R c J J a b c a A R R A A K R F S C A P h t fi t l i d ( ( h 0 Industrial Crops and Products 103 (2017) 39–50 Contents lists available at ScienceDirect Industrial Crops and Products jo ur nal home p age: www.elsev ier .com/ locate / indcrop ice straw ash: A potential pozzolanic supplementary material for ementing systems osefa Rosellóa, Lourdes Sorianob, M. Pilar Santamarinaa, Jorge L. Akasakic, José Monzób, ordi Payáb,∗ Departamento de Ecosistemas Agroforestales, Universitat Politècnica de València, Spain Instituto de Ciencia y Tecnología del Hormigón ICITECH, Universitat Politècnica de València, Spain Departamento de Engenharia Civil, Universidade Estadual Paulista Campus Ilha Solteira, Brazil r t i c l e i n f o rticle history: eceived 11 October 2016 eceived in revised form 9 March 2017 ccepted 21 March 2017 vailable online 1 April 2017 eywords: ice straw ash ESEM podogram hemical composition morphous silica ozzolanic reactivity a b s t r a c t Biomass waste from rice straw has many management problems, including field firing causing severe air pollution and natural organic decomposition resulting in methane emission. The conversion of this waste to ashes may offer the possibility of reusing them in cementing systems. For the first time ashes from different parts of the rice plant (Oryza sativa) were characterised from the chemical composition point of view: rice leaf ash (RLA), rice leaf sheath ash (RlsA) and rice stem ash (RsA). Microscopic studies on ashes revealed heterogeneity in the distribution of chemical elements in the remaining cellular structure (spodograms). The highest concentration of SiO2 was found in dumbbell-shaped phytoliths (%SiO2 > 78%). In the global chemical composition of ashes, SiO2 was also the main oxide present. According to Vassilev’s classification of chemical composition, RLA belongs to the K-MA zone (medium acid), RlsA to the K-zone (low acid) and RsA to the S-zone (high acid). Calcination temperatures ≥550 ◦C completely removed organic matter from the straw and ashes underwent significant sinterisation by calcining at 650 ◦C due to the presence of potassium chloride. Here, ashes from global straw (rice straw ash, RSA) are characterised (via X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetry) and tested from a reactivity point of view (reaction towards calcium hydroxide) in order to assess the possibility for its reuse in cementing systems. Results from pastes made by mixing RSA and calcium hydroxide showed that the pozzolanic reactivity of the ashes is important (hydrated lime fixation of 82% for 7 days and 87% for 28 days in RSA:hydrated lime paste) and cementing C S H gel is formed after 7 and 28 days at room temperature. Compressive strength development of Portland cement mortars with 10% and 25% replacements by RSA yielded 107% and 98% of the strength of control mortar after 28 days of curing. Frattini test confirmed the pozzolanicity of the RSA blended cements. These reactivity results are very promising in terms of the potential reuse of ashes in cementing systems. © 2017 Elsevier B.V. All rights reserved. Abbreviations: AWA, agricultural waste ashes; BLA, Bamboo leaf ash; CH, calcium ydroxide (hydrated lime); C S H, calcium silicate hydrate gel; DTG, deriva- ive thermogravimetric curves; EDS, energy dispersive X-ray spectroscopy; FESEM, eld emission scanning electron microscopy; FTIR, Fourier transform infrared spec- roscopy; OM, optical microscopy; RHA, rice husk ash; RLA, rice leaf ash; RlsA, rice eaf sheath ash; RsA, rice stem ash; RSA, rice straw ash; SCM, supplementary cement- ng material; SLA, sugarcane leaf ash; TG, thermogravimetry; XRD, X-ray powder iffraction. ∗ Corresponding author. E-mail addresses: jrosello@upvnet.upv.es (J. Roselló), lousomar@upvnet.upv.es L. Soriano), mpsantam@eaf.upv.es (M.P. Santamarina), akasaki@dec.feis.unesp.br J.L. Akasaki), jmmonzo@cst.upv.es (J. Monzó), jjpaya@cst.upv.es (J. Payá). ttp://dx.doi.org/10.1016/j.indcrop.2017.03.030 926-6690/© 2017 Elsevier B.V. All rights reserved. 1. Introduction Agricultural wastes are commonly assessed as biomass sources for energy purposes. They can be classified in three groups: energy crops, food production wastes and agricultural wastes (Titiloye et al., 2013). Agricultural wastes are usually composed of straws (leaves and stems) and fruit-shells. Some industrially derived agri- cultural wastes also include bagasse, cobs, seeds, pods and husks. Huge amounts of these wastes are available and the selection and appropriate treatments of them could provide building and infra- structure materials. One of the most important challenges related to the produc- tion of building materials is focused on their environmental impact (ecological footprint, carbon footprint), mainly on the production of dx.doi.org/10.1016/j.indcrop.2017.03.030 http://www.sciencedirect.com/science/journal/09266690 http://www.elsevier.com/locate/indcrop http://crossmark.crossref.org/dialog/?doi=10.1016/j.indcrop.2017.03.030&domain=pdf mailto:jrosello@upvnet.upv.es mailto:lousomar@upvnet.upv.es mailto:mpsantam@eaf.upv.es mailto:akasaki@dec.feis.unesp.br mailto:jmmonzo@cst.upv.es mailto:jjpaya@cst.upv.es dx.doi.org/10.1016/j.indcrop.2017.03.030 4 ps and i e i 5 a e f i t w C i 2 t 2 c a c s p i f i 2 m o s b i b t t e i m t p o w o C ( t p a a p a s S ( f h c d e i w n i 0 J. Roselló et al. / Industrial Cro norganic binders, such as ordinary Portland cement OPC (Barceló t al., 2014). It is well known than the production of OPC is a very ntensive process both in terms of energy and raw materials. About % of total worldwide anthropogenic CO2 emissions are gener- ted from the manufacture of OPC-based cement products (Worrell t al., 2001). Cement production has rapidly increased over the last ew decades and reached annual production of 4.3 billion tonnes n 2014 (CEMBUREAU, 2014). Since 1990, the blending composi- ions of cements have changed significantly (Schneider et al., 2011), hich has involved a reduction in clinker content (also named the linker factor, CF). The CF value in 2003 was 0.85, whereas in 2010 t was 0.77; the prediction for 2050 is for it to be 0.71 (WBCSD, 009). This reduction in CF was due to the use of supplemen- ary cementing materials (SCMs). Traditionally (Siddique and Khan, 011), wastes from industrial activities are blended with Portland ement clinker: ground granulated blast furnace slag, coal fly ash nd silica fumes. The first ash from agricultural biomass used in ement or concrete was rice husk ash (RHA) (Mehta, 1983). Utili- ation of ashes will contribute to the sustainability of biomass for ower generation. Valorisation of bottom ashes, fly ashes and flu- dised bed ashes can be carried out by bulk optimisation options: ertiliser and soil amendment, component of building materials or, n the case of carbon-rich ashes, reuse as fuel (Pels and Sarabèr, 011). Over the last few decades, greater interest on the develop- ent of new SCM derived from agricultural wastes (biomass) is bserved in the scientific literature; although the commerciali- ation of agricultural waste ashes (AWA) and its application in uilding materials is still scarce (Aprianti et al., 2015). Moreover, n the last years interest has increased regarding the reuse of some iomass-derived ashes in geopolymers (alkali activated materials) o partially replace the inorganic precursor (Moraes et al., 2016) or otally replace the sodium silicate in the alkaline activator (Bouzón t al., 2014). In both cases, reactive silica in the ashes plays an mportant role for the