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The current study focusses on possibilities of valorizing the spent Garnets produced by waterjet cutting operations, by integrating it in construction materials, as raw material substitution. The waterjet material processing by the use of abrasive Garnets is also in continuous expansion, due to its versatility and quality performance, this also generating large quantities of waste: the initial waterjet sludge collected in recipients during the process of material processes, dries and gradually turns into waste dumps, usually randomly deserted, especially in countries lacking specific legislation ad applicability methods. Therefore, converting the spent Garnets into filler replacement into concrete mixes could represent a huge benefit for both industries: constructions, lacking fillers, as sand replacement in concrete mix, possibly improving the material durability as well, and also material processing industry, by solving the waste generation problem. The initial, preliminary results, favorable to the use of spent Garnets in concrete and mortars, are confirmed by supplementary, international research, determining local interest for such valorization of the Garnet waste. This paper presents the latest research achievements in this topic and also, the derived possibilities regarding multidisciplinary studies which could determine the applicability of the waste in the construction industry, in Romania.

In the evaluation of an existing reinforced concrete structure, a fundamental issue is determining the concrete compressive strength as accurately as possible. This process can be conducted by using destructive and non-destructive methods. The destructive method presumes a limited number of cores extracted from the concrete structure. A higher number of cores would affect the structural safety and is time and resource consuming. Therefore, the conclusions drawn using exclusively this method can also generate errors in correctly estimating the load bearing capacity of a structure, thus leading to the possibility of implementing deficient measures in order to ensure a structural safety. Data obtained via non-destructive methods are more comprehensive. Due to their non-destructive nature, there are no limitations regarding the number of elements investigated and are fast in delivering results. One of the main concerns of researchers in this field is developing a direct relationship between the measured indicators through non-destructive testing (NDT) methods and concrete compressive strength. Over the years different equations with different mathematical structure (linear, polynomial, power, exponential and logarithmic) were developed with the main purpose of delivering fast and accurate results concerning concrete compressive strength by the means of NDT. The aim of this paper is to validate some of the most important prediction models using an original set of data. The database consists in a number of 96 concrete cores that were subjected to Ultrasonic Pulse Velocity (UPV) and Schmidt Rebound Hammer (SRH) testing. The accuracy of the results was determined by using two statistical parameters the mean absolute error (MAE) and mean absolute percentage error (MAPE). The proposed equations have been analyzed in terms of prediction and dispersion of values. It was noticed that some of the formulations predict values that are higher than the ones obtained destructively, others provide a larger dissipation of values, while some equations deliver a compact distribution of results with higher rate in terms of accuracy. This study proposes a data validation of some of the most popular empirical equations, used for the estimation of the concrete compressive strength, elaborated through the years, using a new set of data.

The constant need for recycling, waste prevention and general environmental protection represent the new directive approaches imposed by the geo-political, industrial and environmental context, at the regional, European and global level. Ensuring the environmental protection and reducing the natural resources consumption represent general purposes of the sustainable development and also considerations to implement the Circular Economy Model [1]. The present study is developed with respect to the previously mentioned principles: the waterjet cutting operations by the use of abrasive GARNETs for quality, speed and accuracy gain, are in continuous expansion, generating proportionally increasing wastes, which could be valorized by innovatively integrating them in advanced cementitious materials for the construction industry. The international research regarding the use of abrasive waterjet Garnet wastes as raw material for construction industry are at incipient stage and quite limited, but preliminary results are promising. Further studies are presently developed, considering the potential benefits and also the reduced toxicity degree of abrasive Garnet wastes. This paper offers a general overview concerning the recent studies performed in the topic of efficient use of abrasive Garnet wastes in different building materials. Supplementary, further research, both theoretical and experimental is considered, for developing green, advanced, high performance cement-based materials by using the abrasive waterjet Garnet wastes, mainly as fine grain addition or replacement in the composites.

