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Materials 2022, 15, 6305. https://doi.org/10.3390/ma15186305 www.mdpi.com/journal/materials
Article
Effect of Processed Volcanic Ash as Active Mineral Addition for
Cement Manufacture
Julia Rosales, Manuel Rosales, José Luis Díaz-López, Francisco Agrela * and Manuel Cabrera
Area of Construction Engineering, University of Cordoba, 14014 Cordoba, Spain
* Correspondence: fagrela@uco.es; Tel.: 957212239
Abstract: In the last quarter of 2021, there was a very significant eruption of the Cumbre Vieja
volcano on the island of La Palma, belonging to the Canary Islands, Spain. It generated a large
amount of pyroclastic volcanic materials, which must be studied for their possible applicability.
This work studies the properties and applicability of the lava and volcanic ash generated in this
process. The need for reconstruction of the areas of the island that suffered from this environmental
catastrophe is considered in this study from the point of view of the valuation of the waste gener-
ated. For this purpose, the possibility of using the fine fraction of ashes and lava as a supplemen-
tary cement material (SCM) in the manufacture of cement is investigated. The volcanic material
showed a chemical composition and atomic structure suitable for replacing clinker in the manu-
facture of Portland cement. In this study, the cementing and pozzolanic reaction characteristics of
unprocessed volcanic materials and those processed by crushing procedures are analysed. To
evaluate the cementitious potential by analysing the mechanical behaviour, a comparison with
other types of mineral additions (fly ash, silica fume, and limestone filler) commonly used in ce-
ment manufacture or previously studied was carried out. The results of this study show that vol-
canic materials are feasible to be used in the manufacture of cement, with up to a 22% increase in
pozzolanicity from 28 to 90 days, showing the high potential as a long-term supplementary ce-
mentitious material in cement manufacturing, though it is necessary to carry out crushing pro-
cesses that improve their pozzolanic behaviour.
Keywords: volcanic ash; cement; pozzolanic behaviour; chemical composition; mechanical be-
haviour
1. Introduction
After 50 years of quiescence in La Palma Island (Canary Islands, Spain), the Cumbre
Vieja volcano—historically the most active volcano in the Canary Islands—began an
eruptive episode on 19 September 2021, forcing the evacuation of 7000 residents, de-
stroying infrastructure worth more than EUR 400 m, and affecting 1.212 hectares and 92.7
km of roads with solidified lava and ash [1]. All this volcanic solidified lava and ash,
together with growing environmental awareness and a circular economy, considering
that the construction industry is perceived as a major contributor to environmental deg-
radation [2] that consumes 40% of the raw materials extracted [3], makes the study of
lava and ash for its application in building materials very interesting. These materials,
formed from the cooling of magma from the volcanic eruption, are known as pyroclastic
materials and have very heterogeneous physical properties, varying in particle size from
microns (ash) to metres (solidified lava) [4], and can have a dense or vesicular structure
[5,6].
Dingwell et al. [7] differentiated typical volcanic ashes as pyroclastic debris no
larger than 2 mm, however, many authors carry out crushing and sieving procedures for
the utilization of volcanic ash [8–12]. Lemougna et al. [10] ground volcanic ashes to pass a
400 μm sieve; Leonelli et al. [11] dry-milled the analysed volcanic ashes to a fineness of
Citation: Rosales, J.; Rosales, M.;
Díaz-López, J.L.; Agrela, F.; Cabrera,
M. Effect of Processed Volcanic Ash
as Active Mineral Addition for
Cement Manufacture. Materials 2022,
15, 6305. https://doi.org/10.3390/
ma15186305
Academic Editor: Lizhi Sun
Received: 31 July 2022
Accepted: 7 September 2022
Published: 11 September 2022
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(https://creativecommons.org/license
s/by/4.0/).
Materials 2022, 15, 6305 2 of 19
150 mm; Tchakoute et al. [12] ground and sieved the ashes to a powder of 80 μm. Some
authors have determined the influence of the particle size of volcanic ash for use as a
construction binder. According to Moufti et al., [13], finely pulverised ash with a particle
size of less than 45 mm and a content of 10% by mass has a compressive strength similar
to a control sample. On the other hand, Khan et al. [14] reported that 15% substitution of
natural pozzolans with finely ground cement had a lower strength compared to controls.
An important property of this type of material is that it has pozzolanic activity, i.e., in
contact with water it can behave as a hydraulic binder, just like cement [15,16].
Currently, the use of lava and volcanic ash has been evaluated by different authors
for use as construction material; the main applications have been as ceramic material,
geopolymers, cement, and concrete [17–20]. Zhang et al. [21], manufactured and analysed
bricks fired with a mixture of volcanic ash and black cotton soil between 1000–1050 °C,
showing good compressive strength (60MPa), a small percentage of dimensional varia-
tion, and similar bulk density to conventional brick. Serra et al. [22] reported the use of
ash as a flux for feldspar replacement in clay-based materials and observed appropriate
brick texture and mechanical properties compared to traditional materials used in brick
manufacturing.
The high content of aluminosilicates for the synthesis of geopolymers has attracted
the interest of a large number of studies of this type of mineral in the production of ge-
opolymer materials, either as the sole source of aluminosilicate material [23,24] or com-
bined with other types of materials such as metakaolin [25].
