Sulfoaluminate-belite Cement Research Articles

Study on the Influence of Nanosilica Sol on the Hydration Process of Different Kinds of Cement and Mortar Properties.

Compared with nanosilica collected in a gaseous state, nanosilica sol has great economic value and application significance for improving the performance of concrete and mortar. In this study, the influence of nanosilica sol on the hydration process of different kinds of cement is studied by means of hydration heat analysis, X-ray diffraction analysis (XRD) and other methods, and the properties of mortar such as setting time, mechanical properties and porosity are also studied to characterize the influence of nanosilica sol on the macroscopic properties of mortar. The experimental results show that nanosilica sol can accelerate the hydration rate of two kinds of cement and promote the hydration reaction degree of cement, and this promotion effect increases with the increase in nanosilica sol content. At the same time, nanosilica sol can significantly shorten the setting time of the two kinds of cement, and it is more obvious with the increase in content. Excessive content of nanosilica sol will adversely affect the permeability resistance of mortar. It may be caused by the weak interval formed by nanosilica particle clusters in the mortar matrix, which can be supported by the mortar pore structure distribution test. At the same time, the influence of nanosilica sol on the hydration of the two kinds of cement is different, and the compressive strength of HBSAC cement mortar increases first and then decreases after adding nanosilica sol; However, the compressive strength of P·O 42.5 cement mortar increases gradually after adding nanometer silica sol. This shows that nanosilica sol does not effectively promote the hydration of β-C2S in high belite sulfoaluminate cement (HBSAC) mortar. Based on the above experimental results, it can be concluded that when the content of nanosilica sol is about 1%, it has the best promotion effect on the hydration of the two kinds of cement and the performance of mortar.

Effects of sodium gluconate on hydration reaction, setting, workability, and strength development of calcium sulfoaluminate belite cement mixtures

Fast setting is an important reason restricting the applications of eco-friendly calcium sulfoaluminate belite (CSAB) cement. To help spread the application of CSAB cement, this study investigated the influence of sodium gluconate (SG) as a setting retarder on the setting, workability, and strength development of CSAB cement mixtures. Quantitative X-ray diffraction (QXRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were performed to understand the effects of SG on the hydration and microstructure of CSAB cement mixtures. The results showed that SG effectively extended the setting time and improved the workability of CSAB cement pastes since it retarded ye’elimite hydration and impeded the loss of workability caused by ettringite formation. Low dosages (≤0.5%) of SG increased the unconfined compressive strength (UCS) of CSAB cement mortars at all ages (from 2 h to 90 days) due to the reduction in void content, fast diminishment of the retarding effect at early ages, and slight acceleration on belite hydration at later ages. However, high dosages (≥1%) significantly degraded the UCS of CSAB cement mortars at all ages since high dosages of SG strongly retarded ye’elimite hydration at early ages and caused a looser microstructure at later ages.

Razvoj por med sintranjem belitno-sulfoaluminatnega cementnega klinkerja z rentgensko računalniško mikrotomografijo

Razvoj por med sintranjem belitno-sulfoaluminatnega cementnega klinkerja z rentgensko računalniško mikrotomografijo

Immobilization of heavy metals, selenate, and sulfate from a hazardous industrial side stream by using calcium sulfoaluminate-belite cement

Release of heavy metals from different industries and industrial waste is a major global threat for as well humans as ecosystems. In this study, immobilization of an industrial filter sludge (FS) with an extremely high content of several heavy metals (24.6 wt% Pb, 21.7 wt% Hg, and 9.00 wt% Se) and sulfate via calcium sulfoaluminate-belite (CSAB) cement was tested. The ratios of 25%, 50% and 75% of CSAB addition were tested, and the target was to achieve immobilization of the hazardous components. The leaching of Pb, Hg, SeO4, SO4, Ni, Cd, Cu, and As was monitored, and the structure of the immobilized materials was examined via X-ray powder diffraction (XRD) and field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) analysis. It was observed that Hg, Cu, As, Cd, and Ni were immobilized completely and leaching of Pb was reduced by 69% from the theoretical release. On the other hand, the leaching of SeO4 and SO4 experienced major increase when CSAB was added. XRD indicated significant ettringite formation as the amount of added CSAB increased, and the formation of gypsum as the amount was decreased. FESEM-EDS indicated that the immobilization was largely based on encapsulation into the CSAB binder, but chemical immobilization into the ettringite binder was also observed. It was concluded that the increased release of SO4 and SeO4 might have resulted from an excess amount of sulfates (added gypsum) during hydration.

