International Concrete Abstracts Portal

The paper investigates the bond behavior between non-pretensioned indented steel wire and high-performance concrete (HPC) to study the effect of embedment length and concrete compressive strength on bonding performance with time. A total of 63 concrete specimens, cross section of 160 x 160 mm reinforced with indented steel wire of 7.5 mm diameter, were cast and tested under uniaxial load. The main test parameters included the embedment lengths: 40, 80, 120, 200, and 240 mm, and concrete compressive strengths: 40, 60, 72, and 88 MPa. The modified pullout test method developed at the Cracow University of Technology was used in the experimental investigation. The results show that the average maximum bond stress (16, 23, 26, and 32 MPa) is increased with an increase of concrete compressive strength (over time) and is decreased with longer development length of indented steel wire for the same concrete compressive strength. An increase of bond stress is slower than an increase of HPC compressive strength. Moreover, it was demonstrated that the maximum bond stress occurs at the slip of 2.8 mm, independently of concrete compressive strength ranging from 40 to 88 MPa. The average values of the adhesive bond of HPC to non-pretensioned indented steel wire range from 2.90 to 3.75 MPa. Finally, a verification of the fib Model Code 2010 concrete bond-slip model for HPC reinforced with non-pretensioned indented steel wires was conducted. It was determined that the model is not applicable to elements made of concrete with a strength of 60 MPa and above.

Current design provisions pertaining to the shear transfer strength of concrete-to-concrete interfaces, including those of the AASHTO LRFD design specifications and ACI 318 Code, are based on limited physical test data from studies conducted decades ago. Since the development of these design provisions, many studies have been conducted to investigate additional parameters. In addition, modern concrete technology has expanded the range of materials available and often includes the use of high-strength concrete and high-strength reinforcing steel. Recent studies examined the applicability of current shear-friction design approaches to interfaces that comprise high-strength concrete and/or high-strength steel and identified a need for revision to the existing provisions. To this end, this study leveraged a comprehensive database of test results collected from the literature to propose a deep-learningbased predictive model for normalweight concrete-to-concrete interfacial shear strength. Additionally, a new computation scheme is proposed to estimate the nominal shear strength with a higher prediction accuracy than the existing AASHTO LRFD and ACI 318 design provisions.

This paper examines the bond behavior between non-pretensioned plain steel wire and high-performance concrete (HPC). It investigates the effects of embedment length and concrete compressive strength on bond performance for the production of railway sleepers. To determine the performance, pullout concrete specimens reinforced with 7 mm diameter plain steel wire were cast and tested under a uniaxial load. The main test parameters include the embedment length: 40, 80, 120, 240, 330, and 460 mm; and concrete compressive strength: 40, 60, 72, and 88 MPa. The modified pullout test method developed at Cracow University of Technology was used in the experimental investigation. The study unequivocally demonstrates that the maximum bond stress between HPC and a non-pretensioned plain steel wire with a diameter of 7 mm decreases as the embedment length increases, irrespective of the concrete’s compressive strength. Furthermore, it was observed that the average bond stress increases with an increase in the concrete’s compressive strength with time. After conducting tests on HPC specimens with compressive strengths ranging from 60 to 88 MPa and embedment lengths ranging from 40 to 120 mm, it was determined that the resulting maximum adhesion bond stress was 2.22 MPa. This was 52% higher than the bond stress found in test pieces made of concrete with fcm = 40 MPa. Additionally, the average residual bond stress was found to be twice that of concrete with a compressive strength of 40 MPa. These findings demonstrate a clear advantage of using HPC in terms of bond stress.

The U.S. National Ocean Service estimates 95,741 miles (154,080 km) of shoreline in the United States, where 163 miles per year are hardened by bulkheads and riprap. These shoreline protection techniques are costly and require frequent maintenance. Different agencies are examining “nature-based” solutions that combine vegetation with traditional concrete. Digital construction, advanced manufacturing, and innovative cementitious composites have also been proposed as potential means to lower material use, cost, and environmental impact. This paper presents a novel advanced manufacturing technique using a reactive-diffusion morphological process, called “dry-forming,” to three-dimensionally (3-D) printed concrete structures of various shapes, sizes, and complexities with standard concrete mixtures. This technology has reduced 60% of material use, enhanced local habitats, and increased the resiliency of the shoreline to sea level rise. The widespread use of this technology would increase the resiliency of coastal communities, protect aquatic life, and protect waterfront public and private real estate investments.

Despite all the recent advances in the development of threedimensional (3-D) concrete printing (3DCP), this technology still has many unresolved problems. In most of the completed projects with the application of 3DCP, the focus was mainly on mastering the printing of vertical walls, while horizontal structural elements were produced with conventional methods—that is, using formwork, which reduces the level of technology automation, or using prefabricated elements, which makes the construction dependent on their availability and supply. In this contribution, the authors propose new methods of manufacturing slabs and beams directly on site by extruding concrete onto a textile reinforcement mesh laid on a flat surface. Specimens obtained from a slab produced following this method were used for mechanical testing and investigation of the concrete-reinforcement interface zone. Finally, as proof of the feasibility of the proposed approach, a demonstrator representing a full-scale door lintel was manufactured.