Pozzolanic materials in the Mediterranean: A natural asset for cement blends

The Mediterranean region, with its rich geological tapestry and history of volcanic activity, is home to abundant natural pozzolanic materials. These materials, prized for their reactivity with calcium hydroxide and contribution to long-term strength and durability in cementitious systems, have long been integrated into construction practices, from Roman times to modern sustainable cement blends.

Pozzolans are predominantly volcanic in origin, and their presence in the Mediterranean correlates strongly with the region’s tectonic and volcanic history. Countries surrounding the Mediterranean Sea, including Italy, Greece, Turkey, and others in North Africa, host numerous deposits of pozzolanic materials in the form of volcanic ashes, tuffs, and pumicites.

The Italian peninsula, particularly around the Bay of Naples, is one of the most famous pozzolan-producing areas, historically supplying «Pulvis Puteolanus» used in Roman concrete. Pozzolanic tuffs from regions like Pozzuoli and volcanic ash from Vesuvius remain of interest due to their high silica and alumina content and fine particle morphology, which contribute to high pozzolanic reactivity.

In Greece, the islands of Santorini and Milos are rich in natural pozzolans. The Santorini earth, in particular, is known for its high reactive silica content and excellent hydraulic properties when mixed with lime or Portland cement. Turkish deposits also include a range of pozzolanic materials, particularly in western Anatolia, often found in rhyolitic and dacitic volcanic formations. 

Northern African countries, particularly Algeria and Tunisia, have notable deposits of volcanic tuffs and ashes with promising pozzolanic potential, although these are less extensively studied than European occurrences. Across the Mediterranean, the common denominator is the volcanic nature of the terrain, which offers a ready supply of suitable pozzolans.

Beyond the Mediterranean, the Canary Islands and Azores represent notable extensions of pozzolanic potential in the Atlantic. These islands are volcanic in origin, and their geomorphology features extensive pyroclastic deposits, pumices, and scoriae that exhibit pozzolanic activity.

The Canary Islands, particularly Tenerife and La Palma, have significant reserves of volcanic ashes and pumices. These materials are characterized by a high content of reactive amorphous silica and a favorable particle size distribution, enabling them to perform well in cementitious matrices. Their performance is comparable to traditional Mediterranean pozzolans and can be considered suitable for large-scale use in blended cements.

The Azores, especially São Miguel and Terceira, contain pozzolanic materials derived from trachytic and basaltic eruptions. These materials demonstrate moderate to high pozzolanic reactivity, though their heterogeneity may require careful processing or classification before use in standardized cement formulations. Nevertheless, their potential for regional use in sustainable construction is significant.

Not all volcanic materials are equal in pozzolanic performance. The most desirable pozzolans are those with a high content of reactive silica and alumina, low crystallinity, and favorable particle fineness. The reactivity of pozzolans is determined by their ability to react with calcium hydroxide to form additional cementitious compounds, notably calcium silicate hydrate (C-S-H), which contributes to strength and durability in cement-based materials.

Mediterranean and Atlantic pozzolans vary in composition and mineralogy, but several share common quality attributes. Many possess low levels of insoluble residues and alkalis, making them suitable for use in sulfate-resisting and alkali-silica reaction (ASR) mitigating cements. The fineness of natural pozzolans is often enhanced through grinding, increasing their surface area and reactivity.

Chemical analysis of representative Mediterranean pozzolans reveals that the most reactive materials exhibit silicon dioxide contents of over 60%, with total reactive oxides (SiO₂ + Al₂O₃ + Fe₂O₃) exceeding the 70% threshold typically required for classification as natural pozzolans under international standards such as ASTM C618 and EN 197-1.

With the global cement industry facing increasing pressure to reduce carbon emissions, pozzolanic materials offer a natural solution for clinker substitution. By partially replacing Portland cement clinker with natural pozzolans, it is possible to significantly reduce the carbon footprint of cement while enhancing long-term durability. The proximity of pozzolan sources to coastal cement production hubs in the Mediterranean enhances their strategic value. Short transport distances reduce costs and emissions associated with logistics. Furthermore, using locally available pozzolans supports circular economy principles and regional supply chains.

The Mediterranean region and its Atlantic extensions offer a wealth of high-quality natural pozzolanic materials, derived from their rich volcanic heritage. These materials possess strong chemical and mineralogical properties that make them well suited for use in sustainable cement and concrete formulations. The strategic distribution of pozzolans across Southern Europe, North Africa, and Atlantic islands such as the Canaries and Azores presents a compelling opportunity for the cement industry to embrace low-carbon alternatives using natural mineral resources. Continued research, classification, and responsible exploitation of these pozzolanic sources will be key to unlocking their full potential in advancing greener construction practices across the region.

Manousos Petrakakis, Mining Engineer, and Vassilis Lazaris, Business Specialist, are partners in MP Advisors, a greek consulting firm specialized in the raw materials and construction materials industry, supporting the European Green Deal. Both of them have over 35 years of professional experience within major multinational companies in the building materials and mining industry.

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