Influence of initial casting temperature and dosage of fly ash on hydration heat evolution of concrete under adiabatic condition

The calorimetric data of binders containing pure Portland cement, 20% fly ash, 20% slag and 10% silica fume respectively are determined at different initial casting temperatures using an adiabatic calorimeter to measure the adiabatic temperature rising of concrete. The calorimetric data of binders with different dosages of fly ash at two water binder ratios (w/b) are determined, too. Elevation of initial casting temperature decreases the heat evolution of binder, enhances the heat evolution rate of binder and increases the heat evolution rate of binder at early age. The dosage of fly ash in concrete has different effects on the heat evolution of binder with different w/b. At high w/b ratio the heat evolution of binder decreases when dosage of fly ash increases. At low w/b ratio the heat evolution of binders increases when dosage of fly ash increases from 0 to 40% of total binder quantity. The heat evolution of binder decreases after the dosage of fly ash over 40%. An appropriate dosage of fly ash in binder benefits the performance of concrete at low w/b ratio.     

Influence of mechanical grinding on pozzolanic characteristics of circulating fluidized bed fly ash (CFA) and resulting consequences on hydration and hardening properties of blended cement

This paper investigates the influence of mechanical grinding on pozzolanic characteristics of circulating fluidized bed fly ash (CFA) from the dissolution characteristics, paste strength, hydration heat and reaction degree. Further, the hydration and hardening properties of blended cement containing different ground CFA are also compared and analyzed from hydration heat, non-evaporable water content, hydration products, pore structure, setting time and mortar strength. The results show that the ground CFA has a relatively higher dissolution rate of Al₂O₃ and SiO₂ under the alkaline environment compared with that of raw CFA, and the pozzolanic reaction activity of ground CFA is gradually improved with the increase of grinding time. At the grinding time of 60 min, the pozzolanic reaction degree of CFA paste is improved from 6.32% (raw CFA) to 13.71% at 7 days and from 13.65 to 28.44% at 28 days, respectively. The relationships of pozzolanic reaction degree and grinding time of CFA also conform to a quadratic function. For ground CFA after a long-time grinding such as 60 min, the hydration heat and non-evaporable water content of blended cement containing CFA are significantly improved. Owing to relatively smaller particle size and higher activity of ground CFA, the blended cement paste has more hydration products, narrower pore size distribution and lower porosity. For macroscopic properties, with increase in grinding time of CFA, the setting time and strength of blended cement are gradually shortened and improved, respectively.     

Study of the hydration of Portland cement blended with blast-furnace slag by calorimetry and thermogravimetry

The hydration of ordinary Portland cement (OPC) blended with blast-furnace slag (BFS) is a complex process since both materials have their own reactions which are, however, influenced by each other. Moreover, the effect of the slag on the hydration process is still not entirely known and little research concerning the separation of both reactions can be found in the literature. Therefore, this article presents an investigation of the hydration process of mixes in which 0–85% of the OPC is replaced by BFS. At early ages, isothermal, semi-adiabatic and adiabatic calorimetric measurements were performed to determine the heat of hydration. At later ages, thermogravimetric (TG) analyses are more suitable to follow up the hydration by assessment of the bound water content w _b. In addition, the microstructure development was visualized by backscattered electron (BSE) microscopy. Isothermal calorimetric test results show an enhancement of the cement hydration and an additional hydration peak in the presence of BFS, whilst (semi-)adiabatic calorimetric measurements clearly indicate a decreasing temperature rise with increasing BFS content. Based on the cumulative heat production curves, the OPC and BFS reactions were separated to determine the reaction degree Q(t)/Q _∞ (Q = cumulative heat production) of the cement, slag and total binder. Moreover, thermogravimetry also allowed to calculate the reaction degree by w _b(t)/w _b∞. The reaction degrees w _b(t)/w _b∞, Q(t)/Q _∞ and the hydration degrees determined by BSE-image analysis showed quite good correspondence.     

