Recycled Etna volcanic ash for cement, mortar and concrete manufacturing

Construction and Building Materials 151 (2017) 704–713

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Recycled Etna volcanic ash for cement, mortar and concrete manufacturing Loredana Contrafatto Department of Civil Engineering and Architecture, University of Catania, Italy

h i g h l i g h t s
Re-use as recycled aggregate of volcanic products from Mt. Etna eruptions.
Reduction of quarries exploitation, waste, disposal costs, landfill overloading.
Experimental tests on cement, mortar and concrete with partial replacement of sand.
Washed and not-washed recycled sand used to evaluate contaminants effect.
Mechanical strength and stiffness of mortar and concrete maintained.

a r t i c l e

i n f o

Article history: Received 3 May 2017 Received in revised form 19 June 2017 Accepted 20 June 2017

Keywords: Volcanic ash Pozzolans Recycled aggregates Mortar Concrete Cement Etna

a b s t r a c t The paper discusses the results of an original experimental research program focusing on the evaluation of the possible re-use of volcanic pyroclastic deposits on the public space generated by Mt. Etna eruptions. The possibilities of using the finer fraction of the recycled material as binder in partial replacement of cement and using the fine and coarse material as recycled aggregate in mortar and concrete production are investigated. The main mechanical properties of mortar and concrete with different percentage of substitution of the natural aggregates with recycled volcanic aggregates are determined. The results show that while the recycling of volcanic pyroclastic deposits as aggregates is feasible, their application in cement production is not practicable, due to poor pozzolanic behavior. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Mt. Etna (eastern Sicily, Italy) is one of the most active basaltic strato-volcanoes in the world, where both summit and flank eruptions take place. In the last decades, the increased frequency of eruptions and the changes in the characteristics of eruptions, for instance the combination of lava flow with explosive phases, have influenced significantly the territory of interest [1–7]. The explosive activity, that may last from a few weeks to several months, produces volcanic plume up to many kilometers high above sea level. Usually copious lapilli and ash fallout over the volcano flanks, disrupting transport systems, contaminating air and damaging buildings and infrastructures. Therefore, eruptions have a considerable effect on urban communities living close to the volcano and are potentially hazardous to human health. Clean-up

E-mail address: [email protected] http://dx.doi.org/10.1016/j.conbuildmat.2017.06.125 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

measures have to be constantly applied in the urban environment, first of all with regard to the road system and the public areas. The problem has been studied in a paper that reviews case studies of tephra clean-up operations in urban environments around the world, spanning 50 years [8]. The distribution of volcanic pyroclastic products depends on the initial particle size of the fragments, the height of the eruption column, the rate and duration of the eruption, the prevailing wind conditions, the slope and the roughness of the surface upon which the ash is deposited. In general, the thickness of deposit decreases exponentially with increasing distance from the volcano. Therefore, the residential areas and the public roads of the cities all around the volcano are repeatedly covered by ash and lapilli layers of different thickness, depending on the phenomenon. Virgin volcanic ashes are largely used; in fact there are several scientific studies focusing on volcanic ashes and their applications, especially the use of alternative materials as cement replacement. A certain number of studies is devoted to volcanic ash, used in

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

different percentage of cement substitution. Typically, volcanic ashes are pozzolanic materials because of their reaction with calcium hydroxide that is liberated during the hydration of cement. For this reason, they are suitable for blended cement production. Hossain et al. [9] conducted several tests on cement with a replacement of Portland cement within the range ½0  50%. Other experiences are reported by Pourkhorshidi et al.[10], Celik et al. [11], Kupwade-Patil et al. [12]. Applications vary in the field of mortar production [13], ceramic materials [14], geopolymers[15–18], soil stabilisation [19], lightweight concrete [20–22], high strength concrete [23,24]. Basaltic aggregates are traditionally used for road sub-base construction and concrete manufacturing in the Etna region [25]. The problem of reinforcement corrosion in volcanic ash based blended concrete is studied in [26], while in [27] the performance of volcanic ash blended cement concrete in mixed sulfate environment is treated. The study of durability performance of volcanic ashes concrete can also be found in [28]. The study of the constitutive behavior of composite materials from recycled aggregate has gained the interest of the scientific community both from the theoretical and the numerical point of view. For instance, in continuum mechanics, the response of these materials is frequently predicted by means of plastic–hardeningdamage-fracture Finite Elements numerical models [29–31] and through homogenisation techniques at meso-scale level accounting for the damaging behaviour of the components [32,32] or internal friction phenomena [33], also due to micro-particle addition [34]. Other numerical tools, based on elements with embedded discontinuities [35] can be also implemented. Volcanic ash is also used for the restoration of agro-ecosystems by addition to the soils of new nutrients derived from volcanic ashfall [36] and in polymer composites [37–39]. The abrasive behavior of composite materials obtained from volcanic ash combined with polymers and ceramics is investigated in [40]. The research presented in the paper was conducted thanks to the support of a ministerial agency and it was developed within the academic research program FIR2014. The main objective of this research was the reuse of the large amount of ash and lapilli that, when removed by the local government from the public spaces, have to be disposed of in landfill, with huge areas occupation and costs. They are classified as waste with code 200303 (Municipal waste) in the List of Wastes (LOW) Regulations, that transpose the European Waste Catalogue (EWC) into domestic legislation and provide codes for all hazardous and non–hazardous wastes. On March 2014, the waste code was temporarily modified in 17 05 04 (Soil and Rock – excavated), as a transitory and special measure in the territory involved in a significant eruption of volcano Etna, occurred on March 2013. The study was motivated by the absence of normative references regarding the reuse of this resource, in principle comparable to the natural one, and by the lack of information about its applications as cement replacement or recycled aggregates in mortar and concrete production. The opportunity of recycling would encourage, as it actually happened in March 2014, the permanent modification of the waste code, so that its re-use as recycled aggregate would be definitely authorised by the competent authority. The Italian standard NTC2008 (Norme Tecniche per le Costruzioni 2008) [41] allows the use of coarse recycled aggregate in the construction but limits the recycle of undifferentiated building demolition material to low strength concrete, while coarse recycled aggregates obtained from concrete and reinforced concrete demolition are permitted for structural purpose only at a maximum percentage of 30%. The use of other recycled materials and of fine particle size of recycled concrete aggregates is not discussed by the national legislation.

