The external jacketing method using cement-based matrices and textile reinforcement has gained popularity for the enhancement of strength and ductility characteristics of reinforced concrete members. In this study, glass fiber–reinforced mortar (GFRM) with or without basalt textile reinforcement was used for external jacketing of low-strength concrete prisms. An innovative spraying method was used during the application of the cement-based matrix to the specimen’s surface. Investigations were carried out on a large number of concrete prisms with five different cross-sectional geometries (circular, square, and rectangular, with cross-sectional aspect ratios of 1.5, 2, and 3). At the end of the tests, it was shown that the proposed retrofit methodology is effective for the enhancement of performance of low-strength concrete members. The spraying technique is practical and feasible, particularly for the cases in which access to the structural members that are destined to be retrofitted is limited. Furthermore, a simple analytical approach based on the effectively confined concrete area concept is also presented for predicting the peak strength and the ultimate strains of the retrofitted specimens.

The production of electrically conductive concrete was introduced years ago among construction materials, generally for anti-icing. The present study investigates the electrical, mechanical, dynamic, and microstructural properties of recycled ferrochrome filled cementitious mortars, containing single-walled carbon nanotubes (SWCNTs) and steel fiber. 7, 14, and 28-day non-destructive and 28-day compressive and bending tests of cementitious conductive mortars obtained from five different mixtures were performed. Two-point uniaxial method was used to determine the electrical conductivity properties of the samples. The damping ratio of the samples was obtained by performing dynamic resonance tests. Ultrasound pulse velocity (UPV) and Leeb hardness tests were performed as other non-destructive testing methods. Microstructure analysis at the interfaces of conductive concrete samples were characterized by scanning electron microscopy (SEM), EDS (Energy-Dispersive X-ray Spectroscopy), and X-ray diffraction (XRD). According to the experimental results, all data agreed and confirmed each other. When SWCNT is used in combination with steel fiber, the conductive mortar samples exhibited reasonable conductivity, while their mechanical properties turned out to below.

Recently, it is known that carbon fiber, which is a conductive fiber, is used in different mixture designs and developing electrically conductive cementitious materials. However, the evaluation of ferrochrome as a recycled aggregate in the mixture of these special concretes has still not been investigated. In this study, electrically conductive mortars were produced by using 100% recycled ferrochrome aggregate with a particle size of less than 1 mm as filling material and using carbon fiber (CF) in 4 different ratios, 0%, 0.5%, 0.75% and 1%. 2, 14, 28, 90 and 180 days electrical resistivity properties of the obtained samples were investigated. In addition, 28-day compressive strength, flexural strength, dynamic resonance, ultrasonic pulse velocity (UPV), Leeb hardness, scanning electron microscope (SEM) and X-Ray Diffraction (XRD) tests were performed on all samples. The obtained results were compared with the literature and it was proved that ferrochrome can be used as a reasonable aggregate in conductive mortars.

The use of glass fiber reinforced concrete (GFRC) in the construction industry is increasing due to its mechanical and physical properties. Waiting time of concrete in the mold and the removal of the mold at the right time are important in terms of strength. In conventional concretes, maturity models are widely used as a non-destructive method for early strength estimate. In this study, it is aimed to develop an estimate model of flexural and compressive strength in GFRCs using the maturity index method. In this context, glass fiber reinforced concretes were produced at the rates of 0%, 1%, 2% and 3%. Calcined kaolin and acrylic polymer were used as modification materials in the mixtures. Properties such as compressive, flexural, hardness, and shrinkage of specimens were investigated at different ages. The maturity-strength relationships of mixtures at different ages were examined by weighted maturity and Nurse-Saul methods. At the end of the study, two new models were developed to estimate the compressive and flexural strengths of GFRCs, taking into account all the data. The suggested models have been confirmed by examining them on all mix-age groups and comparing them with the literature.