Elsevier

Cement and Concrete Research

Volume 115, January 2019, Pages 389-400
Cement and Concrete Research

The use of rice husk ash as reactive filler in ultra-high performance concrete

https://doi.org/10.1016/j.cemconres.2018.09.004Get rights and content

Abstract

In this study, rice husk ash (RHA)-based reactive filler was used in ultra-high performance concrete (UHPC) to improve mechanical properties without heat-treatment. This strategy replaces inert quartz filler with the reactive RHA filler, to increase the amorphous silica content while maintaining the physical role of the micron-sized quartz filler. Due to the high porosity of RHA, internal curing is effective, which promotes the hydration reaction over a long period of time. Experimental results show an outstanding strength around 200 MPa after 91 days, under ambient conditions (20 °C and 60% relative humidity). This was possible due to the promotion of pozzolanic reaction by additional water and amorphous silica provided by the porous (i.e., internal curing effect) and reactive filler, respectively; hence, the volume of capillary pores was reduced. The result reported herein will further promote the utilization of agricultural byproduct for the development of reactive RHA-based construction materials.

Introduction

Rice is one of the most important agricultural products, especially in Asia [[1], [2], [3]]. Its production has increased over the past decade, and global paddy production in 2017 was estimated to be 760 million tons [4]. Moreover, with the prospect of the global population continuing to increase until 2050, this figure is expected to rise [5,6]. Rice husk is a byproduct of the rice milling process, accounting for about 20–23% of the paddy weight [[1], [2], [3],7,8], meaning that >150 million tons of the byproduct are produced annually. However, about 83% of this amount is simply discarded as waste [5], polluting water and soil [1,[9], [10], [11]]. Therefore, research and development for solving these problems have been performed in various industrial fields. In the green technology field, rice husks are considered as a source of biomass [2,12] which is used as a fuel to produce electricity or steam in a power plant [2,11,[13], [14], [15]]. After the husk is burned, about 20% of the original weight of the fuel remains as rice husk ash (RHA) [13,15]. The ash is often disposed of in rivers or landfill and can contaminate the environment [11,12,[16], [17], [18], [19]]. The use of rice husk as a fuel causes another environmental issue related to the treatment of waste RHA; if the ash is not treated properly, use of the rice husks cannot be considered completely “eco-friendly” [20]. Therefore, appropriate treatment and proper utilization of RHA are attracting increasing attentions in industrial fields [14,21].

The chemical composition of RHA varies depending on the combustion conditions (particularly the maximum temperature) [2,22,23]. When it is burned at high temperatures above 700 °C, only crystalline silica remains [24], which can be used in the ceramic and steel industries [2]. However, when crystalline silica is exposed to air, it can be hazardous to human health by causing the disease silicosis; hence, it has been proposed that RHA should be burned at low temperatures [1,24,25]. Burning rice husks below 700 °C produces amorphous silica, which is used as a supplementary cementitious material (SCM) in construction materials and as a filler in rubber or paint [2,21]. The use of RHA in construction materials is an active research field [7,26,27]. RHA is a highly reactive pozzolanic material, and it has been successfully used to replace some of the cement [21,22,[28], [29], [30], [31], [32], [33]] or silica fume (SF) [7,27,34,35] in concrete, without noticeable degradation in strength and durability. Another promising application of RHA is the production of sodium silicate solutions, key materials for producing geopolymers [[36], [37], [38]].

RHA produced via controlled combustion is a porous material containing a high concentration (85–95 wt%) of amorphous silica [16,28,34,35,39]. The optimal combustion temperature for obtaining the highest content of amorphous silica is 500–700 °C [10,28,40,41], and the content can even be as high as that in SF (>90 wt%). The commercial construction material with the largest amount of SF per unit volume is ultra-high performance concrete (UHPC) [27,42]. Hence, studies are being conducted to replace some of the SF with RHA in UHPC [27,34,35].

