International Concrete Abstracts Portal

Concrete mixture design is the foundation of cement and concrete research. Innovations in concrete materials could, should, and would inevitably be incorporated into new mixture designs. Thus, a rigorous method for concrete mixture design can better bridge the research community and the construction industry with high reliability and high fidelity. However, current methods for concrete mixture design vary a lot in the literature, thus compromising the accuracy and consistency in interpreting the properties of concrete subject to changes in its raw ingredients. Moreover, the extraneous variables in controlled experiments are not always controlled well. To solve this old but critical problem, this paper summarizes the prevalent concrete mixture design methods in the literature and in practice. By contrast, the volume-based mixture design method is superior to the mass ratio-based mixture design method in terms of simplicity, accuracy, and consistency. Further discussion on packing density measurement and water or slurry film thickness (SFT) as a basis of volume-based mixture design is elaborated. Mathematically, the hardened properties were linked to the particle packing behavior and fresh properties of concrete. This research contributes to a unified volume-based design method to bridge the research community and the construction industry. In the end, it is conducive to upgrading from concrete technology to science.

Nonlinear macro-models of concrete components are routinely used for performance-based seismic assessment of existing “non-ductile” buildings. Accurate test-calibrated models improve cost and time effectiveness of rehabilitation. ASCE 41-17, the primary standard in the United States for seismic assessment and rehabilitation, offers nonlinear modeling parameters for concrete frame beams and columns that were recently updated to reflect median estimates (50% probability of exceedance). However, the ASCE 41-17 beam-column joint nonlinear modeling provisions are still based on lower-bound estimates shown by many researchers to be highly conservative. Moreover, existing literature backbone models are not suitable for shear-critical “non-conforming” unreinforced joints as they are mostly deterministic, non-sensitive to failure mode, designed for reinforced joints, or calibrated based on small unreinforced joint datasets. This paper proposes new probabilistic nonlinear modeling parameters for shear-critical unconfined (unreinforced) beam-column joints based on a database of cyclic tests to update the current ASCE 41-17 modeling parameters. Three alternatives for deformation modeling parameters are proposed, along with two alternative expressions for residual shear capacity ratio. The proposed models offer the analyst to select the desired probability of exceedance to enable consistent modeling criteria with beams and columns in concrete frames to avoid nonlinear analysis bias that is currently rendering joints unrealistically as the weakest link in non-ductile frames, leading to unnecessary costly retrofits. All the proposed models exhibited very good correlation with the test database and verification dataset. The proposed models offer immediate input to reduce the conservatism of the current seismic assessment standards for unconfined beam-column joints, which resulted from test scarcity at the time of their development.

The lack of durability in concrete repairs induces premature repair deterioration. Drying shrinkage of "new" repair material restrained by "old" concrete substrate results in repair layer cracking, and interface delamination between the repair and the concrete substrate. This paper investigates a material solution to these common repair failures. A high-early-strength engineered cementitious composite (HES-ECC) developed for concrete repair is employed for this study. The HES-ECC possesses high early-age strength (over 47 MPa [6885 psi] in 7 days) and high tensile strain capacity several hundred times that of normal concrete or fiberreinforced concrete (FRC). Experimental and numerical studies on a layered repair system were conducted to verify that the high ductility of HES-ECC can relieve shrinkage-induced stresses in the repair layer and at the repair/old concrete interface, thereby simultaneously suppressing large repair surface cracks and interface delamination. Detailed results of these studies are reported in this paper.

The interior joint shear strength of nonductile frames strengthened with reinforced concrete (RC) jackets, but with no new joint shear hoops and no dowel anchors installed into the new and old concrete interface, was investigated experimentally. Seven oneway interior beam-column joint subassemblages were tested under quasistatic cyclic loading to observe the joint shear strength and overall frame performance. The test measurements are also used to verify two of the analytical models used for predicting the horizontal shear strength of jacketed joints without horizontal joint shear reinforcement. The results show that the RC jacketed scheme is able to efficiently rehabilitate nonductile frames with very poor joint details. An empirical equation for calculating the joint shear strength of RC jacketed frames is proposed in this study.

Bonded concrete overlays are sometimes distressed by early age surface cracking and/or debonding of the interface between old and new concrete. This early age failure is mainly due to volume changes of the overlay concrete by shrinkage, thermal changes, and thermal gradients. To understand the early age behavior of bonded concrete overlays, extensive experimental measurements and numerical analysis were carried out. Laboratory overlay specimens were fabricated to measure opening displacement and debonding profiles at the interface. A finite element model was developed to assess debonding behavior due to volume changes. From the experimental measurements and numerical analysis, it was found that bonded concrete overlays with high-performance concrete (HPC) mixtures have a strong tendency toward early-age debonding. The main reason for this tendency is due to a high shrinkage gradient in the HPC mixtures and low bond strength at the interface.