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The development of cracks is a regular phenomenon that causes water and various chemicals to seep into the structure reducing the strength and longevity of the building. The intrusion of external materials might affect the reinforcements when exposed to moisture and CO2 exposure, degrading the structure. Regular maintenance and treatments are needed to fix the cracks and maintain the structure. Research is in progress identifying solutions to these issues with active and self-processes in concrete which aids in repairing the cracks by generating calcium carbonate (CaCO3) particles which could seal the porosity of concrete and micro-cracks. Various bacteria like Bacillus pasteurii, Bacillus subtilis, Bacillus cohnii and Bacillus sphaericus are chosen for the crack sealing treatment as those bacteria could survive in an alkaline medium. Distinct species of bacteria have various growth conditions. Bacterial self-healing treatments were situated in an environment containing various minerals and chemicals at a constant temperature and for a specific amount of time to develop healing properties. This paper investigates the different experimental works studied on self-healing processes in large concrete samples with different sizes and materials. Studies revealed that bacteria enhanced the systemic toughness, flow ability, durability, and flexural modulus of normal concrete. This paper also investigates the different mathematical formulations established to examine the stress-strain behaviour of bacterium, which has been utilized to increase the strength of concrete.

In this paper, an improved method of sand and mud content detection for concrete is proposed, and a set of sand and mud content detection device for concrete is designed. In this paper, a concrete gas content meter and a bubble parameter analysis system were used to study the effect of sand clay content on the gas content of commercial concrete, the loss rate of gas content in warp time, the bubble spacing coefficient and the distribution of hardened appearance pores. The pore structure test shows that the increase of mud content will appropriately reduce the proportion of harmless pores in machine-made sand concrete, and play a role in refining the pore structure in machine-made sand concrete. By using PLC controller and automatic detection device of liquid level and turbidity, the problems of complicated operation, inconvenient carrying and poor repeatability of test data are solved. It reduces the influence of human operation error and improves the accuracy of test data.

In this paper are presented different approaches of microbiological type, on the concrete matrix, that has the ability to self-healing the micro-cracks in their early phase. Although the prevention of cracks in the concrete structure is not possible, there are many types of techniques that will lead to self-sealing. Thereby we can say the cracks represent the biggest enemy of the elements in the constructions, and if they are not observed and treated in the early phase, they can create real dangers, both for the constructions and for the people. The micro-cracks appeared in the concrete matrix are determined by a number of internal and / or external factors. The determination of the cause of the appearance of the micro-cracks is done by visual inspections and by direct measurements, using special equipment. The identification of the various biological compounds and their use in autonomous processes can represent a sustainable but also efficient alternative on the costs of concrete production. From the researchers’ reports, the application of chemicals and polymers represents a source of risks for human health, plus the fact that these methods are viable in the short term.

Following the previous analytical studies performed with ATENA software for a series of RC moment resisting frame models, it were used in the pre-processing stage the stress-strain relation laws for concrete and steel reinforcement. These mathematical and graphical relations represent a necessity in the current conditions of numerical analysis and imply a correct knowledge of the deformation mode of the „reinforced concrete” which is a composite material. Thus, it is desired through this research paper the theoretical exposition of: equivalent uniaxial law for concrete, biaxial compressive failure and tensile failure consideration laws for concrete, bilinear with hardening law for steel reinforcement, cycling steel reinforcement model and steel reinforcement bond model. Finally, it will be possible to validate the correctness of the analytical RC frame systems through the experimental results of the optimal RC frame model after seismic platform testing.

This paper deals with the carbonation of concrete crack walls before and after healing in comparison to the carbonation of the bulk of the concrete. Natural carbonation tests were carried out on 50 MPa concrete. Disks with 50 mm thickness and 100 mm diameter were tested. A splitting test was applied to generate the crack. Different crack widths were tested, narrow crack widths below 75μm, and wide crack widths, between 75-175μm. The self-healing effect was studied after immersion for 4 months in water. Natural carbonation was carried out at 55±5 %RH 20±3°C for 6, 9 and 12 months. The carbonation front was assessed after splitting and opening the crack walls. The results show the effect of the crack width, crack length and autogenous healing that affect the progression of carbonation in the crack walls. The carbonation in the crack wall is at least twice that of the concrete. Crack widths larger than 75μm carbonate faster. Autogenous healing of the narrow cracks can reduce the carbonation front at the crack walls with compare to the unhealed narrow; however, no improvement was observed in limiting the carbonation front in the crack walls of healed wide cracks.