However, the morphology (i.e., particle shape and size) of SF and RHA are completely different. SF has perfectly spherical ultra-fine particles that act as both a Pozzolan and nano-sized filler in low water-to-cement ratio (w/c) concrete such as UHPC [35,[43], [44], [45], [46]]. In particular, unreacted SF particles can fill nano-sized pores and improve the microstructure of the concrete [47,48]. Although RHA is pulverized after combustion, its average particle size is generally 5–20 μm, which is 50–100 times the size of the nanoscale SF particles [7,27,35,39]. As a result of these physical differences, the use of RHA to replace SF can change the microstructural characteristics of UHPC [27]. One of the most important principles in the development of UHPC is to optimize the particle packing of granular mixtures, where a similar size distribution between adjacent classes of granular materials is critical [43,49]. SF is an essential material for producing UHPC with outstanding mechanical performance and durability [27], because it can fill void between cement particles and participate as pozzolanic material; however, incorporation of micro-sized filler is also essential to achieve the desired properties. Quartz powder (QP) with an average particle size of 5–25 μm is generally considered an ideal physical filler material [43,49]; RHA has a similar size distribution.

Based on the reviewed composition principle and physical properties of raw materials of UHPC, it is more reasonable to use RHA as a substitute for QP, rather than SF. QP is composed of nearly 100% crystalline silica and is an inert material in UHPC, unless it is exposed to temperatures above 150 °C [43,50,51]. Hence, in commercial UHPCs which generally not experience a temperature over 90 °C regardless of heat treatment, the QP simply acts as a micro-sized filler [43,[52], [53], [54], [55]]. However, due to the amorphous silica content, RHA can act as a reactive powder like SF even at ambient temperature [50,56]. Thus, the use of RHA as filler in UHPC can further promote the pozzolanic reaction without relying on heat treatment. This reaction plays a crucial role in determining the outstanding mechanical performance (compressive strength >150 MPa) and durability of UHPC [43,[57], [58], [59]].

The feasibility of using RHA as a SCM of low w/c concrete and UHPC have been well understood after the studies by Zhang et al. [7] and Tuan et al. [27], especially its role compared to SF. However, the use of RHA instead of QP filler in UHPC has not been sufficiently investigated. Thus, the main objective of this work is to study the effect of RHA filler on the material properties of UHPC, in particular, the replacement ratio of QP filler and the RHA combustion conditions. In addition to its use as an alternative to the filler, the use of the ash as a substitute for SF was also considered. This was in order to directly compare two different approaches that utilize RHA to replace QP and SF, such as: 1) similarity in physical characteristics (particle size and shape) with QP despite difference in chemical composition, and 2) similarity in chemical composition (high purity amorphous silica content) with SF despite difference in physical characteristics.

Although amorphous silica can be obtained by controlled combustion of RHA at 500–700 °C, it is not always possible to obtain high purity materials [39]. Due to the temperature difference between the inside and outside of the bunch of rice husk, two types of ash, white RHA (WRHA) and black RHA (BRHA), are generated. WRHA is a high-purity siliceous material, treated under an appropriate temperature (500–700 °C), while the purity of BRHA is very low due to high carbon content [60]. Therefore, the uncontrolled RHA is divided into two types: BRHA containing high carbon contents (<500 °C), and the RHA composed of crystalline silica (>700 °C) [40,61]. It has been reported that crystalline silica in the RHA does not adversely affect the mechanical properties of concrete [15,40]. However, the effect of BRHA on the performance of concrete is not well understood. Therefore, this study investigated the effects of WRHA and BRHA on the mechanical properties, pozzolanic reaction, and pore structure, particularly when these are used as filler in UHPC.

