STUDIES ON SELF COMPACTING CONCRETE USING PHOSPHOGYPSUM

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1 STUDIES ON SELF COMPACTING CONCRETE USING PHOSPHOGYPSUM K.Madhuralalasa 1, Dr.K.Rajasekhar 2 1 PG Student, Department of Civil Engineering, Siddartha Educational Academy Group of Institutions 2 Professor, Department of Civil Engineering,SEAGI Abstract-Self-compacting concrete(scc) possesses enhanced qualities and improves productivity and working conditions due to elimination of compaction. SCC is suitable for placing in structures with congested reinforcement without vibration and it helps in achieving higher quality of surface finishes.this paper demonstrates that Phosphogypsum which is a waste by product of fertilizer industry can be successfully used as an admixture in the preparation of Self-Compacting-Concrete (SCC). In order to prepare suitable mix proportions for different grades of Phosphogypsum based Self Compacting Concrete, investigations were undertaken replacing cement with 0%, 5%, 10%,15% and 20% of Phosphogypsum and with different percentages of Super-plasticizer (Varaplast pc 432) and Viscosity Modifying Agent (Varaplast pc 100). As per EFNARC guidelines Slump flow test, V-funnel test and L-box test have been carried out on Phosphogypsum based on self compacting concrete. The compressive strength, split tensile strength and Flexural Strength of the specimens have been analyzed for 7 days, 28 days and 90days of curing. The various steps involved in the preparation of suitable mix proportions for Phosphogypsum based Self Compacting Concrete are discussed at length in this paper. Keywords-Self-Compacting concrete, Phosphogypsum, EFNARC, Mix, Fresh properties, Strength tests, Super-plasticizer ( SP), Viscosity Modifying Agent (VMA) I. INTRODUCTION Self-compacting concrete (SCC) is a concrete, which flows and compacts only under gravity. It fills the mould completely without any defects. Usually self-compacting concretes have compressive strengths in the range of N/mm 2. However, lower grades can also be obtained and used depending on the requirement. SCC was originally developed at the University of Tokyo in Japan with the help of leading concrete contractors during 1980 s to be mainly used for highly congested reinforced structures in seismic regions. As durability of concrete structures was an important issue in Japan, an adequate compaction by skilled labors was required to obtain durable concrete structures. This requirement led to the development of SCC. The development of SCC was first reported in II. LITERATURE REVIEW. Hajime Okamura [1]: A new type of concrete, which can be compacted into every corner of a formwork purely by means of its own weight, was proposed by Okamura (1997). In 1986, he started a research project on the flowing ability and workability of this special type of concrete, later called self-compacting concrete. The self-compactability of this concrete can be largely affected by the characteristics of materials and the mix proportions. In his study, Okamura (1997) has fixed the coarse aggregate content to 50% of the solid volume and the fine aggregate content to 40% of the mortar volume, so that self-compactability could be achieved easily by adjusting the water to cement ratio and Superplasticizers dosage only. Kazumasa Ozawa:[2] After Okamura began his research in 1986, other researchers in Japan have started to investigate self-compacting concrete, looking to improve its characteristics. One of All Rights Reserved 426

