregate in the concrete mix. Calcium hydroxide comprise upto 25 percent of the volume of hydration products. Calcium hydroxide is not of any benefit to concrete and may actually become detrimental at high levels. When a high amount of calcium hydroxide is present, concrete may be more susceptible to sulfate attack, alkali aggregate reaction, or efflorescence. Any pozzolanic material added to concrete alters the hydration reaction. Silica fume that is used in concrete typically has a Si02 content in excess of 85 percent, while fly ashes typically has an Si02 content of 30 to 60 percent. While fly ash additives will increase the strength of hardened concrete over the course of months, silica fume additives will increase concrete strength in a matter of days. The second mechanism by which silica fume improves concrete is through the so-called "microfiller effect." Most silica fume has an average particle size of 0.1 micrometers, while a typical portland cement has an average particle size of 15 micrometers. The extreme fineness of silica fume allows it to fill the microscopic voids between cement particles. The microfiller effect is credited with greatly reduced permeability and improved paste-to-aggregate bond of silica fume concrete compared to conventional concrete. However, there is little difference in the moisture absorption (a property different from permeability) of silica fume concrete and conventional concrete. The addition of silica fume can also influence the colour of both plastic and hardened concrete. Typically, silica fume concrete has a darker grey colour than the conventional concrete and it can become almost black, in some cases. The colour of the silica fume depends on the carbon content and several other variables. Silica fume from one source could almost be white in colour, while that from another may be black. The colour of the silica fume apparently has no effect on the other properties of concrete. However, in editor@iaeme.com

3 Yield of Concrete with Mineral Admixture certain applications, such as parking structures, a darker colour concrete will reduce the lighting reflectivity of the floor and ceiling members. The addition of silica fume to a conventional concrete mix will significantly increase compressive strength. The actual strength contribution of the silica fume will vary widely, depending on the other constituents of the concrete mix. Even higher compressive strengths are possible when a mix is designed to produce high strength concrete with silica fume. 2. LITERATURE REVIEW An article from NRMCA 1 deals with the basis for calculating the volume of concrete as described in the ASTM C 94, Specification for Ready Mixed Concrete. Bruce A. Suprenant 2 discussed about the causes of variations in concrete yield. ASTM C 94 specially mentions that the volume of hardened concrete appears to be less than expected due to waste and spillage, over-excavation, spreading forms, some loss of entrained air, or settlement of wet mixtures. Yield variations also occur because of changes in the mix proportions or tolerances in weighing out the batch. The batched ingredients do not deliver the same volume that the laboratory test says they should. For instance, a 1% decrease in air content reduces the concrete batched by 1 4 cubic foot in a cubic yard (a 1% variation in yield). Some of these factors may have additive effects on yield and vary constantly during the project. It is rare that all the effects will be additive. If the concrete is consistently under-yielded, proportionally all the batch ingredients are to be adjusted to eliminate the deficiency. Aberden Group 3 developed a method to determine concrete yield. The volume of concrete produced per batch can be found using the formula: S = ( ) Where S = volume of concrete produced per batch, in cubic feet. N = number of bags of cement, in the batch; 94 = net weight of a bag of cement, in pounds; Wf = total weight of fine aggregate in batch in condition, in pounds. Wc= total weight of coarse aggregate in batch in condition used, in pounds; Ww = total weight of mixing water added to batch, in pounds; and W = weight of concrete, in pounds per cubic foot. To calculate yield, the following formula should be used: Y = Where Y = yield of concrete produced per 94-pound bag of cement, in cubic feet; S = volume of concrete produced per batch in cubic feet; N = number of bags of cement in the batch. AASHTO T article discusses about how to calculate the volume of concrete produced from a mixture of known quantities of component materials. Y = DOTD TR discussed about the method of test for yield using the formula mentioned above. From the studies, yield for the freshly mixed concrete mixtures were calculated based on the formulae. Debabrata Pradhan and D.Dutta 6 highlighted about the effects of silica fume in conventional concrete. They reported about the mechanical properties like compressive strength, compacting factor, slump of concrete with silica fume. The editor@iaeme.com

4 Shruthi A, Prince Arulraj G and Jayalin D optimum compressive strength was obtained at cement replacement by silica fume at all age levels (i.e. at 24 hours, 7 and 28 days). Ahmed M. Diab et al 7 gave the guidelines for the determination of compressive strength of silica fume concrete. They reported that concrete mix without of silica fume yielded lower compressive strength when compared with that of concrete mix with silica fume. Zemei Wu et al 8 reported that silica fume content influences the microstructure development and bond to steel fibre in ultra-high strength cement-based materials. They observed that strength increased upto a replacement level of and when the replacement level exceeded, the strength decreased. An attempt has been made to determine the yield of concrete with silica fume. 3. PARAMETERS SELECTED FOR THE EXPERIMENTAL INVESTIGATION M20, M30 and M40 concrete grades were considered in the experimental investigation. Cement was replaced with silica fume and four replacement levels namely (5%,, and ) were considered for this investigation. For each grade and for each replacement, the yield of concrete and the strength was determined. 4. METHODOLOGY OF THE EXPERIMENT The methodology adopted is shown in Fig.1 Figure 1 Methodology Adopted Mix design was carried out for each grade of concrete. Three cubes and three cylinders were cast for each mix. The sizes of the cube are 150x150x150mm and the dimensions of the cylinder are 150mm diameter and 300mm height. The total volume of the cubes and cylinders editor@iaeme.com