development of high-performance geopoly- ers. The main basis for the valorisation of these AWA lies in the fact hat they contain high amounts of silica. This silica is a basic com- onent required for a pozzolanic reaction. This reaction consists f the acid-base reaction between calcium hydroxide (portlandite, hen produced from hydration of Portland cement) and silicon xide (silica): a(OH)2 + SiO2 → C S H(gel) The chemical reaction yields calcium silicate hydrate gel C S H), which has cementing properties. When a SCM presents his behaviour, it is termed a pozzolan and it presents pozzolanic roperties. The presence of silica in ash is a necessary factor for pozzolanic reaction, although it is not the only required factor: small size of ash particle (high specific surface area) and amor- hous state (not crystalline phase) are also required. In some cases, morphous alumina is also involved in the pozzolanic process. Over the last few years, interest has increased regarding the tudy the valorisation of AWA (Vassilev et al., 2013; Pels and arabèr, 2011), specifically on the addition of AWA to cements blended Portland cements, alkali-activated cements) and concrete or the following reasons: (a) biomass is produced worldwide in uge amounts and frequently its management is very compli- ated; (b) valorisation as livestock food, fertiliser, cellulosic-based erived materials (fibres, boards) are not always available or are not conomically viable; (c) energetic valorisation of biomass gained nterest as a substitute for fossil fuels since it is technically viable orldwide; (d) the transformation of biomass into AWA is an CO2 eutral process because the carbon released to the atmosphere dur- ng combustion was recently fixed by photosynthesis; (e) the ashes Products 103 (2017) 39–50 could show pozzolanic properties and be then valorised in build- ing materials and (f) the construction industry has the capacity to take in these ashes due to its large requirements in terms of raw materials. Recently, some advances in the application of new AWA in cementing systems were reported, including: ashes from banana leafs (Musa sp., Kanning et al., 2014), switchgrass (Panicum virga- tum) (Wang et al., 2014), elephant grass (Pennisetum purpureum, Cordeiro and Sales, 2015), bamboo leaf (Bambusa sp., Frías et al., 2012), sugarcane straw (Saccharum officinarum, Moraes et al., 2015), barley straw (Hordeum vulgare, Cobreros et al., 2015) and plane tree (Platanus sp., Binici et al., 2008). Rice straw is an agricultural waste that has some manage- ment problems: field firing causes severe air pollution and natural organic decomposition favours methane emission (Yuan et al., 2014). This last process has a potent environmental effect in terms of greenhouse gas emission, as the global warming potential of methane is much higher than that of CO2: 25-times more for a 100-year horizon and 72-times more for 20-year horizon (IPCC, 2007). Thus, it is crucial to valorise this waste as rice produc- tion accounts for 5–10% of worldwide methane emissions. Huge amounts of rice straw are produced worldwide, considering that 1–1.5 kg of straw is generated for every 1 kg of paddy rice (Binod et al., 2010). The worldwide production of rice straw was 731 mil- lion tonnes in 2008 (Abdel-Rahman et al., 2015) and Asia was the major producer, generating 620 million tonnes of the straw (IRRI, 2016). However, scarce research exists on the characterisation of ashes from rice straw ash (RSA) and their potential applications. An interesting approach for obtaining pure silica from rice straw by a sono-assisted sulphuric acid process was reported (Rehman et al., 2013) and Abou-Sekkina et al. (2010) studied three samples of RSA from Egypt and concluded that the silica content was 65% by mass and that no crystalline phases were identified. Ataie et al. (2015) prepared ashes from rice straw and wheat straw after pre- vious treatment with hydrochloric acid and further calcination at 650 ◦C and 500 ◦C. It is well-known that silicon is an element absorbed by the roots of plants in the form of silicic acid, which is transported through the vascular system and deposited in the form of opal or hydrated amorphous silica (SiO2·nH2O). This silica compound is deposited in: (a) the cellular walls; (b) the interior of the cells (lumen); (c) epidermal appendages (trichomes) and (d) the intercellular spaces in stems and leaves (Prychid et al., 2003). This precipitation process of silica is irreversible (Epstein, 1999): in the three first cases a silica particle replicates the shape of the cellular structure, while for the fourth case no relationship between silica deposit shape and the intercellular space is obtained. Monocot plants accumulate silica (>3 mg of Si per g of dried mat- ter), mainly plants belonging to Poaceae family: rice (Oryza sativa) and sugarcane (Saccharum officinarum) (Ma and Yamaji, 2006). Epi- dermal tissues in Poaceae species present particular characteristics that are used in taxonomy. Some taxonomic classifications are based on these cellular dispositions: siliceous cells (phytoliths), suberous cells and trichomes. Phytoliths are solid deposits in which silica is the main component. Their size (typically 10–20 �m) and their shape vary significantly depending on the plant. The follow- ing main morphotypes are described: dumbbells, saddle and cross; also intermediate shapes can be found (Wilding and Drees, 1971; Piperno, 2006). In the rice plant, the silica is highly concentrated in the husk (more than 20% by mass of dried husk). Leaves (formed by leaf blades and leaf sheaths) also are silica-rich parts and contain 13% and 12% silica, respectively. Finally, roots store less silica (2%) (Anala and Nambisan, 2015). The goal of this paper is to characterise different parts of the rice plant (Oryza sativa) by means of the identification and analysis of J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 41 F l surf c t d o m a r t t 2 l 4 r p p c s h f f a f l F t u o a m m s a a s d m T a i c c o i i S ig. 1. Optical microscopy images of fresh rice leaf: (a) adaxial (40×) and (b) abaxia ell; t = trichome; arrows indicate the longitudinal direction of the leaf. he distribution of chemical elements present in the ash (energy ispersive X-ray spectroscopy, EDS) assessed in terms of the btained spodogram (optical and field emission scanning electron icroscopy), crystalline pattern (X-ray powder diffraction, XRD) nd reactivity towards calcium hydroxide (pozzolanic reactivity, eaction products characterisation and hydrated lime fixation) and owards ordinary Portland cement (compressive strength and Frat- ini test). . Materials and methods Rice straw samples (leaf blade, leaf sheath and stem) were col- ected in L’Albufera (Valencia, Spain). These samples were stored at ◦C in sealed plastic bags until they were used for the analyses. Fresh rice straw samples were washed thoroughly to remove esidual soil contamination. One squared centimetre sections were repared by cutting and paradermal lamellae 40 �m thick were repared using a freezing microtome (Jung AG). These cuts were larified with a 50% sodium hypochlorite solution and then washed everal times with distilled water. Small pieces of rice leaves were eated at 105 ◦C for 24 h in a laboratory oven (Memmert UN model) or the studies on dried samples. For studies on calcined samples, resh pieces of leaf blade, leaf sheath and stem were calcined for 1 h t different selected temperatures (450, 550 and 650 ◦C) in a muffle urnace (Carbolite RHF model 