Variability of Chemical Composition of Some Cements Available on the Sri Lankan Market

Transcription

1 Annual Research Journal of SLSAJ (202),Vol. 2, pp. -5 Variability of Cheical Coposition of Soe Ceents Available on the Sri Lankan Market D.L.N.B. Jayawardana,U.P.A.S. Ukwatta, W.M.N.R. Weerakoon, C.K. Pathirana* and H. Abeyruwan Departent of Civil Engineering, Faculty of Engineering, University of Peradeniya, Sri Lanka *E-ail address: Abstract Hydraulicceent is a binder that hardens when ixed with water. Physical and cheical characteristics of fresh and hardened ceent paste are known to depend heavily on the cheical coposition of ceent. Cheical coposition in turn depends on the raw aterials selected and the process used for the production of ceent. Mainly, there are two types of hydraulic ceent coercially available on the Sri Lankan arket. They are ordinary Portland ceent and blended ceent. Portland ceents are considered to have less than 5 per cent of other inorganic copounds such as suppleentary ceentitious aterial or fillers with negligible reactivity, while blended ceents are coonly considered consisting of ore than 5 per cent of one or ore suppleentary ceentitious aterials (SCM) such as ground granulated blast furnace slag (GGBS) and pulverized fuel ash (PFA) in addition to the Portland ceent clinker. The Sri Lankan standard specification for ordinary Portland ceent is SLS 07 while that for blended ceent is SLS 247. This paper presents loss on ignition, insoluble residue, and contents of CaO, SiO 2, Al 2 O 3, Fe 2 O 3, MgO and SO 3 easureents representing the cheical coposition of soe ceent saples. The tests were perfored according to the ASTM C4 and SLS 07 standard specifications. Coparing the easured cheical coposition of ceents coercially available on the Sri Lankan arket with the standard specified range of values for ordinary Portland ceent and blended ceent, it can be seen that soe saples of ceent have cheical coposition in the acceptable range while there are others falling outside. Keywords: Hydraulic ceent, raw aterials, cheical coposition, acceptable range. Introduction Ceent is an alost essential aterial in the construction industry as it is the binding agent of concrete. It has a property of setting and hardening by a cheical reaction with water called hydration. Ceents with different cheical copositions can achieve different properties when hydrated. Therefore, different ixtures of raw aterials can be selected for the production of ceents with various desired properties. As a result, several types of Portland ceents are coercially available on the arket. Ceent production is a significant source of global carbon dioxide (CO 2 ) eissions, aking up approxiately 5 per cent of global anthropogenic CO 2 eissions (Worrell et al., 200). The interest of searching strategies to reduce these green house gases has been increased in the world. Worell et al. (200) also reports that, by producing blended ceent, it could be reduced at least 5 per cent of total CO 2 eissions fro ordinary Portland ceent aking. Blended ceents are coonly considered consisting of one or ore appropriate suppleentary ceentitious aterials (SCM) such as industrial by-products like ground-granulated blast-furnace slag (GGBS) and pulverised fuel ash (PVA) in aounts ore than 5 per cent, in addition to the Portland ceent clinker. SCMs are a class of ineral-based aterials possessing pozzolanic reactivity, such as coal fly ash (a residue fro coal burning), blast-furnace slag (a residue fro iron aking), or other pozzolanic aterials (e.g., volcanic ashes). These products are blended with the ground clinker to produce a hoogenous product called blended ceent. Pozzolan can be defined as a siliceous or aluino-siliceous inorganic aterial with very fine particles. In the presence of water, it reacts with calciu hydroxide released by the hydration of Portland ceent at ordinary teperatures, to for copounds of possessing ceenting properties. Blended ceents have different properties than those of Portland ceent, e.g., longer setting tie, greater long-ter strength and enhanced cheical resistance. Already, blended ceent is used in ost of the