Furthermore, numerous studies corroborate the suitability of volcanic ash for partial
replacement of cement, paste, and mortar or in the manufacture of concrete [25–29]. For
example, Celik et al. [27] reported that a high-volume mass replacement of Portland ce-
ment (OPC) with volcanic ash produces concrete with good workability, high compres-
sive strength, and high resistance to chloride penetration. Al-Fadala et al. [27] analysed
the mixture of volcanic ash and cement according to international standards, to evaluate
the use of this material, and concluded that it met the technical requirements to be used
for certain percentages of volcanic ash from a chemical, physical, and mechanical point of
view. Regarding treatments applied to volcanic ash prior to its use, Khan et al. [28]
showed that pozzolanic activity increased with the fineness of the material; however, a
heat treatment applied to volcanic ash was not positive. Other studies, such as that of
Abdullah et al. [30], showed that volcanic pumice powder improved the compressive
strength of self-compacting concretes made with it, thus demonstrating the influence of
the degree of fineness of volcanic ashes on the mechanical properties. Al-Swaidani and
Aliyan [31] studied the durability of mortar and concrete made with different slag sub-
stitutions, showing great interest in properties related to chloride ion penetration, acid
attacks, and corrosion of reinforcing steel, and concluded that the volcanic slag studied
was suitable for use as a natural pozzolan in accordance with international standards.
Therefore, taking into account that cement, and especially the process necessary to
produce it, contributes significantly to climate change, emitting 8% of total CO2 emissions
worldwide, the aim of this work is to study the use of ash from the Cumbre Vieja volcano
as a replacement for cement in the production of Portland cement as well as its effects on
the manufacture of mortar. The physical, chemical, mechanical, and environmental
properties, in accordance with international specifications, have been studied. This study
shows the long-term pozzolanic potential of volcanic ashes and how the application of a
crushing treatment influences the mechanical properties of cement mortars. A compara-
tive study has been carried out with other types of commonly used mineral additions.
This study shows the possibility of applying the fly ashes accumulated to date after the
natural catastrophe that occurred on the island of La Palma, which would lead to the
elimination of their accumulation and generate low-emission cement with good me-
chanical properties.
Materials 2022, 15, 6305 3 of 19
2. Materials and Methods
In this study, an analysis of the properties of volcanic material as an active mineral
addition for the manufacture of cement was carried out. For this purpose, an extraction of
volcanic material from two points of the island of La Palma, a collection of material close
to the eruption of the volcano (fine ash) and two collections of material near the coastline
(coarse ash and volcanic lava), were used. The material was processed by mechanical
means through a crusher and impact mill, obtaining as a result two powdery materials
with different degrees of fineness for each of the ashes studied and a powdery material
from the volcanic lava.
An advanced characterisation study was done for each of the materials obtained,
focusing on the fineness of the material, chemical composition, crystallography, and
pozzolanic activity. Once the material was characterised, the evaluation of the volcanic
material as an active mineral addition was carried out. For this purpose, 25% cement
substitutions were made, and the fresh properties of the pastes and the pozzolanic ca-
pacity of the ashes were evaluated by means of different tests. Figure 1 shows a graph of
the experimental methodology developed.
Figure 1. Experimental scheme.
2.1. Raw Materials
In this section, the physical, chemical, and mineralogical properties of raw and
processed volcanic ash and volcanic lava were studied to evaluate their pozzolanic po-
tential and their effect as an additive in the development of new cements.
In addition, two artificial pozzolanic materials, silica fume and fly ash, which are
widely used in the cement industry, were studied as a reference, along with limestone
filler.
2.1.1. Ordinary Portland Cement
For the performance of this research, an ordinary commercial Portland cement of
type CEM I 42.5R was used. A study of the main cement composition elements was car-
ried out by fluorescence study. The main composition and density of OPC used is shown
in Table 1.
Materials 2022, 15, 6305 4 of 19
Table 1. OPC main components and density.
Main components
FRX (%) CaO SiO2 SO3 Al2O3 Fe2O3 MgO K2O Na2O TiO2 Density (g/cm3) (UNE EN
196-6)
CEM I 42.5R 66.22 17.95 5.44 4.25 2.89 1.36 1.12 0.39 0.19 3.11
2.1.2. Fly Ash
The fly ash (FA) used in this study is a commercial artificial pozzolan used in the
manufacture of cements. FA comes from the combustion of coal in power generation
plants and is collected in filters by electrostatic precipitation. As can be seen in the laser
granulometry, as shown in Figure 2, FA is the finest material analysed, with an average
retained size of approximately 20 microns.
Figure 2. Particle size distribution of fly ash (FA) and silica fume (SF).
Table 2 shows that the real density of the FA has a value of 2.34 g/cm3, in addition to
presenting a composition with high amounts of silicon, aluminium, and iron; these val-
ues are typical of coal fly ash [32]. Moreover, the reactive SiO2 value is higher than the
25% imposed by the standard.
Table 2. Physicochemical properties of the raw pozzolans.
