Study of Recycled Aggregate Concrete Containing Silica Fume as Partial Replacement for Cement

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1 ISSN: X Impact factor: (Volume 4, Issue 2) Available online at: Study of Recycled Aggregate Concrete Containing Silica Fume as Partial Replacement for Cement Animesh Awasthi Lakshmi Narain College of, Bhopal, Madhya Pradesh Gourav Soni Lakshmi Narain College of, Bhopal, Madhya Pradesh ABSTRACT Ram Bharosh Lakshmi Narain College of, Bhopal, Madhya Pradesh Recycle Aggregate Concrete (RCA) is the concrete product produced with recycled aggregate to replace part or whole of natural aggregate. The purpose of this study is to find the properties of RCA and compare the same with the concrete produced with natural aggregates2 Recycle Concrete Aggregate has also been described as the most revolutionary development in concrete construction for several decades. It has proved to be beneficial from the point of economic, environmental benefits and Preservation of nonrenewable recourses this thesis presents a study conducted on mechanical and durability properties of recycled aggregates concrete. The investigation covered concrete mixes at water cementitious material with a ratio of 0.4. Ordinary Portland cement of 43-grade was used in this study. The percentage of recycled aggregates that partially replaced natural aggregates by weight were 0%, 10%, 20%, 30%, 40% and 50%. Concrete cubes and cylinders were cast and tested in laboratories. The optimum proportion of replacement was found by conducting tests on mechanical properties like Compressive strength test and Split tensile strength test. The results show that the optimum replacement of recycled aggregates with natural aggregates was 30%. Up to 30% replacement, it is possible to gain the same strength as conventional concrete. Beyond 30% replacement the strength results following the decreasing trend. Keywords: Workability, Compressive Strength, Tensile Strength, Silica Fume. 1. INTRODUCTION Nowadays concrete industry is consuming a lot of natural resources. This causes a lot of damage to environment and mother earth. So, the less cement and natural aggregates that are used in concrete production, the lower the impact on the environment. The increase in the cost of landfill, scarcity of natural resources for aggregate, encourages the use of construction waste as a source of aggregate. A sustainable construction has become a great concern over construction practice at the expense of the future of our planet. This is due to the fact that the construction industry is a massive consumer of natural resources and a huge waste producer as well. The high value of raw material consumption in the construction industry becomes one of the main factors that cause environmental damage and pollution to our mother earth and the depletion of natural and mineral resources. Every year, more than 165 million tones of natural aggregates are used in different civil and industrial constructions. Meanwhile, approximately 109 million tones of construction and demolition residues are generated in the UK; around 60 million tones of this are derived from concrete. The resources such as coarse aggregates, sands, and cement will be at a disadvantaged position, as these resources are not able to cope with the high demand in the construction industry. Therefore, utilizing the recycled aggregate may be one of the significant efforts in achieving a sustainable construction. As Recycled Aggregate (RA) begin to be acknowledged and accepted as a viable alternative to Natural Aggregates (NA), it is important to understand how Recycled Concrete Aggregate (RAC) performs compared with conventional concrete. A correct mix design and the introduction of differently shaped aggregates and different super plasticizers can influence structural concrete s performance and provide it with strengths similar to the corresponding natural aggregates concrete (NAC), or even a possible enhancement, making it Generally, it is important that coarse aggregates have good strength, durability and weather resistance, that its surface be free from impurities such as loam, silt and organic matter, durable particle free from absorbed chemicals in permissible amount that will not affect hydration of cement and water, and bond of cement paste. Aggregates could be classified by their weight, rock type, and their shape. 2018, All Rights Reserved Page 239

