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This study investigates the effects of recycled aggregates (RAs), temperature, humidity, and freeze–thaw cycles on the modulus of elasticity in concrete, using a comparative approach between ultrasonic pulse velocity (UPV) and compressive strength tests. A range of RA proportions (0%, 25%, 50%, 75%, and 100%) was explored. These mixes were subjected to environmental conditions, including temperatures of 25, 0, and −18°C in both dry and wet states, to assess their impact on the mechanical properties of concrete rigorously. The findings reveal that the modulus of elasticity decreases by up to 35% with higher recycled content and more severe environmental exposure, with significant variations observed under different temperatures (25, 0, and −18°C) and moisture conditions. Notably, samples with 25% recycled content maintained higher elasticity, suggesting an optimal threshold for incorporating recycled materials. The study also validates using UPV as a nondestructive method to efficiently evaluate concrete's structural integrity. These insights advocate for the tailored use of RA concrete (RAC) in construction, enhancing durability and sustainability in varying climatic conditions. This research contributes to the development of concrete formulations that are both durable and environmentally adaptive, promoting sustainable construction practices. [ABSTRACT FROM AUTHOR]

This article investigates the durability of recycled self-compacting concrete in relation to its resistance against freeze-thaw cycles and alkali-silica reactions. It explores the properties of fresh concrete, investigates the impact of various additives, and evaluates key factors such as spalling, weight loss, compressive strength, expansion rate, and ultrasonic properties in hardened concrete samples incorporating different levels of recycled aggregates. The findings illustrate the feasibility of achieving self-compacting recycled concrete by increasing the use of superplasticizers and adding 10% beach sand. Furthermore, incorporating 10% micro-silica and 7.5% wollastonite in the recycled mix enhances the strength of all samples, with the 25% recycled material sample demonstrating the highest strength and durability. Despite a decrease in strength and increased expansion as recycling percentages and freeze-thaw cycles rise, the recycled samples maintain acceptable durability. Additionally, this study employs the R programming language to elucidate the relationship between compressive strength and modulus of elasticity, offering valuable insights into recycled concrete performance and behavior. [ABSTRACT FROM AUTHOR]

This article investigates the fracture toughness in self-compacting concrete containing different percentages of recycled concrete materials using edge-notched disc bend (ENDB) samples. For this reason, 0, 25, 50, 75 and 100 percent of recycled aggregate were used instead of natural aggregate in the mixing designs. To obtain the fracture toughness, ENDB samples were used under loading of mixed mode I/III and pure modes I and III. Cubic samples were also used to obtain compressive strength. The results show that the compressive strength of the samples has a direct relationship with the fracture toughness and the reverse ratio with the percentage of recycled concrete materials. Also, samples containing 25% recycled materials have the highest compressive strength and fracture toughness. Furthermore, as the recycled percentage of the samples increases, the performance of samples against shear forces and compressive strength is reduced. [ABSTRACT FROM AUTHOR]

The paper presents results of an investigation carried out to study the fatigue life distribution of plain and steel fiber reinforced concrete with different fiber volume fractions and aspect ratios for various levels of the applied fatigue stress. An extensive experimental investigation was planned in which 210 flexural fatigue tests and 84 complementary static flexural tests were conducted on prismatic plain concrete and fibrous concrete specimens of 100 x 100 x 500 mm size under three point loading in an MTS closed loop testing machine. Two types of crimped-type flat steel fibers with 25 x 2.0 x 0.6 mm and 50 x 2.0 x 0.6 mm, corresponding to fiber aspect ratios of 20 and 40, respectively, were used at each of the fiber volume fractions of 0, 1.0, 1.5, and 2.0%. It has been observed that the probabilistic distribution of fatigue life can be approximately modeled using the two-parameter Weibull distribution with statistical correlation coefficient exceeding 0.90. The shape parameter of the Weibull distribution for the fatigue life of concrete is different for different stress levels and fiber aspect ratios. The present study indicates that the probabilistic distribution of fatigue life of concrete depends on the level of applied fatigue stress, fiber volume fraction, and the aspect ratio of fibers. The graphical method, the method of moments, and the method of maximum likelihood estimation have been used to obtain the distribution parameters of the Weibull distribution. These three methods are shown to yield similar values of distribution parameters for the present fatigue data. CE Database subject headings: Fatigue; Flexure; Fiber reinforced materials; Concrete; Steel.

The durability of concrete to freeze and thaw (F-T) cycles is one of the most important challenges of reinforced concrete structures in regions with cold climate. Thus, studying the effect of this phenomenon on concrete properties to evaluate the vulnerability rate of these structures during frequent F-T cycles seems necessary. The use of nanomaterials in cement-based composites leads to many improvements in concrete properties due to their small particle size and large specific surface area. In this paper, the fabricated self-compacting concrete (SCC) specimens containing different portions of nano-clay (NC) and mineral admixtures including silica fume (SF), fly ash (FA), rice husk ash (RHA) and ground granulated blast furnace slag (GGBFS) were subjected to F-T cycles in the temperature range of −18 to +4 °C according to ASTM C666-A standard specifications. The properties of specimens including the mass, electrical resistivity, dynamic modulus of elasticity and compressive strength were measured during the F-T cycles. Results showed that using 3% NC considerably improves the F-T resistance of SCC, as compared to the control mix. Also, improvements were observed on the frost resistance of SCC containing mineral admixtures by the addition of 3% NC to the mix proportions. [ABSTRACT FROM AUTHOR]