Fly Ash
(FA)
Silica Fume
(SF)
Limestone
Filler (LF)
Fine Volcanic
Ash (FVA)
Coarse Volca-
nic Ash (CVA)
Volcanic
Lava (VL) Standard
Real density (g/cm3) 2.34 2.24 2.67 2.9 2.3 2.72 EN 1097-6
Water absortion (%) - - - 0.38 0.44 1.91
Reactive SiO2 (%) 12.2 64.9 1.52 44.3 42.8 61.9 EN 80225
Organic matter con-
tent (%) 0.00 0.00 0.00 0.00 0.00 0.003 UNE 103204
Water-soluble sulp-
hate (% SO3) 0.26 0.38 0.00 0.00 0.00 0.0001 EN 196-2
Main components
EDX/EDS (%)
Na 0.35 0.08 0.21 2.91 3.07 2.27
P 0.22 0.07 0.01 0.38 0.33 0.26
Si 15.8 35.4 0.66 19.14 19.04 14.73
Ca 1.83 0.63 38.98 7.64 8.31 6.75
Materials 2022, 15, 6305 5 of 19
Al 9.92 0.38 0.02 7.82 7.76 5.67
S 0.16 0.16 0.04 0.08 0.09 0.05
K 2.5 0.43 0.02 1.54 1.54. 1.34
Mg 0.81 0.26 0.39 3.11 3.52 3.03
Fe 3.69 0.18 0.01 9.12 9.75 8.08
Figure 3 shows the XRD pattern of the FA. As can be observed, the analysed FA
shows a image in the diffractogram that indicates an important presence of amorphous
phase as well as peaks of SiO2 crystalline found in different phases and mullite; this
composition is coherent with that presented in other studies [33].
Figure 3. XRD pattern of FA.
2.1.3. Silica Fume
Silica fume (SF), or microsilica, is an inorganic product consisting of fine spherical
particles formed from the reduction of quartz with carbon in the silicon metal and fer-
ro-silicon manufacturing processes in electric arc furnaces. The dust produced is a by-
product collected in baghouses and silica dust collectors.
The silica fume analysed in this study has a particle average size of approximately 40
microns, as shown in Figure 2, as well as an actual density of 2.24 g/cm3. It is composed
entirely of amorphous SiO2, as can be observed in Table 2 and in the XRD pattern in
Figure 4. For this reason, silica fume has a great pozzolanic potential, which is observed
with a SiO2 percentage higher than 60% and is widely applied in the manufacture of ce-
ments and concretes [34,35].
Figure 4. XRD pattern of SF.
10 20 30 40 50 60 70 80
2θ
FA
SiO2 (Po lymorphic)
Muli lite (8A l4+2xS i2-2xO1 0-x (x ~0.4))
(8Al
4
+2xSi
2
-2xO
10
-x(x
0.4
))
SiO
2
(Polymorphic)
5 152535455565
2θ
SF SiO2
SiO
2
Materials 2022, 15, 6305 6 of 19
2.1.4. Limestone Filler
A study of limestone filler, as a mineral addition without activity, was carried out to
compare the effect of using volcanic material. It is a material of inorganic nature and
mineral origin composed mainly of calcium carbonate (at least 75%), with a clay content
of less than 1.2%. As shown in Table 2, its main composition is CaO.
2.1.5. Volcanic Lava and Volcanic Ash
In this section, the physical, chemical, and mineralogical properties of the volcanic
materials analysed are shown, and, in the following section, their pozzolanic potential
compared to FA and SF is evaluated in order to determine the possibility of applying
them in cementitious materials.
Three volcanic materials were analysed: one sample of volcanic lava and two sam-
ples of pyroclasts.
- Volcanic lava, from the solidified magma ejected by the volcano and collected from
solidified lava flows close to the coastline, is called VL.
- Lapilli pyroclastic are particles between 2 and 64 mm in size ejected from the crater
during ejection. Due to their size, lapilli pyroclastic precipitate by gravity in the areas
near the crater, where the samples were collected, and are referred to as CVA (coarse
volcanic ash).
- Ash type pyroclastic are particles smaller than 2 mm expelled during ejection; due
to their size they can be deposited over long distances. They were collected near the
coastline of the island and are referred to as FCV (fine volcanic ash).
Analysing the data shown in Table 2 for the three volcanic materials, it is observed
that the densities of the volcanic ash vary between 2.30 g/cm3 and 2.90 g/cm3, with the
lowest density in the FVA and the lowest in the CVA, due to the more compact granu-
lometry of the fine ash, which gives them a higher density. Volcanic lava has an inter-
mediate density value of 2.72 g/cm3; similar values have been shown in studies of vol-
canic ash from other eruptions. [15]
The three materials present a practically identical composition, due to the fact that
they come from the same volcanic material in the interior of the earth, varying in the
process of expulsion and subsequent deposit and cooling of the materials. VL, FVA, and
CVA present a composition with silica as the major element, with values between 14%–
19%, followed by Fe, with values between 8%–9%, Al and Ca, with values between 6%–
8%, and Na and Mg, with values close to 3%.
However, the reactive SiO2 content is similar in both types of ash, in the order of
45%, but higher than 60% for volcanic lava, indicating a higher pozzolanic potential in
this material.
