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There is renewed interest in using advanced techniques to characterize ancient Roman concrete due to its exceptional durability and low-carbon footprint. In the present work, samples were drilled from the “Hospitium” in Pompeii and were analyzed by synchrotron microtomography (μCT) and neutron radiography to study how the microstructure, including the presence of induced cracks, affects their water adsorption. The water distribution and absorptivity were quantified by neutron radiography. The 3D crack propagation, pore size distribution and orientation, tortuosity, and connectivity were analyzed from μCT results using advanced imaging methods. Porosity was also measured by mercury intrusion porosimetry (MIP) as a reference. Ductile fracture patterns were observed once cracks were introduced. Compared to Portland cement mortar/concrete, the Pompeii samples had relatively high porosity, low connectivity, and a similar coefficient of capillary penetration. In addition, permeability was predicted from models based on percolation theory and pore structure data to evaluate the fluid transport properties. Understanding the microstructure of ancient Pompeii concrete is important because it could inspire the development of modern concrete with high durability.

In 2019 global cement production has been estimated at 4.1 billion tonnes and CO2 emissions from cement plants were nearly 3.0 billion tonnes. Belite-rich Portland cements (BPCs) have been suggested as innovative environmentally-friendly materials, inasmuch as they can allow a reduction of CO2-emissions up to 35% with respect to ordinary Portland cements (OPCs); in fact, the manufacturing process of BPCs, compared to that of OPCs, is characterized by reduced limestone requirement, lower synthesis temperatures and decreased specific fuel consumption. The peculiar composition of BPCs can be also exploited for achieving valuable technical properties (e.g. better durability against sulfate and carbonation attacks as well as low heat of hydration). This paper examined the hydration behaviour and the physical characteristics of a pilot-scale industrial belite cement hydrated with different water/cement ratios (w/c=0.35 and 0.50) for curing times comprised in the interval 2-90 days; an OPC (class 52.5 R), hydrated with a w/c=0.5, has been employed as a reference term. The experimental findings showed that BPCs systems had better performances, especially at the longest curing periods. [ABSTRACT FROM AUTHOR]

The manufacture of Ordinary Portland cement (OPC) generates about 8% of all anthropogenic CO2 emissions; therefore, carbon dioxide footprint reduction represents the main challenge for the cement industry. The development of environmentally friendly binders, as alternative to OPC, absolutely represents an efficient way to cut carbon emissions. In this regard, during the last twenty years particular attention has been paid to calcium sulfoaluminate (CSA) cements thanks to their valuable technical properties as well as the environmentally friendly features mainly related to their manufacturing process. In addition, a further reduction in carbon dioxide emissions can be achieved diluting CSA cements with supplementary cementitious materials (SCMs) such as industrial wastes. In this title, biomass fly ashes (BFAs) were used as SCMs in CSA-blended cements; BFAs were preliminarily washed (W_BFAs) in order to lower their content in alkali. The influence of the ashes on both hydration properties and technical behaviour of two CSA blended cements, respectively containing 10% and 20% by mass of W_BFAs, was investigated by means of mechanical compressive strength and dimensional stability measurements associated with X-ray diffraction, differential thermalthermogravimetric and mercury intrusion porosimetric analyses. [ABSTRACT FROM AUTHOR]

This work investigates the hydration behaviour and the physico-mechanical properties of mortars based on calcium sulfoaluminate (CSA) cements and fly ash-based geopolymers (GEO) as alternatives to ordinary Portland cement. According to the EN 1504-3, mortars were prepared in order to reach three compressive strength classes, namely R1, R2 and R3 (R1 with Rc. 10 MPa, R2 with Rc. 15 MPa and R3 with Rc. 25 MPa). CSA mortars were prepared by using sulfoaluminate cement alone (R3) or in mixture with a limestone filler (R1 and R2); GEO mortars were manufactured by alkali-activation of coal fly ash and calcium aluminate cement with a sodium silicate and potassium hydroxide water solution. The hydration behaviour was evaluated on pastes submitted to differential thermal-thermogravimetric and X-ray diffraction analyses. Mortars was analysed through mercury intrusion porosimetry; their mechanical properties were evaluated in terms of compressive strength and dynamic modulus of elasticity. Furthermore, capillary water absorption and drying shrinkage tests were carried out in order to evaluate their durability. Due to the rapid ettringite formation, CSA-based mixtures reached their maximum compressive strength values faster than the corresponding GEO mortars. Results showed that the lower modulus of elasticity of GEO mortars causes the higher drying shrinkage. Moreover, the lower porosity exhibited by GEO mortars was responsible for the lower water capillary absorption. [ABSTRACT FROM AUTHOR]