2 Jayawardana et al, 202 countries like Gerany, Greece, Italy, Poland, Norway, Sweden, Hong Kong, Singapore, etc. The perforance of blended ceents has been docuented in outstanding engineering works such as concrete paveents, arches and coluns, bridge caps, walls, concrete das, counter bearing bridge decks, superstructure of prestressed concrete bridges, highway bridges, etc., in those countries. Table. Types of blended ceents covered by ASTM and SLS standard specifications Specification Ceent type ASTM C595 SLS 247 I(SM), I(SM)-A, IS, IS-A S, SA I(PM), I(PM)-A, P, PA, IP, IP-A Type Portland pozzolana ceent Type 2 - Portland slag ceent There are liits on cheical coposition for the types of ceents given in the respective standard specifications. In order to be, effectively used in the construction industry, ceents ust have certain quailities. It is known that the cheical coposition is controlling various physical and echanical properties of ceent and its products (Escalante-Garcia and Sharp,2004). Therefore, it is highly iportant to ake sure that the cheical copositions are aintained within narrow liits prescribed by standard specifications, for optiu and consistent perforance. According to ASTM C 4-03 and SLS 07 part 2:2008, the paraetersof ceent such as loss on ignition, insoluble residue and contents of CaO, SiO 2, Al2O 3, Fe 2 O 3, MgO, SO 3, and total alkalis have been analyzed and reported in this study. 2. Methods To deterine the loss on ignition, insoluble residue, SiO 2, Fe 2 O 3, SO 3 and total alkalis, reference test ethods prescribed in ASTM C4-03 were perfored and, contents of Al 2 O 3, CaO, and MgO of ceent saples were deterined using SLS 07 part 2. All reagents used in testing were of analytical grade. 2.. Loss on ignition Loss on ignition is the ass loss fro ceent saple when heating in an air or oxygen atosphere to a prescribed teperature. Norally this loss is due to reoving of water and CO 2. Here,.00 g of the ceent saple was weighed in a tarred platinu crucible, and it was covered and ignited at a teperature of 950 ± 50 Cas prescribed in ASTM C4-03.Then the percentage ass loss on ignition was calculated using the following equation and reported to the nearest 0.. LOI (wt%) = 00 (n 2 n 3 )/(n 2 n ) n - ass of epty crucible n 2 - ass of the crucible and saple before ignition n 3 - ass of the crucible and saple after ignition 2.2. Insoluble residue Insoluble residue is a non-ceenting aterial which is present in ceent. This property ainly affects the copressive strength of hydrated ceent. For deterining the insoluble residue content, 25 l of cold water (approx. 20 C) was added to.00 g of the saple. The ceent was dispersed in the water and while swirling the ixture, 5 l of HCl of relative density.9 was quickly added. The solution was diluted to 50 l with hot water (approx. 60 C) and the ixture was digested. Then it was filtered using No. 40 Whatan filter paper. After filtration, it was further digested in NaOH (0 g/l). The resulting insoluble residue was ignited at 900 C to 000 C, cooled in a desiccator, and then weighed. The insoluble residue content was expressed as a percentage of the ass of the insoluble residue after ignition over the ass of ceent saple, using the following equation and reported to the nearest 0.0. IR = 2 00 IR - Insoluble residue - ass of the saple (g) 2 - ass of the residue after ignition 2.3. SiO 2 content A quantity of the ignited saple equivalent to 0.5 g of the as received saple was weighed. Then it was ixed thoroughly with 4 to 6 g of Na 2 CO 3 by grinding in an agate ortar. A thin layer of Na 2 CO 3 2

3 Annual Research Journal of SLSAJ (202),Vol. 2, pp. -5 was placed on the botto of a platinu crucible. The ceent - Na 2 CO 3 ixture was added and the ixture was covered with a thin layer of Na 2 CO 3. Placing the covered crucible over a oderately low flae and the saple was fused by Na 2 CO 3. Double evaporation was followed to dryness of the hydrochloric acid solution of the fusion product to convert SiO 2 to the insoluble for. The solution was filtered using a fast filter paper (open texture) and the insoluble siliceous residue was ignited and weighed. SiO 2 was volatilized by HF and the reduction of ass was reported as pure SiO 2. The percentage of SiO 2 was calculated using the following equation and reported to the nearest 0.. S = ʹ 00 S- content of SiO 2 (per cent) ʹ- reduction of ass of the precipitate after treating with HF(g) - ass of the saple (g) 2.4.Fe 2 O 3 content This was deterined on a separate proportion of the ceent by reducing the iron to the ferrous state with stannous chloride (SnCl 2 ) and titrating with a standard solution of potassiu dichroate (K 2 Cr 2 O 7 ). Here, 0.5 g of ceent saple was blended with.0 g of LiBO 2 by using a ortar and pestle, and transferred to a previously fired 8 l carbon crucible that has 0. g LiBO 2 sprinkled in the botto. Following the procedure prescribed in ASTM C4-03, the percentage of Fe 2 O 3 content was calculated using the equation given below and reported to the nearest 0.0. Fe 2 O 3 % = E V 00 E - equivalent strength of K 2 Cr 2 O 7 in g/l V- volue of K2Cr 2 O 7 solution required by one gra saple of ceent, expressed in l 2.5. SO 3 content In this test ethod, 25 l of cold water (approx. 20 C) was added to.0 g of ceent saple and while the ixture was stirred vigorously. Then 5 l of concentrated HCl was added and as prescribed in ASTM C4-03, sulfate was precipitated fro the acid solution of the ceent with BaCl 2. The precipitate was filtered with a slow filter paper (close texture), ignited and weighed as BaSO 4 and the SO 3 equivalent percentage was calculated using the following equation and reported to the nearest 0.0. SO 3 % = ass of BaSO 4 (g) 34.3 is the ratio of olecular ass of sulphuric anhydride to that of bariu sulphate (0.343) ultiplied by Al 2 O 3 content The filtrate at finding SiO 2 content was used to deterine this content. War water was added to the filtrate to ake approxiately 200 l. Then it was neutralized by adding aqueous aonia (+) to produce a precipitate of hydroxide, as prescribed in SLS 07 part 2. Then the precipitate was filtered with a fast filter paper (open texture), ignited and weighed for Al 2 O 3 content. The percentage of Al 2 O 3 content was calculated using the following equation and reported to the nearest 0.0. Al = ʹ 00 Fe Al- content of the Al 2 O 3 (%) ʹ- ass of precipitate (g) - ass of the saple (g) Fe- content % of the Fe 2 O CaO and MgO content The contents of calciu oxide and agnesiu oxide were deterined separately using the filtrate after finding the Al 2 O 3 content. Aliquots of the filtrate were used according to the procedure specified in SLS 07 part 2 for the deterination. The filtrate was cooled to roo teperature. While washing, it was transferred in to 500 l voluetric flask and water was added up to the arked line and agitated. 50 l of each saple solutions were transferred in to two 300 l beakers and water was added to ake 200 l each. To deterine the content of the calciu oxide, ph was regulated fro 2.7 to 3.2 by adding potassiu hydroxide solution and titrating with EDTA standard solution using indicator for calciu. To deterine the content of agnesiu oxide, ph was regulated fro 9.5 to 0.0 by adding the buffer solution, titrating with EDTA standard solution using EBT indicator. Then 3

4 Jayawardana et al, 202 percentage of CaO and MgO content were calculated using the following equations and reported to the nearest 0.0. CaO = V E 0 00 MgO = (V 2 V ) E CaO- content of the calciu oxide (per cent) MgO- content of the agnesiu oxide (per cent) V - consuption of the EDTA std solution (l) deterined for CaO titration V 2 - consuption of the EDTA std solution (l) deterined for MgO titration E -CaO equivalent per l of the EDTA std solution (g) E 2 -MgO equivalent per l of the EDTA std solution (g) - ass of the saple (g) 2.8. Total alkalis Alkalis are the cobination of Na 2 O and K 2 O. In various specifications/standards, the total alkali content in the ceent is regulated as Na 2 O-equivalent..000 g of ceent saple was placed in a 50 l beaker and dispersed with 20 l of water using a swirling otion. While still swirling 5.0 l of HCl was added all at once and iediately diluted to 50 l with water. The standard solutions were also prepared and the test was continued in accordance with the procedure specified in ASTM C4-03. The percentage of Na 2 O and K 2 O were calculated and the total alkalis were calculated using the following equation and reported to the nearest 0.0. Total Alkalis = Na 2 O K 2 O 3. Results and Discussion Table 