- Email: [email protected]
The influence of SiMn slag on chemical resistance of blended cement pastes
Construction and Building Materials 23 (2009) 1472–1475
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The influence of SiMn slag on chemical resistance of blended cement pastes Moisés Frías a,*, M. Isabel Sánchez de Rojas a, Cristina Rodríguez b a b
Eduardo Torroja Institute (CSIC), c/Serrano Galvache No. 4, 28033 Madrid, Spain Ferroatlántica, Ferroalloys Division, Bóo de Guarnizo Plant, Cantabria, Spain
a r t i c l e
i n f o
Article history: Received 13 February 2008 Received in revised form 25 June 2008 Accepted 25 June 2008 Available online 16 August 2008 Keywords: SiMn slag Blended cements Chemical resistance Physico-mechanical properties
a b s t r a c t During the last decades, industrial by-products and wastes recycling as complementary building materials is focusing a large number of researching studies, most of them dedicated to the cement and concrete production, studying technical, economical and environmental aspects. This paper presents an original contribution to this tendency, which consists on the possibility of recycling a SiMn slag from ferroalloys industry as a complementary construction material and its influence on the resistance of cement paste in different aggressive solutions. Different parameters, such as waste nature, additions, mechanical resistance, different aggressive solutions or morphological and microporosity changes were investigated. The results have showed that blended cement pastes elaborated with SiMn slag (5% and 15% additions) after 56 days of curing have a good resistance in some aggressive solutions, no losing weight and presenting an excellent resistance index compared to the reference matrix. Aggressive solutions presence do not alter elaborated pastes microporosity not minding if they are prepared with and without SiMn slag additions in the working conditions studied in this study. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction It is well known that technical, economical and mainly environmental benefits are obtained from using alternative construction materials [1–4]. Since the Kyoto Protocol entered into force on February 2005, 35 countries have the obligation of reducing their gaseous emissions between 2008 and 2012 in order to achieve a target of greenhouse effect gas emissions 8% reduction (CO2, methane, nitrous oxide, etc), including CO2 which represents the 80% of the total harmful gases. Construction is one of the most affected industrial sectors because of its relationship with cement and concrete industries. This an other environmental regulations, that increase their severity day by day, have make this industries do a great effort to reduce their pollution, that is mainly caused by the process of calcite decarbonation that leads to the formation of about 800 kg of CO2/ton of clinker. Looking for a reduction of atmospheric contamination, has been and is the cause of looking for new complementary and alternative building materials to substitute traditional ones, being this a priority research line [5,6]. The building sector by their characteristics has enough capacity to recycle large volumes of by-products and wastes generated in different industrial activities, like silica fume, fly ash or blast furnace and electric arc furnace slags [7,8].
* Corresponding author. Tel.: +34 91 30 20 440x220; fax: +34 91 30 20 700. E-mail address: [email protected] (M. Frías). 0950-0618/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2008.06.012
One of these industrial wastes is SiMn slag obtained during SiMn production, as an agglutination of the non profitable part of the raw materials and the additives that are added into ferroalloys production furnaces in order to make the casting achieve certain physical properties (fluxes as quartz or lime). During the casting, this slag is separated from the ferroalloy (SiMn) by density difference, is then poured on a slag bed, and once a day is transported from its bed to be classified, if necessary, and stored. SiMn slag is characterized by its high manganese content, compared with traditional slag (blast furnace slag) [9–11]. Recently, Frías et al. [12,13] reported investigations carried out with a Spanish SiMn slag, working on a detailed study of its basic and engineering properties when it is used as recycled material in blended cements manufacturing. This study stated the pozzolanic activity of this kind of slag (pozzolanic activity intermediate between silica fume and fly ash), its good rheological behaviour, its volume stability and a mechanical behaviour similar to the fly ashes one. These facts make it possible from the chemical and technical point of view to say that the use of SiMn slag as a pozzolanic material in blended cements is viable. In spite of the good quality of SiMn blended cement matrixes, no experimental studies have been found in bibliography about these matrixes durability under aggressive conditions. This aspect is very important because a large number of building materials (mortar, concrete) are exposed to very aggressive environments (sea water, salts, freez-thaw cycles). The current research objective is to study the influence of this new complementary building material on blended cement paste
1473
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
properties, paying special attention on SiMn slag content, chemical resistance, external damages and internal damage by means of the microporosity evolution.
15.0
Weight variation (gr)
REFERENCE PASTE
2. Experimental study 2.1. Preparing SiMn slag The sample was crushed and grounded in order to get an optimal fineness to be used in Portland cement manufacture. The final fineness obtained was 4,569 cm2/g (456.9 m2/kg), measured using the Blaine permeability method [14]. SiMn slag chemical and mineralogical composition is shown in Table 1. Further information about this data can be found in previous papers [12,13].
14.0 13.0
12.0 11.0
Ref. Water
Sea-water
NaCl
Na2SO4
10.0 0
10
20
30
40
50
60
Time (days) 15.0
Weight variations (gr)
SiMn 5%
2.2. Aggressive solutions The following aggressive solutions were used in this study: – – – –
Sodium sulphate 0.5 M Sodium chloride 0.5 M Artificial seawater according to ASTM-D1141 Reference water
14.0 13.0 12.0 11.0
Ref. water
Sea-water
NaCl
Na2SO4
10.0 0
10
20
30
40
50
60
Time (days)
2.3. Specimen manufacture 15.0
Prismatic specimens of 1 1 6 cm used in this study were manufactured and cured according to Koch–Steinegger method [15], a rapid method to evaluate the resistance of blended cement pastes against different aggressive solutions. The pastes studied were: Reference paste (Portland Cement Type I-42.5R) and blended pastes with 5% and 15% of SiMn slag additions.
Weight variations (gr)
SiMn 15%
2.4. Parameters
14.0
13.0
12.0
11.0
Ref. water
The parameters selected in order to evaluate the durability of blended pastes at 56 days of curing were:
Sea-water
NaCl
Na2SO4
40
50
10.0 0
10
20
30
60
Time (days)
– Weight variations – Flexural strength variations – Microporosity variations by means of MIP
Fig. 1. Weight variations with exposure time.
This fact shows that the incorporation of SiMn slag as building material has no negative influence on the external chemical resistance. 3. Results and discussion 3.2. Chemical resistance to aggressive agents 3.1. Weight variations of cement pastes One of the quickest ways to study the degradation process of cement matrixes in presence of aggressive agents is to apply the Koch–Steinegger method that knowing the flexural strengths after the test makes it possible to calculate the resistant index. From the data obtained and shown in Table 2, an important increase of flexural strength values was detected for all specimens immersed in aggressive solutions, mainly for the seawater and Na2SO4 ones, including the reference paste. The incorporation of this complementary building material (SiMn slag) shows lower flexural strengths than those obtained for reference ones. This
Cement matrixes with SiMn slags additions as complementary building materials did not show significant weight variations during the 56 days of exposure (Fig. 1). However, cement paste submitted to a seawater solution showed a gradual increase of weight along the curing time, may be due to the hydroscopic effect of NaCl (there are high contents of NaCl in the aggressive solution (24.5 g/l)), that retains water on the cement matrix surface. Visually, once the exposure time finished, specimens did not show any external degradation signs as it is shown in Figs. 2 and 3.
Table 1 SiMn slag chemical and mineralogical composition Oxides
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
MnO
TiO2
SO3
(%)
42.6
12.2
1.0
25.2
4.2
0.36
2.2
9.9
0.36
0.12
Main mineralogical compounds: akermanite, manganese oxides, larnite, quartz, dolomite and sulphides.