2 2. MATERIALS USED 2.1 Cement Although all materials that go into the concrete mix are essential, cement is very often the most important because it is usually the delicate link in the chain. The function of cement is, first of all, to bind the sand and stone together and second to fill up the voids in between sand and stone particles to form a compact mass. Although it constitutes only about 20 per cent of the volume of concrete mix, it is the active portion of binding medium and is the only scientifically controlled ingredient of concrete. Any variation in its quantity affects the compressive strength of the concrete mix. In the present investigation, Ordinary Portland Cement (OPC) of 43 Grade was used for all concrete mixes. 2.2 Aggregate The aggregate is the matrix or principal structure consisting of relatively inert and coarse particles. The coarse aggregate is used primarily for the purpose of providing bulk to the concrete. The most important function of fine aggregates is to assist in producing a workable and a uniform concrete mix. The fine aggregate also assists the cement paste to hold the coarse aggregate particles in suspension. This action promotes plasticity in the concrete mix and prevents segregation of the paste and coarse aggregates during its transportation. The aggregates provide about 75 per cent of the body of concrete and hence their influence is extremely important. The properties of these particles greatly affect the performance of concrete Fine Aggregate IS: defines the fine aggregate, as the one passing 4.75mm IS sieve. The fine aggregate is often termed as a sand size aggregate. Locally available riverbed sand was used in the present study. The per cent passing 600 micron sieve = The sand conforms to grading Zone III as per IS respectively Course Aggregate The coarse aggregate is defined as that retained on 4.75 mm IS sieve. To increase the density of the resulting concrete mix, the coarse aggregate is frequently used in two or more sizes. Two types of aggregates with different sizes have been used in the present study. The details of the same are as below: Aggregate passing 20 mm sieve Aggregate passing 10 mm sieve. The coarse aggregate used were washed and kept in water for 24hr s to remove dust and dirt and were dried to surface dry condition Natural Course Aggregate Crushed granite with nominal sizes of 10 mm and 20 mm were used as natural coarse aggregate Recycled Course Aggregate Concrete wastes of the material testing laboratory were used as coarse aggregates. Both natural and recycled aggregates followed the same grading and the same is shown in Table 1 & Table 2 Table-1: Cube Compressive Strength at 28 days for 20 mm Size of Aggregate 20mm size % retained per 100kg sieve size % retained on the sieve Cumulative % retained 20 mm 5% 5% mm 60% 65% 4.75 mm 25% 90% 2.36 mm 10% 100% Table-2: Cube Compressive Strength at 28 days for 10mm Size of Aggregate 10mm size % retained per 100kg sieve size % retained on sieve Cumulative % retained 12.5 mm 8% 8% 10mm 32% 40% 4.75 mm 55% 95% 2.36 mm 5% 100% 2018, All Rights Reserved Page 240

3 2.2.5 Silica Fume The terms of micro silica, condensed silica fume, and silica fume are often used to describe by-products extracted from the exhaust gases of ferrosilicon, silicon. And other metal alloy smelting furnaces. However, the terms of silica fume and micro silica are used for those condensed silica fumes that are of high quality for using in the cement and concrete industry. In the European standard, the term of silica fume has been used. Silica fume was first discovered in Norway in 1947 when the environmental controls started the filtering of the exhaust gases from furnaces. The main portion of these fumes was a finely composed of a high per cent of silicon dioxide. As the pozzolanic reactivity for silicon dioxide was well known, many studies have been done on it. There are over 3000 publications that have been published about silica fume and silica fume concrete. Conforming to AASHTO M 307 ASTM C 1240, silica fume can be utilized as material for supplementary cementations to increase the strength and durability. According to the Florida Department of Transportation (2004), the quantity of cementation materials. Silica fume consists of the fine particles with specific surface about six times of cement because its particles are very finer than cement particles. Hence, it has been found that when silica fume mixes with concrete the minute pore spaces decreases. Silica fume is pozzolanic, because it is reactive, like volcanic ash. Its effects are related to the strength, modulus, ductility, sound absorption, vibration damping capacity, abrasion resistance, air void content, bonding strength with reinforcing steel, shrinkage, permeability, chemical attack resistance, alkali-silica reactivity reduction, creep rate, corrosion resistance of embedded steel reinforcement, freeze-thaw durability, coefficient