Indian Patents. 215799:A NOVEL COMPOSITION FOR THE MANUFACTURE OF IMPROVED CORROSION RESISTANT PORTLAND POZZALONA CEMENT.

Title of Invention	A NOVEL COMPOSITION FOR THE MANUFACTURE OF IMPROVED CORROSION RESISTANT PORTLAND POZZALONA CEMENT.
Abstract	The present invention provides a process for the manufacturing of improved Portland pozzalona cement from the novel composition ,which comprises(a)organic inhibitors such as sodium citrate— 0.1 to 1% by weight of cement;inorganic inhibitors such as sodium nitrite— 0.1 to 1% by weight of cement; fly ash ---- 15 to 20% of cement; Portland cement— 80 to 85%.

Full Text	The present invention relates to a novel composition for the manufacture of improved corrosion resistant portland pozzolana cement cement made thereby . Portland pozzalona cements using the waste product namely fly ash obtained from thermal power stations, steel plants etc., are being used in most of the construction works without having satisfactory performance against corrosion especially in marine environments. By addition of suitable synergistic admixture to portland pozzalona cement (PPC) during the manufacture, the corrosion resistance property of cement is enhanced by several folds and hence this synergistic admixed PPC can be used in the construction industries situated in highly aggressive environments. This serves the dual purpose of disposal of waste product and utilisation of the same for durable construction even in severe corrosive environments. It is well known that the following factors mainly contribute to corrosion of steel reinforcement embedded in concrete viz. porosity, carbonation and chloride. Hitherto, it has been reported that the rate of carbonation of the different mix compositions increased in the sequence ordinary portland cement - portland fly ash cement - ordinary portland cement with fly ash - portland blast furnace slag cement - portland blast furnace slag cement with fly ash. Reference may be made to Gert Van Der Wegan and Jan Bijen; The influence of fly ash in concrete on the corrosion of prestressing steel, corrosion of reinforcement in concrete edited by C.L.Page, K.W.J.Treadway and P.B.Bamforth, published by Elservier Applied Science, London, 1990, pp 237-245. Hitherto it has been reported that the total chloride level at which corrosion commences become progressively lower with increasing proportion of fly ash. Reference may be made to 1. Thomas M.D.A., Chloride thresholds in marine concrete, Cement and Concrete Research, Vol.26, No.4, 1996, p.513-519. 2. Thomas M.D.A and Mathews J.D., Chloride penetration and reinforcement corrosion in fly ash concrete exposed to a marine environment, proceedings of Third C ANMET/ACI- International conference on performance of concrete in a marine environment editor V.M.Malhotra, American Concrete Institute SP - 162, pp.317-338. Hitherto it has been reported that the corrosion propagation period is shorter for concretes containing fly ash and slag than for ordinary portland cement concretes. Reference may be made to Arya.C., and Xu.Y. Effect of cement type in chloride binding and corrosion of steel in concrete, Cement and Concrete Research Vol.25, No.4, 1995 pp.893-902. Hitherto it has been reported that the corrosivity of the portland pozzolana cement is due to increased permeation of water and increased carbonation depth. Reference may be made to Omar-Saeed Baghabva. Al-Amoudi, Cement and Concrete Research, Vol.21, 1991. Hitherto it has been reported that portland pozzolana cement offers lesser protection to steel reinforcements when compared to ordinary portland cement. Studies on porosity have shown that portland pozzolona cement tends to make the mortar more porous. Reference may be made to Vasanthi Sundaram, N.S.Rengaswamy, S.Srinivasan and K.Balakrishnan, Evaluation of Indian Pozzalona cements for their corrosion resistance, Transactions of the SAEST, Vol.23, No.2-3, 1988, pp.273-277. The main object of the present invention is to provide a novel composition for the manufacture of corrosion resistant portland pozzalona cement, a process for the manufacturing of improved portland pozzalona cement and improved portland pozzalona cement made thereby, which obviates the drawbacks in the existing portland pozzalona cement. Accordingly the present invention provides a novel composition for the manufacture of improved corrosion resistant portland cement, which comprises: a) organic inhibitors such as sodium citrate — 0.1 to 1% by weight of cement; b) inorganic inhibitors such as sodium nitrite — 0.1 to 1% by weight of cement; c) fly ash — 15 to 20 % of cement, d) portland cement — 80 to 85 % . In an embodiment of the present invention, the ingredients used are in powder form of mesh size 200 microns. Accordingly the present invention provides a process for the manufacturing of improved portland pozzalona cement from the novel composition of the present invention, which comprises blending the novel composition by known methods to obtain improved corrosion resistant portland pozzalona cement. Accordingly the present invention provides improved corrosion resistant portland pozzalona cement manufactured using the novel composition and process as described above. The present invention provides for the manufacture of a corrosion resistant portland pozzalona cement by addition of the novel composition having suitable organic and inorganic inhibitors in powder form at the cement factory during manufacture of portland pozzalona cement. Resistance of the cement against chloride corrosion of steel is thus enhanced by several fold. The novel composition of the present invention is not a mere admixture but a synergistic mixture have properties which are different from the mere aggregated properties of the individual ingredients. The process involves addition of tri-sodium citrate (0.1 to 1% by weight of cement) and sodium nitrite (0.1 to 1 % by weight of