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Calcium sulfate hemihydrate activated low heat sulfate resistant cement
Construction and Building Materials 16 Ž2002. 181᎐186
Calcium sulfate hemihydrate activated low heat sulfate resistant cement Manjit SinghU , Mridul Garg EST Di¨ ision UP, Central Building Research Institute, Roorkee 247667, India Received 20 May 2000; received in revised form 21 August 2001; accepted 25 October 2001
Abstract Investigations were undertaken to produce low heat sulfate resistant cement by activation of granulated slag obtained from the blast furnace process of iron making and phosphate industries with the calcium sulfate hemihydrate. Experimental data showed that cement gives fast setting characteristics in addition to high strength development. The setting time of cement was regulated with a small addition of set retarder without adversely affecting the strength development of cement. It is noted that beta hemihydrate plaster gives better strength results than the anhydrite activated cement. The results also confirm that granulated blast furnace slag can be replaced with phosphatic slag up to 10% by mass without loosing strength. DTA and X-ray diffraction analysis have been used to identify the hydration products formed in the hydrated cement. The heat of hydration data of cement is reported in the paper. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Granulated slag; Calcium sulfate hemihydrate; Cement
1. Introduction Slags are known as ancient building material. Egyptian produced glassy slags containing minerals like melilite and tridymite by burning wheat straw with opal w1x. At present, it is produced as a by-product in the manufacture of pig iron using iron ore. Slag is available both in crystalline or glassy granulated forms which can be used as a useful building material such as a component of slag cements or for bricks, tiles, binders and concrete aggregate w2x. Blast furnace slag is used to greater extent in many countries like Germany, France, China and UK. The industrial application of blast furnace slags as a
U
Corresponding author. Tel.: q91-1332-72235; fax: q91-133272272. E-mail address: [email protected] ŽM. Singh..
binder is due to their power of activation. The granulated slag can be activated by alkali w3x, lime w4x and sulfate w5x to form bindersrcements of significant engineering properties. Recently, rapid hardening cementitious mixes comprising slag, fly ash, gypsum, cement or lime have been introduced as economic building materials w6x. The metallurgical slags obtained from electrothermal production of phosphorous and ferrotitanium industries having a CaOrSiO 2 ratio between 1.1 and 1.3 are also used for making binders w7x. Generally, the slags are blended with 10᎐15% gypsum anhydrite in presence of 2᎐5% of cement or lime to form a binder, popularly known as supersulfated cement or low heat sulfate resistant cement as they give low heat of hydration and adequate sulfate resistance than the ordinary portland cement. The Indian slags are characterized by low lime and high alumina content and as such are less reactive than the foreign slags. To overcome this problem, researches have been
0950-0618r02r$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 0 1 . 0 0 0 2 6 - 5
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
182
Table 1 Chemical composition of raw materials Constituents Ž%.
GBFSa
Phosphatic slag
Phosphogypsum
Portland cement clinker
P 2 O5 F Organic matter SiO2 q insoluble in HCl Al2 O3 q Fe2 O3 CaO MgO SO3 Na2 O LOI Cl Mn2 O3
᎐ ᎐ ᎐ 33.83 22.93 34.93 7.46 0.84 ᎐ 0.20 ᎐ 0.10
0.56 ᎐ ᎐ 40.14 5.66 49.02 3.94 ᎐ ᎐ ᎐ ᎐ ᎐
0.47 0.86 0.59 0.29 0.54 31.09 1.31 43.21 0.29 18.38 ᎐ ᎐
᎐ ᎐ ᎐ 22.50 9.80 61.70 2.80 0.06 Tr. 2.1 ᎐ ᎐
a
GBFS: granulated blast-furnace slag.