Effect of water/binder ratio and temperature on the hydration heat and properties of ternary blended cement containing slag and iron tailing powder

Journal of Thermal Analysis and Calorimetry - The effects of water/binder ratio and temperature on hydration heat and properties of ternary blended cement containing slag and iron tailing powder...     

Morphology and physical properties of a novel Ramie‐PU blended nonwoven by electrospinning: The effect of cosolvent ratio

A novel macro/nano blended nonwoven with excellent physical properties was prepared by electrospinning polyurethane (PU) nanofibers onto the surface of ramie webs under different weight ratios of N,N‐dimethylacetamide (DMAc)/acetone cosolvents. The ratio of cosolvents has a significant influence on the morphology, tensile properties, resilience, and thermal properties of the resultant samples. Bead‐free and fine interconnected nanofibers were obtained with an increase of acetone content up to 60 wt%. The total physical properties of the blended nonwovens were optimal for a DMAc/acetone ratio of 40/60, in which the tensile load at break, extension at break and Young's modulus were 441, 54, and 256% higher than that of pure ramie web, respectively. The resilience of the blended nonwovens was ～20% higher than that of nonblended ramie web. The significant improvement of physical properties may be due to the good connection between PU nanofiber membranes and ramie webs and the molecular chain structure differences, interconnected structural differences, and high extensibility of PU nanofibers, according to the results of crystallization by differential scanning calorimetry (DSC) and morphological observation by scanning electronic microscopy (SEM). © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1–14, 2010     

Calorimetry and other methods in the studies of expansive cement hydrating mixtures

In this study, the calorimeter was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The shrinkage-less and expansive binders were produced by mixing of Portland cement with an expansive additive produced by sintering and composed of calcium sulfoaluminate (yeelimite), calcium sulfate (anhydrite) and lime. The studies were focused on the synthesis of this aluminate??sulfate??lime additive (temperature of burning process as a parameter controlling the relative activity of components) from the materials being the by products and subsequently on the mixture proportions to ensure the hydration process resulting in non-shrinkage or expansion effect. In the experiments the proportions of expansive mixture and cementitious materials were variable. The investigations with aim to find the relationship between the volume changes and composition of initial mixtures in cement pastes and mortars (with sand) were also carried out. The phase composition and microstructure of products were characterized. The expansive additive in the environment of hydrating cement transforms into ettringite and gives an increase of volume when the plastic material transforms to the more rigid matter but before the ultimate hardening takes place. Proper, moderate setting and hardening in strongly modified mixtures is achieved when the calorimetric curve corresponding to the heat evolution on hydration is analogous to that for the basic Portland cement. The rate of heat evolution data are well compatible with the other results related to the other methods of hydration kinetics assessment (e.g. chemical shrinkage) and discussed in terms of the phase composition of hydration products.     

Hydration heat evolution of high-belite cement–phosphate slag binder

The influence of phosphate slag with different finenesses and activators on the hydration of high-belite cement has been studied by using the hydration heat of binders, the DTA curves, the SEM images, and the specific strength. Results indicated that doped phosphorus slag in the cement will reduce heat of hydration. The activity of phosphate slag was low at early stage, but pozzolanic activity of phosphorus slag is higher than that of fly ash. Increasing the specific surface area and curing time and using Ca(OH)₂ combined with gypsum can clearly promote the hydration degree of phosphorus slag. The findings in this paper show that since phosphorus slag can promote the hydration of high-belite cement, the strength contribution of cement is increased. Moreover, the greater the specific surface area is, the more significant the promotion effect at 90 d is.

