A Fresh View on Limestone Calcined Clay Cement (LC3) Pastes

In this work, the factors controlling the fresh state properties of limestone calcined clay cement (LC3) are assessed and compared to Portland and binary cements, extending the scope of previous research by combining rheological measurements with setting time determination and the evaluation of plastic shrinkage by a novel method. Yield stress and elastic modulus are considered indicators for the structural build-up/breakdown process when stress is applied to the system. On the other hand, plastic shrinkage occurs from the mixing to the setting of fresh paste and plays an important role in governing microstructural changes due to settlement and evaporation. Evaluation of the rheological properties with time was appropriate to give an overview of the influence and behavior of different added materials. The elastic modulus of all binders (clinker, LC3, clinker–limestone, and clinker–calcined clay) was increased from mixing to 60 min of curing as follows: 5.27 × 103 to 9.50 × 105 Pa, 5.94 × 103 to 9.87 × 105 Pa, 6.89 × 103 to 5.62 × 105 Pa and 7.85 × 103 to 1.27 × 106 Pa, respectively. Moreover, during the first three hours of curing, LC3 exhibited a reduction of plastic shrinkage by more than a factor of 2 compared to clinker cement. The use of calcined clay with clinker increases the elastic modulus of the system due to the flocculation effect and increased water absorption, while a dilution effect is contributed due to deflocculation and a free-water increase in the system when a high fraction of limestone is present in the binary cement. The combination of limestone and calcined clay with clinker can induce additional chemical reactions, which control the early age properties, such as plastic shrinkage. The obtained results can contribute to optimizing the fresh state properties of ternary blends of OPC, calcined clay, and limestone through a knowledge-based approac

In-situ XRPD of hydrating cement with lab instrument: reflection vs. transmission measurements

The complex system of reactions taking place during cement hydration can be investigated by means of in-situ XRPD. Time-resolved synchrotron XRPD is the optimal source although it is hardly accessible for routine measurements. The present work was aimed to test the feasibility of in situ measurements of hydrating cement pastes using a labo-ratory diffractometer (PANalytical X\u2019Pert PRO) in reflecting and focusing transmission geometries. Ordinary CEM-I 52.5 R paste (w/c = 0.5) was measured using three different instrumental settings: reflection Bragg-Brentano geometry, focusing transmission capillary geometry and focusing transmission flat sample geometry. Semi-quantitative phase analysis were performed using a Rietveld full profile fitting approach. Advantages and disadvantages of the three different experimental configurations are critically discussed

On the preparation of concentrated gypsum slurry to reuse sulfate-process TiO2 byproduct stream

The efficient use and transport of byproduct gypsum to be used as a secondary raw material implies its conditioning in a suitable physical form. Most frequently demands are to supply a concentrated suspension, which is sufficiently fluid and stable to be pumped and stored in tanks. The preparation of a fluid concentrated gypsum slurry is a demanding task, since particle anisotropy and surface interactions prevent the attainment of high solid loadings. In this paper we present the testing of different families of dispersants, and discuss the modifications of the surface interactions exerted by each, in terms of surface potential and macroscopic rheological properties. We show that by appropriately choosing the dispersing system it is possible to prepare pumpable concentrated slurries with a solid content approaching 80% by weight. Star-shaped polymers are shown to enable the preparation of highly concentrated suspensions, which exhibit good rheological properties and retain stability both under rest and at the highest shear rates, thus being adapted to be stored in tanks, and to be transferred by pumping. These dispersing agents do not induce electrostatic repulsion among the particles, ζ-potential being nearly zero. Steric repulsion is responsible for the dispersion, and even at the highest concentration the suspension does not show jamming and thickening

X-ray powder diffraction diagram clustering and quantitative phase analysis on historic mortars

This paper deals with the application of cluster analysis to X-ray powder diffraction patterns to define homogeneous groups of mortar-based materials according to their mineralogical composition. For this purpose, the diffraction patterns of 110 samples of mortars from the Temple of Venus (Pompeii, southern Italy) were used to test this method. Rietveld refinement, for quantitative mineralogical phase analysis, was performed on the most representative sample of each cluster. The mineralogical grouping yielded by the cluster analysis of XRPD data turned out to be consistent with the petrographic groups

Co- and Ni-exchanged ferrierite: The contribution of synchrotron X-ray diffraction data to siting of TMIs

High-silica zeolites exchanged with transition metal ions (TMIs) are the subject of great interest for their unusual catalytic activity and selectivity. Structural information like coordination and accessibility of TMIs in zeolites are important factors for understanding their catalytic activity. Siting of TMIs in zeolites is typically obtained by spectroscopic (EXAFS, EPR, UV-vis and IR) and computational methods, as in the case of Co-ferrierite. However, some controversy exists in the literature concerning the model for incorporation of bare Co ions in ferrierite. We show here that the results of our synchrotron X-ray powder diffraction studies on Co- and Ni-exchanged ferrierite (Si/Al = 8.5) are in a good agreement with the model of Co siting based on an indirect spectroscopic approach and help to validate this model. By direct structural evidences, a possible explanation for the larger catalytic activity of Co sites in the main channels of ferrierite can be inferred. A combination of data from in situ XRD continuous monitoring of the Co ion migration during calcination and crystal-chemical considerations allows to device a strategy for the design of optimised co-cations containing Co-ferrierite catalysts