carried out w8x which shows that by increasing the anhydrite content to 20᎐25%, the strength of cement can be increased considerably. However, for the production of anhydrite, high thermal energy Ž0.5᎐0.55= 10 6 kcalrton. is required. There are two major aims of the study reported in this paper: Ž1. to find out the effect of replacing anhydrite with the calcium sulfate hemihydrate on the activation of granulated blast furnace slag; and Ž2. to see effect of partial replacement of granulated blast furnace slag with phosphatic slag on the properties of low heat sulfate resistant cement. Investigations were therefore, undertaken to activate the slag with calcium sulfate hemihydrate ŽCaSO4 ⭈ 1r2H 2 O. with lower thermal energy consumptions Ž0.30᎐0.35= 10 6 kcalrton.. Experimental cements were produced by blending the ground granulated slag with hemihydrate plaster and portland cement clinker in suitable proportions and their characteristics were compared with the same slag blends using anhydrite as well as portland cement. The low heat sulfate resistant cements were also produced by partial replacement of granulated slag with the phosphatic slag. The hydration of these cements was checked by DTA and X-ray diffraction. The heat of hydration and sulfate resistance of these cements was determined and discussed in the paper.
2. Experimental 2.1. Raw materials The raw materials such as granulated blast furnace slag ŽGBFS., phosphatic slag, phosphogypsum and portland cement clinker collected from various sources in the country were used to formulate low heat sulfate resistant cement. The chemical composition of these materials is depicted in Table 1. 2.2. Preparation of low heat sulfate resistant (LHSR) cement The LHSR cements were produced by intimately blending the finely ground granulated blast furnace slag Ž410 m2rkg, Blaine. with the calcium sulfate hemihydrate Ž320 m2rkg, Blaine. and cement clinker Ž330 m2rkg, Blaine. in different proportions Table 2. While the calcium sulfate hemihydrate ŽCaSO4 ⭈ 1r2H 2 O. was produced by heating phosphogypsum at 150 ⬚C, the anhydrite CaSO4 ŽII. was made at 850 ⬚C. The cements were made by partial replacement of granulated slag with phosphatic slag Ž420 m2rkg, Blaine.. A portland cement was also produced using the cement clinker q 4% of gypsum for comparative study. The LHSR cements were tested for their various properties as per
Table 2 Composition of LHSR cements Cement design
A B C D E
Mix composition Ž% by mass. GBFS
CaSO4 ⭈ 1r2H2 O
Portland cement clinker
Retarder
75 75 75 75 ᎐
15 15 15 15 Žanhydrite. ᎐
10 10 10 10 96
᎐ 0.2 Žborax. 0.1 Žtartaric acid. ᎐ 4.0 Žgypsum.
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
183
Table 3 Properties of LHSR cements Cement design
Properties Setting time Žmin.
Compressive strength ŽMPa.
Initial
Final
3 days
7 days
28 days
Soundness Žcold expn.. Žmm.
A B C D E
10 60 55 62 110
65 120 106 170 205
16.1 15.9 16.9 15.8 17.5
23.7 22.3 38.4 35.2 28.0
35.4 43.1 56.1 55.3 46.0
1.0 1.1 1.2 0.9 1.6
IS:6909-1990 Limits
Min. 30
Max. 600
Min. 15
Min. 22
Min. 30
Max. 5.0
Table 4 Properties of LHSR cement produced by partial replacement of GBFS with phosphatic slag Properties Setting time Žmin. Initial
70
Compressive strength ŽMPa. Final
142
Soundness Žcold expan.. Žmm.
Time of hardening 3 days
7 days
28 days
15.7
23.0
44.7
methods given in IS: 4031-1988 w9x. The strength development in LHSR cements was evaluated with DTA ŽStanton Red Croft, UK. and X-ray diffraction ŽPhilips, Holland.. The sulfate resistance of LHSR cement was checked as per procedure laid down in IS: 12330-1988 w10x. According to test, a mixture of LHSR cement and natural gypsum was prepared in such a way that the total SO 3 content was 7.0% by mass. The granulometry of natural gypsum was maintained as 100% passing 150 m IS sieve, at least 95% passing 75 m sieve and at least 75% passing 45 m IS sieve, respectively. Bars of size 250 mm= 25 mm= 25 mm were cast using cement Žcontaining gypsum. and sand in the proportion 1:2.75 at WrC 0.485. The bars were demoulded after 24 h of their casting and then immersed in the water horizontally. The average expansion of three bars was recorded at 14 days.
