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Novel material i.e. magnesium phosphate cement (MPC) as repairing material in roads and buildings
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 17 (2019) 70–76
www.materialstoday.com/proceedings
ICAMEES2018
Novel material i.e. magnesium phosphate cement (MPC) as repairing material in roads and buildings Amit Aroraa, Birpal Singhb, Parampreet Kaurc a
Department of Chemical Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur,152004, Punjab, India
b
Department of Civil Engineering, Ferozepur College of Engineering and Technology, Ferozshah,142052, Punjab, India c
Department of Civil Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur,152002, Punjab, India
Abstract Repairing materials for the construction has become the frequent topic of discussion now-a-days. The abundant number of concrete structures and hot-mix asphalt roads requires a massive demand of repairing materials. Instead of replacing the whole damaged structure, the feasible thing to do is by using the good repairing material considering the economic benefits. As, these days the most commonly used material for repair is polymer mortars and ordinary Portland cement (OPC) as these materials are temperature sensitive and hence, they degrade so there is demand in industry to replace these materials by some novel materials which can sustain harsh weather conditions and one such material in the current context is found to be Magnesium Phosphate cement (MPC) which can replace the ordinary Portland cement (OPC). Magnesium phosphate cement (MPC) is chemically bonded phosphate ceramic which is made by an acid-base reaction and generally the basic material is cationic metal and acidic one is phosphate and generally this process is expensive but there is a possibility of obtaining a MPC made by the low- grade magnesium oxide which can be acquired by calcination of natural magnesite. In this way, we can improve the structures by using new improved materials which in turn will reduce the costs of repairs in the long term in the building and transportation sector. In the present study, a systematic review for replacing ordinary Portland cement (OPC) by magnesium phosphate cement (MPC) is presented with detailed investigation. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials, Energy & Environmental Sustainability, ICAMEES2018 Keywords: Magnesium Phosphate; Compressive strength; Flexural Strength; Repairing Material; Sustainable Construction.
1. INTRODUCTION Repair programs are dependent on the proper selection of the materials and generally it is considered more important than new construction projects [1]. The repair materials which we are using in repair program should also go well together with concrete. The large number of concrete structures requires a good repairing material as 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials, Energy & Environmental Sustainability, ICAMEES2018
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concrete structures deteriorate unexpectedly which ultimately leads to the failure of structure [2,3] so regular repairing is required for safety purposes. There are many rapid hardening cements available for the repair of concrete, but recently magnesium phosphate cement has received more attention as it gains the strength rapidly in the short duration as compared to that of strength gained in several hours by Ordinary Portland cement [4,5,6]. Phosphate cements are inorganic material which is made by reaction between the phosphate and metal oxide [7]. MPC is divided into six types based on the phosphates used all along with the magnesia: (1) Diammonium hydrogen phosphate; (2) Monoammonium hydrogen phosphate; (3) Orthosphoric acid solution; (4) Aluminum acid phosphate; (5) Ammonium polyphosphate; (6) Potassium phosphate [8]. MPC also possesses some advantages over the ordinary Portland cement like (1) quick setting (2) Attaining high early compressive strength (3) Good adhesive bonding with old concrete [4,5,9]. This paper reviews the research advancement happened in MPC in terms of its strength and durability. In conclusion, the need for future aspects are also suggested. 2. LITERATURE REVIEW MPC is made by mixing the MgO and phosphate with some inert fillers in certain proportions and MgO which is used has to be calcinated at a temperature above 1400¬0 C and it generally have specific surface area ranges from 230 to 320 m2/kg [10]. For the production of MPC most widely used phosphate is NH¬4H2PO4 or KH2PO4 [11,12]. Magnesium oxide and phosphate reacts very quickly and generally large amount of heat is released so, to control the reaction retarders are added and Inert fillers are incorporated in the MPC cement so that temperature rise can be minimized. Most widely used retarder is Borax (Na2B4O7⋅10H2O). (Na2HPO4⋅12H2O) is also used as retarder as stated by [13] because it leads to the endothermic reaction due to increase in pH level and ultimately cooling the MPC paste. Generally, the traditional MPC consist of magnesia and ammonium dihydrogen phosphate (ADP) gives us major reaction product of phosphate cement namely magnesium ammonium phosphate hexahydrate (NH4MgPO4.6H2O) or also called as mineral struvite showed in reaction (1) and (2) [14]. MgO + 2NH4H2PO4 + 3H2O → (NH4)2Mg (HPO4)2·4H2O (1) MgO + 7H2O + (NH4)2 Mg (HPO4)2·4H2O → 2NH4MgPO4·6H2O (2) This reaction leads to emission of ammonia during mixing which has very foul odour so, in recent years a new type of MPC has developed in which no ammonia is liberated during the reaction because instead of ADP, potassium dihydrogen phosphate (KDP) is used. In the new reaction when potassium dihydrogen phosphate is used in reaction then a new crystal of MgKPO4.6H2O are formed which is considered as adequate replacement of MgNH4PO4.6H2O as ammonium ions are well replaced by potassium ion. [15,16] stated that when cement paste is prepared with KDP then properties of MPC depends upon reactivity of the magnesia and molar ratio of magnesium and phosphate and the MPC prepared with KDP generally gives better strength and quick setting time. In Table 1 various hydration products are shown when water is added in different types of magnesium phosphate cement. Table 1. Hydration products of different MPCs when water is added Raw materials
