Technical Paper THE OPTIMISATION OF THE HARDENING PROPERTIES OF REFRACTORY CASTABLES USING NON DESTRUCTIVE TECHNIQUES TO MEASURE EARLY AGE PROPERTIES

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1 Reference : TP-GB-RE-LAF-58 Page : 1/16 THE OPTIMISATION OF THE HARDENING PROPERTIES OF REFRACTORY CASTABLES USING NON DESTRUCTIVE TECHNIQUES TO MEASURE EARLY AGE PROPERTIES Christopher Parr, Michael Lievin, Christoph Wöhrmeyer, Charles Alt * * Kerneos, France Presented at 31 st ALAFAR congress, Cartagena, Columbia, November 26 Tel : 33 () Fax : 33 ()

2 Reference : TP-GB-RE-LAF-58 Page : 2/16 ABSTRACT A significant part of downtime during the installation of refractory castables is spent waiting for hardening to occur so that moulds and formwork can be stripped. In order to reduce this downtime an optimization of the hardening properties is necessary. Traditional methods used to measure the hardening profile of a refractory castable do not provide enough information for significant breakthroughs to be made in the optimization of the hardening phase. There is therefore a need for better information about the early age hardening profile and volume change characteristics which can help the formulator optimize the castable binder systems. This paper will present an approach by which the early age properties of refractory castables can be followed with two complementary techniques. The techniques measure hardening kinetics through ultrasonics and early age linear shrinkage through a unique piece of equipment. Both can be done in an automated and continuous fashion. Different model castable formulations will be presented and comparisons made with existing tests such as flow, set and compressive strength measurements to demonstrate the additional information that can be gained. Conclusions will be drawn about the impact of changes in binder composition and their effects upon the castable hardening. Tel : 33 () Fax : 33 ()

3 Reference : TP-GB-RE-LAF-58 Page : 3/16 1 Introduction Whether in the precast shop or in the steel mill, downtime costs money. Up to 2% to 3% of the total installation time of refractory castables is due to the time spent waiting for hardening to occur after the refractory castable is placed. Any reduction in this dead time from casting to mould stripping can be translated into value. Calcium aluminate cement (CAC) is the most widely used binder in refractory castables which have evolved from conventional castables to low and ultra low cement castables (LCC and ULCC) containing ultra fine fillers and reactive powders [1]. It is of interest to study its impact in refractory castables with respect to hardening in order to reduce the time from casting to mould stripping. Various classical techniques allow the different steps in the castable placing chain, from the loss of workability, to the completely hardened state, to be characterised. The major problem encountered with these methods is the sensitivity to external conditions and the inability to relate the data to the mechanical resistance. They generally only provide partial information at a given moment or for a short period of time. Thus, there is a clear need for practical and reliable methods, achievable for the whole refractory castable to follow the change in characteristics as function of time from the fresh state to the final hardened state. A capability to continuously measure the developing structure coupled with the measurement of dimensional change during hardening would be particularly attractive as a route to optimise hardening properties. Consequently two techniques were selected for investigation in this paper; A first technique uses ultrasonics to follow in real time the developing structure from the placing phase to the hardened state. The use of ultrasonics in the field of Portland cement concretes as a means to follow setting and the development of structure has been studied for many years [2]. The technique presented here has been adapted from equipment [3] originally developed for Portland cement concretes. A second technique attempts to measure the linear shrinkage during the hardening phase. Numerous methods have been developed in recent years [4,5] to follow the autogenous shrinkage of high performance concretes and cements pastes. This was considered to be an important parameter to follow as LCC and ULCC refractory castables systems contain an increased quantity and fineness of matrix components which could modify dimensional changes. Understanding dimensional change during the setting phase is important in predicting future cracking patterns of refractory linings and necessary for accurate dimensional control of pre-cast pieces prior to demoulding. A literature review revealed the existence of numerous techniques to measure linear [6,7] and volume shrinkage [8,9] of cement based systems. Charron and others [1,11] compared both approaches using a number of experimental methods developed in recent years and concluded there was good agreement between the two methods although there was an order of magnitude of difference between the values recorded. A technique, taken from the dry mix mortar industry [12] was selected to measure the linear shrinkage as the structure develops. This technique which measures linear shrinkage was adopted as it most closely resembled the geometry of many refractory pre cast pieces. Thus, the aim of this paper is to investigate whether non destructive techniques developed in the allied fields of Portland cement based concretes and dry mix mortars can be applied to refractory concretes. A secondary objective is to determine whether the information generated by these techniques could be used to optimise and shorten the hardening time of refractory castables. Tel : 33 () Fax : 33 ()