705

Three different possibilities for the re-use of Etna volcanic ash were investigated and primarily its suitability for blended cement production. Experimental tests were conducted on modified Portland cement, varying the cement replacement ratio. Some mechanical properties were analysed to evaluate the influence of the replacement on cement properties. Further investigations regarded the possible re-use in the manufacture of mortar and concrete, with partial replacement of the fine fraction of the natural aggregates with recycled lava sand. Only the aggregates with fine fractions lower than 0.5 mm was replaced. Since the recycled sand was derived from the volcanic waste obtained from the cleaning of urban public roads and spaces, the influence of the contaminants present in the waste on the mechanical properties of the products was investigated, by comparing the results obtained using both washed and not-washed recycled sand. The paper is organised as follows. The introduction presents the problem at hand and the motivation of the research. Section 2 focuses on the characterisation of the volcanic ash and the recycled volcanic sand. Section 3.1 focuses on the pozzolanic behaviour of the material. The results of the experimental program are discussed. Sections 3.2 and 3.3 provide a description of the mix design procedure, the characterisation of the designed mixtures and the setting of the experiments are given, respectively, for mortar and concrete with recycled Etna sand. Section 3.4 reports the results of the experiments performed and comments on the mechanical properties of mortar and concrete. The paper is completed with the conclusions.

2. Etna volcano pyroclasts The formation of the material is strictly connected to the eruptive event producing the ejection of volcanic ash, lapilli and bombs. Depending on the nature and magnitude of the phenomenon, pyroclastic particles may be carried by the wind for tens or hundreds of kilometers away from their origin, before reaching the ground. During the eruption of March 16th, volcanic bombs, characterized by a width greater than ten centimeters (see Fig. 1), fell over within a distance of 14 km from Etna’s New Southeast Crater. A great amount of volcanic ash covered the area of the East slope of Mount Etna, affecting private and public places. The roads and urban public spaces were cleaned using mechanical shovels and traditional street sweepers. As a consequence, the volcanic waste was contaminated by the presence of other elements, including paper, rubber, metals, mud and oils. Finally, the debris was collected in disposal areas. The material used in the experimental testing was taken from a heap of debris collected in Santa Venerina territory (Italy) and stored at the Laboratory of Material Testing at the University of Catania. The initial humidity was evaluated equal to 5.91%.

Fig. 1. Bomb found at the Santa Venerina territory (Italy) approximately 14 km from Etna’s New Southeast Crater on 16 March 2013.

706

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

Fig. 2. Procedures of grain size reduction. (a) Pestle and mortar reduction. (b) Roller reduction.

Table 1 Increment of the passing percentage after the grain size reduction process. Sieve

Passing [%]

d [mm]

H

PM

R

2 1 0.5

70.5 40 16.85

77 48 22

88.3 60.3 27.5

Table 2 Density of natural and reduced sand Passing

Density [kg/dm3]

d [mm]

H

PM

R

3 2 1 0.5

0.95 0.97 1.18 1.21

1.07 1.18 1.21 1.25

1.08 1.15 1.33 1.37

Volcanic lapilli and bombs are extremely porous and brittle, crumbling under very low pressure. A comparison of the percent passing three consecutive sieves is reported in Table 1 for three different samples. The first is constituted by the material taken from the heap (H). remaining two samples are constituted by crumbled material, obtained by means of two different procedures. The first was produced by pestle and mortar (PM), while the second one by means of a heavy roller (R), according to the standardised procedure, see Fig. 2. Table 1 shows how the size of the fine fraction of the material, under 2 mm, can be reduced with respect to its natural state, with an increment of the passing to sieve 2 mm and 1 mm in the order of 20% and of the passing the sieve 0.5 mm in the order of 10%. Successively, the material was subjected to further reduction procedures. However, no significant variation in the passing percentage was obtained, as confirmed by the increasing trend of the density (Table 2). Hence, procedure (R) was used in preparing the material for the experimental tests. 3. Experimental program Etna volcanic ash, both in its natural state and in the form of volcanic waste, has a peculiar siliceous nature different from other volcanic ash. A study on the effects of its recycling in the manufacture of traditional construction materials is necessary. An experimental campaign was carried out, where applications to cement, mortar and concrete manufacture were studied in terms of mechanical properties of the resulting material containing recycled Etna sand. The response of control samples with natural volcanic sand was used in each case as basis for comparison.

Testing results on the chemical composition of the ash are not included herein, since this was the subject of a parallel research program. Typically the products are K-trachybasalts with SiO2 (wt%) in the order of 40 and alkali (wt%) in the order of 5 [7]. However, the reader can find accurate information about the petrography and composition of lavas and pyroclast products of Mt. Etna in the specialised literature [5,42]. Since the volcanic waste derives from the cleaning of urban public roads and spaces, it can be contaminated by the presence of oils and other impurities that could influence the hydration process of the cement. After the grain size reduction of the volcanic waste, a sieve analysis was performed, using material dried in oven at 100 °C. Each fraction of the retained material at the different sieves was washed with distilled water in the volume ratio waste/water equal to 1:2. After sedimentation of the solid, the water, very cloudy at the first washing, was spilled and the procedure repeated until the water was clear. A mud suspension was observed floating on the water free surface. Ten washing steps were necessary to obtain an almost pure water of sedimentation, as it is shown in Fig. 3. The presence of oil, hydrocarbon or other substance in the waste was investigated performing concentration test of chemical substances in the ash washing water of the first step. The only significant result revealed 570 mg/l of SO4, exceeding the admissible value for the soils of 250 mg/l. The influence of the organic contaminants present in the waste was verified by comparing the experimental results using washed and not-washed recycled sand. The treatment and disposal of the washing water introduces additional and significant costs, hence a separate investigation is devoted to the evaluation of the cost-benefits analysis of the overall recycling process. The experimental testing was performed at the Laboratory of Material Testing at the University of Catania. A steel frame equipped with a 5 kN load cell, connected to an HBM UPM 60 data acquisition system was used for bending tests on cement and mortar samples. A CONTROLS system, composed by a 100 kN frame complete with pressure and strain transducer and connected to an Advantest 9 computerised control console, was used for uniaxial compression tests and Young modulus testing on cement and mortar samples and for bending tests on concrete samples. A CONTROLS system composed by the 50  C7600=FR 5000 kN compression four column frame, complete with pressure, strain and displacement transducers, was used for concrete uniaxial compression tests, both monotonic and cyclic, and Young modulus tests. The management softwares Data manager, E-module and Advantest 9 performed the remote control of the CONTROLS system. The study at the micro-scale of the effects of early and late age curing of hardened cement pastes prepared using volcanic ash as a