Hydration products
References
H3PO4.MgO
Mg(H2PO4)2·2H2O (more) and Mg(H2PO4)2·4H2O (less)
[17]
NH4H2PO4.MgO
NH4MgPO4·6H2O and (NH4)2Mg (HPO4)2·4H2O
[4,5]
KH2PO4.MgO
MgKPO4·6H2O
[18,19]
3. IMPACT ON DIFFERENT PROPERTIES WHEN MPC IS USED: In the field of construction, cement is the most widely used material in the production of concrete and concrete structures generally suffer from unpredicted deterioration in the form of cracking which in the long term leads to the
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structural failure [3]. So, in order to avoid this problem regular repairing is must require to keep the structure safety and serviceability. Repairing of concrete building is comparatively easy as compared to the repairing of pavement structure as in the pavement repairing expenses are more and we only get couple of hours for repair treatment so we need a material which has tendency to gain strength rapidly and has fast setting time. 3.1 Mechanical strength The application of magnesium phosphate cement as patching material has the tendency to increase the compressive strength over the short span of time as MPC paste consist of magnesium oxide and phosphate hydrates in which the strength of MgO is considerable higher than that of phosphate hydrates so, phosphate hydrates are used to fill the pores of MgO grains, which in turn increase the strength of paste. Various researchers [10,18,20] reported that Magnesium phosphate cement attained high compressive strength value in shorter span of time. It was explained that compressive strength increased by 75.21% from 1hr curing period to 1-day curing period when P/M (phosphate/magnesium) ratio was 1:2 and after 28 days of curing period compressive strength was increased by 85.33%. Maximum compressive strength was attained by MPC having P/M ratio of 1:5 and after 28 days curing period compressive strength was increased about 84.8% as compared to specimen after 1hr curing period [1]. [21] stated that as the water binder ratio changes from 0.16 to 0.21 the early development of strength showed a decrease in compressive strength at 1h, 3h, 7h and 24h of curing age, although the strength of M7(MgO content 71.50%) was slightly higher than M9(MgO content 89.51%). It was also stated that when absolute compressive strength was seen the M9 sample showed higher strength than M7 sample as at 28 days of curing the M9 sample showed 20 MPa more strength at 0.16 water binder ratio. [18] stated that compressive strength of MPC mortar increased by 18%, 21.1%, 15.7% and 15.62% from time span of 7 days to 28 days curing period for M/P ratio of 06, 08, 10 and 12 respectively. [20] stated that when NH¬¬4-MPC mortar was used it increases compressive strength by 38.77% from 1hr to 2hr curing span but after that compressive strength tends to decrease continuously up to 7 days of curing period, but when NH4¬+Na MPC mortar was used compressive strength increased by 37.5% from 1hr to 1-day curing period but after that up to 7 days compressive strength decreased by 62.5%. [22] stated that when W/B ratio was kept 0.22 and concentration of fly ash was increased from 0.6 to 1.0 then decreasing pattern of compressive strength was seen as when fly ash concentration was 0.6 the maximum compressive strength of 49MPa was seen at 28 days of curing period and it was 93.1% more than MPC mortar at 1-day of curing period. Similarly, when fly ash ratio was increased to 1.0 then maximum compressive strength of 33MPa was seen at 28 days of curing period which was 69.7% higher than that of MPC mortar at 1-day of curing period. Zheng et al. [23] stated the effect of concentration of silica fume on compressive strength of MPC when fly ash content of 5%, 10%, 15% and 20% was used under air and water curing. It was stated that when fly ash content of 5% was used then compressive strength of MPC incorporated with 10% silica fume in air curing condition showed increase of 13.09% compressive strength as compared to control specimen at 56 days of curing age and when water curing condition was present maximum compressive strength at 56 days of curing was 78.94 MPa which was 32.17% higher than control specimen. When 10% fly ash was used with silica fume in air curing condition and water curing condition the compressive strength at 56 days of curing was 8.8% and 28.11% higher than control specimen respectively. Similar pattern was seen when 15% and 20% fly ash was used. Yang et al. [8] stated that flexural strength of MPC paste was comparatively more than that of ordinary Portland cement at 28 days of curing age but as the curing period reached to 90 days the flexural strength of MPC paste was lesser than that of ordinary Portland cement. [22,24,25] stated that flexural strength was increased up to certain curing age but as the curing period was increased the flexural strength started decreasing.
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Table 2. Mechanical Characteristics of Magnesium Phosphate Cement Constituents of MPC used
W/B ratio
Compressive strength
Magnesium Oxide, Ammonium dihydrogen phosphate, sodium dihydrogen phosphate, Borax
0.13
It was noted that when MPC was made with ammonium dihydrogen phosphate and sodium dihydrogen phosphate and both combined then in all these cases compressive strength increased up to 1 day of curing and after that up to 7 day of curing compressive strength decreased. One thing was common in all these was at 1 Day of curing compressive strength was approximately 50 MPa.
Magnesium oxide, sodium hexa phosphate, Silica Fume
0.275
It was stated that compressive strength of MPC incorporated with silica fume leads to increasing pattern from 7 days to 90 days of curing age and it was also seen that MPC showed approximately 17.07% higher compressive strength than Portland cement
Dead burnt magnesia, Mono-potassium phosphate, class F fly ash, Boric acid and water
0.22
It leads the MPC paste to achieve 20MPa strength in 1-day curing and after 28 days of curing strength was 45MPa which was 55% more.
