Electrical resistivity is an important physical property of concrete, directly related to the chloride-induced corrosion process. This paper analyses the surface resistivity (SR) and bulk resistivity (BR) of structural lightweight waste aggregate concrete (SLWAC). The studied concrete mixture contained waste material—red ceramics fine aggregate and artificial expanded clay coarse aggregate. Red ceramic is a frequent waste material remaining after the demolition of buildings or unsatisfactory building material production and is among the least used construction waste. Therefore, its use is desirable in terms of sustainability; in some cases, it can reliably replace the conventional aggregate in a concrete mixture. The relationship between SR and BR was determined in the case of standard specimens and mechanically damaged specimens (to 50% and 100% of ultimate strength capacity—USC). Two different instruments were utilised for the investigation—a 4-point Wenner probe meter and an RCON tester. The results of standard specimens support the theoretically derived correction ratio, but in the case of mechanically damaged specimens, the ratio is more scattered, which is related to the mechanical damage and the amount of fibre.
The presented research program is focused on the design of a structural lightweight fiber-reinforced concrete harnessing an internal curing process. Pre-soaked waste red ceramic fine aggregate and pre-soaked artificial clay expanded coarse aggregate were utilized for the creation of the mix. Copper-coated steel fiber was added to the mix by volume in amounts of 0.0%, 0.5%, 1.0%, and 1.5%. Test specimens in forms of cubes, cylinders, and beams were tested to specify the concrete characteristics. Such properties as consistency, compressive strength, splitting tensile strength, static and dynamic modulus of elasticity, flexural characteristics, and shear strength were of special interest. The achieved concrete can be classified as LC12/13. A strength class, according to fib Model Code, was also assigned to the concretes in question. The proposed method of preparation of concrete mix using only pre-soaked aggregate (with no extra water) proved to be feasible.is the creation of a concrete mixture which contains the already-mentioned pre-soaked aggregates, limited amount of cement (about 300 kg per 1 m 3 ) and different amount of steel fiber without using additional water. Determined material characteristics of the fresh mix and hardened concrete would be influenced solely by water trapped in both porous aggregates and the process of internal curing [3]. Using only pre-soaked aggregate and no extra water would significantly simplify the production process of lightweight concrete. The novelty of the conducted research program is fully associated with this issue.The suitability of lightweight concrete for construction applications is conducted by the needed properties: density, strength, and thermal conductivity. Nevertheless, other properties, such as workability, water absorption, drying shrinkage and moisture movement should also be considered. The porous structure of lightweight aggregates causes high and rapid water absorption during preparation of the fresh mix. Thus, if dry porous aggregate is used for the creation of a mixture, it rapidly absorbs free water, and the workability of the fresh concrete mix is significantly affected [2]. Although the saturation of aggregates can initially cause the increase of the concrete density, it improves the concrete's long-term maturation by slowly releasing water from pores. The internal curing process significantly influences the speed and quality of cement hydration. It leads to the enhancement of mechanical properties of hardened concrete and reduces autogenous shrinkage [3].An important aspect of the research program is to deepen the knowledge about the usage of waste red ceramic aggregate. The recycling and usage of waste material in the construction field have been discussed by many research groups [3][4][5][6][7][8][9][10][11], but in practice, it is still not very common to reuse the old material as a part of new concrete. However, to encourage extensive further usage, there is need to establish a standardization for waste aggregate concrete.
The paper presents a numerical calculation of the service life of concrete structures considering the effect of chlorides in the case of the material properties of structural lightweight waste aggregate concrete. Different amounts of fibres (0.0%, 1.0%, and 1.5%) and different values of compressive preloading (0%, 50%, and 100% of the ultimate strength capacity-USC) were considered. The subject of the research was the comparison of the influence of the constant diffusion coefficient and the time-dependent diffusion coefficient regarding the service life of the selected structure. Nine groups of material characteristics in combination with two numerical models are compared. A time-dependent diffusion coefficient and maturation coefficient, which were determined based on long-term monitoring (up to 461 days), were accepted for the numerical modelling. Thanks to time-dependent parameters, it is possible to observe the results of the theoretical service life of the structure and the influence of the mentioned factors. The analysed structure can be considered as the upper layer of an industrial floor in a chemical plant. It is important to determine the theoretical service life at which the structure shall be inspected or replaced. The results, in general, show that a higher amount of fibres reduces the service life as well as the preloading of the structure. An exception was a mixture with 1% of fibre loaded to 50% USC, which shows a lower diffusion coefficient than the specimens without preloading.
The article aims to observe durability parameters of red ceramic waste aggregate concrete based on a measured chloride profile by the standardized NT Build 443 method, and to compare the results to the values measured by a test based on electrical resistivity measurements. The parameters related to the chloride ion diffusion are investigated on the new type of concrete designed in the previous project, which contains waste material–red ceramics fine aggregate, and artificial expanded clay coarse aggregate. Ceramic materials contribute to the highest percentage of the construction and demolition wastes and, in most cases, this type of waste is disposed of in landfills. Significant factors limiting the use of the studied material are the unavailability of standards, avoidance of risk, and lack of knowledge and experience in using ceramic wastes for construction purposes. The obtained results of the studied mixture are compared to a reference concrete in terms of mechanical properties and durability parameters. The calculated diffusion coefficient is a crucial input parameter for modeling of the degradation process and the prediction of concrete durability; therefore, proper identification is of interest in order to allow for a broader application of ceramic waste aggregate-based concrete. The research showed unproportionality of results measured by the two methods in the case of waste aggregate concrete (60% difference in comparison with reference concrete), therefore it was proved that the electrical resistivity measurements need correlation of the resulting diffusion coefficient for proper modeling.
Probabilistic procedures considering the durability with respect to corrosion of reinforcement caused by aggressive substances are widely applied; however, they are based on narrow assumptions. The aspects need to be evaluated both in terms of the search for suitable application of the various experimental results and in terms of their impact on the result of the stochastic assessment itself. In this article, sensitivity analysis was used as an ideal tool to prove how input parameters affect the results of the evaluation, with consideration of different types of concrete (ordinary or self-compacting with and without fibres). These concretes may be used in aggressive environments, as an industrial floor or as a part of the load-bearing bridge structure. An example of a reinforced concrete bridge deck was selected as the solved structure. The results show that in the case of a classic evaluation, a larger amount of fibre reports a lower resistance of concrete, which contradicts the assumptions. The sensitivity analysis then shows that self-compacting concrete is more sensitive to the values of the diffusion coefficient, and with the consideration of fibres, the effect is even greater.
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