2 was Ozawa (1989) who has done some research independently from Okamura, and in the summer of 1988, he succeeded in developing self-compacting concrete for the first time. The year after that, an open experiment on the new type of concrete was held at the University of Tokyo. Khayat et al(1997)[3]the use of self-consolidating concrete can facilitate the placement of concrete in congested members and in restricted areas. Given the highly flowable nature of such concrete, care is required to ensure adequate stability. This is especially important in deep structural members and wall elements where concrete can segregate and exhibit bleeding and settlement, which can result in local structural defects that can reduce mechanical properties. Dehn et al.: [5] Dehn (2000) et al. have focused their research work on the time development of SCC compressive and splitting tensile strength and the bond behavior between the reinforcing bars and the self-compacting concrete compared to normal concrete. In order to ensure a good production of SCC, a mix design should be performed, so that the predefined properties of the fresh and hardened concrete would be reached for sure. All the components should be coordinated so that bleeding and segregation would be prevented. III. EXPERIMENTAL INVESTIGATIONS. 3.1 Materials Cement (OPC) 53 grade Fine Aggregate Coarse Aggregate Phosphogypsum Viscosity Modifying Agent (Varaplast PC 100) Superplasticizer (Varaplast PC 432) 3.1.1Ordinary Portland Cement The most common cement used is an ordinary Portland cement. Grade 53 Cement was used for all casting cubes for all concrete mixes as per IS 383:1987 The cement was of uniform colour i.e. grey with a light greenish shade and was free from any hard lumps. Many tests were conducted on cement; some of them are consistency tests, setting tests,etc Coarse Aggregate The material which is retained on BIS test sieve no. 480 is termed as a coarse aggregate. The broken stone is generally used as a coarse aggregate. The nature of work decides the maximum size of coarse aggregate. Locally available coarse aggregate having the maximum size of 16mm was used in our work. The aggregates were washed to remove dust and dirt and were dried to surface dry condition. The aggregates were tested per Indian Standard Specifications IS: Fine aggregate Those fractions from 4.75 mm to 75 micron are termed as fine aggregate. The river sand and crushed sand is be used in combination as fine aggregate conforming to the requirements of IS:383. The river sand is wash and screen, to eliminate deleterious materials and over size particles Water Water is an important ingredient of concrete as it actually participates in the chemical reaction with cement. Since it helps to from the strength giving cement gel, the quantity and quality of water is required to be looked into very All Rights Reserved 427

3 3.1.5 Phosphogypsum In India, about 6 million tons of waste gypsum such as phosphogypsum, flourogypsum etc., are being generated annually. Phosphogypsum is a by-product in the wet process for manufacture of phosphoric acid (ammonium phosphate fertilizer) by the action of sulphuric acid on the rock phosphate. It is produced by various processes such as dihydrate, hemihydrate or anhydrite processes. In India the majority of phosphogypsum is produced by the dehydrate process due to its simplicity in operation and lower maintenance as compared to other processes. The other sources of phosphogypsum are by-products of hydrofluoric acid and boric acid industries Chemical composition of Phosphogypsum Constituents (%) Normal moisture content 15-25% Analysis on moisture free sample components (%) Gypsum (CaSO4.2H2O) Silica (SiO2+insolubles) 4.0 max Iron oxide + Alumina 0.3 max (Fe2O3+Al2O3) Lime (CaO) Magnesia (MgO) 0.1 max Alkalis (Na2O+K2O ) (0.5 max) Total phosphate P2O Total Sulphuric anhydride (SO3) Fluorides as F (0.7 max) Chlorides as C (0.6 max) ph of 10% solution (4 min) Loss of ignition Superplasticizers Varaplast PC 432:has been primarily developed for applications in the ready mixed and precast concrete industries where the highest durability and performance is required. Superplasticizing action of Varaplast PC 432 is different Superplasticizer based on sulfonated melamine and naphthalene formaldehyde condensate, which create electrostatic repulsion of particles. Varaplast PC 432 initially creates the same electrostatic repulsion and further stabilizes the mixes due to static repulsion of long lateral chains linked to the polymer backbone Viscosity-Modifying Admixtures: (Varaplast PC 100) Viscosity modifiers are high molecular-weight, water-soluble polymers used to raise the viscosity of water. Such compounds increase the cohesiveness of fresh concrete, reducing its tendency to segregate and bleed. They work by attaching their long molecules to the water molecules, process which inhibits the free displacement of water. These admixtures are helpful in improving the properties of lean concretes with low cement contents, concrete placed under water, and concretes or grouts that are placed by pumping. Viscosity-modifying admixtures are added in concretes used in places with extreme congestions due to reinforcement configurations or unusual geometry forms, where fluid but cohesive concrete is required in order to resist bleeding and segregation. 3.2 Mix Proportioning: Based on the Mix design procedures and considering the EFNARC guide lines and The European Guidelines for typical ranges of proportions and quantities the following conclusions were made and used in the Mix designing process for preliminary mix design trials in this All Rights Reserved 428