FVA, CVA, and LV were studied by using X-ray diffraction (XRD). XRD data were
collected at room temperature using Cu-Kα radiation (λ = 1.5406 Å) operated in the re-
flection geometry (θ/2θ). Data were recorded from 10° to 60° (2θ) with a step-size of 0.02.
The X-ray tube was operated at 40 kV and 40 mA. Analysing the main component de-
termined by X-ray fluorescense for the three volcanic materials, the XRD pattern shown
in Figure 5, and the legend of the majority phases found (Table 3), it is observed that they
were mainly composed of pyroxenes belonging to the inosilicate family, such as diopside
and augetite, followed by feldspars of the tectosilicate family, where the presence of an-
desine, albite, and anorthoclase stand out. In addition, other crystalline phases were ob-
served in the form of titanium oxides (rutile) and silicon oxide (quartz). Although the
composition of volcanic materials depends on several factors, such as location and type
of eruption, similar compositions have been found in volcanic ashes analysed by other
authors [36,37].
Materials 2022, 15, 6305 7 of 19
Figure 5. XRD patterns of VL, FVA, and CVA.
Table 3. Mineralogical phases in volcanic materials.
Oxides and Hydroxides
Magnetite (Fe
3
O
4
)
Quartz (SiO
2
)
Rutile (TiO
2
)
Inosilicates
Diopside (Ca Fe
0.205
Mg
0.895
O
6
Si
1.9
)
Augite (Ca Fe
0.25
Mg
0.74
O
6
Si
2
)
Tectosilicates
Andesine (Al
0.735
Ca
0.24
Na
0.26
O
4
Si
1.265
)
Bytownite (Al
7.76
Ca
3.44
Na
0.56
O
32
Si
8.24
)
Labradorite (Al
0.81
Ca
0.325
Na
0.16
O
4
Si
1.19
)
Sanidine (Al
1.04
Ca
0.04
K
0.65
Na
0.31
O
8
Si
2.96
)
Albite (Al Na O
8
Si
3
)
Anorthoclase (Al
1.1
Ca
0.1
K
0.27
Na
0.63
O
8
Si
2.9
)
The morphology of the volcanic material was determined with scanning electron
microscopy (SEM), complemented with EDX to complete the compositional studies. A
Hitachi S4800 electron microscope (Tokyo, Japan) was used for the morphology study.
For the determination by energy dispersive spectroscopy (EDX) of the chemical compo-
sition of the samples, a Bruker Nano XFlash 5030 silicon drift detector was used.
Figure 6 shows the micrographs of FVA (a), CVA (b) and VL (c). A non-uniform
microstructure is observed with the presence of larger angular particles in CVA and
smaller ones in FVA. The presence of crystals was observed in all three volcanic materials
analysed.
Materials 2022, 15, 6305 8 of 19
Figure 6. SEM micrographs of volcanic materials: (a) FVA 500 μm; (b) CVA 500 μm; (c) VL 500 μm;
(d) FVA 50 μm; (e) CVA 50 μm; and (f) VL 50 μm.
The existence of large quartz crystals, as observed in Figure 6, corresponds to the
mineralogy of the volcanic material (Figure 5). The higher proportion of calcium and
aluminum observed by XRD patterns (Table 4) would explain the formation of inosili-
cates and tectosilicates (Table 3) and corresponds with what has been observed by other
authors who carried out analyses of volcanic material.
Table 4. Chemical composition of volcanic materials performed by energy dispersive spectroscopy
determines the (wt%).
SiO2 Al2O3 Fe2O3 MgO CaO Na2O SO3 K2O TiO2
FVA 40.72 18.34 12.82 4.69 9.81 7.11 0.01 2.04 4.06
CVA 40.65 18.11 13.46 1.77 17.85 2.26 0.01 1.91 3.89
VL 36.58 16.74 25.79 0.36 13.54 1.05 0.01 1.09 4.82
Volcanic lava is extracted from the lava flows by mechanical means, which involves
obtaining particle sizes of several centimetres in diameter. Furthermore, volcanic ash
(FVA and CVA) present coarser granulometry than FA and SF, as shown in Figure 7,
which prevents their direct application as a mineral addition in the manufacture of new
cements.
Materials 2022, 15, 6305 9 of 19
Figure 7. Particle size distribution of raw and processed VA and VL.
For this reason, a size reduction process is carried out on the samples to obtain the
necessary particle size for the application as a mineral addition. The processing applied is
as follows:
1) Drying of the material in an oven at 60 degrees Celsius.
2) Previous size reduction in a jaw crusher. Reduction in the initial fraction to a size
of less than 4 mm (VL and CVA)
3) Grinding by impact mill with different abrasive loads and processing times.
The processes applied on volcanic ash and volcanic lava were two, from more abra-
sive (P1) to less abrasive (P2). This micronisation process aims to have a sufficient specific
surface area to act as a cementitious material. The processes were carried out by intro-
ducing a determined quantity of material and abrasive load in a standardised friability
test machine, subjecting them to a determined number of turns for their correct pulveri-
sation.
After the size reduction process, five processed materials were obtained. The no-
menclature of these materials is shown in Table 5.
Table 5. Nomenclature volcanic material.