Developing a non-destructive method which delivers fast, accurate and non-invasive results regarding the concrete compressive strength, is an important issue, currently investigated by many researchers all over the world. Different methodologies, like using the simple non-destructive testing (NDT) or the fusion of different techniques approach, were taken into consideration in order to find the optimal, most suitable method. The purpose of this paper is to present a new approach in this direction. The methodology consists in predicting the concrete compressive strength through ultrasonic testing, for non-destructive determination of the dynamic and static moduli of elasticity. One important, basic assumption of the proposed methodology considers values provided by technical literature for concrete dynamic Poisson’s coefficient. The air-dry density was experimentally determined on concrete cores. The dynamic modulus of elasticity was also experimentally determined by using the ultrasonic pulse velocity (UPV) method on concrete cores. Further on, the static modulus of elasticity and the concrete compressive strength can be mathematically calculated, by using the previously mentioned parameters. The experimental procedures were performed on concrete specimens, namely concrete cores extracted from the raft foundation of a multistorey building; initially they were subjected to the specific NDT, namely ultrasonic testing, and the validation of the results and the proposed methodology derives from the destructive testing of the specimens. The destructive testing is generally recognized as the most trustable method. The precision of the proposed method, established with respect to the destructive testing, revealed a high level of confidence, exceeding 90% (as mean value). It was noticed that even the cores with compressive strength outside of mean range interval (minimum and maximum values) presented high rate of precision, not influencing the overall result. The high rate of accuracy makes this method a suitable research background for further investigations, in order to establish a reliable NDT methodology which could substitute the very invasive and less convenient, destructive method.

This research is focused on a characterization of Engineered Cementitious Composites (ECC) with self- healing properties used in infrastructure. Because the demand for concrete increase, developing a material that can regain loss of performance due to cracking in highly desirable. Many challenges could be solved by developing a concrete that is capable of self-healing. The purpose of this paper is to present the advantages of using new local materials and could represent, sustainable solutions for the infrastructure industry, also as repair solutions, where ECCs could be competitive for their performances and costs for a long term.

Developing non-destructive methods (NDT) that can deliver faster and more accurate results is an objective pursued by many researchers. The purpose of this paper is to present a new approach in predicting the concrete compressive strength through means of ultrasonic testing for non-destructive determination of the dynamic and static modulus of elasticity. For this study, the dynamic Poisson’s coefficient was assigned values provided by technical literature. Using ultra-sonic pulse velocity (UPV) the apparent density and the dynamic modulus of elasticity were determined. The viability of the theoretical approach proposed by Salman, used for the air-dry density determination (predicted density), was experimentally confirmed (measured density). The calculated accuracy of the Salman method ranged between 98 and 99% for all the four groups of specimens used in the study. Furthermore, the static modulus of elasticity was deducted through a linear relationship between the two moduli of elasticity. Finally, the concrete compressive strength was mathematically determined by using the previously mentioned parameters. The accuracy of the proposed method for concrete compressive strength assessment ranged between 92 and 94%. The precision was established with respect to the destructive testing of concrete cores. For this research, the experimental part was performed on concrete cores extracted from different elements of different structures and divided into four distinct groups. The high rate of accuracy in predicting the concrete compressive strength, provided by this study, exceeds 90% with respect to the reference, and makes this method suitable for further investigations related to both the optimization of the procedure and = the domain of applicability (in terms of structural aspects and concrete mix design, environmental conditions, etc.).

This work is an interdisciplinary study which combines reinforced concrete construction domain with analytical techniques, specific for electrochemistry. This paper presents a synthesis of research in this field and own experimental results. The aim of the research was to highlight, both in terms of thermodynamic and kinetic, the enhanced corrosion resistance hot dip galvanized reinforcement embedded in concrete, compared with the steel reinforcement anticorrosive unprotected. The experimental researches were conducted during the concrete curing. In parallel, it was analyzed the reinforcement corrosion, in embedding conditions in a concrete with Cl − content, artificially induced. The experimental results showed the efficiency of the corrosion protection obtained through galvanizing: the slowing of the corrosion process and the endurance probability of a higher chlorine concentrations till to the initiation of corrosion.