4 Reference : TP-GB-RE-LAF-58 Page : 4/16 2 Experimental In order to explore the different methods a series of castable systems were used in conjunction with 7% alumina cement, Secar 71 (Kerneos). Castable formulations are presented in Table I along with the raw materials used in each system. Different Low Cement Castables are used, based on tabular alumina, one with fume silica (LCCFS) and Table I. Castables composition one without (LCC-A). Other formulation variables were calcined alumina compared to reactive alumina, two different additive systems as well as the effect of metallic aluminium which was chosen for its reaction with water to liberate hydrogen gas and therefore impact the dimensional stability [13]. The additive systems ensure a good compromise between fluidity and working time to allow proper placing of the castable Tabular alumina 7mm Tabular alumina -325M Calcined alumina (BET~1m^2/g) Reactive alumina (BET>4m^2/g) SECAR Fume Silica (97% SiO2) 5 5 Total Sodium Hexa metaphosphate (HMP),2,2 Citric acid (CA),7,7 Sodium Tripolyphosphate (TPP),1,1,1,1 Aluminium metal <2M,1,1 Systems 1 to 4 are LCC A types whereas 5 and 6 have an addition of fume silica. The variation of system types is based upon two alumina types, either calcined or reactive alumina and two base additive systems. One using, Sodium Tripolyphosphate (TPP) alone as the main dispersing agent the other based upon Sodium Hexmeta Phosphate (HMP) and a retarder in the form of citric acid. In LCC-A systems without fume silica, previous studies [14] have shown the need to couple retarders with reactive alumina in order to achieve a suitable working time. Placing properties for each system were characterized through the flow profile and working time. For each sample two measurements of the placing properties were made and the average reported. Flow value: determined using a cone with 1mm base diameter, 5 mm high and 7 mm top diameter. The cone is placed on a vibrating table (according to the ASTM 23C) filled with the castable, then taken away and subjected to 2 seconds of vibration. Flow value resulting of the cake is calculated as a percentage as follows: FV (%) = (cake diameter initial diameter) / initial diameter * 1 Working time: time after mixing at which the castable will not flow under vibration. Measurement of castable hardening kinetics: Hardening kinetics were followed by exothermic profile. These were determined at 2 C with castable samples placed in an insulated chamber. A thermocouple (type K), imbedded in the cast sample, is linked to a data capture system and the temperature recorded as a function of time [15]. Tel : 33 () Fax : 33 ()