0.26
0.30
Low grade magnesium oxide (63.66%MgO), Monopotassium phosphate, Boric Acid and water
0.24
The strength of MPC paste after 28 days of curing was 43MPa and it was 58.31% more than that of paste after 1-day of curing. The strength of MPC paste after 28 days of curing was 38MPa and it was 57.89% more than that of paste after 1-day of curing. It was stated that when ratio of Boric acid and Solid (magnesium oxide and mono potassium phosphate) was kept 0.25 then compressive strength showed increasing pattern and at 28 days of curing period maximum compressive strength (42.19±4.65) MPa was seen when ratio of 0.50 was used.
Flexural strength
Findings
References
It was found out that just after 1 hr of curing compressive strength was very high which was considered superior than calcium phosphates
[20]
It was stated that flexural strength of MPC was 2.94% higher than that of Portland cement at 28 days of curing whereas up to 90 days of curing the flexural strength of MPC was 2.98% less than Portland cement.
It was found that MPC attained higher strength in shorter span of time therefore, making it more durable than ordinary Portland cement.
[9]
Flexural strength showed increasing pattern in MPC mortar for 7 days of curing period when fly ash increased from 0.4 to 1.0 whereas, when fly ash content increased from 0.8 to 1.0 then flexural strength of MPC paste decreased drastically.
It was found that with the increase of W/B ratio compressive strength was decreased.
[22]
-----------------
-----------------
It was found that MPC mortar show more flexural strength than MPC paste.
-----------------
When ratio of 0.25 and 1.00 was used then flexural strength first increased up to 7days of curing age and then showed decreasing pattern up to 28 days of curing age whereas, when ratio of 0.50 and 2.00 was used then flexural strength showed increasing pattern up to 28 days and maximum value of flexural strength (6.06±0.09) MPa at 28
It was found that as the content of boric acid was increased the compressive strength was decreased whereas flexural strength was increased at 28 days of curing.
[24]
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A. Arora et al./ Materials Today: Proceedings 17 (2019) 70–76 days of curing age was when ratio of 2.00 was used
Magnesia (MgO) powder, Fly ash, Silica Fume, Potassium dihydrogen Phosphate, Borax
Low grade magnesium oxide (MgO), Monopotassium Phosphate, Microencapsulated phase change material (MPCM) and air-entraining additive (AEA)
0.16
0.34
The compressive strength of MPC cement showed first increase in compressive strength and then decrease in strength when content of silica fume was 5% to 15%.
It was stated that with the increase in concentration of AEA from 0% to 5% as well as MPCM from 0% to 15% there was decreasing trend seen in compressive strength at 28 days of curing age.
-----------------
Similar trend of decrease of flexural strength was seen which was present in case of compressive strength but a slight change was seen as value of flexural strength increased when 10% MPCM was used but when MPCM increased further flexural strength decreased.
It was found that fly ash and silica fume combined in MPC fill the pores and cracks which ultimately improve the mechanical properties. It was found that addition of admixtures in the MPC leads to decrease in the mechanical as well as durability properties.
[23]
[25]
Researchers stated that the change in water-binder ratio effects the compressive strength of MPC paste as [21] stated that with the increase of w/b ratio the compressive strength decreased suddenly and at 3, 7 and 28 days of curing the strength loss was 39.7%, 39.4% and 40% respectively. [22] stated that when w/b ratio was increased from 0.22 to 0.30, compressive strength was decreased from 45 MPa to 38 MPa after 1 day of curing age because of extra water present in matrix the structure became permeable and resulting in decrease in strength. It was revealed in Table 2 that when MPC is made with different W/B ratio the mechanical properties showed dissimilar trends. 4. CHALLENGES FACED WHEN USING MPC: When MPC is used, its hydration reaction is highly exothermic and it has very less setting time and early development of compressive strength is high as compared to ordinary Portland cement so supervision is required in handling this cement. The water resistivity of MPC paste is not great, as strength of MPC paste decrease when it is engrossed in the water. It was stated that strength of MPC was decreased by 42.34% after curing age of 28 days [26]. The phosphate present in MPC affect the different properties and water resistivity is one of them as remaining unreacted phosphate get dissolved in water and reduce the pH of solution in which hydration product of MgKPO4·6H2O [27] get dissolved in solution which increase the porosity and ultimately reduce the strength of MPC. 5. FUTURE PROSPECTS: MPC formation has very violent exothermic reaction and setting time is very quick so suitable retarder like borax etc. are required to make it suitable for using in different fields. MPC can be further used on many places when water resistivity can be improved as when water is bringing in contact with MPC strength decreases substantially. So, the improvement of water resistance can further open some new pathways to utilize on different places.
