International Concrete Abstracts Portal

Mixed recycled aggregate (MRA) is considered a sustainable construction material, and its use in precast concrete is currently banned due to its poor engineering performance. This paper aims to evaluate the feasibility of partial replacement of natural coarse aggregate with MRA in self-consolidating concrete (SCC) for manufacturing architectural precast concrete sandwich wall panels. To this end, five MRAs from recycling plants were characterized, out of which two were selected to develop SCC. SCC mixtures with three replacement levels and three water compensation degrees were produced, and their physical, mechanical, durability, and aesthetic properties were examined. The results showed that the incorporation of MRA dominated the mechanical properties of SCC, while the water compensation degree primarily affected the flowability and carbonation resistance. The presence of MRA had no considerable effect on the aesthetic characteristics. Up to 10% MRA in weight of total aggregates could be used in precast SCC.

Three-dimensional (3D) printing, also known as additive manufacturing, is a revolutionary technique, which recently has gained a growing interest in the field of civil engineering and the construction industry. Despite being in its infancy, 3D concrete printing is believed to reshape the future of the construction industry because it has the potential to significantly reduce both the cost and time of construction. For example, savings between 35 and 60% of the overall cost of construction can be achieved by using this technique due to the possibility of relinquishing the formwork. Moreover, this innovation would free up the architectural gesture by offering a wider possibility of shapes. However, key challenges should be addressed to make this technique commercially viable. The effect of mixture composition on the rheological properties of the printed concrete/mortar is vital and should be thoroughly investigated. This paper investigates the effect of using red mud, nanoclay, and natural fibers on the fresh and rheological properties of 3D-printed mortar. The rheological properties were evaluated using the penetrometer test, flow table test, and cylindrical slump test. The estimated yield stress values were then calculated based on the cylindrical slump test. Further, relationships between the tested parameters were established. The main findings of this study indicate that the use of an optimum dosage of a nanoclay was beneficial to attain the required cohesion, stability, and constructability of the printed mortar. The use of natural fibers reduced pulp flow by improving cohesion with a denser fiber network and reducing the cracks. With respect to red mud, it may be appropriate for printable mortar, but more testing is still required to optimize its use in a printable mixture. A printability box to define the suitability of mixtures for 3D printing was also established for these mixtures.

The Bahá’í House of Worship is one of the most famous exposed aggregate concrete structures in the world. The stairs at the main entry of the building were cast and placed in 1942 and has combated the weathering elements of Wilmette, Ill., a northern Chicago suburb, for more than 50 years. The stairs were replaced in 1989 due to deterioration. These replacement stairs, however, have exhibited characteristics of accelerated deterioration. This research project addresses the historical references of the original concrete work done, past testing and investigations of the concrete structure, and a performance evaluation by mechanical and microstructural tests of both the 1942 original concrete and 1989 restoration concrete. It is found that one of the causes of the deterioration of the 1989 restoration concrete is a weak paste matrix. The cause of deterioration of the 1942 original concrete is a weak aggregate-matrix interface.

Post-consumer glass represents a major component of solid waste, yet its use as an aggregate in concrete is problematic because of the strong alkali-silica reaction (ASR) between the cement paste and the glass aggregate. In a research project at Columbia University, the use of crushed waste glass as aggregate for concrete products was investigated. Fundamental aspects of ASR in concrete with glass aggregate were studied. It was shown that waste glass ground to U.S. standard sieve size No. 50 or smaller causes mortar bar expansions in the ASTM C 1260 test of less than 0.1%, which is less than that of reference bars without any glass. Also, green glass does not cause any expansion to speak of, and finely ground green glass has the potential of an inexpensive ASR suppressant. Specific concrete products with glass aggregate are currently under development. These include concrete masonry blocks with 10% mixed-color waste glass aggregate and “glascrete” products with 100% color-sorted glass aggregate for numerous architectural and decorative applications.

These specifications are a reference standard which the engineer or architect may make applicable to any building project by citing them in the project specifications. He supplements them as needed by designating or specifying individual project requirements. The document covers materials and proportioning of concrete; reinforcing and prestressing steels; production, placing, and curing of concrete; and formwork design and construction. Methods of treatment of joints and embedded items, repair of surface defects, and finishing of formed surfaces are specified. Separate chapters are devoted to slab construction and finishing, architectural concrete, massive concrete, and materials and methods for constructing post-tensioned concrete. Provisions governing testing, evaluation, and acceptance of concrete as well as for acceptance of the structure are included.