Altered Volcanic Tuffs from Los Frailes Caldera. A Study of Their Pozzolanic Properties

Abstract

This work presents the results of the study of the physical, chemical, mineralogical and pozzolanic properties of the altered volcanic tuffs (AVT) that lie in the Los Frailes caldera, south of the Iberian Peninsula, and demonstrates their qualities as pozzolans for the manufacturing of mortars and pozzolanic cements of high mechanical strength. The main objective of this research is to show to what extent the AVTs can replace portland cement (PC) in mortars, with standardised proportions of 75:25% and 70:30% (PC-AVT). To achieve these objectives, three AVT samples were studied by a petrographic analysis of thin section (PATS), DRX, FRX and MEB. The pozzolanic properties were determined by three methods: electrical conductivity (ECT), chemical pozzolanicity tests (CPT) at 8 and 15 days and mechanical strength tests (MS) of the specimens at 2, 7, 28 and 90 days. Studies of a PATS, DRX, FRX and MEB showed that the AVT samples’ constitutions are complex where smectite (montmorillonite), mordenite, quartz, halloysite, illite, kaolinite, volcanic glass and lithic fragments coexist. The results of the ECT and CPT tests confirmed the pozzolanic properties of the samples analysed and proved an increase in mechanical strength from 2 to 90 days of testing.

A New Study of the Lower Levels of the Los Frailes Caldera (Spain) for the Location and Characterisation of Pozzolans as Construction Materials

“…This fact can be interpreted as one of the main causes of the pozzolanic reactivity of the samples together with the significant presence of SiO 2 and Al 2 O 3 , which is in accordance with the conclusions of Rosell et al [21]. The Loss on Ignition (LOI) values presented have been related in this research to the intrinsic properties of zeolites, such as the extremely large active surface, absorption capacity, and low sulphate contents [9], which are indispensable for their use as a pozzolan and as a possible construction material. In addition, the calculation of the ratio Si/Al:4.3-4.6 (Table 2) has allowed us to establish that the zeolite found in each of the samples investigated corresponds to the mordenite variety.…”

“…Fe 2 O 3 contents range from 1.2% (LFCS-06) to 2.17% (LFCS-02); however, we must highlight ranges of values between 1.45% (LFCS-05) and 2.17% (LFCS-02), which are larger and comparable with those calculated by Costafreda et al [9] in zones proximal to the research area. The higher contents of MgO (2.94-3.2%) may indicate the possible relationship that exists between the andesite host rock that lies in the study area, which has been affected by hydrothermal processes as stated by Arribas [1] and Costafreda et al [9]. The values calculated for CaO, K 2 O, and Na 2 O are within the ranges of results presented and discussed by García-Romero et al [14] for calc-alkaline environments of formation from zeolite and bentonite deposits.…”

“…Fe2O3 contents range from 1.2% (LFCS-06) to 2.17% (LFCS-02); however, we must highlight ranges of values between 1.45% (LFCS-05) and 2.17% (LFCS-02), which are larger and comparable with those calculated by Costafreda et al [9] in zones proximal to the research area. The higher contents of MgO (2.94-3.2%) may indicate the possible relationship that exists between the andesite host rock that lies in the study area, which has been affected by hydrothermal processes as stated by Arribas [1] and Costafreda et al [9]. Fe 2 O 3 contents range from 1.2% (LFCS-06) to 2.17% (LFCS-02); however, we must highlight ranges of values between 1.45% (LFCS-05) and 2.17% (LFCS-02), which are larger and comparable with those calculated by Costafreda et al [9] in zones proximal to the research area.…”

“…The higher contents of MgO (2.94-3.2%) may indicate the possible relationship that exists between the andesite host rock that lies in the study area, which has been affected by hydrothermal processes as stated by Arribas [1] and Costafreda et al [9]. Fe 2 O 3 contents range from 1.2% (LFCS-06) to 2.17% (LFCS-02); however, we must highlight ranges of values between 1.45% (LFCS-05) and 2.17% (LFCS-02), which are larger and comparable with those calculated by Costafreda et al [9] in zones proximal to the research area. The higher contents of MgO (2.94-3.2%) may indicate the possible relationship that exists between the andesite host rock that lies in the study area, which has been affected by hydrothermal processes as stated by Arribas [1] and Costafreda et al [9].…”

“…According to Arribas [1] Los Frailes Caldera is a circular volcanic structure which is approximately 5 km in diameter, which was formed 14.4 ± 0.8 ma ago because of eruptive processes of several pyroclastic flows of dacitic and andesitic composition. At the same time, Benito et al [6], Costafreda [7], Costafreda and Martin [8], Costafreda et al [9], Presa et al [10], and Stamatakis et al [11] have recently investigated and described minerals and industrial rocks inside Los Frailes Caldera, consisting of strongly zeolitized and bentonitized cineritic tuffs (ZBT) and glassy volcanic tuffs (GVT), to be used in the production of pozzolanic cements, mortars, concretes, and as light aggregates for concrete. Other researchers [12][13][14] have focused their research on the bentonite deposits of the Los Frailes Caldera and surrounding distal areas.…”