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6. CONCLUSION MPC formation is an Environmentally friendly method, as ordinary Portland cement manufacturing releases huge amount of carbon dioxide so proper alternate is required to replace the OPC for repairing works. MPC has very high early development of strength as compared to ordinary Portland cement because of highly exothermic reaction which reduce the setting time. MPC showed high compressive strength but it is badly influenced by the water reactivity as the water is bring in contact with the MPC the compressive strength decreased substantially, that is why water-binder ratio is important aspect in using the MPC as replacement of OPC. References [1]. Q. Yang, X. Wu, “Factors influencing properties of phosphate cement-based binder for rapid repair of concrete.” Cement Concr. Res., 29(3) (1999) 389–396. [2]. M. A. Frabizzio and N. J. Buch, “Performance of transverse cracking in jointed concrete pavements,” Journal of Performance of Constructed Facilities, 13(4) (1999) 172–180. [3]. K. Y. Ann, J. H. Ahn, and J. S. Ryou, “Te importance of chloride content at the concrete surface in assessing the time to corrosion of steel in concrete structures,” Construction and Building Materials, 23(1) (2009) 239–245, 2009. [4]. T. Sugama, L. Kukacka, “Characteristics of magnesium polyphosphate cements derived from ammonium polyphosphate solutions.” Cement Concr. Res., 13(4) (1983a) 499–506. [5]. T. Sugama, L. Kukacka, “Magnesium monophosphate cements derived from diammonium phosphate solutions.” Cement Concr. Res., 13(3) (1983b) 407–416. [6]. S. S. Seehra, S. Gupta, and S. Kumar, “Rapid setting magnesium phosphate cement for quick repair of concrete pavements— characterisation and durability aspects,” Cement and Concrete Research, 23(2) (1993) 254–266. [7]. D. Roy “Recent advances in phosphate chemically bonded ceramics.” MRS Intl. Mtg. Adv. Mater., 13(2) (1989) 213–227 [8]. N. Yang, C. Shi, J.Y.Y. Chang “Research Progresses in Magnesium Phosphate Cement–Based Materials” J. Mater. Civ. Eng. 26 (2014). (DOI: 10.1061/(ASCE)MT.1943-5533.0000971) [9]. T. Zhang, L. J. Vandeperre, C. R..Cheeseman “Magnesium-silicate-hydrate cements for encapsulating problematic aluminium containing wastes” Journal of Sustainable Cement-Based Materials, (2012) (http://dx.doi.org/10.1080/21650373.2012.727322). [10]. Y. Chang, C. Shi, N. Yang, J. Yang, “Effect of fineness of magnesium oxide on properties of magnesium potassium phosphate cement.” J. Chinese Ceram. Soc., 41(4) (2013) 492–499. [11]. J. W. Park, K. H. Kim, and K. Y. Ann, “Fundamental Properties of Magnesium Phosphate Cement Mortar for Rapid Repair of Concrete”, Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2016, Article ID 7179403. [12]. W. A. Wilson, and J.W. Nicholson, “Acid-base cement (their biomedical and industrial applications)”, Cambridge University Press, Cambridge, (1993) U.K [13]. C. Qian, and J. M. Yang, “Effect of disodium hydrogen phosphate on hydration and hardening of magnesium potassium phosphate cement.” J. Mater. Civ. Eng., (2011) 1405–1411 10.1061/(ASCE)MT.1943-5533.0000305, [14]. B. Abdelrazig, J. Sharp, and B. El-Jazairi, “The chemical composition of mortars made from magnesiaphosphate cement.” Cement Concr. Res., 18(3) (1988) 415–425.
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[15]. F. Qiao, W. Lin, CK Chau, Z. Li, “Property assessment of magnesium phosphate cement”. Key Eng Mater (2009) 115–20. [16]. F. Qiao, W. Lin, CK Chau, Z. Li., “Setting and compressive strength characteristics of magnesium phosphate cement paste”. Adv. Cem. Res. 2009. [17]. T. Finch and J. Sharp, “Chemical reactions between magnesia and aluminium orthophosphate to form magnesia-phosphate cements.” J. Mater. Sci., 24(12) (1989) 4379–4386. [18]. F. Qiao, W. Lin, CK Chau, Z. Li, “Property evaluation of magnesium phosphate cement mortar as patch repair material.” Constr. Build. Mater., 24(5) (2010) 695–700. [19]. X. Li, L. Du, and D. Li “The preparation and study on the new high early strength magnesium phosphate cement.” Bull. Chinese Ceram. Soc., 27(1) (2008) 20–25 [20]. G. Mestres, M.P. Ginebra, “Novel magnesium phosphate cements with high early strength and antibacterial properties”, Acta Biomaterialia 7 (2011) 1853–1861. [21]. Z. Ding, Z. Li. “High-early-strength magnesium phosphate cement with fly ash” ACI Mater J 102(6) (2005) 375–81. [22]. Z. Ding, J.G. Dai and S. Muner, “Study on an Improved Phosphate Cement Binder for the Development of Fiber-Reinforced Inorganic Polymer Composites”, Polymers 6 (2014) 2819-2831; doi:10.3390/polym6112819. [23]. D.D Zheng, T. Ji, C. Q. Wang, C.J. Sun, X.J. Lin, K. M. A. Hossain, “Effect of the combination of fly ash and silica fume on water resistance of Magnesium–Potassium Phosphate Cement”, Construction and Building Materials 106 (2016) 415–421. [24]. J. Formosa, A.M. Lacasta, A. Navarro, R. del Valle-Zermeño, M. Niubó, J.R. Rosell, J.M. Chimenos, “Magnesium Phosphate Cements formulated with a low-grade MgO by-product: Physico-mechanical and durability aspects” (2015). [25]. A. Maldonado-Alameda, A.M. Lacasta, J. Giro-Paloma, J.M. Chimenos, L. Haurie, J. Formosa, “Magnesium phosphate cements formulated with low grade magnesium oxide incorporating phase change materials for thermal energy storage”, Construction and Building Materials 155 (2017) 209–216. [26]. Li, X., Du, L., and Li, D. “The preparation and study on the new high early strength magnesium phosphate cement.” Bull. Chinese Ceram. Soc., 27(1) (2008) 20–25. [27]. Li, D., Li, P., and Feng, C. “Research on water resistance of magnesium phosphate cement (in Chinese).” J. Build. Mater., 12(5) (2009) 505–510.