cement) in the powder form while blending fly ash with portland cement during the manufacture of portland pozzalona cement at the blending stage. This blended portland pozzalona cement can be identified as corrosion resistant portland pozzalona cement [CRPPC], which is able to offer higher corrosion resistance due to the corrosion inhibiting properties of the inhibitors added to it. The synergistic effect of the inhibitors is able to offer better passivation to the steel reinforcement embedded in such concrete in spite of the lower alkalinity of the portland pozzalona cement [PPC]. The following examples are given by way of illustrations and should not be construed to limit the scope of the present invention. EXAMPLE -1 ANODIC POLARIZATION STUDIES Under this example, the corrosion resistance of the cements has been compared by anodic polarisation of mild steel in aqueous extract. Test solutions have been prepared for PPC and PPC containing sodium nitrite and tri-sodium citrate inhibitors. At first, 100 grams of portland pozzalona cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. Then, 1000 ppm of chloride in the form of NaCl was added to the cement extract [Test solution 1]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The test specimen was anodically polarised by applying a current density of 290 u,A/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 1 are given in Table -1. Then, 100 grams of portland pozzalona cement was taken in a steel pan. 0.1 % by weight of cement of sodium nitrite and tri-sodium citrate inhibitors were taken and they were thoroughly mixed with portland pozzalona cement. Then this cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. 1000 ppm of chloride in the form of NaCl was added to the cement extract. [Test solution 2]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The test specimen was anodically polarised by applying a current density of 290 µA/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 2 are also given in Table -1. Table -1: Results on anodic polarisation studies (Table Removed) From the experimental results, it can be seen that the potential of steel in the test solution 1 was raised to oxygen evolution potential and immediately fell back. This indicates the break down of passive film on the steel by chloride in test solution 1. Where as in the case of test solution 2, the potential of steel raises above the oxygen evolution potential and it remains steady throughout the test period at that potential. This indicates the passive state of the steel in test solution 2 even in the presence of 1,000 ppm of chloride. The visual observations on the steel specimens revealed that severe rust spots were observed on the steel exposed in the test solution 1, where as, bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2. EXAMPLE -2 PEAK POTENTIAL STUDIES Under this example, the corrosion resistance of the cements has been compared by peak potential of mild steel in aqueous extract. Test solution 1 was prepared as described in example 1. For this experiment, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The open circuit potential of the test specimen was measured with reference to saturated calomel electrode (SCE) for 60 minutes and the peak potential value of the open circuit potential was noted. Later this peak potential value was maintained constant by means of a Wenking Potentiostat (Model 70 TSI) and the change in current was monitored for 60 minutes. The results obtained on the test solution 1 are given in Table - 2. Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The open circuit potential of the test specimen was measured with reference to saturated calomel electrode (SCE) for 60 minutes and the peak potential value of the open circuit potential was noted. Later this peak potential value was maintained constant by means of a Wenking Potentiostat (Model 70 TSI) and the change in current, if any, was monitored for 60 minutes. The results obtained on the test solution 2 are given in Table - 2. Table - 2: Results on peak potential studies (Table Removed) From the experimental results, it can be seen that the steel immersed in test solution 2 is showing a very low current where as the steel immersed in the test solution 1 is showing a very high current. This indicates the break down of passive film by chloride in test solution 1. The visual observations on the steel specimens revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2. EXAMPLE -3 POLARISATION RESISTANCE STUDIES Under this example, the corrosion resistance of the cements has been compared by polarisation resistance of steel in aqueous extract. Test solution 1 was prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. The mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The polarisation resistance of steel in the test solution 1 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 1 are given in Table - 3. Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The polarisation resistance of steel in the test solution 2 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 2 are given in Table - 3. Table - 3: Results on polarisation resistance studies (Table Removed) From the experimental results it can be seen that the polarisation resistance of steel immersed in test solution 2 is 31.554 K ohm cm2, which is about five times higher than the polarisation resistance value of steel immersed in test solution 1. This indicates the high corrosion resistance property of test solution 2. The visual observations on the steel specimens also revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2. EXAMPLE -4 IMPEDANCE STUDIES Under this example, the corrosion resistance of the cements has been compared by impedance behaviour of steel in aqueous extract. Test solution 1 was prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. The mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The impedance behaviour of steel in the test solution 1 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 1 are given in Table -4. Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The impedance behaviour of steel in the test solution 2 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 2 are given in Table -4. Table - 4: Results on impedance studies (Table Removed) From the experimental results it can be seen that the impedance of steel in test solution 2 is 49.377 K ohm cm2, which is higher than the impedance of steel in test solution 1 by about 14 times indicative of high corrosion resistance property of test solution 2. The visual observations on the steel specimens also revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2. EXAMPLE - 5 WEIGHT LOSS STUDIES Under this example, the corrosion resistance of the cements has been compared by means of corrosion rate of steel exposed in aqueous extract. Test solutions 1 and 2 were prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Mirror polished and degreased mild steel specimens of size 25 x 50 mm was accurately weighed and then exposed in the respective test solutions for 240 days. At the end of the test period, the specimens have been removed from the test solutions , de-rusted and re-weighed to assess the weight loss due to corrosion in mm per year. From the weight loss values the corrosion rate has been calculated by using the formula, 87.6 x weight loss (mg) Corrosion rate (mmpy) = Area (cm2) x Time (hrs) x Density The results obtained by this method are given in Table -5. Table - 5: Results on weight loss studies (Table Removed) From the weight loss studies, it can be seen that the corrosion rate is several times lower in test solution 2 than in test solution 1. The visual observations on the steel specimens also reveal that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2. EXAMPLE -6 ANODIC POLARIZATION STUDIES [for higher concentration of inhibitors] Under this example, the corrosion resistance of the cements has been compared by anodic polarisation of mild steel in aqueous extract. Test solutions have been prepared for PPC and PPC containing sodium nitrite and tri-sodium citrate inhibitors. Test solution 1 was prepared as described in example 1. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The test specimen was anodically polarised by applying a current density of 290 µA/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI1280 electrochemistry system (Solartron UK). The results obtained on this test solution 1 are given in Table - 6. Then, 100 grams of portland pozzalona cement was taken in a steel pan. 0.5 % by weight of cement of sodium nitrite and tri-sodium citrate inhibitors were taken and they were thoroughly mixed with portland pozzalona cement. Then this cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. 1000 ppm of chloride in the form of NaCl was added to the cement extract.[Test solution 3]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 3. The test specimen was anodically polarised by applying a current density of 290 u.A/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 3 are also given in Table - 6. Table - 6: Results on anodic polarisation studies (Table Removed) From the experimental results, it can be seen that the potential of steel in the test solution 1 was raised to oxygen evolution potential and immediately fell back. This indicates the break down of passive film on the steel by chloride in test solution 1. Where as in the case of test solution 3, the potential of steel raises above the oxygen evolution potential and it remains steady throughout the test period at that potential. This indicates the passive state of the steel in test solution 3 even in the presence of 1,000 ppm of chloride. The visual observations on the steel specimens revealed that severe rust spots were observed on the steel exposed in the test solution 1, where as, bright surface without any rust spot was observed on the steel specimen immersed in the test solutions. The main advantages of the present invention are 1. The process involves a simple step of adding inhibitors during manufacturing of portland pozzalona cement. 2. The added chemicals are in powder form and can be mixed at the factory itself, while blending fly ash with portland cement. 3. The durability factor against corrosion of steel reinforcement is increased by several times due to excellent corrosion resistance property of this product even in severe environment. 4. This development will lead to large scale utilization of waste by product viz. Fly ash obtained from different thermal power stations. 5. The corrosion resistant portland pozzalona cement is able to with stand 1000 ppm of chloride in the aggressive test known as anodic polarisation test. 6. The corrosion resistant portland pozzalona cement is able to with stand 10,000 ppm of chloride under peak potential technique. 7. The behaviour of CRPPC reveals that it is able to perform better impedance behaviour than PPC even in the presence of 10,000 ppm of chloride. 8. The polarization resistance of CRPPC is about 5 times higher than the PPC even in the presence of 10,000 ppm of chloride. 9. The weight loss studies reveal that CRPPC is showing about 6 times lower corrosion rate than PPC. We Claim: 1. A novel composition for the manufacture of improved corrosion resistant Portland pozzalona cement, which comprises: a. organic inhibitors such as sodium citrate : 0.1 to 1% by weight of cement; b. inorganic inhibitors such as sodium nitrite : 0.1 to 1% by weight of cement; c. fly ash : 15 to 20% of cement; d. Portland cement : 80 to 85%. 2. A novel composition as claimed in claim 1,wherein the ingredients used are in powder form of mesh size 200 micron. 4, A novel composition for the manufacture of improved corrosion resistant Portland pozzalona cement substantially as herein described with reference to the examples.