4 Trail no Mix Cement PG FA International Journal of Recent Trends in Engineering & Research (IJRTER) Table 1. Details of mix proportions CA in mm SP ml VMA ml w/p Water Scc Scc Scc Scc Scc IV. TEST RESULTS AND DISCUSSIONS. Table 2. Fresh Properties of SCC S NO Mix Slump Dia(mm) T50cm Slump(sec) V-Funnel (sec) L-Box (h2/h1) 1 Scc Scc Scc Scc Scc Table 3. Compressive Strength on Cubes percentage of Compressive strength in N/mm 2 S no Mix phospogypsum 7 days 28 days 90 days 1 Scc1 0% Scc2 5% Scc3 10% Scc4 15% Scc5 20% Table 4. Split Tensile Strength On Cylinders Percentage of Split Tensile Strength in N/mm 2 S NO Mix phospogypsum 28 days 90 days 1 Scc1 0% Scc2 5% Scc3 10% Scc4 15% Scc5 20% 2.31 All Rights Reserved 429

5 Table 5.Flexural Strength test S NO Mix percentage of Flexural strength N/mm 2 phospogypsum 28 days 90 days 1 Scc1 0% Scc2 5% Scc3 10% Scc4 15% Scc5 20% Graph 1.Variation in Compressive strength for 7 days,28 days and 90 days Graph 2. Split tensile strength for 28 days and 90 All Rights Reserved 430

6 Graph 3.Flexural strength for 28 days and 90 days IV. CONCLUSIONS. 1. SCC mix requires high powder content, lesser quantity of coarse aggregate, high range Superplasticizer and VMA to give stability and fluidity of the concrete mix. 2. The workability of SCC is equilibrium of fluidity, deformability, filling ability and resistance to segregation. This equilibrium has to be maintained for a sufficient time period to allow for transportation, placing and finishing. 3. An industrial waste like Phosphogypsum impairs the strength development of calcined products and hence it can be used in construct industry for preparation of concrete replacing some quantity of cement, which is a valuable ingredient of concrete to achieve economy. 4. Up to 10% replacement of cement with Phosphogypsum, the compressive strength increased significantly with age at 90 days. However, further replacement of cement with Phosphogypsum lead to drastic reduction not only in compressive strength and also in the split tensile strength. 5. At 10% replacement of cement with Phosphogypsum gives maximum flexural strength than the other replacement of cement with Phosphogypsum, the width and number of cracks increased with the 15% and 20% replacement of Phosphogypsum. REFERENCES 1. Okamura H, Mix design for self-compacting concrete. Concrete Library of Japanese Society of Civil Engineers, 1995, Vol. 25, No. 6, pp Ozawa, K., Development of high performance concrete based on the durability design of concrete structures, EASEC-2, Vol. 1, pp (1989). 3. Khayat, K.H., M.Vachon, and M. C. Lanctot, Use of Blended Silica Fume Cement in Commercial Concrete Mixtures, ACI Materials Journal, pp (1997). 4. Dehn, F., K. Holschemacher, and D. Weisse, Self-Compacting Concrete - Time Development of the Material Properties and the Bond Behavior, LACER No. 5, pp (2000). 5. Subramanian, S. and D. Chattopadhyay, Experiments for mix proportioning of self-compacting concrete, The Indian Concrete Journal, pp (2002). 6. B.Krishna Rao et. al. steel fiber reinforced self compacting concrete incorporating class F fly ash International Journal of Engineering Science and Technology Vol. 2(9), 2010, EFNARC (European Federation of national trade associations representing producers and applicators of specialist building products), Specification and Guidelines for self-compacting concrete, February 2002, Hampshire, U.K. 8. M.S. Shetty- Concrete Technology,S.Chand & Co.Ltd. 9. Neville, A. M., Properties of concrete, Third Edition, Longman Scientific & Technical, UK All Rights Reserved 431