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.).

The main objective of the proposed research is to preserve the vernacular urban heritage of Romania by identifying realistic and innovative solutions for the conceptual and applied capitalization of the traditional technologies used in creating living spaces. This can be achieved by using modern methods, techniques, and tools (such as specific design methods and detailing, material mix design, specific material parameters, etc.) to redesign traditional Romanian housing entities, utilising existing construction materials and techniques predominantly of rural origin, empirically validated over the centuries, and reformatting them with modern scientific knowledge to generate a new model that is valid and compatible with current safety, aesthetic, and quality requirements. Earthen buildings, whether vernacular or constructed with qualified personnel such as craftsmen and traditional masons, use different techniques and construction technologies (rammed and poured, load-bearing walls, adobe bricks, mixed wood-earth structures, etc.) and were developed differently across the Romanian territory, depending on the climatic and relief zoning. By optimising these techniques and technologies, identifying their vulnerabilities and corresponding engineering solutions to counter them, and establishing pertinent fields of applicability in direct relation to their physical, mechanical, and durability characteristics and their evaluated bearing capacity, the conservation of the Romanian traditional housing legacy can be achieved. The opportunity of the proposed research is clearly connected to the current context of almost half of the Romanian population leaving for rural areas, including residential buildings made of earth. Supplementary, traditional building materials, like earth, clay, wood, etc., are based on primary natural resources, and they will generate ecologic housing concepts with a high degree of eco-efficiency in terms of use/re-use and recyclability, energy saving, and the health of the living space, in accordance with the general drive for resource savings and Circular Economy implementation in all fields, including the construction industry.

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.

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 present research aims to simultaneously have positive contribution in two environmental issues identified on global scale, but also locally, in Romania: the waste generation due to industrial processes, on one hand, and on the other hand, the exhaustible natural resources constant increasing demand and consumption, in the construction industry as well. The use of abrasive waterjet (AWJ) sand in specific industries, for material processing purpose, represents an advantageous and efficient methodology, with increased domain of applicability and experiencing a significant development and improvement in the last years; still, besides the numerous benefits of the AWJ cutting and material processing techniques, they also generate collateral by-products, mostly converted into wastes: the abrasive materials (Garnet Sands) used during the AWJ cutting generate a sludge, generally unutilized and randomly deserted into damps (Spent Garnets, SG). In the same time, the construction industry and the corresponding mortar and concrete production segments, present accelerated growth, associated with global population fast increase (mainly in urban poles) and also with the industrial drive. The population growth and the industry expansion demand the corresponding infrastructure, civil, industrial, agrozootechnical, road and energetic, etc., leading to related request for building materials, concrete and natural resource consumption, like aggregates. This was the context which induced the idea of potentially valorizing the SG industrial by-products, generated by the local AWJ cutting industry, into construction materials, namely fine grain aggregates substitution in mortar and concrete. In order to evaluate the waste compatibility to a typical composition of cementitious material, a regular mortar was developed, considered the Reference (R) and further partial substitution of the usual sand was performed, by using the Spent Garnet wastes generated by two local companies. The substitution percentage was established in accordance to the previous studies in the topic, and ranged from 10 to 50% with respect to the sand quantity in the Reference mix. The mechanical performance of the mortars was analyzed at specific ages, in order to establish the viability of the substitution: 7day-testing, 14-day testing, 28 day-testing. The first results of the experimental study, focused on mechanical and physical characteristics of the mixes, are clearly encouraging, leading to the conclusion that SG by-products could be efficiently integrated in concrete and mortar mixes, as partial replacement of the regular sand; thus, the study opens the path to a sustainable, preventive solution for industrial waste generation and natural resources consumption as well. The potential use of SG as aggregate partial replacement in pavement eco-blocks is also considered, as future direction of research.

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.