International Concrete Abstracts Portal

For decades, concrete structures have been constructed using cementitious materials through conventional methods using formworks (either cast-in-place or precast). Concrete with a sufficient slump is needed to fill up the formwork. This approach results in significant material wastage and increases the carbon footprint of structures. Additive construction offers unique opportunities to build form-free structural elements with complex geometry which enable topology and structural optimization. Topology optimization is a method of optimizing geometries using algorithmic models to optimize material layout within a user-defined space for a given set of loads, conditions, and constraints. Topology optimization maximizes the performance and efficiency of the design by removing redundant material from areas that do not need to carry significant loads to reduce the amount of material being used or solve design challenges like reducing resonance or thermal stress. One of the factors to consider between the marriage of additive construction and topology optimization is the placement of reinforcement. Therefore, this presentation focusses on compression only structures, which have no need for reinforcement. Furthermore, this presentation discusses (1) topology optimization with regards to concrete, (2) numerical simulations for topology optimized structures with different loading conditions, (3) the overall printing process, as well as the CAD designs from each numerical simulation, (3) computational analysis of the final designs, and (4) any quality issues of the print conducted by Lidar scanning. The methodology provides evidence that integrating topology optimization with additive construction creates more opportunities for freedom of design manufacturing.

Coral reefs are critical to marine biodiversity yet face severe threats from climate change, pollution, and overexploitation. This research explores the application of concrete made with high calcium and phosphorus content as a material for artificial reef construction, focusing on implementation in the Galápagos Islands.

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.

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.