The content of individual amorphous supplementary cementitious materials (SCMs) in anhydrous and hydrated blended cements was quantified by the PONKCS 1 X-ray diffraction (XRD) method. The analytical ...precision and accuracy of the method were assessed through comparison to a series of mixes of known phase composition and of increasing complexity. A 2σ precision smaller than 2–3wt.% and an accuracy better than 2wt.% were achieved for SCMs in mixes with quartz, anhydrous Portland cement, and hydrated Portland cement.
The extent of reaction of SCMs in hydrating binders measured by XRD was 1) internally consistent as confirmed through the standard addition method and 2) showed a linear correlation to the cumulative heat release as measured independently by isothermal conduction calorimetry.
The advantages, limitations and applicability of the method are discussed with reference to existing methods that measure the degree of reaction of SCMs in blended cements.
•Carbonation of two types of steel slag (EAF and BOF).•Time resolved mineralogical and microstructural analysis of carbonated steel slag compacts.•Compressive strength and microstructure of ...carbonated compacts and the effect of precursor mineralogy.•Effect of mineralogy on leaching of carbonated steel slags.
Accelerated carbonation is a treatment for converting alkaline industrial residues into added-value products and storing CO2 in solid form. This work investigated the influence of reacting phases and CO2 uptake on microstructure development, mechanical properties and the environmental behavior of carbonated compacts produced from Basic Oxygen Furnace (BOF) and Electric Arc Furnace (EAF) slags, characterized by a different mineralogy. The compacts were cured under a 100% CO2 atmosphere at 50 °C and pressure of 1.3 or 10 bar for 15 min to 4 h. The BOF slag reacted very fast in the first 30-60 min due to the complete conversion of portlandite to calcite, amorphous calcium carbonate and aragonite, and continued to react over time due to the presence of slower reacting Ca-silicate phases. For the EAF slag, rich in Ca-silicates, the CO2 uptake was lower, and increased only slightly over time at 1.3 bar and became almost stable after 15 minutes at 10 bar; the EAF slag products however presented a higher compressive strength than the BOF slag ones, because of the different phases involved in the carbonation reaction. For the BOF slag, portlandite dissolution caused the formation of voids, only partially filled up by the reaction products. For the EAF slag, formation of a carbonate and amorphous silica layer around the reacting silicates yielded a denser matrix. pH and Ba leaching decreased for both types of slag, whereas V release increased due to the dissolution of reactive phases such as dicalcium silicates, which initially contained this element.
In this work, we investigate the use of pyrite-rich tailings from an operational mine as mineral admixture in different cement matrices Portland cement, calcium aluminate cement (CAC), and calcium ...sulfoaluminate cement (CSA). Hydration and microstructure changes were studied on cement pastes produced with a 30 wt% replacement of cement with tailings, up to 200 days. Based on our results, the effect of the tailings on the hydration of Portland cement is limited to a physical effect, and no sulfide-induced degradation is observed. In the CAC and CSA pastes, minor mineral phases present in the tailings chemically react, leading to changes in the mineral phase composition of CAC and CSA hydrated pastes. In addition, in all cement pastes studied, and more effectively in the CSA pastes, most of the metal(loid)s contained in the tailings were safely immobilized. Cement chemistry notation: C: CaO; A: Al
2
O
3
; F: Fe
2
O
3
; S: SiO
2
; S̅: SO
3
; c: CO
2
; H: H
2
O.
The pozzolanic reaction between portlandite and different types of nearly pure natural zeolites was studied. Analcime, phillipsite, chabazite, erionite, mordenite and clinoptilolite-rich tuffs were ...mixed with portlandite and water (1:1:2 by weight), and the progress of the pozzolanic reaction was quantitatively determined by thermogravimetrical analyses from 3 to 180 days.
A thorough characterization of the raw materials was performed by quantitative XRD, XRF, SEM-EDX, BET specific surface area measurements, grain-size analyses, FTIR and Cation Exchange Capacity measurements. The difference in reactivity of the samples containing zeolites with varying Si/Al ratios, as well as between clinoptilolite-rich samples exchanged with different cations or ground to different grain sizes was assessed.
The results indicate that the external surface area only influences the short-term reactivity, whereas the cation content has an effect on both the long- and short-term reactivity. The early reactivity of the unexchanged samples can be explained by these two parameters, but their long-term reactivity is mainly related to the Si/Al ratio of the zeolites. Samples with zeolites rich in Si react faster then their Al-rich counterparts.
The
in situ early-age hydration and pozzolanic reaction in cements blended with natural zeolites were investigated by time-resolved synchrotron X-ray powder diffraction with Rietveld quantitative ...phase analysis. Chabazite and Na-, K-, and Ca-exchanged clinoptilolite materials were mixed with Portland cement in a 3:7 weight ratio and hydrated
in situ at 40
°C.
The evolution of phase contents showed that the addition of natural zeolites accelerates the onset of C
3S hydration and precipitation of CH and AFt. Kinetic analysis of the consumption of C
3S indicates that the enveloping C–S–H layer is thinner and/or less dense in the presence of alkali-exchanged clinoptilolite pozzolans. The zeolite pozzolanic activity is interpreted to depend on the zeolite exchangeable cation content and on the crystallinity. The addition of natural zeolites alters the structural evolution of the C–S–H product. Longer silicate chains and a lower C/S ratio are deduced from the evolution of the C–S–H
b-cell parameter.
