PERFORMANCE STUDY OF SELF COMPACTING FLYASH CONCRETE

Transcription

1 PERFORMANCE STUDY OF SELF COMPACTING FLYASH CONCRETE 1 Shibi Varghese, 2 Anju Ebrahim, 3 Neethu B, 4 Priyanka Teresa Mathew, 5 Remya Muraleedharan 1 Professor, Civil Engineering Department, Mar Athanasius College of Engineering, 2 B. Tech Students, Civil Engineering Department, Mar Athanasius College of Engineering, 3 B. Tech Students, Civil Engineering Department, Mar Athanasius College of Engineering, 4 B. Tech Students, Civil Engineering Department, Mar Athanasius College of Engineering, 5 B. Tech Students, Civil Engineering Department, Mar Athanasius College of Engineering, ABSTRACT Self compacting concrete is a fluid mixture suitable for placing in structures with congested reinforcement without vibration. Self compacting concrete development must ensure a good balance between deformability and stability. Also, compact ability is affected by the characteristics of materials and the mix proportions. This paper presents a performance study of M35 Grade self compacting concrete with fly ash as partial replacement for cement and also a comparison with M35 Grade Normally vibrated concrete. The test results for acceptance characteristics of self compacting concrete such as slump flow; V funnel and L Box and also the results of workability tests on normally vibrated concrete such as slump cone and compaction factor are presented. Further, compressive strength at the ages of 7 and 28 days, tensile strength, modulus of elasticity, flexural strength of both M35 self compacting concrete and M35 Normally vibrated concrete was also determined and results are included here. INDEX TERMS: Self compacting Concrete, Normally vibrated concrete, Fly Ash, EFNARC, Mix Design, Workability, Fresh Properties, Hardened Concrete Properties, Strength tests, Super plasticizer. INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 1

2 1. INTRODUCTION Self compacting concrete (SCC), which flows under its own weight does not require any external vibration for compacting, has revolutionized concrete placement. SCC, was first introduced in the late 1980 sby Japanese researchers. It is highly workable concrete that can flow into place and compact under its own weight into a uniform void free mass even in areas of congested reinforcement without segregation and bleeding. Such concrete should have a relatively low yield value to ensure high flowability, a moderate viscosity to resist segregation and bleeding, and must maintain its homogeneity during transportation, placing and curing to ensure adequate structural performance and long term durability. The successful development of SCC must ensure a good balance between deformability and stability. Researchers have set some guidelines for mixture proportioning of SCC, which include i) reducing the volume ratio of aggregate to cementitious material; (ii) increasing the paste volume and water cement ratio (w/c); (iii) carefully controlling the maximum coarse aggregate particle size and total volume; and (iv) using various viscosity enhancing admixtures (VEA). For SCC, it is generally necessary to use super plasticizers in order to obtain high mobility. Adding a large volume of powdered material or viscosity modifying admixture can eliminate segregation. The powdered materials that can be added are fly ash, silica fume, lime stone powder, glass filler and quartzite filler. In the present work, it is proposed to use fly ash as powdered material in the production of self compacting concrete. Self compatibility is largely affected by the characteristics of materials and the mix proportions. For the mix design of SCC, the guidelines given by EFNARC were followed. EFNARC is the European federation dedicated to specialist construction chemicals and concrete systems. One of the limitations of SCC is that there is no established mix design procedure yet. The mix design of M35 NVC was done according to the specifications and procedure given in IS 10262: 2009 INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 2

3 2. MATERIALS USED Cement Ordinary Portland cement (Grade 53) was used. Its physical properties are as given in Table 1. Table 1. Physical Properties of Cement Physical property Results obtained Specific gravity 3.15 Standard consistency 32% Initial setting time 90 Fly ash Class C Fly ash obtained from Alan Hydraulic Bricks, Angamali, Kerala, India. Admixtures The super plasticizer used is Master Glenium Sky It is manufactured by BASF construction chemical India Pvt. Ltd, Mumbai Aggregates Locally available natural sand with 4.75 mm maximum size was used as fine aggregate 5 and crushed stone with 12mm maximum size for SCC and 20 mm size for NVC was used as coarse aggregate. Water Water is an important ingredient of concrete as it as it actively participates in chemical reaction with cement. The strength of cement concrete comes from the bonding action of hydrated cement gel. In the present investigation, potable water was used for mixing and curing. INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 3