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

707

Fig. 3. Presence of mud suspension in the volcanic waste. Sedimentation in water. (a) Initial step. (b) Intermediate step. (c) Final step.

partial substitute to Portland cement requires Laser Light Scattering technique for the determination of the particle size distribution (specifically the mean, median, mole values of the volcanic ash) [12]. In the present study the experimental methodology was differently addressed and based on a macroscopic particle size distribution analysis, following the standard mechanical procedure of the sieve analysis. Classical techniques of mix design were used in the design of mixtures with recycled volcanic ash. Some experiments were performed to test the suitability of the material for blended cement production (see section 3.1). Following, a the possible re-use in the manufacturing of mortar and concrete, with partial replacement of the fine fraction of the natural aggregates with recycled lava sand was investigated (see Sections 3.2, 3.3). Washed and not-washed recycled sand was used. The acronyms listed below are introduced:









ENSPCP: Etna Natural Sand Portland Cement Paste ERSPCP: Etna Recycled Sand Portland Cement Paste ENSM: Etna Natural Sand Mortar ERSM: Etna Recycled Sand Mortar EWRSM: Etna Washed Recycled Sand Mortar ENSC: Etna Natural Sand Concrete ERSC: Etna Recycled Sand Concrete EWRSC: Etna Washed Recycled Sand Concrete

3.1. Cement experimental test. Results and discussion. It is well known that pozzolanic ash is commonly used in cement production. The European standard EN 197–1 classifies cement both according the class of strength and depending on the composition, establishing five classes from CEM I to CEM V. Inside class CEM II, four subclasses contain pozzolanic components, in varying percentage. Two subclasses contain natural pozzolans (CEM II/A-P, CEM II/B-P) while two subclasses contain calcined pozzolans (CEM II/A-Q, CEM II/B-Q). Pozzolanic properties of volcanic ash depend strongly on the chemical composition, that varies with varying volcanic site, deposit and content of reactive SiO2 . The process of generation makes pyroclastic ashes not pozzolanic, due to their glass content and low activity. Moreover, the pozzolanic activity is affected by the specific surface area, defects, and degree of crystallinity [43]. In [44] it is indicated that only pyroclastic rocks/ash that are acidic and possess high zeolitic contents demonstrate pozzolanic properties. Among the standards that can be followed to test the pozzolanic behaviour of the materials, the Italian Royal Decree n. 2230 of November 16, 1939 [45] and the more recent standard ASTM C 618 [46] were considered. Both standards require the fulfillment of physical and mechanical requirements. If the material fails one requirement it cannot be considered pozzolanic and it cannot be used in cement manufacture.

Therefore, it was decided to check preliminary the satisfaction of two mechanical requirements, i.e. the time of setting, according the Royal Decree n. 2230 and the Strength Activity Index (SAI), according ASTM C 618. 3.1.1. Time of setting The test method adopted was the one prescribed by the Italian Royal Decree n. 2230. In the first case, a sample of Etna recycled ash, passing the sieve 3 mm was dried in oven at 100 °C. A mix containing 25% of lime and 75% of recycled ash was prepared. The water content was such that a plastic consistency was obtained. Two cylindric samples of radius 100 mm and height 50 mm were prepared for testing the consistency and time of setting, using a standard Vicat apparatus. The test was repeated for 3 days and on the 7th day. The needle always totally penetrated the samples. Therefore, the test was considered unsuccessful, because normally the initials setting time of the ordinary Portland cement is 30 min and the final setting time is 10 h to 12 h, as confirmed by the control samples. At the same time, six prismatic samples 40  40  160 mm3 for three point bending test and six cubic samples of side 70 mm for uniaxial compression test were cast following standard procedures. The samples, removed from the moulds after 3 days, were immersed for cure in a saturated limewater solution. However, the dissolution of the samples took place immediately, revealing and confirming the absence of hardening of the paste. As it was observed by Hossain [47], that used the same Italian standard to test the pozzolanic activity of volcanic ash and pumice from volcano Mount Tavurvur (Papua, New Guinea) which were used as cement additives, the increase in setting time or lack of setting can also be due to fact that volcanic ash is much coarser than cement. The same consideration can be found in [48], where it has been shown that an increase in the particle size of the volcanic ash affects the early age hydration process in volcanic ash cements. The influence on the setting time of concrete with partial substitution of cement with pumice is also documented in [49], while a wide literature on cement replacement materials can also be found in [50]. Because a granular consistency of the paste and a very low cohesion was qualitatively observed during the preparation of the samples described above, the tests were repeated using a second set of samples prepared by using finer sand, passing sieve 0.5 mm. The results were identical and the absence of hardening of the paste was attributed to the vitreous nature of the pyroclastic ash, rather than the grain size, and to the presence of un-reacted volcanic ash, even after 7 days of curing. 3.1.2. Strength Activity Index The tests performed according t. the Italian standard were totally negative, The Strength Activity Index (SAI) was evaluated, following the specifications of ASTM C618. Cement CEM II/B-LL 32.5 R was used, that complies with the chemical properties pre scribed by EN 196/2 [51,52] (SO3 6 3:5%, Cl 6 0:1%) and EN

708

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

196/10 (CrVI 6 2 ppm). A control mix ENSPCP and a test mix ERSPCP were designed. Cubic samples of side 50 mm were prepared for each mixture following ASTM C109/C109M standard [53]. The test methods were based on standard ASTM C311/ C311M [54]. The proportions of materials for mixture ENSPCP were one part of cement to 2.75 parts of graded natural sand by weight and the water-cement ratio was 0.485. In the case of mixture ERSPCP the 20% of cement was replaced by recycled sand passing sieve 45 lm. The amount of mixing water was such that the same fluidity of the control mix was obtained and equal to 0.7. The specimens were removed from the molds after 72 h and immersed in saturated lime water at the constant temperature of 22 °C. The SAI, given as a percent of the compressive strength of the specimens prepared with the control mix ENSPCP, was 33.3% as against the threshold value of 75%, largely exceeded. Further tests designed to investigate the chemical properties would explain the mechanical deficiency of the material, following for instance the procedure given in [55], where the authors investigate the possibility of using volcanic powders as supplementary cementitious materials. Several volcanic rocks are considered (basalt, olivine andesite, amphibole-biotite andesite, amphibole andesite, hyodacite and scoria), all derived from volcanic deposits, not from eruptive processes.