A comparison was made between the early-age hydration of cements blended with micronized zeolitite and quartzite powders. The Portland cement replacement in the mixes was 30%, and the effect of ...introducing a superplasticiser to lower the required water to solid ratio was assessed. The cement pastes were hydrated at 40°C and monitored in situ by time-resolved synchrotron X-ray powder diffraction combined with Rietveld quantitative phase analysis.
The quantitative evolution of phase weight fractions showed that the addition of the zeolite tuff accelerated the hydration rate of the main C3S cement component. Blending with the quartzite powder of similar fineness did not affect the C3S hydration rate. Reduction of the water to solid ratio by introduction of the superplasticiser had a retarding effect on the hydration of the zeolitite-blended cement over the early hydration period up to 3days.
The AFt or ettringite reaction products, formed promptly after the addition of water to the mixtures, underwent a crystal structural modification over the induction period up to 4 to 6hours of reaction. The continuous contraction of the c-cell parameter and expansion of the a-cell parameter towards the ideal values for AFt or ettringite reflects the structural adaptation of the AFt to the changing availability of sulphate over the course of the first hours of hydration. The observed structural changes were less pronounced in the zeolitite blended cement. This is related to the dilution of the overall sulphate content in the blended cement and highlights the need to control and optimise sulphate additions in blended cements.
► Synchrotron XRD clearly shows the complex sequence of blended cement hydration reactions. ► The addition of natural zeolite advance the main cement hydration reactions. ► Quartzite addition of similar fineness did not lead to an acceleration of hydration. ► The AFt reaction product shows structure chemical changes during the first 4–6h of hydration.
The pozzolanic reaction between natural zeolite tuffs, portlandite and water was investigated over the course of the early reaction period up to 3 days. Isothermal conduction calorimetry experiments ...supplemented by TG/DTG and XRD analyses assisted in the elucidation of the sequence of reaction processes taking place. The calorimetry experiments clearly showed the dependence of the pozzolanic reaction rate and associated heat release on the fineness of the zeolite tuff. Higher external surface areas of pozzolans yield higher total heat releases. Also the exchangeable cation content of the zeolites influences the reaction rate. Release of exchangeable alkalis into solution promotes the pozzolanic reaction by raising the pH and zeolite solubility. The appearance of an exotherm after approximately 3 h of reaction is more conspicuous when alkali-rich zeolites are reacted. This exotherm is conceived to be related to a transformation or rupture of initially formed reaction products covering the zeolite grains. The formation of substantial amounts of ‘stable’ calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H) reaction took place after an induction period of more than 6 h. The openness of the zeolite framework affects the proneness of the zeolite to dissolution and thus its reactivity. Open framework zeolites such as chabazite were observed to react much more rapidly than closed framework zeolites such as analcime.
This paper describes the quantitative mineralogy, the mineral chemistry and the distribution of natural zeolites over the outcrop area of the Late Cretaceous Cayo Formation of Coastal Ecuador ...(>1000km2) and develops a model for zeolite alteration in the Cayo volcanic arc. Different zeolite types were identified: Ca-heulandite-type zeolites (clinoptilolite and heulandite), mordenite, laumontite, analcime, stilbite, epistilbite, chabazite, thomsonite and erionite. Zeolites occur over nearly the entire outcrop area and the entire stratigraphical thickness of the Cayo Formation, in percentages varying between less than 20 and nearly 100wt.%. A substantial amount of the analysed samples (1/8) has zeolite contents higher than 50wt.% and could potentially be used in agriculture, aquaculture, for waste water treatment or as supplementary cementitious materials. A clear difference in zeolite type and content was observed when comparing the lower and upper units of the Cayo Formation and the distribution of these units determines the zeolite distribution over the outcrop area. In the upper unit, Ca-HEU-type zeolites are the main zeolite minerals and rarely laumontite and analcime occur. A smectite-rich smectite/chlorite (C/S) is the major associated alteration mineral, while quartz contents are relatively low. In the lower unit, the zeolite mineralogy is more variable and mordenite, Ca-HEU-type zeolites and laumontite are common. Stilbite, epistilbite and analcime occur rarely. Further quartz, albite, C/S and celadonite occur as associated alteration minerals. Little burial metamorphism or volcanically induced hydrothermal alteration has affected the deposits of the Cayo formation. Mineral alteration occurred mainly by interaction of hot pyroclastic glass with marine water, present as pressurized steam in cooling pyroclastic flow deposits on one hand or by low temperature diagenesis of already cooled pyroclastic or epiclastic deposits on the other hand. A model similar to the “geoautoclave” model is proposed to explain the genesis of zeolites, in which an autoclave is formed by the hydrostatic pressure exerted by the marine water column overlying the pyroclastic deposits, preventing gas escape and promoting glass dissolution, zeolite formation and, conversion to higher-grade phases possible if heat can be maintained for a long enough period.
•Natural zeolites of the Late Cretaceous Cayo Formation of Coastal Ecuador.•Quantitative mineralogy, mineral chemistry and areal distribution have been examined.•Zeolites are common over the outcrop area of >1000km2, in percentages 20-100%.•Ca-heulandite-type zeolites and less Ca-Na-mordenite and laumontite occur.•Genesis by diagenesis and by interaction of cooling glass with seawater.
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