In 2015 total world cement manufacture was estimated at 4.6 billion tons and the CO2 emissions from cement plants were equal to approximately 3.7 billion metric tons, representing about 7% of the global anthropogenic emissions. The utilization of innovative cements and/or supplementary cementitious materials (SCMs) represent a powerful tool for both reducing the CO2 footprint and producing more durable environmentally friendly materials. This paper investigates the possibility of using clayey reservoir sediments (RSs) calcined at 830°C as SCMs in a blended Portland cement; this binder, together with a reference one containing natural pozzolan, was submitted to hydration and mechanical tests for curing times ranging from 2 to 56 days. It has been found that RSs are very interesting SCMs inasmuch as their utilization, allowing a clinker dilution, leads to both CO2 emission decrease and energy saving; furthermore, the hydration behaviour and the mechanical properties of the blended cement were positively affected by the RSs addition. [ABSTRACT FROM AUTHOR]

According to the findings of X-ray diffraction analysis, calcium looping (CaL) spent sorbent (as a main source of CaO), anodization mud (as a source of Al2O3and additional sulfate), and fluidized bed combustion (FBC) fly and bottom ashes, separately or in mixture (as main sources of CaSO4plus alumina and uncarbonated lime) can replace limestone, bauxite, and gypsum as components of calcium sulfoaluminate (CSA) clinker-generating raw mixes. All of the hydrated CSA cements obtained from the corresponding clinkers and investigated by means of differential thermal-thermogravimetric analysis displayed a similar behavior. It has been demonstrated that the well-recognized environmentally friendly character of CSA cement manufacture can be further improved not only by using industrial wastes instead of natural materials, but also by virtue of the reduced CO2emission and increased energy saving associated with the limestone substitution with poorly carbonated sources of lime, such as CaL spent sorbent and FBC ashes. [ABSTRACT FROM PUBLISHER]

Calcium sulfoaluminate (CSA) cements show some desirable environmentally friendly features that include the possibility of using several industrial byproducts as raw materials in their manufacturing process. Alumina powder, from the secondary aluminum manufacture, and anodization mud, from the production process of anodized aluminum, have proved to be suitable as partial or total substitutes for an expensive natural material like bauxite. CSA clinker generating raw mixtures, containing limestone, natural gypsum, bauxite, and/or one of the alumina-rich byproducts, were heated 2 h in a laboratory electric oven at temperatures ranging from 1150 to 1300 °C. Conversion of reactants into 4CaO·3Al2O3·SO3 (the key component of CSA cements), evaluated using X-ray diffraction (XRD) analysis, increased with an increase of both burning temperature and byproduct concentration. When examined through differential thermogravimetric and XRD analyses, a synthetic CSA clinker (made from the raw mixture incorporating alumina powder as a total replacement of bauxite) mixed with 20% gypsum showed a hydration behavior almost similar to that of an industrial CSA cement containing the same amount of gypsum. [ABSTRACT FROM AUTHOR]

Abstract: Fluidized bed combustion (FBC) enables the in situ capture of SO2, but generates large amounts of wastes whose composition and physico-chemical properties make both landfilling and reuse in traditional fields of application (e.g., cement and concrete industries) problematic. Reactivation by water hydration of the desulphurizing ability of these residues is considered a viable mean for their recycling: besides Ca(OH)2, this process can generate other hydration products, such as ettringite. This paper is devoted to a comparison between the behaviour of Ca(OH)2 and ettringite as SO2 sorbents. To this end, synthetic preparations (in the particle size range 0.4–0.6 mm) of the two materials were dehydrated and then sulphated in a lab-scale fluidized bed reactor. Sulphation tests were carried out at 850 °C by fluidizing the bed with an SO2–N2–O2 mixture (1800 ppm SO2) at 0.8 m/s. Calcium conversion degree and fines elutriation rate were evaluated as a function of sulphation time. The propensity of the sorbents to undergo fragmentation was also estimated by particle sizing of in-bed exhausted sorbent particles, with the aid of laser granulometry. Mercury intrusion porosimetry of samples was directed to the assessment of the influence of sorbent dehydration and subsequent sulphation on pore size distribution and porosimetric texture. X-ray diffraction and differential thermal analysis on the synthetic sorbents complemented the characterization. Results showed that dehydration/thermal decomposition brought about a significant increase of the overall porosity for both sorbents, more extensive than it is commonly observed with calcined commercial limestones. Upon sulphation, the two sorbents showed satisfactory degrees of calcium conversion, larger than those usually observed with limestones. Sulphation resulted into a decrease of particle voidage (that of the Ca(OH)2-based sorbent was negligible after the process). Ettringite was more prone to attrition/fragmentation than calcium hydroxide. Results are discussed with a focus on differences between calcium hydroxide and ettringite and on key-parameters affecting the performance of the two materials as sorbents. [Copyright &y& Elsevier]