ScienceDirect Materials Today: Proceedings 17 (2019) 70–76
www.materialstoday.com/proceedings
ICAMEES2018
Novel material i.e. magnesium phosphate cement (MPC) as repairing material in roads and buildings Amit Aroraa, Birpal Singhb, Parampreet Kaurc a
Department of Chemical Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur,152004, Punjab, India
b
Department of Civil Engineering, Ferozepur College of Engineering and Technology, Ferozshah,142052, Punjab, India c
Department of Civil Engineering, Shaheed Bhagat Singh State Technical Campus, Ferozepur,152002, Punjab, India
Abstract Repairing materials for the construction has become the frequent topic of discussion now-a-days. The abundant number of concrete structures and hot-mix asphalt roads requires a massive demand of repairing materials. Instead of replacing the whole damaged structure, the feasible thing to do is by using the good repairing material considering the economic benefits. As, these days the most commonly used material for repair is polymer mortars and ordinary Portland cement (OPC) as these materials are temperature sensitive and hence, they degrade so there is demand in industry to replace these materials by some novel materials which can sustain harsh weather conditions and one such material in the current context is found to be Magnesium Phosphate cement (MPC) which can replace the ordinary Portland cement (OPC). Magnesium phosphate cement (MPC) is chemically bonded phosphate ceramic which is made by an acid-base reaction and generally the basic material is cationic metal and acidic one is phosphate and generally this process is expensive but there is a possibility of obtaining a MPC made by the low- grade magnesium oxide which can be acquired by calcination of natural magnesite. In this way, we can improve the structures by using new improved materials which in turn will reduce the costs of repairs in the long term in the building and transportation sector. In the present study, a systematic review for replacing ordinary Portland cement (OPC) by magnesium phosphate cement (MPC) is presented with detailed investigation. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials, Energy & Environmental Sustainability, ICAMEES2018 Keywords: Magnesium Phosphate; Compressive strength; Flexural Strength; Repairing Material; Sustainable Construction.
1. INTRODUCTION Repair programs are dependent on the proper selection of the materials and generally it is considered more important than new construction projects [1]. The repair materials which we are using in repair program should also go well together with concrete. The large number of concrete structures requires a good repairing material as 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Advanced Materials, Energy & Environmental Sustainability, ICAMEES2018
A. Arora et al. / Materials Today: Proceedings 17 (2019) 70–76
71
concrete structures deteriorate unexpectedly which ultimately leads to the failure of structure [2,3] so regular repairing is required for safety purposes. There are many rapid hardening cements available for the repair of concrete, but recently magnesium phosphate cement has received more attention as it gains the strength rapidly in the short duration as compared to that of strength gained in several hours by Ordinary Portland cement [4,5,6]. Phosphate cements are inorganic material which is made by reaction between the phosphate and metal oxide [7]. MPC is divided into six types based on the phosphates used all along with the magnesia: (1) Diammonium hydrogen phosphate; (2) Monoammonium hydrogen phosphate; (3) Orthosphoric acid solution; (4) Aluminum acid phosphate; (5) Ammonium polyphosphate; (6) Potassium phosphate [8]. MPC also possesses some advantages over the ordinary Portland cement like (1) quick setting (2) Attaining high early compressive strength (3) Good adhesive bonding with old concrete [4,5,9]. This paper reviews the research advancement happened in MPC in terms of its strength and durability. In conclusion, the need for future aspects are also suggested. 2. LITERATURE REVIEW MPC is made by mixing the MgO and phosphate with some inert fillers in certain proportions and MgO which is used has to be calcinated at a temperature above 1400¬0 C and it generally have specific surface area ranges from 230 to 320 m2/kg [10]. For the production of MPC most widely used phosphate is NH¬4H2PO4 or KH2PO4 [11,12]. Magnesium oxide and phosphate reacts very quickly and generally large amount of heat is released so, to control the reaction retarders are added and Inert fillers are incorporated in the MPC cement so that temperature rise can be minimized. Most widely used retarder is Borax (Na2B4O7⋅10H2O). (Na2HPO4⋅12H2O) is also used as retarder as stated by [13] because it leads to the endothermic reaction due to increase in pH level and ultimately cooling the MPC paste. Generally, the traditional MPC consist of magnesia and ammonium dihydrogen phosphate (ADP) gives us major reaction product of phosphate cement namely magnesium ammonium phosphate hexahydrate (NH4MgPO4.6H2O) or also called as mineral struvite showed in reaction (1) and (2) [14]. MgO + 2NH4H2PO4 + 3H2O → (NH4)2Mg (HPO4)2·4H2O (1) MgO + 7H2O + (NH4)2 Mg (HPO4)2·4H2O → 2NH4MgPO4·6H2O (2) This reaction leads to emission of ammonia during mixing which has very foul odour so, in recent years a new type of MPC has developed in which no ammonia is liberated during the reaction because instead of ADP, potassium dihydrogen phosphate (KDP) is used. In the new reaction when potassium dihydrogen phosphate is used in reaction then a new crystal of MgKPO4.6H2O are formed which is considered as adequate replacement of MgNH4PO4.6H2O as ammonium ions are well replaced by potassium ion. [15,16] stated that when cement paste is prepared with KDP then properties of MPC depends upon reactivity of the magnesia and molar ratio of magnesium and phosphate and the MPC prepared with KDP generally gives better strength and quick setting time. In Table 1 various hydration products are shown when water is added in different types of magnesium phosphate cement. Table 1. Hydration products of different MPCs when water is added Raw materials