5 Reference : TP-GB-RE-LAF-58 Page : 5/16 Ultrasonic hardening profile: The hardening kinetics of the whole refractory castable can be continuously followed and monitored using an ultrasonic method. The technique is based on the propagation velocity of ultrasonic waves through a sample. It can be applied from the end of mixing to the complete hardened state of the castable. Figure I: Ultrasonic apparatus (8 channels) In this paper, the compressive wave is used to follow the propagation velocity which is directly linked to the structured state of the material. Ultrasonic methods have been firstly widely used in the field of Portland based civil concretes, and especially for the control of the final hardened state: strength estimation, thickness measurements, elastic modulus or crack locations in the dense structure [3,16,17]. This method has also been successfully used to follow the evolution of elastic modulus of refractory concrete during heating up, from 2 C to 16 C [18]. This technique has been previously applied to follow the hydration of calcium aluminate cements and is shown to be reproducible within 5%. Generally, two samples are run simultaneously and the results discarded and repeated if a divergence of more than 5% is observed. [19,2,21]. The apparatus is presented Figure I. and is based on a previously developed technique [22]. The equipment used is an IP-8 8 channel ultrasonic apparatus supplied by Ultratest Gmbh, Germany. Measurement of the ultrasonic wave (25kHz) through a freshly placed castable is via two piezoelectric sensors attached to either end of material with a distance of 3mm. The measurements are performed during very short time periods (a few µs) which are converted from the electrical signals by the two piezoelectric transducers (transmitter and receiver). Propagation speed is measured, amplified and converted directly by the software into m/s. This gives a continuous velocity or propagation speed measurement as a function of time (V = distance/time). The wet mixed castable, with a maximum grain size of 6mm is placed in the cylindrical mould (3mm diameter) with 3mm distance between the transmitter and receiver. The placed castable is then vibrated during one minute to ensure that entrapped air doesn t disturb the signal during the period of measurement [23,24]. Classical demoulding oil is used to facilitate the demoulding of hardened castable. Since the shrinkage of the castable could lead to a decoupling of the material and the mould, silicon grease is used to ensure a good interface between the cells and the castable. Once vibration is complete the sensors are connected to the recording software and the measurement started. Linear shrinkage measurement; an apparatus similar to one designed by Sika and manufactured by Walter and Bai ( was used [12]. The apparatus is shown in Figure 2. The method works with a mould in which the mortar to be investigated is placed. Two moving end walls are connected to length transducers which monitor the movement of the end walls. Measurement of movement in both directions is possible through a system of attachment since the end walls are always in contact with the mortar. This can start as soon as the material is cast, poured or vibrated into the mould. Samples can be in air or covered. The sample geometry uses a mould with 36 mm length and a triangular cross section with a mm triangle. The volume to surface ratio corresponds to the ratio of a Tel : 33 () Fax : 33 ()

6 Reference : TP-GB-RE-LAF-58 mm standard prism mould. After hardening the prism can be de-moulded and its further length changes can be measured by classical comparator methods. Both moulds are made of steel and the interior surfaces are coated with a plastic film in order to reduce friction. Figure 2: Shrinkage measurement apparatus The measurements are followed continuously by two LVDT displacement transducers linked to a PC for data collection. Repeatability is around 1 microns/meter (.1%). During the plastic phase and the beginning of Table 2. Basic Data Page : 6/16 microstructure development, there is an excellent reproducibility. Experience has shown that when drying starts the variations between different test runs becomes more pronounced and can reach about 2% of the total cumulative value measured. Two samples are run and the data presented is the average of the two runs. 4 Results and discussions Table 2 shows the key data from the measurement of placing properties, exothermic profile, ultrasonic curves and the shrinkage measurements. The derivative calculations are derived from the continuous curves and are estimated over 3 second intervals to provide a smoothing effect on the graphical representations. The initial placing properties were measured via vibration flow profiles and these are show in Table 2. The purpose of the experiments was not to optimise placing properties and this can be seen in the relative rapid flow decays for most samples and the short working times. Water additions were adjusted to yield an initial vibration flow to around 1-13%. All measurements were done at 2 C. Units Water addition 6, Vibration Flow T % T3 % T6 % 93 working time mins Shrinkage data Maximum Shrinkage micron -,52 -,155 -,576 -,278,256,434 Maximum Shrinkage % -,1 -,4 -,16 -,8,7,1 Maximum Shrinkage mic/metre Time to max shrinkage mins Max rate mm/min -,2 -,13 -,79 -,24,114,34 Max rate mic/m/min -, Time at max rate mins , Exothermic data Exo max temp C 26,7 25,4 27, ,8 Exo max time mins N/D Maximum rate C/min,17,83,33,258,18 Max rate at time time N/D Tel : 33 () Fax : 33 ()

