Effect of Rice Husk Ash Fineness on the Properties of Concrete

Transcription

1 Applied Mechanics and Materials Vol. 554 (2014) pp (2014) Trans Tech Publications, Switzerland doi: / Effect of Rice Husk Ash Fineness on the Properties of Concrete Dewi Sri Jayanti 1,a, Ramadhansyah Putra Jaya 2,b*, Norhidayah Abdul Hassan 3,c, Md. Maniruzzaman A. Aziz 4,d, Mohd Rosli Hainin 5,e and Mohd Haziman Wan Ibrahim 6,f 1 Faculty of Agriculture, Department of Agricultural Engineering, Universitas Syiah Kuala, Darussalam, Banda Aceh, Indonesia 2, 3, 4, 5 Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor Bahru, Malaysia 6 Faculty of Civil & Environmental Engineering, Universiti Tun Hussein Onn Malaysia, Batu Pahat, Johor Bahru, Malaysia a dee_jayanti@yahoo.com, b ramadhansyah@utm.my, c hnorhidayah@utm.my, d mzaman@utm.my, e mrosli@utm.my, f haziman@uthm.edu.my * corresponding author: ramadhansyah@utm.my Keywords: Concrete; RHA; Fineness; Strength; Workability. Abstract. In the present research, the effect of rice husk ash fineness on the properties of concrete was studied. Eight different fineness grades of rice husk ash were examined. A rice husk ash dosage of 15% by weight of binder was used throughout the experiments. The water-to-binder ratio was 0.49 to produce concrete having target strength of 40MPa at 28 d. Workability, compressive strength and gas permeability tests were carried out to identify the properties of concrete. The results revealed that increasing the fineness of RHA by mechanical grinding was found to improve the workability of RHA blended cement concrete. In addition, the use of RHA3 with mean particle size of 9.52μm produces the concrete with good strength. Finally, significant improvement was observed in mixtures incorporating RHA in terms of permeability coefficient. Introduction The utilisation of RHA as a pozzolanic material in cement and concrete provides several advantages, such as improved strength and durability [1]. The reactivity of RHA is attributed to its high content of amorphous silica and to its very large surface area, which is governed by the porous structure of the constituent particles [2]. Reactivity can be increased by increasing the fineness of the pozzolanic material. Previous studies showed that grinding of pozzolanic material, such as POFA, FA and RHA, into a high degree of fineness is the major factor affecting compressive strength of cement concrete [3]. Ramadhansyah et al. [4] also reported that at a certain stage of RHA grinding, the porous structure of the particles would collapse, resulting in reduced surface area. Grinding medium and grinding time may be conveniently adopted as RHA is highly fragile and porous [5]. In related study, Jaturapitakkul et al. [6] reported that the use of ground RHA as a cementitious material in mortars and concretes results in higher strengths with no negative effect on workability. Several papers have been published on the performance of RHA blended concrete. However, only limited information is available on the effect of RHA fineness on the concrete. The objective of the present investigation is to evaluate the influence of RHA fineness on the properties of hardened concretes. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: /05/14,06:29:50)