Full Text

The present invention relates to a novel composition for the manufacture of improved corrosion resistant portland pozzolana cement
cement made thereby .
Portland pozzalona cements using the waste product namely fly ash obtained from thermal power stations, steel plants etc., are being used in most of the construction works without having satisfactory performance against corrosion especially in marine environments. By addition of suitable synergistic admixture to portland pozzalona cement (PPC) during the manufacture, the corrosion resistance property of cement is enhanced by several folds and hence this synergistic admixed PPC can be used in the construction industries situated in highly aggressive environments. This serves the dual purpose of disposal of waste product and utilisation of the same for durable construction even in severe corrosive environments.
It is well known that the following factors mainly contribute to corrosion of steel reinforcement embedded in concrete viz. porosity, carbonation and chloride.
Hitherto, it has been reported that the rate of carbonation of the different mix compositions increased in the sequence ordinary portland cement - portland fly ash cement - ordinary portland cement with fly ash - portland blast furnace slag cement - portland blast furnace slag cement with fly ash. Reference may be made to Gert Van Der Wegan and Jan Bijen; The influence of fly ash in concrete on the corrosion of prestressing steel, corrosion of reinforcement in concrete edited by C.L.Page, K.W.J.Treadway and P.B.Bamforth, published by Elservier Applied Science, London, 1990, pp 237-245.
Hitherto it has been reported that the total chloride level at which corrosion commences become progressively lower with increasing proportion of

fly ash. Reference may be made to 1. Thomas M.D.A., Chloride thresholds in marine concrete, Cement and Concrete Research, Vol.26, No.4, 1996, p.513-519. 2. Thomas M.D.A and Mathews J.D., Chloride penetration and reinforcement corrosion in fly ash concrete exposed to a marine environment, proceedings of Third C ANMET/ACI- International conference on performance of concrete in a marine environment editor V.M.Malhotra, American Concrete Institute SP - 162, pp.317-338.
Hitherto it has been reported that the corrosion propagation period is shorter for concretes containing fly ash and slag than for ordinary portland cement concretes. Reference may be made to Arya.C., and Xu.Y. Effect of cement type in chloride binding and corrosion of steel in concrete, Cement and Concrete Research Vol.25, No.4, 1995 pp.893-902.
Hitherto it has been reported that the corrosivity of the portland pozzolana cement is due to increased permeation of water and increased carbonation depth. Reference may be made to Omar-Saeed Baghabva. Al-Amoudi, Cement and Concrete Research, Vol.21, 1991.
Hitherto it has been reported that portland pozzolana cement offers lesser protection to steel reinforcements when compared to ordinary portland cement. Studies on porosity have shown that portland pozzolona cement tends to make the mortar more porous. Reference may be made to Vasanthi Sundaram, N.S.Rengaswamy, S.Srinivasan and K.Balakrishnan, Evaluation of Indian Pozzalona cements for their corrosion resistance, Transactions of the SAEST, Vol.23, No.2-3, 1988, pp.273-277.
The main object of the present invention is to provide a novel composition for the manufacture of corrosion resistant portland pozzalona cement, a process for the manufacturing of improved portland pozzalona cement and improved portland pozzalona cement made thereby, which obviates the drawbacks in the existing portland pozzalona cement.