7 Reference : TP-GB-RE-LAF-58 Page : 7/16 Exothermic profiles The exothermic profiles for the six castable systems are shown in Figure 3. Strong exothermic peaks can be seen for the castables 5 and 6 containing aluminium metal and these appear at shorter intervals than the other castables systems. For the LCC-A castables the exothermic peak the maximum heat generation rate is more than 1 times slower than systems with Aluminium (numbers 5 and 6). The peak temperature also occurs over a much longer timescale than the other peaks with only system 4 being in the same region around 5 minutes. No peak was recorded for sample number 3 and this was attributed to an equipment problem and the exothermic result for this sample have not been considered further Temperature ( C) Figure 3: Exothermic profiles of six castables Ultrasonic measurements The ultrasonic profiles are shown in Figure 4. Based on the analysis of the experimental results, and for most examples three characteristic stages can be distinguished in the evolution of ultrasonic wave velocity: - The first stage is a transition from a suspension of cement particles, partially dissolved, and ultra fines to the first solid phase percolation. In this first stage, the velocity remains low and stable. The measured values are smaller than the velocity in water (around 14 m/s) and even smaller than in air (33 m/s). According to previously studies [12], this phenomenon can be caused by entrapped air in the castable, playing a dominant role compared to the small quantity of hydrates which would have formed at this point. - In the second phase a solid percolation path is formed in the paste creating a solid. The ultrasonic wave propagates through a solid instead of through the liquid phase. At this critical time, it has been shown that [21] the shear wave begins to propagate through the material. This is well correlated with the end of castable working time indicating a flocculation of the system more than the development of a hydrate structure. A sharp increase of velocity is observed. Just before this critical time a slight decrease of the velocity is sometimes detected. This corresponds to an increase Tel : 33 () Fax : 33 ()

8 Reference : TP-GB-RE-LAF-58 Page : 8/16 of tortuosity in the paste due to a growing solid network which is not yet completely connected [24]. It is believed that the increasing velocity is controlled by the amount of the connected solid phase [3,24]. - A plateau is then reached in the third stage where the propagation speed only increases slightly as a function of time. These three identified stages can be linked to the castable placing properties which can in turn be linked to the CAC hydration phases and the developing microstructure. During the first stage when castable is fluid, the flow can be measured under vibration (see Table 2). This corresponds to the installing period. The end of the first stage, marked by a sharp increase of ultrasonic velocity approximately corresponds to the end of workability, called here working time, corresponding with a major loss of flow under vibration. This is associated [25] with the reaction of calcium ions from the cement reacting with the dispersing additives and forming precipitates which block the system deflocculation. 6 Velocity (m/s) Loss of signal Figure 4: Ultrasonic Hardening profile During this period the bulk dissolution of calcium ions occurs. The second period with increasing velocity corresponds to the initiation of the CAC hydration cycle with nucleation and precipitation occurring during this step [21]. The classical setting times measured by the Vicat method are localized as follow: at the beginning of increasing velocity for initial setting time and soon after for the final setting time. In this second stage, both elastic modulus and strength increase, in parallel the main exothermic peak occurs (Figures 3, 4). This corresponds to the massive precipitation and the growth of hydrates content and solid phase. The comparison with the massive precipitation observed by conductimetry is difficult because the situation in a diluted system is significantly far from a concentrated solution. When the velocity remains stable, both elastic modulus and strength reach a plateau. Many attempts have been made to try to link the ultrasonic compressive wave velocity to the compressive strength, but the relation is not trivial and depends on the castable formulation. The method is able to distinguish the different castable systems and each has their own characteristics curve. In particular, the curves for castables 5 and 6 are quite distinct. In fact it is believed that there is a loss of signal during the period 2 to 3 minutes. This is probably due to the vigorous aluminium reaction generating hydrogen provoking large dimensional changes in the samples. Different mould configurations from different sized Tel : 33 () Fax : 33 ()