Effect of Residual CaSO4 in Clinker on Properties of High Belite Sulfoaluminate Cement Based on Solid Wastes.

The high belite sulfoaluminate cement (HBSAC) containing CaSO4, and without CaSO4, based on solid wastes were successfully prepared from petroleum coke desulfurization slag (PCDS), fly ash (FA), carbide slag (CS), and bauxite (BX). The mineral composition of clinkers after different calcination history were investigated by X-ray fluorescence (XRF), X-ray diffraction (XRD)/Quantitative X-ray diffraction (QXRD), and scanning electron microscopy (SEM), so as to determine the calcination temperatures. The difference between residual CaSO4 and dihydrate gypsum (DG) and the optimal content of residual CaSO4 were discussed by studying the properties of HBSAC. The results revealed that the residual CaSO4 in clinker could replace DG to participate in hydration, and showed some advantages in strength and early hydration heat, but meanwhile increased the water requirement of normal consistency and hydration heat at 72 h, and prolonged the setting time. With the increase of residual CaSO4 content in clinker, the lower limit temperature of clinker formation gradually increased, and the crystal size of clinker minerals became finer and the boundary between crystals became more blurred. However, the optimal calcination temperature (1300 °C) of HBSAC clinker did not change. Considering the effect of residual CaSO4 content on the water requirement of normal consistency, setting time, hydration heat, strength, and hydration products, the optimal design content of residual CaSO4 in HBSAC clinker based on solid wastes, such as PCDS and FA, was 15%.

Solidification/stabilization of gold mine tailings using calcium sulfoaluminate-belite cement

In this study, calcium sulfoaluminate-belite cement (CSAB) was used to stabilize gold mine tailings, which are challenging materials to effectively immobilize due to high heavy metal and sulfate content. The hydration of CSAB cement yields ettringite and monosulfate with good capability for immobilizing sulfates and oxyanions in their crystal structure, in addition to physical encapsulation/solidification in a cementitious matrix. Different mix designs of CSAB cement and mine tailings were prepared, and the samples were cured at room temperature. Mechanical strength and heavy metal leaching were analyzed after 7 days, 28 days, and 90 days of curing, and the phase composition (XRD), thermogravimetric analysis (TGA), and microstructure (FESEM) were also studied. All harmful elements (cationic and oxyanion elements) were effectively immobilized during 7 days of curing, and the heavy metal immobilization remained constant after longer curing, according to an environmental leaching test. High mechanical strength results and good sulfate immobilization were obtained with mine tailing content up to 50 w-% of total binder material. With higher mine tailing content (75 w-% and 90 w-%), the mechanical strength and immobilization ability substantially decreased.

Effects of comb-like PCE and linear copolymers on workability and early hydration of a calcium sulfoaluminate belite cement

Fluidity control and setting adjustment are two critical issues for practical applications of calcium sulfoaluminate cement because of rapid hydration. A commonly used comb-like polycarboxylate superplasticizer (PCE) and linear copolymers (PAS) of acrylic acid (AA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with varied monomer ratio were synthesized to study their impacts on fluidity and early hydration of calcium sulfoaluminate belite cement (CSAB). Results show that the linear PAS polymers are very effective in dispersing fresh cement pastes (fcps) and effectively inhibit early hydration of the cement. More AA unit in the PAS molecules leads to stronger inhibition effect on cement hydration. Compared with the PAS polymers, PCE exhibits almost no inhibition effect on cement hydration despite the high initial dispersibility. Thus, cement pastes containing PAS polymers exhibits excellent fluidity retention compared with the PCE containing fcp due to strong retardation effect of the PAS polymers on early formation of AFt crystals.

Self-Cleaning of Photocatalytic Mortar with Glass Aggregate and Calcium Sulfoaluminate-Belite Cement

