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Thermal properties, environmental deterioration and applications of macro-defect-free cements
Mojumdar, S. C.
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T he r m a l prope r t ie s, e nvironm e nt a l
de t e riorat ion a nd a pplic at ions of m a c
ro-de fe c t -fre e c e m e nt s
N R C C - 4 7 6 6 5
M o j u m d a r , S . C .
A version of this document is published in / Une version de ce document se trouve dans: Research Journal of Chemistry and Environment, v. 9, March 2005, pp. 23-27
Thermal Properties, Environmental Deterioration and Applications of
Macro-Defect-Free Cements
S. C. Mojumdar
Institute for Research in Construction, National Research Council of Canada, M-20, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada e-mail: Subhash.Mojumdar@nrc-cnrc.gc.ca
Abstract
Macro-Defect-Free (MDF) cements using the blends of sulfoaluminate ferrite belite (SAFB) clinkers and ordinary Portland cement (OPC) in mass ratio 85 : 15 and hydroxypropylmethyl cellulose (HPMC) or polyphosphates (poly-P) were subjected to various moist atmosphere to investigate their environmental deterioration. Their thermal decomposition studies were also carried out before and after moisture attack. The effect of individual relative humidity (RH) on moisture resistance of MDF cements is more intensive than the effects of composition of MDF cements or duration of the original MDF cements synthesis. There are three main temperature regions on TG curves of both series of MDF cement samples (before and after moisture attack). In the inter-phase section of MDF cements, the content of classical cement hydrates (CSH, gypsum, AFm and AFt phases) decomposing by 250 oC is increased, while the content of cross-links section and Ca(OH)2 with typical thermoanalytical traces in temperature range 250 - 550 oC remains almost identical before and after moisture attack. In the temperature range 550 - 800 oC, decomposition of CaCO3 is occurred. Some important applications of MDF cements also have been reviewed in this work*.
Key words : MDF cements, polymers, thermal properties, environmental deterioration, applications *The use of cement chemistry notation is as follows: C = CaO, A = Al2O3, F = Fe2O3, S = SiO2, S = SO3, H = H2O, C - CO2, AFm = C4(A,F) S H12 , w/s = water : solids mass ratio.
Introduction
Look around you and you are likely to see things made of a wealth of diverse materials: metals, plastics, ceramics, glass and cement and cement based materials. They are the stuff of a technological society. Materials are evolving faster now than at any previous time in history; concurrently incredible industrial needs are also increasing faster than in the past. Industries are very enthusiastic about searching for new materials; on the other hand, they are still not fully satisfied. Hence, this is the time to find places that can replace cement with better performing products. Cement and cement based materials have more influence on people’s lives than ever before. As the world’s premier building materials, cements and cement based materials are a tremendous challenge to the industries concerned, and to the ceramic and civil engineering professions. Polymer-cement composites can give high flexural strengths as well as high compressive strengths. A noteworthy example is so-called MDF cements. In general, MDF cements are prepared by using OPC, alumina cements1 or sulfate clinkers with water-soluble polymers, and by applying mechanochemical processing techniques at very low water-cement ratios (8-20%). The term “Macro-Defect-Free” refers to the absence of relatively large voids or defects that are normally present in conventional cement pastes because of entrapped air or inadequate mixing2. MDF cements display unique properties relative to traditional cement pastes. For example, their flexural strength is roughly 200 MPa as compared to 5 - 10 MPa for hardened OPC pastes. Such high strengths may be achieved by the removal of relatively large pores and water from their microstructures and an adhesive effect of the polymers at the interfaces between interacting calcium silicate hydrate gels. MDF cements also have several other attractive features such as low fabrication temperature (<100oC), high toughness and good dielectric properties1. It is not surprising therefore, that many authors have investigated MDF cements and related materials, and also examined their properties and applications3-13. Increasing knowledge in the area of MDF cements, together with definition of chemically bonded ceramics as a class, lead to the gradual acceptance of a chemical
hypothesis of the origin of their properties. According to that hypothesis, chemical cross-links and changes in bulk properties (relative to those in polymer-free cements) are the result of reactions occurring in the fabrication of MDF cements. In these materials the polymer and cement react synergistically to create a unique microstructure with distinct characteristics. Repeated extrusion helps to eliminate the critical flaws responsible for mechanical failure. Polymer chains cross-linked by metal ions impart tensile strength to the cement. The matrix of MDF cements consists of two interpenetrating phases: a cross-linked clinker with polymer and a nanocomposite interphase region around the cement particles. Sensitivity to moisture, as a technologically critical parameter, is caused through adsorption of water by the polymer phase and diffusion to the reactive cement filler, which then hydrates. The microstructure is thus degraded to a hydrate-bonded matrix.