5 Yield of Concrete with Mineral Admixture were calculated and the corresponding quantities of the mix were calculated. The empty weight of the moulds were noted down. The fresh concrete is placed inside the mould and compacted. The weight of the mould with fresh concrete was noted down. First the cylinders were filled and then the cubes were filled. Theoretical yield was calculated by adding the volume of cement, volume of silica fume, volume of fine aggregate and volume of coarse aggregate. Density of concrete was calculated by dividing the weight of fresh concrete by volume of the concrete. The actual yield was found by adding the volume of cylindrical moulds and cubical moulds that were completely filled with concrete and adding the actual volume of concrete in the last mould. All the specimens were cured for 28 days. At 28 th day, the compressive strength and split tensile strengths test were found. A compression testing machine was used to determine the strength of concrete. The tests were carried out at a uniform rate of 14N/ mm 2 / min after the specimen had been centered in the testing machine. 5. RESULTS AND DISCUSSIONS Estimation of yield Yield of concrete was found experimentally for M20, M30 and M40 grades of concrete at various replacement levels of silica fume. Yield of concrete was found experimentally as details below. The quantity of materials required to fill the three cubes and three cylinders as per the mix design was determined. The weighed materials were mixed thoroughly, placed on the moulds and compacted in a table vibrator. The shortage or the excess quantity of concrete was measured. Expected volume of concrete = volume of 3 cubes + volume of 3 cylinders = 3 x 0.15 x 0.15 x x ᴫ/4 x x 0.3 = m 3. For M20 concrete at a replacement level of 0%, the estimation of yield is shown below. Actual volume of = 3x ᴫ/4 x x x 0.15x 0.15x x 0.15x(0.15-S/100) concrete = 3x ᴫ/4 x x x 0.15x 0.15x x 0.15x (0.15-9/100) = m 3. S is the shortage in cm. Experimental yield = X 1 m 3 = X 1 Experimental yield = m 3. The Experimental yield of concrete at various replacement levels are given in Table 1. S.No % Replacement of silica fume Table 1 Experimental yield for M20, M30 and M40 grade. Yield Experimental yield M20 M30 M40 % increase in yield Yield % increase in yield Yield % increase in yield editor@iaeme.com

6 Shruthi A, Prince Arulraj G and Jayalin D From table 1, it can be seen that as the replacement level increases, yield of concrete also increases for M20 concrete. In case of M30 and M40 concrete, the yield increases upto the replacement level of. Beyond, the yield is found to be decrease. From table 1, it can also be seen that the maximum increase in the yields of M20, M30 and M40 concrete are 5.63%, 4.86% and 3.71% respectively. The compressive and tensile strengths of the specimens are given in Table 2. S.No Table 2 Values of Compressive and Tensile Strength for M20, M30 and M40 grade % Replacement of silica fume CS M20 M30 M40 TS CS TS CS TS CS- Compressive strength; TS- Tensile strength From Table 2, it can be seen that as the replacement percentage increases the compressive and tensile strengths increase upto and decrease beyond it. The variations in the compressive strength at 28 th day with respect to yield of concrete for various grades are shown in figure 2, figure 3 and figure 4 respectively for M20, M30 and M40 grade of concrete. The variations in the yield of concrete with respect to the split tensile strength for M20, M30 and M40 grade of concrete are shown in figure 5, figure 6 and figure 7 respectively. M20 M30 COMPRESSIVE STRENGTH % 5% COMPRESSIVE STRENGTH % % Figure 2 Relation between Yield & Compressive strength for M20 grade Figure 3 Relation between Yield & Compressive strength for M30 grade editor@iaeme.com

7 Yield of Concrete with Mineral Admixture COMPRESSIVE STRENGTH M % % TENSILE STRENGTH M % 5% Figure 4 Relation between Yield & Compressive strength for M40 grade Figure 5 Relation between Yield & Tensile strength for M20 grade TENSILE STRENGTH % M30 5% TENSILE STRENGTH M % % Figure 6 Relation between Yield & Tensile strength for M30 grade Figure 7 Relation between Yield & Tensile strength for M40 grade From figure 2 and figure 5, it can be seen that even though the yield of concrete increases upto a replacement level of, the strength increases only upto a replacement level of in case of M20 concrete. In case of M30 and M40 concrete, both the yield and the strength increase upto a replacement level of. Beyond the yield as well as the strength decreases. 6. CONCLUSIONS The actual yield of concrete with various percentages of silica fume were found. Their corresponding compressive and split tensile strengths of concrete were also found. A replacement level of, both the yield of concrete and the strengths were found to be maximum editor@iaeme.com

8 Shruthi A, Prince Arulraj G and Jayalin D REFERENCES [1] Concrete in practice (CIP), NRMCA., Discrepancies in yield. [2] Bruce A. Suprenant., Causes of variation in concrete yield publication #J by the Aberdeen Group. [3] How to determine the concrete yield publication #C by the Aberdeen Group. [4] AASHTO T121, Density (Unit weight), Yield, and Air Content (Gravimetric) of concrete by WAQTC. [5] DOTD TR , Method of test for Weight per cubic foot, yield, and air content (Gravimetric) of concrete. [6] Debabrata Pradhan and Dutta.D, Effects of Silica Fume in Conventional Concrete, International Journal of Engineering Research and Applications, 2013, pp [7] Ahmed M. Diab, Abd Elwahab M. Awad, Hafez E. Elyamany and Abd Elmoaty.M, Guidelines in compressive strength assessment of concrete modified with silica fume due to magnesium sulfate attack, Construction and Building Materials 36, 2012, pp [8] Zemei Wu, Caijun Shi and Khayat.K.H., Influence of silica fume content on microstructure development and bond to steel fiber in ultra-high strength cement-based materials (UHSC), Cement and Concrete Composites 71, 2016, pp editor@iaeme.com