Hydration products
References
H3PO4.MgO
Mg(H2PO4)2·2H2O (more) and Mg(H2PO4)2·4H2O (less)
[17]
NH4H2PO4.MgO
NH4MgPO4·6H2O and (NH4)2Mg (HPO4)2·4H2O
[4,5]
KH2PO4.MgO
MgKPO4·6H2O
[18,19]
3. IMPACT ON DIFFERENT PROPERTIES WHEN MPC IS USED: In the field of construction, cement is the most widely used material in the production of concrete and concrete structures generally suffer from unpredicted deterioration in the form of cracking which in the long term leads to the
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structural failure [3]. So, in order to avoid this problem regular repairing is must require to keep the structure safety and serviceability. Repairing of concrete building is comparatively easy as compared to the repairing of pavement structure as in the pavement repairing expenses are more and we only get couple of hours for repair treatment so we need a material which has tendency to gain strength rapidly and has fast setting time. 3.1 Mechanical strength The application of magnesium phosphate cement as patching material has the tendency to increase the compressive strength over the short span of time as MPC paste consist of magnesium oxide and phosphate hydrates in which the strength of MgO is considerable higher than that of phosphate hydrates so, phosphate hydrates are used to fill the pores of MgO grains, which in turn increase the strength of paste. Various researchers [10,18,20] reported that Magnesium phosphate cement attained high compressive strength value in shorter span of time. It was explained that compressive strength increased by 75.21% from 1hr curing period to 1-day curing period when P/M (phosphate/magnesium) ratio was 1:2 and after 28 days of curing period compressive strength was increased by 85.33%. Maximum compressive strength was attained by MPC having P/M ratio of 1:5 and after 28 days curing period compressive strength was increased about 84.8% as compared to specimen after 1hr curing period [1]. [21] stated that as the water binder ratio changes from 0.16 to 0.21 the early development of strength showed a decrease in compressive strength at 1h, 3h, 7h and 24h of curing age, although the strength of M7(MgO content 71.50%) was slightly higher than M9(MgO content 89.51%). It was also stated that when absolute compressive strength was seen the M9 sample showed higher strength than M7 sample as at 28 days of curing the M9 sample showed 20 MPa more strength at 0.16 water binder ratio. [18] stated that compressive strength of MPC mortar increased by 18%, 21.1%, 15.7% and 15.62% from time span of 7 days to 28 days curing period for M/P ratio of 06, 08, 10 and 12 respectively. [20] stated that when NH¬¬4-MPC mortar was used it increases compressive strength by 38.77% from 1hr to 2hr curing span but after that compressive strength tends to decrease continuously up to 7 days of curing period, but when NH4¬+Na MPC mortar was used compressive strength increased by 37.5% from 1hr to 1-day curing period but after that up to 7 days compressive strength decreased by 62.5%. [22] stated that when W/B ratio was kept 0.22 and concentration of fly ash was increased from 0.6 to 1.0 then decreasing pattern of compressive strength was seen as when fly ash concentration was 0.6 the maximum compressive strength of 49MPa was seen at 28 days of curing period and it was 93.1% more than MPC mortar at 1-day of curing period. Similarly, when fly ash ratio was increased to 1.0 then maximum compressive strength of 33MPa was seen at 28 days of curing period which was 69.7% higher than that of MPC mortar at 1-day of curing period. Zheng et al. [23] stated the effect of concentration of silica fume on compressive strength of MPC when fly ash content of 5%, 10%, 15% and 20% was used under air and water curing. It was stated that when fly ash content of 5% was used then compressive strength of MPC incorporated with 10% silica fume in air curing condition showed increase of 13.09% compressive strength as compared to control specimen at 56 days of curing age and when water curing condition was present maximum compressive strength at 56 days of curing was 78.94 MPa which was 32.17% higher than control specimen. When 10% fly ash was used with silica fume in air curing condition and water curing condition the compressive strength at 56 days of curing was 8.8% and 28.11% higher than control specimen respectively. Similar pattern was seen when 15% and 20% fly ash was used. Yang et al. [8] stated that flexural strength of MPC paste was comparatively more than that of ordinary Portland cement at 28 days of curing age but as the curing period reached to 90 days the flexural strength of MPC paste was lesser than that of ordinary Portland cement. [22,24,25] stated that flexural strength was increased up to certain curing age but as the curing period was increased the flexural strength started decreasing.
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Table 2. Mechanical Characteristics of Magnesium Phosphate Cement Constituents of MPC used
W/B ratio
Compressive strength
Magnesium Oxide, Ammonium dihydrogen phosphate, sodium dihydrogen phosphate, Borax
0.13
It was noted that when MPC was made with ammonium dihydrogen phosphate and sodium dihydrogen phosphate and both combined then in all these cases compressive strength increased up to 1 day of curing and after that up to 7 day of curing compressive strength decreased. One thing was common in all these was at 1 Day of curing compressive strength was approximately 50 MPa.
Magnesium oxide, sodium hexa phosphate, Silica Fume
0.275
It was stated that compressive strength of MPC incorporated with silica fume leads to increasing pattern from 7 days to 90 days of curing age and it was also seen that MPC showed approximately 17.07% higher compressive strength than Portland cement
Dead burnt magnesia, Mono-potassium phosphate, class F fly ash, Boric acid and water
0.22
It leads the MPC paste to achieve 20MPa strength in 1-day curing and after 28 days of curing strength was 45MPa which was 55% more.