Present work is focused on MDF cements system in SAFB clinkers with OPC and HPMC or poly-P dried at 50 oC immediately or after 24h of finishing the pressure application (delayed dried). Blends of SAFB clinkers with OPC exhibit upgraded properties compare to SAFB clinkers alone, i.e. setting times and mortar making technological procedures14. HPMC and poly-P in reaction mixtures support the MDF cements processability and may improve the moisture resistance15,16. The aim of our study was to check the effects of OPC in the raw mix and delayed drying on MDF cements process and also on subsequent moisture resistance and thermal stability. This paper describes a progress in three areas (a) environmental deterioration of MDF cements (special emphasis has been given to delayed dried samples), (b) thermoanalytical investigation of MDF cements, cross-links and phases arising due to the moisture attack and (c) applications of MDF cements.
Material and Methods
Complex SAFB clinkers, in which the clinker phases C4AF, C4A3S were present along with belite (C2S), 25% by mass, were synthesized at 1250 oC. Sintering conditions (raw materials, potential phase
composition, sintering temperature and duration) have been optimized previously17,18. OPC (CEM I 42.5, a trademark of Hirocem, Slovakian cement plant), SAFB clinkers premixed with OPC in mass ratio 85 : 15 were used for the MDF cements process, to test their thermal properties and subsequent moisture treatment.
Processing of MDF cements was as follows:
(a) Initial dry premixing of SAFB clinkers and OPC was followed by either
(b) addition of HPMC or Na5P3O10 (5% of total mass) and water to give w/s = 0.2 or
(c) addition of an aqueous solution of sodium polyphosphate (poly-P) to incorporate 5% (by mass) of poly-P and give w/s = 0.2 (‘s’ includes clinker and mass equivalent of the dissolved poly-P).
(d) Traces of glycerol were used as plastifier/processing agent.
(e) Twin-rolling was employed until the mixture reached the consistency of dense dough (up to 5 min).
(f) Static 5 MPa pressure in a pellet die (diameter 10 mm) was applied for intervals ranging from 0.5, 1, 3 and 5 h and
(g) Chemical reactions were completed by air drying at 50 oC either immediately (xdi) or 24h after finishing the pressure application (xdd).
HPMC (Aldrich) used corresponds to the viscosity of a 2% aqueous solution 80-120 cP. Sodium polyphosphates (Aldrich) were of formulae (NaPO3)n and Na5P3O10.
The environmental deterioration of model MDF cements was investigated at two different RHs. Cylindrical samples were kept in desiccators with controlled RH values, namely (a) above saturated NaHSO4(aq) (52% RH) and (b) above deionized water (100% RH). Mass changes recorded by periodic weighing until constant mass (incremental change Δm<0.01%) defined equilibrium at 52 and 100% RH. Further measurements of the (decreasing) mass of test pieces previously equilibrated at extreme humidity (100% RH) were similarly carried out during re-equilibration under ambient conditions.
These measurements resulted in an estimation of irreversible portion of mass changes due to the moisture attack at 100% RH
Simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) were conducted from ambient temperature to 1000 oC by using the T.A.I. SDT 2960 instrument (sample mass 10-20 mg, heating rate 10oC/min, in flowing air). Thermoanalytical studies were carried out on powders of two series of MDF cement samples (before and after moisture attack).
