Elsevier

Transportation Geotechnics

Volume 24, September 2020, 100383
Transportation Geotechnics

Geomechanical characterization of volcanic aggregates for paving construction applications and correlation with the rock properties

https://doi.org/10.1016/j.trgeo.2020.100383Get rights and content

Highlights

  • A characterization database of the main volcanic aggregate lithotypes is provided for construction purposes.

  • Utility of the simplified classification of volcanic aggregates into massive, vesicular and pyroclastic is confirmed.

  • Relations among aggregate properties and between aggregate and rock properties are provided.

  • Massive aggregates are recommended for road surface layers, vesicular for bases, and pyroclastic for permeable subgrades and fillings.

Abstract

In volcanic terrains and in particular island regions, the aggregates come from the mechanical crushing of lava rocks and pyroclastic deposits. This study offers an experimental database of the geomechanical characteristics of different volcanic rock lithotypes and the aggregates obtained from these rocks. For this purpose, 971 aggregate samples and 643 rock samples of 11 different common volcanic lithotypes (including basalts, trachybasalts, trachytes, phonolites, ignimbrites and pyroclasts) were tested. These represent the majority of stone materials found in volcanic islands. Furthermore, correlations between the different properties of the aggregates (volumetric, geometric and mechanical properties) have been established, as well as between certain aggregate properties and the source rock. This allows an estimation of the foreseeable characteristics of the aggregates based on their origin. The results show that the aggregates from massive lithotypes provide superior resistance, partly due to their high density. These generally comply with the standard specifications although the particle shape may present an excessive flakiness index. However, the most abundant volcanic aggregates come from very porous rocks with a vesicular or scoriaceous structure, non-cubic particles, low resistance and high absorption, though they provide good drainage capacity. The high statistic dispersion of the geomechanical properties is due to the different viscosity of the magmas, degrees of explosiveness of the volcanic eruption and random spatial distribution. Even the abundant vesicular and scoriaceous volcanic aggregates, generally considered as marginal materials, may offer adequate quality and properties for certain construction applications. In this sense, the use of these aggregates might contribute to the development of infrastructures in these regions and thus a sustainable utilization of this natural material.

Introduction

Aggregates are fundamental in the construction industry. They constitute one of the most consumed products in the world and one of the four most important raw materials in world mining [1]. In volcanic regions, and especially on island territories, there are numerous environmental, technical and economic limitations and constraints regarding the exploitation of these aggregates. In this sense, it is fundamental to know the properties of all the natural aggregates in order to consider possible applications for different construction uses. The endogenous origin of volcanic territories determines a great variability and heterogeneity of existing materials and their properties even within the same quarry or natural deposit. The spatial distribution of the different rocks is usually unpredictably irregular and discontinuous [2], either due to the wide diversity of possible lithologies (basalts, basanites, trachytes, phonolites, rhyolites, etc.), the different rock structure (massive, vesiculated, isotropic, anisotropic), the type of alteration (hydrothermal, diagenetic, weathering, thermal contact) or the type of eruption that produced the rocks quarried for aggregates (effusive, explosive). This accumulation of constraints explains the lack of scientific-technical literature regarding the implementation of volcanic aggregates [2].

The main objective of this study is to promote the diversification of usable volcanic material for construction implementation in these regions where resources and territory are limited as well as protected environmentally. Bearing this in mind, an exhaustive geomechanical characterization of the main lithotypes is offered for possible use in the construction of road or airport pavements, used as unbound granular material, or as an aggregate for asphalt mixture or for cement concrete. However, for this last application additional testing would be necessary: chemical stability, alkali-silica reactivity, long-term durability of unstable minerals. From these properties, characterized by the European test standard (EN), correlations between the different properties of volcanic aggregates and between these and the source rock are presented in order to infer expected properties as long as the origin is known. In this way, the following characteristics were determined: particle density (EN 1097-6), water absorption (EN 1097-6), flakiness index (EN 933-3), percentage of crushed and broken surfaces (EN 933-5), sand equivalent (EN 933-8), sand friability (UNE 83-115-89), resistance to wear (EN 1097-1) and resistance to fragmentation (EN 1097-2); as well as the following properties of the original rock: bulk density (EN 1936) and uniaxial compressive strength (EN 1926). Finally, a simplified classification of volcanic aggregates for engineering applications is confirmed which will simplify the complex geological classifications and thus allow technicians and operators take decisions regarding the possible construction uses of a certain type of volcanic aggregate.

There are studies that support the use of certain volcanic aggregates in road engineering [1], [2], [3], [4], [5], [6]. Some studies even analyse the use of certain marginal volcanic aggregates (ashes, scoriae, tuffs, basaltic lapilli) in cement concrete [7], [8], [9], [10], [11] and in asphalt mixtures [2], [12], [13], [14] based on the hydraulic capacity, profitability and low environmental impact [2], [8]. However, the performance of the final product will always depend on the individual properties of each one of the component materials and the proportion in which they are used [15], [16].