Section snippets

Materials

Ordinary Portland cement (OPC)-type I (Hanil Cement, Korea), SF (Grade 940U, Elkem, Norway), QP, silica sand, and WRHA or BRHA (Suncheon, Korea) were used to manufacture UHPC samples. BRHA was obtained by uncontrolled combustion at about 400 °C in a plant. WRHA and grey RHA (GRHA) were produced by burning in a programmable temperature furnace at 650 °C for 2 h (heating and cooling rates of 2 °C/min), as shown in Fig. 1a. The combustion program was optimized during preliminary tests to obtain a

Hydration reaction at early ages

The heat flow and cumulative heat of the paste samples are shown in Fig. 6a and b, respectively. When 50% of the SF or QP were replaced by WRHA without changing w/c or the SPPL-to-cement ratio (SPPL/c), the hydration reaction was greatly accelerated, comparing SF(W-50%) or QP(W-50%) with the corresponding reference sample (Ref). Thus, the beginning of the acceleration period occurred earlier. This could be attributed to a reduction in the effective w/c due to water absorption by porous

Discussion

It is an unusual case that the compressive strength of UHPC exceeds 200 MPa without heat treatment [102]. The Ref sample in this study showed a lower strength than this (164 MPa at 91 days), and the strategy of replacing half the SF with WRHA did not result in any significant change in the strength. Although this method effectively promoted the pozzolanic reaction, it negatively affected the capillary pore structure. Moreover, when BRHA was used as a filler, the unburned carbon therein had a

Conclusion

This study was aimed at utilizing RHA as a reactive filler of ambient-cured UHPC to improve its mechanical property. Based on the results obtained, following conclusions can be drawn.

  • -

    A porous and pure white RHA (amorphous silica content: 92 wt%) was manufactured by the process optimized in this study: combustion at 650 °C for 2 h with heating and cooling rates of 2 °C/min. The obtained unground WRHA showed 18.3% of moisture absorbency at 30 h, while it reduced to 15.0% after grinding process.

Acknowledgment

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03007381). The Institute of Engineering Research in Seoul National University provided research facilities for this work.

References (107)

  • R.-S. Bie et al.

    Studies on effects of burning conditions and rice husk ash (RHA) blending amount on the mechanical behavior of cement

    Cem. Concr. Compos.

    (2015)
  • K. Kunchariyakun et al.

    Properties of autoclaved aerated concrete incorporating rice husk ash as partial replacement for fine aggregate

    Cem. Concr. Compos.

    (2015)
  • G. Rodríguez de Sensale

    Strength development of concrete with rice-husk ash

    Cem. Concr. Compos.

    (2006)
  • W. Xu et al.

    Effect of rice husk ash fineness on porosity and hydration reaction of blended cement paste

    Constr. Build. Mater.

    (2015)
  • Y. Chen et al.

    Application studies of activated carbon derived from rice husks produced by chemical-thermal process—a review

    Adv. Colloid Interf. Sci.

    (2011)
  • G. Sua-iam et al.

    Utilization of high volumes of unprocessed lignite-coal fly ash and rice husk ash in self-consolidating concrete

    J. Clean. Prod.

    (2014)
  • L.C. da Rosa et al.

    Use of rice husk and sunflower stalk as a substitute for glass wool in thermal insulation of solar collector

    J. Clean. Prod.

    (2015)
  • Y. Liu et al.

    Simultaneous preparation of silica and activated carbon from rice husk ash

    J. Clean. Prod.

    (2012)
  • Z.-H. He et al.

    Creep analysis of concrete containing rice husk ash

    Cem. Concr. Compos.

    (2017)
  • G.R. de Sensale et al.

    Effects of RHA on autogenous shrinkage of Portland cement pastes

    Cem. Concr. Compos.

    (2008)
  • J. James et al.

    Reactivity of rice husk ash

    Cem. Concr. Res.

    (1986)
  • M. Alkaysi et al.

    Effects of silica powder and cement type on durability of ultra high performance concrete (UHPC)

    Cem. Concr. Compos.

    (2016)
  • N. Van Tuan et al.

    Hydration and microstructure of ultra high performance concrete incorporating rice husk ash

    Cem. Concr. Res.

    (2011)
  • D.G. Nair et al.

    A structural investigation relating to the pozzolanic activity of rice husk ashes

    Cem. Concr. Res.

    (2008)
  • V.G. Papadakis et al.

    Supplementary cementing materials in concrete: part I: efficiency and design

    Cem. Concr. Res.

    (2002)
  • V. Saraswathy et al.

    Corrosion performance of rice husk ash blended concrete

    Constr. Build. Mater.

    (2007)
  • M.F.M. Zain et al.