0.8
higher concentration of SO42y ions in aqueous media containing high alumina. To overcome this problem, number of chemical retarders such as borax, tartaric acid, sugar, polyphosphates, citrate, etc. were tested to prolong setting time of cement. Two retarders namely borax and tartaric acid were found effective to give satisfactory setting times desired by the standard. The retarder concentration beyond 0.2% was avoided to cause any detrimental affect on the strength development of LHSR cements. It is interesting to note that compressive strength of LHSR cements increased appreciably with the progress in hydration of cements. It can be seen that on retardation, the cements do not show any fall in the strength,
3. Results and discussion 3.1. Properties of low heat sulfate-resistant cement The physical properties of optimum mixes of LHSR cements produced by blending granulated blast furnace slag ŽGBFS. duly activated with calcium sulfate hemihydrate and anhydrite in presence of portland cement clinker are reported in Table 3. It can be seen that cements set fast on addition of water. The fast setting of LHSR cement may be ascribed to the quick setting of calcium sulfate hemihydrate on account of much
Fig. 1. Differential thermograms of LHSR cement Žmix C. hydrated for different periods of hardening.
184
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
rather strength values are enhanced. The strength properties of LHSR cements ‘C’ and ‘D’ are better than the cement ‘E’ listed in Table 3. The LHSR cements have been found sound as their cold expansion was much below the maximum specified value of 5.0 mm. The LHSR cements demonstrate by documentation that it compared fairly well with the traditional supersulfated cement produced by blending the slag with anhydrite and portland cement. The results confirm that LHSR cement can be produced by activating the slag with CaSO4 ⭈ 1r2 H 2 O in stead of CaSO4 Žanhydrite.. The properties of LHSR cement produced by substituting GBFS with 10% Žby mass. phosphatic slag are reported in Table 4. Data show that LHSR cement complied with the requirements laid down in IS: 69091990 w11x. No detrimental affect was noticed on the strength development of cement when GBFS was replaced with 10.0% of the phosphatic slag. The findings are quite encouraging and may be applied to other metallurgical slags produced from Fe Mn, SiMn, copper and nickel industries. The hydration products formed during the hardening of LHSR cements have been identified with the help of DTA and XRD. DTA of LHSR cements namely ‘C’ and ‘D’ are shown in Figs. 1 and 2, respectively. In case of cement ‘C’ ŽFig. 1., the endotherms formed at 100,
Fig. 2. Differential thermograms of LHSR cement Žmix D. hydrated for different periods of hardening.
125, 150, 220᎐230, 640᎐830 ⬚C and the exotherms at 890 and 920 ⬚C may be attributed to the decomposition of gel water, ettringite, dehydration of calcium sulfate hemihydrate, C 4 AH 13 , CSHŽI. Žtobermorite. and devitrification of slag, respectively. The intensity of ettringite endotherms at 125 ⬚C increased with the depletion of calcium sulfate hemihydrate peaks at 150 ⬚C. Similarly, CSHŽI. endotherms at 640᎐830 ⬚C are enhanced with the increase in curing period. The appearance of endotherms at 490 ⬚C at 3 days may be due to decomposition of CaŽOH. 2 .
Fig. 3. XRD patterns of hydrated cement Žmix C. for different periods of hardening.
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
185
Fig. 4. XRD patterns of hydrated cement Žmix D. for different periods of hardening.