9 Reference : TP-GB-RE-LAF-58 Page : 9/16 cylinders up to 7mm as well as similarly sized cubes have been tried to eliminate this effect. Further work is needed to optimise the mould configuration for aluminium containing castables. Since the sample is constrained in a cylindrical mould the presence of cracks cannot be ruled out as the castable expands upwards in the only free direction. The samples with single TPP additives have amongst the highest propagation speeds after 11 minutes and also the most rapid increase in velocity as time progresses. The two HMP based systems with citric acid retarders have a slower increase and presumably this is linked to the slower hydration reaction as exemplified by the broader and slower exothermic peaks shown in figure 3. Of note is the initial profile with sample 4 (TPP and reactive alumina) and sample 3 (TPP with calcined alumina). The latter shows a flat period lasting almost 7 minutes before the propagation speed increases whereas the sample with the reactive alumina shows an almost continuous increase in ultrasonic velocity. This is also,4 reflected in the flow decay which is for slower (i.e. less reactive) for sample 4. This difference in ultrasonic velocities is clear example of the impact of alumina type upon the placing properties. Shrinkage measurements The Walter and Bai shrinkage measurements are shown in Figures 5 and 6 along with an extraction of key data in Table 2. The shrinkage in mm expressed as a function of time is illustrated in Figure 5 for the 6 castable types. The corresponding derivative curves giving the rate of dimensional change as a function of time are shown in Figure 6. Table 2 summarises the data and expresses the dimensional change in the plastic state as either an absolute measurement in mm, as a percentage or as a value in microns/metre. The time to maximum dimensional changes in the plastic state occurs at different intervals for all systems and the final shrinkage or expansion also varies somewhat. 5,2 Shrinkage (mm) -,2 -, ,6 3 -,8 Time (mins) Figure 5: Shrinkage measurements Samples 1 and 2 have a very small shrinkage which occurs over time and is only really measured after 6 minutes unlike the other samples where changes occur at much shorter time intervals. The presence of HMP and CA act as retarders and the shrinkage as measured by the rate of change or the total amount is less than the systems without such retarders. The final shrinkage values are less Tel : 33 () Fax : 33 ()

10 Reference : TP-GB-RE-LAF-58 Page : 1/16 than half the comparative systems using only TPP as an additive and the maximum shrinkage rate is a fraction of that recorded with the other systems. The two aluminium metal containing castables (samples 5 and 6) show a very clear expansion albeit at different time intervals. Both samples exhibit a small initial shrinkage followed by a large expansion which lasts for <1 minutes. The rate of which is 4 times quicker for sample 5 (32 mic/m/min) compared to sample 6 (9mic/m/min). The residual expansion is positive (,26mm) in the case of sample 5 and almost zero for sample 6. The sample 6 with reactive alumina is therefore more dimensionally stable than the equivalent sample based upon calcined alumina. It is not known whether this is due to particle size effects or the impact on CAC hydration Shrinkage (mm/min) Figure 6: Dimensional rate of change with time Tel : 33 () Fax : 33 ()

11 Reference : TP-GB-RE-LAF-58 Page : 11/16 Temp ( C) Shrink (mm) x1^-1 Number Δ2 C Exothermic Ultrasonic Shrinkage Number 2 Propagation speed m/s Temp ( C) Shrink (mm x1^-2 ) Number Ultrasonic Shrinkage Number 4 Propagation speed (m/s) Temp ( C) Shrinkage (mm x 1^-3) Exothermic Shrinkage Δ2 C Ultrasonic Propagation speed (m/s) Temp ( C) Shrink (mm*1^-2) Exothermic Shrinkage Δ4 C Ultrasonic Propagation speed (m/s) Figure 7: Comparison of ultrasonic, exothermic and shrinkage data (samples1 to 4) Samples 3 and 4 (single TPP addition) show a significant shrinkage at early age around 1 to 2 minutes. The shrinkage rate is 3 times larger with sample 3 compared to sample 4 and final shrinkage is also almost double that of sample 4.The difference between these two systems being only the added alumina type. In order to compare the different techniques and build a picture of the early age properties the exothermic profiles, shrinkage measurements and the ultrasonic hardening curves have been plotted on the same graph with one graph for each sample. These graphs are exhibited in figure 7 for samples 1 to 4 and figure 8 for samples 5 and 6. Figure 9 shows the corresponding derivative curves for samples 5 and 6. The scales have been adjusted to facilitate comparison of curves with widely differing units. It is for this reason that the shrinkage curves particularly are expressed as mm x1-1 to 1-3. The exothermic curves are shown but again due to scaling effects the maximum delta temperature is shown on the graph to main the exothermic peak more visible. Samples 1 to 4 have a striking symmetry in that the ultrasonic velocity increases as the samples shrink. These events normally occur before the exothermic max peak is reached and an inflection on the curve is observed at a time corresponding to the maximum rate of temperature increase i.e. when the exothermic reaction is at its fastest rate. This shows the Tel : 33 () Fax : 33 ()

