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The influence of chemical activators on the hydration behavior and technical properties of calcium sulfoaluminate cements blended with ground granulated blast furnace slags
No full textThe manufacture of Ordinary Portland cement (OPC) generates around 8% of the global CO2 emissions related to human activities. The last 20 years have seen considerable efforts in the research and development of methods to lower the carbon footprint associated with cement pro-duction. Specific focus has been on limiting the use of OPC and employing alternative binders, such as calcium sulfoaluminate (CSA) cements, namely special hydraulic binders obtained from non-Portland clinkers. CSA cements could be considered a valuable OPC alternative thanks to their dis-tinctive composition and technical performance and the reduced environmental impact of their manufacturing process. To additionally reduce CO2 emissions, CSA cements can also be blended with supplementary cementitious materials. This paper investigates the influence of two separately added chemical activators (NaOH or Na2CO3) on the technical properties and hydration behavior of four CSA blended cements obtained by adding to a plain CSA cement two different ground granulated blast furnace slags. Differential thermal-thermogravimetric, X-ray diffraction and mercury intrusion porosimetry analyses were done, along with shrinkage/expansion and compressive strength measurements
Fabrication and Properties of Blended Calcium Sulfoaluminate Cements Based on Thermally Treated Reservoir Sediments
No full textIn 2021, approximately 4.1 billion tonnes of cement were globally produced and the annual
CO2 emissions from cement plants reached almost 2.8 billion metric tonnes. In recent years, many
efforts have been made to manufacture low-CO2 cements. In this regard, great consideration has been
given towards calcium sulfoaluminate (CSA) binders for both their technical features and sustainable
properties, principally connected to their industrial process. The use of blended cements composed
by CSA binders and supplementary cementitious materials (SCMS) can be an effective way to (a)
reduce the CO2 footprint and (b) produce greener binders. This scientific work studied the utilization
of different amounts (15–35 wt%) of calcined reservoir sediments (RS) as SCMS in blended CSA
binders, where the binders were cured for up to 56 days and characterised by various analytical
techniques. It was found that thermally treated RS were particularly noteworthy as their utilization
allowed for a dilution of the CSA clinker, thus implying a decrease in CO2 emissions and a reduction
in costs related to their production. However, compared to a plain CSA cement, the blended systems
showed rather similar volume stability levels, whilst their compressive strength and porosity values
were, respectively, lower and higher at all the investigated aging periods
Production of eco-friendly blended calcium sulfoaluminate cements by using biomass-fly ashes
No full textThe 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 thermal-thermogravimetric and mercury intrusion porosimetric analyses
Hydration properties and physical characteristics of belite cements
No full textIn 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
Calcium sulfoaluminate and geopolymeric binders as alternatives to OPC
No full textThis work presents calcium sulfoaluminate (CSA) cement and geopolymeric binder (GEO) as environment-friendly alternatives to ordinary Portland cement (OPC). Mortars based on these binders were tested and compared at the same non-structural strength class (R2 = 15 MPa, according to EN 1504-3). Binder pastes were preliminarily prepared to study their hydration behaviour by means of differential thermal-thermogravimetric (DT-TG) and X-ray diffraction (XRD) analyses. Afterwards, the relative mortars were compared in terms of both fresh (workability) and hardened state properties (compressive strength, dynamic modulus of elasticity, adhesion to bricks, and water vapor permeability). Durability was also investigated in terms of capillary water absorption, drying and restrained shrinkage. Porosimetric analysis allowed to better correlate experimental results with microstructural features of the investigated mixtures. Results showed that GEO-based mortar exhibits the lowest modulus of elasticity, causing the lowest restrained shrinkage and the highest free drying shrinkage. Moreover, its highest porosity determines both the highest capillary water absorption and permeability to water vapor. On the contrary, the CSA-based mortar displays the lowest drying shrinkage, the greatest modulus of elasticity, and the lowest porosity which ensures the lowest capillary water absorption
Tartaric acid effects on hydration development and physico-mechanical properties of blended calcium sulphoaluminate cements
No full textThe fast setting of calcium sulphoaluminate (CSA) cement-based systems is typically controlled using set-retarding admixtures, despite the notable efficiency of tartaric acid (TA) in adjusting CSA-based mixtures setting times, its use has only been marginally investigated, with an almost exclusive focus on the early age properties of TA manufactured mortars. This paper aims at evaluating the effect of the addition of tartaric-acid retarder on the hydration mechanism and physical properties of CSA-based mixtures from 4 h to 84 days. Macro- and microstructural properties were investigated using X-ray diffraction and differential thermal-thermogravimetric analyses, mercury intrusion porosimetry measurements, mechanical tests and analyses at fresh and hardened state. The experimental results reveal that the use of TA delays the formation of ettringite, modifies the porosity of hardened mixtures and strongly reduces strength in the short term. Nevertheless, the addition of TA slightly influences the properties at longer periods
EVALUATION OF ZEOLITIC BEARING TUFFS AS POZZOLANIC ADDITION IN BLENDED CEMENTS
No full textEIGHT CANMET/ACI INTERNATIONAL CONFERENCE ON FLY ASH, SILICA FUME, SLAG, AND NATURAL POZZOLANAS IN CONCRET
Re-use of natural clayey waste as supplementary cementitious material
Full text linkIn 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
Potential application of ettringite generating systems for hazardous waste stabilization
No full textThe potential of ettringite generating systems in hazardous waste stabilization processes is studied by means of a mixture of anhydrous calcium sulphoaluminate and anhydrite doped with the nitrates of the six heavy metals Cu, Cr, Cd, Pb, Zn and Fe. The study has been carried out by means of differential thermal and X-ray diffraction analyses, infra-red spectroscopy, scanning electron microscopy coupled with an energy dispersion system and three different leaching tests. The presence of the metals has only a small negative effect on the hydration kinetics. The hydrated samples retain their structural integrity when submitted to the dynamic leaching test in water and pH 4 HNO3 solution, while they are disintegrated when the leachant is a pH 4.74 acetate buffer. The sulphoaluminate phases can partially accommodate any metal in the crystal lattice, thus giving rise to chemical entrapment
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