of thermal expansion (CTE), specific heat, defect dynamics, thermal conductivity, dielectric on Water Generally, water that is suitable for drinking is satisfactory for use in concrete. Water from lakes and streams that contain marine life also usually is suitable. When water is obtained from sources mentioned above, no sampling is necessary. When it is suspected that water may contain sewage, mine water, or wastes from industrial plants or canneries, it should be used in concrete unless tests indicate that it is satisfactory. Water from such sources should be avoided since the quality of the water stant, and degree of fibre dispersion in mixes containing short microfibers. could change due to low water or by intermittent discharge of harmful wastes into stream. The water used was the potable water as supplied in the structures laboratory of our institute. Water used for mixing and curing should be clean and free from injurious amounts of oils, acids, alkalies, salts and sugar, organic materials or other substances that may be deleterious to concrete. As per IS: potable water is generally considered satisfactory for mixing and curing of concrete. Accordingly potable water was used for preparation of all concrete specimens Admixtures Water-reducing and set-retarding admixtures are permitted in order to increase the workability of the concrete and to extend the time of discharge from 60 to 90 minutes. These admixtures are permitted and often required for superstructure concrete. Chemical admixtures and mineral admixtures as defined by ASTM C 494 are as follows: Super plasticizer CONPLAST SP 430 is a chloride free workability retention admixture based on selected organic polymers. Designed to provide workability retention where rapid workability loss is caused by high ambient temperatures or to compensate for delays in transportation. It is particularly suited to concrete mixes containing micro silica. Silica fume was used as a mineral admixture. It acts as a filler material, and gives the early strength to the concrete. Could change due to low water or by intermittent discharge of harmful wastes into stream. The water used was the potable water as supplied in the structures laboratory of our institute. Water used for mixing and curing should be clean and free from injurious amounts of oils, acids, alkalies, salts and sugar, organic materials or other substances that may be deleterious to concrete. As per IS: potable water is generally considered satisfactory for mixing and curing of concrete. Accordingly potable water was used for preparation of all concrete specimens 3. MIX PROPORTIONS Different quantities of materials and the mix proportions of the materials for each mix is shown in Table 3 Table 3. Quantities of Materials for Mix of Concrete Mixes Opc S.F Cag (20mm) Cag (10mm) RCA (20mm) RCA (10mm) M1 90% 10% 50% 50% 0% 0% M2 90% 10% 45% 45% 5% 5% M3 90% 10% 40% 40% 10% 10% M4 90% 10% 35% 35% 15% 15% M5 90% 10% 30% 30% 20% 20% M6 90% 10% 25% 25% 25% 25% 2018, All Rights Reserved Page 241

4 4. RESULT AND DISCUSSION ON EXPERIMENTAL TESTS 4.1 Slump Test Slump test is the most commonly used method of measuring the consistency of concrete Slump test was carried out on all the concrete mixes in the concrete laboratory. This test was very useful in detecting variation in the uniformity of a mix of given proportions. It also gives an idea of Water cement ratio to be used for different mixes. Fresh unsupported concrete flows to and sinking in the height takes place. This vertical settlement is known as Slump. Concrete is said to be workable if it can be easily mixed, compacted and easily finished. The results of all slump values of all mixes are shown in Table 4 The internal surface of mould was cleaned thoroughly and free from moisture and any concrete before commencing the test. The mould was placed on rigid, horizontal and non- absorbent surface. The mould filled in 4 layers, each approximately one quarter of the height of the mould. Each layer shall tamper with 25 strokes. After leveling the top, the mould was removed from concrete immediately by raising it slowly in a vertical direction. This allows the concrete to subside and slump shall be measured by measuring the difference between the heights of mould and highest point of the specimen being tested. Table-4: Slump Values for Different Concrete Mixes Mix description Slump (mm) M1 0%RA +100%NA + 10% SF 113 M2 10%RA +90%NA + 10%SF 108 M3 20%RA +80%NA + 10%SF 100 M4 30%RA +70%NA + 10%SF 98 M5 40%RA +60%NA + 10%SF 95 M6 50%RA +50%NA + 10%SF 90 Fig-1: Workability of Different Mix From Table 4, it can be seen that the slump value is decreasing with increase in the recycled concrete percentage in the mix. This is because the recycled aggregates absorb more water than the normal aggregates because of the presence of dust and the mortar on the surface of recycled aggregates. All slump values were maintained in between mm by varying the dosage of super plasticizer. 