POLYCARBOXYLATE ETHER BASED SUPERPLASTICISER FOR CALCIUM ALUMINATE CEMENT MORTARS

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1 POLYCARBOXYLATE ETHER BASED SUPERPLASTICISER FOR CALCIUM ALUMINATE CEMENT MORTARS N. UKRAINCZYK, J. SIPUSIC and N. VRBOS Faculty of Chemical Engineering and Technology, University of Zagreb, Marulicev trg 19, Zagreb, Croatia SUMMARY: This work investigates the effect of polycarboxylate ether (PCE) based superplasticiserplasticiser onto the fresh and hardened properties of mortars based on commercial CACs. Mortar specimens were prepared aiming at constant workability; PCE addition was varied as 0%; 0.3%; 0.6% and 0.9% of cement mass. The required water to cement ratio to maintain the workability of fresh mortar was recorded. Cohesion of the fresh mortar was improved by addition of methyl-cellulose, thus avoiding segregation induced by the superplasticiser action. As PCE significantly retard the setting time, Li 2 CO 3 was investigated as an accelerator. Compressive and flexural strengths were tested after 1 day and 9 days cured at 23 C and after transformation of metastable hydration products at 60 C. Deleterious effect of transformation of metastable hydration products to stable ones on mechanical properties was successfully reduced by lowering of water to cement ratio while maintaining the workability. In conclusion, the usage of PCE showed promising superplasticizing properties for CAC based materials. Keywords: calcium aluminate cement, hydration, mechanical properties, rheology, setting time, superplasticiserplasticiser. INTRODUCTION Calcium aluminate cement (CAC) is a special cement with many specific applications [1-5] mainly attributed to its fast hardening [4-8] and excellent resistance to chemical attack [1-3]. The CAC hydration is highly temperature dependent, yielding CAH 10 as main products at temperatures less than 20 C, C 2 AH 8 [9] and AH 3 at temperatures around 30 C, whereas C 3 AH 6 and AH 3 at temperatures greater than 55 C. CAH 10 and C 2 AH 8 are known to be metastable at ambient temperature and transform to more stable C 3 AH 6 and AH 3 with consequent increase in material porosity and permeability, and loss of strength. This conversion is accelerated by temperature and moisture availability. The water to cement ratio and the amount of the most active minerals in CAC are the principal variables governing the porosity and strength development during conversion of metastable hydration products [10]. Deleterious effect of transformation of metastable Calcium Aluminates: Proceedings of International Conference, Avignon, May Fentiman CH, Mangabhai RJ and Scrivener KL (Editors). IHS BRE Press, 2014, EP104. ISBN

2 Ukrainczyk, Sipusic and Vrbos hydration products to stable ones on properties of calcium aluminate cement (CAC) based materials could be reduced by lowering of water to cement ratio. To achieve this in practice, superplasticisers should be used to yield a good workability with a low water to cement ratio as well as low cement content. Contrary to Portland cement, past experience in superplasticazing of CAC showed difficulties producing a workable concrete [11,12]. New generations of superplasticisers offer novel possibilities to improve workability and lower water to cement ratio (and cement content) which by consequence could aid to long-term performance of CAC based materials [12]. While the influence and benefits of polycarboxylate ether (PCE) based superplasticiser on ordinary (Portland) cements are widely reported in the literature, little is known on the modification of the special CAC based materials. Fryda et al [12] investigated the effect of polycarboxylate-polyox and polynaphthalene sulfonate superplasticisers on the flow and setting time of low-iron grade CAC mortars. This work investigates the effect of polycarboxylate ether (PCE) based superplasticiser onto both fresh and hardened properties of mortars based on commercial high-iron grade CACs. EXPERIMENTAL Materials Commercial CAC (type ISTRA 40) was taken from a regular production of Calucem Pula, Croatia. The cement has the oxide mass fraction composition listed in Table 1. Physical properties of the cement used are given in Table 2. The main compounds are CA and ferrite phase (C 4 AF-C 6 AF 2 ), with mayenite (C 12 A 7 ), gehlenite (C 2 AS) and β- C 2 S as minor compounds. Polycarboxylate ether (PCE) based superplasticiserplasticiser Sika Viscocrete -20 Gold was used with the physico-chemical characteristics shown in Table 3. Mortars were prepared with distilled water and crushed carbonate stone with the size of mm (100% passed 4 mm sieve). Analar grade Li 2 CO 3 salt was used as an accelerator. Table 1. Chemical composition of investigated CAC (mass %). CaO Al 2 O 3 Fe 2 O 3 FeO SiO 2 TiO 2 MgO SO 3 Na 2 O K 2 O Table 2. Physical properties of investigated CAC. >90 μm, Blaine, % cm 2 /g Specific gravity, g/cm 3 Setting time, min Standard consistency, % initial Final Table 3. Physico-chemical characteristics of the employed superplasticiser (Sika Viscocrete -20 Gold)). Density (20 oc ), kg dm -3 ph Cl -, mas. % Alkalies, mas. % Solid, mas. % < 0.1 <