     

Development of novel elastomeric blends derived from chlorinated nitrile rubber and chlorinated ethylene propylene diene rubber

Chlorinated nitrile rubber (Cl-NBR) has been blended with chlorinated ethylene propylene diene rubber (Cl-EPDM) in different ratios by a conventional mill mixing method. The effect of the blend ratio on processing characteristics, mechanical properties (such as tensile and tear strength, elongation at break, hardness, abrasion resistance, heat build-up and resilience), structure, morphology, glass transition temperature (Tg), thermal stability, flame retardancy, oil resistance, AC conductivity, dielectric properties and transport behavior of petrol, diesel and kerosene were investigated. The shift in absorption bands of blends studied from FTIR spectra, single Tg from DSC analysis and decrease in amorphous nature from XRD showed the molecular miscibility in Cl-NBR/Cl-EPDM blends. SEM images showed the uniform mixing of both Cl-NBR and Cl-EPDM in a 50/50 blend ratio. The TGA curves indicated the better thermal stability of the polymer blend. The elongation at break, heat build-up, resilience and hardness of the polymer blend decreases with an increase in Cl-NBR content in the blend whereas the flame and oil resistance were increased with increase in Cl-NBR content. Among the polymer blends, the maximum torque, tensile strength, tear and abrasion resistance was obtained for the 50/50 blend ratio because of the effective interfacial interactions between the blend components. AC conductivity and dielectric properties of polymer blend increased with increase in the ratio of Cl-NBR in the blend. Different transport properties such as diffusion, permeation and sorption coefficient were measured with respect to nature of solvent and different blend ratios. Temperature dependence of diffusion was used to estimate the activation parameters and the mechanism of transport found to be anomalous.     

Thermodynamics and kinetics of hydrogen absorption–desorption of vanadium synthesized by aluminothermy

This paper studies the addition (0–40% w/w) of natural zeolite (NZ, 84% clinoptilolite) in blended cements made with Portland cement (PC) with low and medium C₃A content. The isothermal calorimetry was used to understand the effect of NZ on the early cement hydration. For low C₃A cement, the addition of NZ produces mainly a dilution effect and then the heat released curve is similar to plain cement with lower intensity. For medium C₃A cement, the curve shows the C₃S peak in advance and a high intensity of third peak attributed to C₃A hydration. The high cation fixed of NZ reduces the ions concentration (especially alkalis) in the mixing water stimulating the PC hydration. The flowability decreases when the NZ replacement level increases. Results of Fratini’s test show that NZ with both PCs used presents slow pozzolanic activity. At early age, XRD and FTIR analyses confirm that hydration products are the same as that of the corresponding PC and the CH is progressively reduced after 28 days and some AFm phases (hemi- and monocarboaluminate) appear depending on the NZ percentage and the PC used. For low replacement levels, the compressive strength is higher than the corresponding PC from 2 to 28 days. For high replacement levels, the early compressive strength is lower than that of corresponding plain PC and the pozzolanic reaction improves the later compressive strength of blended cements.     

The synthesis and characterisation of an expansive additive for M-type cements

The expansion effect of laboratory-prepared expansive additives for M-type expansive cement was investigated at the early stage of hydration by the multicell isoperibolic calorimeter and volumetric technique based on Archimedes’ principle. The relative volume changes and heat released during hydration are strongly affected by the content of lime in the expansive additive due to the influence of CaO on the kinetics and mechanism of formation of ettringite. The increasing content of lime favours the formation of monosulphate and its later transformation to ettringite generating expansion stress. The effect of expansive additive on the behaviour of mortar samples was measured as linear elongation of test blocks using Graf-Kaufman dilatometer. Lower or higher content of lime in expansion additive slightly decreases the 7th-day compressive and flexural strength of samples while this effect is negligible for expansive additive with nominal composition of ettringite.     

Effects of posttreatment on the properties of modified PLLA/PDLA fibers

Poly(L ‐lactic acid)/poly(D ‐lactic acid) (PLLA/PDLA) blended with plasticizer poly(ethylene glycol) and nucleation agent TMC‐306 as‐spun fibers were prepared by melt spinning. The posttreatment was applied by hot drawing at 70°C and then heat‐treating at different temperatures for 30 minutes. In the process of hot drawing, orientation induced the further formation of the sc crystals and increased the degree of crystallinity of drawn fibers. When the hot drawing ratio reached 3 times, the properties of the fibers were relatively better. The highly oriented fibers containing pure sc crystals with high crystallinity were obtained by heat‐treating at a temperature above the melting point of α crystals. The posttreated PLLA/PDLA fibers with poly(ethylene glycol) and TMC‐306 (LDTP) obtained by hot drawing to 3 times at 70°C and then annealing at 170°C for 30 minutes exhibited the best antioxidative degradation and heat resistance properties. The initial decomposition temperature (T_5%) and heat resistance of posttreated LDTP fiber were about 94°C and 20°C higher than those of the commercial PLLA fiber, respectively.     

