International Concrete Abstracts Portal

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.

The shortage of high-quality fine aggregate as an essential component of concrete has become an emerging worldwide concern for the construction industry. Concrete typically comprises up to 30% fine aggregate, which largely influences the strength and durability of the final product. Therefore, finding suitable substitutes for natural fine aggregate has become an important aspect of current concrete research.

In this study, we investigated the suitability of using remediated thermal-treated soil and tar-containing asphalt as secondary raw materials in a self-compacting concrete (SCC) mixture. The remediated materials were used as both (1) fine aggregate replacement to replace all the river sand and (2) partial filler/supplementary cementitious material (SCM) replacement. The modified Andreasen and Andersen (A&A) particle packing model was used to determine the optimal replacement level. Based on the optimal mixture design, the impact of the replacement on the fresh and mechanical properties of SCC was evaluated. Additionally, the pozzolanic reactivity of the fine fraction (<125 μm) within the secondary sand was assessed and compared to that of limestone powder. Our findings confirm that using remediated thermal-treated soil and tar-containing asphalt can produce a more circular, sustainable SCC by replacing high-quality natural sand and limestone filler and reducing the environmental impact of conventional SCC. This study contributes to finding viable alternatives to natural fine aggregate and promotes the use of recycled materials in construction.

The use of recycled aggregates in concrete has gained popularity due to its contribution to the reduction of primary resource extraction. In Germany, the use of recycled fine aggregates is not standardized while recycled aggregates larger than 2 mm can be used in concrete depending on their origin, exposure class, and humidity class. In this research framework, we investigated the workability, mechanical, and durability performance of low-clinker mortars using recycled fine aggregates compared to natural sands. Three polycarboxylate ether-based superplasticizers, differing in their polymer structure (chain lengths and charging density) were tested to achieve a comparable initial workability. Four mortar test series with recycled fine aggregates were analyzed with different supplementary cementitious materials to keep the clinker amount low. The initial water demand, presoaking of recycled aggregates, and the workability over time were tested. The workability of low-clinker mortars with recycled aggregates, analyzed through slump flow measurements, proved comparable results to natural aggregates once mixture proportions and superplasticizer type and content were adjusted. However, mechanical tests on mortars with optimized workability properties showed decreased compressive strength and increased capillary suction when using recycled fine aggregates and supplementing cement. An optimized workability procedure for enhanced mechanical properties is still ongoing research. The results are the basis for further mortar and concrete mixture optimizations to reach high-performance low-clinker mortars and concrete with recycled aggregates.

As the worldwide availability of natural sand for concrete continues to decline, attention has turned to manufactured sand obtained from coarse aggregates as an alternative. However, there is still limited information regarding its use in concrete mixtures beyond adhering to standard particle gradation bounds (e.g., CSA A23.1 bounds in Canada). To address the gap, this study presents a central composite design of experiments to analyze the influence of mix proportions on the packing density of concrete mixtures incorporating four types of aggregates: 2 mm sand and manufactured sand, 5-14 mm and 10-20 mm coarse aggregates. The packing density was measured using an intensive compaction tester and results were analyzed using a response surface methodology. The study also included four optimized mix designs obtained using the Fuller-Thompson and the Funk and Dinger methods. Results indicate that a higher proportion of manufactured sand and a higher packing density can be achieved with a particle gradation having a higher proportion of smaller-sized particles. Moreover, the TFA/TA (total fine aggregates/total aggregates) ratio significantly influenced the packing density, whereas the impact of the ratio of 5–14 mm/total coarse aggregates (TCA) was minimal. A prediction model for packing density was developed using multiple regression analysis. These findings provide information on how manufactured sand affects the packing density, which can serve as a foundation for designing concrete mixtures with manufactured sand.