0.26
0.30
Low grade magnesium oxide (63.66%MgO), Monopotassium phosphate, Boric Acid and water
0.24
The strength of MPC paste after 28 days of curing was 43MPa and it was 58.31% more than that of paste after 1-day of curing. The strength of MPC paste after 28 days of curing was 38MPa and it was 57.89% more than that of paste after 1-day of curing. It was stated that when ratio of Boric acid and Solid (magnesium oxide and mono potassium phosphate) was kept 0.25 then compressive strength showed increasing pattern and at 28 days of curing period maximum compressive strength (42.19±4.65) MPa was seen when ratio of 0.50 was used.
Flexural strength
Findings
References
It was found out that just after 1 hr of curing compressive strength was very high which was considered superior than calcium phosphates
[20]
It was stated that flexural strength of MPC was 2.94% higher than that of Portland cement at 28 days of curing whereas up to 90 days of curing the flexural strength of MPC was 2.98% less than Portland cement.
It was found that MPC attained higher strength in shorter span of time therefore, making it more durable than ordinary Portland cement.
[9]
Flexural strength showed increasing pattern in MPC mortar for 7 days of curing period when fly ash increased from 0.4 to 1.0 whereas, when fly ash content increased from 0.8 to 1.0 then flexural strength of MPC paste decreased drastically.
It was found that with the increase of W/B ratio compressive strength was decreased.
[22]
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It was found that MPC mortar show more flexural strength than MPC paste.
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When ratio of 0.25 and 1.00 was used then flexural strength first increased up to 7days of curing age and then showed decreasing pattern up to 28 days of curing age whereas, when ratio of 0.50 and 2.00 was used then flexural strength showed increasing pattern up to 28 days and maximum value of flexural strength (6.06±0.09) MPa at 28
It was found that as the content of boric acid was increased the compressive strength was decreased whereas flexural strength was increased at 28 days of curing.
[24]
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Magnesia (MgO) powder, Fly ash, Silica Fume, Potassium dihydrogen Phosphate, Borax
Low grade magnesium oxide (MgO), Monopotassium Phosphate, Microencapsulated phase change material (MPCM) and air-entraining additive (AEA)
0.16
0.34
The compressive strength of MPC cement showed first increase in compressive strength and then decrease in strength when content of silica fume was 5% to 15%.
It was stated that with the increase in concentration of AEA from 0% to 5% as well as MPCM from 0% to 15% there was decreasing trend seen in compressive strength at 28 days of curing age.
-----------------
Similar trend of decrease of flexural strength was seen which was present in case of compressive strength but a slight change was seen as value of flexural strength increased when 10% MPCM was used but when MPCM increased further flexural strength decreased.
It was found that fly ash and silica fume combined in MPC fill the pores and cracks which ultimately improve the mechanical properties. It was found that addition of admixtures in the MPC leads to decrease in the mechanical as well as durability properties.
[23]
[25]
Researchers stated that the change in water-binder ratio effects the compressive strength of MPC paste as [21] stated that with the increase of w/b ratio the compressive strength decreased suddenly and at 3, 7 and 28 days of curing the strength loss was 39.7%, 39.4% and 40% respectively. [22] stated that when w/b ratio was increased from 0.22 to 0.30, compressive strength was decreased from 45 MPa to 38 MPa after 1 day of curing age because of extra water present in matrix the structure became permeable and resulting in decrease in strength. It was revealed in Table 2 that when MPC is made with different W/B ratio the mechanical properties showed dissimilar trends. 4. CHALLENGES FACED WHEN USING MPC: When MPC is used, its hydration reaction is highly exothermic and it has very less setting time and early development of compressive strength is high as compared to ordinary Portland cement so supervision is required in handling this cement. The water resistivity of MPC paste is not great, as strength of MPC paste decrease when it is engrossed in the water. It was stated that strength of MPC was decreased by 42.34% after curing age of 28 days [26]. The phosphate present in MPC affect the different properties and water resistivity is one of them as remaining unreacted phosphate get dissolved in water and reduce the pH of solution in which hydration product of MgKPO4·6H2O [27] get dissolved in solution which increase the porosity and ultimately reduce the strength of MPC. 5. FUTURE PROSPECTS: MPC formation has very violent exothermic reaction and setting time is very quick so suitable retarder like borax etc. are required to make it suitable for using in different fields. MPC can be further used on many places when water resistivity can be improved as when water is bringing in contact with MPC strength decreases substantially. So, the improvement of water resistance can further open some new pathways to utilize on different places.
