Ultrasonic sound speed of hydrating calcium sulphate\ud hemihydrate; part 2, the correlation of sound velocity to\ud hydration degree

In this article the sound velocity through a mix is correlated to the hydration degree of\ud the mix. Models are presented predicting the sound velocity through fresh slurries and\ud hardened products. These two states correspond to the starting and finishing point of the\ud hydration process. The present research shows that a linear relation between the amount\ud of hydration-product (gypsum) formed (Smith et al., 2002) and sound velocity can be\ud used to describe this process. To this end, the amount of hydration-product formed is\ud determined by the using the equations of Schiller (1974) for the hydration process and\ud of Brouwers (2010) for the volume fractions of binder, water and hydration products\ud during the hydration process. The presented model shows that the induction time and\ud gypsum growth rate are linear related to the water/gypsum-ratio

Multi-scale hydration modeling of calcium sulphates

Computer models for cement hydration has been proven to be a useful tool for\ud understanding the chemistry of cement hydration, simulating the microstructure\ud development of hydrating paste and predicting the properties of the hydration process /1/.\ud One of these advanced models is CEMHYD3D, which is used and extended within the\ud University of Twente for the last 12 years with pore water chemistry /2/, slag cement /3/\ud and multi-time modeling /4/. Chen and Brouwers /5/ pointed out that the smallest size\ud handled in CEMHYD3D, called the ‘system resolution’ is important for a digitized model.\ud Features smaller than the voxel sizes cannot be represented since the model works based on\ud the movement and phase change of each discrete voxel. Furthermore, the system resolution\ud determines the amount of computing time needed for a specific task, a higher system\ud resolution will lead to longer computational time. Due to better computational possibilities,\ud the use of higher resolutions is possible nowadays.\ud This article shows the effects of using different resolutions with CEMHYD3D. This is done\ud for the ‘fresh’ mixtures as well as during hydration modeling of the binder. The model has\ud been modified to cope with several different resolutions from 0.20-2 μm (or 500-50 voxels\ud in the system in a box of 100 μm x 100 μm x 100 μm). This paper shows two methods for\ud the multi-scale modeling. The first method consists of a system, which use a modified\ud PSD-line for each resolution. The second method uses the same digitized initial\ud microstructure, but in stead of 1 voxel of 1 x 1 x 1 μm3 for 200 μm-system 8 voxels of 0.5\ud x 0.5 x 0.5 μm3 are used and for the 300-μm system 27 voxels of 0.33 x 0.33 x 0.33 μm3

Ultrasonic sound speed measurement as method for the determining the hydration degree of gypsum

This article addresses the sound velocity through slurries as well as non-porous and porous\ud materials. The focus is on using the sound velocity for the microstructure prediction of porous\ud materials, especially gypsum plasterboards, during and after hydration.\ud For a slurry, the model of Robeyst et al. [1] showed a good agreement with experimental\ud data when taking into account an air content of 10 ml per kg of hemi-hydrate. This model\ud takes into account the bulk moduli of the continuous (fluid) and discontinuous (solid) phase as\ud well as the size and shape of the solid particles. The bulk modulus of the fluid is corrected for\ud the presence of entrapped air.\ud For gypsum materials, the best agreement was found between the experimental and\ud theoretical values using a series arrangement according to Ye [2] with a solid sound velocity\ud (cs) of 6800 m/s.\ud Finally, the sound velocity during the hydration of gypsum is studied. The use of linear\ud relation between the amount of hydration-product (gypsum) formed and sound velocity gives\ud a reasonable result. Furthermore a relation between initial volume fraction hemihydrate and\ud hydration time is shown

Ultrasonic sound speed analysis of hydrating calcium sulphate hemihydrate \ud

This article focuses on the hydration, and\ud associated microstructure development, of b-hemihydrate\ud to dihydrate (gypsum). The sound velocity is used to\ud quantify the composition of the fresh slurry as well as the\ud hardening and hardened—porous—material. Furthermore,\ud an overview of available hydration kinetic and volumetric\ud models for gypsum is addressed. The presented models\ud predict the sound velocity through slurries and hardened\ud products. These states correspond to the starting and ending\ud times of the hydration process. The present research shows\ud that a linear relation between the amount of hydrationproduct\ud (gypsum) formed and sound velocity (Smith et al.,\ud J Eur Ceram Soc 22(12):1947, 2002) can be used to\ud describe this process. To this end, the amount of hydrationproduct\ud formed is determined using the equations of\ud Schiller (J Appl Chem Biotechnol 24(7):379, 1974) for the\ud hydration process and of Brouwers (A hydration model of\ud Portland cement using the work of Powers and Brownyard,\ud 2011) for the volume fractions of binder, water and\ud hydration products during the hydration proces

Hydration Modeling of Calcium Sulphates

The CEMHYD3D model has been extended at the University of Twente in the last ten years [1,2]. At present the cement hydration model is extended for the use of gypsum. Although gypsum was present in the model already, the model was not suitable for high contents of gypsum and did not include the transitions between the different calcium sulphate phases (anhydrite, hemihydrate and gypsum). Besides that gypsum was seen as intermediate phase instead of a final phase. The presented model addresses these problems and has the possibility to simulate the microstructure development of gypsum, including reaction kinetics (dissolution, diffusion and precipitation) and the formation of gypsum needles. The model enables multi-time modelling which means the possibility to zoom in and out on the hydration process with respect to time. Multi-time modelling enables the user to study the hydration in more detail in both the early phase (hours) and on the long term (years). This modelling is needed, since the hydration of calcium sulphates is very short compared to that of cement

Gypsum hydration: a theoretical and experimental study

Calcium sulphate dihydrate (CaSO4·2H2O or gypsum) is used widely as building\ud material because of its excellent fire resistance, aesthetics, and low price. Hemihydrate occurs in two formations of α- and β-type. Among them β-hemihydrate is mainly used to produce gypsum plasterboard since the hydration product of the α-hemihydrate is too brittle to be used as building material /10/. This article addresses the hydration of hemihydrate since it determines the properties of gypsum and it is influenced strongly by water and the properties of hemihydrate. The microstructure development of gypsum during hydration is investigated. The influence of water is studied from its effect on fresh behavior and void fraction of the gypsum

MASS LOSS AND FLAMMABILITY OF INSULATION MATERIALS USED IN SANDWICH PANELS DURING THE PRE-FLASHOVER PHASE OF FIRE

In this study, the mass-loss and flammability limits of different sandwich panels and their cores (PUR, PIR, stone wool, EPS and XPS) are studied separately using a special developed furnace. The focus is on the pre-flashover phase of fire (up to 400°C), because exceeding the lower flammability limit in this phase may lead to a smoke layer explosion, a hazardous situation for an offensive intervention by the fire brigade. The research has shown that the actual mass-loss of synthetic and stone wool based cores is comparable up to 300°C. From 300°C onwards, the mass-loss of PUR panels is significant. EPS and XPS cores become fluid before pyrolysis starts. Furthermore delamination of the panels can be observed at exposure to temperatures above 250°C for the synthetic and 350°C for the mineral wool panels. The lower flammability limits have been established experimentally at 39% m/m (PUR) and 36% m/m (PS) of the pyrolysis gasses on the air mass, respectively. For PIR and mineral wool no flammability limits could be established