The use of concrete as the primary building construction material caused serious problems in the construction industry. Concrete is not regarded as an environmentally friendly material since the use of cement results in high carbon emissions during the manufacturing process. One effort to replace cement without reducing concrete strength is to use fly ash as a concrete ingredient, which is known as geopolymer concrete. The goal of this research was to determine the basic mechanical properties of geopolymer concrete and compare it to conventional concrete with the same material proportions. The mix design of the three different proportions with the ratio of aggregates to binder as 70% : 30%, 60% : 40% and 50% : 50% was maintained such that the concrete mix has a good workability. As a result, the so-called workable fly ash-based geopolymer concrete has higher compressive strength, splitting tensile strength, and modulus of elasticity compared to conventional concrete, while its Poisson's ratio is slightly lower.

Precast reinforced concrete (RC) structures offer advantages in terms of construction efficiency and quality control; however, their seismic performance is governed by the behavior of the beam–column connections. This study presents an experimental investigation of the cyclic response of precast RC beam–column joints that include a composite steel connection, designed to enhance strength, stiffness, and damage control in critical regions. A composite joint specimen was tested under displacement-controlled cyclic loading, and its behavior was compared with that of a corresponding pure RC connection. Experimental results showed that the composite configuration effectively prevented premature failure at the beam–column interface, relocated plastic hinges away from the joint core, and significantly improved the load-carrying capacity, stiffness, and energy dissipation. To interpret the experimental observations and examine the internal stress transfer and evolution of damage, a three-dimensional nonlinear finite-element model was developed. The simulations reproduced the observed modes of failure, shapes of deformation, hysteretic responses, and moment distribution trends, particularly in the post-yield and strain-hardening ranges. Although the pinching effects observed experimentally were not fully captured numerically, the overall levels of agreement in the ultimate strength and plastic hinge locations were satisfactory. The combined results indicate that composite steel-reinforced precast beam–column joints represent a promising solution for improving seismic performance.