Table 3 Dosage per dm3 for the preparation of the ENSM, ERSM and EWRSM samples with 0% and 100% replacement of the sand passing 0.5 mm sieve.

Sand [g] Cement [g] Water [g] a=c s=c

ENSM

ERSM/EWRSM

2639 879 440 0.5 3

2636 977 488 0.5 2.7

Table 4 Sand grain assortment.

Sieve d [mm]

ENRM 2639 [g] Retained [g]

ERSM 2636 [g] Retained [g]

2 1 0.5

0 908 641

0 907 641

NS

RS

0.420 0.250 0.125 0.105 0.074 0.001

129 325 319 66 114 137

129 324 319 66 113 137

3.2. Mortar mix design and experimental test 3.2.1. Mix-design According to EN 196-1, for cement mortar the content of the components to cast two prismatic samples 40  40  160 mm3 is cement c ¼ 450 g, sand s ¼ 1350 g, water w ¼ 225 g, to obtain a water/cement ratio is w=c ¼ 0:5 and the sand/cement ratio in weight is s=c ¼ 3. However, in the mix-design of ENSM and ERSM a constant volume ratio sv =cv ¼ 3 was fixed. The density of Natural Sand (NS) and Recycled Sand (RS) was measured and a little difference was observed, being qNS ¼ 1:88 kg/l and qRS ¼ 1:75 kg/l. Therefore, to obtain the constant volume ratio sv =cv ¼ 3 for both mixtures, in the case of RS a sand/cement ratio in weight equal to 2.7 was considered. A commercial Portland-limestone blended cement type CEM II/ B-LL 32.5 R according to EN-197/1 [56] was used. The reference ENSM mortar was prepared with natural volcanic sand. The ERSM mortar was prepared substituting 100% of sand passing to sieve 0.5 mm with recycled volcanic sand of same grain size. The sand assortment was generated according to a Bolomey grading curve:

pi ¼

 12 i A þ ð100  AÞ Ddmax C 100  C

100

ð1Þ

where pi is the percent passing the ith sieve, di is the opening size of ith sieve, Dmax is the maximum aggregate particle size and A is a parameter that accounts for the particle shape of the aggregate and the consistency. In the present case Dmax ¼ 2 mm, following EN 196-1, and A ¼ 12, for a plastic-semifluid consistency and c crashed aggregates. C ¼ cþs 100 ¼ 25 is the quantity of cement with respect to all of the solids c þ s. 3.2.2. Samples preparation For ENSM, ERSM and EWRSM nine prismatic samples 40  40  160 mm3 were cast following standard procedures. The dosage of the components per dm3 of mortar is given in Table 3 and the grain assortment in Table 4. The samples were removed from the moulds after 24 h and cured at a constant temperature of 22 °C under water until strength testing.

3.2.3. Experimental tests Only the mechanical properties of hardened mortar were evaluated. The following tests were carried for ENSM, ERSM and EWRSM: - Three point bending test, according to EN 196-1; - Uniaxial compression test, according to EN 196-1; - Elastic modulus, according to EN 6556. Three point bending tests were carried out on the prismatic samples, applying a linear ramp at rate of loading of 50 N/s until the specimen breaks. Compression tests were successively performed on the cubes obtained from the resulting half prisms after the breakage. Flexural and compressive strength were measured at 28 and 60 days of cure. The elastic modulus at 28 days of cure was also determined, performing axial tests, analogous to concrete tests, on prismatic samples with width/heigth ratio 1:2, obtained by cutting in half three of the prisms per type, as shown in Fig. 4b. 3.3. Concrete mix design and experimental test 3.3.1. Mix-design Two mixtures containing Etna recycled sand were designed. Only the sand fraction with maximum grain size lower than 0.5 mm was replaced with recycled not-washed and washed sand, to a ratio of, 50% (ERSC-50, EWRSC-50) and 100% (ERSC-100, EWRSC-100) respectively. The concrete mix-design was aimed to have optimal proportions to resist segregation, avoid over-cohesion and yield a low water demand. In the present context the method was applied neglecting durability requirements. The mix design was performed according to the Bolomey ideal grading curve, introduced previously in section 3.2. A Portland cement CEM II/B-LL 32.5 R was selected, as defined by EN 196-1 [56]. Crushed natural basalt aggregates were used, with a maximum diameter size of 25 mm. Following Lyse’s Rule and neglecting the dependence from additives, the quantity of water necessary for the consistency class S3 (semi-fluid) of fresh concrete was found to be 210 kg/m3, where additional 10 kg/m3

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

709

Fig. 4. (a) Compression test. (b) E modulus test.

Table 5 Materials weight per unit volume.

m [kg/lt]

Water

Cement

Aggr.

Gravel

NS

RS-50

RS-100

1.0

3.1

2.66

2.69

2.60

2.59

2.58

Table 6 Mix-design per dm3 of concrete.