3 Polycarboxylate Ether Based Superplasticiser for Calcium Aluiminate Cement Mortars Specimen preparation and experimental plan Mortar specimens were prepared aiming at maintaining their workability. PCE addition was varied as 0%; 0.3%; 0.6% and 0.9% of cement mass. The required water to cement ratio to fix the workability of fresh mortar was recorded. Cohesion of the fresh mortar was improved by addition of methyl-cellulose (MC), thus avoiding segregation induced by the superplasticiser action. Mortar was mixed in a standard laboratory planetary mixer following ASTM C Li 2 CO 3 accelerator was dissolved in freshly deionised water prior to mixing with cement with a mass fraction relative to cement weight according to Table 4. First, the influence of the accelerator on the setting time was investigated for the highest addition of PCE, i.e. on the P9Lx series as indicated in Table 4. Then, series P0 - P9 were prepared to investigate properties of fresh and hardened mortars. Fresh mixtures were cast into prismatic moulds (40 x 40 x 160 mm) and vibrated. Specimens were cured in mould for 24 hours at 23 C and 95% of relative humidity. In order to investigate properties of hardened CAC mortars with morphologically different hydration products, the aimed specimens were obtained according to a designed experimental hydration program shown in Table 5. The specimens were hydrated at 23 C to obtain principally metastable hydration products and tested immediately after demoulding and also after 8 additional days at 45% R.H. The metastable hydration products were transformed to the stable ones (nominally C 3 AH 6 and AH 3 ) by additional heating of the specimens at 60 C in a temperature controlled water bath for 24 h, and tested after additional curing at 23 C and 45% relative humidity (RH). Table 4. Experimental plan, variables and sample notation (PCE- polycarboxylate ether; MC- methylcellulose; additions are in % of cement mass). Sample PCE Li 2 CO 3 MC Workability, sand:cement notation % % % flow table P9L P9L P9L P9L P0 0 P3 0.3 P6 0.6 P ± 10 mm 3:1 Table 5. Specimen curing conditions for samples P0 - P9. Curing series in mould after demoulding 1d 9d Trans 24 h at 95% RH and 23 C tested immediately 8 days at 23 C 45% RH 1 day transformed in water bath at 60 C + 8days at 23 C 45% RH Experimental methods Times of initial sets t 0 were established from the obtained time temperature curves of mortar samples filled in a styrofoam cup and sealed with a styrofoam stopper and immersed in temperature controlled water bath T = 23 C (±0.03 C). Initial set was

4 Ukrainczyk, Sipusic and Vrbos acquired from the intersection of two straight lines [5] : one fitted through the induction period of the curve and the other fitted through the inflection point of the rising slope of the main peak. Time of maximal temperature (i.e. heat generation) is also recorded. The consistency (fluidity) of the fresh state mortar was tested using the standard flow table test according to EN The test procedure involved placing the mould (60 mm in height, internal diameter: base 100 mm - top 70 mm) in the centre of the flow table. A period of 15 seconds was allowed to elapse before the mould is removed, the table was jolted 15 times at a rate of one jolt per second. The mean diameter of the spread mortar was recorded. Bending and compression test of hardened mortars were done as per EN The bending tests were performed on 40 x 40 x 160 mm prisms, while the compression tests were carried out on two pieces of original prisms for each specimen. The standard moulds were filled by placing on a vibrating table. RESULTS AND DISCUSSION The addition of PCE resulted in a poor cohesion and a high segregation of the mortar components. The samples exhibited a high bleeding effect. Therefore, cohesion of the fresh mortar was improved by addition of methyl-cellulose (MC), thus avoiding segregation induced by the superplasticiser action. The addition of 0.045% of MC (by cement mass) resulted in good cohesion and stability of the mixture for all additions of PCE. Furthermore, the addition of PCE showed extensive retardation of setting. Thus, next the influence of the addition of Li 2 CO 3 accelerator on the setting time was investigated for the mixtures that contain highest addition of PCE (i.e. 0.9%). Table 6 shows the results of the setting time (t 0 ) and time of maximal heat generation (t m ) as obtained from the temperature measurements of mortars. Without accelerator, the P9L0 mixture resulted to set only after 22 h, while the reaction rate reached a maximum at 29.5 h. From the results presented in Table 6 it can be seen that very small addition of Li 2 CO 3 (0.004% relative to weight of cement) significantly accelerates the hydration. The addition of Li 2 CO 3 acted also as an accelerator even in the case of superplasticiser addition. Thus, there is a combined opposing effect of PCE and Li 2 CO 3 addition that regulates the setting time. As the addition of Li 2 CO 3 increases, both of the setting time parameters t 0 and t m continuously decrease. The high retardation of the hydration by small addition of PCE superplasticiser could be attributed to a steric hindrance of the long side chains linked to the polymer backbone providing a physical barrier on the reacting surface of cement [13]. On the other hand, the acceleration of hydration by Li 2 CO 3 may be attributed to the removal of the nucleation barrier, through an initially fast precipitation of alkali metal hydration products (e.g. lithium hydrometaaluminate) that act as a heterogeneous nucleation substrate, promoting the nucleation of the CAC hydration products [5]. For further investigate addition of PCE superplasticiser on properties of fresh and hardened mortars, a concentration of 0.002% of Li 2 CO 3 was employed. This still resulted in setting times that are significantly shorter than for the reference cement at standard consistency (namely w/c = 0.24 and t 0 = 300min, Table 2). Furthermore, Table 6 shows that with the increase of PCE addition (and the decreases of w/c), the setting time t 0 continuously increases, due to the PCE retardation effect. On the other hand, the