Up to now, characterization studies of volcanic materials have focused on determining the properties of certain aggregates after analysing the rock characteristics [17], [18]. Generally speaking, when it comes to analysing the quality of an aggregate, a resistance characterization is carried out using tests such as Los-Angeles (LA) and Micro-Deval (MDE) [6]. Other studies have sought a way to estimate the values of LA and MDE coefficients by indirect tests that are quicker and more affordable [19], [20], [21], [22]. Certain studies explored the way to deduce the LA coefficient from the results obtained with the Schmidt hammer, Point Load Test (PLT) and the porosity [22]. To this effect, this study analysed samples of igneous, metamorphic and sedimentary rocks with different LA coefficients (10–76%). The results showed a certain correlation between the LA coefficient and the Is of the Point Load Test (R2 = 0.72) and with the Ir results obtained by the Schmidt hammer (R2 = 0.62). Furthermore, the correlations clearly improved separating the samples according to their porosity (n < 1% y n > 1%). Further studies [20], [21], that analysed different non volcanic lithotypes according to petrology, porosity and density, provided LA values from electric resistivity, density and porosity, accomplishing a good correlation between electric resistivity and the LA coefficient. In Ref. [19] the LA coefficient, the uniaxial compressive strength (UCS) and the bulk density (ρb) of various volcanic lithotypes from the Canary Islands (Spain) were correlated and it was concluded that it is possible to estimate the UCS from the LA and ρb; these last properties can be obtained in an easier, quicker and more affordable manner.

Among volcanic rocks it is possible to find a variety of materials with very different compositions (basaltic, basanitic, trachytic, phonolitic, tephritic or rhyolitic) and rock structure (lava flows, cemented or non-cemented pyroclasts, volcanic breccia, ignimbrites) [23], [24]. A characterization of these rocks has been carried out with the works in Ref. [25], [26], [27] about lithotypes in the Canary Islands (Spain); an archipelago of volcanic origin situated in the Atlantic Ocean near the NW coast of Africa (N28°, W15°30′). In these works, a classification of volcanic rocks has been organized according to petrology and texture, and providing data concerning the geomechanical properties. These studies allowed the Regional Government of the Canary Islands to publish a Guide for Geotechnical Studies in Building in the Canary Islands (GETCAN-011) [28], which classifies lava rocks by cohesion, lithology, texture and vesicularity; and the pyroclastic materials according to lithology, welding grade and particle size. However, although this rock classification may be a starting point to classify volcanic aggregates, it does not allow the deduction of properties for constructive applications of those aggregates obtained by fragmentation as the engineering characterization of aggregates has not been addressed in these studies. Consequently, up until now the main properties of the wide range of volcanic aggregates have not been characterized systematically. The lack of knowledge concerning their characteristics and the absence of specific technical regulations for their use, means that frequently works support additional costs due to the importation of materials or due to doubts regarding non-compliance with certain specifications [5].

A first step towards an engineering classification of volcanic aggregates for construction purposes has been established in Ref. [2], within the framework of a research of the utilization of marginal high-porosity volcanic aggregates in asphalt mixtures for pavements. The present study aims to present a thorough and systematic research that will allow the property characterization of different lithotypes of volcanic aggregates for practical construction applications as well as provide the correlations among these properties and with the source rock.

Section snippets

Materials

The volcanic aggregate samples (Fig. 1) and the volcanic rocks (Fig. 2) were obtained in different quarries and natural deposits around the different islands of the Canarian archipelago, and were initially gathered according to the classification in Ref. [27], [28]. Most of the aggregate crushing plants in these quarries use jaw crushers for breaking rocks. A total of 971 aggregate samples (without any alteration) were tested. These were obtained using normalized sample procedures, including 3

Results

Table 3 shows the results of the average values of each property for the samples of different aggregate fractions from the same site or quarry.

In order to provide certain reference values of the volcanic aggregate properties that might have a more universal application and thus serve as a guide in the construction sectors, the previous results were averaged for the samples of the same lithotype with the three grading fractions. These results are shown in Table 4. Furthermore, in order to

Discussion

Prior to the establishment of correlations among the different aggregate properties, each one has been correlated with the density of each grading fraction separately. In this way, the influence due to the density-porosity change among fractions has been assessed. As a reference the particle density [dry] (ρrd) was used, except for the finest fraction (0–4 mm); in this case the apparent particle density (ρa) was employed. In this manner, the measurement of the density of the saturated particles

Conclusions

From the analysis of the results of this experimental study the following conclusions may be drawn:

  • Volcanic aggregates for engineering purposes may be classified for practical reasons in three extensive groups according to density, porosity (absorption) and resistance: massive, vesicular and pyroclastic. This simple classification allows users to take immediate decisions regarding possible construction applications depending on the volcanic aggregate available; and simplifying the much more

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the Ministry of Economy and Competitiveness (MINECO) from the Government of Spain, through the Research Project “MW-VolcAsphalt” (Ref. BIA2017-86253-C2-2-R, “Sustainable self-healable perpetual asphalt pavements with volcanic aggregates using microwaves and additions of metallic wastes and nanoparticles”).

The authors are also very grateful to the Construction Laboratory of the Government of Canary Islands (J. Jubera and J. Santana) for accessing to the quality control

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