Accordingly the present invention provides a novel composition for the manufacture of improved corrosion resistant portland cement, which comprises:
a) organic inhibitors such as sodium citrate — 0.1 to 1% by weight of cement;
b) inorganic inhibitors such as sodium nitrite — 0.1 to 1% by weight of cement;
c) fly ash — 15 to 20 % of cement,
d) portland cement — 80 to 85 % .
In an embodiment of the present invention, the ingredients used are in powder form of mesh size 200 microns.
Accordingly the present invention provides a process for the manufacturing of improved portland pozzalona cement from the novel composition of the present invention, which comprises blending the novel composition by known methods to obtain improved corrosion resistant portland pozzalona cement.
Accordingly the present invention provides improved corrosion resistant portland pozzalona cement manufactured using the novel composition and process as described above.
The present invention provides for the manufacture of a corrosion resistant portland pozzalona cement by addition of the novel composition having suitable organic and inorganic inhibitors in powder form at the cement factory during manufacture of portland pozzalona cement. Resistance of the cement against chloride corrosion of steel is thus enhanced by several fold.
The novel composition of the present invention is not a mere admixture but a synergistic mixture have properties which are different from the mere aggregated properties of the individual ingredients.
The process involves addition of tri-sodium citrate (0.1 to 1% by weight of cement) and sodium nitrite (0.1 to 1 % by weight of cement) in the powder form while blending fly ash with portland cement during the manufacture of portland pozzalona cement at the blending stage.
This blended portland pozzalona cement can be identified as corrosion resistant portland pozzalona cement [CRPPC], which is able to offer higher corrosion resistance due to the corrosion inhibiting properties of the inhibitors

added to it. The synergistic effect of the inhibitors is able to offer better passivation to the steel reinforcement embedded in such concrete in spite of the lower alkalinity of the portland pozzalona cement [PPC].
The following examples are given by way of illustrations and should not be construed to limit the scope of the present invention.
EXAMPLE -1 ANODIC POLARIZATION STUDIES
Under this example, the corrosion resistance of the cements has been compared by anodic polarisation of mild steel in aqueous extract. Test solutions have been prepared for PPC and PPC containing sodium nitrite and tri-sodium citrate inhibitors. At first, 100 grams of portland pozzalona cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. Then, 1000 ppm of chloride in the form of NaCl was added to the cement extract [Test solution 1]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The test specimen was anodically polarised by applying a current density of 290 u,A/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 1 are given in Table -1.
Then, 100 grams of portland pozzalona cement was taken in a steel pan. 0.1 % by weight of cement of sodium nitrite and tri-sodium citrate inhibitors were taken and they were thoroughly mixed with portland pozzalona cement. Then this cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. 1000 ppm of chloride in the form of NaCl was added to the cement extract. [Test solution 2]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The test specimen was anodically polarised by applying a current density of 290 µA/cm2 using a

platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 2 are also given in Table -1. Table -1: Results on anodic polarisation studies

(Table Removed)
From the experimental results, it can be seen that the potential of steel in the test solution 1 was raised to oxygen evolution potential and immediately fell back. This indicates the break down of passive film on the steel by chloride in test solution 1. Where as in the case of test solution 2, the potential of steel raises above the oxygen evolution potential and it remains steady throughout the test period at that potential. This indicates the passive state of the steel in test solution 2 even in the presence of 1,000 ppm of chloride.
The visual observations on the steel specimens revealed that severe rust spots were observed on the steel exposed in the test solution 1, where as, bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2.
EXAMPLE -2 PEAK POTENTIAL STUDIES
Under this example, the corrosion resistance of the cements has been compared by peak potential of mild steel in aqueous extract. Test solution 1 was prepared as described in example 1. For this experiment, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The open circuit potential of the test specimen was measured with reference to saturated calomel electrode (SCE) for 60 minutes and the peak potential value of the open circuit potential was noted. Later this