1500). The obtained ashes were: rice eaf ash (RLA), rice leaf sheath ash (RlsA) and rice stem ash (RsA). urthermore, large samples (20 g) of rice straw were calcined at he same temperatures as above to obtain ashes (RSA), which were sed for reactivity studies. For optical microscopy (OM) studies the cuts of fresh material, nce clarified, were stained with safranin-light green, dehydrated nd mounted using a synthetic mix of resins (Eukit, Mounting edium for microscope preparation) for observation under a light icroscope (Olympus PM-10AK3). For the field emission scanning electron microscopy (FESEM) elected samples (dried rice leaves and ashes) were studied using ZEISS ULTRA 55 microscope. Samples were studied at 1 kV and at working distance of 3–5 mm. Samples for chemical microanaly- is (EDS) were not covered and were studied at 15 kV at working istance of 5–7 mm. For reactivity studies, the following equipment was used: Ther- ogravimetric analysis was performed using a Mettler-Toledo GA850 instrument. Analysis performed on ashes was carried out in temperature range of 35–1000 ◦C at a heating rate of 20 ◦C min−1 n a dried air atmosphere (75 mL min−1 gas flow) in 70 �L alumina rucibles. Analysis performed on ash:calcium hydroxide pastes was arried out in a temperature range of 35–600 ◦C at a heating rate f 10 ◦C min−1 in a nitrogen atmosphere (75 mL min−1 gas flow) n sealed 100 �L pin-holed aluminium crucibles. Fourier transform nfrared spectroscopy (FTIR) was performed using a Bruker TEN- OR 27 in the wavenumber range between 400 and 4000 cm−1. XRD ace (100×). Key: p = phytolith; s = stoma; c = suberous cell; e = elongated epidermal patterns were obtained by a Bruker AXS D8 Advance with a voltage of 40 kV, current intensity of 20 mA and a Bragg’s angle (2�) in the range of 10–60◦. EDS chemical composition results were submitted to variance analysis (ANOVA) with significant values at P < 0.05. Data analysis was performed using Statgraphics Centurion XVI.II. Mortars were prepared according to UNE-EN 196-1 standard: water/cement ratio was 0.5 and sand/cement ratio was 3. Prismatic specimens (40 × 40 × 160 mm) were cast, and after demoulding they were cured under water for 7 and 28 days. Control mortar was prepared by using ordinary Portland cement (OPC), Spanish cement CEM I-52.5R. RSA containing mortars were prepared by replacing 10% and 25% of OPC by RSA. The ash was previously ground and its mean particle diameter was 13 �m. Compressive strength values of mortars were obtained by means a universal testing machine according to UNE-EN 196-1. Pozzolanicity studies (Frattini test) were carried out according to UNE-EN 196-5. 3. Results and discussion The rice straw is a mixture of different parts of the rice plant and usually contains leaf blades, leaf sheaths and stems. The easi- est part to study using microscopy is the leaf blade, as it is thinner (from herein, we refer to leaf blade as ‘leaf’). When calcining leaf, the spodogram is maintained and different parts of the cells and structures can be identified. This is why the first analyses were conducted on the rice leaf and the ashes obtained after the vari- ous temperature treatments. Ashes obtained from leaf sheaths and stems will be discussed later in the manuscript. Finally, an approach to reactivity studies from the pozzolanic point of view will be dis- cussed using ash produced from a mixture of the different parts in the straw. 3.1. Microscopic studies on fresh leaves Optical microscopy studies on fresh rice leaves were carried out in order to understand the character of cells in the tissue. The upper (adaxial) and the lower leaf surfaces (abaxial) were analysed. In the adaxial surface image (Fig. 1a) trichomes and phytoliths were easily identified. The phytolits showed a bilobated shape and the major axis of the phytoliths was perpendicular (Fig. 1b) to the longitudinal axis of the leaf (bambusoide dermotype (Prat, 1936)). Phytoliths are arranged short distances from each other and among them suber- ous cells are disposed. Elongated epidermal cells and stomata are displayed surrounding the aligned phytoliths and suberous cells. 3.2. Microscopic studies on dried leaves Some leaves were dried at 105 ◦C for FESEM studies (Fig. 2). In these conditions, free water was released and organic and inor- ganic structures were maintained in their original arrangements. 42 J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 F ce; (b) ( B s d s o c a 3 n r s d w w c m a t s o b d s r r T m I K e S w g ig. 2. FESEM micrographs of 105 ◦C dried rice leaf: (a) general view of adaxial surfa d) detailed view of cross shape phytolith (pc). oth surfaces (Fig. 2a and b, adaxial; and Fig. 2c and d, abaxial) pre- ented the same type of epidermal cells and structures. After the rying process, the shape of phytoliths was revealed: some of them eemed to be dumbbell shape (Fig. 2b and d). Apparently, the shape f phytoliths is not homogeneous within the leaf (some appear as a ross shape). Stomata appeared aligned in parallel to the phytoliths rrangement. Abaxial surface showed a wavier form. .3. Microscopies studies on calcined leaves Calcination of leaves was carried out to remove organic compo- ents. Thus, the spodogram (structural residue resulting from the emoval of organic matter by burning, which maintains the leaf’s tructure) was clearly observed. Samples of leaves were calcined at ifferent temperatures, 450, 550, 600 and 650 ◦C, for 1 h. Then, they ere studied by FESEM. Samples obtained at 450, 550 and 650 ◦C ere also assessed by EDS. Fig. 3 shows some micrographs corresponding to samples cal- ined at 450 ◦C. It can be noted than some parts of the leaf aintained a similar structure to the dried samples: the spodogram t 450 ◦C maintained the original arrangement. Thus, aligned phy- oliths are surrounded with an inorganic matrix (Fig. 3a and b) and tomata are arranged parallel to phytoliths (Fig. 3a). However, the riginal structure is not maintained for other parts of the leaf, as can e seen in Fig. 3c. Only phytolith chains were unaltered. In Fig. 3d, a etailed view of some phytoliths is shown, in which their dumbbell hape is highlighted. The removal of organic matter rendered the eal shape for the phytoliths. Some EDS analysis (spots) were car- ied out in order to compare the chemical composition of the ashes. able 1 summarises the chemical composition (in oxide form, by ass) for four selected spots (two phytoliths and two matrix spots). t is very noticeable that phytoliths are mainly formed of SiO2 and 2O (more than 90%) and the surrounding matrix presents more lements in significant percentages: Cl, P2O5, SO3, CaO and MgO. iO2 in the matrix was less than half that value found in phytoliths, hile K2O increased by twofold. These results reflect the hetero- eneity in the disposition of inorganic elements in the ash. Thus, detailed view of dumbbell shape phytolith (pd); (c) general view of abaxial surface; recording 15 EDS signals from 10,000 �m2 areas, on both abaxial and adaxial surfaces, carried out a general analysis. The mean com- position results are summarised in Table 2. Chemical compositions of each area analysed were different and this behaviour is reflected in the standard deviation values for oxide contents. The mean val- ues for the main oxides were: 38.0% and 43.4% SiO2 for adaxial and abaxial surfaces and 28.1% and 27.0% for K2O. From the statistical analysis (comparison of mean values from two populations, that is adaxial and abaxial surfaces), it can be concluded that all com- pound contents are not significantly different, except for chloride and Na2O (P < 0.05). The chemical composition of the RLA was similar to that found for sugarcane leaf ash (SLA) calcined at the same temperature (Roselló et al., 2015). In this case, the SiO2 content was higher (mean value of 40.7% for RLA vs 30.0% for SLA); K2O content was simi- lar (27.5% vs 29.0%, respectively). The most important difference is in the chloride content, which was much lower for RLA than in SLA (1.0% vs 4.0%, respectively). This fact becomes crucial for appli- cations in cements and concrete (Angst et al., 2009) because the presence of chloride ions favours the corrosion of steel in reinforced concrete; thus, RLA will be better in terms of corrosion behaviour. Regarding other elements, RLA presented lower contents of alkaline earth oxides (CaO and MgO) and higher in P2O5. The SO3 contents were similar for both RLA and SLA. Vassilev et al. (2010) proposed a classification of biomass ashes according to the chemical composition (Fig. 4). Thus, they designed a ternary diagram in which the corners were occupied by the sum of selected oxide contents: (a) the sum of silicon, aluminium, iron, sodium and titanium oxides (this will be referred to as � in this manuscript); (b) the sum of calcium, magnesium and manganese oxides (�) and (c) the sum of potassium, phosphorus, sulphur and chlorine oxides (�). In this way, seven zones were defined, depend- ing on the proportion of these groups of oxides in the ash. Rice husk ash (RHA) is a typically siliceous ash, with very low content of other oxides and consequently is represented in the S-type ash zone. Bamboo leaf ash (BLA) is also located in the S-type zone, as it has similar composition, although it is richer in potassium. Biomass J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 43 Fig. 3. FESEM micrographs for rice leaf calcined at 450 ◦C. Key: p = phytolith; m = matrix; p1 and p2, phytolith spots; m1 and m2, matrix spots (see Table 2). Table 1 Spot chemical compositions (EDS, % by mass) for rice leaf ash obtained at 450 ◦C (spots identified in Fig. 3). Spot analysis SiO2 K2O Cl CaO MgO P2O5 SO3 Na2O Phytolith 1 (Fig. 3a) 86.2 8.4 1.0 0.1 0.8 1.6 0.7 1.3 Matrix 1 (Fig. 3a) 40.0 23.8 6.7 4.0 4.6 12.8 6.0 2.2 Phytolith 2 (Fig. 3b) 78.2 11.8 1.9 1.2 1.2 1.7 2.0 2.0 Matrix 2 (Fig. 3b) 25.8 27.4 5.8 11.3 6.7 10.3 10.8 2.0 Table 2 Mean values of chemical composition for RLA (adaxial, abaxial and both zones) obtained at 450 ◦C and 550 ◦C. Values were calculated from EDS analysis on 115 �m × 85 �m area. Sample Parameter SiO2 K2O Cl CaO MgO P2O5 SO3 Na2O RLA 450 ◦C adaxial (1) Mean value 38.0 28.1 1.2 6.2 5.9 13.6 6.5 0.6 Std. Dev. 13.4 5.6 0.3 2.0 2.1 5.2 1.6 0.2 Max. 62.5 37.2 1.6 9.0 10.7 24.2 9.3 1.2 Min. 15.5 20.0 0.9 3.0 2.7 6.1 4.0 0.3 RLA 450 ◦C abaxial (2) Mean value 43.4 27.0 0.8 5.7 4.5 12.2 5.9 0.4 Std. Dev. 14.4 5.5 0.3 1.7 1.4 4.5 1.7 0.1 Max. 62.4 38.6 1.5 8.2 7.2 22.7 8.7 0.7 Min. 14.6 19.5 0.5 3.0 2.8 6.8 3.2 0.3 RLA 450 ◦C total (3) Mean value 40.7 27.5 1.0 6.0 5.2 12.9 6.2 0.5 Std. Dev. 14.0 5.5 0.3 1.8 1.9 4.8 1.6 0.2 Max. 62.5 38.6 1.6 9.0 10.7 24.2 9.3 1.2 Min. 14.6 19.5 0.5 3.0 2.7 6.1 3.2 0.3 RLA 550 ◦C total (4) Mean value 39.3 24.6 0.6 8.9 7.1 14.3 4.8 0.4 Std. Dev. 9.7 2.0 0.1 2.7 2.8 4.1 1.5 0.1 Max. 50.7 27.0 0.7 12.4 11.4 20.1 6.5 0.6 Min. 26.6 22.1 0.4 5.0 3.9 9.6 3.1 0.3 Std. Dev. = standard deviation; Max. = maximum recorded value; Min. = minimum recorded value. (1) Calculated from analyses on 15 different areas. ( ( ( a a w c � 2) Calculated from analyses on 15 different areas. 3) Combined results from (1) and (2). 4) Calculated from analyses on 8 different areas. shes from herbaceous and agricultural grass, straw and residues re located in K-type and K-MA-type zones. This is the case of RLA, hich is located in K-MA zone: � = 51.2%, � = 11.1%, � = 47.7%. Very lose but in K-type zone, is located SLA (from Roselló et al., 2015: = 30.3%, � = 24.4%, � = 45.4%). In Fig. 5 the spodogram of the adaxial surface for RLA obtained at 550 ◦C is observed. Some line-arranged dumbbell phytoliths were identified (Fig. 5a) surrounded by a smooth inorganic matrix. Inter- estingly, when the images are magnified (Fig. 5b–d), one can see that the phytholiths have rounded edges (compare to Fig. 3d) and 44 J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 Fig. 4. Ternary diagram for the classification of biomass ashes (according to Vassilev et al., 2010). Location of some examples of reported agricultural waste ashes: rice husk ash (RHA), bamboo leaf ash (BLA), sugarcane leaf ash (SLA); location of ashes characterised in this research: rice leaf ash (RLA), rice leaf sheath ash (RlsA) and rice stem ash (RsA). F view o s d c I l i f o t m g ig. 5. FESEM micrographs of a RLA (adaxial surface) obtained at 550 ◦C: (a) general ome of them are connected along certain sides. Apparently, this eformation is related to a semi-fusion or sinterisation process arried out during the calcination. The same behaviour was observed for the abaxial surface (Fig. 6). n Fig. 6a and b, a double chain of phytoliths corresponding to the ongitudinal centre of the leaf (midrib, the central vein of the leaf) s shown. Fig. 6c shows highly altered phytoliths, probably due to a ocalised high temperature during calcination. In Fig. 6d, a picture f the inorganic matrix after organic matter removal is shown: in his case, more rounded structures are observed compared to the atrix depicted in Fig. 3d. The melting point of ashes depends on the percentage of inor- anic elements (Biedermann and Obernberger, 2015). Thus, high f the spodogram; (b and c) enlarged zones; (d) detailed view of sintered phytoliths. percentages of alkalis (Na, K) and chlorides result in a decrease in melting temperatures; on the contrary, presence of alkaline earth elements (Ca, Mg) increasing it. In general, straw ashes with low Ca content and high K and Si contents start to sinter and melt at lower temperatures than wood ashes (which are richer in Ca) (Biedermann and Obernberger, 2015). Potassium is the key ele- ment that participates in the formation of troublesome species (e.g., formation of potassium salts, such as KCl and K2SO4). The K2O- SiO2 binary system starts to melt in the range of 600–700 ◦C (Wang et al., 2012). Despite the temperature furnace being 550 ◦C, tem- peratures on the surface of the materials were probably higher as the combustion of organic matter released a significant quantity of heat. In these conditions, the temperature close to the sample was J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 45 F in of p m c s t p c r b t i d M s c a i a t o s m T w c r r w d 3 F t p ig. 6. FESEM micrographs of RLA (abaxial surface) obtained at 550 ◦C: (a) double cha atrix. ertainly higher than 600 ◦C. This is the reason why all remaining tructures after burning at 550 ◦C appeared rounded. Furthermore, he matrix surrounding the phytoliths was affected: in this case, the resence of Ca and Mg did not prevent the sintering/melting pro- ess, as can be seen in Fig. 6d for the matrix in the abaxial surface of ice leaf burned at 550 ◦C. This behaviour supports the relationship etween initial deformation temperature (IDT) and the K2O con- ent observed for biomass ashes, whereby IDT lowered when K2O ncreased (Niu et al., 2010). The chemical composition of RLA calcined at 550 ◦C was also etermined by EDS (eight individual analyses were carried out). ean values are given in Table 2. In this case, statistical analysis hown that there are differences (P < 0.05) in Cl, CaO, MgO and SO3 ontents when compared with sample prepared at 450 ◦C. RLA samples also were obtained by calcining the straw at 600 nd 650 ◦C. Fig. 7 shows selected FESEM micrographs. Phytoliths n Fig. 7a–c showed that spodograms of ashes calcined at 600 ◦C ppeared slightly sintered. In samples obtained at 650 ◦C, the sin- erisation effect is highlighted: many phytoliths changed from their riginal shape to rounded dumbbell shape (Fig. 7d), spheroidal tructures (Fig. 7e) or to produce a continuous line through the erging of phytoliths (Fig. 7f). EDS analyses were performed on samples obtained at 650 ◦C. he calculated chemical compositions did not vary significantly ith respect to those obtained at lower temperatures, except for hloride content. These analyses yield chloride contents in the ange 0.15–0.04%. This means that there was a removal of chlo- ides during treatment at this temperature. Probably, the chlorine as removed in the form of potassium chloride by volatilisation ue to the low melting point of this salt (776 ◦C). .4. Microscopic studies on rice leaf sheath and rice stem ashes Samples of leaf sheath (ls) and stem (s) were calcined at 450 ◦C. ESEM micrographs of the obtained ashes (RlsA and RsA, respec- ively) are showed in Fig. 8. External parts (Fig. 8a and c) showed hytoliths and similar texture to that of leaf blades described above. hytoliths; (b) detail of the twin lines; (c) highly spheroidal phytoliths; (d) inorganic However, internal structures (Fig. 8b and d) were different and a very porous skeleton was identified. Chemical analysis (EDS) of the ashes was conducted in order to compare the percentages of the main oxides. Values are summarised in Table 3. Statistical analy- sis showed that the chemical compositions for RLA and RlsA are different (P < 0.05) for all oxides, except for SiO2. The SiO2 content was higher for the external part of the leaf sheath (37.7%) than for the internal part (23.3%), although the difference is not statisti- cally significant. Significant differences (P < 0.05) were only found for K2O, SO3 and Na2O. Interestingly, K2O and chloride contents were higher for RlsA than RLA: chloride content was more than five times greater in RlsA. In the Vassilev’s ternary diagram (see Fig. 4), RlsA belongs to K-zone (� = 32.6%, � = 4.2%, � = 63.2%). On the contrary RsA showed a high percentage of SiO2 (mean value 84.3%). Obviously, the rest of components were low, espe- cially chloride, which scarcely reached 0.1%. From a statistical point of view, there is a significant difference (P < 0.05) between all oxides, except CaO and Na2O, with respect to the RLA. Thus, the position of RLA in the Vassilev’s diagram (see Fig. 4a) is in the S-zone: � = 84.7%, � = 8.7%, � = 6.6%. 3.5. Reactivity studies on rice straw ashes In general terms, rice straw collected from the field is com- posed of leafs, stems and leaf sheaths; additionally, is very common that some soil particles (sand, clays, feldspar) appear together the biomass. In this study, a sample of rice straw was collected and cal- cined in order to analyse the pozzolanic properties of the ash. Three calcining temperatures (450 ◦C, 550 ◦C and 650 ◦C) were selected for producing the corresponding ashes (RSA-450, RSA-550, RSA- 650). These samples were characterised by means of thermogravime- try (TG), FTIR and powder XRD. The thermogravimetric analysis curve (Fig. 9) for RSA-450 showed that decomposition of the organic matter/carbon was not completed at 450 ◦C, although there was a mass loss (6.92%) in the 350–650 ◦C range. Also a mass loss was beginning at 900 ◦C, which 46 J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 Fig. 7. FESEM micrographs for RLA obtained at 600 ◦C (a, b, c: slightly sintered phytoliths) and at 650 ◦C (d, e, f: highly sintered phytoliths). F tem; ( t i K d m ig. 8. FESEM micrographs of samples obtained at 450 ◦C: (a) external part of the s he leaf sheath. s related to the fusion/evaporation of potassium sulphate (pure 2SO4 melts at 1069 ◦C). Conversely, the sample obtained at 550 ◦C id not show (Fig. 9) any significant mass loss related to organic atter/carbon, which means that this temperature is enough for b) internal part of the stem; (c) external part of the leaf sheath; (d) internal part of removing organic compounds in rice straw; RSA-550 ◦C also shows a similar initiation of mass loss at 900 ◦C. FTIR spectra for these ashes are depicted in Fig. 10. The main absorption bands are related to Si O vibrations, in accordance J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 47 Table 3 Mean values of chemical composition for rice leaf sheath ashes (RlsA) and rice stem ashes (RsA) (external, internal and both zones) obtained at 450 ◦C. Values were calculated from EDS analysis on a 115 �m × 85 �m area. Sample Parameter SiO2 K2O Cl CaO MgO P2O5 SO3 Na2O RlsA 450 ◦C external (1) Mean value 37.7 33.4 4.7 1.5 2.7 16.2 3.2 0.7 Std. Dev. 17.8 5.8 2.0 1.6 1.6 7.2 1.1 0.4 Max. 63.5 41.2 8.7 3.8 5.7 28.1 5.1 1.4 Min. 9.8 24.5 1.3 0.00 0.5 7.4 1.3 0.2 RlsA 450 ◦C internal (2) Mean value 23.3 40.6 6.9 1.0 3.4 18.1 4.9 1.3 Std. Dev. 19.7 8.0 5.0 1.3 1.0 5.9 1.3 0.4 Max. 59.8 49.4 16.5 3.0 4.6 25.8 7.0 2.0 Min. 0.00 27.9 1.3 0.00 1.1 7.2 2.2 0.5 RlsA 450 ◦C total (3) Mean value 32.0 36.3 5.6 1.3 3.0 17.2 3.9 0.9 Std. Dev. 19.56 7.51 3.60 1.48 1.44 6.70 1.45 0.48 Max. 63.5 49.4 16.5 3.8 5.7 28.1 7.0 2.0 Min. 0.00 24.5 1.3 0.00 0.5 7.2 1.3 0.2 RsA 450 ◦C external (4) Mean value 83.0 4.7 0.2 4.8 4.2 1.1 1.5 0.5 Std. Dev. 7.2 2.1 0.2 2.4 2.8 0.8 0.8 0.2 Max. 95.0 9.0 0.6 9.6 11.9 3.1 3.6 1.1 Min. 67.3 2.1 0.00 0.8 1.3 0.00 0.6 0.2 RsA 450 ◦C internal (5) Mean value 86.1 3.0 0.00 6.3 2.0 1.1 1.2 0.4 Std. Dev. 2.4 0.5 0.00 1.1 0.7 0.3 0.4 0.1 Max. 90.8 3.8 0.00 8.1 3.1 1.6 1.7 0.6 Min. 83.3 2.3 0.00 4.1 1.2 0.8 0.6 0.2 RsA 450 ◦C total (6) Mean value 84.3 4.0 0.1 5.4 3.4 1.1 1.4 0.5 Std. Dev. 5.9 1.9 0.2 2.1 2.4 0.6 0.7 0.2 Max. 95.0 9.0 0.6 9.6 11.9 3.1 3.6 1.1 Min. 67.3 2.1 0.0 0.8 1.2 0.0 0.6 0.2 Std. Dev = standard deviation; Max = maximum value recorded; Min = minimum value recorded. (1) Calculated from analyses on 15 different areas. (2) Calculated from analyses on 15 different areas. (3) Combined results from (1) and (2). (4) Calculated from analyses on 15 different areas. (5) Calculated from analyses on 15 different areas. (6) Combined results from (4) and (5). F 2 w 1 r t 8 t p X a 4 ig. 9. Thermogravimetric curves for RSA-450 and RSA-550 (dried air atmosphere, 0 ◦C min−1 heating rate). ith the siliceous nature of the ashes. The most intense bands are 056–1035, 795–785, 617 and 453 cm−1. Also, absorption bands elated to the presence of carbonate anions (probably due to he presence of calcium carbonate) are observed: 1411–1406 and 77 cm−1. These C O bands disappeared for RSA-650, suggesting hat the small amount of carbonate present in the ash is decom- osed (decarbonation) at 650 ◦C. Finally, in order to complete the characterisation of the ashes, RD patterns were collected (Fig. 11). Significant major peaks (28.4◦ nd 40.6◦) are related to the presence of sylvite (KCl, PDFcard 11476). This crystalline compound is easily identified because Fig. 10. FTIR spectra (400–1600 cm−1 range) for RSA-450, RSA-550 and RSA-650. solid phases in ashes are mainly amorphous in nature. The baseline deviation in the range 2� = 15–30◦ is representative of amorphous silica. Some traces of quartz (SiO2, PDFcard 331161) are proba- bly due to soil contamination of the rice straw. Interestingly, there was no evidence of the formation of cristobalite or trydimite. This means that conversion of the straw into ashes at a temperature in the 450–650 ◦C range, does not achieve the crystallisation of amorphous silica. This behaviour has an important consequence because the pozzolanic reactivity of ashes depends on the silica phases: crystalline phases do not react easily towards calcium hydroxide (CH), whereas amorphous silica reacts at room temper- ature in wet conditions. Secondary minerals are also present in 48 J. Roselló et al. / Industrial Crops and Products 103 (2017) 39–50 Fig. 11. XRD patterns for RSA-450, RSA-550 and RSA-650. Key: S = sylvite; C = calcite; Q = quartz; A = arcanite. t P i t r m a a t c D p h q C t t a w t t b t h Fig. 13. TG curves of RSA-650:CH (3:7) pastes cured for 7 and 28 days. Fig. 11), practically disappeared and the baseline deviation moved Fig. 12. DTG curves of RSA-450:CH (1:1) pastes cured for 7 and 28 days. he ashes: arcanite (K2SO4, PDFcard 050613) and calcite (CaCO3, DFcard 050586). The peaks corresponding to calcite have less ntensity in the RSA-650 sample, confirming the decomposition of he carbonated mineral at this temperature, as suggested from FTIR esults. In order to quantify the reactivity of RSA samples, selected ixtures with calcium hydroxide (Ca(OH)2, CH) were prepared nd hydrated. Pastes with RSA-450 and RSA-550, prepared with RSA:CH (1:1) mass ratio were characterised by thermogravime- ry (after 7 and 28 days hydration). Derivative thermogravimetric urves (DTG) of RSA-450 pastes are depicted in Fig. 12. In both TG curves (7 and 28 days), a peak centred at about 150 ◦C was resent, related to the dehydration process of calcium silicate ydrate (C S H). This compound is typically produced as conse- uence of the pozzolanic reaction between amorphous silica and H. Also, a peak appeared at 450 ◦C related to the decomposition of he small amount of remaining (Ca(OH)2). The total mass loss for the emperature range of 35–600 ◦C was very high: 16.09% for 7 days nd 15.47% for 28 days; conversely, the mass loss attributed to CH as very low (2.15 and 1.63%, respectively). These data revealed hat the pozzolanic reaction was fast and that most of the reac- ion products were produced in the first 7 days of hydration. This ehaviour implies the amorphous nature of the silica present in he ash. The total amount of CH fixed by the RSA-450 ash was very igh: 82% for 7 days and 87% for 28 days. Similar results were found Fig. 14. XRD patterns for RSA-450:CH (1:1) paste and RSA-650:CH (3:7) paste, both cured at room temperature for 28 days. Key: S = sylvite; C = calcite; A = arcanite; P = portlandite; T = tobermorite. for RSA-550, suggesting that both calcining temperatures yielded excellent reactive ashes. RSA-650 reactivity was also assessed by means of the reactivity towards calcium hydroxide in a RSA:CH (3:7) ratio. In this case, with respect to the above-mentioned pastes, the relative amount of CH is much higher (70%). In these conditions, this reagent was in high excess and will be not totally consumed, as can be seen in the TG curves for 7 and 28 days of curing depicted Fig. 13. In these curves, a mass loss in the range 540–580 ◦C corresponding to the decomposition of Ca(OH)2 was observed. From the corresponding calculated mass losses for both curing ages, it can be stated that 40% and 54%, respectively, of the Ca(OH)2 was chemically combined in the reaction. In the TG curve, mass loss related to the dehydration of C S H gel (range 120–200 ◦C) is also observed, similar to that found in 1:1 pastes. These pastes also were characterised by means XRD. In Fig. 14, XRD patterns for 1:1 RSA-450:CH paste and 3:7 RSA-650:CH paste, both cured at room temperature for 28 days, are shown. Firstly, for the paste with the lowest CH proportion (1:1 paste), it may be noticed that the baseline deviation, which occurred in the ash (see to a higher diffraction angle range (2� = 27–33◦). This was due to the transformation of the amorphous silica to C S H gel as a con- sequence of the pozzolanic reaction. The most intense and broad J. Roselló et al. / Industrial Crops and Fig. 15. Frattini test results after 8 days curing at 40 ◦C for blended cements with RSA (10% and 25% replacement percentages). Table 4 Compressive strengths (in MPa, standard deviation in parentheses) for mortars after 7 days and 28 days of curing. Mortar 7 days 28 days OPC control 54.9 (0.7) 62.7 (0.6) p p p i F i P s t f i w p c p i e t t s c r t F c c p C R d 8 t o 10% RSA 54.1 (1.8) 67.1 (2.0) 25% RSA 45.8 (1.3) 58.9 (1.8) eak was found at 2� = 29.9◦, which corresponds to the tobermoritic hase (Ca5Si6O16(OH)2·4(H2O)) and this peak overlapped the main eak of calcite (which was present in the ash and also as an impurity n the calcium hydroxide used as reagent for the paste preparation). urthermore, peaks belonging to sylvite and arcanite were easily dentified. Additionally, main peaks from the portlandite (Ca(OH)2, DFcard 040733) also are shown: these peaks were of low inten- ity, demonstrating the low remaining quantity of portlandite in he paste after 28 days of curing. These results corroborate those rom the thermogravimetric studies and confirm the high reactiv- ty of the ash towards CH in the pozzolanic process. For the paste ith the highest CH proportion (3:7 paste) and because important art of the calcium hydroxide remained unreacted after 28 days of uring (assessed by thermogravimetric analysis), the most intense eaks observed (Fig. 14) belonging to portlandite. Also, calcite was dentified as the main crystalline component because of its pres- nce in the CH reagent. Sylvite and arcanite were not observed due o the intensity of the portlandite peaks. For the same reason the obermoritic phase was also difficult to observe. Reactivity of RSA was also assessed by means compressive trength of mortars and pozzolanicity test (Frattini). Blended ements by mixing OPC and RSA were prepared: 10% and 25% eplacement percentages of RSA were tested. Results from the Frat- ini test obtained after 8 days of reaction at 40 ◦C are showed in ig. 15. It can be noticed that the points corresponding to RSA ontaining blends are below the saturation curve. This behaviour onfirms the pozzolanic reactivity of the ash. Mortars cured after 7 and 28 days of curing were tested in com- ression (six values for each cement and for each curing time). ompressive strengths are summarised in Table 4. Mortar with 10% SA reached 98.4% of the strength found for OPC control after 7 ays, and 107.1% after 28 days; and mortar with 25% RSA reached 3.3% at 7 days and 98.4% after 28 days. All these results confirmed he high pozzolanic reactivity of RSA and the strong contribution f this type of reactivity on the strength development of mortars. Products 103 (2017) 39–50 49 4. Conclusions RSA is characterised from microscopic, chemical composition and reactivity point of views. Different parts of the rice straw have different chemical compositions when transformed to ashes: rice leaf ash (RLA), rice leaf sheath ash (RlsA) and rice stem ash (RsA). Microscopic studies (optical and FESEM) revealed heterogene- ity in the distribution of chemical elements in ashes according to the cellular structure remaining after organic matter removal (spodograms). The highest concentration of SiO2 was found for dumbbell shape phytoliths. In the global chemical composition of ashes, SiO2 was the main oxide present and K2O was the second main oxide for RLA and RlsA, whereas CaO was the second most abundant for RsA. RLA presented a mean chemical composition with 40.7% SiO2 and 27.5% K2O. Also chloride content was relatively high (1.0% by mass). According to Vassilev’s classification, this ash belongs to the K-MA zone (medium acid). These ashes suffer significant sinterisa- tion at 650 ◦C due to the presence of potassium chloride. RlsA was classified accordingly to Vassilev’s in the K-zone (low acid) because of its low SiO2 content and high K2O percentage. Noticeably, chlo- ride content found for this ash was five-times greater than that found for RLA. RsA presented a very high SiO2 percentage (84.3%) and it was classified in the S-zone (high acid). RSA was tested from the reactivity point of view in order to assess the possibilities for its reuse in cementing systems. Results from pastes made by mixing RSA and calcium hydroxide showed that the pozzolanic reactivity of the ashes is important and cement- ing C S H gel is formed after 7 and 28 days at room temperature. This reactivity was due to the amorphous nature of the silica (SiO2) in the ash. RSA:CH (1:1) pastes showed a fixation of 85% of avail- able calcium hydroxide and (3:7) pastes a fixation of 54%. OPC-RSA blended cements showed a good performance in terms of compres- sive strength development, and 107% and 98% of the strength for the control mortar was achieved after 28 of curing for 10% and 25% RSA replacement percentages. These reactivity results are very promising for the reuse of ashes from this biomass (rice straw) in cementing systems, e.g., as poz- zolanic supplementary materials in Portland cement or also as silica-based supplementary precursor for geopolymers (alkali acti- vated materials). Acknowledgements The authors acknowledge the financial support of the Mini- sterio de Economía y Competitividad MINECO, Spain, and FEDER funding [Project: BIA2015-70107-R]. The authors thank the Elec- tron Microscopy Service of the Universitat Politècnica de València (Spain). References Abdel-Rahman, M.A., Abdel-Shakour, E.H., Hassan, S.E., Refaat, B.M., Nour El-Din, M., Ewais, E.E., Alrefaey, H.M.A., 2015. Effects on environmental factors and compost additives on Bacillus sonorensis 7-1v, a cellulytic strain able to degrade rice straw under solid state fermentation. Int. J. Adv. Res. Biol. Sci. 2, 241–251. Abou-Sekkina, M.M., Issa, R.M.A., Bastawisy, A.E.M., El-Helece, W.A., 2010. Characterization and evaluation of thermodynamic parameters for Egyptian heap fired Rice Straw Ash (RSA). Int. J. Chem. 2, 81–88. Anala, R., Nambisan, P., 2015. Study of morphology and chemical composition of phytoliths on the surface of paddy straw. Paddy Water Environ. 13, 521–527, http://dx.doi.org/10.1007/s10333-014-0468-5. Angst, U., Elsener, B., Larsen, C.L., Vennesland, O., 2009. Critical chloride content in reinforced concrete – a review. Cem. Concr. Res. 39, 1122–1138, http://dx.doi. org/10.1016/j.cemconres.2009.08.006. Aprianti, E., Shafigh, P., Bahri, S., Farahani, J.N., 2015. Supplementary cementitious materials origin from agricultural wastes – a review. Constr. Build. Mater. 74, 176–187, http://dx.doi.org/10.1016/j.conbuildmat.2014.10.010. Ataie, F.F., Juenger, M.C.G., Taylor-Lange, S.C., Riding, K.A., 2015. Comparison of the retarding mechanisms of zinc oxide and sucrose on cement hydration and http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0005 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0010 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1007/s10333-014-0468-5 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.cemconres.2009.08.006 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 dx.doi.org/10.1016/j.conbuildmat.2014.10.010 5 ps and B B B B B C C C E F I I K M M M M emissions from the global cement industry. Annu. Rev. Energy Environ. 26, 303–329, http://dx.doi.org/10.1146/annurev.energy.26.1.303. 0 J. Roselló et al. / Industrial Cro interactions with supplementary cementitious materials. Cem. Concr. Res. 72, 128–136, http://dx.doi.org/10.1016/j.cemconres.2015.02.023. arceló, L., Kline, J., Walenta, G., Gartner, E., 2014. Cement and carbon emissions. Mater. Struct. 47 (6), 1055–1065, http://dx.doi.org/10.1617/s11527-013-0114- 5. iedermann, F., Obernberger, F., 2015. Ash-Related Problems During Biomass Combustion and Possibilities for a Sustainable Ash Utilization. http://www. bios-bioenergy.at/uploads/media/Paper-Biedermann-AshRelated-2005-10-11. pdf (accessed 28.7.16). inici, H., Yucegok, F., Aksogan, O., Kaplan, H., 2008. Effect of corncob, wheat straw, and plane leaf ashes as mineral admixtures on concrete durability. J. Mater. Civ. Eng. 20, 478–483, http://dx.doi.org/10.1061/(ASCE)0899- 1561(2008)20:7(478). inod, P., Sindhu, R., Singhania, R.R., Vikram, S., Devi, L., Nagalakshmi, S., Kurien, N., Sukumaran, R.K., Pandey, A., 2010. Bioethanol production from rice straw: an overview. Bioresour. Technol. 101, 4767–4774, http://dx.doi.org/10.1016/j. biortech.2009.10.079. ouzón, N., Payá, J., Borrachero, M.V., Soriano, L., Tashima, M.M., Monzó, J., 2014. Refluxed rice husk ash/NaOH suspension for preparing alkali activated binders. Mater. Lett. 115, 72–74, http://dx.doi.org/10.1016/j.matlet.2013.10.001. EMBUREAU, 2014. Activity Report, http://www.cembureau.eu/sites/default/files/ Activity%20Report%202014 website 1.pdf (accessed 28.7.16). obreros, C., Reyes-Araiza, J.L., Nava, R., Rodríguez, M., Mondragón-Figueroa, M., Apatiga, L.M., Rivera-Muñoz, E.M., 2015. Barley straw ash: pozzolanic activity and comparison with other natural and artificial pozzolans from Mexico. Bioresources 10, 3757–3774, http://dx.doi.org/10.15376/biores.10.2.3757- 3774. ordeiro, G.C., Sales, C.P., 2015. Pozzolanic activity of elephant grass ash and its influence on the mechanical properties of concrete. Cem. Concr. Compos. 55, 331–336, http://dx.doi.org/10.1016/j.cemconcomp.2014.09.019. pstein, E., 1999. Silicon. Annu. Rev. Plant Physiol. Plant Mol. Biol. 50, 641–664, http://dx.doi.org/10.1146/annurev.arplant.50.1.641. rías, M., Savastano, H., Villar, E., Sánchez de Rojas, M.I., Santos, S., 2012. Characterization and properties of blended cement matrices containing activated bamboo leaf wastes. Cem. Concr. Compos. 34, 1019–1023, http://dx. doi.org/10.1016/j.cemconcomp.2012.05.005. PCC, 2007. International Panel on Climate Change. Climate Change. The Physical Science Basis. Cambridge University Press, Cambridge https://www.ipcc.ch/ publications and data/publications ipcc fourth assessment report wg1 report the physical science basis.htm (accessed 28.07.16). RRI International Rice Research Institute. http://irri.org/our-work/research/value- added-rice/rice-straw-and-husks/ (accessed 28.7.16). anning, R.C., Portella, K.F., Braganç a, M.O.G.P., Bonato, M.M., Jeannette, C.M., Dos Santos, J.C.M., 2014. Banana leaves ashes as pozzolan for concrete and mortar of Portland cement. Constr. Build. Mater. 54, 460–465, http://dx.doi.org/10. 1016/j.conbuildmat.2013.12.030. a, J.F., Yamaji, N., 2006. Silicon uptake and accumulation in higher plants. Trends Plant Sci. 11, 392–397, http://dx.doi.org/10.1016/j.tplants.2006.06.007. ehta, P.K., 1983. Pozzolanic and Cementitious Byproducts as Mineral Admixtures for Concrete – A Critical Review. American Concrete Institute, ACI Special Publication 79 (46 pages). oraes, J.C.B., Akasaki, J.L., Melges, J.L.P., Monzó, J., Borrachero, M.V., Soriano, L., Payá, J., Tashima, M.M., 2015. Assessment of sugar cane straw ash (SCSA) as pozzolanic material in blended Portland cement: microstructural characterization of pastes and mechanical strength of mortars. Constr. Build. Mater. 94, 670–677, http://dx.doi.org/10.1016/j.conbuildmat.2015.07.108. oraes, J.C.B., Tashima, M.M., Akasaki, J.L., Melges, J.L.P., Monzó, J., Borrachero, M.V., Soriano, L., Payá, J., 2016. Increasing the sustainability of alkali-activated binders: the use of sugar cane straw ash (SCSA). Constr. Build. Mater. 124, 148–154, http://dx.doi.org/10.1016/j.conbuildmat.2016.07.090. Products 103 (2017) 39–50 Niu, Y., Tan, H., Wang, X., Liu, Z., Liu, H., Liu, Y., Xu, T., 2010. Study on fusion characteristics of biomass ash. Bioresour. Technol. 101, 9373–9381, http://dx. doi.org/10.1016/j.biortech.2010.06.144. Pels, J.R., Sarabèr, A.J., 2011. Utilization of biomass ashes. In: Grammelis, P. (Ed.), Solid Biofuels for Energy (series Green Energy and Technology). Springer-Verlag, London, pp. 219–235, http://dx.doi.org/10.1007/978-1- 84996-393-0 10. Piperno, D.R., 2006. Phytoliths: A Comprehensive Guide for Archaeologists and Paleoecologists. AltaMira Press, Oxford. Prat, H., 1936. La Systematique des Graminées: Annals des Sciences Naturelles. Series 10. Botanique, Paris. Prychid, C.J., Rudall, P.J., Gregory, M., 2003. Systematics and biology of silica bodies in monocotyledons. Bot. Rev. 69, 377–440, http://dx.doi.org/10.1663/0006- 8101(2004)069[0377:SABOSB]2.0.CO;2. Rehman, M.S.U., Umer, M.A., Rashid, N., Kima, I., Han, J., 2013. Sono-assisted sulfuric acid process for economical recovery of fermentable sugars and mesoporous pure silica from rice straw. Ind. Crops Prod. 49, 705–711, http:// dx.doi.org/10.1016/j.indcrop.2013.06.034. Roselló, J., Soriano, L., Santamarina, M.P., Akasaki, J.L., Melges, J.L.P., Payá, J., 2015. Microscopy characterization of silica-rich agrowastes to be used in cement binders: bamboo and sugarcane leaves. Microsc. Microanal. 21, 1314–1326, http://dx.doi.org/10.1017/S1431927615015019. Schneider, M., Romer, M., Tschudin, M., Bolio, H., 2011. Sustainable cement production-present and future. Cem. Concr. Res. 41, 642–650, http://dx.doi. org/10.1016/j.cemconres.2011.03.019. Siddique, R., Khan, M.I., 2011. Supplementary cementing materials. Springer-Verlag, Berlin Heidelberg, http://dx.doi.org/10.1007/978-3-642- 17866-5. Titiloye, J.O., Bakar, M.S.A., Odetoye, T.E., 2013. Thermochemical characterisation of agricultural wastes from West Africa. Ind. Crops Prod. 47, 199–203, http://dx. doi.org/10.1016/j.indcrop.2013.03.011. Vassilev, S.V., Baxter, D., Andersen, L.K., Vassileva, C.G., 2010. An overview of the chemical composition of biomass. Fuel 89, 913–933, http://dx.doi.org/10.1016/ j.fuel.2009.10.022. Vassilev, S.V., Baxter, D., Andersen, L.K., Vassileva, C.G., 2013. An overview of the composition and application of biomass ash. Part 2. Potential utilisation, technological and ecological advantages and challenges. Fuel 105, 19–39, http://dx.doi.org/10.1016/j.fuel.2012.10.001. Wang, L., Hustad, J.E., Skreiberg, Ø., Skjevrak, G., Grønli, M., 2012. A critical review on additives to reduce ash related operation problems in biomass combustion applications. Energy Procedia 20, 20–29, http://dx.doi.org/10.1016/j.egypro. 2012.03.004. Wang, Y., Shao, Y., Matovic, M.D., Whalen, J.K., 2014. Recycling of switchgrass combustion ash in cement: characteristics and pozzolanic activity with chemical accelerators. Constr. Build. Mater. 73, 472–478, http://dx.doi.org/10. 1016/j.conbuildmat.2014.09.114. WBCSD, 2009. Cement Technology Roadmap. World Business Council for Sustainable Development, Geneva, Switzerland, https://www.iea.org/media/ freepublications/technologyroadmaps/cementroadmapreferences.pdf (accessed 28.7.16). Wilding, L.P., Drees, L.R., 1971. Biogenic opal in Ohio soils. Soil Sci. Soc. Am. Proc. 35, 1004–1010, http://dx.doi.org/10.2136/sssaj1971.03615995003500060041x. Worrell, E., Price, L., Martin, N., Hendriks, C., Ozawa Meida, L., 2001. Carbon dioxide Yuan, Q., Pump, J., Conrad, R., 2014. Straw application in paddy soil enhances methane production also from other carbon sources. Biogeoscience 11, 237–246, http://dx.doi.org/10.5194/bg-11-237-2014. dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1016/j.cemconres.2015.02.023 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 dx.doi.org/10.1617/s11527-013-0114-5 http://www.bios-bioenergy.at/uploads/media/Paper-Biedermann-AshRelated-2005-10-11.pdf 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dx.doi.org/10.1016/j.biortech.2009.10.079 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 dx.doi.org/10.1016/j.matlet.2013.10.001 http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf http://www.cembureau.eu/sites/default/files/Activity Report 2014_website_1.pdf 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dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1016/j.cemconcomp.2014.09.019 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1146/annurev.arplant.50.1.641 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 dx.doi.org/10.1016/j.cemconcomp.2012.05.005 https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) https://www.ipcc.ch/publications_and_data/publications_ipcc_fourth_assessment_report_wg1_report_the_physical_science_basis.htm (accessed 28.07.16) http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ http://irri.org/our-work/research/value-added-rice/rice-straw-and-husks/ dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.conbuildmat.2013.12.030 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 dx.doi.org/10.1016/j.tplants.2006.06.007 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0105 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2015.07.108 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.conbuildmat.2016.07.090 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1016/j.biortech.2010.06.144 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 dx.doi.org/10.1007/978-1-84996-393-0_10 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0130 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 http://refhub.elsevier.com/S0926-6690(17)30188-7/sbref0135 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1663/0006-8101(2004)069[0377:SABOSB]2.0.CO;2 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1016/j.indcrop.2013.06.034 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1017/S1431927615015019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1016/j.cemconres.2011.03.019 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1007/978-3-642-17866-5 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.indcrop.2013.03.011 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2009.10.022 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.fuel.2012.10.001 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.egypro.2012.03.004 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 dx.doi.org/10.1016/j.conbuildmat.2014.09.114 https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf https://www.iea.org/media/freepublications/technologyroadmaps/cementroadmapreferences.pdf dx.doi.org/10.2136/sssaj1971.03615995003500060041x 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dx.doi.org/10.5194/bg-11-237-2014 dx.doi.org/10.5194/bg-11-237-2014 dx.doi.org/10.5194/bg-11-237-2014 dx.doi.org/10.5194/bg-11-237-2014 dx.doi.org/10.5194/bg-11-237-2014 Rice straw ash: A potential pozzolanic supplementary material for cementing systems 1 Introduction 2 Materials and methods 3 Results and discussion 3.1 Microscopic studies on fresh leaves 3.2 Microscopic studies on dried leaves 3.3 Microscopies studies on calcined leaves 3.4 Microscopic studies on rice leaf sheath and rice stem ashes 3.5 Reactivity studies on rice straw ashes 4 Conclusions Acknowledgements References