The self-cleaning performance and mechanism of photocatalytic mortars with different cementitious materials and aggregates was evaluated through a rhodamine B (RhB) degradation test. The self-cleaning property of photocatalytic concrete helps to preserve its aesthetics, NOx removal potential, and surface reflectance. In this study, the addition of TiO2 to calcium sulfoaluminate-belite cement (CSAB) demonstrated a self-cleaning potential like ordinary Portland cement (OPC). Photocatalytic mortar mixes with OPC demonstrated increased self-cleaning efficiency with glass fine aggregate and with higher TiO2 content. However, glass addition was not effective in improving the self-cleaning efficiency of CSAB mortar with TiO2. Replacement of OPC with class F fly ash significantly decreased self-cleaning efficiency. The decrease in pore solution pH with fly ash replacement of OPC or CSAB cement instead of OPC was hypothesized as the cause for the decline in self-cleaning efficiency. An experiment to study the photocatalytic degradation rate of RhB revealed that it increased with higher pH. RhB photocatalytically degrades through N-de-ethylation and cleavage of the chromophore structure depending on the reaction surface characteristics with the first path investigated in this paper. It was shown that some of the RhB on the photocatalytic mortar surface was degraded by the N-de-ethylation path regardless of the cement and aggregate constituents and increasing TiO2 (anatase) content increased RhB degradation through N-de-ethylation.

Use of fly ash and phosphogypsum for the synthesis of belite-sulfoaluminate clinker

Fly ash and phosphogypsum were used as Naturally Occurring Radioactive Materials (NORM) by-products for the synthesis of belite-sulfoaluminate clinkers. The influence of raw mixture composition and firing temperature was investigated. Clinkers and cements were examined by X-ray powder diffraction and scanning electron microscopy with energy dispersive X-ray spectroscopy. The compressive strength of the cements was determined after 28 days. Clinker phases identified included ye’elimite, ß-phase of belite, ternesite and gehlenite, while the main hydration product of the cement pastes was ettringite. The results showed that belite-sulfoaluminate cements can be fabricated with a compressive strength of 45.9 N/mm2 by firing the raw mixture (70 wt.% marl, 10 wt.% bauxite and 20 wt.% phosphogypsum) at a temperature of 1320°C/1h.

Synthesis and calorimetric study of hydration behavior of sulfate-rich belite sulfoaluminate cements with different phase compositions

Sulfate-rich belite sulfoaluminate (BSA) cements with varied phase compositions were synthesized in this work. The presence of sulfate in the clinker is in the form of anhydrite in addition to calcium sulfoaluminate. The aim of this paper is to study the effect of mineral composition on cement properties. Experimental results indicate that the improvement of early-age strengths mainly depends on the hydration of ye’elimite. The increase of ferrite content promotes the compressive strength after 7 days of hardening, but has adverse effect on cement strength at early ages. The optimum content of ferrite is between 10 and 20% for BSA cement containing approximately 35% ye’elimite. Different amounts of natural gypsum were added to the synthetic sulfate-rich BSA clinkers and we found that anhydrite formed in BSA clinkers can replace natural gypsum to facilitate the hydration of ye’elimite.

Synthesizing of calcium sulfoaluminate-belite (CSAB) cements from industrial waste materials

Calcium sulfoaluminate-belite cement (CSAB) was synthesized using several industrial waste materials such as marble dust waste, FGD gypsum, ceramics dust waste and Napier grass ash as the raw materials. The chemical composition and the phase content of the raw materials were investigated by EDXRF and XRD patterns, respectively. The mixed materials with designed component were calcined at 1,200, 1,250 and 1,300 °C, following with the phase formation observation using the Rietveld refinement from XRD patterns. The XRD patterns indicated that CSAB shows around 58% of ye'elimite and 35% of C2S. The CSAB clinker, which was calcined at 1250 °C for 2 h, was mixed together with 15 wt% of dihydrate gypsum and water-to-cement ratio of 0.6 to study the hydrated pastes at various times (6 h, 1, 3, 7 and 28 days). The hydration mechanism was investigated by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The hydration of CSAB led to the formation of anhydrite, ettringite, portlandite and AFm phases.

Synthesis of low-temperature calcium sulfoaluminate-belite cements from industrial wastes and their hydration: Comparative studies between lignite fly ash and bottom ash

The aim of this research was to study the production of calcium sulfoaluminate-belite (CŜAB) cement from industrial waste materials via hydrothermal-calcination process. Lignite fly ash and bottom ash were used as starting materials for comparison. Other waste materials viz., Al-rich sludge and flue gas desulfurization gypsum were also key players in raw mixes for the synthesis of CŜAB cement. For lignite fly ash as a starting material, mixed phases between ye'elimite and larnite were obtained, whereas for lignite bottom ash as starting material, only ye'elimite was obtained The hydration reaction was studied in terms of heat evolution, setting time, compressive strength and hydration product formation with various gypsum contents. The results showed a rapid formation of ettringite as a main hydration product mixed with calcium silicate hydrate, monosulfate and strätlingite phases as minority, with a fast final setting time of 24–26 min and high early compressive strength of 16.0 and 18.0 MPa in 1 day for CŜAB cements made of fly ash and bottom ash, respectively.