Results and Discussion
Environmental deterioration of MDF cements
The control of moisture resistance of MDF cements is an exceptionally important task not only for scientists but also for technologists. The incompleteness of conversion of clinkers is obvious at the given w/s (typically ranges from 0.1 to 0.2) ratios and this incompleteness exhibits a negative effect - low moisture resistance (high environmental deterioration). The moisture resistance of above series of MDF cements was investigated. A superior information capacity of mass changes as the measure of the moisture resistance, favored the profitable use in the present study. The mass changes of delayed dried MDF cements with dissolved poly-P, as the function of duration of the exposure in the environments with given RH are displayed in Fig. 1 as an example. The mass changes as the measure of the environmental deterioration, give important information for an effective check of the attack of various levels of humidity on a variety of MDF cements15,16,19. The evolution of mass (Fig. 1) to the equilibrium values enlarges the information about the effects of various levels of humidity as well as composition upon the moisture resistance of MDF cements. The equilibrium is achieved in any of the studied humidity within 6 to 17 days. It is in accord with data about MDF cements where cementitious phase is exclusively SAFB clinkers15,16,19-21. The effect of individual humidity on the environmental deterioration is more intensive than the effects of composition of MDF cements or duration of the
original MDF cements synthesis. However, detailed values at 100% RH and re-equilibrated at ambient conditions are strongly affected by the nature of polymer in both in SAFB clinkers-based MDF cements15,20,21 and in MDF cements, based on blends of SAFB clinkers and OPC. The most important improvement of moisture resistance of MDF cements has been achieved in MDF cement containing dissolved poly-P and delayed dried (Fig. 1). Delayed drying improves the impregnation effect of cross-links. We have received only 1 % mass increase at 100% RH of delayed dried MDF cements samples containing dissolved poly-P while 5 MPa pressure was applied for 3 hours (Fig. 1, curve c). According to our knowledge, it is the best result of moisture resistance of MDF cements, comparing to the interval of 10 - 20% mass increase at 100% RH of the other types of MDF cements. The lower mass increase is the evidence of the higher moisture resistance (lower environmental deterioration). Comparing to the effects of polymers, our studies display the advantage and prospectus of poly-P for the MDF cements. Compactness of Al(Fe)-O-P( C) cross-links increases the intrinsic density and impregnates the system against the uptake of moisture.
The results show step-wise environmental deterioration in moist atmosphere: (a) the effect of 52% RH and (b) the effect of 100% RH, the latter being subdivided into irreversible change (the residual mass at ambient condition) and reversible change (difference of the mass at 100% RH and the residual mass). The results show nearly negligible mass change (environmental deterioration) of studied MDF cement samples at 52% RH. An equilibrium mass increase after the treatment at 100% RH strongly depends on the nature of polymer, Δm(HPMC) > Δm(poly-P) and on the drying, Δm(di) > Δm(dd). Dissolved Poly-P is the better polymer for the processing of MDF cements and the result, which has been received, is very important for the perspective utilization of MDF cements. The lowest values exhibit the delayed dried samples containing soluble poly-P. Total mass increase at 100% RH ranges from 1% (probes with dissolved poly-P, 3 MPa pressure for 3h and delayed dried) through 14% (probes with dry premixed poly-P, dried immediately) to 20 % (probes with HPMC, dried immediately). The lower mass change being the evidence of higher moisture
resistance and generalising formerly postulated15,16,21 barrier / impregnation effect of cross-links comprising Al, Fe, O, C and P atoms in unique local structures. The influence of moisture was also investigated on powdered MDF cements samples and described in22. Both, destruction of cross-links in powdered samples and partial conversion of clinkers during the MDF cements syntheses are responsible for several times higher mass increase of powdered samples than the tablated samples.
Thermoanalytical identification of MDF cements
Data relating to the whole range of studied compositions during thermal treatment are presented in Table I. The effects of polymer used in the original synthesis upon the TG curves of moist attacked probes remain the same as we discussed earlier19-21. Individual sequences, as well as total mass losses (15 - 17.5 % if poly-P is present vs. 23 - 26 % if HPMC is present) for immediately dried MDF cements attacked by extreme moisture do support the hypothesis about the impregnation/barrier effect of poly-P. Thus, presence of poly-P and delayed drying minimise the scope of mass (reversible and irreversible) as well as phase changes due to the moisture uptake of MDF cements from SAFB clinkers, OPC and HPMC or poly-P at 100 % RH.