DTA of cement ‘D’ ŽFig. 2., shows development of endotherms at 150, 180, 230, 500, 700᎐800 and exotherms at 845᎐920 ⬚C which may be assigned to the decomposition of ettringite, dehydration of calcium sulfate hemihydrate, C 4 AH 13 , CaŽOH.. 2 , appearance of CSHŽI. and devitrification of slag, respectively. An increase in intensity of ettringite and CSHŽI. endotherms with the enhancement in hydration was significant. No CaŽOH.. 2 peak was detected at 28 days. DTA data thus confirms that formation of ettringite, CSHŽI. and C 4 AH 13 are essentially responsible for the strength of LHSR cements. The XRD patterns of LHSR cements ‘C’ and ‘D’ are plotted in Figs. 3 and 4, respectively. It can be seen that major peaks are ettringite, CSHŽI. and C 4 AH 13 .The intensity of ettringite and CSHŽI. peaks increased with
the increase in curing period. However, the intensity of gypsum and CaŽOH. 2 reflections are reduced. No peak for Ca ŽOH. 2 was recorded. In essence, the XRD data corroborate the findings of DTA regarding formation of major hydration products. The heat of hydration of LHSR cements is reported in Table 5. It can be seen that the heat of hydration of cements is within the requirements of IS: 6909-1990 and hence can be recommended for use in mass concrete. The sulfate resistant test conducted for LHSR cements C and D showed the sulfate expansion values in the range 0.01᎐0.03% against the maximum specified value of 0.045%. Hence, the cement is sulfate resistant. The durability studies of LHSR cements in sulfate environment are in progress.
Table 5 Heat of hydration of LHSR cements Cement design
C D E IS: 6909-1990 Limits
Heat of dissolution Žcalrg.
Heat of Hydration ŽCalrg.
Unhydrated
Time of hardening
505.6 522.2 532.2
Time of hardening 3 days
7 days
28 days
3 days
7 days
28 days
529.8 549.3 570.0
539.2 559.2 575.4
555.8 576.8 586.4
24.2 27.1 37.8
33.6 37.0 43.4
50.5 54.6 64.2
᎐
Max. 60
Max. 70
186
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
4. Conclusions The low heat sulfate resistant cement can be produced by the activation of slag with calcium sulfate hemihydrate formed at 150 ⬚C against the traditional use of anhydrite, i.e. hard burnt gypsum produced at 850 ⬚C. Thus, net saving of thermal energy can be achieved. The major phases responsible for strength development in LHSR cement have been identified as ettringite, CSHŽI. and C 4 AH 13 . The rapid setting of these cements can be overcome by the small addition of borax or tartaric acid retarders. The use of calcium sulfate hemihydrate is recommended for making LHSR cement.
Acknowledgements The authors are grateful to the Director, Central Building Research Institute, Roorkee for allowing publication of this paper. References w1x Dana DJ. Manual of Mineralogy and Petrography. 7th ed. New York: Wiley, 1989:443᎐448.
w2x Singh M. Portland slag cement as building material, Seminar on Portland Slag cement ᎏ Its Superior Characteristics and Suitability for All Civil Constructions and Mass Concrete Works, Bhubneshwar, 25th April, 1992, pp. 31᎐51. w3x Narang KC, Chopra SK. Studies on alkaline activation of BF, steel and alloy slags. Silicate Ind. 1983;9:175᎐182. w4x Diamon M. Mechanism and kinetics of slag cement hydration, 7th International Congress on Chemistry of Cement, Paris, vol. 1 ŽIII., June 1980, pp. 2r1᎐2r9. w5x Taneja CA, Singh M, Tehri SP, Raj T. Super sulfated cement from waste phosphogypsum, 12th International Conference on Silicate Industry and Silicate Science, Budapest, Hungary, June 1977, pp. 621᎐627. w6x Davidovits J. Geopolymers, processing and applications of high ultra temperature, inorganic matrix resin for cast composite structures, molds and tools for RPrC and metal industries, PECTEC 83, Society of Plastic Engineers, Anaheim, 1983, pp. 222᎐230. w7x Boehme O, Ulrick B. Investigations of the phosphatic slags. Silikattechnik 1987;38Ž2.:60᎐63. w8x Chopra SK, Lal K. Manufacture of super sulfated cement from the Indian slags, experimental work at C.B.R.I.. Indian Concrete J. 1961;35Ž4.:114᎐116. w9x IS: 4031-1988, Methods of physical test for hydraulic cement, Bureau of Indian Standards, New Delhi, 1988, p. 2. w10x IS: 12330-1988, Specification for sulfate resistant portland cement, Bureau of Indian Standards, New Delhi, 1988, p. 3. w11x IS: 6909-1990, Specification for super sulfated cement, Bureau of Indian Standards, New Delhi, 1990, p. 6.