4 3. TEST METHODS Self Compacting Concrete is characterized by filling ability, passing ability and resistance to segregation. Many different methods have been developed to characterize the properties of SCC. No single method has been found until date, which characterizes all the relevant workability aspects, and hence, each mix has been tested by more than one test method for the different workability parameters. Table 2. Recommended Limits for Different Properties No. Property Range 1. Slump Flow mm Diameter 2. T 50cm 2 5 sec 3. V funnel 6 12 sec 4. L Box H2/H V funnel at T 5min 0 3 sec The slump flow test is used to assess the horizontal free flow of SCC in the absence of obstructions. On lifting the slump cone, filled with concrete, the concrete flows. The average diameter of the concrete circle is a measure for the filling ability of the concrete. The time T is a secondary indication of flow. It measures the time taken in seconds 50cm from the instant the cone is lifted to the instant when horizontal flow reaches diameter of 500mm. The flow ability of the fresh concrete can be tested with the V funnel test, whereby the flow time is measured. The funnel is filled with about concrete and the time taken for it to flow through the apparatus is measured. Further, T is also measured with V funnel, 5min which indicates the tendency for segregation, wherein the funnel can be refilled with concrete and left for 5 minutes to settle. If the concrete shows segregation, the flow time will increase significantly. A funnel test flow time less than 6s is recommended for a concrete to qualify for an SCC. INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 4

5 The passing ability is determined using the L box test as. The vertical section of the L Box is filled with concrete, and then the gate lifted to let the concrete flow into the horizontal section. The height of the concrete at the end of the horizontal section is expressed as a proportion of that remaining in the vertical section (H2/H1). This is an indication of passing ability. 4. EXPERIMENTAL PROCEDURE Mix Proportioning Using EFNARC guidelines for mix design, initial mix design of SCC was carried out at coarse aggregate content of 28 percent by volume of concrete and water content as 200 l/m 3. Also, there was 30% replacement of the the total powder content required with fly ash. The design was done by varying the water / powder ratio by volume from 0.90 to 1.1.The required water /powder ratio is determined by conducting a number of trials. The mix design of NVC was done according to the procedure in IS : Preparation of mixes SCC mixes were prepared with 12mm aggregates and with various percentages of Super plasticizer and water/powder ratio. In this test program, three mixes were prepared and the mix proportions are presented in Table 3. Table 3. Mix Proportions of M35 SCC All units in kg/m 3, except S.P. which is in % Mix Cement Fly ash F.A C.A Water S.P W/p ratio TR TR TR INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 5

6 NVC mixes were prepared by varying the water/cement ratio to obtain the required workability and the mix proportions are given in Table 4. Table 4: Mix Proportions of M35 NVC Mix Cement Fine aggre Coarse Water Water (kg/m 3 ) gate (kg/m 3 ) aggregate (kg/m 3 ) (kg/m 3 ) cement ratio NVC NVC RESULTS AND TABLES The standard flow tests for SCC like Slump Flow test, L Box test, V Funnel test were conducted on the three mixes of SCC (TR1, TR2, TR3) and the results were compared with the values as per EFNARC guidelines. Among these trials, TR2 (SCC1) and TR3 (SCC2) satisfied all the properties of self compacting concrete. The results are shown in Table 5. Table 5 : Workability results of M35 SCC Mix Slump flow T 50cm (sec) V funnel V funnel L box (H 2 /H 1) (mm) T f(sec) T 5mmin (sec) TR1 400 TR TR The workability tests like Slump cone test and compaction factor test were conducted on the mixes of NVC (NVC1, NVC2) and the results were compared with the values given INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 6