Description Nomenclature
Non-Processed Pulverized Fine Volcanic Ash FVA-NP
Pulverized Fine Volcanic Ash Implementing Process 1 FVA-1
Pulverized Fine Volcanic Ash Implementing Process 2 FVA-2
Non-Processed Pulverized Coarse Volcanic Ash CVA-NP
Pulverized Coarse Volcanic Ash Implementing Process 1 CVA-1
Pulverized Coarse Volcanic Ash Implementing Process 2 CVA-2
Pulverized Volcanic Lava VL-P
2.1.6. Evaluation of the Pozzolanic Potential of Raw Materials
Once the materials involved in the research have been analysed, a preliminary study
is carried out to evaluate the pozzolanicity of the raw materials using the fixed lime
method.
To study the pozzolanic activity of these materials, an accelerated method was used
to measure the evolution of the material–lime reaction as a function of time. The test
consisted of placing the different pozzolanic materials in contact with the saturated lime
solution at 40 ± 1 °C for 3, 7, 28, and 90 days. At the end of this period, the CaO concen-
tration in the solution was measured. The fixed lime (mM/L) was obtained from the dif-
Materials 2022, 15, 6305 10 of 19
ference between the concentration in the saturated lime solution and the CaO in the so-
lution in contact with the sample at the end of the given period. The fixed lime value is a
good indicator of the pozzolanic activity of the materials. It is higher as the amount of
fixed lime increases. This method has been extensively described and applied by De Ro-
jas and Frias, Rojas et al., and Frías et al. [38–40], allowing a preliminary evaluation of the
pozzolan activity of raw materials with high reliability.
Figure 8 shows the lime absorption results for the two artificial pozzolanic materials
and the three natural, volcanic pozzolanic materials. According to the results obtained,
SF shows a high pozzolanic reactivity from the beginning of the test at 3 days, which is
maintained up to 90 days. This is due to the high fineness presented by the silica fume
samples together with their morphology mainly composed of amorphous silica.
Figure 8. Fixed lime in pozzolans over time.
The AF summarises a lime absorption that increases with time, reaching its maxi-
mum level at 90 days and presenting a 50% absorption with respect to the SF at 28 days.
VL presents a similar behaviour to the AF, exceeding its pozzolanic activity by 60% at 28
days; however, it presents a similar activity at 90 days.
Finally, analysing the pozzolanic reactivity for volcanic ash, it is observed that the
difference in particle size does not have a significant effect, presenting similar values.
Compared to the rest of the values, it shows the lowest amounts of fixed lime, increasing
to levels comparable with FA and VL, indicating that the pozzolanic activity of the ash is
a long-term process from the beginning of the reaction.
2.2. Mix Proportions
In this section, the proportions of each material to be used to mix the mortars to be
analysed were shown. Table 6 shows the dosages of each material, and the nomenclature
of the mortar performed. Standardized sand (SNS) was used for the manufacture of the
mortars, in accordance with UNE EN 196-1. However, because the amounts of materials
included in the mixtures are too numerous to be tabulated, and the percentage of each
material added is the same, replacing 25% of cement by each pozzolan, the materials de-
rived from the volcanic ashes (FVA-NP, FVA-P1, FVA-P2, CVA-NP, CVA-P1, CVA-P2)
are referred to as FVA, CVA, and LF.
Table 6. Dosages of mortar made in laboratory.
Materials 2022, 15, 6305 11 of 19
Mix-
ture Description Dosages (g)
SNS OPC SF FA LF FVA CVA VL Water
OPC OPC – Cem I 1350 450 - - - - - 225
SF 10% Silica Fume 1350 450 112.5 - - - - - 225
FA 25% Fly Ash Ad-
dition 1350 337.5 112.5 - - - - 225
LF 25% Limestone
Filler 1350 337.5 - 112.5 - - - 225
FVA-N
P
25% Fine Volcanic
Ash Addition;
Non-Processed
1350 337.5 - - 112.5 - - 225
FVA-1
25% Fine Volcanic
Ash Addition;
Process 1
1350 337.5 - - 112.5 - - 225
FVA-2
25% Fine Volcanic
Ash Addition;
Process 2
1350 337.5 - - 112.5 - - 225
CVA-N
P
25% Coarse Vol-
canic Ash Addi-
tion;
Non-Processed
1350 337.5 - - - 112.5 - 225
CVA-1
25% Coarse Vol-
canic Ash Addi-
tion;
Process 1
1350 337.5 - - - 112.5 - 225
CVA-2
25% Coarse Vol-
canic Ash Addi-
tion;
Process 2
1350 337.5 - - - 112.5 - 225
VL Volcanic Lavage
Addition 1350 337.5 - - - - 112.5 225
2.3. Test Procedures
The tests carried out to evaluate the pozzolanicity of the volcanic material are shown
below.
2.3.1. Pozzolanicity and Frattini Tests (UNE_EN 196-5:2011)
Pozzolanicity is a test carried out on cement substitutes. By performing this test, it is
possible to quantify the amount of calcium oxide that a material is capable of fixing. To
determine the pozzolanicity, the material to be tested is immersed in a saturated calcium
oxide solution, and the levels of calcium oxide absorbed by the sample were measured.