Calcium sulfate hemihydrate activated low heat sulfate resistant cement Manjit SinghU , Mridul Garg EST Di¨ ision UP, Central Building Research Institute, Roorkee 247667, India Received 20 May 2000; received in revised form 21 August 2001; accepted 25 October 2001
Abstract Investigations were undertaken to produce low heat sulfate resistant cement by activation of granulated slag obtained from the blast furnace process of iron making and phosphate industries with the calcium sulfate hemihydrate. Experimental data showed that cement gives fast setting characteristics in addition to high strength development. The setting time of cement was regulated with a small addition of set retarder without adversely affecting the strength development of cement. It is noted that beta hemihydrate plaster gives better strength results than the anhydrite activated cement. The results also confirm that granulated blast furnace slag can be replaced with phosphatic slag up to 10% by mass without loosing strength. DTA and X-ray diffraction analysis have been used to identify the hydration products formed in the hydrated cement. The heat of hydration data of cement is reported in the paper. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Granulated slag; Calcium sulfate hemihydrate; Cement
1. Introduction Slags are known as ancient building material. Egyptian produced glassy slags containing minerals like melilite and tridymite by burning wheat straw with opal w1x. At present, it is produced as a by-product in the manufacture of pig iron using iron ore. Slag is available both in crystalline or glassy granulated forms which can be used as a useful building material such as a component of slag cements or for bricks, tiles, binders and concrete aggregate w2x. Blast furnace slag is used to greater extent in many countries like Germany, France, China and UK. The industrial application of blast furnace slags as a
U
Corresponding author. Tel.: q91-1332-72235; fax: q91-133272272. E-mail address: [email protected] ŽM. Singh..
binder is due to their power of activation. The granulated slag can be activated by alkali w3x, lime w4x and sulfate w5x to form bindersrcements of significant engineering properties. Recently, rapid hardening cementitious mixes comprising slag, fly ash, gypsum, cement or lime have been introduced as economic building materials w6x. The metallurgical slags obtained from electrothermal production of phosphorous and ferrotitanium industries having a CaOrSiO 2 ratio between 1.1 and 1.3 are also used for making binders w7x. Generally, the slags are blended with 10᎐15% gypsum anhydrite in presence of 2᎐5% of cement or lime to form a binder, popularly known as supersulfated cement or low heat sulfate resistant cement as they give low heat of hydration and adequate sulfate resistance than the ordinary portland cement. The Indian slags are characterized by low lime and high alumina content and as such are less reactive than the foreign slags. To overcome this problem, researches have been
0950-0618r02r$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 9 5 0 - 0 6 1 8 Ž 0 1 . 0 0 0 2 6 - 5
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
182
Table 1 Chemical composition of raw materials Constituents Ž%.
GBFSa
Phosphatic slag
Phosphogypsum
Portland cement clinker
P 2 O5 F Organic matter SiO2 q insoluble in HCl Al2 O3 q Fe2 O3 CaO MgO SO3 Na2 O LOI Cl Mn2 O3
᎐ ᎐ ᎐ 33.83 22.93 34.93 7.46 0.84 ᎐ 0.20 ᎐ 0.10
0.56 ᎐ ᎐ 40.14 5.66 49.02 3.94 ᎐ ᎐ ᎐ ᎐ ᎐
0.47 0.86 0.59 0.29 0.54 31.09 1.31 43.21 0.29 18.38 ᎐ ᎐
᎐ ᎐ ᎐ 22.50 9.80 61.70 2.80 0.06 Tr. 2.1 ᎐ ᎐
a
GBFS: granulated blast-furnace slag.