peak potential value was maintained constant by means of a Wenking Potentiostat (Model 70 TSI) and the change in current was monitored for 60 minutes. The results obtained on the test solution 1 are given in Table - 2.
Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The open circuit potential of the test specimen was measured with reference to saturated calomel electrode (SCE) for 60 minutes and the peak potential value of the open circuit potential was noted. Later this peak potential value was maintained constant by means of a Wenking Potentiostat (Model 70 TSI) and the change in current, if any, was monitored for 60 minutes. The results obtained on the test solution 2 are given in Table - 2.
Table - 2: Results on peak potential studies

(Table Removed)
From the experimental results, it can be seen that the steel immersed in test solution 2 is showing a very low current where as the steel immersed in the test solution 1 is showing a very high current. This indicates the break down of passive film by chloride in test solution 1.
The visual observations on the steel specimens revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2.

EXAMPLE -3 POLARISATION RESISTANCE STUDIES
Under this example, the corrosion resistance of the cements has been compared by polarisation resistance of steel in aqueous extract. Test solution 1 was prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. The mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The polarisation resistance of steel in the test solution 1 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 1 are given in Table - 3.
Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The polarisation resistance of steel in the test solution 2 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 2 are given in Table - 3.
Table - 3: Results on polarisation resistance studies

(Table Removed)
From the experimental results it can be seen that the polarisation resistance of steel immersed in test solution 2 is 31.554 K ohm cm2, which is about five times higher than the polarisation resistance value of steel immersed in test solution 1. This indicates the high corrosion resistance property of test solution 2.
The visual observations on the steel specimens also revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface

without any rust spot was observed on the steel specimen immersed in the test solution 2.
EXAMPLE -4 IMPEDANCE STUDIES
Under this example, the corrosion resistance of the cements has been compared by impedance behaviour of steel in aqueous extract. Test solution 1 was prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. The mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The impedance behaviour of steel in the test solution 1 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 1 are given in Table -4.
Similarly, test solution 2 was prepared as described in example 1. Here again 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Then the mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 2. The impedance behaviour of steel in the test solution 2 has been found out using SI 1280 electrochemistry system (Solartron UK). The results obtained on the test solution 2 are given in Table -4.
Table - 4: Results on impedance studies

(Table Removed)
From the experimental results it can be seen that the impedance of steel in test solution 2 is 49.377 K ohm cm2, which is higher than the impedance of steel in test solution 1 by about 14 times indicative of high corrosion resistance property of test solution 2.

The visual observations on the steel specimens also revealed that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2.
EXAMPLE - 5 WEIGHT LOSS STUDIES
Under this example, the corrosion resistance of the cements has been compared by means of corrosion rate of steel exposed in aqueous extract. Test solutions 1 and 2 were prepared as described in example 1. Then, 10.000 ppm of chloride in the form of NaCl was added to the cement extracts. Mirror polished and degreased mild steel specimens of size 25 x 50 mm was accurately weighed and then exposed in the respective test solutions for 240 days. At the end of the test period, the specimens have been removed from the test solutions , de-rusted and re-weighed to assess the weight loss due to corrosion in mm per year. From the weight loss values the corrosion rate has been calculated by using the formula,
87.6 x weight loss (mg)
Corrosion rate (mmpy) =
Area (cm2) x Time (hrs) x Density
The results obtained by this method are given in Table -5. Table - 5: Results on weight loss studies

(Table Removed)
From the weight loss studies, it can be seen that the corrosion rate is several times lower in test solution 2 than in test solution 1.
The visual observations on the steel specimens also reveal that rust spots were observed on the steel exposed in test solution 1 where as bright surface without any rust spot was observed on the steel specimen immersed in the test solution 2.