SH-FECM (Fibre Engineered Cementitious Materials with Self-Healing capacity), developed at NIRD “URBAN-INCERC” Cluj-Napoca Branch in the last five years, are consistently based on Engineered Cementitious Composites (ECCs) concept, elaborated in the early nineties at Michigan University (USA). They all represent a cement-based typology of dispersed reinforcement composites able to develop high deformability by the means of multiple cracking pattern under loading, leading to a cumulative set of valuable material features: metal like behaviour when subjected to loads, brittle failure prevention, increased self-healing potential via the compositional design, etc. The process of development and constant improvement of the SH-FECMs represents a long term theoretical and experimental approach, aiming to establish the optimum raw materials (mostly locally available) compatibility within the cementitious matrix so that the composites would present superior performance under comparative evaluation. This paper presents the first results, evaluated as positive for both, fresh and hardened state materials, regarding the inclusion of Slurry Lime (SL) addition as replacement of the initial lime powder addition (L) in the material composition. The long-term effects are on ongoing investigation, but the initial results are clearly promising, starting from a better fresh state aspect and evaluating for faster setting time and improved early age mechanical behaviour. The beneficial effects are also in terms of economic and ecological aspects, considering that the used lime slurry (SL) addition represents an actual waste resulted from a local, natural stone processing factory. Its use as direct addition in the SH-FECMs mixtures could represent an efficient recycling and waste prevention action, with long term beneficial potential, in terms of Circular Economy principles.

Development of Fibre Engineered Cementitious Materials with Self-Healing Capacity (SH-FECM) was an important goal of the recent research programmes conducted in NIRD “URBAN-INCERC” Cluj-Napoca Branch. Several theoretical and experimental studies were performed in order to improve the composites, considering both, fresh and hardened state properties and also the performance as filling material of the narrow spaces at the beam to column interface within the Hybrid spatial joint model [1]. Present studies are focused in optimising the already developed mixtures regarding several aspects: the self-compacting behaviour of the fresh composites, considering the increased risk of “balling” effect when using 2% (of volume) of polymeric fibres as disperse reinforcement of the cementitious matrix, bleeding control during and after the mixes sequences by using supplementary powder addition, evaluation of the mixes when using a combination of two distinct types of polypropylene fibres, and development of controlled multiple cracks under loading, etc. The present paper offers the first results regarding the performance of the cement based composites, namely the fresh state self-compacting effect and also the flexural and compressive strengths at 7 and 28 days of age. Initial conclusions when replacing the traditional silica sand as aggregate of initial mixes with regular sand (0/1 mm fraction) are also considered. The Self-Healing potential of the mixes will be evaluated further on, ensuring the complete range of characteristics related to durability improving, repair and maintenance cost reduction and superior structural performance, in the context of the expected features of the sustainable development.

As concrete demand is constantly increasing in recent years and also considering that cement production is both a consumer of natural resources and a source of carbon dioxide release into the atmosphere, there have been worldwide investigations into green alternatives for making concrete environmentally friendlier and simultaneously to satisfy the development of infrastructure facilities. The use of fly ash as a component of cementitious binders is not new but when considering the specific case of alkaline activation and fly ash representing the only source for the binder formation, it necessitates a more complete understanding of its specific reactions during the alkaline activation process. Since the fly ash varies dramatically, not only from one source to another, but also from one batch to another even when provided by the same power plant, its chemistry in obtaining alkali-activated materials during the geopolymerisation process and the final mechanical properties are considered crucial for the performance of geopolymer concrete. This paper will provide a review of the experimental results concerning the physical and mechanical evaluation of the alkali-activated fly ash-based geopolymer materials, developed with different types of fly ash, for a better understanding of geopolymer concrete production control.

