The impact of natural and synthetic zeolite when used in cementitious based systems

Abstract

The production of Portland cement, the most commonly used binding material in the construction and maintenance industry, is one of the principle carbon dioxide emission contributors. Indeed, up to 85% of the cement quantity produced is discharged into the atmosphere. As a result, efforts are being made to introduce new and advanced alternative construction materials to combat this adversity. Despite the recent introduction of new advanced materials such as polymer rubbers and alternative mineral sands, the overall percentage emission of carbon dioxide has not decreased. Improvement of cement mortar characteristics and the reduction of carbon emissions is of keen interest to researchers and industry experts in the field of construction materials engineering. Interestingly in the literature, zeolite minerals have the ability to absorb carbon dioxide and thus aid in reducing the concentration levels present in the atmosphere. Zeolites are very stable solids that are resistant to environmental conditions that challenge many other materials. They possess high melting points and can exhibit resistance to temperatures exceeding 1000°C. They can also resist high pressure, do not dissolve in water or inorganic solvents and their unreactive nature means that they exhibit no harmful environmental impacts. I believe that this makes them an ideal investigative compound to consider in terms of being adopted as a cement replacement in construction material. Zeolites have been used as a supplementary cementitious material in the construction industry and both natural and synthetic zeolites have shown interesting properties as mineral additions, notably increased compressive strength, resistance to sulphate attack and favourable leaching properties. However, there has been minimal research carried out on synthetic zeolites in this area in contrast to the abundance of natural zeolite study and notably research considering using zeolites as replacements for rather than in addition to cement. In this research programme, synthetic and natural zeolites were used to partially replace cement in mortar samples. Synthetic zeolites 3A, 4A and 13X were used to replace 5, 10 and 15% of the total cement mass in the mortar specimens with chabazite, mordenite, natrolite and philipsite chosen as a selection of natural zeolites. Ordinary Portland cement was used with a water-cement ratio of 0.40 and a sand-cement ratio of 1:3. All specimens were water-cured at 20°C before a suite of laboratory tests were performed, comprising of; specific gravity, ultrasonic pulse velocity, compressive strength testing, scanning electron microscopy, x-ray diffraction and Fourier transform infrared spectroscopy. All test results were determined at ages of two, seven, twenty-eight and seventy curing days. The research study demonstrated that mortar samples produced with zeolite incorporation as a replacement of cement demonstrated comparatively good engineering and chemical compositional properties when compared to control mixes. Encouraging data was recorded namely for the utilisation of mordenite and philipsite zeolite types, in that the zeolites demonstrated increased compressive strength in comparison to the control mortar as well as having decreased density and increased compactness. Notably, mordenite and philipsite can be utilised as a way of decreasing the cement content needed in a given mortar mix, indeed replacement of cement at 10 and 15% both produced increased compressive strength recordings when compared to both the control and synthetic zeolite incorporated samples.