carried out w8x which shows that by increasing the anhydrite content to 20᎐25%, the strength of cement can be increased considerably. However, for the production of anhydrite, high thermal energy Ž0.5᎐0.55= 10 6 kcalrton. is required. There are two major aims of the study reported in this paper: Ž1. to find out the effect of replacing anhydrite with the calcium sulfate hemihydrate on the activation of granulated blast furnace slag; and Ž2. to see effect of partial replacement of granulated blast furnace slag with phosphatic slag on the properties of low heat sulfate resistant cement. Investigations were therefore, undertaken to activate the slag with calcium sulfate hemihydrate ŽCaSO4 ⭈ 1r2H 2 O. with lower thermal energy consumptions Ž0.30᎐0.35= 10 6 kcalrton.. Experimental cements were produced by blending the ground granulated slag with hemihydrate plaster and portland cement clinker in suitable proportions and their characteristics were compared with the same slag blends using anhydrite as well as portland cement. The low heat sulfate resistant cements were also produced by partial replacement of granulated slag with the phosphatic slag. The hydration of these cements was checked by DTA and X-ray diffraction. The heat of hydration and sulfate resistance of these cements was determined and discussed in the paper.
2. Experimental 2.1. Raw materials The raw materials such as granulated blast furnace slag ŽGBFS., phosphatic slag, phosphogypsum and portland cement clinker collected from various sources in the country were used to formulate low heat sulfate resistant cement. The chemical composition of these materials is depicted in Table 1. 2.2. Preparation of low heat sulfate resistant (LHSR) cement The LHSR cements were produced by intimately blending the finely ground granulated blast furnace slag Ž410 m2rkg, Blaine. with the calcium sulfate hemihydrate Ž320 m2rkg, Blaine. and cement clinker Ž330 m2rkg, Blaine. in different proportions Table 2. While the calcium sulfate hemihydrate ŽCaSO4 ⭈ 1r2H 2 O. was produced by heating phosphogypsum at 150 ⬚C, the anhydrite CaSO4 ŽII. was made at 850 ⬚C. The cements were made by partial replacement of granulated slag with phosphatic slag Ž420 m2rkg, Blaine.. A portland cement was also produced using the cement clinker q 4% of gypsum for comparative study. The LHSR cements were tested for their various properties as per
Table 2 Composition of LHSR cements Cement design
A B C D E
Mix composition Ž% by mass. GBFS
CaSO4 ⭈ 1r2H2 O
Portland cement clinker
Retarder
75 75 75 75 ᎐
15 15 15 15 Žanhydrite. ᎐
10 10 10 10 96
᎐ 0.2 Žborax. 0.1 Žtartaric acid. ᎐ 4.0 Žgypsum.
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
183
Table 3 Properties of LHSR cements Cement design
Properties Setting time Žmin.
Compressive strength ŽMPa.
Initial
Final
3 days
7 days
28 days
Soundness Žcold expn.. Žmm.
A B C D E
10 60 55 62 110
65 120 106 170 205
16.1 15.9 16.9 15.8 17.5
23.7 22.3 38.4 35.2 28.0
35.4 43.1 56.1 55.3 46.0
1.0 1.1 1.2 0.9 1.6
IS:6909-1990 Limits
Min. 30
Max. 600
Min. 15
Min. 22
Min. 30
Max. 5.0
Table 4 Properties of LHSR cement produced by partial replacement of GBFS with phosphatic slag Properties Setting time Žmin. Initial
70
Compressive strength ŽMPa. Final
142
Soundness Žcold expan.. Žmm.
Time of hardening 3 days
7 days
28 days
15.7
23.0
44.7
methods given in IS: 4031-1988 w9x. The strength development in LHSR cements was evaluated with DTA ŽStanton Red Croft, UK. and X-ray diffraction ŽPhilips, Holland.. The sulfate resistance of LHSR cement was checked as per procedure laid down in IS: 12330-1988 w10x. According to test, a mixture of LHSR cement and natural gypsum was prepared in such a way that the total SO 3 content was 7.0% by mass. The granulometry of natural gypsum was maintained as 100% passing 150 m IS sieve, at least 95% passing 75 m sieve and at least 75% passing 45 m IS sieve, respectively. Bars of size 250 mm= 25 mm= 25 mm were cast using cement Žcontaining gypsum. and sand in the proportion 1:2.75 at WrC 0.485. The bars were demoulded after 24 h of their casting and then immersed in the water horizontally. The average expansion of three bars was recorded at 14 days.
