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Alkali-activated calcined clays are promising candidates for playing a prominent role in the future construction industry. These binders may achieve excellent mechanical performance, but one issue deserving attention is the proneness to plastic shrinkage and surface cracking. Tackling this issue requires the deployment of laboratory techniques that allow shrinkage-inducing mechanisms to be quantitatively assessed. Here, we demonstrate that time-lapse X-ray imaging can be used to quantify shrinkage immediately after mixing, when the binder is still in its fresh state, with excellent time and space resolution. The numeric quantification of strain is complemented by the real time visual inspection of the displacing sample interface and of the bleed aqueous solution layer that may form. Implementation of this method to a set of alkali-activated cement pastes, prepared by combining calcined clays having different mineralogical composition with sodium silicate activating solutions having different $$\hbox {SiO}_2$$ SiO 2 /$$\hbox {Na}_2\hbox {O}$$ Na 2 O ratios, suggests that two main mechanisms control the early dimensional stability of alkali-activated calcined clays. These mechanisms are: (a) volumetric contraction occurring in response to capillary stress arising from water evaporation and (b) segregation by particle settling, favoured in the water-saturated regime.

This contribution reports on some preliminary studies on the use of lateritic soils from Cameroon as raw materials for the production of alkali-activated binders.These soils contain about 40-60% kaolinite and variable amounts of quartz, hematite and other minor phases. After calcination at 800 °C, this material is blended with up to 30% waste marble powder, which is produced in large amounts during quarrying, cutting and processing of marble.The results of our tests show that a careful mix design allows a good mechanical performance to be achieved, with values of the cubic compressive strength larger than 30 MPa after 28 days. The role of Fe on the performance of this material is investigated by comparison with Fe-free blends of commercial metakaolin, waste marble powder and quartz. Calorimetric data suggest that the use of alkanolamines as Fe chelating agents may accelerate the early age reactivity, depending on dosage, although the effect on the development of mechanical properties is minor.It is argued that alkali-activated calcined laterite represents a viable option for the development of sustainable binders, especially for the African market, where it could be used, for example, to produce compressed stabilized earth blocks, in substitution of masonry units based on Portland cement or fired clay bricks. The use of waste marble powder adds further environmental value to this material.

<p>The main goal of the EU funded GEO4CIVHIC project is the development of more efficient and low-cost geothermal systems for conditioning retrofitting civil and historical buildings. In this framework, the identification of the most appropriate grout for different heat exchangers is a key factor for improving the overall efficiency of shallow geothermal systems. Therefore, a dedicated investigation was focused on the selection and optimization of the thermo-physical properties of grouting products to be used for:</p><ul><li>the sealing of the coaxial geothermal probes’ head characterized by different installation depths</li> <li>the sealing of the coaxial geothermal heat exchangers by filling the annular gap between the outer casing and the geological formations exposed to the wellbore</li> </ul><p> </p><p>In both cases, the thermo-physical behavior of conventional and thermal enhanced grouts has been determined in laboratory for the purpose of manufacturing satisfactory cement based grouts with a real in-situ application. On the one hand, it is important to identify the grout mixtures having a suitable in situ workability, that is those satisfying specific conditions in terms of injection pressure, grout flowability, open working time and costs. On the other, it is essential to determine those providing optimal heat transfer between the probe and the surrounding ground.</p><p>Several lab experiments were performed on commercially available and enhanced selected mixtures to define (i) the workability and the flowability of the grouts; (ii) fundamental properties like mechanical strength, thermal conductivity and permeability of the hardened materials; (iii) leakage and calorimetric behavior, useful to identify sealing properties and grout setting times; (iv) viscosity and (v) density of the cement based mixture able to give information about the grout rate of descent and thus its pumpability under pressure.</p><p>Lastly, according to the lab results, few grout mixtures were selected as the best choice to be applied in situ for sealing the head of the geothermal probes’ and the annular space between the outer casing and the geological formations exposed to the wellbore. Therefore, this work attempts to address a knowledge gap of the thermo-physical properties, behavior and characterization of grouts for borehole heat exchangers (BHE), that are little studied and known.</p><p> </p>

The quest for a new-generation concrete, designed to be compatible with the need of mitigating the effect of greenhouse gas emissions on the climate, has prompted applied research to define a broad range of low-CO2 cement-based materials. While minimizing CO2 emissions is a goal of the utmost importance, research into sustainable building materials must also tackle the issue of raw material depletion (including limestone, clay and aggregate deposits, as well as water resources) in favor of secondary raw materials. One possible solution is that of minimizing the impact of quarrying by a circular economy approach that envisages the reuse of waste from stone extraction and processing. It is estimated that 200 Mt waste are produced by the stone industry worldwide each year. This includes slurries obtained from the quarrying, cutting and polishing of marble, which can be used as a source of calcium carbonate, alternative to primary limestone. This contribution illustrates the use of waste calcium carbonate, obtained from marble slurry (waste marble, WM), in sustainable cement materials alternative to Portland cement. The possibility of exploiting locally available resources is explored, and the effect of WM additions up to 50% by total mass on the macroscopic properties is investigated experimentally. It is shown that binders with adequate fresh and hardened state properties can be obtained by moderate additions of WM, which greatly enhances the environmental performance by reducing the amount of primary resources used in the mix. By reducing the amount of thermally treated clay in alkali-activated blends, the use of WM also results in a net decrease of the embodied energy.