International Concrete Abstracts Portal

Advances in concrete material science have led to the development of a new class of cementitious materials, namely ultra-high-performance concrete (UHPC), which offers superior mechanical and durability properties. The control and characterization of the fresh properties of UHPC are crucial for successful mixture design. Among the methods for evaluating these properties, the mini-cone test has gained prominence due to its practicality. It requires smaller sample volumes than the standard slump cone test, making it especially suited for laboratory assessments of UHPC mixtures. In contrast, the slump flow test is the simplest and most widely used test for both laboratory and field testing of concrete. This study aims to establish a correlation between mini-cone flow and standard slump flow test results. A linear relationship is identified, which forms the basis for proposing consistency classes for UHPC using mini-cone flow values. These proposed classes align with the established consistency classifications for self-compacting concrete.

The composition of OPC changed in North America with the addition of ground limestone in 2004 (since the adoption of ASTM C150-04a), which reacts to form carboaluminate hydration products. This paper discusses the potential influence of limestone addition on porosity, pore connectivity, formation factor, and electrical properties of cementitious systems. The carboaluminate reaction products can result in a system with limestone that has an equivalent water-to-powder ratio (w/p) that is approximately 0.07 lower than the system without limestone (occurring at the minimum porosity). When reactive alumina is added to the system, a greater amount of limestone reacts, and a reduction in porosity occurs. The carboaluminate phases impact the transport properties of mixtures to a greater extent for mixtures with moderately low w/p and aluminous SCMs. This has implications on standards and specifications, which are based on historic research and testing using cements not containing limestone, and therefore would have a higher porosity and lower formation factor than cements manufactured in the US after approximately 2004 at the same w/p.

This study investigates the impact of the quicklime and gypsum ratio on the grouting material made of sulfoaluminate cement. Gypsum and quicklime were selected to verify that sulfoaluminate cement retained AFt. Sulfoaluminate cement's efficiency as a grouting material was evaluated using gypsum and quicklime. Sulfoaluminate cement with varying gypsum to quicklime ratios was subjected to tests for compressive strength, pH, setting time, expansion rate, X-ray diffraction (XRD), and scanning electron microstructure (SEM). The microstructure of the X-ray diffraction was investigated at 1d and 28d. The result obtained points to two key findings:

The retention of AFt was excellent (≥99%) regardless of the gypsum-to-quicklime ratio.

The retention of AFt without gypsum and quicklime depends on the sulfoaluminate cement; in this case, the setting time prolongs, leading to expansion strain.

A machine learning (ML) model is developed using a gradient-boosted decision-tree algorithm to estimate the drift capacity of reinforced concrete (RC) columns. A reliable estimate of the drift capacity of a structure is critical to both its design and assessment. The drift capacity of a structure is also broadly interpreted as a measure of its seismic vulnerability. The estimated drift capacity from the ML model is compared against that of existing methods using test results from a dataset of 341 RC columns subjected to cyclic loading. The mean of the ratio of measured to estimated drift capacity for the developed ML model was 1.0 with a coefficient of variation (CV) of 0.31. In comparison, the regression equation currently adopted in New Zealand and the US to estimate the drift capacity of RC columns has a mean of 3.13 and a CV of 1.07. Other empirical methods assessed in this study also led to large scatter and no discernible correlation between estimated and measured drift capacity. The developed ML model provides more accurate results than existing methods and can estimate the drift capacity for a broad range of RC columns. The developed model is published under an open-source license and is freely available to practitioners and researchers.

Ultra-high performance concrete (UHPC) is a forward-looking material ideal for use in large-scale civil infrastructure systems. However, due to its unique mix, when UHPC is used in actual structures in conjunction with materials like steel reinforcement, it may lead to unexpected behavior. Therefore, this study analyzed the behavior of reinforced UHPC (R-UHPC) for use in actual structures, focusing specifically on beams among various structural components, with a particular emphasis on their flexural behavior. For this purpose, the study collected and comprehensively analyzed experimental data from flexural tests of R-UHPC beams conducted to date, identifying basic mechanics, peculiarities, and considerations in structural design. This study highlights that, besides the commonly known longitudinal reinforcement ratio, numerous factors such as beam length, height, number of tension reinforcement layers, strength, etc., can influence the flexural behavior of R-UHPC beams and demonstrate how these elements impact the performance.