12 Reference : TP-GB-RE-LAF-58 Page : 12/16 link between the developing structure and the associated shrinkage. The ultrasonic curve shows two period of rate increase with a varying period where the increase in velocity is relatively restrained. The second of these rate increases appears to precede the exothermic peak and is accompanied by a rate increase in the shrinkage. Examining the shrinkage curves two forms can be discerned. Samples 2 and 4 have a curve with two periods of a significant shrinkage rate, in between these curves there is a period where the shrinkage rate decreases. These are contrasted with curves 1 and 3 where the majority of shrinkage is confined within a single period. This could be indicative of the difference in hydration induced by the different alumina types. The two systems (3 and 4) based upon TPP additive alone show a rapid initial shrinkage which is accompanied by a large increase in the propagation speed from the ultrasonic measurement. This would seem to indicate a more rapid hydration and structure development. By 4 minutes the shrinkage is largely complete and the maximum temperature rise rate also occurs at this time. The main exothermic peak reaction starts at around 3 minutes i.e. a large part of the shrinkage has occurred by the time the main hydration reactions start. The initial structure development and shrinkage coming from a supposed flocculation rather than the formation of bulk CAC precipitates at the massive hydration stage. This can be seen clearly with sample 4 where more than 8% of the total shrinkage has occurred at 2 minutes which is prior to the main hydrate reaction. A secondary shrinkage accounting for around 13% of the measured total occurs in parallel with the main hydration reactions. The retarded samples (1 and 2) develop a shrinkage curve more slowly and the increase in propagation speed is also lengthy occurring between 4 and 8 minutes in the case of sample 1 and between 1 and 7 minutes in the case of sample 2. The total shrinkage is less than for samples 3 and 4. It appears that sample 2 which, uses reactive alumina, has an almost immediate development of structure and this is accompanied by a significant shrinkage (approx 5% of total shrinkage is achieved by 2 minutes). The shrinkage due to hydration occurs much later between 6 and 7 minutes and precedes the exothermic peak. This is in phase with the maximum temperature rate change at around 63 minutes (from Table 2). Number 5 Number 6 Temp ( C) Shrink/Expansion (mm x 1^-2) Shrinkage Exothermic Ultrasonic Propagation speed (m/s) Temp ( C) Shrink (mm x1^-3 ) Exothermic 15 5 Ultrasonic Shrinkage Propagation speed (m/s) Figure 8: Comparison of ultrasonic, exothermic and shrinkage data (samples 5 and 6) Tel : 33 () Fax : 33 ()

