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.

The adoption of blended cements is the most feasible strategy to achieve a more sustainable industry. In this regard, reducing the clinker factor, while retaining performance, is the key parameter to address. Limestone calcined clays are a promising technology as they offer similar performance to OPC from 7 days onwards while enabling a reduction of the clinker content of 50%. In some regions of the world like South America, pozzolanic cements (i.e., blended cements that combine clinker with natural pozzolans) have been used for decades. Their clinker factors range from 80 down to 50%. However, their mechanical properties are in general lower as compared to OPC. In this study, we show that by using LC³-type formulations, cements with the same performance as commercial pozzolanic cements can be produced with clinker contents significantly below 50%. This is explained by the high reactivity of calcined clays and the synergetic reaction of metakaolin and limestone that allows offsetting the clinker reduction.

This paper analyzes waste fines generated during the mining, crushing, and washing of aggregates in quartzite quarries (Mar del Plata, Argentina). The waste fine consists mainly of a mixture of quartzite and clay. The characterization of the materials included chemical analysis, XRD, TGA, particle size distribution, morphology, and composition of particles by SEM-EDS. Both the dry raw materials and the calcined material (temperatures of 500º C, 700º C, and 950º C) were analyzed. The pozzolanic activity of the calcined powders at different temperatures was evaluated by the modified Chapelle method. The original composition of the material, consisting of angular quartz, kaolinite "face to face" and laminar illites, was modified as calcined clays vary in their morphology and mode of aggregation due to the effect of temperature. The result of the TGA showed some limited loss on ignition (3%) between 400º C and 800º C, reflecting the dehydroxylation of clays. The pozzolanic activity effectively increased with increasing calcination temperature. Therefore, the material is considered to have pozzolanic activity when thermally activated.

The present paper preliminarily illustrates the mechanism of damages caused by the alkali-silica reaction (ASR) between the high alkali content of the dry shake-hardener due to the high cement content on the top of the concrete industrial floors and the alkali-reactive coarse aggregate in the concrete substrate. To mitigate or prevent these damages a special dry shake-hardener, based on the partial replacement of the Portland cement by siliceous fly ash, is used. The beneficial influence of the fly ash, as well as that of other fine pozzolanic materials, is due to the distribution of a very large number of amorphous silica-based fine particles which can potentially react with the alkali in the same way as the amorphous or badly crystallized silica of the alkali-reactive coarse aggregates. The introduction of a very high number of pozzolanic particles significantly reduces the alkali availability for the reaction with the few alkali-reactive coarse aggregates. In other words, the alkalis instead of concentrating their aggression on a few grains of the alkali-reactive coarse aggregates, usually 5 to 15 mm (2 to 6 in.) in size, spread their action on a large number of very fine pozzolanic particles so that their expansive and destructive power is lost. However, another problem can arise when the Portland cement is partially replaced by fly ash due to the longer setting time, particularly in cold weather, of the dry shake-hardener, so that the workers must wait a very long time before the mechanical troweling and the opening of the finished surface to the pedestrian traffic. To avoid this drawback a combined use of the siliceous fly ash and a setting accelerator, based on tetra-hydrate calcium nitrate in powder form [4H₂O∙Ca(NO₃)₂ > 4H₂O∙CaO∙N₂O₅ > H₄CN₂] has been studied at three different temperatures: 35°C (95°F), 20°C (68°F) and 5°C (41°F). In warm weather, at temperatures as high as 35°C (95°F), there is no need for H₄CN₂ since the Portland cement hydration occurs at a very great rate and only the dry shake-hardener containing fly ash without H₄CN₂ can be applied within few hours and incorporated into the concrete substrate. At 20°C (68°F) the delay in the setting times caused by the partial replacement of Portland cement by fly ash can be compensated by the use of H₄CN₂ at 1% by weight of the cementitious materials. In cold weather, such as that caused by a temperature as low as 5°C (41°F), a much higher percentage of H₄CN₂, up to 5% by weight of the cementitious materials, must be used to reduce the setting times at approximately the same values as those recorded at 20°C (68°F) when the dry shake-hardener without fly ash is used.

The use of calcined clays as clinker replacement requires the addition of effective superplasticizers. Phyllosilicates in clays are known for their contribution to the pozzolanic reactivity after calcination. Previous investigations on single components of clays identified metaphases of phyllosilicates as the challenging minerals, whereas quartz can promote a proper workability and effectiveness of superplasticizers. It is still under discussion which type of calcined phyllosilicate (1:1 or 2:1), namely metakaolin or metamuscovite/metaillite is more challenging regarding their interaction with superplasticizers. A comparison of these single phyllosilicates among each other and with calcined clays relevant to the cement industry is limited due to physical properties differing too significantly. The study focuses on the question of whether calcined clays with 1:1 or 2:1 phyllosilicates interact better with polycarboxylate ether-based superplasticizers (PCEs) in cementitious systems under the consideration of their physical properties. Five calcined common clays originating from German clay pits are used. The clays differ significantly in their mineralogical composition before calcination, especially regarding their amount of kaolinite, muscovite, and quartz. A Portland limestone cement is replaced by 30% by weight of calcined clay. Two PCEs are used that exhibited good compatibilities with calcined clays in investigations beforehand. Measurements with a rotational viscometer determine the flow resistance each 5, 30, 50, and 105 minutes after water addition. In combination with the adsorption behavior analyzed via zeta potential measurements, the results give fundamental knowledge about the efficiency of superplasticizers depending on the type of calcined clay.