The results were shown as the percentage of calcium oxide fixed in the sample out of the
total calcium oxide in the solution.
The Frattini test, similar to the pozzolanicity test, is carried out on cements and
mixtures of cements with substitutes. In accordance with the standard, the cement is
immersed in a solution in which, after 8 and 15 days, the amount of hydroxyl ions and
the amount of calcium oxide that has been absorbed by the sample were evaluated. To
evaluate its pozzolanic capacity, the values obtained were presented in a graph that plots
the concentrations of hydroxyl ions against the concentrations of calcium oxide on its
axes.
Materials 2022, 15, 6305 12 of 19
The standard presents a curve that divides the graph into two zones. If the point
resulting from the test is below this curve, the material is potentially pozzolanic. If it is
above, the material is not pozzolanic.
This is a method for evaluating the pozzolanicity of pozzolanic cement, which,
therefore, serves to evaluate the pozzolanic behaviour of a material when mixed with
cement in different proportions. To evaluate the effect of volcanic material (FVA, CVA,
and VL), cement/volcanic material mixtures were prepared.
To test the effect of volcanic material in a cement, cement/volcanic material mixtures
were prepared in 75/25 proportions. The Portland cement used as a reference was CE-
MI/42.5R, which has a clinker content equal to or greater than 95%, so it can incorporate
additional components up to 5%.
2.3.2. Resistant Activity Index (UNE_EN 196-1:2018)
The determination of the pozzolanic activity index in Portland cement is defined as
the ratio between the maximum load supported by the test mortars (standard cement
with added pozzolan) and the maximum load supported by the standard mortars
(standard cement), expressed in percentage terms. In other words, it is the variable that
allows a pozzolan to be classified for use in the cement production process, a value that is
internationally considered to be at least 75%. The existing physical–mechanical methods
for the determination of this index require waiting 28 days from the completion of the
test expressed in the standard, to stipulate whether a material has acceptable pozzolanic
properties for use.
Additionally, to evaluate the pozzolanic activity of the material, a study of the re-
sistant activity index was carried out in accordance with the UNE 450-1 standard. It
should be noted that this standard refers to the use of fly ash; its application is not man-
datory for natural pozzolans, and, therefore, the established minimum compressive
strength requirements do not have to be met.
This method includes the determination of compressive and flexural strengths, ac-
cording to UNE 196-1 of prismatic specimens, of dimensions 40 mm × 40 mm × 160 mm,
prepared with 75% of the test cement plus 25% by mass of volcanic ashes. The specimens
were kept in the mould in a humid atmosphere for 24 h, and, after demoulding, the
specimens were immersed in water until the strength tests were performed at the re-
quired age, in this case at 7, 28, and 90 days.
2.3.3. Setting Time and Volumetric Expansion (UNE-EN 196-3:2017)
Setting time is expressed in two values, the initial setting time and the final setting
time. The initial setting time refers to the number of minutes that elapse from the time the
cement comes into contact with water until the cement paste begins to lose its plasticity.
The final setting time is expressed as the number of minutes that have elapsed, since the
water comes into contact with the cement, until the cement paste loses its plasticity to-
tally and is completely hardened.
To quantify these times in a standardised way, the test is performed according to EN
196-3 standard. The Vicat apparatus is used in this test, in which the degree of penetra-
tion of its needles will determine the hardening of the cement paste, thus being able to
determine the initial and final setting times.
Volumetric expansion determines the change in volume that the cement undergoes
during hardening. These values are relevant because they determine the soundness of
cement. To determine the volumetric expansion, the cement paste is tested according to
EN 196-3, and, through the measurements on the Le Chatelier needles, we can determine
the volumetric expansion of the cement under test.
Materials 2022, 15, 6305 13 of 19
3. Results and Discussion
3.1. Pozzolanity and Frattini Tests
Figure 9 shows the results obtained for the [CaO] and [OH−] concentrations of each
of the mixtures analysed at 8 and 15 days according to the standardised test. The results
were compared with the portlandite solubility curve.
The analysed mixture is considered to comply with the test, i.e., to be pozzolanic,
when the concentration of calcium ions is lower than the saturation concentration indi-
cated by the reference curve.
Figure 9. Fixed lime in pozzolans over time.
To test the effect of volcanic material in a cement, cement/volcanic material mixtures
were prepared in 75/25 proportions. The Portland cement used as a reference was CE-
MI/42.5R, which has a clinker content equal to or greater than 95%, so it can incorporate
additional components up to 5%.
Figure 8 shows the values of [Ca]2+ and [OH−] oxides, which decrease in solution as a
consequence of the depletion of calcium hydroxide, after the pozzolanic reaction of each
of the mixes analysed at 8 and 15 days, according to the standardised test. The results
were compared with the portlandite solubility curve.
The analysed mixture is considered to comply with the test, i.e., to be pozzolanic,
when the concentration of calcium ions is lower than the saturation concentration indi-
cated by the reference curve. It was observed that all ash mixtures analysed were above
the curve, unlike the results obtained in other studies [41], in which volcanic ashes
showed high pozzolanicity as well as fly ash and silica fume [42,43].