The concept of self-healing concrete is becoming more necessary as sustainability in construction is more desirable. Amongst the current solutions in this technology are autogenous, chemical, and bacterial self-healing. It is paramount that secondary raw materials be used in the production of selfhealing concrete as a form of a sustainable solution. Therefore, in this paper, the admixture “Betocrete-CP-360-WP”, which is a crystallizing waterproofing admixture with hydrophobic effect and is 100% recyclable, has been used and its effect on the physical, chemical, and mechanical properties of concrete, as well as selfhealing capabilities of concrete, have been determined. According to the obtained results, the crystalline additive “Betocrete-CP-360-WP” has no effect on density and slightly increases the amount of entrained air in the concrete mix. However, it does decrease the workability of the concrete mixture which could prove problematic in transportation to the construction site or in concreting in general. Also, with the crystalline admixture in the concrete mix, a 60% reduction in concrete compressive strength after one day of hardening has been estimated, but after 7 and 28 days, the strength attained is within the ranges of the control samples. In addition, concrete containing Betocrete-CP360-WP was 30% less water permeable as compared to control samples. The self-healing efficiency of the concrete was determined by a water flow test through a formed crack (approximately 0.35 mm wide). This was done by gluing a plastic pipe to the top of the cracked concrete specimens and maintaining a constant pressure of the water in the pipe. The experiment was continued for 28 days, and the crack self-healing efficiency of the concrete was calculated from the differences in the amount of water passed through the crack before healing and after 7, 14, 21 and 28 days of the healing process. After 28 days of the water flow test, the cracks in the concrete with the crystalline admixture and recycled concrete dust were completely healed, while the control specimens were not.

The paper presents experimental research performed on fiber reinforced concrete slabs. For the preparation of the concrete elements, three different dosages of polypropylene fibers were used. The size of the specimens and the test methodology were established according to the SR EN 14488-5 - Testing sprayed concrete. Part 5: Determination of energy absorption capacity of fiber reinforced slab specimens. The slabs were tested in the Central Laboratory of the Faculty of Civil Engineering, Cluj-Napoca, using a flexural frame and the Advantest 9 console, capable of applying load in displacement control. Using the area under the load-displacement diagram, the energy absorption capacity of the fiber reinforced slabs was determined, at the age of 28 days.

Partial substitution of the Ordinary Portland Cement (OPC) with mineral admixtures is an acknowledged procedure to build with concrete of low environmental impact. The identification of the basic criteria for an ecological construction product is correlated with the fabrication process of the traditional cement to obtain the necessary technological adjustments for new cements based on specific study and analysis. The paper presents the recent research of a new generation of cements, the eco-friendly cements, and the domain of use where OPC can be totally replaced, at superior working parameters.

When assessing the quality of concrete on site, it is necessary to base the interpretation on reliable and representative test results. Generally, core tests are the most reliable and effective method for assessing the quality of concrete. Unfortunately, this type of testing is expensive and time consuming and only a limited number of cores can be carried out in practice. Non-destructive tests (NDT) can be used to overcome these drawbacks. The most popular and widely used NDT methods for assessing concrete strength are rebound hammer (RH) and the ultrasonic pulse velocity (UPV). The use of these methods provide unreliable predictions unless their results are correlated to destructive tests. A sufficient number of cores is needed to accurately predict the compressive strength of concrete. Recent researches have been carried out for identifying and optimizing the number of cores able to stabilize the calibration model on data from recent structures and from synthetic data. However, more case studies are needed to draw conclusions. In addition, the effect of the degradation of reinforced concrete elements on the number of cores needed for obtaining a reliable prediction needs to be investigated. In this paper, RH and UPV in conjunction with core tests are used to evaluate the concrete compressive strength in existing structures built in the 1970s and degraded mainly by steel corrosion. More than 234 elements were tested by RH and 86 elements by UPV. Also, 36 cores were drilled and tested under compression. A regression analysis is adopted to establish the correlations between NDT and strength measurements. The accuracy of the predictive assessment was evaluated using two indicators: the root mean square error (RMSE) and the coefficient of determination (r2). The results of this case study showed that seven to nine cores is the minimal number of cores that guarantees the improvement of concrete strength assessment by combined or single NDT methods.

When assessing the quality of concrete on site, it is necessary to base the interpretation on reliable and representative test results. Generally, core tests are the most reliable and effective method for assessing the quality of concrete. Unfortunately, this type of testing is expensive and time consuming and only a limited number of cores can be carried out in practice. Non-destructive tests (NDT) can be used to overcome these drawbacks. The most popular and widely used NDT methods for assessing concrete strength are rebound hammer (RH) and the ultrasonic pulse velocity (UPV). The use of these methods provide unreliable predictions unless their results are correlated to destructive tests. A sufficient number of cores is needed to accurately predict the compressive strength of concrete. Recent researches have been carried out for identifying and optimizing the number of cores able to stabilize the calibration model on data from recent structures and from synthetic data. However, more case studies are needed to draw conclusions. In addition, the effect of the degradation of reinforced concrete elements on the number of cores needed for obtaining a reliable prediction needs to be investigated. In this paper, RH and UPV in conjunction with core tests are used to evaluate the concrete compressive strength in existing structures built in the 1970s and degraded mainly by steel corrosion. More than 234 elements were tested by RH and 86 elements by UPV. Also, 36 cores were drilled and tested under compression. A regression analysis is adopted to establish the correlations between NDT and strength measurements. The accuracy of the predictive assessment was evaluated using two indicators: the root mean square error (RMSE) and the coefficient of determination (r2). The results of this case study showed that seven to nine cores is the minimal number of cores that guarantees the improvement of concrete strength assessment by combined or single NDT methods.

