Technical Paper MCC AND HCC: DEFLOCCULATED HIGH PERFORMING CASTABLES RICH IN CALCIUM ALUMINATE BINDER. Christoph Wöhrmeyer, Chris Parr*,

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1 Reference : TP-GB-RE-LAF-64 Page : 1/8 MCC AND HCC: DEFLOCCULATED HIGH PERFORMING CASTABLES RICH IN CALCIUM ALUMINATE BINDER Christoph Wöhrmeyer, Chris Parr*, * Kerneos GmbH, Oberhausen, Germany; Kerneos SA, Paris, France,christoph.wohrmeyer@kerneos.com, Presented at Refractories, Furnaces and Thermal insulations conference, 22 nd 24 th April 28, Strebske Pleso, High Tatras, Slovakia

2 Reference : TP-GB-RE-LAF-64 Page : 2/8 ABSTRACT Conventional castable still represent a non-negligible part of the refractory concrete market. Their robustness to varying installation conditions and the simplicity of application has secured their market acceptance. But since they don t contain any deflocculant or filler they have a high water demand and consequently a high porosity and a low strength. Low porosity and a micro-porous structure are required to give for example highest abrasion and thermal shock resistance at medium temperatures. From conventional castables it is known that their strength is quite low in the temperature range above the dehydration temperature of calcium aluminate hydrates and below the sintering temperature. Especially for this temperature range deflocculated medium and high cement castables (MCC and HCC) are an interesting and robust alternative. Some compositions in this system have been found with unexpectedly high hot strength. But not all applications can accept high lime contents in the castable. In applications like blast furnace troughs or tundishes, Microsilica containing lime reduced concretes have their place. But their hardening characteristics are very sensitive to raw material interactions in the fine matrix of these castables. In order to make these ULCC and LCC as robust as MCC and HCC a new calcium aluminate binder, SECAR Xeniom TM, is the focus of the second part of this investigation. It was found that this new binder makes strength acquisition less dependent on interaction with other raw materials like microsilica or andalusite fines. The retarding effect of andalusite compared to bauxite and fireclay is buffered and variabilites induced by lot-to-lot variations of Microsilicas are levelled out. This new 84% Al2O3-containing calcium aluminate binder allows higher binder dosage compared to a 7% calcium aluminate cement and makes castable hardening less dependent on interactions with other raw materials and on ambient temperature.

3 Reference : TP-GB-RE-LAF-64 Page : 3/8 1 Introduction One of the main negative points of conventional castables is their high water demand and consequently their high porosity and low strengths level. Therefore the first point to look after was the question if cement rich formulations can be easily deflocculated to reduce water demand and porosity to transform them into HCC and MCC (Tab.1). In this case some of the cement would be used as functional filler since the water/cement ratio for these recipes would be lower than the required amount to hydrate all the calcium aluminate phases in the cement. High purity 7% Al2O3 containing CAC like SECAR 71 contain a significant amount of the phase CA2 which hydrates only slowly in the presence of water. In the case of deflocculated HCC the amount of water would not been enough to hydrate all CA2 completely since the calcium mono-aluminate phase, the main hydraulic phase in this type of CAC, would preferentially trap almost all of the mixing water in its hydrate phases. Since CA2 is a phase with low thermal expansion it can work as a functional filler which improves the thermal shock resistance of these mixes at low and intermediate temperatures where mullite formation can not be achieved yet in microsilica containing LCC and ULCC. Binder system combinations of microsilica with a 7% Al2O3 containing calcium aluminate cement have been investigated to identify the most performing compositions in the cement rich system. Cement reduced microsilicacontaining LCC and ULCC have their advantages in the temperature range of 13 to 15 C but castable hardening behaves very sensitive to many factors like water addition, mixing technology, raw material interactions and ambient temperatures. A new binder with 84% Al2O3, SECAR Xeniom TM, can be added in a higher dosage compared to a 7% Al2O3 containing CAC to reach the same overall castable chemistry but provides a more robust and homogeneous castable setting. The binder has been tested in model formulations with a large range of different raw materials. Some results are shown in the second part of the presentation. They underline the robustness for example to lot-tolot variations of microsilica, different aggregates fines like andalusite and low ambient temperatures. Tab.1: Segmentation of castables into conventional (CC) and deflocculated HCC, MCC, LCC, ULCC castables and their related cement resp. binder content Classification by CaO content Typical content (wt%) of 7% calcium aluminate cement Filler addition Deflocculant addition CC 15-3 non non HCC 15-3 yes/non yes MCC >2,5 >8 yes yes LCC 1-2,5 4-8 yes yes ULCC <1 1-3 yes yes Typical content (wt%) of 84% calcium aluminate binder LCC 1-2, Microsilica integrated in binder integrated in ULCC <1 2-6 Microsilica binder