2. Cheical Properties of the tested ceent saples Property Results % Standard Blended Ordinary Portland Requireent % B A A2 A3 A4 A5 Loss on < 3.0 (for A) Ignition < 2.5 (for B) Insoluble <.5 (for A) Residue Total alkalis ND ND ND > 0.2 and <.3 SiO > 7 and < 25 Al 2 O > 3 and < 8 CaO > 60 and < 67 MgO > 0. and < 4.0 Fe 2 O > 0.5 and < 6 SO < 3.0 (for A) Paraeter falling outside the specified liit ND Not deterined A Ordinary Portland ceent (Specifications- SLS 07 & ASTM C50) B Blended ceent (Specifications- SLS 247 & ASTM C595) < 3.5 (for B) 3.. Loss on Ignition (LOI) The percentage of loss on ignition should be less than 3 for ordinary Portland ceent. This value should be less than 2.5 according to the Sri Lankan specification for blended hydraulic ceent (SLS 4

5 Annual Research Journal of SLSAJ (202),Vol. 2, pp ). In the tested ceent types, B and s A, A4 and A5 show a reasonable result for their categories and s A2 and A3 show higher than specified. According to the results, B can be considered eeting the requireent for blended ceent Insoluble residue (IR) The requreent for insoluble residue content of OPC should be less than.5%. But all OPC ceent brands tested, except A4 and A5 have higher values for IR content. The extreely high IR content in the pozzolana ceent ( B) can be tolerated as it contains fly-ash. Though there is no liit iposed on IR in blended ceent, SLS 247 entions that the pozzolanic aterial content could be varied fro 6 to 35 per cent Total alkalis The alkali percentage should be within 0.2 and.3. All saples tested for the paraeter satisfy the requireent Oxide s SO 3 content should be less than 3% for ordinary ceent, and for blended ceent the liit is 3.5%. All the tested ceent brands satisfy the liit. Fe 2 O 3 percentage should be within 0.5 and 6.0 while MgO percentage should be within 0. and 4.0. All ceent saples tested showed the respective copounds are in the required range. The SiO 2 content should be within 7% and 25%. In B ceent this value is in the required range but in A, the aount is in excess. The Al 2 O 3 percentage should be within 3 and 8. There is a higher Al 2 O 3 content in B and A saples of ceent. The CaO content should be within 60% and 67%. In s B, A and A2 the content is less than the specified aount. Majority of the properties of A ceents confor to the standard requireents and those brands ay give reasonable results in use. 4. Conclusions acceptable and consistent properties, irrespective of the brand of ceent chosen. According to the values deterined in this liited study of cheical coposition of ceents available on the Sri Lankan arket, it can be seen that soe properties of ceents are in the acceptable range while there are others falling outside the range. In suary, out of five brands of ceents, two brands in category A have satisfied all requireents. Insoluble residue and CaO are the ost frequently violated paraeters. LOI and Al 2 O 3 are the next to violate. Only a single brand has violated the liit on SiO 2 content. In all tested ceents, MgO, Fe 2 O 3, SO 3 and alkali contents are within the specified liits. Acknowledgeent The authors are grateful to Mr. Y. M. Tikiri Banda and the staff of Materials laboratory, Dept. of Civil Engineering, University of Peradeniya for supporting this work. References Aerican Society for Testing Materials, ASTM C4-03, Annual Book of ASTM Standards, Hydraulic Ceent, Vol. 04.0, Aerican Society for Testing Materials, ASTM C595-03, Annual Book of ASTM Standards, Hydraulic Ceent, Vol. 04.0, Escalante-Garcia J.I. and Sharp J.H., The Cheical Coposition and Microstructure of Hydration Products in Blended Ceents, Ceent & Concrete Coposites, : Sri Lanka Standards Institution, SLS 07 : Part 2 : 2008, Sri Lanka Standards, Specifications for Ordinary Portland Ceent, Part 2 : Test Methods, UDC : 543. Sri Lanka Standards Institution, SLS 247 : 2008, Sri Lanka Standards, Specifications for Blended Hydraulic Ceents, UDC Worrell E., Price L., Martin N., Hendriks C. and MeidaL.O., Carbon Dioxide Eissions fro the Global Ceent Industry, Annual. Rev. Energy Environ., : It is knowledge that aintaining cheical copositions of a given generic type of ceents within narrow liits given in standard specifications is vital for aking concrete with 5