Papers by Keyword: Thermal Activation

Abstract: . The ground granulated slag is a wide spread component of various types of cement and binding substances. Its pozzolanic activity depends on different factors. It is searched out, that there are no minerals able to liquid maturing in the slag under consideration, the slag activity data according to domestic and foreign standards specifies it as low-active, third rate. Altering the chemical composition to a small degree, specific to a definite type of slag, does not alter its functioning much. The same stands for the slag dispersiveness at the high rate of amorphous state – the dispersiveness rise increases slag activity and water demand, and more dispersed slag does not increase the resistibility of matrix samples in high-flow concrete mix. Thus, this type of slag is supposed to be grounded up to BET surface area equal to 250-300 m²/kg, compared to dispersive capacity СEM 1, and the substitution of a part of cement by slag would not have a significant ifluence on mix water demand. With the increase in the slag content within the cementing component the slag effectiveness index increases and reaches its maximum at 70% cement replacement by slag. A large portion of slag can substantially decrease the hydration of lime in the hardened cement paste of the concrete and lessen the solidity of reinforcement corrosion protection in concrete structures. The article deals with different methods of ground granulated blastfurnace slag activation within the mixed cementing substance: Portland-cement CEM1 + GGBFS. The most widely used way of activation – the usage of sodium and potassium alkalies and liquid glass is quite effective, but it demands expensive artificial components, while the alkali compounds forming at hardening of such a cementing component would be soluble.

Abstract: The article deals with risks of subsoil freezing which lead to volumetric changes of frozen water contained in the soil. These changes can cause damage of foundations of building objects. The issue was solved by steady-state and transient 1D and 2D numerical simulations of heat conduction in the floor and subsoil under a freezer room. These simulations were performed in software CalA. Several possibilities of operating conditions of the freezer room were examined within different boundary conditions. Impact of different simulation setups on subsoil temperature fields was observed. Use of exhaust heat from condenser of a freezing system is suitable method for thermal activation of the floor structure. This solution eliminates risks of subsoil freezing more economically than commonly used electrical heating cables.

Abstract: This research presents the results of an investigation on the influence of thermally activated alum sludge ash (AASA) as a partial cement replacement on the near-surface characteristics of binary and ternary blended binder (TBB) concretes incorporating silica fume (SF), ground granulated blast furnace slag (GGBS), and palm oil fuel ash (POFA). All of the mixtures were prepared with a water/binder ratio and total binder content of 0.30 and 493 kg/m³, respectively. Initial surface absorption (ISAT) and sorptivity tests were conducted at the age of 28 days. Results indicate decrease in the ISAT and sorptivity values of binary blended binders with 15% AASA cement replacement compared with the control and 20% AASA concretes. A higher replacement level of 20% AASA did not help improve inner core durability but improved surface durability characteristics. All TBB concretes performed better than the binary blends with AASA at the same replacement levels.

Abstract: The crack growth behaviors loaded in mode I under strain and stress control at different temperatures were presented in α-Fe by atomistic simulations using LAMMPS code. The interatomic bonds of atoms were characterized using the embedded atom method interatomic potential. The simulation models were built with initial edge crack subjecting to cyclic uniaxial constant strain rate and constant stress. A temperature range from 100 K to 1200 K was considered to probe the influence of the temperature on crack growth. The crack growth mechanism and the radial distribution function (RDF) during crack growth were investigated. The results indicated that the crack propagation mechanisms were sensitive to temperature and the boundary conditions. By proposed image adjusting technology the dislocation slip bands can be more clearly displayed on screen. In order to include the effect of temperature on crack growth, a temperature factor defined as a function of temperature in exponential form was introduced to modify the theoretical expressions based on thermal activation theory. Its coefficient and index can be determined by the RDF peak value obtained from atomistic simulations. For cyclic loading the crack growth process was dependent on both temperature and cyclic loading period in terms of simulations.

Abstract: Compositional and structural features of peat allow creating efficient additives for cement systems by means of the various processing methods. The basic selection criteria of the method of production are feedstock composition and required properties of the product. This paper presents outcomes of research of thermal and chemical conversion of peat and influence of processing method on the properties of the obtained substance.