Thermoanalytical treatment supports the differences between attacked and non-attacked MDF cements, cf. Table I. The temperature intervals of thermal events (TG and DTA curves) are similar to that reported for MDF cement systems from SAFB clinkers and HPMC or poly-P19-21. Totally, three distinct temperature regions on the thermoanalytical traces of both series of MDF cements (before and after moisture attack) are seen:
i) Upto 250oC - temperature region of classical cements hydrates (C-S-H, ettringite, gypsum and AFm phases) decomposition23,24, where TG curves exert in moisture attacked probes by 1.5 - 7 % higher mass loss (depending on the polymer and delayed dried condition). It clearly displays an increase of the content of “classical” cement hydrates. These arise due to the moisture attack of clinker grains only partly converted in original MDF cements15,20. The interpretation of the
thermogravimetric curves in this region is very difficult because the decomposition temperatures of C-S-H, ettringite, gypsum and AFm phases lie close together
ii) 250 - 550oC - temperature region of cross-links and Ca(OH)2 decomposition15,20,21. Closely identical TG and DTA characteristics in both series confirm that the clusters of Al(Fe) - O - C(P) cross-links appear unaffected by moisture attack under the test conditions. Thus, if OPC is properly mixed with SAFB clinkers, does not affect the moisture resistance of AFm-like cross-linked section of MDF cements and the impregnation effect of Al(Fe) -O- C(P) cross-links remains conserved18-20.
iii) Above 550oC - temperature region of CaCO3 decomposition23–26, while the higher content of CaCO3 was observed in the moisture attacked probes as the additional mass loss, 0.5 - 4%, with maximum of typical DTA effect at 660 - 690oC. TG and DTA characteristics in this temperature region provide evidences that the other crucial phase change of MDF cements in the moist environment is carbonation. Generally, cement-based materials with inter-phase region containing portlandite, free lime and/or partly converted clinker grains suffer frequently for this type of phase change23-26. The moisture attack also causes the formation of CaCO3.
Minimisation of these changes together with minimal direct mass changes in moist environment occurring when MDF cements are delayed dried. This is the further signal of a possibility to lower the environmental deterioration of MDF cements.
Applications of MDF Cements
There have been examined a few potential applications of MDF cements, which are designed to meet market needs. Thermal insulator for specific applications, reinforcement for ordinary cement paste or mortars, and shells for specific applications are promising. The technology utilized in making a cement shell of a solar powered car can be easily applied to form armors also. Loudspeaker cabinets
were also introduced by Alford and Birchall. Generally a material higher in damping (tan δ), Young smodulus and specific gravity has good acoustic properties. More comprehensive overview of potential applications has been given in Table II as described by Maeta Techno-Research Inc. in its concise market survey of Japanese and European manufacturing industries27,28.
Conclusion
1. The scope of moisture attack on MDF cements, synthesised from the blends of SAFB clinkers, OPC and HPMC or poly-P has been quantified using the values of mass changes as the measure of the moisture resistance. The method was proved as a powerful tool for an effective check of moisture attack on various MDF cements.
2. The effect of individual humidity upon the evolution of mass is more intensive than the effects of composition of MDF cements or duration of the original MDF cements synthesis. However, detailed values of mass change at 100 % RH are strongly affected by the nature of polymer, where the mass increase ranges from 1 to 20 %. The lowest values (lowest environmental deterioration) correspond to the delayed dried MDF cements with dissolved poly-P and 5MPa pressure for 3h. 3. The irreversible mass gain is tightly connected as determined by methods of thermal analysis with
the carbonation and secondary hydration of cement grains both in the inter-phase region of the structure of MDF cements. Minimisation of the above phase changes together with minimal direct mass changes in moist environment of delayed dried MDF cements indicates a possibility to improve the processability (environmental deterioration) of MDF cements.