7 in IS 456: Among the two mixes, only NVC2 was sufficiently workable. The results are presented in Table 6. Table 6: Workability results of M35 NVC Sl.NO. Mix Slump Compaction factor 1 NVC NVC Casting specimens and conducting tests: For those mix proportions which satisfied all the properties of self compacting concrete i.e for TR2 (SCC1) and TR3 (SCC2), specimens were prepared to know the compressive strength. The compressive strength of SCC1 at 7 days was only 32 N/mm 2, which was more than that required for 7 day compressive strength of M35 concrete. SCC2 gave comparatively good compressive strength of N/mm 2 at 7 days. Therefore, specimens of SCC2 were prepared to know the split tensile strength, flexural strength and Modulus of Elasticity and the results are shown in Table 7. Table 7: Strength tests results of M35 SCC Mix Compressive strength Tensile Flexural Modulus of Strength Strength of Elasticity 7 days 28 days concrete SCC SCC x10 6 Specimens were casted for the mix of M35 NVC which was comparatively workable (NVC2) to determine the compressive strength, split tensile strength, flexural strength and Modulus of Elasticity and the results are shown in Table 8. INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 7

8 Table 8 : Strength tests results of M35 NVC Sl. Mix Compressive strength Tensile Flexural Modulus of No. 7 days 28 days Strength Strength of concrete Elasticity 1 NVC NVC x CONCLUSION 1. SCC mix of grade M35 was proportioned with 30% replacement of powder content with fly ash. The test results indicate that the mix satisfy the requirements of M35 concrete both at fresh and hardened state. 2. At the water/powder ratio of 1.0 and 1.08, slump flow test, V funnel test and L box test results were found to be satisfactory, i.e. passing ability; filling ability and segregation resistance are well within the limits. 3. SCC mix requires high powder content, lesser quantity of coarse aggregate and high range of super plasticizer to give stability and fluidity to the concrete mix. 4. Fly ash which is a cheaply available material can be used in the construction industry for preparation of concrete replacing some quantity of cement, which is a valuable ingredient of concrete to achieve economy. 5. For SCC and NVC of same grade, the flexural strength was comparable. 6. From the study conducted it was found that modulus of elasticity as well as splitting tensile strength of M35 SCC was slightly higher than that of M35 NVC. 7. Though the materials used for SCC is more than that required for a normal concrete of comparable strength, there is a reduction in the cost of compaction, finishing etc for SCC which makes SCC not a costly concrete. INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 8

9 REFERENCES [i] N. Bouzouba and M. Lachemi, Self Compacting Concrete Incorporating High Volumes of Class F Fly Ash:Preliminary Results, Cement and Concrete Research, Vol. 31, No. 3, Mar. 2001, pp ( ) [ii] F.M. Almeida Filho, B.E. Barragán, J.R. Casas, A.L.H.C. El Debs, Hardened properties of self compacting concrete A statistical approach, Construction and Building Materials 24 (2010) [iii] Prashant Bhuva, Anant Patel, Elizabeth George, Darshana Bhatt, Development of Self Compacting Concrete using Different Range of Cement Content, National Conference on Recent Trends in Engineering & Technology < > [iv] S. N. Tande, P. B. Mohite, Applications Of Self Compacting Concrete < > [v] Nan Sua, Kung Chung Hsub, His Wen Chai, A simple mix design method for selfcompacting concrete, Cement and Concrete Research 31 (2001) [vi] Zoran Grdić, Iva Despotović, Gordana Topličić Ćurčić Properties Of Self Compacting Concrete With Different Types Of Additives, Architecture and Civil Engineering Vol. 6, No 2, 2008, pp [vii] EFNARC Specification and Guidelines for Self Compacting Concrete < > [viii] The European Guidelines for Self Compacting Concrete Specification, Production and Use < > [ix] Luis A Mata Implementation of Self Consolidating Concrete (SCC) for Prestressed ConcreteGirders, Respository.lib.ncsu.edu/ir/bitstream/ /2563/1/etd.pdf> INTERNATIONAL JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGY 9