The crushing processing of the volcanic ash led to an improvement in the pozzolanic
capacity of the material; in the short term, the material was not considered to be poz-
zolanic, but the values were close to the solubility curve. Previous studies showed that
mechanical activation of ashes increases the reactivity of the pozzolanic material [44].
As shown by other authors, crushing volcanic material to be used as a supplemen-
tary cementitious material improved the pozzolanic properties of the mixes [45–47]. The
approximation to the solubility curve of the crushed material is due to the fact that higher
amounts of calcium silicate hydrate (C-S-H) and calcium aluminate silicate hydrates
(C-A-S-H) gel phases were formed, and finer sizes of the material lead to a higher amount
of these phases.
Materials 2022, 15, 6305 14 of 19
3.2. Resistant Activity Index
It can be seen in Table 7 that the processed volcanic ash improves its resistance
compared to unprocessed volcanic ash; that is, the degree of fineness has a very relevant
influence on the resistance obtained. If FVA-2 and CVA-2 were compared with the mix-
ture in which FA was used, it remains slightly below, not reaching 85% in the case of
volcanic ash. However, a much higher increase than the mixture with LF is obtained,
which allows one to think that they are usable in the manufacture of cement and as a
mineral addition to concrete.
Table 7. Results of compressive strength in resistant activity index.
Compressive Strength MPa (Age) % Regarding
Control 28D
% Regarding
Control 90D
Resistance
Increase
28–90 days
7 28 90
CEM I (42.5) 41.5 46.2 49.1 - - 6.4%
SF 35.6 42.4 45.5 91.8% 92.6% 7.3%
FA 31.5 38.4 42.5 83.1% 86.5% 10.7%
LF 29.7 33.8 36.2 73.2% 75.7% 7.1%
FVA-NP 26.7 31.6 37.1 68.4% 75.5% 17.4%
FVA-1 26.2 31.5 36.2 68.2% 73.7% 14.9%
FVA-2 27.6 34.6 40.7 74.9% 82.8% 17.6%
CVA-NP 19.7 31.1 37.8 67.3% 76.9% 21.5%
CVA-1 24.3 33.7 38.6 72.9% 78.5% 14.5%
CVA-2 27.6 35.4 41.1 76.6% 83.6% 16.1%
VL 25.5 33.8 37.1 73.2% 75.5% 9.8%
In Figure 10, only the five most significant mixtures have been included. It is clearly
observed how there is a more relevant increase in resistance in the two samples made
with processed volcanic ash (CVA-2 and FVA-2), compared to the control or in the mix-
ture made with FA. This fact indicates that the volcanic ash gradually increases its re-
sistance over time, with its growth being greater after 28 days, compared to the case of
mixtures made with a conventional cement. This is due to an increase in pozzolanicity at
90 days, as observed in Figure 8, which contributes higher strength to the mortars made
with FVA and CVA. On the other hand, in the mixture made with LF, it does not show
significant growth after day 28 because it is a mineral addition with little pozzolanic ac-
tivity.
Materials 2022, 15, 6305 15 of 19
Figure 10. Progress in resistance activity index.
Therefore, based on these results, it can be concluded that volcanic ashes processed
with an adequate degree of fineness can be used in the manufacture of cement, present-
ing a higher reactive silica content at 42%, which is very important for the validation of
these volcanic materials as a cement substitute.Lastly, it should be noted that the unpro-
cessed volcanic ash presented similar results to the mortars made with LF at 90 days,
with the behaviour being less than 28 days and the growth of resistance being between 28
and 90 days. For example, in both mixtures, FVA-NP and CVA-NP, it is possible to ob-
serve the increase in resistance between 28 days and 90 days, going from 31.1 MPa to 37.8
MPa in CVA-NP (increase of 21.5%), and from 31.6 MPa to 37.1 MPa in FVA-NP (increase
of 17.4%).
These results clearly show that volcanic ash can be used as SCM, and, although it
can be processed, improving behaviour, it can be applied in the manufacture of cements
and as a mineral addition in concrete manufacturing
3.3. Setting Time and Volumetric Expansion
Table 8 shows the results obtained for the initial and final setting times and volu-
metric expansion for all mortars. As can be observed, the OPC initial and final setting
times were 105 and 190 min, respectively, consistent with high percentages of clinker and
rapid hardening cement.
The addition of LF retarded both setting times. On the contrary, the addition of FA
implies a lengthening of both times. This behaviour has been extensively studied and
described for decades [48–50].
Table 8. Setting time and volumetric expansion of mortar.
Mixture Setting Time (min) Expansion (mm)
Initial Final
OPC 105 190 1.50 mm
SF 110 180 1.40 mm
FA 125 235 2.10 mm
LF 85 175 1.30 mm
FVA-NP 90 140 1.0 mm
FVA-P1 105 155 0.9 mm
FVA-P2 90 140 1.1 mm
CVA-NP 90 140 1.0 mm
25
30
35
40
45
50
72890
Resistant Activity Index (Mpa, days)
CEM I (42.5) FA LF FVA-2 CVA-2
Materials 2022, 15, 6305 16 of 19
CVA-P1 95 140 0.9 mm
CVA-P2 90 130 1.0 mm
VL-P 100 135 0.8 mm
Analysing the results for the VL, FVA, and CVA samples, it is observed that the
addition of these materials and their different processing slightly decrease the initial set-
ting time as well as more noticeably reduce the final setting time; however, the times
between the different volcanic materials remain practically stable. Other studies describe
an opposite behaviour after adding these materials, with slight increases in setting times;
however, due to the different origins, compositions, and properties of the volcanic mate-
rials, different effects can be observed [15].