4. The thermoanalytical data showed that Al(Fe)-O-C(P) cross-links in AFm-like region remain intact in the moist environment of either ambient or extreme levels of humidity.
5. Study of mass equilibration and thermal analysis give an effective knowledge and control of the moisture sensitivity phenomenon of MDF cements. The results on MDF cements system in SAFB,
OPC and HPMC or poly-P favour our previous hypothesis on the impregnation / barrier effect of poly-P incorporated in the structure of MDF cements.
6. The applications reviewed in this paper are by no means comprehensive but illustrate the range of potential uses that exist for MDF cements or, at least, provide guidelines for applications oriented experiments.
References
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1. Lewis J.A. and Desai P.G., Microstructure-Property Relations in Organocement composites derived from CaAl2O4-Coated Al2O3 Powders, MAETA Workshop on High Flexural
Polymer-Cement Composite, Proc. Int. Conf., Sakata 1996 (Ed. N. Maeda), Japan, 1, 49-58 (1996)
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3. B. Chowdhury, Thermal and Polarization Studies of Carbonaceous Cement, Solid State Phenomena, 90-91, 25-32 (2003)
4. Odler I., Cementitious Systems Modified with Organic Polymers, E and FN Spon, London, p-226 (2000)
5. Gopinathan K. and Ramano Rao D.V., Influence of Some Water Soluble Polymers on the Mechanical Properties of Cement-Polymer Composites, Proc. 9th Int. Congr. Chem. Cem., New Delhi, 1, 125-152 (1992)
6. Drabik M., Zimermann P. and Slade R.C.T., Chemistry of MDF materials based on Sulfoaluminateferritebelitic Clinkers: Syntheses and Test of Moisture Resistance, Adv. Cem. Res., 10, 129-133 (1998)
7. Birchal J.D., Howard A.J. and Kendal K., Flexural Strength and Porosity of Cement, Nature, 289(29), 388-390 (1981).
8. Harsh S., Naidu Y.C. and Ghosh S.N., Chemical Interaction between PVA and Hydrating HAC: Infrared Spectroscopic and Thermoanalytical Investigation, Proc. 9th Int. Congr. Chem. Cem., New Delhi, 3, 406-412 (1992)
9. Fu X., Lu W. and Chung D.D.L., Improving the Bond Strength between Carbon Fiber and Cement by Fiber Surface Treatment and Polymer Addition to Cement Mix, 26, 1007-1012 (1996) 10. Chowdhury B., Investigations into the Role of Activated Carbon in a Moisture-Blocking Cement
Formulation, J. Therm. Anal. Cal., 78, 215-226 (2004).
11. Lewis J.A. and Kriven W.M., Microstructure-Property Relationships in Macro-Defect-Free Cement, MRS Bulletin, 18, 72-77 (1993)
12. Poon C.S. and Groves G.W., The Microstructure of Macrodefect-Free Cement, J. Mater. Sci., 23, 657-660 (1988)
13. Janotka I. and Krajči L., An Experimental Study on the Upgrade of Sulfoaluminate-belite Cement Systems by Blending with Portland Cement, Adv. Cem. Res., 11(1), 35-41(1999)
14. Mojumdar S.C., Processing-moisture resistance and thermal analysis of MDF materials, J. Therm. Anal. Cal., 64, 1133-1139 (2001).