Heat evolution in hydrating expansive cement systems

Calorimetry was applied to follow the hydration of special cement mixtures exhibiting expansion or shrinkage compensation. The standard, common cements show generally less or more visible shrinkage on setting and hardening but mixed with and expansive agent, usually of aluminate and sulfate nature, they can exhibit the increase of volume. The calcium aluminate cement CAC 40 was ground together with special sulfate–lime sinter to produce an expansive additive to Portland cement (CEM I 42.5R). The expansive additive in the environment of hydrating cement transforms into ettringite at “right time” to give expansion before the final setting and hardening takes place. In the experiments the proportions of components of expansive mixture and basic cement were variable. The rate of hydration versus time for common cements is commonly known and reflects the moderate setting and early hardening during the first days after mixing with water (two peaks and the induction period between them). The aim of measurements presented in this study was to show the course of heat evolution curve and the heat evolved values, equivalent to the acceleration/retardation of hydration, in case of the paste with the expansive mixture, as well as the pastes produced from Portland cement and the components of expansive additives added in variable proportions. It was possible to see how the calorimetric curve and consequently the hydration process itself declines from the controlled setting/hardening. These measurements were supplied by the examples of phase composition studies by XRD.     

A comparison of hydration properties of cement–low quality fly ash binder and cement–limestone powder binder

The hydration properties of the binder containing low quality fly ash or limestone powder were compared in this study. Isothermal calorimetry was performed to measure the hydration heat of the binders during the first 3 days. Mercury intrusion porosimetry, scanning electron microscope, and thermogravimetry–differential thermal analysis were all used to determine the pore structure and hydration products of paste. The compressive strength of the pastes of age 3, 7, 28, and 90 days was also tested. The results indicate that the ground low quality fly ash can improve the mechanical properties of composite cementitious material and ameliorate the hydration properties and microstructure compared with the inert admixture limestone powder. The chemical activity of low quality fly ash presents gradually and appears high pozzolanic effect at later period, and it can accelerate the generation of hydration products containing more chemically bonded water. This leads to the higher rate of strength growth and cement hydration degree, the more compact microstructure and reasonable pore size distribution. Additionally, low quality fly ash delays the induction period, but shortens the acceleration period, therefore there is no significant influence on the second exothermic peak occurrence time.     

Synthesis and characterization of thermoresponsive poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-<Emphasis Type="Italic">N</Emphasis>-hydroxymethylacrylamide-co-2-hydroxyethyl methacrylate) hydrogels

Thermoresponsive hydrogels based on N-isopropylacrylamide, N-hydroxymethylacrylamide, and 2-hydroxyethyl methacrylate, poly(NIPAM–co-NHMAAm–co-HEMA), have been synthesized and their swelling—deswelling behavior studied as a function of NIPAM concentration, NIPAM/NHMAAm and NIPAM/HEMA mole ratio, and total monomer concentration. Copolymers varying in composition have been obtained by redox copolymerization of these three monomers. Temperature has been changed in the ranges from 4 to 70 °C at fixed pH and total ionic strength. Equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all hydrogel systems. The equilibrium swelling ratios of the copolymeric gels decrease with increasing NHMAAm and HEMA content. The formation of the intermolecular hydrogen bonding between hydroxyl and amido groups decreases the hydrophilic group numbers of the gel and the affinity of the gel towards water decreases. The copolymer gels also showed rapid volume transitions with time. The time required for equilibrium shrinking increased with increasing NHMAAm and HEMA content in the gel.     