This paper approaches the problem of diagnosing the degradation and the safety estate in exploatation of the cylindrical tanks made out of pre-prestressed concrete, affected by execution errors, especially generated by the design non-observance stipulations, being suggested by a situation which hasn’t been signalized into the specialty literature from our country. The effectuated study aimed to evaluate the functional capacity of cylindrical tanks, being proposed an original way (methodology) of identifying the real loading level of the horizontal sections from the walls of the pre-prestressed cylindrical tanks with cables and which relies on an original grapho-analytical procedure. This way there were realized etalon-graphics for different types of tanks and their geometrical and technical characteristics which allow a soft evaluation of the nominal functioning capacity of the analysed objectives, by comparing the quantity of existing reinforcement with the need quantity.

Mechanical joining techniques are used in construction industry all over the world on a daily basis. A further method of joining has proven to be highly successful – adhesive bonding. Known for thousands of years, adhesive bonding has become as important as other joining techniques as a result of the pace of developments in recent years. In many areas, this bonding technology has become a key technology. Virtually, all solid materials can be connected with one another using adhesives. Although bonding fibre reinforced polymeric composites to the concrete substrate is a relatively simple technique, the proper installation of the fibre reinforced polymeric composites is essential to ensure the adequate performance of the hybrid system. Since the installation procedures differ from one system to another, appropriate specifications will be clearly presented. The paper will include requirements to provide a quality joint assembly, meaning the special pre-treatments of the concrete surface. The material to be bonded is cleaned and prepared so that adhesives can adhere better to them.

The cement and concrete industries are huge. What does this mean in terms of the environment? Concrete and other cementitious materials have both environmental advantages and disadvantages. This paper takes a look at how these materials are made, then reviews a number of environmental considerations relating to their production and use.

Fire safety regulations can have a major impact on many aspects of the overall design of a building, including layout, aesthetics, function, and cost. Rapid developments in modern building technology in the last decades often have resulted in unconventional structures and design solutions. Because the world is developed continuously, the physical size of buildings increases continually; there is a tendency to build large underground car parks, warehouses, and shopping complexes. As a result, we have a worldwide movement to replace prescriptive building codes with ones based on performance. The paper presents the basic principles for the designing process of reinforced concrete elements under fire.

Technology of concrete has been advanced recently to improve the properties of concrete. Utilization of ash as the substitute of cement or filler of concrete also indicates good result in compressive strength concrete in certain amount. Harnessing the bacteria for self-healing concrete has also been successfully performed in order to maintain the destruction of the concrete by itself. Past research indicated that bacteria can be beneficiary to improve the compressive strength, absorption, permeability, and so on. In this paper, Bacillus Altitudinis was extracted from the karst (source from the limestone mountain) and bred through liquid media to be impregnated inside the volcanic ash. The impregnated bacteria in volcanic ash were used as the filler to the concrete mixture with the proportion of filler varied from 1%, 1.5% and 2% to the weight of cement. Mechanical properties of the concrete specimen showed that the compressive strength reached its best when the filler proportion was 1.5%. The absorption referred analogously to the increment of compressive strength due to the success of filling the void inside the concrete. Based on compression test to all the concrete specimens, there was enhancement about 18% and the average absorption can be abated around 23%. Future research due to some drawbacks turning up is the need of developing another media for bacteria to live and making sure the exact amount of bacteria impregnated to the media so that the desired advance of concrete compressive strength can be acquired.

In this paper, the freeze-thaw performance of concrete using granulated blast-furnace slag (GBS) as fine aggregate was studied. According to the test method for slow freezing and thawing, degradation of mechanical properties about GBS concrete with 2 kinds W/B ratio and 3 kinds GBS replacement ratio were tested, and micromorphology of GBS concrete were analyzed by scanning electron microscopy (SEM). Furthermore, relations between degradation of mechanical properties and micromorphology about GBS concrete are discussed. Test results show that: after freeze-thaw cycles, the relative compressive strength of GBS concrete is greater than ordinary river sand concrete, and the GBS concrete will produce more mutual interlacing fibrous and flowers from crystal, the growth of these crystals can improve the compressive strength of concrete. Therefore, the frost resistance of GBS concrete is little better than ordinary river sand concrete.