5 Polycarboxylate Ether Based Superplasticiser for Calcium Aluiminate Cement Mortars time of maximal heat generation (t m ) is continuously decreasing for samples P0, P3 and P6, but then increases again for sample P9. This opposing effect on the t 0 and t m could be attributed to a combined effect of the Li 2 CO 3, PCE and w/c: PCE prolongs the induction period, while Li 2 CO 3 and lower w/c increase the reaction rate after the onset of the massive precipitation. Table 6. Results of setting time (t 0 ), time of maximal heat generation (t m ) from the temperature measurements of mortar and the water requirement for fixed workability (160 ± 10 mm) of fresh mortar. sample notation t 0, min t m, min w/c Workability, flow table, mm P9L P9L P9L P9L P P P P Mortar specimens were prepared aiming at a constant workability of 160 ± 10 mm by flow table test. The required water to cement ratio to fix the workability of fresh mortar at different PCE dosage is shown in 4 th row of Table 6. Maintaining the workability the water requirement was decreased by 20%, 32% and 38% compared to the reference mortar P0. For all curing series there is a marked improvement in flexural and compressive strength (Figure 1 and 2) in comparison to the reference samples P0. The main reason to this improvement is lower w/c that lowers the material porosity. Test results show that mortars of curing series 9d have higher strengths (flexural and compressive) than 1d due to the higher degree of hydration that results in lower porosity. The lowest compressive strength values between series are achieved for the fully transformed mortar series Trans, due to the well-known transformation process that results in the increase of material porosity. Specimens of all curing series show the same trend: mixes with a higher PCE content increase strength, due to lower w/c. It is interesting to observe that the Trans curing series P9 mixture has a higher strength than the mortar P0 after 8 days which has mainly untransformed hydration products. Figure 1 shows the effect of the mixture type (P0-P9, Table 5) and curing conditions on the flexural strength of CAC mortar specimens. The improvement is up to 37% for mortars with mainly metastable hydration products and by up to 58% for samples with transformed hydration products. The effect of the mixture type (P0-P9, Table 5) and curing conditions on the compressive strength is depicted in Figure 2. The improvement is up to 41% for mortars with mainly metastable hydration products and by up to 90% for samples with transformed hydration products. Long term strength of CAC based materials depends mainly on material porosity, and this is a function of w/c ratio, so using PCE as a means to reduce w/c at the same time as maintaining workability yields a high performance CAC based materials. Figure 2 demonstrates the possibility of long term strength higher than 60 MPa after

6 Compressive strength, MPa Flexural strength, MPa Ukrainczyk, Sipusic and Vrbos transformation of all metastable hydration products. Therefore, CAC based materials, with a w/c<0.4 could be employed for a variety of construction applications d 1d Trans PCE, % Fig. 1: Effect of the mixture type (P0-P9, Table 4) and curing conditions on flexural strength of CAC mortar specimens d 1d Trans PCE, % Fig. 2: Effect of the mixture type (P0-P9, Table x) and curing conditions on compressive strength of CAC mortar specimens.

