International Concrete Abstracts Portal

Ultra-high performance concrete (UHPC) has seen growing use in the construction industry because of its high compressive, tensile, and flexural strength. The tensile and flexural strength are in part due to the steel fibers added to the UHPC mix. Yet, fibers can segregate due to poor material rheological properties and construction practices, resulting in less than expected material strength. Due to the importance of these fibers, there is a need to verify the volume and orientation of the steel fibers in the UHPC. In this work, we report on the design and testing of electromagnetic sensor systems that are able to test the integrity of the steel fibers in the UHPC structure. We test our sensor system using UHPC samples containing 1% to 3% fiber content by volume and created a calibration based on the results. Our results show a linear relationship between the inductance change versus the fiber percentage with an R-squared value of 99.7 %, which shows that our approach successfully demonstrated the potential of using our approach for characterizing steel fibers in UHPCs.

The addition of supplementary cementitious materials (SCMs) to low-carbon concrete mixtures has been investigated in recent years as part of the sustainability of the concrete sector. Recently, most traditional SCMs, such as fly ash and blast furnace slags, have become unavailable in several developed countries, mostly due to environmental restrictions. Consequently, several new by-products from fast-growing sectors are being considered as potential replacements for traditional SCMs. However, the durability of these new by-products in low-carbon concrete has not been thoroughly explored. As a result, this paper presents the first part of a project related to an extensive experimental characterization, in which low-carbon concrete with high compactness, paste optimization, and partial cement replacement by the addition of waste by-products from the agricultural, metallurgical, paper, and glass industries is studied. Alternative SCMs including rice husk ash, biomass fly ash, rock wool residues, or waste foundry sand are incorporated into corresponding mortar matrices and the results concerning the mechanical properties (flexural and compressive strength) and durability (capillary water absorption, surface electrical resistivity, and carbonation resistance) are presented and analyzed. The outcomes indicate that it is possible to reduce the Portland cement content without compromising the mechanical and durability properties of the concrete.

This study focuses on evaluating the mechanical, microstructural, and durability properties of 3D printing mortar (3DPM), with a specific emphasis on the influence of incorporating recycled fine aggregates (RFA). These RFA are produced from construction and demolition waste (C&DW) in Belgium and are sieved to a maximum particle size of 2 mm [0.08 in].

Cast and printed samples of mortar containing 100% RFA, with a sand-to-cement ratio of approximately 1:1 and a water-to-cement ratio of 0.29, were subjected to mechanical tests, including flexural, compressive, and tensile strength, at 2, 7, 28, and 56 days. The possible anisotropic behavior of the printed material was also investigated. The results show that using RFA does not significantly affect the mechanical properties of the mortar, and some anisotropic behavior was observed based on the compression test results. The end goal of the project is to print non-reinforced urban furniture; in order to assess its durability, only freezing and thawing (F-T) behavior was investigated. The F-T behavior was analyzed based on the quantity of spalling particles after 7, 14, 28, 56, and 91 F-T cycles. The results show that up to 91 F-T cycles, no significant surface damage occurred.

The increasing demand for sustainable building products with lower carbon footprints is a huge global challenge that can hardly be faced by conventional cementitious mixtures. In this context, the use of alternative primary binders, such as hydraulic lime, should be explored. Research in this direction should aim at the development of innovative eco-friendly materials with suitable mechanical performance. For the retrofitting of masonry structures, for instance, it may be necessary to improve their mechanical properties by incorporating supplementary cementitious materials (SCMs), further reducing, at the same time, their environmental impact.

This study investigates the effects of silica fume and metakaolin included either individually or together alongside natural hydraulic lime. The mechanical performance of such binary and ternary binders has been characterized in terms of flexural and compressive strength. Moreover, scanning electron microscopy (SEM) has been used to study the microstructure of the mixtures. Finally, a preliminary investigation concerning the effect of curing time in lime-based mixtures with combined silica fume and metakaolin has been performed to investigate the possible benefits of this approach. The results highlight the superior pozzolanic efficacy of silica fume compared to metakaolin and point towards the proper dosages of SCMs to achieve optimal mechanical performance.

This research studies the use of a fractional coarse aggregate replacement product (PA). PA is a unique blend comprised of recycled plastics, glass, and minerals; all collected from the waste stream. The use of PA and other similar products may contribute to reducing plastic waste in the waste stream. To test the feasibility of PA as a partial, natural aggregate replacement, four different mixtures of concrete were batched and tested. The concrete mixtures were based on the standard commercial interior normal-weight concrete mixture. This is a non-air-entrained mixture, provided by a local concrete batching plant (MCM), with a design strength of 4000 psi (27.6 MPa). The four concrete mixtures tested were a control mixture with no variations to the original mixture design as well as three mixtures with 15%, 30%, and 45% coarse aggregate replacement by volume. The compression strength, tensile splitting strength, modulus of rupture, and density of the concrete are examined. The focus of the paper is the concrete compressive strength because it is the primary determining factor in concrete design. Fresh concrete properties and hardened concrete properties were examined and recorded. Slight changes to the overall fresh concrete properties of workability, density, and slump were recorded. The hardened concrete properties include compression, tensile splitting, and modulus of rupture. The results of the compression tests show a strength proportionally decreased with the percent increase in PA replacement – 15% replacement with an 18.1% decrease, 30% replacement with a 35.6% decrease, and a 45% replacement indicated a 45.3% decrease at the 28-day test. The results of the tensile splitting tests and modulus of rupture tests both indicate similar results of a decrease in strength as the replacement rate of PA increased.