2 204 Mechanical and Materials Engineering Materials and methods Cement. Type-I ordinary Portland cement (OPC, Blue Lion Cement) was used in this investigation. Crushed granite of size 20 mm was used as the coarse aggregate and local natural sand derived from granite was used as the fine aggregate in the concrete mixtures. Rice husk ash. Rice husk was burnt at 700 C for 6 h in a gas furnace at a heating rate of 10 C/min. The ash was left to cool inside the furnace and removed the following day. The ash was ground using a laboratory ball mill with porcelain balls up to eight different fineness lots: RHA0, 17.96μm; RHA1, 10.93μm; RHA2, 9.74μm; RHA3, 9.52μm; RHA4, 9.34μm; RHA5, 8.70μm; RHA6, 6.85μm; and RHA7, 6.65μm, respectively. Mix proportions and curing. The mixes were designed to achieve concrete of grade 40 N/mm 2 at 28 days. A mass water-to-binder ratio of 0.49 was used. Specimens were cast in three layers and were compacted using a vibrating table in order to remove any entrapped air. Each layer was vibrated for about 20 s. After casting, the moulded specimens were covered with wet hessian for 24 h to avoid evaporation. The specimens were demoulded on the following day, and then were placed in a water tank for curing at 100% relative humidity and temperature of 20±1 C until the time of testing. Workability. Workability is expressed as an ease of concrete that can be handled, placed, compacted, and finished with minimum segregation. The workability in this investigation was measured by a slump test according to BS EN [7]. Compressive strength. Compressive strength testing was carried out on concrete cubes of size mm. During moulding, the cubes were mechanically vibrated. After 24 h, the specimens were removed from the mould and subjected to water curing for 7, 28, and 56 days. After a specified period of curing, the specimens were tested for compressive strength using an AIMIL compression testing machine of 2000 kn capacity at a rate of loading of 140 kn/min. The reported compressive strengths are the average of three samples. Gas permeability. In the permeability test, the specimens were dried in an oven at 105 C for 24 h before testing. Next, the specimens were removed from the oven, and a thin layer of silicon rubber was applied to their curved surfaces. They were kept to dry in a desiccator for 24 hours. During testing, the specimens were placed in the permeability cell, and a gas pressure of 2 bars was applied. The specimens were then kept for 20 min to allow the gas pressure to stabilize in the cell systems before taking the readings. The time of gas flow was measured using the appropriate bubble flow meter within a 100 mm length of the flow meter with a 3 mm diameter. The flow time was repeatedly measured and recorded at least five times. The gas permeability value was determined using Eq. 1. K = 2P 2 (1) Where K is Permeability coefficient (m 2 ); P 1 is Pressure plus atmosphere pressure (bar); P 2 is Pressure at which the flow rate is measured (bar); V is Velocity (m 3 /s); L is Length of specimen (m); is Nitrogen gases coefficient; and A is Measured cross-sectional area (m 2 ). Results and discussion Workability. The workability of controlled specimen and RHA blended cement at different grinding times is summarized in Table 1. It shows the influence of RHA with different particle fineness on the workability of mixtures at constant water to binder ratio of Clearly, all investigated RHA blended mixtures had acceptable workability with high slump values of more than

3 Applied Mechanics and Materials Vol mm. On the other hand, increasing the fineness of RHA by mechanical grinding was found to improve the workability of RHA blended cement concrete. This is due to an increase in specific surface are of RHA [8]. The increase of RHA fineness resulted in more water observed against the outer surface of RHA particles. Consequently, a superplasticizer is required to achieve a slump value of more than 110 mm. From Table 1, the superplasticizer value increases as the RHA fineness increases. In the recent study, it was found that increasing superplasticizer content depended on mean particle size and specific surface area of pozzolanic materials [4]. Finally, it can be concluded that the improving workability of concrete was primarily due to the increase of RHA fineness, as a result reduce internal friction in fresh concrete, this phenomenon named lubricant effect [9]. Similarly, Pan et al. [10] also reported that the workability of sewage sludge ash (SSA) mortar increased due to the lubricant effect and morphology improvement. Table 1. Mix proportions of concrete containing RHA at different grinding time Symbol w/c SP (%) Slump (mm) Water Cement Fine Aggregate Coarse Aggregate OPC RHA RHA RHA RHA RHA RHA RHA RHA Compressive strength. The compressive strength of the concrete containing RHA0 is lower than that of the controlled concrete (OPC) at all ages as shown in Figure 1. For instance, for concrete with RHA0, the 7 days strength is 32.92% of that of the OPC concrete at the same age. Nevertheless, at the age of 28 and 56 days, the strength of the RHA0 concrete is and 8.38% of that of the OPC concrete at the same age. The amorphous silica and the fine particle size of RHA are the principal reasons for the excellent pozzolanic activity and increase in compressive strength as described by Abu Bakar et al. [8]. However, when rice husk ash was subjected to grinding processed, the rate of strength gain of concrete was improved significantly with the increase of fineness. It was found that RHA3 concrete exhibited the maximum strength. The use of RHA3 results in an increase in strength compared with RHA0, RHA1, RHA2, RHA4, RHA5, RHA6, and RHA7 at all ages. This is probably due to the fineness of the particles and the irregular particle shape [4, 11].