4.2 Compressive Strength Cubes of sizes 150 x 150 x 150 mm were cast for strength testing. These cubes were cured for 7, 14, 28, 56 and 90 days and tested in Compression testing machine having a capacity of 200 T. The specimens were allowed to dry in sunlight for 1 day and are placed centrally in the testing machine and the load was applied continuously, uniformly and without any shock. mixes cured at different ages are presented and discussed in this section. The compressive strength test results of all the mixes at different curing ages are shown in Table 5. Variation of compressive strength of all the mixes with curing age is shown in Fig. - 2 Mix Name Table-5: Compressive Strength (MPa) Values of all Mixes at Different Curing Ages Mix Description Compressive Strength (MPa) 7 days 14 Days 28 Days 56 Days 90 days M1 0%RA+100%NA M2 10%RA+90%NA , All Rights Reserved Page 242

5 M3 20%RA+80%NA M4 30%RA+70%NA M5 40%RA+60%NA M6 50%RA+50%NA Fig-2: Compressive Strength at 28 days From the above test results and the graphical variation as shown in Fig 4.1, it was observed that the compressive strength results of the M2, M3, and M4 are comparable with the mix M1. This shows that the compressive strength of recycled aggregate concrete with up to 30% replacement of natural aggregates with recycled aggregates gives the same values as compared to the normal aggregates concrete or conventional concrete. The percentage loss in strength from 0%RA mix to 30%RA mix was 5.30% after 90 days, and at 28 days the loss of strength from M1 to M4 is 1.15%. After 30% replacement i.e., 40% and 50% replacement of NA with RA shows the irregular behaviour in compressive strength values at both 28 days and 90 days. At the early age of curing i.e. 28 days, the difference in compressive strength of M1, M2, M3 and M4 is very less, whereas at 90 days the difference in compressive strength of M1, M2, M3 and M4 is large. So it was observed that the optimum percentage of replacement of NA with RA is 30%. Beyond 30% replacement, the results showing a decreasing trend in terms of compressive strength at all curing ages. 4.3 Split Tensile Strength The cylinder of size mm were cast and cured for 7, 14, 28, 56 and 90 days. After curing age the cubes were allowed to dry in the sunlight for 1 day and were tested under strength testing machine by placing the cubes diagonally in the centre. The load was increased until the specimen fails. The maximum load taken by the specimen was noted. The experiment was repeated for two specimens of the same mix and the average value was taken as final. The results of the strength tests conducted on concrete specimens of different mixes cured at different ages are presented and discussed in this section. The split tensile strength test results of all the mixes at different curing ages are shown in Table - 6. Variation of compressive strength of all the mixes with curing age is shown in Fig. - 3 Mix Name Table-6: Split Tensile Strength Test (MPa) Values of all Mixes at Different Curing Ages Mix Description Split Tensile Strength (MPa) 7 days 14 Days 28 Days 56 Days 90 days M1 0%RA+100%NA M2 10%RA+90%NA M3 20%RA+80%NA M4 30%RA+70%NA M5 40%RA+60%NA M6 50%RA+50%NA , All Rights Reserved Page 243

6 Fig-3: Split Tensile Strength at 28 days From the above test results and the graphical variation as shown in Table 4.4 and Fig 4.2, it was observed that the split tensile strength results of the M2, M3, and M4 are comparable with the mix M1. This shows that the split tensile strength results of recycled aggregate concrete with 30% replacement of natural aggregates with recycled aggregates gives the same values as compared to the normal aggregates concrete or conventional concrete. After 30% replacement i.e., 40% and 50% replacement of NA with RA shows the irregular behaviour in split tensile strength values. The percentage loss in strength from 0%RA mix to 30%RA mix was 5.01%. From the above test results and the graphical variation as shown in Table 4.4 and Fig 4.2, it was observed that the split tensile strength results of the M2, M3, and M4 are comparable with the mix M1. This shows that the split tensile strength results of recycled aggregate concrete with 30% replacement of natural aggregates with recycled aggregates gives the same values as compared to the normal aggregates concrete or conventional concrete. After 30% replacement i.e., 40% and 50% replacement