Search Results

You are looking at 1 - 10 of 35 items for :

  • "hydration of cement" x
  • Refine by Access: All Content x
Clear All

Abstract  

The physicochemical properties of spent fluidized bed cracking catalyst and its influence on hydration process of cement slurry were studied. The samples were cement slurries prepared with water/solid=0.5 and additions of used catalyst amounted to 0, 5, 10, 15, 20 and 25%with resp. to the solid. After definite time they were subjected to thermogravimetric analysis (TG, DTG, DTA) and, in order to determine the progress of reaction with water, the heat of hydration was measured by means of isotherm calorimetry. The studies disclosed that the spent cracking catalyst is not merely an inactive filler in cement slurries, but it modifies the course of the hydration process. The spent catalyst is a pozzolana additive and its presence leads to a decrease of calcium hydroxide contents in the system. The spent catalyst affect on the heat of cement hydration. Small amounts additive accelerate the process of binding.

Restricted access

Abstract  

The influence of spent catalyst from catalytic cracking in fluidized bed on the hydration process of cement and the properties of cement mortars were studied. The spent catalyst was used as an additive to cement in the mortars (10 and 20% of cement). The samples of mortars kept in water for28 days, then they were placed in sulfate and chloride media for 2 months (the control samples were kept in water for 3 months). After this time they were subjected to bending strength and compressive strength determinations. Thermogravimetric and infrared absorption studies were performed and capillary elevation, capability of binding heavy metals, and changes in mass and apparent density were determined too. The studies disclosed the pozzolana nature of spent catalyst and its influence on cement mortars being in contact with corrosive media.

Restricted access
Pollack Periodica
Authors: Laith Sh. Rasheed, Laith Mohammed Ridha Mahmmod, Sara Alaa Abed Alameer, and Abdulrasool Thamer Abdulrasool

%, respectively. Indeed, an improvement in the hydration process occurred by the additional water provided by CBW granules, which work as small water reservoirs separate inside concrete, on the other hand, progression of hydration of cement enhances the transition

Restricted access

Abstract

Cementitious systems based on portland cement are used for immobilization of toxic and hazardous wastes. The addition of waste material may impact the hydration reaction in cement matrix and consequently the setting and hardening process. The progress of reaction can be monitored by heat evolution measurements and the calorimetric results can indicate the declination from standard behaviour.

In this study the microcalorimetry was used to evaluate the heat output during the hydration of cements in the presence of different chromium containing salts, viz. CrCl3, Cr2(SO4)3, Na2CrO4 and K2CrO4.

Restricted access

Abstract  

In this study a calorimeter was applied to investigate the hydration of cements with fly ash (pulverised fuel ash – PFA) admixture. Four cements were used to produce the binders containing from 5 to 60% fly ash. The process of hydration in cementitious systems with fly ashes is slower than in reference pastes without admixtures. However, the calorimetric calculations and the shape of heat evolution curves seem to indicate a complex interaction between the components of cement and ash resulting in the increasing total heat evolved values per unit of cement. At higher fly ash content the accelerating effect of alkalis and alumina should be taken into account and discussed in terms of the composition of initial cement. The modifications of hydration kinetics and mechanism in this case is very well visualised by means of calorimetry.

Restricted access

Abstract  

The rate of heat evolution as well as total heat output are strongly affected by other components of hydrating mixture, apart from neat portland cement, such as slag, fly ash and other industrial by-products; among them the wastes from fluidised bed combustion (FBC) has been taken into account recently. In this study the calorimeter was applied to follow the early hydration of cements produced with these materials. They interact with cement paste in a few ways: as set controlling agent and as active pozzolanic admixtures. Thus the rate of heat evolution/hydration is modified, depending on the composition of clinker and percentage of waste in the mixture. After the series of measurements for clinker-waste mixture hydrated systems also some ‘model’ mixtures were investigated to separate the effects from particular waste components.

Restricted access

The majority of previous studies of the hydration of cements using heat flow calorimetry have been carried out isothermally. However, with oilwell cements the slurry is mixed on the surface at ambient temperature and then gradually increases in temperature as it is pumped down the well. A Setaram C-80 calorimeter has been used to simulate the temperature ramp in API oilwell cement test schedules. This approach has enabled cementing reactions to be studied for the first time under conditions approaching those encountered in the field, and has shown that the results obtained from isothermal experiments may be misleading.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Barbara Pacewska, I. Wilińska, and G. Blonkowski

Abstract  

The paper describes an attempt of chemical activation of fly ash and claims the usefulness of combination of such investigation methods as calorimetry and infrared absorption for investigations of early periods of cement hydration. The research samples were cement pastes made with an addition of fly ash and admixtures of chemical activators, CaCl2, Na2SO4 and NaOH, whereas a cement paste without fly ash addition and a cement-fly ash paste (both without admixtures) were used as reference samples. In order to investigate early periods of cement pastes hydration, the amount and rate of heat release were registered, and IR spectrums were checked at appointed hydration moments. As a result, it was shown that the combination of calorimetric and IR absorption methods in the investigations of early periods of cement hydration was useful. It was confirmed that the use of chemical activators CaCl2, Na2SO4 and NaOH accelerated the hydration of cement pastes containing fly ash additive in early hours after adding water. The action of activators on hydrating cement system is different for each of investigated compounds.

Restricted access

Abstract

Fly ash-based geopolymer fine aggregate is a potential replacement material for the natural river sand as it has similar physicochemical properties. This paper reports the experimental investigation of a study conducted using this fine aggregate in concrete with a focus on the properties of fresh and hardened concrete. The geopolymer fine aggregate was developed by air curing process and oven curing method. The oven curing method yielded relatively better mechanical properties in concrete specimens. The oven curing results in better behavior at later age also. Laboratory tests were conducted to ascertain the fresh concrete density, slump value, hardened concrete density, compressive strength, tensile strength, and flexural strength of the concrete specimens. The microstructure of the concrete specimens was analyzed using scanning electron microscope which indicated the agglomeration of the fly ash particles with few voids demonstrating the higher water adsorption capacity of the same. The unreacted particles noted in the microstructure later tend to merge with the lime obtained from the hydration of cement so as to develop improved later age mechanical strength. The results on mechanical properties of the concrete indicate much similar results to that of the concrete developed with the normal river sand, which confirms that the geopolymer sand is an ideal replacement choice for natural river sand.

Open access

The paper describes the results of statistical analysis of DTA diagrams. A connection is found between the second and third endothermal effects. An analysis of geometrical characteristics of theT, S andh values of DTA diagrams confirms the absence of reliable connections. The rank correlation coefficients are determined according to Spearman. Non-linear programming is formulated to obtain the kinetic dependencies of the process of hydration of cement studied by DTA.

Restricted access