International Concrete Abstracts Portal

Ultra-high-performance concrete (UHPC) features tensile strain-hardening behavior and a high compressive strength. Existing studies on the shear behavior of UHPC structural members have been focused on prestressed UHPC girders. More experimental data of the shear behavior of non-prestressed UHPC beams are necessary to quantify the safety margin of shear designs for structures. Moreover, while the UHPC members in most studies did not contain coarse aggregate to strengthen their microstructure, the inclusion of coarse aggregate has been shown to substantially reduce the autogenous shrinkage and enhance the elastic modulus for UHPC materials, which is beneficial for structural applications of UHPC. This study experimentally investigated the shear failure behavior of eighteen non-prestressed rectangular UHPC beams. The experimental variables included the volume fraction of fibers, shear span-to-depth ratio of the beams, and coarse aggregate. The detailed shear failure responses of the UHPC beams were discussed in terms of the damage pattern, shear modulus, shear strength, shear strain, and strain energy. The test results showed that the inclusion of coarse aggregate increased the beam shear strength, and its enhancement became more significant with a higher volume fraction of fibers and a lower shear span-to-depth ratio of the beam. In addition to the experimental investigation, a shear strength model for non-prestressed rectangular UHPC beams that accounts for the interactive effect of the key design parameters was developed. An experimental database of the shear strength of the UHPC beams in existing studies was established to assess the performance of the proposed model. It was shown that the proposed model reasonably predicted the shear strength of the UHPC beams in the database with a higher accuracy and lower scatter compared to the results of existing models.

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.

This article reviews the challenges in the rational use of limestone and supplementary cementitious materials in the optimization of low carbon cement and concrete with machine learning (ML), and introduces preliminary results of the corresponding program of research at HeidelbergMaterials.

The mining of the Global R&D database showed that the main challenge was not the algorithm type—the general linear model performed as well as artificial networks—but the underlying dataset quality, the rational design of the experiment in the face of the high dimensionality of the problem, and the model testing methodology.

Preliminary results of show that a clinker ratio as low as 50% can be obtained at equal or better strength and workability performance. The surface area of limestone and aggregates was found to be as important as their weight proportion on rheology and early age properties. Regarding the predictors of early age strength, the best subset selection method identified no less than seven variables in addition to C3S and Blaine fineness. The prediction model thus identified a CEM I composition that could reach 50 MPa in one day, thus paving the way to higher SCM replacement levels.

A possible way to reduce CO₂ emissions linked to cementitious materials is to use alternative resources, particularly co-products from other industries. Oyster shell co-products are a calcareous resource produced by aquaculture currently available in coastal areas and must be valorized. The present study investigates the impact of crushed oyster shells used as aggregates in concrete on its mechanical behavior. Thus, concrete samples with 50% aggregates replaced by crushed oyster shells were formulated. Two different types of cement were used: CEMI for reference and low-carbon cement CEMIII-C. Mechanical strength and Young’s modulus were assessed at 28 days, and cracking under compression was followed by acoustic emission technique. Results show that oyster shell aggregates slightly reduce concrete's mechanical resistance but significantly decrease its Young’s modulus. However, cracking behavior under compression remains similar during compression loading.

Accelerated carbonation of recycled concrete aggregates (RCA) is one way to convert them into carbon stores by capturing CO₂ from cement plants. This study investigates the CO₂ captured depending on composition (paste, mortar, or concrete), origin (laboratory, platform), production process (crushing, molding, sawing), and age of RCA. The CO₂ captured is quantified by means of calcimetry (CaCO₃ content evolution). RCA studied ranged in size from 4 to 16 mm (0.16 to 0.63 in.). They were carbonated on a laboratory or semi-industrial scale. It has been shown that the CaCO₃ content of young RCA or RCA protected from natural carbonation, crushed and composed of CEMI is more likely to evolve. It was shown that the cement paste content and the duration of accelerated carbonation increase the amount of CO₂ captured. The composition of the parent aggregates affects the non-carbonated and carbonated CaCO₃ contents, which requires accurate sampling to limit bias in the results. Carbonation efficiency is more difficult to estimate on a semi-industrial scale and the assessment by calcimetric measurement is biased when the parent concrete is made of slag-based cement. The study was carried out within the framework of the French national program FastCarb.