of NA with RA shows the irregular behaviour in split tensile strength values. The percentage loss in strength from 0%RA mix to 30%RA mix was 5.01% after 90 days, and at 28 days the loss of strength from M1 to M4 is 0.7%. So the optimum percentage of replacement of NA with RA is 30% Beyond 30% replacement the results showing a decreasing trend in terms of split tensile strength. The highest value of split tensile strength was observed for mix with 0% recycled aggregates at both initial stage and later stages of curing. The lowest value of split tensile strength was observed for mix with 50% recycled aggregates at both initial stage and later stage of curing. The decrease in the split tensile value of recycled aggregate concrete from one mix to other is high in the initial stages i.e. 7, 14, 28 days, whereas the decrease in split tensile value at 56, 90 days is uniform this can be clearly shown in the diagram. So, recycled aggregate concrete performed better with less than 30% replacement in the initial stages 5. CONCLUSIONS The higher water absorption capacity of recycled aggregates has great influence on the water added to the mix, which can affect concrete s workability It is possible to gain the same compression and split tensile strength as conventional concrete up to 30% replacement of natural aggregate with recycled ones. But from the overall study, both the compression and split tensile strength values are decreasing with the increase in replacement levels of recycled aggregates The increase of recycled aggregates content beyond 30% has a negative effect on compressive strength of recycled aggregates concrete. The reduction in compressive strength after 28 days is about 10% when 50% recycled aggregates are used. Split Tensile results also show down trend like compressive strength beyond 30% replacement of recycled aggregates. The pores filling capacity of silica fume enhances the both mechanical and durability properties of recycled aggregates concrete. The use of silica fume as a partial replacement of cement decrease the water absorption of recycled aggregate concrete. 6. REFERENCES [1] AASHTO M 307 ASTM C Standard Specification for Silica Fume Used in Cementitious Mixtures, American Society for Testing and Materials, Annual Book of ASTM Standards, Volume04.02, West Conshohocken, Pennsylviania. [2] Ajdukiewicz, A., and Kliszczewicz, A. (2002). Influence of recycled aggregates on mechanical properties of HS / HPC, 24, [3] Asamoah, M., and Afrifa, R. O. (2010). A study of concrete properties using phyllite as coarse aggregates. Materials and Design, 31(9), , All Rights Reserved Page 244

7 [4] ASTM standards C "Standard test method for measurement of the rate of adsorption of water by hydraulic cement concrete", American Society for Testing and Materials, Annual Book of ASTM Standards, Volume04.02, West Conshohocken, Pennsylviania. [5] British Standard, BS :1996 Recommendations for the determination of the initial surface absorption of concrete, BSI 389 Chiswick High Road London W4 4AL [6] British Standard, BS 812 series, Describes methods for determining the flakiness index of coarse aggregate, BSI 389 Chiswick High Road London W4 4AL [7] Binici, H., Shah, T., Aksogan, O., and Kaplan, H. (2008). The durability of concrete made with granite and marble, Materials Processing, 8, [8] Brito, J. De., Matias, D., Rosa, A., and Pedro, D. (2013). Mechanical properties of concrete produced with recycled coarse aggregates Influence of the use of superplasticizers. Construction and Building Materials, 44, [9] Butler, L., West, J. S., and Tighe, S. L. (2013). Effect of recycled concrete coarse aggregate from multiple sources on the hardened properties of concrete with equivalent compressive strength. Construction and building materials, 47, [10] Cabral, B., Eduardo, A., Schalch, V., Carpena, D., Dal, C., Luis, J., and Ribeiro, D. (2010). Mechanical properties modeling of recycled aggregate concrete. Construction and Building Materials, 24(4), [11] Chen, H., Yen, T., and Chen, K. (2003). Use of building rubbles as recycled aggregates, Cement and Concrete Research, 33(May 2002), [12] Corinaldesi, V., and Moriconi, G. (2009). The behaviour of cementitious mortars containing different kinds of recycled aggregate. Construction and Building Materials, 23(1) [13] Corinaldesi, V., and Moriconi, G. (2009). Influence of mineral additions on the performance of 100 % recycled aggregate concrete. Construction and Building Materials, 23(8), [14] Corinaldesi, V. (2010). The mechanical and elastic behaviour of concretes made of recycled-concrete coarse aggregates. Construction and Building Materials, 24(9), , All Rights Reserved Page 245