13 Reference : TP-GB-RE-LAF-58 Page : 13/16 Number 5 Number 6 temp ( C/min) velocity rate (m/s/min),5,4,3,2,1 -,1 -,2 -,3 -,4 -,5 Ultrasonic Exothermic Shrink/Exp,14,12,1,8,6,4,2 -,2 shrink/exp (mm/min) Temp ( C/min) Velocity (m/s/min),3,25,2,15,1,5 -,5 -, ,4,3,2,1 -,1 -,2 ShrinkExp (mm/min) Figure 9: Comparison of ultrasonic, exothermic and shrinkage rate change curves (samples 5 and 6) Max Temperature ( C) y = -,99x + 34,853 R 2 =, Time to max shrinkage/expansion (mins) maximum rate of temperature increase C/min,3,25,2,15,1,5 -,5 -,1 y = 19,4x +,575 R 2 =,888 -,15 -,1 -,5,5,1,15 max shrinkage/expansion rate mm/min Figure 1: Relationship between time to reach maximum volume change and exothermic reactions The sample with calcined alumina (number 1) shows almost no shrinkage during the initial stages up to 4 minutes; thereafter shrinkage increases up to 8 minutes where the maximum value is reached. There is a second increase in ultrasonic velocity after this phase which is accompanied by the maximum temperature rate increase at 753 minutes and the main exothermic peak at 9 minutes. The differences induced just by changing the alumina type are quite surprising. Although it must be stated that the absolute shrinkage values are much less than the non accelerated samples (3 and 4). By careful selection of the alumina type and additive the initial shrinkage can be controlled. The samples with added aluminium show quite different profiles. The loss of ultrasonic signal occurs at the same time as the large expansion (up to 32 microns/metre/min) in both cases. This is followed by a reduction in the expansion rate and the arrival of the main exothermic peak. The ultrasonic velocity continues once a coupling is re-established after the large linear movements. However, some significant differences appear to exist between the two model systems. Sample, 5 with the calcined alumina maintains a positive expansion thereafter with a residual expansion of 711 microns/metre. Sample 6, with reactive alumina after the initial expansion shrinks back to almost the initial Tel : 33 () Fax : 33 ()

14 Reference : TP-GB-RE-LAF-58 Page : 14/16 value and ends up with a slightly positive residual expansion of only 121 microns/metre. If the derivative curves of rates are studied then it can be seen that the maximum rate of,26 C/min is achieved with sample 5 almost double that of sample 6. The exothermic peak also occurs earlier with sample 5 and almost as soon as the expansion reaction has terminated. In the case of sample 6 the exothermic peak occurs more than 1 minutes after the expansion reaction initiated by the aluminium addition. Further study is necessary to more clearly understand the exact reasons behind this behaviour and as to how much is due to hydration kinetics or other factors such as the particle interactions. The impact of temperature on the autogenous shrinkage through the self heating of the samples containing aluminium cannot be ignored and this merits further investigation. This example however, shows that the final expansion as a result of the hydrogen gas reaction can be influenced by the other formulation parameters. The coupling of the different techniques is a useful means by which the young age properties of apparently fairly similar castables can be studied. It is premature based on this data to draw definitive conclusions but there does appear to be a trend which indicates that the greater exothermic reaction the greater the final dimensional change at the end of the setting period. This is exemplified in Figure 1 which shows the apparent relationship between the time to maximum dimensional change and the exothermic properties. As the exothermic reaction becoming more vigorous as measured by peak temperature or time to the max peak then the dimensional change is bigger. 5 Conclusion From the results presented the two techniques are able to discern different characteristics of model castables during the initial setting and stiffening of refractory castables. - The measurement of ultrasonic wave propagation velocity is a reliable method to follow the various steps in the castable placing chain, from the loss of workability to the completely hardened state. It is sensitive to different parameters such as the type of admixtures or fine fillers used in the matrix component. - A continuous monitoring of the dimensional change during the young age of refractory castables provides complimentary information as to the developing structure. It also appears to be sensitive to formulation changes and can detect relatively small movements in the order of microns. From the model systems evaluated the effect of the different formulation parameters can be seen on the early age properties: - Slower hardening systems (e.g. additives HMP and Citric acid) result in a lower linear shrinkage (<5micron/metre) than with an additive systems (e.g. TPP) that gives a more rapid acquisition of mechanical strength. However, the degree of difference depends upon the associated type of reactive fillers that are used. - The use of different types of fine calcined and reactive alumina promotes different hardening profiles and shrinkage rates. This is particularly true in the case of aluminium containing castables where the addition of reactive alumina resulted in a much lower overall expansion than when calcined alumina was used. When these techniques are coupled with exothermic profiles these three techniques provide a powerful array of tools in which the young age properties of placed castables can not only be studied but be optimised. For example, it has been shown that the choice of fine alumina can have a significant effect upon the hardening profile and shrinkage. Use of this information can be incorporated into the formulation development phase and lead to castables with more rapid hardening profiles or lower linear shrinkage. Similarly, the large expansions induced by the reaction of Tel : 33 () Fax : 33 ()