0.8
higher concentration of SO42y ions in aqueous media containing high alumina. To overcome this problem, number of chemical retarders such as borax, tartaric acid, sugar, polyphosphates, citrate, etc. were tested to prolong setting time of cement. Two retarders namely borax and tartaric acid were found effective to give satisfactory setting times desired by the standard. The retarder concentration beyond 0.2% was avoided to cause any detrimental affect on the strength development of LHSR cements. It is interesting to note that compressive strength of LHSR cements increased appreciably with the progress in hydration of cements. It can be seen that on retardation, the cements do not show any fall in the strength,
3. Results and discussion 3.1. Properties of low heat sulfate-resistant cement The physical properties of optimum mixes of LHSR cements produced by blending granulated blast furnace slag ŽGBFS. duly activated with calcium sulfate hemihydrate and anhydrite in presence of portland cement clinker are reported in Table 3. It can be seen that cements set fast on addition of water. The fast setting of LHSR cement may be ascribed to the quick setting of calcium sulfate hemihydrate on account of much
Fig. 1. Differential thermograms of LHSR cement Žmix C. hydrated for different periods of hardening.
184
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
rather strength values are enhanced. The strength properties of LHSR cements ‘C’ and ‘D’ are better than the cement ‘E’ listed in Table 3. The LHSR cements have been found sound as their cold expansion was much below the maximum specified value of 5.0 mm. The LHSR cements demonstrate by documentation that it compared fairly well with the traditional supersulfated cement produced by blending the slag with anhydrite and portland cement. The results confirm that LHSR cement can be produced by activating the slag with CaSO4 ⭈ 1r2 H 2 O in stead of CaSO4 Žanhydrite.. The properties of LHSR cement produced by substituting GBFS with 10% Žby mass. phosphatic slag are reported in Table 4. Data show that LHSR cement complied with the requirements laid down in IS: 69091990 w11x. No detrimental affect was noticed on the strength development of cement when GBFS was replaced with 10.0% of the phosphatic slag. The findings are quite encouraging and may be applied to other metallurgical slags produced from Fe Mn, SiMn, copper and nickel industries. The hydration products formed during the hardening of LHSR cements have been identified with the help of DTA and XRD. DTA of LHSR cements namely ‘C’ and ‘D’ are shown in Figs. 1 and 2, respectively. In case of cement ‘C’ ŽFig. 1., the endotherms formed at 100,
Fig. 2. Differential thermograms of LHSR cement Žmix D. hydrated for different periods of hardening.
125, 150, 220᎐230, 640᎐830 ⬚C and the exotherms at 890 and 920 ⬚C may be attributed to the decomposition of gel water, ettringite, dehydration of calcium sulfate hemihydrate, C 4 AH 13 , CSHŽI. Žtobermorite. and devitrification of slag, respectively. The intensity of ettringite endotherms at 125 ⬚C increased with the depletion of calcium sulfate hemihydrate peaks at 150 ⬚C. Similarly, CSHŽI. endotherms at 640᎐830 ⬚C are enhanced with the increase in curing period. The appearance of endotherms at 490 ⬚C at 3 days may be due to decomposition of CaŽOH. 2 .
Fig. 3. XRD patterns of hydrated cement Žmix C. for different periods of hardening.
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
185
Fig. 4. XRD patterns of hydrated cement Žmix D. for different periods of hardening.
DTA of cement ‘D’ ŽFig. 2., shows development of endotherms at 150, 180, 230, 500, 700᎐800 and exotherms at 845᎐920 ⬚C which may be assigned to the decomposition of ettringite, dehydration of calcium sulfate hemihydrate, C 4 AH 13 , CaŽOH.. 2 , appearance of CSHŽI. and devitrification of slag, respectively. An increase in intensity of ettringite and CSHŽI. endotherms with the enhancement in hydration was significant. No CaŽOH.. 2 peak was detected at 28 days. DTA data thus confirms that formation of ettringite, CSHŽI. and C 4 AH 13 are essentially responsible for the strength of LHSR cements. The XRD patterns of LHSR cements ‘C’ and ‘D’ are plotted in Figs. 3 and 4, respectively. It can be seen that major peaks are ettringite, CSHŽI. and C 4 AH 13 .The intensity of ettringite and CSHŽI. peaks increased with
the increase in curing period. However, the intensity of gypsum and CaŽOH. 2 reflections are reduced. No peak for Ca ŽOH. 2 was recorded. In essence, the XRD data corroborate the findings of DTA regarding formation of major hydration products. The heat of hydration of LHSR cements is reported in Table 5. It can be seen that the heat of hydration of cements is within the requirements of IS: 6909-1990 and hence can be recommended for use in mass concrete. The sulfate resistant test conducted for LHSR cements C and D showed the sulfate expansion values in the range 0.01᎐0.03% against the maximum specified value of 0.045%. Hence, the cement is sulfate resistant. The durability studies of LHSR cements in sulfate environment are in progress.