    Production of rice husk ash for use in concrete as a supplementary cementitious material

    Constr. Build. Mater.

    (2011)
  • R. Zerbino et al.

    Concrete incorporating rice-husk ash without processing

    Constr. Build. Mater.

    (2011)
  • G. Giaccio et al.

    Failure mechanism of normal and high-strength concrete with rice-husk ash

    Cem. Concr. Res.

    (2007)
  • V.-T.-A. Van et al.

    Rice husk ash as both pozzolanic admixture and internal curing agent in ultra-high performance concrete

    Cem. Concr. Compos.

    (2014)
  • H. Huang et al.

    Influence of rice husk ash on strength and permeability of ultra-high performance concrete

    Constr. Build. Mater.

    (2017)
  • J.M. Mejía et al.

    Rice husk ash and spent diatomaceous earth as a source of silica to fabricate a geopolymeric binary binder

    J. Clean. Prod.

    (2016)
  • R.H. Geraldo et al.

    Water treatment sludge and rice husk ash to sustainable geopolymer production

    J. Clean. Prod.

    (2017)
  • E. Kamseu et al.

    Substitution of sodium silicate with rice husk ash-NaOH solution in metakaolin based geopolymer cement concerning reduction in global warming

    J. Clean. Prod.

    (2017)
  • A. Salas et al.

    Comparison of two processes for treating rice husk ash for use in high performance concrete

    Cem. Concr. Res.

    (2009)
  • J.H.S. Rêgo et al.

    Microstructure of cement pastes with residual rice husk ash of low amorphous silica content

    Constr. Build. Mater.

    (2015)
  • S.-H. Kang et al.

    Absorption kinetics of superabsorbent polymers (SAP) in various cement-based solutions

    Cem. Concr. Res.

    (2017)
  • T. Oertel et al.

    Influence of amorphous silica on the hydration in ultra-high performance concrete

    Cem. Concr. Res.

    (2014)
  • T. Oertel et al.

    Amorphous silica in ultra-high performance concrete: first hour of hydration

    Cem. Concr. Res.

    (2014)
  • G. Long et al.

    Very-high-performance concrete with ultrafine powders

    Cem. Concr. Res.

    (2002)
  • P. Richard et al.

    Composition of reactive powder concretes

    Cem. Concr. Res.

    (1995)
  • H. Zanni et al.

    Investigation of hydration and pozzolanic reaction in reactive powder concrete (RPC) using 29Si NMR

    Cem. Concr. Res.

    (1996)
  • A. Korpa et al.

    Phase development in normal and ultra high performance cementitious systems by quantitative X-ray analysis and thermoanalytical methods

    Cem. Concr. Res.

    (2009)
  • Z. Wu et al.

    Effects of different nanomaterials on hardening and performance of ultra-high strength concrete (UHSC)

    Cem. Concr. Compos.

    (2016)
  • Z.A.M. Ishak et al.

    An investigation of the potential of rice husk ash as a filler for epoxidized natural rubber—II. Fatigue behaviour

    Eur. Polym. J.

    (1997)
  • H. Kizhakkumodom Venkatanarayanan et al.

    Effect of grinding of low-carbon rice husk ash on the microstructure and performance properties of blended cement concrete

    Cem. Concr. Compos.

    (2015)
  • S.-H. Kang et al.

    Importance of monovalent ions on water retention capacity of superabsorbent polymer in cement based solutions

    Cem. Concr. Compos.

    (2018)
  • S.-H. Kang et al.

    Importance of drying to control internal curing effects on field casting ultra-high performance concrete

    Cem. Concr. Res.

    (2018)
  • S.-H. Kang et al.

    Shrinkage characteristics of heat-treated ultra-high performance concrete and its mitigation using superabsorbent polymer based internal curing method

    Cem. Concr. Compos.

    (2018)
  • S.-H. Kang et al.

    The effect of superabsorbent polymer on various scale of pore structure in ultra-high performance concrete

    Constr. Build. Mater.

    (2018)
  • Cited by (201)

    View all citing articles on Scopus
    View full text