An isothermal heat flow calorimeter for large-volume applications

Design, construction, calibration, and testing of a new isothermal heat flow calorimeter suitable for investigation of large-volume specimens are presented. The measuring vessel has the volume of 1370?cm³, and the calorimeter allows for the measurement at surrounding air temperatures of 5?C60?°C. A practical application of the device is demonstrated at the determination of specific hydration heat of cement paste and concrete with silica-aggregate size of up to 16?mm, having the same water/cement ratio. The differences over the whole measuring time period of about 100?h are lower than 2% which indicates a good potential of the calorimeter for the measurement of total hydration heat of composite materials. A reference measurement of hydration heat of cement paste using common isothermal heat flow calorimeter with the measuring vessel of 1?cm³ shows an agreement within ±7%, which seems acceptable, taking into account the heat transport processes in the far larger specimens. The designed calorimeter may find use in future also in other applications where larger specimens are required, such as the measurement of adsorption heat, solution heat, various reaction heats, and enthalpy of liquid?Csolid transition in heterogeneous systems with large representative elementary volumes.     

Comparing study on hydration properties of various cementitious systems

The hydration properties of slag sulfate cement (SSC), slag Portland cement (PSC), and ordinary Portland cement (POC) were compared in this study by determining the compressive strength of pastes, the hydration heat of binders within 72 h, the pore structure, the hydration products, and the hydration degree. The results indicated that main hydration products of PSC paste and POC paste are calcium hydroxide and C–S–H gel, while those of SSC paste are ettringite and C–S–H gel from the analyses of XRD, TG–DTA, and SEM. At the early curing age, the compressive strength depends on the clinker content in the cementitious system, while at the late curing age, which is related to the potential reactivity of slag. From hydration heat analysis, the cumulative hydration heat of PSC is lower than that of POC, but higher than that of SSC. Slag can limit chemical reaction and the delayed coagulation of gypsum, which also plays a role in the early hydration. So SSC shows the lowest heat release and slag can’t be simulated without a suitable alkaline solution. Based on MIP analysis, the porosity of POC paste is the smallest while the average pore size is the biggest. At the age of 90 days, the compressive strength of SSC can get higher development because of its relative smaller pore size than that of PSC and POC paste.     

Relationship between the hydration degree of poly-N-isopropylacrylamide gel and activity of immobilized α-chymotrypsin

The influence of the pH, temperature, and dimethyl sulfoxide concentration on the hydration degree of the poly-N-isopropylacrylamide gel and the activity of -chymotrypsin immobilized into the polymer was studied. The behavior of more hydrophilic preparations based on polyacrylamide and copolymer of acrylamide and acrylic acid was studied for comparison. An increase in both the temperature and dimethyl sulfoxide content decreases the hydration of the poly-N-isopropylacrylamide, which correlates with a decrease in the activity of the immobilized enzyme. The use of substrates with different structures and an irreversible inhibitor proves that the change in the properties of -chymotrypsin immobilized into the poly-N-isopropylacrylamide gel is related to the change in the rate constants of enzymatic reactions. Comparison of all experimental data obtained suggested an opportunity of local interactions between the protein globule and polymeric chains with a change in the hydration degree of poly-N-isopropylacrylamide during its phase transition.     

Water Solubilization in Mixed Nonionic Surfactants Microemulsions

The systems investigated were water/sucrose laurate/ethoxylated mono-di-glyceride/oleic phase. The oleic phase used first was the pure oils R (+)-limonene, isopropylmyristate, and caprylic-capric triglyceride; these oils were then mixed with ethanol at different mixing ratios (w/w). The total area of the one phase microemulsion region is dependent on the mixing ratios (w/w) of the mixed surfactants and that of the ethanol/oil. The largest microemulsion phase area formed with a surfactants mixing ratio (w/w) equals unity. For the systems where the oleic phase was a mixture of oil and ethanol, the total area of the monophasic microemulsion increases with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization was estimated. It increases as the mixing ratio (w/w) of ethoxylated mono-di-glyceride/sucrose laurate increases and with the increase in the ethanol/oil mixing ratio (w/w). The Gibbs free energy of solubilization decreases with the increase in the water content in the water-in-oil microemulsions. The values of the Gibbs free energy of solubilization are higher for oil-in-water microemulsions compared to those of the water-in-oil microemulsions.     