EXAMPLE -6
ANODIC POLARIZATION STUDIES [for higher concentration of inhibitors]
Under this example, the corrosion resistance of the cements has been compared by anodic polarisation of mild steel in aqueous extract. Test solutions have been prepared for PPC and PPC containing sodium nitrite and tri-sodium citrate inhibitors. Test solution 1 was prepared as described in example 1. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 1. The test specimen was anodically polarised by applying a current density of 290 µA/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI1280 electrochemistry system (Solartron UK). The results obtained on this test solution 1 are given in Table - 6.
Then, 100 grams of portland pozzalona cement was taken in a steel pan. 0.5 % by weight of cement of sodium nitrite and tri-sodium citrate inhibitors were taken and they were thoroughly mixed with portland pozzalona cement. Then this cement was shaken with 100 cc of distilled water in a Microid flask shaker for one hour. The extract was then filtered through No.l Wattman filter paper. 1000 ppm of chloride in the form of NaCl was added to the cement extract.[Test solution 3]. Mild steel test specimen of size 6 mm diameter and 20 mm height was polished, degreased and immersed in this test solution 3. The test specimen was anodically polarised by applying a current density of 290 u.A/cm2 using a platinum electrode as cathode. The variation in potential with time was measured with reference to saturated calomel electrode (SCE). This variation in potential was monitored for five minutes using SI 1280 electrochemistry system (Solartron UK). The results obtained on this test solution 3 are also given in Table - 6.

Table - 6: Results on anodic polarisation studies

(Table Removed)
From the experimental results, it can be seen that the potential of steel in the test solution 1 was raised to oxygen evolution potential and immediately fell back. This indicates the break down of passive film on the steel by chloride in test solution 1. Where as in the case of test solution 3, the potential of steel raises above the oxygen evolution potential and it remains steady throughout the test period at that potential. This indicates the passive state of the steel in test solution 3 even in the presence of 1,000 ppm of chloride.
The visual observations on the steel specimens revealed that severe rust spots were observed on the steel exposed in the test solution 1, where as, bright surface without any rust spot was observed on the steel specimen immersed in the test solutions.

The main advantages of the present invention are
1. The process involves a simple step of adding inhibitors during manufacturing
of portland pozzalona cement.
2. The added chemicals are in powder form and can be mixed at the factory
itself, while blending fly ash with portland cement.
3. The durability factor against corrosion of steel reinforcement is increased by
several times due to excellent corrosion resistance property of this product
even in severe environment.
4. This development will lead to large scale utilization of waste by product viz.
Fly ash obtained from different thermal power stations.
5. The corrosion resistant portland pozzalona cement is able to with stand 1000
ppm of chloride in the aggressive test known as anodic polarisation test.
6. The corrosion resistant portland pozzalona cement is able to with stand 10,000
ppm of chloride under peak potential technique.
7. The behaviour of CRPPC reveals that it is able to perform better impedance
behaviour than PPC even in the presence of 10,000 ppm of chloride.
8. The polarization resistance of CRPPC is about 5 times higher than the PPC
even in the presence of 10,000 ppm of chloride.
9. The weight loss studies reveal that CRPPC is showing about 6 times lower
corrosion rate than PPC.

We Claim:
1. A novel composition for the manufacture of improved corrosion resistant
Portland pozzalona cement, which comprises:
a. organic inhibitors such as sodium citrate : 0.1 to 1% by weight of cement;
b. inorganic inhibitors such as sodium nitrite : 0.1 to 1% by weight of cement;
c. fly ash : 15 to 20% of cement;
d. Portland cement : 80 to 85%.
2. A novel composition as claimed in claim 1,wherein the ingredients used
are in powder form of mesh size 200 micron.
4, A novel composition for the manufacture of improved corrosion resistant Portland pozzalona cement substantially as herein described with reference to the examples.

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Patent Number

215799

Indian Patent Application Number

1421/DEL/1999

PG Journal Number

12/2008

Publication Date

21-Mar-2008

Grant Date

03-Mar-2008

Date of Filing

27-Oct-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	SRINIVASAN MURALIDHARAN	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMIL NADU-630006, INDIA
2	SESHADRI SRINIVASAN	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMIL NADU-630006, INDIA
3	GOPALACHARI VENKATACHARI	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMIL NADU-630006, INDIA
4	NERUR SANKARANARAYANAN RENGASWAMY	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMIL NADU-630006, INDIA
5	KRISHNAN SARAVANAN	CENTRAL ELECTROCHEMICAL RESEARCH INSTITUTE, KARAIKUDI, TAMIL NADU-630006, INDIA

PCT International Classification Number

C04B 7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA