Enhancement in early strengths of slag-cement mortars by adjusting basicity of the slag prepared from fly-ash of MSWI

The insufficient early strengths of cement mortars in which partial cement had been replaced by pulverized slag melted from municipal solid waste incinerator (MSWI) fly-ash were tackled in this study by adjusting the basicity of the slag through the addition of various amounts of CaCO₃ into MSWI fly-ash, melted into a ‘modified slag’, pulverized to partially replace cement. Increased basicity in the modified slag manifestly improves the early compressive strengths of cement mortar with 20% Portland cement replaced by the modified slag powder (20 wt.% CaCO₃ added). The 14-day and 28-day compressive strengths of the mortars evidently increased to nearly that of the reference specimen made of only Portland cement mortar. The 90-day compressive strength is even higher than that of the reference specimen. Porosity and Fourier transform infrared spectra (FTIR) analyses evidenced the improvement in early strengths by hydration while the enhancement in long-term strength by pozzolanic reaction in the CaCO₃ added slag-cement mortar.     

Characteristics of pastes from a Portland cement containing different amounts of natural pozzolan

This work is concerned with assessing the influence of natural pozzolan on the physical, mechanical and durability properties of blended Portland cement pastes. The results indicate that final setting times of natural pozzolan blended Portland cement pastes range from 4 to about 5 h. Naphthalene-type superplasticizer tends to retard the hydration process of plain and natural pozzolan blended Portland cement pastes. These blends show slightly higher setting times than those without superplasticizer. The use of superplasticizer is found to have a significant influence on the workability. At a lower level of Portland cement replacement by natural pozzolan, the addition of 1% superplasticizer by weight of blended Portland cement leads to a significant decrease in the water to Portland cement plus natural pozzolan ratio for a given workability. However, for the blended Portland cement with a high proportion of natural pozzolan, the increase in water content causes the porosity to increase with an accompanying decrease in compressive strengths. The variations in composition and cure time are found to provide significant changes in compressive strength. Depending on these parameters, the variation in compressive strength can be estimated by using the equation, σ=σ₀/[1+exp(a+bp+cp²)]ⁿ, where σ is the compressive strength of natural pozzolan blended Portland cement paste at a given cure time and natural pozzolan replacement level (MPa); σ₀ is the compressive strength of plain Portland cement pastes with or without superplasticizer at a given cure time (MPa); p is the natural pozzolan replacement level (%); a, b, c, n are the empirical constants to be determined. The blend with a composition of 80% Portland cement and 20% natural pozzolan and 1% superplasticizer provides superior strength and durability characteristics in comparison to the counterparts without superplasticizer and to the blends with a high proportion of natural pozzolan. At high contents of natural pozzolan, the resistance to freezing and thawing is found to be impaired. Moreover, these blended cements do not provide high durability performance against sulfate attack.     

In situ synchrotron X-ray powder diffraction study of the early age hydration of cements blended with zeolitite and quartzite fines and water-reducing agent

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 3 days.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 6 hours 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.     

碱-磷渣水泥的研究

碱-矿渣水泥具有较高的强度,它的其它物理力学性能也均优于硅酸盐水泥。本文研究了用水玻璃和粒化电热磷渣来生产碱-磷渣水泥时,水玻璃的模数、磷渣中可溶性磷及水固比对碱-磷渣水泥特性的影响。实验结果表明:水玻璃模数对碱-磷渣水泥的性能有较大的影响;可溶性磷对碱-磷渣水泥的凝结时间几乎无影响;增大水固比,对碱-磷渣水泥的早期水化及强度都不利。     

Effect of calcium chloride on the volume contraction,non-evaporable water content and bound chloride content of hydrated portland cement and blast-furnace slag

The change in volume during hydration, Δv, and the water retained at 105°C at ultimate hydration, w_n^o, have been measured for cement-calcium chloride-water systems in which the cements consisted of portland cement, blastfurnace slag and mixtures of portland cement and blastfurnace slag in equal parts by mass.The results showed that the quantity of chloride bound in the solid phases increased with the initial concentration of chloride in the aqueous phase but the parameters Δv and w_n^o for a particular system were independent of the initial chloride concentration in the aqueous phase.     

Hydration behavior of spinel containing high alumina cement from high titania blast furnace slag

Hydration behavior of the spinel containing high alumina cement prepared from high titania blast furnace slag via smelting reduction method is studied. Cooling condition has considerable effect on the phase compositions and hydration behavior of the prepared cements. Hydraulic CA, CA₂, inert spinel and gehlenite are the main mineral phases of the naturally cooling cement. Glassy phase, CA and some spinel are the main phases of the splat cooling cement. Both of the prepared cements have controllable setting time, water requirements. Strength of splat cooling cement develops slowly than naturally cooling cement. The naturally cooling cement has satisfactory compressive strength, which is higher than splat cooling cement, but lower than commercial CA80 and Secar71. XRD and SEM observation confirms that CAH₁₀ is the main hydrate of splat cooling cement. Metastable CAH₁₀, C₂AH₈, are the main hydrates of naturally cooling cement, which will convert to stable C₃AH₆ with continuing hydration.     

Study on modification of the high-strength slag cement material

The influence of the slag powder's fineness, the amounts of activator, type and contents of modification addition on the dry-shrinkage and strength of the high-strength slag cement material was investigated. The experimental data showed that adding 9% Na₂SiO₃ activator and 10% Portland cement (PC) made the ratios of drying-shrinkage of high-strength slag cement material similar to the ratios of Portland cement and the compressive strengths as higher. The main hydration products are calcium alumina-silicate gels and a little CH; the gel ratio of CaO/SiO₂ is close to 1 and includes a little Na₂O and MgO for high-strength slag cement material, as shown by means of scanning electron microscope (SEM) and energy-dispersive X-ray analyzer (EDXA).     

Investigation of blended cement hydration by isothermal calorimetry and thermal analysis

Hydration of portland cement pastes containing three types of mineral additive; fly ash, ground-granulated slag, and silica fume was investigated using differential thermal analysis, thermogravimetric analysis (DTA/TGA) and isothermal calorimetry. It was shown that the chemically bound water obtained using DTA/TGA was proportional to heat of hydration and could be used as a measure of hydration. The weight loss due to Ca(OH)₂ decomposition of hydration products by DTA/TGA could be used to quantify the pozzolan reaction. A new method based on the composition of a hydrating cement was proposed and used to determine the degree of hydration of blended cements and the degree of pozzolan reaction. The results obtained suggested that the reactions of blended cements were slower than portland cement, and that silica fume reacted earlier than fly ash and slag.     

Drying and autogenous shrinkage of pastes and mortars with activated slag cement

Activated slag cement (ASC) shows significantly higher shrinkage than ordinary Portland cement agglomerates. Cracking generated by shrinkage is one of the most critical drawbacks for broader applications of this promising alternative binder. This article investigates the relationship between ASC hydration, unrestrained drying and autogenous shrinkage of mortar specimens. The chemical and microstructure evolution due to hydration were determined on pastes by thermogravimetric analysis, conduction calorimetry and mercury porosimetry. Samples were prepared with ground blast furnace slag (BFS) activated with sodium silicate (silica modulus of 1.7) with 2.5, 3.5 and 4.5% of Na₂O, by slag mass. The amount of activator is the primary influence on drying and autogenous shrinkage, and early hydration makes a considerable contribution to the total result, which increases with the amount of silica. Drying shrinkage occurred in two stages, the first caused by extensive water loss when the samples were exposed to the environment, and the second was associated with the hydration process and less water loss. Due to the refinement of ASC porous system, autogenous shrinkage is responsible for a significant amount of the total shrinkage.     

Hydration of calcium sulfoaluminate cements — Experimental findings and thermodynamic modelling

Calcium sulfoaluminate cements (CSA) are a promising low-CO₂ alternative to ordinary Portland cements and are as well of interest concerning their use as binder for waste encapsulation. In this study, the hydration of two CSA cements has been investigated experimentally and by thermodynamic modelling between 1 h and 28 days at w/c ratios of 0.72 and 0.80, respectively.The main hydration product of CSA is ettringite, which precipitates together with amorphous Al(OH)₃ until the calcium sulfate is consumed after around 1-2 days of hydration. Afterwards, monosulfate is formed. In the presence of belite, strätlingite occurs as an additional hydration product. The pore solution analysis reveals that strätlingite can bind a part of the potassium ions, which are released by the clinker minerals. The microstructure of both cements is quite dense even after 16 h of hydration, with not much pore space available at a sample age of 28 days.The pore solution of both cements is dominated during the first hours of hydration by potassium, sodium, calcium, aluminium and sulfate; the pH is around 10-11. When the calcium sulfate is depleted, the sulfate concentration drops by a factor of 10. This increases pH to around 12.5-12.8.Based on the experimental data, a thermodynamic hydration model for CSA cements based on cement composition, hydration kinetics of clinker phases and calculations of thermodynamic equilibria by geochemical speciation has been established. The modelled phase development with ongoing hydration agrees well with the experimental findings.     

Modification of cement with succinic anhydride‐based hyperbranched polyesteramide

Two hyperbranched polyesteramides (HYP₁ and HYP₂) were prepared by reacting succinic anhydride (ScAn) with both of diisopropanolamine (DiPA) and diethanolamine, respectively, via one‐pot polycondensation reaction. The prepared polymers were analyzed using gel permeation chromatography, infrared spectra, and 1HNMR. The resulting hydroxyl‐ended resins have been successfully applied as polymeric admixtures in two types of cements such as Ordinary Portland cement and Portland limestone cement. The water of consistency decreased by addition of the hyperbranched polymers in both types of cements. Better hydration was observed by incorporation of small amounts of polymers. The infrared spectra and scanning electron microscopy photos of Ordinary Portland cement and Portland limestone cement pastes premixed with HYP₁ and HYP₂ showed no effect on the chemical composition of the cement hydrates where only the morphology and the crystallinity of the formed hydrates were changed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

硫铝酸盐水泥与硅酸盐水泥复配性能研究

基于硫铝酸盐水泥、硅酸盐水泥各自的特点,研究了二者复配后的标准稠度用水量、凝结时间、水化热效应、胶砂强度、膨胀性、水化产物的物相及微观形貌。结果表明,复配水泥的标准稠度用水量因复配比例不同而变化,凝结时间相对于占主导地位的单组分水泥明显缩短;复配水泥的早期水化速率得到提高,1d、7d的水化放热量均低于占主导地位的单组分水泥;28d抗压、抗折强度低于任何单组分水泥;膨胀性的大小取决于两种水泥的复配比例;硫铝酸盐水泥与硅酸盐水泥的复配使二者的水化相互促进,随着硫铝酸盐水泥掺量的增加,Ca(OH)2相的衍射峰减弱,AFt相的衍射峰增强;纯硅酸盐水泥水化后的微观形貌是致密的,而与硫铝酸盐水泥复配后则出现微观裂纹。     

Preparation and performance of slag-based binders for the cementation of fine tailings

To achieve effective cementation of fine tailings, slag-based binders were prepared using Portland cement clinker stimulation, early strength activator (ESA, mixture of anhydrite and triethanolamine at 97:3 (w/w)) activation and slag pulverization methods. The compressive strength, hydration products, slag reaction degree and non-evaporable water content of the consolidated samples under different curing times were analyzed to clarify the application performance and early strength action mechanisms of this slag-based binder. The results showed that clinker alone was able to effectively stimulate the slag’s cementitious property, but the cementation strength was relatively low. The addition of ESA in the clinker activated slag promoted the conversion of C₄AH₁₃ into ettringite (AFt) and accelerated the consumption of Ca(OH)₂, all of which significantly improved the early cementation strength of fine tailings. Slag pulverization promoted the slag reaction degree and increased the yield of hydrated products, which led to a further increase in the early strength of the slag-based binder. Eventually, a more efficient and higher early strength slag-based binder was prepared with the composition of 27% clinker, 10% ESA and 63% pulverized slag, and the cementation strength at 3 curing days for the fine tailings sample was 231% more than that of P.O 42.5 Portland cement.     

Study of alinite cement hydration by impedance spectroscopy

Two types of alinite cements, Mg-alinite and Zn-alinite, were synthesized using the reagent grade chemicals. Their hydration behavior was compared with ordinary Portland cement (OPC) using impedance spectroscopy (IS) and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy. The bulk resistance in the IS spectra and the intensity ratio of the hydrous (Q₁ and Q₂) to anhydrous (Q₀) phases in the NMR spectra were estimated as the extent of hydration. The results obtained from both techniques were consistent each other. Mg-alinite had a comparable hydration rate to OPC and Zn-alinite exhibited faster hydration kinetics than Mg-alinite.     