1474
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
Fig. 2. Aspect of cement pastes after 56 days of curing in reference water and seawater solutions.
strength decreases when slag content increases. This fact could be related to the increase of total porosity for the slag blended pastes as it is explained in the item 3.3. According to the Koch–Steinegger methodology the specimens are resistant to the sulphates (at 56 days of curing) when the relation (resistant index) between the flexural strength value of the specimen submitted to Na2SO4 solution and the flexural strength value of the same specimen conserved into reference water is equal or superior to 70% [Index = (flexural value into the Na2SO4 solution/flexural value into reference water) 100 P 70%]. Applying this index to all aggressive solutions, it is possible to note that the new cement matrixes elaborated with SiMn slag are resistant to these solutions (Table 2). All values are superior to 100% (value the reference water solution), except the blended cement with 15% of slag exposed to the NaCl solution one, that had a lower value (84%) but superior to 70%. These new matrixes cured under aggressive conditions strength increase is a good indicator of the no existence of internal damages inside the matrixes. 3.3. Pore structure evolution A detailed study of a possible negative influence of aggressive agents on the degradation process of cementing building materials has carried out by means of Hg porosimetry data. The total, capillary, and very fine pore porosity after 56 days of reaction for all
Fig. 3. Aspect of cement pastes after 56 days of curing in NaCl and Na2SO4 solutions.
Table 2 Resistant index at 56 days of curing Solutions/paste
Reference
SiMn (5%)
SiMn (15%)
Sea water NaCl Na2SO4
251% 116% 315%
170% 131% 186%
126% 84% 149%
pastes are shown in Fig. 4. At this age, all cementing matrixes show a similar total porosity in different solutions (Fig. 4a). The values observed for the reference paste were between 22% and 23%. For 5% SiMn slag cement pastes the values obtained were between 24.5% and 25.5% and for 15% SiMn pastes 25–28%. SiMn blended mixes show a greater total porosity than the OPC paste and the slag content has a direct effect on the total porosity. This same phenomenon is reported for other pozzolanic materials such as fly ash, slag and silica fume cement pastes [6] and metakaolin cement pastes [16–18]. The same evolution is observed for the capillary porosity (5–0.01 lm)(Fig. 4b), like in the case of total porosity, the capillary porosity increases with the SiMn slag content (5–15%) if compared with the reference paste. In the same way, there is no evidence of negative influence of the aggressive solutions on the capillary porosity, since data obtained was similar. The positive effect of the incorporation of SiMn slag in the elaboration of blended pastes is clearly observed with the data obtained from porous size less than 100A (Fig. 4c). A refinement
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
Total porosity (%)
30
PC
SiMn 5%
SiMn 15%
a) Total
25 20 15 10 5 0 Ref water
NaCl
Sea water
Na2S04
Solutions
1475
3. According to the resistance index proposed by Koch–Steinegger, all the blended pastes prepared are resistant to the aggressive solutions (values higher than that recommended by the Author of the 70%). In most cases, indexes reached values between 125% and 190%. In general, the highest index values were obtained for reference cement and a decrease of flexural strengths was detected with increasing slag content. 4. The incorporation of SiMn slag modifies substantially the porous structure of blended pastes, observing a refineness process for the lowest pore sizes (gel pores) that gets importance with slag addition increase. This refinement converts the new cement into more durable matrix than the reference one. No traces of a possible microporosity alteration due to the presence of aggressive agents were observed.
30
Partial porosity (%)
PC
SiMn 5%
SiMn 15%
b)5-0.01 um
25 20 15 10 5 0
Ref water
NaCl
Sea water
Na2S04
Solutions
From the results obtained in current research, it is important to highlight that after 56 days of exposure, the addition of SiMn slag as complementary building material (5% and 15%) for blended cements manufacturing show a good behaviour under very aggressive environments. From an engineering point of view, this improvement has a direct repercussion in structures close to the sea, like bridges or gypsum soils where the durability of structures plays an important role on the concrete performances. In spite of these satisfactory results at short terms, nowadays, further exposures are being carried out at longer terms in order to dispose of a more complete additional information.