Abstract: The clay types, kaolinite and smectite, are the most used industrially, mainly due to its sorption characteristics. There have been several attempts to improve the quality and characteristics of the clays, modifying them with different techniques. Two of the common techniques are thermal activation and acid activation. For acid activation, hydrochloric acid was used with a reaction time of 1 hour while the thermal activation the samples calcined at 300oC for 24 hours. This work aims to characterize the gray clay (supplied by Süd-Chemie LTDA) and Brasgel (provided by Bentonit), both in its natural form, as well as in the acid and thermal activation form (300°C). Natural and treated clays were characterized by X-ray Spectroscopy Energy Dispersive (EDX), X-ray diffraction (XRD) and nitrogen adsorption (BET). The results showed a reduction of impurities in the samples and did not comprise changes in the structure of the constituent minerals.

Abstract: The age hardening response of a quasi-binary Al-Mg₂Si alloy was studied using activation distance analysis of precise strain rate sensitivity experiments at 78 and 300K. The alloy of Al-0.7Mg-0.33Si-0.024Fe-0.006Ti(at.%) has a stochiometrically balanced composition of Mg₂Si. The alloy was solutionized at 550°C and ice water quenched before ageing in one of two ways: single-step or multi-step ageing. For single-step ageing: specimens were naturally aged for 70 days at room temperature (RT); pre-aged for 16 hours at 70°C; or artificially aged for 30 min or 10 hours at 175°C. For multi-step ageing: specimens were pre-aged at 70°C for 16 hours after natural ageing for 70 days at RT; artificially aged for 30 min or 10 hours at 175°C after pre-aging at 70°C for 16 hours; or artificially aged for 10 hours at 175°C after natural aging for 70 days at RT. The activation analysis reveals rate controlling obstacle dimensions ranging from 0.3 to 10 nm depending upon the ageing condition. A comparison is made to a prior three dimensional atom probe ageing study of the same alloy [Murayama and Hono, Acta Mater., 47 (1999) 1537-1578.].

Abstract: In this research the performance of ultrasonic pulse velocity in concrete is examined as a nondestructive experiment, in order to estimate compressive strength of thermally activated alum sludge multiple blended high performance concretes (HPC) that contain AAS, silica fume (SF), ground granulated blast furnace slag (GGBS) and palm oil fuel ash (POFA) are determined in both binary and ternary blends of cement. The water/binder ratio and total binder content are fixed at 0.30 and 493 kg/m3 for all types of mixes. The ultrasonic pulse velocity (UPV) of each concrete mix was measured using 100mm cubes after a curing period of ages of 3, 7, 28, 56 and 90 days. The results indicate a very positive exponential relationship between compressive strength and UPV for both binary and ternary blends of HPC mixtures, with coefficient correlation (R²) of 0.889.

Abstract: In this work the two epoxy composites the controlled behavior of composite material (CBCM) and the thermally activated symmetrical composite (SYMM) have been tested for their shape memory property. These composites have been heated above their glass transition temperature (Tg) and deformed to the same displacement. The activated position has been taken as the reference point for displacement measurements during the fixing cycle. During the recovery, two types of tests have been conducted: Unconstrained recovery test and constrained recovery test. It has been found that the recovery of CBCM plate is better as compared to the SYMM plate (unconstrained recovery test). Similarly, it has been found that CBCM plate produces larger forces of recovery than SYMM plates (constrained recovery test).

Abstract: In this paper, the Neimenggu high alumina coal gangue was calcined at 400°C~1000°C, its micro-structure in different calcining temperature was studied using XRD and IR, and then the preferred activated condition and the PAI were investigated by testing the strength of cement mortars with activated coal gangue. The result shows that: the optimal calcining temperature of the gangue is 800°C, at this temperature the high activated SiO₂ and AI₂O₃ can be decomposed from the gangue. The activity of the original gangue is very high, the PAI of the cement mortars with 800°C activated coal gangue can achieve to 126%, and thus can be used as high activity cement admixture. The PAI of the high alumina gangue is higher than that of coal gangue from other parts of China.