International Concrete Abstracts Portal

The significant amount of waste generated in the processing of ornamental stones is a major problem related to civil construction. In this way, numerous international organizations and countries have performed studies on waste recycling in order to reduce its negative effects. Besides, the use of supplementary cementitious materials (SCMs) in cementitious formulations has also gained prominence in several studies aimed at improving these materials in terms of performance, sustainability, and cost. Therefore, this study examined the fresh and carbonation analysis of self-compacting concrete (SCC) made with marble and granite waste as part of ternary cement mixtures. To achieve this objective, an experimental program was developed with four mixtures of SCC. Slump flow test, T500 test, V-funnel test, L-box test, and density were conducted on the fresh concrete. The carbonation properties of the hardened concrete were also determined. The incorporation of marble and granite waste in the mixtures had no influence on the density of the self-compacting concrete and also contributed to the stabilization of the fresh-state properties. It can be inferred from the carbonate analysis that the utilization of marble and granite waste acted as fillers, contributing to the dysconnectivity of the concrete pores and improving the interaction between the concrete constituents. Thus, the results indicated that the use of marble and granite waste in the composition of ternary cement mixtures provides alternative sustainability although it is necessary to pay attention to the amount of cement replacement to avoid a reduction in resistance to carbonation.

The emergence of 3D printing (3DP) technology in construction is limited by the overdependence on conventional Portland cement (PC). This is problematic in remote areas where procuring large quantities of raw materials requires sourcing from greater distances. Additionally, the rapid decline of coal combustion limits the availability of fly ash. This study aims to evaluate the feasibility of substituting high content (larger than 50%) of PC with natural pozzolans, including clay, pumice, and natural zeolite, as well as limestone filler that can be suitable for 3DP. The binder combinations were initially optimized to enhance packing density and robustness by evaluating the minimum water content and relative water demand of cement paste. A series of assessment methods, including slump flow loss test, rheological test, filtration test, axial deformation test, and unconfined uniaxial compression test, were carried out to determine the extrudability and shape stability of mortar made with the optimized binder candidates. Finally, the printability of these mixtures was validated using an extrusion-based 3D printer.

Calcined clays are a very promising supplementary cementitious material. A remaining challenge for a widespread application is the rheology of calcined clay containing cementitious materials. The water and superplasticizer demand and the viscosity of calcined clay binders are higher than for normal Portland cement (PC) binders. Consequently, there is a need to improve the understanding of the rheological properties of calcined clay-based binders. Here, we report on the rheological characteristics of four polycarboxylate ether superplasticizers in Portland cement and LC³ pastes. The superplasticizer chemistry is controlled through polymer synthesis. We chose simple slump flow tests to characterize the rheology of the pastes at different superplasticizer dosages. Furthermore, we characterize the initial reactivity of the binder using in-situ calorimetry. All four polymers exhibit very similar properties in the LC³ system, while the differences are much more prominent in Portland cement. The dosage efficiency in the LC³ system is lower for all polymers, and the most dosage-efficient superplasticizer in the LC³ system is only ranked third in Portland cement. Finally, the very early heat flow of the suspensions indicates that dissolution and early hydrate phase formation of the PC are promoted in LC³ systems. We propose that the increased PC reactivity is partly responsible for the larger slump loss of LC³ binders.

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.

Sixty percent of the nation's highly toxic and radioactive mixed wastes are stored at Hanford in 177 deteriorating underground storage tanks. To close or remove these storage tanks from service and place them in a condition that is protective of human health and the environment, the tanks must be physically stabilized to prevent subsidence once wastes have been retrieved. Remaining residual liquid waste in the tanks that cannot be removed must be solidified and the solid wastes encapsulated to meet the Nuclear Regulatory Commission, Department of Energy, Environmental Protection Agency, and the State of Washington requirements. The Department of Energy has developed cementitious flowable concretes to restrict access and provide chemical stabilization for radionuclides. Formulation, laboratory, and field testing for application at Hanford began with flowable, self-leveling structural and non-structural fills. A slump flow equal to or greater than 610 mm, 0% bleed water, and 0.1% (by volume) shrinkage measurements were key parameters guiding reformulation efforts that resulted in highly flowable, self-consolidating concretes that met Hanford 241-C Tank closure short- and long-term regulatory and engineering performance requirements.