This paper discussed the effects of modified metakaolin (MK) with nano-silica (NS) on the mechanical properties and durability of concrete. In the first phase, trial mixes of concrete were prepared for achieving the desired value of the 28 days compressive strength, and the charge passed in rapid chloride permeability test (RCPT). In the second phase, statistical analysis was performed on the experimental results using the response surface method (RSM). The RSM was applied for optimizing the mix proportions for the required performance by exploiting the relationship between the mix characteristics and the corresponding test results. A blend of 10% MK + 1% NS as part of cement replacement exhibited the highest mechanical properties and durability characteristics of concrete; concrete mix showed that the 28-days compressive strength (CS) was 103 MPa, which was 15% greater than the CS of the control mix without MK or NS. The same mix showed more than 40% higher flexural and split-tensile strength than the control mix; also it resulted in a reduction of 73% in the rapid chloride permeability value. ANOVA technique was used for optimizing the nano-silica and metakaolin content for achieving maximum compressive strength and minimum RCPT value. Statistical analysis using ANOVA technique showed that the maximum compressive strength and lowest RCPT value could be achieved with a blend of 10% MK and 1.55% NS.

This paper presents the results of an experimental study that investigated the effects of two parameters: sand/fly ash (S/FA) ratio and water to geopolymer-solid (W/GS) ratio on the engineered geopolymer composite. The trial mix designs were optimized using the response surface method. These parameters influence the properties of the fresh and hardened geopolymer matrix, such as slump flow, compressive strength, flexural strength, elastic modulus, flexural toughness, ductility index and drying shrinkage. The optimizing process was conducted by developing statistical models using the response surface methodology (RSM) technique. The developed models were statistically validated and could be used to determine the desired response of engineered geopolymer composite (EGC) with a significance level of more than 95%. In this study, the optimized values of the S/FA ratio and W/GS ratio were obtained as 0.341701 and 0.225184, respectively. To validate the optimized S/FA ratio and W/GS ratio, an experimental study was performed, and a difference of less than 5% was found between predicted and experimental results.

Effective waste management is a matter of global concern. The utilization of widely recognized waste materials, such as plastics, rubber, and glass, in the construction industry is being investigated for their cost efficiency, enhanced material properties, and reduced environmental impact, contributing to broader sustainability efforts. This study investigates the development of an engineered geopolymer composite with a focus on sustainability by utilizing industrial waste materials. Gamma-irradiated polyethylene terephthalate was employed as a partial replacement for silica sand, while graphene nanoplatelets were incorporated to enhance composite properties and reduce environmental waste. A statistical technique known as response surface methodology was used to optimize the effects of gamma-irradiated polyethylene terephthalate and graphene nanoplatelets on the properties of the engineered geopolymer composite. Key findings indicate that gamma-irradiated polyethylene terephthalate, with higher crystallinity and robust interfacial bonding with the geopolymer matrix, significantly enhances compressive strength, elastic modulus, flexural strength, and flexural toughness. However, graphene nanoplatelets, while improving mechanical properties, reduce the ductility index. Optimal composite properties were achieved with 26.4% gamma-irradiated polyethylene terephthalate and 0.12% graphene nanoplatelets. This research underscores the potential of gamma-irradiated polyethylene terephthalate in creating high-performance, sustainable construction materials and highlights the trade-offs between mechanical reinforcement and ductility. Future research should explore the chain scission effects of gamma irradiation on polyethylene terephthalate, further optimize composite properties, and investigate mechanisms to enhance ductility, advancing the utilization of polyethylene terephthalate in sustainable construction materials.

This paper presents the results of the behavior of end zone of post-tensioned (PT) beams made of fiber reinforced concrete (FRC). The principal aim of using FRC was to enhance the ductility and post-cracking behavior of end-zone of post-tensioned beams. A stronger and tougher end-zone of PT-beams is necessary when it is subjected to dynamic loading. Post-tensioned (PT) beams are typically used for the construction of bridges and industrial buildings, which are often subjected to vibrations and cyclic loading. Pre-mature cracking of the end zone (EZ) of a PT-beam is considered the type of problem that may cause the structural collapse. In this research program, polyvinyl alcohol (PVA) and copper-coated steel (CCS) fibers were used in concrete for improving the EZ performance of PT-beams. The use of FRC caused a 50% reduction in the shear reinforcement within the end zone of the PT-beam, which also avoided the congestion of steel in the end zone. Hence, the concrete was placed homogeneously, and smooth finished surfaces of the beams were obtained. FRC controlled the bursting of the end zone during the transfer of the full pre-stress force, and approximately 25% increment in the strain energy of the end zone was observed, which was also found efficient in strain diminution along the length of the beam.