4 206 Mechanical and Materials Engineering Figure 1. Compressive strength of OPC and rice husk ash concrete Coefficient of permeability. In this study, the result of gas permeability was calculated at five pressures reading for 7, 28 and 56 days concrete mixed at different grinding time are presented in Figure 2. From this figure, it can be clearly seen that the coefficient of permeability decreases with an increase in grinding time. All specimens undergo a significantly drop in permeability after 7 days. The original rice husk ash (unground) concrete shows the greatest permeability at all age while the other mixes have achieved the lowest permeability (RHA7). For instance, at 28 days of curing, the permeability of original rice husk ash (RHA0), RHA1, RHA2, RHA3, RHA4, RHA5, RHA6, and RHA7 mixes were 1.53x10-17, 1.27x10-17, 1.28x10-17, 0.92x10-17, 0.85x10-17, 0.71x10-17, 0.75x10-17, and 0.70x10-17 m 2 compared with 1.28x10-17 m 2 of the controlled specimen at the same age. Still, specimen associated with 5 hours grinding has shown lower permeability in comparison with normal concrete and other mixes. In addition, the finer the particles, the lower the coefficient of permeability of concrete. This may be due to grinding time variation in these mixes which produced fewer pores. Similar finding was also reported by Li et al. [12]. Figure 2. Permeability of the OPC and rice husk ash concrete

5 Applied Mechanics and Materials Vol Conclusions The results obtained in this study clearly indicate that increasing the fineness of RHA was found to improve the workability of blended cement concrete. On the other hand, the rate of strength gain of concrete was improved significantly with the increase of RHA fineness. RHA3 with mean particle size of 9.52μm produces concrete with the maximum strength. Furthermore, the coefficient of permeability decreases with an increase in RHA fineness. Acknowledgements The support provided by Malaysian Ministry of Higher Education (MOHE), Universiti Sains Malaysia (USM) and Universiti Teknologi Malaysia (UTM) in the form of a research grant (Vote No. 00K52) for this study is very much appreciated. References [1]. K. Ganesan, K. Rajagopal and K. Thangavel: Constr. Build. Mater Vol. 22 (2008), p [2]. M.R. Karim, M.F.M. Zain, M. Jamil and F.C. Lai: Constr. Build. Mater Vol. 49 (2013), p [3]. M. Jamil, A.B.M.A. Kaish, S.N. Raman and M.F.M. Zain: Constr. Build. Mater Vol. 47 (2013), p [4]. P.J. Ramadhansyah, A.W. Mahyun, M.Z.M. Salwa, B.H. Abu Bakar, M.A. Megat Johari and M.H. Wan Ibrahim. Thermal analysis and pozzolanic index of rice husk ash at different grinding time. Procedia Eng Vol. 50 (2012), p [5]. W. Kroehong, T. Sinsiri, C. Jaturapitakkul and P. Chindaprasirt: Constr. Build. Mater Vol. 25 (2011), p [6]. C. Jaturapitakkul, J. Tangpagasit, S. Songmue and K. Kiattikomol: Constr. Build. Mater Vol. 25 (2011), p [7]. BS EN :2009. Testing fresh concreteslump-test. British European Standard. London, United Kingdom. [8]. B.H. Abu Bakar, P.J. Ramadhansyah and M.A. Megat Johari: Mag. Concrete. Res Vol. 63 (2011), p [9]. E. Peris-Mora, J. Payá and J. Monzó: Cement. Concrete. Res Vol. 23 (1993), p [10]. S-C. Pan, D-H. Tseng, C-C. Lee and C. Lee: Cement. Concrete. Res Vol. 33 (2003), p [11]. G.C. Cordeiro, R.D.T. Filho, L.M. Tavares, E. de Moraes Rego Fairbairn and S. Hempel: Cement. Concrete. Res Vol. 33 (2011), p [12]. S.T. Lee, H.Y. Moon, R.D. Hooton and J.P. Kim: Cement. Concrete. Res Vol. 35 (2005), p