Effect of Anhydrite on the Early Hydration Performance of Rapid Setting and Hardening Belite Sulfoaluminate Cement

In order to investigate the early hydration behavior of rapid setting and hardening belite sulfoaluminate cements, the methods of X-ray Diffraction, Scanning Electron Microscope, Compressive Strength test and Setting Times test were used to identify and quantify the hydration kinetics and microstructure of this new-found cements in China. The results showed that the main mineral compositions of high belite sulfoaluminate cement clinker included calcium sulfoaluminate (4CaO·3Al2O3·CaSO4), belite (2CaO·SiO2), ferrite phase, free gypsum and free lime. It was found that not only the setting time and compressive strength but also the composition of hydration products were influenced by anhydrite to some extent. Meanwhile, a mass of AFt and AFm generated along with the hydration process at different ages, overlapped, crossed and penetrated through calcium silicate hydrate gel and aluminum oxide to form a relatively dense structure which could contribute to the high strength of cement.

Active sulfate-rich belite sulfoaluminate cement

This work focuses on the activation of belite to improve the strength development of sulfate-rich belite sulfoaluminate cements. Borax was used to act as an activator to promote stabilisation of high-temperature belite polymorphs. The phase compositions of clinkers were analysed by using quantitative X-ray powder diffraction. The transformation of β-belite (C2S) to α′-C2S mainly depends on the dosage of borax, and the change in polymorphs is almost complete when the dosage of borax reaches 5%. The formation of α′-C2S can significantly increase the compressive strength and the concentration of borax has a great effect on the strength development of the activated cements. The hydration products of activated cements were also investigated. The results show that the activation of belite can promote the formation of ettringite. Moreover, the crystallisation of ettringite is also affected by the polymorphs of belite, and a fine microstructure of ettringite is found in the activated cement paste.

Hydration and Physico-mechanical Properties of Blended Calcium Sulfoaluminate-belite Cement Made of Industrial By-products

Portland cement blended Calcium Sulfoaluminate-belite (CŜAB) cements were studied in order to improve its binding properties and workability for specific applications. The binders consisted of calcium sulfoaluminatebelite, Flue Gas Desulfurization-gypsum and Ordinary Portland Cement (OPC). In this research, effects of OPC contents (25, 50, 75 wt%) as a CŜAB replacement on hydration behaviors and physico-mechanical properties of the binders were observed. Used CŜAB cement was synthesized using industrial by-products viz., fly ash, Flue Gas Desulfurization-gypsum, Al-rich sludge as starting materials via hydrothermal-calcination method. The results revealed that the replacement of CŜAB cement with OPC extended the setting times of pastes. The reduction of hydration rate with higher OPC content was due to dilution of fast setting phases such calcium sulfoaluminate and mayenite. Hydration products of calcium sulfoaluminate cement were ettringite responsible for high early strength together with Al(OH)3. From 6 h onwards, hydration of tricalcium silicate phase from the OPC generated calcium silicate hydrate. Stratlingite was also found in low OPC content mix resulting from the reaction between the Al(OH)3 and either alite phase in OPC or belite phase in CŜAB cement. Ettringite could also react with Al(OH)3 to generate monosulfate at later ages. The calcium sulfoaluminate phase was mainly responsible for the early mechanical properties, while OPC played an important role to improve strength at later ages.

Production and hydration of calcium sulfoaluminate-belite cements derived from aluminium anodising sludge

Calcium sulfoaluminate-belite cement (CSAB) offers lower CO2 emissions in its production, compared with Portland cement. However, for the production of CSAB a high amount of alumina is required, and the scarcity and high cost of high-purity bauxite make these cements costly at present. In this study, the use of uncalcined aluminium anodising sludge (AAS) as the main source of alumina to produce CSAB clinkers, replacing bauxite, was assessed. The CSAB clinkers produced were mainly composed of ye’elimite and belite, along with minor traces of alite, and/or brownmillerite, depending on the alumina source. Clinkers derived from AAS as a source of aluminium showed a lower content of ye’elimite (35.5%), as well as the formation of alite (8.2%) when compared to a reference clinker produced with reagent-grade materials. Comparable hydration products were identified in the hydrated cements independent of the alumina source used. The use of AAS to produce CSAB cement was proven to be technically feasible, and the cement thus produced has desirable technical characteristics, presenting high mechanical strength (>40MPa in paste samples).