4 Reference : TP-GB-RE-LAF-64 Page : 4/8 Working time (min) 2 Test methods Castable rheology and other physical properties have been measured according to EN and ASTM norms as described in [1]. Working time is the period during which the castable can still be installed with vibration. The model formulations used in this study are indicated in Tab.2 for the study of the MCC and HCC and Tab.3 for the investigation with the new LCC and ULCC binder. Hot modulus of rupture has been measured after drying of the samples at 11 C and a pre-firing inside the test equipment during 24h at the test temperatures (8, 1, 12, 13 C). Tab. 2: Castable model with varying CAC (SECAR 71) and Microsilica content Tabular Alumina wt.% 2-5 mm mm 15,5-1 mm 1,2-,6 mm 13 -,3 mm 5 (2-6) -,45 mm 7 (-9) CAC SECAR Elkem Microsilica 971U - 8 Na hexa-metaphosphate +.2 Citric acid % Microsilica % Microsilica CAC content in formulation (%) Fig. 1: Impact of CAC and Microsilica content on castable working time I 3 Test results Deflocculated castables with medium and high cement content (MCC and HCC) In pre-trials an admixture system based on a combination of sodium hexa-metaphosphate (HMP) and citric acid (CA) has been found as convenient for the full range of formulations as exposed in Tab.2. This HMP/CA deflocculation system provides a good fluidity at a low amount of mixing water even for the most cement rich recipes. In the range of 18 to 26% CAC a water addition of 6,5 to 7% was sufficient both, for microsilica-free and microsilica-containing systems. The same mixes but without any addition of deflocculants would need between 8% for the microsilica-free and 11% water for the microsilica-containing mixes. The amount of citric acid has been kept constant during all trials to study the impact of microsilica and CAC on the castable working time. As can be seen in Fig.1 the working time remains on a nearly constant level for all tested cement contents when the system is silica-free. With increasing microsilica content, working time increases at low cement contents much more drastically than at high cement contents. With MCC and HCC the retarding effect of microsilica becomes much less critical and a quite robust system can be achieved compared to the more sensitive LCC and ULCC. In Fig. 2 and 3 the impact of the deflocculation system on the density and the strength of an MCC with 1% CAC without silica addition are shown. An increase of bulk density by,1 g/cm3 results in a more than 1% increase in cold crushing strength.

5 Reference : TP-GB-RE-LAF-64 Page : 5/8 CCS (MPa) Bulk density (g/cm3) 3,1 3, 2,9 2,8 2,7 2,6 2, With HMP/CA Without HMP/CA Temperature ( C) With HMP/CA Without HMP/CA silica free HCC mixes give here the highest densities and strength values. The corresponding strengths at high temperatures expressed as hot modulus of rupture are shown below. Silica free systems (Fig.8) have a very stable but relatively low hot strength over the full range from LCC over MCC to HCC. HMOR between 8 and 13 C is nearly constant. By adding a small dose of microsilica (2%), the strength increases significantly for all temperatures and all cement contents up to temperatures of 12 C (Fig.9). At 13 C the cement rich formulations (22-26% SECAR 71) have still remarkable high hot strength, equal or even higher than the silica free mixes. The cement reduced systems with 6 to 14% cement and 2% silica have lower hot strength at 13 C compared to their silica-free homologues Temperature ( C) Fig.2: Bulk density of MCC without and with deflocculant (1% S71, microsilica-free) Fig.3 CCS of MCC without and with deflocculant (1% S71, microsilica-free) By increasing the cement content in the deflocculated systems and moving from MCC to HCC the bulk density (135 C) decreases slightly. This is the case for both silica free mixes and mixes that contain 2% microsilica. The decrease is somewhat faster when silica is present (Fig.4). With increasing cement content the strength evolution after firing at 135 C is different for the silica containing (2%) and the silica free system (Fig.5). The silica free system has increasing strength values with increasing cement content, while the addition of silica has a reverse effect on cold crushing strength. For MCC the addition of silica has a positive effect on strength while for HCC silica free systems expose higher strength values. For application temperatures up to 11 C the addition of small amounts of silica results in a significant bulk density and strength increase (Fig.6 and 7). For the high temperature range of 135 to 15 C this effect turns around and Bulk Density 135 C (g/cm3) CCS 135 C (MPa) 3,2 3,1 3 2,9 2,8 2,7 2,6 2, Silica free S71 in formulation (wt.%) S71 content in formulation (wt.%) Silica free Fig.4: Bulk density (135 C) of deflocculated MCC and HCC with zero and 2% microsilica Fig.5: CCS (135 C) of deflocculated MCC and HCC with zero and 2% microsilica

6 Reference : TP-GB-RE-LAF-64 Page : 6/8 Bulk density (g/cm3) CCS (MPa) 3,1 3, 2,9 2,8 2,7 2,6 2, % Microsilica % Microsilica Temperature ( C) Temperature ( C) 22% S71 26% S71 22% S71 26% S71 22% S71 26% S71 22% S71 26% S71 Fig.6: Bulk density of HCC with zero and 2% microsilica (22 and 26% CAC) Fig.7: CCS of HCC with zero and 2% microsilica (22 and 26% CAC) HMOR (MPa) HMOR (MPa) 28, 24, 2, 16, 12, 8, 4,, 28, 24, 2, 16, 12, 8, 4,, Secar 71 content in formulation (%) Silica free Secar 71 content in formulation (%) Fig.8: HMOR of silica free mixes Fig.9: HMOR of 2% silica containing mixes The silica free system is a pure A-CA2 system which turns at temperatures higher than 13 C into a A-CA2-CA6 system with excellent refractory properties. The silica containing system creates at an addition level of 2% silica as well mainly A and CA2 with initially some additional CAS2 (Anorthite) which turns with increasing temperatures and cement content into C2AS, Gehlenite [2]. Both, Anorthite and Gehlenite have melting temperatures above 15 C. But eutectics and peritectics create already some liquid phase between 135 and 14 C which leads to softening of the silica containing mixes. In the HCC a significant amount of the calcium aluminate phase CA2 occurs. CA2 is a phase with a low and anisotropic thermal expansion, a phase especially useful when the concrete is exposed to thermal shocks [3]. CA2 can play a role similar to Mullite in cement reduced LCC and ULCC. But Mullite formation occurs at higher temperatures only while CA2 is employed into the system via the calcium aluminate cement. The CA2 remains to a bigger extent non-hydrated due to the low water demand of the deflocculated HCC. Therefore a part of the cement itself can be considered here as active filler. A new binder to make Microsilica containing LCC and ULCC more robust and reliable Typically LCC and ULCC contain between 1 and 8% of a 7% Al 2 O 3 containing calcium aluminate cement. In these formulations microsilica can become a dominant factor in the concurring chemical interactions that occur during the early phase when the concrete has been mixed with water. A sufficient calcium aluminate hydration can only occur if the dissolution of the cement creates saturation of calcium and aluminium ions in the correct ratio inside the pore solution. From this saturated solution the precipitation of solid hydrates can occur which creates the bond and strength acquisition of a concrete. Everything which disturbs the dissolution process and the correct ratio between Ca- and Al-ions has a variation in set

