Abstract
This paper shows the results of a study focused on the evolution and properties of mortars made with a mixture of portland cement (PC) and natural mordenite (Mor). To begin, samples of mordenite, cement and sand were studied with X-ray diffraction (XRD), X-ray fluorescence (XRF) and granulometric analysis (GA). Next, mortars with a ratio of 75% PC and 25% mordenite were prepared to determine their initial and final setting times, consistency and density. Continuing, the density, weight and compressive strength of the specimens were determined at 2, 7, 28, 90 and 365 days. Finally, the specimens were studied using SEM, XRD and XRF. The results of the study of the mordenite sample showed a complex constitution where the major mineral component is mordenite, and to a lesser degree smectite (montmorillonite), halloysite, illite, mica, quartz, plagioclase and feldspar, in addition to altered volcanic glass. Tests with fresh cement/mordenite mortar (CMM) showed an initial setting time of 320 min and a final setting time of 420 min, much longer than the 212–310 min of portland cement mortar (PCM). It was established that the consistency of the cement/mordenite mortar (CMM) was greater than that of the PCM. The results of the density study showed that the CMM has a lower density than the PCM. On the other hand, the density of cement/mordenite specimens (CMS) was lower than that of portland cement specimens (PCS). The CMS compressive strength studies showed a significant increase from 18.2 MPa, at 2 days, to 72 MPa, at 365 days, with better strength than PCS at 28 and 365 days, respectively. XRD, XRF and SEM studies conducted on CMS showed a good development of primary and secondary tobermorite, the latter formed at the expense of portlandite; also, ettringite developed normally. This work proves that the partial replacement of PC by mordenite does not have a negative effect on the increase in the mechanical strength of CMS. It indicates that the presence of mordenite inhibits the spontaneous hydration of C3A and controls the anomalous formation of ettringite (Ett). All this, together with the mechanical strength reported, indicates that mordenite has a deep and positive influence on the evolution of the mortar setting and is an efficient pozzolan, meaning it can be used in the manufacture of mortars and highly resistant pozzolanic cement, with low hydration heat, low density, stability in extremely aggressive places and a low impact on the environment.
Highlights
According to the X-ray diffraction (XRD) analysis, the investigated sample is mainly composed of mordenite
Comparison of the angular positions of the main peaks in the sample highlights some displacement compared to the models of Treacy and Higgins [48], which proves that the sample analysed is not monomineral; that is to say, mordenite is spatially associated with other complex phases that alter the reflection of its peaks during analysis
In the fresh cement/mordenite mortar (FCMM) the initial and final times of settings varied between 320–420 min, respectively, while for the fresh portland cement mortar (FPCM) it was 212–310 min, respectively (Figure 9). These results found that the effect produced on mortars was due to the pozzolanic character of mordenite which manifested as an alteration of the setting process in the early curing stages, as was mentioned before by Bilim [15]
Summary
The mixture of zeolite with cement in the presence of water creates more reaction stable products, with hydraulic properties, such as portlandite and tobermorite [20] These mineral phases are formed by a combination of other anhydrous phases present in the original chemical composition of portland cement. Portland cement mixes with pozzolans have high mechanical strength, durability and low reactivity against alkalis [24] These mixtures have been successfully used in the manufacture of seawater-resistant concretes, and in structures built in soils composed of calcium and magnesium sulphates. The extensive knowledge of the properties of natural zeolites depicts their advantage over other non-metallic natural raw materials, due to low extraction and processing costs, easy access to deposits, versatility and low environmental impact [28]. Sedaghatdoost et al [31]
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