Fibre Engineered Cementitious Materials (FECM) represent composites with similar overall performance as Engineered Cementitious Composites (ECC), namely developing strain hardening behaviour under loading, which generates the material capacity of high deformability. The pattern of multiple microcracks successively developed under increasing loading is proved to be the key of material self-consolidating potential and ability to support loads after the first crack occurrence. The matrix to fibre compatibility is considered to be one essential parameter controlling the multiple micro-cracking pattern (MC) and consequently, the strain hardening effect in the material. Factors like fibre type and reinforcement percent in the mixture represent sensitive variables, with major influence for matrix to fibre compatibility and overall performance of the composite. Cement based materials, whose compositional heterogeneity traditionally represents a lack in their regular usage, can be valorised and designed to produce the width controlled cracking typology, beneficial for material behaviour. This paper presents an experimental study on the fibre to matrix compatibility effect in the FECM design and producing process. Several types of dispersed reinforcing typologies for FECM development are experimentally tested and analysed. The results confirm the importance of matrix to fibre compatibility in enhancing superior material performance: physical, mechanical and even durability (Self-Healing potential evaluation).

Contemporary urban architecture faces two important issues: degradation of buildings, caused by exposure to various environmental factors (air and water pollution, mainly generated by the fuels combustion used for transport and heating) and also the costs for repair, cleaning and maintenance of the buildings facades. Regarding the last mentioned aspects, recent research led to development of materials with self-cleaning potential and consequently pollution reduction. Self-cleaning concrete represents a state-of-the-art material with photocatalytic properties generated by the addition in its composition of nanomaterials like TiO2. Already known for its intrinsic photocatalytic character, TiO2 has the ability to catalyse the decomposition of organic substances like grease and dirt, facilitating their quick removal only by rainwater action. Therefore, a building façade made of TiO2-SiO2-containing material develops substantial savings regarding maintenance costs, water consumption and less detergents contamination due to its intrinsic super hydrophilic effect of the surface in the presence of UV radiation, leading to easy dirt removal when water reaches it. The aim of present paper is presenting the latest stage of worldwide research regarding the obtaining of self-cleaning concrete and also the possibility of adapting the concept to the actual Romanian architecture needs, as a sustainable solution for urban pollution reduction.

As the demand for concrete and the needs to satisfy development of infrastructure facilities increase, it is essential to find alternatives to create environment-friendly concrete. The particular procedure of alkaline activation of fly ash - in which ash resulting from a power plant is combined with a specific alkaline activator in order to create a solid material, then dried at a certain temperature - opened new opportunities for this new material to get attention worldwide. In order to obtain a material with similar properties of ordinary Portland cement concrete and to obtain desirable compressive strengths, the parameters that affect this type of binders should be fully understood. The aim of this paper is to study the main parameters affecting the mechanical strength of the fly ash-based geopolymer paste and their interactions. Parameters such as molarity of sodium hydroxide (from 8M to 12M) and alkaline activators ratio (from 0,5 to 2,5) were analysed to observe how they affect the mechanical properties of the geopolymer paste. Experimental results show that the compressive strength of the fly ash-based geopolymer paste produced using Romanian local raw materials increases with the increase of the concentration of sodium hydroxide and higher ratios of Na2SiO3/NaOH solution.

Alkaline activation of fly ash is a particular procedure in which ash resulting from a power plant combined with a specific alkaline activator creates a solid material when dried at a certain temperature. In order to obtain desirable compressive strengths, the mix design of fly ash based geopolymer pastes should be explored comprehensively. To determine the preliminary compressive strength for fly ash based geopolymer paste using Romanian material source, various ratios of Na2SiO3 solution/ NaOH solution were produced, keeping the fly ash/alkaline activator ratio constant. All the mixes were then cured at 70 °C for 24 hours and tested at 2 and 7 days, respectively. The aim of this paper is to present the preliminary compressive strength results for producing fly ash based geopolymer paste using Romanian material sources, the effect of alkaline activators ratio on the compressive strength and studying the directions for future research.