Preparation of calcium sulfoaluminate-belite cement from marble sludge waste

Marble sludge waste was used as a major cement raw material in sintering sulfoaluminate cement clinker successfully in the laboratory. The influences of raw mix composition as well as different burning temperatures were investigated. Starting materials and prepared cement were characterized through different techniques including; Fourier transform infrared spectroscopy (FTIR); X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results reveal that calcium sulfoaluminate–belite cement can be produced by burning a raw mixture contains in weight percent (25% kaolin, 20% gypsum and 55% marble sludge waste) at firing temperature ranging between 1200 and 1250°C.

Hydrothermal synthesis of calcium sulfoaluminate–belite cement from industrial waste materials

This study investigated the use of industrial waste materials viz., fly ash, Al-rich sludge and flue gas desulfurization gypsum in the production of calcium sulfoaluminate–belite cement using hydrothermal–calcination method. The lime deficit in the waste starting materials was recompensed by the addition of hydrated lime. Various factors viz., type of hydrothermal solvent, time of hydrothermal process and calcinations temperature of the hydrothermal products were studied. Phase developments during various synthesized conditions were studied using X-Ray Diffraction. The cement products were mixed with 20 wt% flue gas desulfurization to allow ettringite formation for solidification. The hydration development was investigated in terms of mineralogical composition, microstructures and compressive strength of the hydration products. The largest numbers of calcium sulfoaluminate–belite cement could be obtained by calcination at temperature of 1050 °C. The synthesized cement developed an acceptable 28-day compressive strength of 30.0 MPa. The main hydration products were ettringite, portlandite, calcium silicate hydrate and calcium aluminosilicate hydrate resulting from the hydration of calcium sulfoaluminate and belite phases.

Utilisation of phosphogypsum for sulfate-rich belite sulfoaluminate cement production

Phosphogypsum is an industrial by-product from phosphoric acid production. In order to consume as much phosphogypsum as possible, sulfate-rich belite sulfoaluminate cements are produced by incorporating high amounts of phosphogypsum into the raw mix. The presence of sulfate in the clinker is in the form of anhydrite, in addition to calcium sulfoaluminate. The aim of this paper is to study the effect of anhydrite on cement properties and the hydration process. Experimental results indicate that burning at 1270°C for 30 min is suitable for clinker production. The presence of anhydrite can prolong the setting time and improve the compressive strength. Compared with natural gypsum, anhydrite in the clinkers can promote the formation of ettringite. Results also show that the incorporation of phosphogypsum in the production of sulfate-rich belite sulfoaluminate cement is a promising way to utilise phosphogypsum.

Natural analogs of belite sulfoaluminate cement clinkers from Negev Desert, Israel

Ye’elimite-larnite rocks in the Hatrurim formation of the Negev Desert, Israel, are natural analogs of belite sulfoaluminate (BSA) cement clinkers. They have been produced by ultrahigh-temperature combustion metamorphism at ambient pressure of a calcareous sedimentary precursor. Their mineralogy consists of 35-50 vol% β-Ca2SiO4, 15-20 vol% ye’elimite, 7-15 vol% ferrites, and 15-20 vol% fluorapatite and/or fluorellestadite. A few grains of hatrurite (Ca3SiO5) and α′-Ca2SiO4 have been observed as well. The composition of α′- and β-Ca2SiO4 polymorphs by EPMA are near Ca1.96-1.98Na0.01-0.02 Si0.96P0.03Al0.01O4, whereas ye’elimite has an approximate composition by EPMA of Ca3.99Mg0.02Ba0.01 Na0.02K0.02Al5.73Fe3+0.16Si0.10S0.97P0.02O16. The Al content of brownmillerite Ca2(Fe1-xAlx)2O5 ranges from x = 0.20-0.27. Fe-analog of shulamitite (Ca3Fe2TiO8) contains up to 15.1 wt% TiO2. Ye’elimite-larnite rocks were derived from chalky sediments by burning of combustible gas with a Tmax at 1200-1350 °C. The mineral content, microstructure, and texture/fabric of the ye’elimite-larnite rocks imply that chalky and/or marly sediments with randomly distributed clay, phosphorite, and gypsum may be utilized as cheap naturally homogenized and pulverized mixtures for industrial production of BSA cement clinker, as an environment-friendly alternative to ordinary Portland cement (OPC).