15 Reference : TP-GB-RE-LAF-58 Page : 15/16 aluminium with water can be managed through the complementary choice of other matrix components. The use of these methods can help the formulator to create refractory castables with controlled hardening times and rates and also with known total volume change parameters. Further studies are in progress to compare different methods of determining autogenous shrinkage and early age properties of refractory castables 6 References 1 C. Parr, T. Bier, N. Bunt, E. Spreafico, Calcium Aluminate Cement based castables for demanding applications, 1 st Monolithics Conference Proceedings, Tehran, IRAN, (1997). 2 J. Weiss, K. Kovier, J. Marchand, S. Mindess, Advances in concrete through science and engineering, RILEM proceedings pro 48, (24) 3 A. Boumiz, C. Vernet, F. Cohen-Tenoudji, Mechanical properties of cement and mortars at early ages, Adv. Cem. Based Mater., [1], 12-21, (1996). 4 T. Nawa, T. Horita, Autogenous shrinkage of high-performance concrete, Proc. International Workshop on microstructure and durability to predict service life of concrete structures, Sapporo, Japan, (24) 5 S. Miyazawa, E. Tazawa, Autogenous shrinkage and drying shrinkage of high strength concrete, Proc. 5 th Int. Symp. On Utilization of high strength/high performance concrete, Sandefjord, pp , (1999) 6 O.M. Jensen, P.F. Hansen A dilatometer for measuring autogenous deformation in hardening cement paste, Mater. Struct. [181] , (1995) 7 P. Lura, K. van Breugel, I. Maruyama, Effect of curing temperature and type of cement on early-age shrinkage of high-performance concrete, Cement and Concrete Research, [31], , (21) 8 S.Garcia Boivin, Early age shrinkage of concrete. Setting up a test method for autogenous shrinkage and contribution to its physical analysis (in French), Th. Doct, Struct. Matér., Ecole Nationale des ponts et chausses, Paris, FRA, (21) 9 P. Mounanga, V. Baroghel-Bouny, A.Loukili, A.Khelidj, Autogenous deformations of cement pastes :Part 1. Temperature effects at early age and micro-macro correlations, Cement and Concrete Research, [36], , (26) 1 L. Barcelo, S. Boivin, S. Rigaud, P. Acker, C. Boulay, B. Clavaud, Linear vs volumetric autogenous shrinkage measurement; material behaviour or experimental artifact?, in B. Persson, G. Fagerlaund, (Eds), Proceedings of the Second International Research Seminar Self-dessication and its importance in concrete technology, Lund, Sweden, pp19-125,(1999) 11 J.P. Charron J. Marchand, B. Bissonnette, Early age deformations of hydrating cements systems: comparison of linear and volumetric shrinkage measurements, in K. Kovler, A. Bentur, (Eds), Proceedings of the International RILEM conference on early age cracking in cementitious systems EAC 1, Haïfa, Israel, pp , RILEM Publ, Cachan, (21) 12 Th. A. Bier, F. Estienne, L. Amathieu, "Shrinkage and Shrinkage Compensation in Binders Containing Calcium Aluminate Cement, Conference on Calcium Aluminate Cements, , Edinborough (21). 13 C. Parr, R. Roesky, C. Wöhrmeyer, Calcium Aluminate Cements for Unshaped refractories, CN Refractories Special Issues, [5], pp6-12, (21). 14 H. Fryda, K. Scrivener, T. Bier, B. Espinosa, "Relation between setting properties of Low Cement Castables and interactions within the Tel : 33 () Fax : 33 ()

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