7 Polycarboxylate Ether Based Superplasticiser for Calcium Aluiminate Cement Mortars CONCLUSIONS The addition of PCE resulted in poor cohesion, high segregation and high bleeding of the mortar components. The addition of 0.045% of methyl-cellulose (by cement mass) resulted in good cohesion and stability of the mixtures. PCE behaved as set retarder, but small additions (0.002%) of Li 2 CO 3 effectively regulate the induction period. Mortar specimens were prepared aiming at a constant workability of 160 ± 10 mm by flow table test. PCE dosage of 0.3%, 0.6% and 0.9% lowered the water to cement ratio to maintain the workability of fresh mortar by 20%, 32% and 38%, respectively compared to the reference mortar. The improvement in flexural strengths was up to 37% for mortars with mainly metastable hydration products and by up to 58% for samples with transformed hydration products. For compressive strengths the improvement was up to 41% for mortars with mainly metastable hydration products and by up to 90% for samples with transformed hydration products. In conclusion, the usage of PCE showed promising superplasticizing properties for CAC based materials. Lowering of w/c while maintaining workability by means of PCE yields to a high performance CAC based materials. Long term strengths in excess of 60 MPa can be anticipated after transformation of metastable hydration products. Therefore, CAC based materials could be employed for construction purposes if the w/c is kept below 0.4. ACKNOWLEDGEMENT The authors acknowledge support from the Croatian Ministry of Science, Education and Sports under project s no Development of hydration process model and Sika Croatia d.o.o. (Lučko, Croatia) for providing the superplasticiser, and Calucem d.o.o. (Pula, Croatia) for providing cement samples. REFERENCES [1] Bensted J. Calcium aluminate cements. In: Structure and Performance of Cement. London: J. Bensted, P. Barnes, 2002 [2] Scrivener K.L, Capmas A., Calcium Aluminate Cements, in Lea's Chemistry of Cement and Concrete, fourth edition, Peter C. Hewlett Ed., 1998, p 743. [3] Scrivener K.L, Cabiron J.L, Letourneux R, High-performance concretes from calcium aluminate cements, Cement and Concrete Research, Vol. 29, 1999, pp [4] Ukrainczyk N, Rogina A, Styrene butadiene latex modified calcium aluminate cement mortar, Cement & Concrete Composites, Vol. 41, 2013, pp [5] Ukrainczyk N, Vrbos N, Šipušić J. Influence of metal chloride salts on calcium aluminate cement hydration, Advances in Cement Research, Vol. 24, 2012, No. 5, pp

8 Ukrainczyk, Sipusic and Vrbos [6] Sipusic J, Ukrainczyk N, Vrbos N. Compressive strength of calcium aluminate mortar determined by ultrasonic non-destructive test method, Advances in Cement Research, Vol. 25, 2013, No. 1, pp [7] Ukrainczyk N. Kinetic modeling of calcium aluminate cement hydration, Chemical Engineering Science, Vol. 65, 2010, No. 20, [8] Ukrainczyk N, Matusinović T, Thermal properties of hydrating calcium aluminate cement pastes. Cement and Concrete Research, Vol 40, 2010, No. 1, pp [9] Ukrainczyk N, Matusinovic T, Kurajica S, Zimmermann B, Sipusic J. Dehydration of a layered double hydroxide-c 2 AH 8. Thermochimica Acta, Vol 464, 2007, No. 1-2, pp [10] Ukrainczyk N, Matusinović T. Modeling of Solid Fraction Evolution During Calcium Aluminate Cement Hydration, in Proceedings of the International Conference on Material Science and 64th RILEM Annual Week in Aachen - MATSCI, Vol II Modeling of Heterogenous Materials (HetMat) (PRO 76), ed. W. Brameshuber, Aachen 2010, RILEM Publications SARL France, 2010, pp [11] Banfill P.F.G, Gill S.M. Superplasticiserplasticisers for Ciment Fondu. Part 1: Effects on rheological properties of fresh paste and mortar, Advances in Cement Research, Vol. 5, 1993, No. 20, pp [12] Fryda H, Gachet V, Bost P and Scrivener K. L, Interaction of Superplasticiserplasticisers with Calcium Aluminate Cements, American Concrete Institute Special Publication SP Vol. 195, 2000, pp [13] Hommer H, Interaction of polycarboxylate ether with silica fume, Journal of the European Ceramic Society Vol. 29, 2009, No. 10, pp

MODELING OF SOLID FRACTION EVOLUTION DURING CALCIUM ALUMINATE CEMENT HYDRATION

International Conference on Material Science and 64th RILEM Annual Week in Aachen - MATSCI 189 MODELING OF SOLID FRACTION EVOLUTION DURING CALCIUM ALUMINATE CEMENT HYDRATION N. Ukrainczyk, T. Matusinović,