Gravel [g] Sand [g] Cement [g] a/c Water [g]

CLS-0%

CLS-50%

CLS-100%

1051 646 382 0.55 210

1051 644 382 0.55 210

1051 641 382 0.55 210

were added due to the sharp nature of the aggregate shape. The cement content was calculated in order to reach a compressive strength of the control mixture of 35 MPa at 28 days. Therefore, the water/cement ratio w=c was equal to 0.55 and the cement content was equal to 381.8 kg/m3. The last step in the project of the mixture was the calculation of the aggregates quantity, obtained balancing the total volume of the mixture V and the volume of water V w , cement V c and entrained air V a :

V aggr ¼ V  V w  V c  V a

ð2Þ

In formula 2 V ¼ 1000 l=m3 ; V a represents the volume in liters per m3 of the entrained air, estimated equal to 17 l/m3. Introducing the weights per unit volume of each component reported in Table 5, the volume of aggregates in the mixture was found equal to V aggr ¼ 649:83 l/m3. Table 5 reports the weights per unit volume of gravel and sand, both natural (NS) and recycled (RS-50, RS100), considered under Saturated Surface-Dry (SSD) conditions, according to EN 1097–6. The resulting aggregate volume V aggr is given by the sum of the gravel and sand contents V g and V s . A particle size analysis was performed in order to calculate the quantity of gravel and sand necessary to obtain the particle size distribution of reference, minimising the inter-granular voids. Eq. 1 with Dmax ¼ 2 mm and A ¼ 12, for a plastic-semifluid consistency of concrete and crashed aggregates, was used, referred to the total amount of aggregates. C ¼ cþV aggrc maggr 100 ¼ 18:1 is the quantity of cement with respect to all of the solids. In the calculation of the aggregates assortment, the water absorption was considered, equal to 1% for gravel, 3% for NS, RS50 and RS-100. Tables 6 and 7 reports the mix-design and the related grain assortment, respectively, per dm3 of concrete.

3.3.2. Samples preparation For ENSC and ERSC-50/ERSC-100 mixtures eight cubic samples of side 100 mm and four cylinders per type of diameter d ¼ 100 mm and height h ¼ 200 mm were cast following standard procedures. The samples were removed from the moulds after 24 h and cured at a constant temperature of 22  C under water until strength testing. 3.3.3. Experimental tests Only the mechanical properties of hardened concrete were evaluated. Uniaxial compression tests under load control were performed after 28 days on four cubic specimens per type of mixture. The loading direction was perpendicular to the direction of casting. Moreover four cylinders per type were tested to evaluate the Young modulus, in the case of mixtures with washed sand. Additional tests were carried out for the determination of the strength and stiffness degradation. Specifically, four displacement controlled uniaxial tests were performed, only for type EWRSC, on cubic samples: two monotonic tests and two tests following a cyclic loading time history. A velocity of 2 lm/s was used. The unloading was instead performed under load control, with a rate of 0.2 N/s, in order to reach the prescribed residual stress of 6 MPa. The cyclic tests were stopped when a residual strength of about 3  5 MPa was reached. Fig. 5 shows the testing apparatus and the crack pattern at failure. 3.4. Mortar & concrete – results and discussion 3.4.1. Mechanical properties of ENSM, ERSM and EWRSM Table 8 reports the flexural and compressive strength at the age of cure of 28 and 60 days for mixtures ENSM, ERSM and EWRSM. The figures within brackets correspond to the the standard deviation of the measurements. The data show how EWRSM undergoes a reduction in flexural strength in the order of 0.6% at 28 days of cure and 7.6% at 60 days. The compressive strength of EWRSM presents an increment of 1.7% at 28 days and 13% at 60 days. However, this result is influenced by the reduction of the compressive strength of ENSM, equal to Rcm ¼ 30:56 MPa, with respect to the design characteristic compressive strength, i.e. Rck = 32.5 MPa. The decrease was due to the supplemental water required in the mixing process of ENSM to ensure workability, probably for an erroneous initial wetting of the natural aggregate, that was not in Saturated Surface-Dry condition. The water cement ratio raised to w=c ¼ 0:62. Compared to the design value of the strength, mortar EWRSM shows a reduction in compressive strength in the order of 4.3% at 28 days of cure. The elasticity modulus was determined at 28 days of cure. The results in Table 8 show a mean value of 18797 MPa for EWRSM, with a decrement of 3.4% w.r.t ENSM.

710

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

Table 7 Grain assortment of aggregates per dm3 of concrete.

Sieve d [mm]

ENRC Retained [g]

25 20 15 10 4.76 2 1 0.5

0.0 119.3 135.2 160.5 636.0 244.3 131.8 92.7

0.420 0.250 0.125 0.105 0.074 0.001

EWRSC-50 Retained [g]

EWRSC-100 Retained [g]

0.0 119.3 135.2 160.5 636.0 243.0 131.4 92.8

0.0 119.3 135.2 160.5 636.0 242.5 130.5 92.8

NS

NS

RS

RS

19.2 47.1 46.5 9.4 16.5 38.4

9.3 23.5 23.2 4.7 8.2 19.0

9.3 23.5 23.2 4.7 8.2 19.0

18.6 46.7 46.3 9.2 16.3 37.8

Fig. 5. Experimental uniaxial compression test. Displacement control. (a) Testing apparatus. (b) Crack pattern.

Table 8 Flexural strength, compressive strength and elasticity modulus of ENSM, ERSM and EWRSM samples. The figures in parentheses correspond to the standard deviation of the measurements. Rfm

DRfm

Rcm

DRcm

Em

DEm

Type

Age [days]

[MPa]

[%]

[MPa]

[%]

[MPa]

[%]

ENSM

28 60

6.78 (0.95) 6.84 (0.42)

0 0

30.56 (1.78) 30.94 (2.72)

0 0

19469 (653) –

0 –

ERSM

28 60

5.69 (0.27) 5.73 (0.31)

16.2 16.2

29.83 (1.61) 30.21 (0.66)

2.4 2.3

– –

– –

EWRSM

28 60

6.74 (0.42) 6.32 (0.36)

0.6 7.6

31.09 (3.02) 35.12 (1.77)