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6. CONCLUSION MPC formation is an Environmentally friendly method, as ordinary Portland cement manufacturing releases huge amount of carbon dioxide so proper alternate is required to replace the OPC for repairing works. MPC has very high early development of strength as compared to ordinary Portland cement because of highly exothermic reaction which reduce the setting time. MPC showed high compressive strength but it is badly influenced by the water reactivity as the water is bring in contact with the MPC the compressive strength decreased substantially, that is why water-binder ratio is important aspect in using the MPC as replacement of OPC. References [1]. Q. Yang, X. Wu, “Factors influencing properties of phosphate cement-based binder for rapid repair of concrete.” Cement Concr. Res., 29(3) (1999) 389–396. [2]. M. A. Frabizzio and N. J. Buch, “Performance of transverse cracking in jointed concrete pavements,” Journal of Performance of Constructed Facilities, 13(4) (1999) 172–180. [3]. K. Y. Ann, J. H. Ahn, and J. S. Ryou, “Te importance of chloride content at the concrete surface in assessing the time to corrosion of steel in concrete structures,” Construction and Building Materials, 23(1) (2009) 239–245, 2009. [4]. T. Sugama, L. Kukacka, “Characteristics of magnesium polyphosphate cements derived from ammonium polyphosphate solutions.” Cement Concr. Res., 13(4) (1983a) 499–506. [5]. T. Sugama, L. Kukacka, “Magnesium monophosphate cements derived from diammonium phosphate solutions.” Cement Concr. Res., 13(3) (1983b) 407–416. [6]. S. S. Seehra, S. Gupta, and S. Kumar, “Rapid setting magnesium phosphate cement for quick repair of concrete pavements— characterisation and durability aspects,” Cement and Concrete Research, 23(2) (1993) 254–266. [7]. D. Roy “Recent advances in phosphate chemically bonded ceramics.” MRS Intl. Mtg. Adv. Mater., 13(2) (1989) 213–227 [8]. N. Yang, C. Shi, J.Y.Y. Chang “Research Progresses in Magnesium Phosphate Cement–Based Materials” J. Mater. Civ. Eng. 26 (2014). (DOI: 10.1061/(ASCE)MT.1943-5533.0000971) [9]. T. Zhang, L. J. Vandeperre, C. R..Cheeseman “Magnesium-silicate-hydrate cements for encapsulating problematic aluminium containing wastes” Journal of Sustainable Cement-Based Materials, (2012) (http://dx.doi.org/10.1080/21650373.2012.727322). [10]. Y. Chang, C. Shi, N. Yang, J. Yang, “Effect of fineness of magnesium oxide on properties of magnesium potassium phosphate cement.” J. Chinese Ceram. Soc., 41(4) (2013) 492–499. [11]. J. W. Park, K. H. Kim, and K. Y. Ann, “Fundamental Properties of Magnesium Phosphate Cement Mortar for Rapid Repair of Concrete”, Hindawi Publishing Corporation Advances in Materials Science and Engineering Volume 2016, Article ID 7179403. [12]. W. A. Wilson, and J.W. Nicholson, “Acid-base cement (their biomedical and industrial applications)”, Cambridge University Press, Cambridge, (1993) U.K [13]. C. Qian, and J. M. Yang, “Effect of disodium hydrogen phosphate on hydration and hardening of magnesium potassium phosphate cement.” J. Mater. Civ. Eng., (2011) 1405–1411 10.1061/(ASCE)MT.1943-5533.0000305, [14]. B. Abdelrazig, J. Sharp, and B. El-Jazairi, “The chemical composition of mortars made from magnesiaphosphate cement.” Cement Concr. Res., 18(3) (1988) 415–425.
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[15]. F. Qiao, W. Lin, CK Chau, Z. Li, “Property assessment of magnesium phosphate cement”. Key Eng Mater (2009) 115–20. [16]. F. Qiao, W. Lin, CK Chau, Z. Li., “Setting and compressive strength characteristics of magnesium phosphate cement paste”. Adv. Cem. Res. 2009. [17]. T. Finch and J. Sharp, “Chemical reactions between magnesia and aluminium orthophosphate to form magnesia-phosphate cements.” J. Mater. Sci., 24(12) (1989) 4379–4386. [18]. F. Qiao, W. Lin, CK Chau, Z. Li, “Property evaluation of magnesium phosphate cement mortar as patch repair material.” Constr. Build. Mater., 24(5) (2010) 695–700. [19]. X. Li, L. Du, and D. Li “The preparation and study on the new high early strength magnesium phosphate cement.” Bull. Chinese Ceram. Soc., 27(1) (2008) 20–25 [20]. G. Mestres, M.P. Ginebra, “Novel magnesium phosphate cements with high early strength and antibacterial properties”, Acta Biomaterialia 7 (2011) 1853–1861. [21]. Z. Ding, Z. Li. “High-early-strength magnesium phosphate cement with fly ash” ACI Mater J 102(6) (2005) 375–81. [22]. Z. Ding, J.G. Dai and S. Muner, “Study on an Improved Phosphate Cement Binder for the Development of Fiber-Reinforced Inorganic Polymer Composites”, Polymers 6 (2014) 2819-2831; doi:10.3390/polym6112819. [23]. D.D Zheng, T. Ji, C. Q. Wang, C.J. Sun, X.J. Lin, K. M. A. Hossain, “Effect of the combination of fly ash and silica fume on water resistance of Magnesium–Potassium Phosphate Cement”, Construction and Building Materials 106 (2016) 415–421. [24]. J. Formosa, A.M. Lacasta, A. Navarro, R. del Valle-Zermeño, M. Niubó, J.R. Rosell, J.M. Chimenos, “Magnesium Phosphate Cements formulated with a low-grade MgO by-product: Physico-mechanical and durability aspects” (2015). [25]. A. Maldonado-Alameda, A.M. Lacasta, J. Giro-Paloma, J.M. Chimenos, L. Haurie, J. Formosa, “Magnesium phosphate cements formulated with low grade magnesium oxide incorporating phase change materials for thermal energy storage”, Construction and Building Materials 155 (2017) 209–216. [26]. Li, X., Du, L., and Li, D. “The preparation and study on the new high early strength magnesium phosphate cement.” Bull. Chinese Ceram. Soc., 27(1) (2008) 20–25. [27]. Li, D., Li, P., and Feng, C. “Research on water resistance of magnesium phosphate cement (in Chinese).” J. Build. Mater., 12(5) (2009) 505–510.