Use of recycled copper slag for blended cements

Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry     

Properties and hydration of blended cements with steelmaking slag

The present research study investigates the properties and hydration of blended cements with steelmaking slag, a by-product of the conversion process of iron to steel. For this purpose, a reference sample and three cements containing up to 45% w/w steel slag were tested. The steel slag fraction used was the “0-5 mm”, due to its high content in calcium silicate phases. Initial and final setting time, standard consistency, flow of normal mortar, autoclave expansion and compressive strength at 2, 7, 28 and 90 days were measured. The hydrated products were identified by X-ray diffraction while the non-evaporable water was determined by TGA. The microstructure of the hardened cement pastes and their morphological characteristics were examined by scanning electron microscopy. It is concluded that slag can be used in the production of composite cements of the strength classes 42.5 and 32.5 of EN 197-1. In addition, the slag cements present satisfactory physical properties. The steel slag slows down the hydration of the blended cements, due to the morphology of contained C₂S and its low content in calcium silicates.     

Effects of Al2O3 on the hydration activity of municipal solid waste incinerator fly ash slag

This study investigates the effects of slag composition on the hydration activity of slag-blended cement (SBC) pastes. Synthetic slag samples were prepared by melting Al₂O₃-modified, municipal solid-waste incinerator (MSWI) fly ash. In addition to the original slag (containing 25.0% CaO and 17% Al₂O₃), two other synthetic slag types, A1 and A2 slag, were prepared, having a 15% or 5% Al₂O₃ content, respectively. These synthetic slags were blended with ordinary Portland cement (OPC) at weight ratios ranging from 10% to 40%. The results indicate that the incorporation of 10% A1 slag tended to enhance the degree of hydration in SBC pastes during the early ages (3-28 days), but at later ages, significant difference in the degree of hydration between the OPC and SBC pastes with 10% A1 slag was not observed. The tendency of the 10% A2 slag case was similar, but with a limited enhancement during the early ages (3-28 days). However, samples that incorporated the Al₂O₃-modified slag (AMS) showed decreased degrees of hydration. The degree of hydration of the 40% blend ratio sample decreased significantly.     

Early age hydration of rice hull ash cement examined by transmission soft X-ray microscopy

Early age hydration of barium-doped β-Ca₂SiO₄ cement, produced from rice hull ash (RHA), is examined by transmission soft X-ray microscopy. Use of low-energy cements produced from by-product materials, such as the cement considered here, may be economically and environmentally advantageous. However, the hydration kinetics and morphology and composition of the products of RHA-based β-Ca₂SiO₄ cements have not been investigated. Observation of the early age cement hydration shows evidence of cement dissolution and hydration product formation, including the formation of Hadley grains. The rates of the reaction and amount product formed appear to be related to the hydrothermal processing temperature and the chemical composition of the cement. That is, more rapid hydration is observed for barium-doped RHA cements produced at higher temperatures and for cements produced with higher barium contents, within the ranges examined.     

Effect of Temperatures up to 90°C on the Early Hydration of Portland–Blastfurnace Slag Cements

Isothermal conduction calorimetry has been used to monitor the early hydration of Portland–blastfurnace slag (BFS)-blended cements. Portland:BFS composite cements with ordinary Portland cement replacements from 0 to 90 wt% were studied at curing temperatures from 12° to 90°C. Peak II, principally associated with alite (Ca₃SiO₅) hydration, was accelerated with increasing temperature for all blends. Peak S, associated with BFS hydration, was particularly noticeable at 40° and 60°C. At higher curing temperatures, peak S merged with peak II, indicating thermal activation of BFS. Novel plots of total heat output against percentage replacement show that BFS contributes to the heat of hydration, even at temperatures below its thermal activation.     

Pore solution chemistry of the hydrated system tricalcium silicate/sodium chloride/water

The relative tendency of different Portland cements to remove chloride ions from concrete mix water by forming insoluble complexes is an important determinant of the corrosion behaviourod steel in concrete. Whilst the C₃A phase plays a dominant role in binding chloride ions, other cement minerals may be of secondary importance but their effects are not well established. The reported investigation is an attempt to elucidate the extent to which chloride binding occurs within the hydration products of the C₃S (alite) phase of Portland cement when sodium chloride is present in the mix water.