International Concrete Abstracts Portal

A 2-year research project funded by the ACI Foundation measured ultimate strain and stress behavior with controlled experiments to verify that the flexural capacity procedures in ACI 318-19(22) can work for concrete made with belite calcium sulfoaluminate (BCSA) cement. The results indicate that BCSA cement concrete behaves similarly to portland cement concrete in compression and has similar modulus of elasticity and compression strain characteristics.

New hydraulic binders have been extensively studied as potential substitutes for Ordinary Portland Cement worldwide. Very often these binders contain a significant amount of iron and aluminum oxides, as a Ca₄Al_2-xFe_2+xO₁₀ like phase and generate AFm phases as a hydration product. To properly characterize the hydration process (anhydrous phases consumption versus hydrates precipitation), investigating the existence of (Fe/Al)-AFm solid solutions becomes important.

Consequently, layered AFm samples intercalated with various anions (nitrate, chloride, and carbonate) and with varying Fe/Al molar ratios were synthesized. Rietveld refinements were conducted to control the existence of the solid solutions between the two trivalent metallic end-members.

This study presents definitive evidence establishing continuous solid solutions within the three investigated systems of layered AFm phases containing nitrates, chlorides, or carbonates. These solid solutions conform to the Vegard’s law, and reflect the distances between trivalent cations, notably expanding with the iron substitution rate (in accordance with ionic radius R_Al³⁺ = 0.53 Å and R_Fe³⁺ = 0.64 Å). A similar evolution was observed for the three series of AFm compounds.

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.

Masonry structures are very sensitive to out-of-plane mechanisms under horizontal actions. A common traditional technique to avoid or mitigate the activation of these mechanisms is represented by injected anchors made of steel bars aimed to improve the connections between orthogonal masonry walls or between floors and masonry walls. The bars are usually embedded in the masonry by means of cement-based grout in holes realized inside the elements to be connected. Recently, an increased interest has developed in the scientific community about the use of Fibre Reinforced Plastic (FRP) bars as alternative to the steel ones for injected anchors, mainly because of their high tensile strength and inertia to corrosion, which can give them high durability, in addition to the use of high-performance grouts. The paper reports the results of experimental pull-out tests realized by the Authors on several types of FRP bars used as injected anchors in small masonry specimens made of yellow tuff blocks. A hydraulic lime and pozzolana-based grout is used to fix the bars in holes realized in the masonry specimens along an embedded length of 250 mm. The set-up is realized in order to apply pure tension to the bars and shear stresses along the bar-grout and the grout-masonry interfaces. The results are analysed in terms of maximum pull-out forces, failure modes and force-displacement relations in order to evidence the global performance of each tested system, especially in relation with the diameter and the surface treatment of the bars. Some comparisons with literature formulation for predicting the pull-out force are developed too.

Although normal portland cement is made from natural and recyclable materials its manufacture causes significant pollution, especially because of clinkerization which leads to important CO₂ releases into the atmosphere. The use of supplementary cementitious materials (SCMs) to partially replace clinker in normal portland cement and reduce its environmental cost is now well known (e.g., fly ash, metakaolin, glass powder or blast-furnace slag). This study investigates the potential for calcination and reactivity of a carbonate sample containing phyllosilicates. Samples were calcined at different temperatures and investigated using X-ray diffraction (XRD) with Solid State Nuclear Magnetic Resonance (NMR). The results show that the calcination of the sample leads to a dehydroxlation phenomenon of the clay fraction resulting in a change in the coordination of the aluminium atoms. Furthermore, the reaction between the Dolomite and the Palygorskite present in the sample leads to the formation of poorly-crysallized Belite during calcination. Hydration tests on the red-clay sample have demonstrated the hydraulic reactivity of the Belite and the pozzolanic reactivity of the calcined Palygorskite that lead to the formation of hydrates phases (C-S-H ; C-(A)-S-H). The multi-technique analysis applied in this study allows to highlight a direct correlation between the structural modification induced by calcination and the reactivity of the calcined sample.