Geopolymers are zeolites like structures based on hydrated aluminosilicates units of SiO4 and AlO4. These units, known as poly(sialate), poly(sialate)-siloxo or poly(sialate)-disiloxo are chemically balanced by the group I cations of K+, Li+, or Na+. Simultaneously, the chemical reaction of formation, known as geopolymerization, governs the orientation of the unit, generating mesoporous structures. Multiple methods can be used for pore structure and porosity characterization. Among them, nuclear magnetic resonance (NMR) relaxometry allows the detection of the porous structure in a completely nonperturbative manner. NMR relaxometry may be used to monitor the relaxation of protons belonging to the liquid molecules confined inside the porous structure and, thus, to get access to the pore size distribution. This monitoring can take place even during the polymerization process. The present study implements transverse relaxation measurements to monitor the influence introduced by the curing time on the residual liquid phase of geopolymers prepared with two different types of reinforcing particles. According to our results, the obtained geopolymers contain three types of pores formed by the arrangement of the OH− and Si groups (Si-OH), Si-O-Si groups, Si-O-Al groups, and Si-O rings. After 48 days, the samples cured for 8 h show a high percentage of all three types of pores, however, by increasing the curing time and the percentage of reinforcing particle, the percent of pores decrease, especially, the gel pores.

Global industrialization generates large amount of waste which strongly affects the depositing areas and the living creatures from the surroundings. In the same time, the construction sector meets an exponential development process, resulting in materials and construction areas increase. Therefore, the need of new materials was felt worldwide. One solution that knew a rapid development, especially in this sector, was to obtain new eco-friendly materials through a mechanism called geopolymerization. True this powerful chemical reaction between a waste, rich in aluminum and silicon, and a strong alkaline solution, a tetragonal structure of Al-O-Si is obtained that possess properties comparable to those of Portland cement-based concrete. In the present paper the effect of aggregates on local fly ash based geopolymers is analyzed from the structure and mechanical properties point of view. According to this study, the aggregates strongly influence the density, compression strength and flexural strength at any age of samples.

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The present work investigates the effect of freeze–thaw cycles on the porosity of three mixtures of road concrete containing blast furnace slag in comparison with two mixtures made with conventional materials. The main technique used in our investigations is nuclear magnetic resonance (NMR) relaxometry. This permitted the extraction of information with respect to the freeze–thaw effect on pore-size distribution, which influences both the mechanical strength and the molecular transport through the material. Moreover, by using this technique, the structure of the air voids was analyzed for the entire pore system in the cement paste and the aggregate particles. The samples under study were first dried in a vacuum oven and then saturated with water or cyclohexane where the distribution of the transverse relaxation times of the protons was recorded. The NMR relaxation measurements were performed on samples extracted from specimens maintained at 300 freeze–thaw cycles and on control samples extracted from specimens kept in water during the freeze–thaw period. Scanning Electron Microscopy (SEM) was used to analyze the microstructure of concrete samples in order to obtain information about the pore sizes and the distance between them. The results from the NMR relaxation measurements were consistent with those obtained by using standard techniques for determining the porosity and the freeze–thaw resistances. The investigations made it possible to establish the optimal composition of blast furnace slag that can be incorporated into road concrete compositions. This non-invasive technique can also complete standard techniques for assessing the porosity and the progress of internal cracks during the freeze–thaw test.

This paper presents an experimental study, which has been lacking to date, into the properties and applications of waste glass–plastic cementitious (WGPC) composites incorporating recycled aggregates as a full replacement of natural aggregates, with direct application in highly eco-efficient construction components. Detailed experimental assessments of the fresh properties, strength and durability characteristics of such composites are undertaken. Particular focus is given to the mix rationale and optimisation process as well as possible routes of exploitation of such materials in construction elements. The experimental assessments showed that such composite materials meet the strength and durability criteria for direct application in practice. The best balance in terms of strength and workability was achieved for a waste glass-to-plastic aggregate ratio of 92/8. The presence of relatively large amounts of recycled waste glass particles with small sizes acted as secondary hydration products and contributed to achieving an adequate strength of the material. Besides a lower unit weight and superior thermal properties compared with those of conventional concrete, WGPC components have shown a reliable behaviour under vehicle impact loading and potential wider application in sustainable non-structural construction applications.

In order to streamline the mixes of concrete with powder waste glass as small as < 0.250 mm, a postdoctoral program objective was to test the activity rate of its pozzoolanic reaction, through various methods and by comparing it with other powders reactions in a standardized cement composition. The first method was to determine the compressive strength of cement mortars, partially substituted by glass powder, silica fume, ash and clay. The second method was determining the chemical composition of the powder with fluorescence X-ray, XRF type. The third method, was based on fragments of mortar studied and subjected to microscopic observations – SEM determination (scanning electron microscopy) to investigate the microstructure of the raw material.

The rate of recycling and recovery of construction and demolition waste for the year 2020 is set at 70%. Currently in Romania, the waste recovery level is far below the set value, the collected waste is mostly disposed of by storage in landfills, without any other recovery or reuse. This paper presents practices in recycling of waste obtained from the construction of new buildings and demolition of existing buildings, with the potential of recovering large amounts of construction waste as filling material for road infrastructure or for heavy loaded industrial floors as well as possible other applications for using construction waste to substitute natural resources in concrete composition, obtaining material embedding waste with low energy consumption. The presented solutions might lead to an important increase of the recycling and recovery percentages, contributing to the fulfilment of the targeted and recycling, recovery and reuse rate. The viability of the possible applications is demonstrated with practical examples.

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