Table 5 Heat of hydration of LHSR cements Cement design
C D E IS: 6909-1990 Limits
Heat of dissolution Žcalrg.
Heat of Hydration ŽCalrg.
Unhydrated
Time of hardening
505.6 522.2 532.2
Time of hardening 3 days
7 days
28 days
3 days
7 days
28 days
529.8 549.3 570.0
539.2 559.2 575.4
555.8 576.8 586.4
24.2 27.1 37.8
33.6 37.0 43.4
50.5 54.6 64.2
᎐
Max. 60
Max. 70
186
M. Singh, M. Garg r Construction and Building Materials 16 (2002) 181᎐186
4. Conclusions The low heat sulfate resistant cement can be produced by the activation of slag with calcium sulfate hemihydrate formed at 150 ⬚C against the traditional use of anhydrite, i.e. hard burnt gypsum produced at 850 ⬚C. Thus, net saving of thermal energy can be achieved. The major phases responsible for strength development in LHSR cement have been identified as ettringite, CSHŽI. and C 4 AH 13 . The rapid setting of these cements can be overcome by the small addition of borax or tartaric acid retarders. The use of calcium sulfate hemihydrate is recommended for making LHSR cement.
Acknowledgements The authors are grateful to the Director, Central Building Research Institute, Roorkee for allowing publication of this paper. References w1x Dana DJ. Manual of Mineralogy and Petrography. 7th ed. New York: Wiley, 1989:443᎐448.
w2x Singh M. Portland slag cement as building material, Seminar on Portland Slag cement ᎏ Its Superior Characteristics and Suitability for All Civil Constructions and Mass Concrete Works, Bhubneshwar, 25th April, 1992, pp. 31᎐51. w3x Narang KC, Chopra SK. Studies on alkaline activation of BF, steel and alloy slags. Silicate Ind. 1983;9:175᎐182. w4x Diamon M. Mechanism and kinetics of slag cement hydration, 7th International Congress on Chemistry of Cement, Paris, vol. 1 ŽIII., June 1980, pp. 2r1᎐2r9. w5x Taneja CA, Singh M, Tehri SP, Raj T. Super sulfated cement from waste phosphogypsum, 12th International Conference on Silicate Industry and Silicate Science, Budapest, Hungary, June 1977, pp. 621᎐627. w6x Davidovits J. Geopolymers, processing and applications of high ultra temperature, inorganic matrix resin for cast composite structures, molds and tools for RPrC and metal industries, PECTEC 83, Society of Plastic Engineers, Anaheim, 1983, pp. 222᎐230. w7x Boehme O, Ulrick B. Investigations of the phosphatic slags. Silikattechnik 1987;38Ž2.:60᎐63. w8x Chopra SK, Lal K. Manufacture of super sulfated cement from the Indian slags, experimental work at C.B.R.I.. Indian Concrete J. 1961;35Ž4.:114᎐116. w9x IS: 4031-1988, Methods of physical test for hydraulic cement, Bureau of Indian Standards, New Delhi, 1988, p. 2. w10x IS: 12330-1988, Specification for sulfate resistant portland cement, Bureau of Indian Standards, New Delhi, 1988, p. 3. w11x IS: 6909-1990, Specification for super sulfated cement, Bureau of Indian Standards, New Delhi, 1990, p. 6.