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.

Boron efficiently absorbs neutrons due to its large cross section. Thus, boron containing materials are an effective shield to neutrons and are commonly used as containment barriers in nuclear reactors. The most economical way to include boron into shielding structures is to prepare B-rich mortars or concretes, to be used as structural elements or as plastering. However, colemanite [Ca(B₃O₄(OH)₃)∙(H₂O)], the most abundant Bcontaining mineral, is sufficiently soluble to release enough borate ions in solution to indefinitely stop Portland cement hydration.

Here we present the formulation of hydraulically active binders containing 50% of colemanite. They are based on blends of calcium aluminate cements and blastfurnace slag. The main hydration product in the absence of colemanite is strätlingite along with other AFm phases. MgO causes an increasing hydrotalcite precipitation, and fly ashes further increase strätlingite content. The presence of colemanite causes the precipitation of B-ettringite, where B(OH)₄^¯ ions substitute for sulphate ions. These binders set in one day and harden in 4 days. The addition of hydrated lime in the formulations brings about the additional precipitation of B-containing AFm phases, where the trigonal HBO₃^2- ion constitutes the interlayer between positive [Ca₂Al(OH)₆]+ sheets. These binders set in few hours and harden in one day.