1 Partial porosity (%)
PC
SiMn 5%
SiMn 15%
c) < 0.01 um
0.8 0.6 0.4 0.2 0 Ref water
NaCl
Sea water
Na2S04
Solutions Fig. 4. Evolution of the porosities with exposure time.
of pore size can be appreciated in blended matrixes, mainly with 15% of SiMn slag. Therefore, from the porosity data obtained is possible to note that the addition of SiMn slag as complementary building material to blended cement matrixes manufacturing modifies slightly the microporosity of pastes if compared to the reference ones, and produces a porous structure refinement process below 100A. However, there is no evidence of degradation due to the presence of different aggressive agents; data obtained about external (weight variation) and internal (flexural strength variation) damages is absolutely in agreement with this conclusion. 4. Conclusions From this research it can be concluded that: 1. After a visual observation, no superficial alteration was observed in any pastes into aggressive solutions. 2. SiMn blended cement pastes did not experiment significant weight variations when submitted to different aggressive solutions. The starting weight is kept nearly constant during the exposure time (56 days). Only pastes exposed to seawater solutions showed a slight weight gain at the end of test.
References [1] Singh M, Garg MDurability of cementing binders based on fly ash and other wastes. Constr Build Mater 2007;21(11):2016–21. [2] Sahmaran M, Erdem TK, Yaman IO. Sulfate resistance of plain and blended cements exposed to wetting-drying and heating-cooling environments. Constr Build Mater 2007;21(8):1771–8. [3] Pappu A, Saxena M, Asolekar SR. Solid wastes generation in India and their recycling potential in building materials. Build Environ 2006;42(6): 2311e2311–20e2320. [4] Agullo L, Aguado A, García T. Study of the use of paper manufacturing waste in plaster composite mixtures. Build Environ 2006;41:821–7. [5] Masazza F. Pozzolanic cements. Cem Concr Comp 1993;15(4):185–214. [6] Taylor HFW. Cement Chemistry. Thomas Telford Publishing, Thomas Telford Services Ltd; 1997. [7] Ramezanianpour AA, Malhotra VM. The effect of curing on the compressive strength, resistance to chloride-ion penetration and porosity of concretes incorporating slag or fly ash or silica fume. In: Malhotra VM, editor. Third CANMET/ACI international conference on durability of concrete; 1994. p. 739– 52. [8] Frías M, Sánchez de Rojas MI. Chemical assessment of the electric arc furnace slag as construction material: expansive compounds. Cem Concr Res 2004;34:1881–8. [9] Taneja CA, Tehri SP, Singh M. High manganese and alumina slag for cement manufacture. In: Septima, editor. Proceedings of the 7th international congress on the chemistry of cement, París; 1980. p. 48–51. [10] Pera J, Ambroise J, Chabannet M. Properties of blast furnace containing high amounts of manganese. Cem Concr Res 1999;29:171–7. [11] Pera J, Ambroise J. Properties of concrete incorporating slag from the ferroalloy industry. In: Malhotra VM, editor. Seventh CANMET/ACI international conference on fly ash, silica fume, slag and pozzolans in concrete, Madras; 2001. p. 665–79. [12] Frías M, Sánchez de Rojas MI, Santamaría J, Rodríguez C. Recycling of silicomanganese slag as pozzolanic material: Basic and engineering properties. Cem Concr Res 2006;36:487–91. [13] Frías M, Sánchez de Rojas MI, Menéndez I, Rodríguez C, García de Lomas M. Properties of SiMn slags as pozzolanic material in the manufacture of Portland cements. Mater Constr 2005;55(280):53–62. [14] European Standard EN 196-6. Methods of testing cement. Determination of fineness; 1989. [15] Koch A, Steinegger H. A rapid method for testing the resistance of cements to sulphate attack. Zement-Kalk-Gips 1960;7:317–24. [16] Frías M, Cabrera JG. Pore size distribution and degree of hydration of metakaolin cement pastes. Cem Concr Res 2000;30(4):561–9. [17] Frías M, Sánchez de Rojas MI. Influence of the metakaolin on porous structure of matrixes based in MK/cement. Mater Constr 2000;50(259):57–67. [18] Wild S, Khabit JM, Jones A. Relative strength, pozzolanic activity and cement hydration in superplasticised MK concrete. Cem Concr Res 1996;26(10): 1537–44.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
The influence of SiMn slag on chemical resistance of blended cement pastes Moisés Frías a,*, M. Isabel Sánchez de Rojas a, Cristina Rodríguez b a b
Eduardo Torroja Institute (CSIC), c/Serrano Galvache No. 4, 28033 Madrid, Spain Ferroatlántica, Ferroalloys Division, Bóo de Guarnizo Plant, Cantabria, Spain
a r t i c l e
i n f o
Article history: Received 13 February 2008 Received in revised form 25 June 2008 Accepted 25 June 2008 Available online 16 August 2008 Keywords: SiMn slag Blended cements Chemical resistance Physico-mechanical properties
a b s t r a c t During the last decades, industrial by-products and wastes recycling as complementary building materials is focusing a large number of researching studies, most of them dedicated to the cement and concrete production, studying technical, economical and environmental aspects. This paper presents an original contribution to this tendency, which consists on the possibility of recycling a SiMn slag from ferroalloys industry as a complementary construction material and its influence on the resistance of cement paste in different aggressive solutions. Different parameters, such as waste nature, additions, mechanical resistance, different aggressive solutions or morphological and microporosity changes were investigated. The results have showed that blended cement pastes elaborated with SiMn slag (5% and 15% additions) after 56 days of curing have a good resistance in some aggressive solutions, no losing weight and presenting an excellent resistance index compared to the reference matrix. Aggressive solutions presence do not alter elaborated pastes microporosity not minding if they are prepared with and without SiMn slag additions in the working conditions studied in this study. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction It is well known that technical, economical and mainly environmental benefits are obtained from using alternative construction materials [1–4]. Since the Kyoto Protocol entered into force on February 2005, 35 countries have the obligation of reducing their gaseous emissions between 2008 and 2012 in order to achieve a target of greenhouse effect gas emissions 8% reduction (CO2, methane, nitrous oxide, etc), including CO2 which represents the 80% of the total harmful gases. Construction is one of the most affected industrial sectors because of its relationship with cement and concrete industries. This an other environmental regulations, that increase their severity day by day, have make this industries do a great effort to reduce their pollution, that is mainly caused by the process of calcite decarbonation that leads to the formation of about 800 kg of CO2/ton of clinker. Looking for a reduction of atmospheric contamination, has been and is the cause of looking for new complementary and alternative building materials to substitute traditional ones, being this a priority research line [5,6]. The building sector by their characteristics has enough capacity to recycle large volumes of by-products and wastes generated in different industrial activities, like silica fume, fly ash or blast furnace and electric arc furnace slags [7,8].
* Corresponding author. Tel.: +34 91 30 20 440x220; fax: +34 91 30 20 700. E-mail address: [email protected] (M. Frías). 0950-0618/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2008.06.012
One of these industrial wastes is SiMn slag obtained during SiMn production, as an agglutination of the non profitable part of the raw materials and the additives that are added into ferroalloys production furnaces in order to make the casting achieve certain physical properties (fluxes as quartz or lime). During the casting, this slag is separated from the ferroalloy (SiMn) by density difference, is then poured on a slag bed, and once a day is transported from its bed to be classified, if necessary, and stored. SiMn slag is characterized by its high manganese content, compared with traditional slag (blast furnace slag) [9–11]. Recently, Frías et al. [12,13] reported investigations carried out with a Spanish SiMn slag, working on a detailed study of its basic and engineering properties when it is used as recycled material in blended cements manufacturing. This study stated the pozzolanic activity of this kind of slag (pozzolanic activity intermediate between silica fume and fly ash), its good rheological behaviour, its volume stability and a mechanical behaviour similar to the fly ashes one. These facts make it possible from the chemical and technical point of view to say that the use of SiMn slag as a pozzolanic material in blended cements is viable. In spite of the good quality of SiMn blended cement matrixes, no experimental studies have been found in bibliography about these matrixes durability under aggressive conditions. This aspect is very important because a large number of building materials (mortar, concrete) are exposed to very aggressive environments (sea water, salts, freez-thaw cycles). The current research objective is to study the influence of this new complementary building material on blended cement paste
1473
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
properties, paying special attention on SiMn slag content, chemical resistance, external damages and internal damage by means of the microporosity evolution.
15.0
Weight variation (gr)
REFERENCE PASTE
2. Experimental study 2.1. Preparing SiMn slag The sample was crushed and grounded in order to get an optimal fineness to be used in Portland cement manufacture. The final fineness obtained was 4,569 cm2/g (456.9 m2/kg), measured using the Blaine permeability method [14]. SiMn slag chemical and mineralogical composition is shown in Table 1. Further information about this data can be found in previous papers [12,13].
14.0 13.0
12.0 11.0
Ref. Water
Sea-water
NaCl
Na2SO4
10.0 0
10
20
30
40
50
60
Time (days) 15.0
Weight variations (gr)
SiMn 5%
2.2. Aggressive solutions The following aggressive solutions were used in this study: – – – –
Sodium sulphate 0.5 M Sodium chloride 0.5 M Artificial seawater according to ASTM-D1141 Reference water
14.0 13.0 12.0 11.0
Ref. water
Sea-water
NaCl
Na2SO4
10.0 0
10
20
30
40
50
60
Time (days)
2.3. Specimen manufacture 15.0
Prismatic specimens of 1 1 6 cm used in this study were manufactured and cured according to Koch–Steinegger method [15], a rapid method to evaluate the resistance of blended cement pastes against different aggressive solutions. The pastes studied were: Reference paste (Portland Cement Type I-42.5R) and blended pastes with 5% and 15% of SiMn slag additions.
Weight variations (gr)
SiMn 15%
2.4. Parameters
14.0
13.0
12.0
11.0
Ref. water
The parameters selected in order to evaluate the durability of blended pastes at 56 days of curing were:
Sea-water
NaCl
Na2SO4
40
50
10.0 0
10
20
30
60
Time (days)
– Weight variations – Flexural strength variations – Microporosity variations by means of MIP
Fig. 1. Weight variations with exposure time.
This fact shows that the incorporation of SiMn slag as building material has no negative influence on the external chemical resistance. 3. Results and discussion 3.2. Chemical resistance to aggressive agents 3.1. Weight variations of cement pastes One of the quickest ways to study the degradation process of cement matrixes in presence of aggressive agents is to apply the Koch–Steinegger method that knowing the flexural strengths after the test makes it possible to calculate the resistant index. From the data obtained and shown in Table 2, an important increase of flexural strength values was detected for all specimens immersed in aggressive solutions, mainly for the seawater and Na2SO4 ones, including the reference paste. The incorporation of this complementary building material (SiMn slag) shows lower flexural strengths than those obtained for reference ones. This
Cement matrixes with SiMn slags additions as complementary building materials did not show significant weight variations during the 56 days of exposure (Fig. 1). However, cement paste submitted to a seawater solution showed a gradual increase of weight along the curing time, may be due to the hydroscopic effect of NaCl (there are high contents of NaCl in the aggressive solution (24.5 g/l)), that retains water on the cement matrix surface. Visually, once the exposure time finished, specimens did not show any external degradation signs as it is shown in Figs. 2 and 3.
Table 1 SiMn slag chemical and mineralogical composition Oxides
SiO2
Al2O3
Fe2O3
CaO
MgO
Na2O
K2O
MnO
TiO2
SO3
(%)
42.6
12.2
1.0
25.2
4.2
0.36
2.2
9.9
0.36
0.12
Main mineralogical compounds: akermanite, manganese oxides, larnite, quartz, dolomite and sulphides.
1474
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
Fig. 2. Aspect of cement pastes after 56 days of curing in reference water and seawater solutions.
strength decreases when slag content increases. This fact could be related to the increase of total porosity for the slag blended pastes as it is explained in the item 3.3. According to the Koch–Steinegger methodology the specimens are resistant to the sulphates (at 56 days of curing) when the relation (resistant index) between the flexural strength value of the specimen submitted to Na2SO4 solution and the flexural strength value of the same specimen conserved into reference water is equal or superior to 70% [Index = (flexural value into the Na2SO4 solution/flexural value into reference water) 100 P 70%]. Applying this index to all aggressive solutions, it is possible to note that the new cement matrixes elaborated with SiMn slag are resistant to these solutions (Table 2). All values are superior to 100% (value the reference water solution), except the blended cement with 15% of slag exposed to the NaCl solution one, that had a lower value (84%) but superior to 70%. These new matrixes cured under aggressive conditions strength increase is a good indicator of the no existence of internal damages inside the matrixes. 3.3. Pore structure evolution A detailed study of a possible negative influence of aggressive agents on the degradation process of cementing building materials has carried out by means of Hg porosimetry data. The total, capillary, and very fine pore porosity after 56 days of reaction for all
Fig. 3. Aspect of cement pastes after 56 days of curing in NaCl and Na2SO4 solutions.
Table 2 Resistant index at 56 days of curing Solutions/paste
Reference
SiMn (5%)
SiMn (15%)
Sea water NaCl Na2SO4
251% 116% 315%
170% 131% 186%
126% 84% 149%
pastes are shown in Fig. 4. At this age, all cementing matrixes show a similar total porosity in different solutions (Fig. 4a). The values observed for the reference paste were between 22% and 23%. For 5% SiMn slag cement pastes the values obtained were between 24.5% and 25.5% and for 15% SiMn pastes 25–28%. SiMn blended mixes show a greater total porosity than the OPC paste and the slag content has a direct effect on the total porosity. This same phenomenon is reported for other pozzolanic materials such as fly ash, slag and silica fume cement pastes [6] and metakaolin cement pastes [16–18]. The same evolution is observed for the capillary porosity (5–0.01 lm)(Fig. 4b), like in the case of total porosity, the capillary porosity increases with the SiMn slag content (5–15%) if compared with the reference paste. In the same way, there is no evidence of negative influence of the aggressive solutions on the capillary porosity, since data obtained was similar. The positive effect of the incorporation of SiMn slag in the elaboration of blended pastes is clearly observed with the data obtained from porous size less than 100A (Fig. 4c). A refinement
M. Frías et al. / Construction and Building Materials 23 (2009) 1472–1475
Total porosity (%)
30
PC
SiMn 5%
SiMn 15%
a) Total
25 20 15 10 5 0 Ref water
NaCl
Sea water
Na2S04
Solutions
1475
3. According to the resistance index proposed by Koch–Steinegger, all the blended pastes prepared are resistant to the aggressive solutions (values higher than that recommended by the Author of the 70%). In most cases, indexes reached values between 125% and 190%. In general, the highest index values were obtained for reference cement and a decrease of flexural strengths was detected with increasing slag content. 4. The incorporation of SiMn slag modifies substantially the porous structure of blended pastes, observing a refineness process for the lowest pore sizes (gel pores) that gets importance with slag addition increase. This refinement converts the new cement into more durable matrix than the reference one. No traces of a possible microporosity alteration due to the presence of aggressive agents were observed.
30
Partial porosity (%)
PC
SiMn 5%
SiMn 15%
b)5-0.01 um
25 20 15 10 5 0
Ref water
NaCl
Sea water
Na2S04
Solutions
From the results obtained in current research, it is important to highlight that after 56 days of exposure, the addition of SiMn slag as complementary building material (5% and 15%) for blended cements manufacturing show a good behaviour under very aggressive environments. From an engineering point of view, this improvement has a direct repercussion in structures close to the sea, like bridges or gypsum soils where the durability of structures plays an important role on the concrete performances. In spite of these satisfactory results at short terms, nowadays, further exposures are being carried out at longer terms in order to dispose of a more complete additional information.
1 Partial porosity (%)
PC
SiMn 5%
SiMn 15%
c) < 0.01 um
0.8 0.6 0.4 0.2 0 Ref water
NaCl
Sea water
Na2S04
Solutions Fig. 4. Evolution of the porosities with exposure time.
of pore size can be appreciated in blended matrixes, mainly with 15% of SiMn slag. Therefore, from the porosity data obtained is possible to note that the addition of SiMn slag as complementary building material to blended cement matrixes manufacturing modifies slightly the microporosity of pastes if compared to the reference ones, and produces a porous structure refinement process below 100A. However, there is no evidence of degradation due to the presence of different aggressive agents; data obtained about external (weight variation) and internal (flexural strength variation) damages is absolutely in agreement with this conclusion. 4. Conclusions From this research it can be concluded that: 1. After a visual observation, no superficial alteration was observed in any pastes into aggressive solutions. 2. SiMn blended cement pastes did not experiment significant weight variations when submitted to different aggressive solutions. The starting weight is kept nearly constant during the exposure time (56 days). Only pastes exposed to seawater solutions showed a slight weight gain at the end of test.
References [1] Singh M, Garg MDurability of cementing binders based on fly ash and other wastes. Constr Build Mater 2007;21(11):2016–21. [2] Sahmaran M, Erdem TK, Yaman IO. Sulfate resistance of plain and blended cements exposed to wetting-drying and heating-cooling environments. Constr Build Mater 2007;21(8):1771–8. [3] Pappu A, Saxena M, Asolekar SR. Solid wastes generation in India and their recycling potential in building materials. Build Environ 2006;42(6): 2311e2311–20e2320. [4] Agullo L, Aguado A, García T. Study of the use of paper manufacturing waste in plaster composite mixtures. Build Environ 2006;41:821–7. [5] Masazza F. Pozzolanic cements. Cem Concr Comp 1993;15(4):185–214. [6] Taylor HFW. Cement Chemistry. Thomas Telford Publishing, Thomas Telford Services Ltd; 1997. [7] Ramezanianpour AA, Malhotra VM. The effect of curing on the compressive strength, resistance to chloride-ion penetration and porosity of concretes incorporating slag or fly ash or silica fume. In: Malhotra VM, editor. Third CANMET/ACI international conference on durability of concrete; 1994. p. 739– 52. [8] Frías M, Sánchez de Rojas MI. Chemical assessment of the electric arc furnace slag as construction material: expansive compounds. Cem Concr Res 2004;34:1881–8. [9] Taneja CA, Tehri SP, Singh M. High manganese and alumina slag for cement manufacture. In: Septima, editor. Proceedings of the 7th international congress on the chemistry of cement, París; 1980. p. 48–51. [10] Pera J, Ambroise J, Chabannet M. Properties of blast furnace containing high amounts of manganese. Cem Concr Res 1999;29:171–7. [11] Pera J, Ambroise J. Properties of concrete incorporating slag from the ferroalloy industry. In: Malhotra VM, editor. Seventh CANMET/ACI international conference on fly ash, silica fume, slag and pozzolans in concrete, Madras; 2001. p. 665–79. [12] Frías M, Sánchez de Rojas MI, Santamaría J, Rodríguez C. Recycling of silicomanganese slag as pozzolanic material: Basic and engineering properties. Cem Concr Res 2006;36:487–91. [13] Frías M, Sánchez de Rojas MI, Menéndez I, Rodríguez C, García de Lomas M. Properties of SiMn slags as pozzolanic material in the manufacture of Portland cements. Mater Constr 2005;55(280):53–62. [14] European Standard EN 196-6. Methods of testing cement. Determination of fineness; 1989. [15] Koch A, Steinegger H. A rapid method for testing the resistance of cements to sulphate attack. Zement-Kalk-Gips 1960;7:317–24. [16] Frías M, Cabrera JG. Pore size distribution and degree of hydration of metakaolin cement pastes. Cem Concr Res 2000;30(4):561–9. [17] Frías M, Sánchez de Rojas MI. Influence of the metakaolin on porous structure of matrixes based in MK/cement. Mater Constr 2000;50(259):57–67. [18] Wild S, Khabit JM, Jones A. Relative strength, pozzolanic activity and cement hydration in superplasticised MK concrete. Cem Concr Res 1996;26(10): 1537–44.