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The construction industry continually seeks to optimize the materials used in building projects to balance structural integrity with economic and environmental concerns. Particularly in urban high-rise construction and seismic zones, the choice of material can significantly affect the project’s feasibility and safety. This study investigated the mechanical response of regular and lightweight concrete to bending stresses, which are critical factors in the structural design process. By comparing the strain–stress relationships, densities, and deformation capacities of these two varieties of concrete, this research aimed to clarify their fundamental differences. Lightweight concrete, with its lower density of 1800 kg/m3, offers noticeable weight reductions, thus presenting a viable solution for structures where reduced mass is beneficial, such as in areas with load-bearing limitations or for components that require ease of transportation and assembly. However, this study found that the reduction in weight is accompanied by lower compressive and flexural strength compared to normal concrete, which, with a density of 2400 kg/m3, exhibited greater mechanical strength and resilience under bending stresses. Stress–strain graphs generated from the experimental data illustrated both types of concrete’s elastic and plastic deformation behaviors, highlighting the material’s transition from elasticity to plasticity at specific stress points. This nuanced understanding of the materials’ behaviors is vital for construction professionals as it equips them with the information necessary to make informed decisions on material selection, ensuring safety, sustainability, and cost-effectiveness in construction projects.

As a high-quality building material exhibiting excellent toughness and durability, ultrahigh-performance concrete (UHPC) is increasingly being used in the construction industry and as building reinforcement. During the reinforcement of existing concrete structures with UHPC, their interface is the weakest part of a structure. Interface bonding ensures the operation of two types of materials together. However, existing studies rarely report the bonding of the UHPC–normal concrete (NC) interface. Herein, the existing test methods and interface bonding mechanisms are summarized. Subsequently, the differences among relevant design codes are investigated by comparing different theoretical formulas. Important influencing factors of the reinforcement method, namely, interface roughness, fiber type and content, interface agent type and content, moisture content, existing concrete strength, cementitious material content, curing conditions, freeze–thaw cycles, and chloride ions, are also considered. Further, the enhancement mechanism of the characteristics of the UHPC–NC interface is clearly described. Finally, the shortcomings and application prospects of the interfacial bonding properties are highlighted.

In this research, different amounts of nano-MgO were added to normal concrete samples, and the effect of these particles on the durability of the samples under freeze and thaw conditions was investigated. The compressive and tensile strength as well as the permeability of concrete containing nanoparticles were measured and compared to those of plain samples (without nanoparticles). The age of concrete samples, percentage of nanoparticles, and water-to-binder ratio are the variables of the current research. Based on the results, the addition of 1% nano-MgO to the normal concrete with a water-to-binder ratio of 0.44 can reduce the permeability up to 63% and improve the compressive and tensile strengths by 9.12% and 10.6%, respectively. Gene Expression Programming (GEP) is applied, and three formulations are derived for the prediction of mechanical properties of concrete containing nano-MgO. In this method, 80% of the dataset is used randomly for the training process and 20% is utilized for testing the formulation. The results obtained by GEP showed acceptable accuracy.

Seawater and sea sand concrete (SWSSC) is a highly attractive alternative to normal concrete (NC) that requires huge amounts of fresh water and river sand. However, reinforcements of stainless steel (instead of mild steel that is used in NC) may be required for SWSSC. This article reports investigation of stress corrosion cracking (SCC) of AISI 316 stainless steel (SS) in simulated SWSSC and NC environments, with and without addition of silica to SWSSC and NC, employing slow strain rate testing (SSRT) at 25 and 60 °C. For the purpose of comparison, SCC of SS was also investigated in simulated seawater (SW) solution. SS showed no SCC at 25 °C in any of the test solutions. Indications of SCC were seen in SW at 60 °C, but no features of SCC in SWSSC and NC at 60 °C, as suggested by scanning electron microscopy (SEM) fractographs. While the absence of SCC in SWSSC and NC is attributed to the highly passivating alkaline condition, its absence in SWSSC also indicates the role of alkalinity to predominate the deleterious role of chloride content of SWSSC. However, the addition of silicate to SWSSC or NC triggers transgranular SCC to SS at 60 °C, as evidenced by the fractography.

Ultra high performance concrete (UHPC) is self-compacting, reaching compressive strength over 200 MPa and flexural strength exceeding 30 MPa material. The used very low W/C ratio and high amount of Portland cement often exceeding 900 kg/m3, addition of up to 30% of silica fume produces a very dense and nearly impermeable binder matrix. In this research, cement was substituted with limestone filler to lower the effective CO2 footprint. Prepared concrete mixes had high slump flow of 850 mm and reached the compressive strength of 150 MPa after 28 days. Full-scale columns having dimension of 30 × 30 × 250 cm were produced using self-compacting concrete (Figure 1a,b), having the 28 days compressive strength of 40 MPa. External surfaces of the 3 months old columns were water jetted to simulated real case scenario (Figure 1c). For the test, the columns were surrounded by a plywood formwork leaving less than 3 cm of spacing between the concrete surface and the formwork (Figure 1d). The concrete was poured from top of the column and with no segregation reached the bottom and perfectly filled the mold. Test included determination of basic mechanical properties, bond strength between UHPC and “old” concrete, crack formation and frost durability. All results exceeded expectations.