Concerning the results for the determination of volumetric expansion, all materials
show values below the limits for cementitious specifications according to EN 197-1. The
addition of SF has no significant effect on the expansion of the cementitious pastes [49],
although the addition of FA does lead to an increase in expansion. The addition of vol-
canic material slightly reduces the volumetric expansion of the cementitious pastes and,
as with the setting times, the values for all volcanic materials are similar. This decrease in
expansion with respect to the mortars manufactured with FA may be mainly due to the
increased absorption of the mortar pastes manufactured with FA [51,52]. The FVA and
CVA samples presented low absorption (Table 2); therefore, the manufactured mortars
presented low dimensional changes at early ages, due to the fact that there are no large
pores or occluded water in the mortars that could modify their dimensions at initial
curing ages.
4. Conclusions
In the present study, the effect of applying volcanic material (pyroclasts and vol-
canic lava) from the eruption of the Cumbre Vieja volcano in La Palma, Spain, as an ac-
tive mineral addition for the manufacture of pozzolanic cements, is analysed. In addition,
silica fume and fly ash from coal combustion were analysed as pozzolanic material ref-
erences. After studying the physical, chemical, and mineralogical properties of volcanic
materials and their application in mortars, the following conclusions are drawn:
- Volcanic material (fine ash, coarse ash, and lava) is mainly composed of SiO2,
Al2O3, Fe2O3, and CaO. A natural pozzolan is essentially composed of reactive silicon
dioxide (SiO2), aluminium oxide (Al2O3), and iron oxide (Fe2O3). Therefore, the material
has suitable characteristics to be used as natural pozzolanic material as SCM.
- The three materials analysed (coarse ash, fine ash, and lava) have reactive silicon
dioxide values well above the 25% required by the UNE-EN 197-1 standard for the ap-
plication of natural pozzolan in the manufacture of cement. This demonstrates that their
use is viable and complies with the minimum requirements established.
- The pozzolanicity study showed that the volcanic lava presented high poz-
zolanicity at early ages; however, the volcanic ash evolved more positively, obtaining
high pozzolanicity at 90 days. This is a positive fact, since natural pozzolans cannot be
evaluated only in the short term: it is necessary to evaluate their mechanical behaviour in
the medium and long term.
- The unprocessed volcanic ash showed a resistance in the 28-day resistant activity
index test that was lower than the rest of the SCM studied in this work, but the increase in
resistance between 28 and 90 days was much higher, obtaining up to a 21.5% increase in
resistance in the sample in the mortar mix made with CVA-NP.
- A relevant increase was observed in resistance in the processed volcanic ash, and
the mixtures made with them increase their resistance over time, so the increase between
28 and 90 days was very relevant.
- In the long term (90 days), the compressive strength results of mortars manufac-
tured with FVA and CVA increased considerably, exceeding the results obtained in the
LF mixtures.
Materials 2022, 15, 6305 17 of 19
- In the long term, it is demonstrated that unprocessed and crushed volcanic ash can
be used as a natural pozzolan for the manufacture of cement, obtaining higher results
than a mortar made with limestone filler.
In view of the results, the pozzolanic potential of the volcanic ash from the La Palma
eruption is feasible for the manufacture of cement, and it is possible to apply substitution
percentages of SCM of up to 25%. This application shows the environmental and social
benefits in relation to the volcsanic process that occurred in 2021 on the island of La
Palma, Spain, due to the large volume of fly ash generated during the eruption of the
volcano.
Author Contributions: Conceptualization, F.A. and J.R.; methodology, M.R. and M.C.;; formal
analysis, J.L.D.-L. and J.R.; investigation, F.A., J.R., M.R., J.L.D.-L., M.C.; writing—original draft
preparation, F.A. and J.R.; writing—review and editing, FA. and J.R.; supervision, F.A. and J.R.;
project administration, F.A. and J.R. All authors have read and agreed to the published version of
the manuscript.
Funding: This research was funded by the project Development of ’Smart’ surfacing and repair
Materials from low-carbon by products for more effective active and predictive safety. Advanced
applications for Roads, SMATCAR funded by the Minister of Science and Innovation of Spain.,
grant number PID2019-107238RB.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The authors acknowledge the financial support provided by the company
Sacyr, the promoter and principal researcher of the project, and especially Francisco Javier Mateos
and Ana Esteban. The authors would also like to thank the project Development of ’Smart’ sur-
facing and repair Materials from low-carbon by products for more effective active and predictive
safety. Advanced applications for Roads, SMATCAR funded by the Minister of Science and Inno-
vation of Spain. In addition, the authors would like to thank María Isabel Sánchez de Rojas, a
member of the Eduardo Torroja Institute for Construction Science.
Conflicts of Interest: The authors declare no conflict of interest.
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