+1.7 +13.5

17123 (466) –

3.4 –

Sample

In the case of ERSM a more important decay w.r.t. EWRSM of the mechanical properties is present, equal to 16% for the flexural strength. The decrement in the compressive strength, compared to the design value of the ENSM, is 8.2% at 28 days of cure and 7% at 60 days. While the compressive strength increase with the days of cure, the flexural one shows a drop, that should be verified with a more extensive experimentation. 3.4.2. Mechanical properties of ENSC, ERSC and EWRSC The uniaxial compressive strength at 28 days of cure is reported in Table 9, for mixtures ENSC, ERSC and EWRSC. The table also reports the value of the elasticity modulus. All mixtures were designed for concrete class 35 MPa. Therefore, both the mixtures EWRSC-50, EWRSC-100 containing washed recycled sand satisfy the requirement of the class. Note that EWRSC-50 presents an increment of 8.5% in the compressive strength and of 5% in the Young modulus w.r.t. the control

concrete ENSC. It seems that for the lower percentage of replacement of the washed sand (50%) a benefic effect appears. On the contrary, when the replacement is 100% the strength and the elasticity modulus show a slight decrease with respect to the reference values. This result should be further investigated, given the lack of reactivity of the volcanic sand. In any case, the results of EWRSC-50 and EWRSC-100 are in the variability range of the results of ENSC, so that it can be concluded that the recycled sand obtained from Etna pyroclasts grinding can be favorably used in concrete. A drastic reduction in the strength is observed in the case of ERSC, greater than 50% in both ERSC mixtures. The negative influence of the organic components in the not-washed sand is once more confirmed. The results of the displacement controlled tests are reported in Figs. 6a and 6b for the uniaxial monotonic and cyclic loading, respectively. The secant modulus of the unloading branches (that represents a measure of the damaged elastic modulus) is plotted in Fig. 6c against the maximum deformation reached before

711

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713 Table 9 Compressive strength and elasticity modulus of ENSC, ERSC and EWRSC samples. The figures in parentheses correspond to the standard deviation of the measurements. Sample

Rcm

Type

Age [days]

[MPa]

ENSC ERSC-50 EWRSC-50 ERSC-100 EWRSC-100

28 28 28 28 28

37.36 16.40 40.55 16.52 36.71

(3.08) (0.38) (0.96) (0.56) (0.19)

DRcm

Em

DEm

[%]

[MPa]

[%]

0 56.1 +8.5 55.8 1.7

19830 (1219) – 20834 (1249) – 18656 (682)

0 – +5 – 5.9

Fig. 6. Experimental uniaxial cyclic compression test. Displacement control. (a) Monotonic tests. (B) Cyclic tests. (C) Degradation of the secant modulus.

unloading. The degradation of the secant elastic modulus during unloading can be observed. The limit value of the modulus in the origin yields the initial Young modulus of the material, that was found to be about 32.5 GPa. It is evident that the presence of the recycled sand in the mixture neither affects the concrete tangent stiffness, nor the secant stiffness on the unloading. Moreover, the peak strength is comparable. 3.4.3. Remarks The fresh properties of mortar and concrete were not determined, since it was observed that the consistency and then the workability of the mixtures were all qualitatively comparable to the corresponding control ones. No need of additional water was observed for the mixtures with recycled sand, so that the design water/cemet ratio w=c was preserved. The increased water demand that usually occurs when recycled aggregates are used was not observed. The reason possibly lies in the fact that only the fine fraction of the aggregate was replaced. As it can be seen from the data in Table 5 concerning the unit volume weight of natural and recycled sand with grain size lower than 0.5 mm, no significant difference exists, being the values 2.60, 2.59, 2.58 for NS, RS-50,RS-100 respectively. As it was anticipated, the usage of the recycled material at this scale of the assortment does not introduce important modifications in the macroscopic mechanical response of the materials. Similar conclusions can be drawn on the influence of the recycled aggregates on the setting time. What actually affects the results is the presence of not-washed sand, as clearly evident from the comparison of the compressive strength of concrete samples (Table 9). 4. Conclusions The paper reports experimental results on the possible re-use of the large amount of pyroclasts produced by the eruptions of Mt.

Etna, that when removed by the local government from the public spaces, have to be disposed, occupying huge areas and resulting to high costs. The novelty of the research lies on the discovery that recycled volcanic sand obtained from the cleaning process of the public areas can be successfully re-used in mortar and concrete manufacture after some washing takes place. This is because the mechanical properties of the composites remain substantially unchanged with respect to the case in which virgin material, derived from quarry rocks, is used. Only the finer fraction of sand, passing 0.5 mm sieve, has been considered both for mortar and concrete, because the higher fractions are extremely porous and brittle. In the case of Etna Recycled Sand Mortar a decay w.r.t. Etna Washed Recycled Sand Mortar of the mechanical properties is present both in the flexural strength and the compressive one. The use of washed sand, on the contrary, ensures good mechanical performance, with reductions in strength and initial stiffness of the order of 3  4%. In concrete, the mixtures containing washed recycled sand satisfy always the class requirement, both for ERSM-50 and ERSM-100, with sand replacement equal to 50% and 100% respectively. Furthermore, the ductility of the material is preserved. A drastic reduction in the strength is registered, on the contrary, in the case of Etna Recycled Sand Concrete, equal to 56% in both ERSC mixtures, due to the presence of organic contaminants in the unwashed sand. The few experiments conducted for testing the pozzolanic behavior of the sand, whose vitreous nature is well known, immediately confirmed the scarce characteristic to be employed in cement production, as demonstrated by the mechanical test concerning the time of setting, according to the Italian Royal Decree n. 2230 and the Strength Activity Index (SAI), according to ASTM C 618. The reason lies in the process of formation of the sand, obtained from pyroclasts produced by the explosive activity of the volcano and lacking of sufficient reactive SiO2 . Different findings exist in the literature related to cement industry, concerning the case of volcanic ash, sometimes from different