15. Mojumdar S.C., Macro-defect-free cements with improved moisture resistance after delayed drying, Challenges for Coordination chemistry in the new century 5, 453-458 (2001)
16. J. Strigáč, M.T. Palou, J. Krištin, J. Majling, Morphology and chemical composition on minerals inside the phase assemblage C-C2S-C4A3S -C4AF-CS relevant to sulphoaluminate belite cements, CERAMICS - Silikaty, 44(1), 26-34 (2000)
17. E. Dan, D. Popescu: Novel Low-Energy Cements Based on Belite, in Final report of the R&D EC Project (CIPA CT 94-0105), Sheffield 1998 (Ed.: J.H.Sharp). U.K. 1998
18. Drabik M., Mojumdar S.C., Galikova L., Changes of thermal events of macro-defect-free (MDF) cements due to the environmental deterioration, Cem. Concr. Res., 31(5), 743-747 (2001)
19. Mojumdar S.C., Macro-defect-free materials: Syntheses, Properties and Applications, Proc. Int. Conf., 21st Cement and Concrete Science, Aberdeen, U.K. p. 13 (2001)
20. Drabik M., Galikova L., Hanic F. and Sharp J.H., MDF-related compositions based on novel low-energy clinker, Chem. Papers, 51, 363-366 (1997)
21. Drabik M., Galikova L. and Mojumdar S.C., Macrodefect-Free Cements: Chemistry and Impact of the Environment, Key Eng. Mater. 206-213, 1867 (2002)
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Table I
TG intervals (°C) and DTA peak temperatures (°C) of MDF cements MDF cements
polymer additives as synthesised after irreversible attack of 100 % RH
TG DTA TG DTA 50-250 50-230 50-250 60-250 HPMC 250-550 *(CH) 290-310, 400-430 250-550 310-340, 380-430 550-800(CC) 600-620 550-700 (CC) 670-690 --- 50-250 40-220 50-250 70-200 poly-P 250-550 *(CH) 300-320, 400-440 250-550 310-330, 390-450 550-800 (CC) 590-610 550-800 (CC) 660-690 (CC) Indicative thermal events : * - decomposition of cross-linked section of MDF cements, CH - decomposition of Ca(OH)2, CC - decomposition of CaCO3.
Table 2
Information about the potential applications of MDF cements Field Intended applications Required performance Construction Roofing (tiles), Permanent Lightweight, Durability, Fire-
form-work, Fire resistant doors proofing, Impact resistance, Cover for cable pits under the Smaller in deflection,
floor, OA floor, Sewage pipe, Productivity, Possible biggest size, Airport bridge, Monument, Cost, Workability, Maximum Electric poles in coastal area, angle sheet can be folded without Partition panel, Door or damage, Nailing
window shutters
Steel , Machinery Replacement for angle steel, Thermal resistance, Acoustic Replacement for steel towers, damping, In-combustibility, Molds for plastics or leather Insulating properties, High industry, Printing rollers for strength, Hardness, Cost, newspapers, Repairing material Machine-ability, Ability to for molds, Thermal insulators apply colors, Dimensional for injection molds, Tube, accuracy, Ability to process by Exhaust, Hand-grip of iron pot injection molding Chemical Corrosion - resistant tank, Corrosion resistance, Setting Engineering Oil tank shrinkage, Cost
Electrical Cover for cable ducts, Globe Lightweight, Thermal
Engineering insulators, Propellers in resistance, Dimensional stability, electrical generators, Pipe, Shaping, Machineability,
Housing for rotator, Ability to apply colors, Surface
Electrical parts roughness, Adhesion
Transportation Tire wheel, Yacht, Airplane, Thermal and chemical Frame for motorcycle, Boat deck, resistance, Outdoor stability, Interior panel for train, Thermal Acoustic damping, Stiffness, insulation, Stiffening plate for Dimensional accuracy,
outer shell of cars, Brake Shaping, Mixing with powders lining, Pallets from waste FRP products Miscellaneous Toy, swing, Playground slide, Low thermal conductivity,
Model plane, Model house, Outdoor stability, Non-toxicity, Signboard, Pipe, Fireproof safety Cost, Smaller in deflection, box, Cooler box, Artificial tooth, Productivity, Strength equal Handicraft material for children to steel
0
5
10
15
20
25
30
0
1
2
3
4
5
a
b
c
d
Δ
m
/ %
Time / days
Fig. 1. Mass change Δm as a function of time for delayed dried MDF cements fabricated from blend of SAFB clinkers and OPC with dissolved poly-P - (NaPO3)n and 5MPa pressure for (a) 0.5h, (b) 1h, (c) 3h and (d) 5h, and treated at 52% RH (until the 7 day), 100% RH (from the 8 to 24 day) and under the ambient conditions (from the 25 to the 30 day).