Fast physics-chemical and calorimetric characterization of natural pozzolans and other aspects

This research reports on the effects of including natural pozzolans in two Portland cements with different mineralogical compositions, with and without excess gypsum at amounts equivalent to 7.0% SO₃. The main analytical techniques used to study these effects were: the amount of water needed to make a paste of normal consistency, the 2-day Frattini pozzolanicity test and conduction calorimetry. The results obtained showed that these natural pozzolans caused contradictory (accelerating and retarding) effects on the rheology of the resulting cements, depending on the mineralogical composition of the respective Portland clinkers as well as the reactive chemical composition of the pozzolans, in particular their reactive alumina content (Al₂O₃ ^r−). The addition of gypsum also caused acceleration and delays in the calorimetric evolution of the resulting pastes, which proved to be heavily dependent upon the more or less aluminic chemical character of the natural pozzolans studied. This, in turn, was conditioned by the higher or lower Al₂O₃ ^r− content (for the SiO₂ ^r− content was of a very similar order of magnitude in all three pozzolans analyzed). The Al₂O₃ ^r− content was likewise responsible for paste behaviour in the afore-mentioned trials and analyses, and the pozzolanic activity exhibited by the compound was found to be more specific than generic, indirectly stimulating C₃A hydration more intensely and rapidly than C₃S hydration in PC1, one of the two Portland cements used. Indeed, when these natural pozzolans exhibited such prior pozzolanic activity in the second cement studied, PC2, the hydration of its 79.5% of C₃S was not indirectly stimulated to the same degree; rather, the contrary effect was observed, i.e., this cement was physically diluted by the three pozzolans. Pozzolan O stimulated hydration directly and non-directly more than indirectly, while pozzolan C acted conversely, and A exhibited varying combinations of the two patterns. The physical state of the reactive alumina, Al₂O₃ ^r−, in these three natural pozzolans, must be more amorphous than vitreous, i.e., resembling metakaolin more than fly ash in this regard. That notwithstanding, the reactive alumina content in each pozzolan must have conditioned the water/cementitious material ratio obtained for the respective blends with both types of Portland cement (a finding that could be used in future for speedy, simple, reliable and economical characterization), as well as their specific pozzolanicity developed and the rate and total heat of hydration generated by such blended cements.     

Investigation of early hydration of high aluminate cement-based binder at different ambient temperatures

The effect of spent FCC catalyst on early hydration (up to 48?h) of high aluminate cement (Al₂O₃ >70%) at different ambient temperatures (10, 20, and 30?°C) was investigated. Cement pastes with constant ratio of water/binder?=?0.35 (binder?=?cement?+?addition) and containing 0, 5, 10, and 15% mass of addition as replacement of cement were studied. The hydration kinetics was determined by calorimetric measurements and the structure of hardened binders after 2?days of curing at an appropriate temperature was also investigated using X-ray, SEM, and thermal analysis methods. Due to the fact that hydration of aluminate cements is highly sensitive to temperature conditions as well as certain changes of temperature are inevitable in practice, the evaluation of the impact of the waste catalyst addition in such conditions is justified. On the basis of obtained results, it was stated that the temperature determines the early hydration of high aluminate cement and decides about the influence of waste aluminosilicate. The introduction of the discussed addition has a big impact on the kinetics of cement hydration closely related to the curing temperature. The presence of spent catalyst accelerates the hydration at the temperatures of 20 and 30?°C, but at the temperature of 10?°C this waste aluminosilicate acts as a retarding agent. The effect of the addition on the microstructure of hardened binders after 48?h of hydration is rather insignificant, especially at 20?°C, compared to the influence of the temperature on hydration. At the temperature of 10?°C, a formation of low amount of C₂AH₈ can be observed because of the presence of spent catalyst, while at the temperature of 30?°C the introduction of the mineral addition prevents the hydrogarnet formation.