7 Reference : TP-GB-RE-LAF-64 Page : 7/8 time as consequence. Both, deflocculants and microsilicas are known for their interactions with the cement [4]. Tab.3: Model formulations with equal castable chemistry but 2 different binder systems LCC1 LCC2 Aggregates -6 mm Silica fume 93% (SiO2+ZrO2) 5 5 New binder SECAR Xeniom TM 84% Al2O3 1 - Reference LCC cement SECAR 71 7% Al2O3-5 Calcined Alumina AC44B4 d 5=4 µm - 5 Na-TPP powder -,8 1 1,8 working time (min) LCC1 (Secar Xeniom) 95% SiO2 - lot A 95% SiO2 - lot B 95% SiO2 lot C Microsilica lot LCC2 (Secar 71-TPP) Fig.1: Bauixte LCC1 and LCC2 with different lots of a 95% microsilica To buffer these variables in the LCC and ULCC systems a new binder which can be dosed at a higher rate compared to microsilica has been developed, SECAR Xeniom TM. It reduces the dominance of microsilica on the castable setting. It is a binder with an Al2O3 content of 84% and an integrated buffering and an adapted deflocculation system. Tab.1 gives the approximate SECAR Xeniom TM binder content in order to achieve for example a LCC composition with 1-2,5% CaO. To compare this new 84% calcium aluminate binder with the existing 7% calcium aluminate cement at constant castable chemistry, the formulation principle as indicated in Tab.3 has been applied. 5% SECAR 71, 5% calcined alumina and the sodium tri-polyphosphate has been replaced Workingtime (min) LCC1 (Secar Xeniom) LCC2 (Secar 71-TPP) LCC2 (Secar 71-PA/CA) 97% SiO2 96% SiO2 95% SiO2 93% SiO2 3% ZrO2 Different silica fume products 89% SiO2 4% ZrO2 Fig.11: Bauxite LCC1 and LCC2 (with TPP, and with polyacrylate/citric acid) and Microsilicas of different purities all together by 1% SECAR Xeniom TM without any further addition of admixtures. Fig.1 to 13 show the working time of different LCC that have been formulated with SECAR Xeniom TM in comparison to SECAR 71. As can easily be seen the new binder levels out the working time variabilities induced by lot-tolot variations of microsilica, different microsilica types and aggregates fines. It reduces the hardening delay at low temperatures even when using andalusite as aggregate.

8 Reference : TP-GB-RE-LAF-64 Page : 8/8 W ork in g tim e (m in ) LCC1 (Secar Xeniom) LCC2 (Secar 71) Tab. alumina Bauxite Andalusite Fireclay 6% Fireclay 47% Type of aggregate Fig.12: LCC1 and LCC2 based on different aggregates and a 97% microsilica 4 Summary Working time (min) LCC1 (Secar Xeniom) LCC2 (Secar 71) 1 C 2 C 3 C Fig.13: Andalusite based LCC1 and LCC2 with a 97% microsilica at different temperatures 5 References The study has shown that castables, rich in calcium aluminate cement and deflocculated yield properties which justify the creation of a new class of castable: HCC or High Cement Castable. They are robust formulations and a significant improvement compared to conventional castables. Compared to LCC they have their advantage in the medium temperature range with high strength and abrasion resistance and a CA2-rich matrix with an expected thermal shock resistance similar to mullite. For applications where reduced lime content in combination with microsilica is required a new binder, SECAR Xeniom TM, achieves a higher robustness compared to existing LCC. Due to its high alumina content the binder can be dosed at higher rates which reduce the dominance of the high surface area microsilicas on castable setting time. It levels out setting variabilities induced by other matrix components like lotto-lot variations of microsilica or aggregates fines. SECAR Xeniom TM reduces as well the delay of setting at low temperatures for example for andalusite based LCC. Both HCC and MCC with a 7% alumina cement and LCC and ULCC with a 84% alumina binder content have a high robustness level similar to what is known from non-deflocculated conventional castable but with a much higher technological performance. [1] F. Simonin, C. Wöhrmeyer, C. Parr: A new method for assessing calcium aluminate cements, Unitecr 25 [2] B. Myhre: Hot strength and bond-phase reactions in low and ultralow-cement castables. UNITECR 1993, [3] S. Jonas, F. Nadachowski, D. Szwagierczak: Low thermal expansion refractory composites based on CaAl 4 O 7, Ceramics International, Vol 25, pp 77-85, 1999 [4] C. Parr, G. Assis, J.M. Auvray, Hu Chong, H. Fryda, C. Wöhrmeyer: Recent advances in refractories aluminate binders and additives for high performance monolithic castables, Irefcon 28.