712

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713

geographical origin, that is derived from deep volcanic deposits and presents high reactivity. Given that Etna pyroclasts, when finely reduced in size, can be used without significatively affecting the mechanical properties of mortar and concrete with the compositions described herein, a deeper analysis concerning some aspects such as the spectrographic analysis of the volcanic ash, the influence of the recycled aggregate on the chemical reactions in cement paste, mortar and concrete and on the time of setting, the alkali-silica activity has to be developed. However, this is part of current and future research work. The preliminary results reported in the paper require further studying and show the way for a government revision of the current legislation, that to date classifies the material as waste. Funding The results reported in this article were obtained from the research work conducted within the framework of the academic research program FIR2014, project ‘‘Evaluation of Alternative ‘‘End-of-Waste”, in the fields of Civil and Environmental Engineering, of Volcanic Ash from Mt. Etna - VALICA-ETNA”, with the financial support of the University of Catania. Moreover, the experimental equipment has been partially financed within the framework of the PO FESR SICILIA 2007–2013, Axis IV, Target 4.1.2, Interventation strategy 4.1.2.A, Project MedNETNA. Acknowledgements The author Gratefully acknowledges S. Gazzo, G. Corazzato, E. Pappalardo and S. Maurici, for their helpful assistance during the experimental investigation at the Laboratory of Material Testing of Catania University. References [1] R.A. Corsaro, M. Pompilio, Magma dynamics in the shallow plumbing system of Mt. Etna as recorded by compositional variations in volcanics of recent summit activity (1995–1999), J. Volcanol. Geoth. Res. 137 (2004) 55–71. [2] S. Scollo, P. Del Carlo, M. Coltelli, Tephra fallout of 2001 Etna flank eruption: analysis of the deposit and plume dispersion, J. Volcanol. Geoth. Res. 160 (2007) 147–164. [3] R.A. Corsaro, L. Civetta, L. Di Renzo, Petrology of lavas from the 2004–2005 flank eruption of Mt. Etna, Italy: inferences on the dynamics of magma in the shallow plumbing system, Bull. Volcanol. 71 (2009) 781–793. [4] D. Andronico, R.A. Corsaro, Lava fountains during the episodic eruption of South-East Crater (Mt. Etna), 2000: insights into magma-gas dynamics within the shallow volcano plumbing system, Bull. Volcanol. 73 (2011) 1165–1178. [5] R.A. Corsaro, V. Di Renzo, S. Distefano, L. Miraglia, L. Civetta, Relationship between petrologic processes in the plumbing system of Mt. Etna and the dynamics of the eastern flank from 1995 to 2005, J. Volcanol. Geoth. Res. 251 (2013) 75–89. [6] B. Behncke, S. Branca, R.A. Corsaro, E. De Beni, L. Miraglia, C. Proietti, The 2011– 2012 summit activity of Mount Etna: birth, growth and products of the new SE crater, J. Volcanol. Geoth. Res. 270 (2014) 10–21. [7] R.A. Corsaro, L. Miraglia, The transition from summit to flank activity at Mt. Etna, Sicily (Italy): Inferences from the petrology of products erupted in 2007– 2009, J. Volcanol. Geoth. Res. 275 (2014) 51–60. [8] L. Hayes, T.M. Wilson, C. Magill, Tephra fall clean-up in urban environments, J. Volcanol. Geoth. Res. 304 (2015) 359–377. [9] K.M.A. Hossain, Blended cement using volcanic ash and pumice, Cem. Concr. Res. 33 (2003) 1601–1605. [10] A. Pourkhorshidi, M. Najimi, T. Parhizkar, F. Jafarpour, B. Hillemeier, Applicability of the standard specifications of astm c618 for evaluation of natural pozzolans, Cem. Concr. Compos. 32 (2010) 794–800. [11] K. Celik, M. Jackson, M. Mancio, C. Meral, A.H. Emwas, P. Mehta, et al., Highvolume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete, Cem. Concr. Compos. 45 (2014) 136–147. [12] K. Kupwade-Patil, A.F. Al-Aibani, M.F. Abdulsalam, C. Maoa, A. Bumajdad, S.D. Palkovic, et al., Microstructure of cement paste with natural pozzolanic volcanic ash and portland cement at different stages of curing, Constr. Build. Mater. 113 (2016) 423–441. [13] K.M.A. Hossain, M. Lachemi, Corrosion resistance and chloride diffusivity of volcanic ash blended cement mortar, Cem. Concr. Res. 34 (2004) 695–702.

[14] J. Vite, M. Vite, M. Castillo, J.R. Laguna-Camacho, J. Soto, O. Susarrey, Erosive wear on ceramic materials obtained from solid residuals and volcanic ashes, Tribol. Int. 43 (2010) 1943–1950. [15] P.N. Lemougna, K. MacKenzie, U. Chinje Melo, Synthesis and thermal properties of inorganic polymers (geopolymers) for structural and refractory applications from volcanic ash, Ceram. Int. 37 (2011) 3011–3018. [16] H. Tchakoute, A. Elimbi, J. Mbey, C. Ngally Sabouang, D. Njopwouo, The effect of adding alumina-oxide to metakaolin and volcanic ash on geopolymer products: a comparative study, Constr. Build. Mater. 35 (2012) 960–969. [17] H. Tchakoute, A. Elimbi, E. Yanne, C. Djangang, Utilization of volcanic ashes for the production of geopolymers cured at ambient temperature, Cem. Concr. Compos. 38 (2013) 75–81. [18] H. Takedan, S. Hashimoto, H. Kanie, S. Honda, Y. Iwamoto, Fabrication and characterization of hardened bodies from japanese volcanic ash using geopolymerization, Ceram. Int. 40 (2014) 4071–4076. [19] K.M.A. Hossain, L. Mol, Some engineering properties of stabilized clayey soils incorporating natural pozzolans and industrial wastes, Constr. Build. Mater. 25 (2011) 3495–3501. [20] S. Demirdag, L. Gunduz, Strength properties of volcanic slag aggregate lightweight concrete for high performance masonry units, Constr. Build. Mater. 22 (2008) 135–142. [21] S. Demirdag, I. Ugur, S. Sarac, The effects of cement/fly ash ratios on the volcanic slag aggregate lightweight concrete masonry unitss, Constr. Build. Mater. 22 (2008) 1730–1735. [22] K.M.A. Hossain, Properties of volcanic pumice based cement and lightweight concrete, Cem. Concr. Res. 34 (2004) 283–291. [23] K.M.A. Hossain, High strength blended cement concrete incorporating volcanic ash: performance at high temperatures, Cem. Concr. Res. 28 (2006) 535–545. [24] K.M.A. Hossain, M. Lachemi, Strength, durability and micro-structural aspects of high performance volcanic ash concrete, Cem. Concr. Res. 37 (2007) 759– 766. [25] G. Pappalardo, R. Punturo, S. Mineo, L. Contrafatto, The role of porosity on the engineering geological properties of 1669 lavas from Mount Etna, Eng. Geol. 221 (2017) 16–28, http://dx.doi.org/10.1016/j.enggeo.2017.02.020. [26] K.M.A. Hossain, Chloride induced corrosion of reinforcement in volcanic ash and pumice based blended concrete, Cem. Concr. Compos. 27 (2005) 381–390. [27] K.M.A. Hossain, M. Lachemi, Performance of volcanic ash and pumice based blended cement concrete in mixed sulfate environment, Cem. Concr. Res. 36 (2006) 1123–1133. [28] M.S. Meddah, Durability performance and engineering properties of shale and volcanic ashes concretes, Constr. Build. Mater. 79 (2015) 73–82. [29] L. Contrafatto, M. Cuomo, A framework of elastic-plastic damaging model for concrete under multiaxial stress states, Int. J. Plast. 22 (12) (2006) 2273–2300. [30] L. Contrafatto, M. Cuomo, Comparison of two forms of strain decomposition in an elastic-plastic damaging model for concrete, Model. Simul. Mater. Sci. Eng. 15 (2007) S405–S423. [31] L. Contrafatto, G. Ventura, Numerical analysis of augmented lagrangian algorithms in complementary elastoplasticity, Int. J. Numer. Methods Eng. 60 (14) (2004) 2263–2287, http://dx.doi.org/10.1002/nme.1042. [32] L. Contrafatto, M. Cuomo, S. Gazzo, A concrete homogenisation technique at meso-scale level accounting for damaging behaviour of cement paste and aggregates, Comput. Struct. 173 (2016) 1–18. [33] D. Scerrato, I. Giorgio, A. Della Corte, A. Madeo, A. Limam, A micro-structural model for dissipation phenomena in the concrete, Int. J. Numer. Anal. Methods Geomech. 39 (18) (2016) 1953–2052. [34] D. Scerrato, I. Giorgio, A. Della Corte, A. Madeo, N. Dowling, F. Darve, Towards the design of an enriched concrete with enhanced dissipation performances, Cem. Concr. Res. 84 (2016) 48–61. [35] L. Contrafatto, M. Cuomo, G. Di Venti, Finite elements with non homogeneous embedded discontinuities. In: ECCOMAS 2012–6th European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers. 2012, pp. 9152–9171. [36] M. Anda, Suparto, Sukarman, Characteristics of pristine volcanic materials: beneficial and harmful effects and their management for restoration of agroecosystem, Sci. Total Environ. 543 (2016) 480–492. [37] E. Avcu, O. Çoban, M.O. Bora, S. Fidan, T. Słnmazçelik, O. Ersoy, Possible use of volcanic ash as a filler in polyphenylene sulfide composites: thermal, mechanical, and erosive wear properties, Polym. Compos. 35 (2014) 1141– 1144, http://dx.doi.org/10.1002/pc.22847. Wiley Online Library. [38] E. Kamseu, Z.N.M. NGouloure, B. Nait-Ali, S. Zekeng, U.C. Melo, S. Rossignol, et al., Cumulative pore volume, pore size distribution and phasespercolation in porous inorganic polymer composites:relation microstructure and effective thermal conductivity, Energy Build. 35 (2015) 45–56. [39] J. Djobo, A. Elimbi, H.K. Tchakoute, S. Kumar, Mechanical properties and durability of volcanic ash based geopolymer mortars, Constr. Build. Mater. 124 (2016) 606–614. [40] J. Vite-Torres, M. Vite-Torres, J.R. Laguna-Camachoc, J.E. Escalante-Martínez, E. A. Gallardo-Hernández, E.E. Vera-Cardenas, Wet abrasive behavior of composite material sobtained from solid residuals mixed with polymer and ceramic matrix, Ceram. Int. 40 (2014) 9345–9353. [41] Norme Tecniche per le Costruzioni D.M. 14 Gennaio 2008. Ministero delle Infrastrutture, 2008. [42] G. Barone, P. Mazzoleni, R. Corsaro, P. Costagliola, F. Di Benedetto, E. Ciliberto, et al. Nanoscale surface modification of Mt. Etna volcanic ashes. Geochimica et Cosmochimica Acta 2014 6;174:70–84.

L. Contrafatto / Construction and Building Materials 151 (2017) 704–713 [43] P. Mehta, Studies on blended portland cements containing santorin earth, Cem. Concr. Res. 11 (4) (1981) 507–518. [44] K. Kupwade-Patil, A.F. Al-Aibani, M.F. Abdulsalam, C. Mao, A. Bumajdad, S.D. Palkovic, et al., Microstructure of cement paste with natural pozzolanic volcanic ash and portland cement at different stages of curing, Constr. Build. Mater. 113 (2016) 423–441. [45] Italian Chemical Society, Symp. on pozzolans and their use, J. Volcanol. Geoth. Res. 44 (1954) 569–768. [46] ASTM C618, Standard specification for coal fly ash and raw or calcined natural pozzolan for use in concrete. American society for testing and materials. 2015. [47] Khandaker M. Anwar Hossain, Volcanic ash and pumice as cement additives: pozzolanic, alkali-silica reaction and autoclave expansion characteristics, Cem. Concr. Res. 35 (2005) 1141–1144. [48] K. Kupwade-Patil, M. Tyagi, C.M. Brown, O. Büyüköztürk, Water dynamics in cement paste at early age prepared with pozzolanic volcanic ash and ordinary portland cement using quasielastic neutron scattering, Cem. Concr. Res. 86 (2016) 55–62. [49] A. Aydin, R. Gul, Influence of volcanic originated natural materials as additives on the setting time and some mechanical properties of concrete, Constr. Build. Mater. 21 (2007) 1277–1281.

713

[50] A.A. Ramezanianpour, Cement replacement materials: properties, durability, sustainability, Springer, 2013. [51] EN 196-2:2013, Method of testing cement – Part 2: chemical analysis of cement. European Committee for Standardization, 2013. [52] EN 196-10:2016, Methods of testing cement. – part 10: determination of the water-soluble chromium (vi) content of cement. European Committee for Standardization, 2016. [53] ASTM C109/C109M, Standard test method for compressive strength of hydraulic cement mortars. American society for testing and materials, 2016. [54] ASTM C311/C311M, Standard test methods for sampling and testing fly ash or natural pozzolans for use in portland-cement concrete. American society for testing and materials, 2016. [55] Y. Labbacy, Y. Abdelaziz, A. Mekkaoui, A. Alouani, B. Labbaci, The use of the volcanic powders as supplementary cementitious materials for environmental-friendly durable concrete, Constr. Build. Mater. 133 (2017) 468–481. [56] EN 196-1:2016, Methods of testing cement - part 1: Determination of strength. European Committee for Standardization 2016;.