Abstract The effect of Sweileh sand (fine silica) additionto concrete mix on corrosion of steel in concrete was stud-ied. Concrete cylinders were prepared with different Sweilehsand additions in which steel reinforcements were embedded.Samples were immersed in chloride solutions for 216 days;potentials of steel were taken according to ASTM C-876.Corrosion rate was calculated using weight loss measure-ments. It was shown that Sweileh sand addition decreasedcorrosion rate by noticeable amounts. Potential of the rein-forcement increased as the addition of Sweileh sand hasincreased.
Concrete usually provides a good protection against corro-sion of the reinforcement. Unfortunately, the ingress of chlo-
S. Masadeh (B) · A. Al-Robaidi · N. AnagrehMaterials Engineering Department, Al-Balqa Applied University,Al-Salt, Jordane-mail: [email protected]
rides coming from deicing salts or marine atmosphere orcarbon dioxide activates corrosion by the destruction of thepassive layer produced by high alkalinity of concrete, or byreducing pH of concrete [1–5]. This action comes from thediffusion of oxygen, carbon dioxide, ions and moisture fromthe concrete/environment to the concrete/rebar interfaces tak-ing place through the pores, which result in the failure of thepassivation provided by the alkalinity of the cement to therebar [6,7]. Corrosion of steel in concrete can be minimizedby reducing permeability of concrete which is considered asthe main cause of deterioration [8]. The penetration of corro-sive ions such as chlorides and sulfates depends on concretepermeability and increases as water/cement ratio increases[9]. Another method of decreasing permeability of concreteis the use of fine silica or slag ash as a concrete mix [10].The steel rebar corrosion onset, the time interval before theattack starts and the rate by which it proceeds are depen-dent on factors influenced by the chemistry of cement, min-eral admixture additions and water to binder ratio, curingand environmental conditions [4,6,11–13]. The durabilityof concrete structures is a function of its composition, cur-ing, and environmental conditions. Cement-based concretematerials are prepared by ordinary Portland cement, sand,aggregates, and water. When fly ash, silica fume, micro sil-ica and super plasticizer are added, concrete can prove tobe excellent, because they provide greater compressive, ten-sile and flexural strength properties [14]. Their dense sur-faces, which often have very low permeability, make themextremely suitable to resist to aggressive chemical exposureor to the ingress of moisture. Jordan has huge quantities ofSweileh sand (fine silica), where Sweileh is the area in Jor-dan which is rich in this type of silica. Physical propertiesare listed in Table 1.
In this study, Sweileh sand was used as an additive toconcrete mix. The effect of such addition to concrete mix
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Table 1 Physical properties of Sweileh sand [15]
Property Value
SiO2 content, % 88.65
Bulk density, ρ (kg/m3) 830
Specific heat, C p (kJ/kg K) 0.710
Thermal conductivity, λ (W/m K) 0.2452
Heat transfer coefficient, h (W/m2 K) 4,000
Porosity, ε 0.374
Permeability, K (cm2) 2 × 10−7–1.8 × 10−6
Surface area per unit volume (m2/m3) 1.245×107–1.826×107
40 cm
5 cm
15 cm
(a) (b)
Fig. 1 Reinforced concrete cylinder design, a top view, and b section
on corrosion behavior of reinforced concrete in 3.5 % NaClsolution was studied.
2 Experimental
Six mixes of concrete were prepared to investigate the effectof Sweileh sand addition on corrosion of steel reinforcementin concrete. Steel reinforcements having 12 mm diameter
and 45 cm length were weighed after proper mechanicaland chemical cleaning (ethylene alcohol). One steel bar wasplaced at the center of each cylindrical mold having 15 cmdiameter and 40 cm length; steel bar was kept 5 cm away fromconcrete bottom; specimen design is shown in Fig. 1. Steelreinforcements outside concrete blocks were coated with coaltar epoxy to 5 cm depth in concrete. A copper wire was sol-dered to the end of the reinforcement prior to epoxy coatingfor use in potential measurements. Sweileh sand was added indifferent amounts (Table 2) to cement, aggregate, and water.After a proper mixing of all ingredients, (including Sweilehsand), the mix was cast in molds containing the steel rein-forcement, and then vibrated for 30 s to ensure good casting.24 h later, concrete blocks were removed from the moldsand kept in a curing room for 28 days. As curing was done,concrete blocks were removed into a container containing3.5 % NaCl solution. Concrete samples then immersed inthe solution.
2.1 Half-Cell Potential Method
The half-cell potential method has been widely used becauseof its simplicity and cost effectiveness [8,13]. This methodallows the evaluation of the probability of corrosion activitythrough the measurement of the potential difference betweena standard portable reference electrode and the reinforcingsteel. The data analysis guidelines described in ASTM C876-99 provide general principles for the evaluation of corro-sion probability of reinforcing steel in concrete structures. Acopper–copper sulfate electrode (CSE) was used to measurethe potential of the reinforcing steel. Daily potential mea-surements were conducted for 216 days according to ASTMC876 using a Cu/CuSO4 electrode (CSE). All of the experi-ments were performed under free corrosion potential and atambient temperature.
2.2 Corrosion Rate Calculation
As 216 days have passed, specimens were split open; steelbars were removed, brushed and cleaned by chemical mix as
follows: 1,000 ml hydrochloric acid, 20 g antimony trioxideand 50 g stannous chloride. Cleaning was performed at 25 ˚Cfor 25 minutes. Steel cleaning and weight loss analysis weredone according to ASTM G1-03 standard. The initial totalsurface area of the specimen and the mass lost during thetest were determined. The average corrosion rate may thenbe obtained as follows:
Corrosion rate = K × W/(A × T × D),
where K is a constant, T is the time of exposure in hours, Ais the area in cm2, W is the mass loss in grams, and D is thedensity (7.85) in g/cm3.
Corrosion rate was calculated and given in mm/y.
3 Results and Discussion
3.1 Half-Cell Potential of Reinforcing Steel
Half-cell potentials were measured on the reinforcing steelbars embedded in concrete with different Sweileh sand con-tent. Figure 2 shows the half-cell potential vs. time (averageof three steel reinforcing bars with same concrete mix andimmersion conditions). The potentials indicate that the rein-forcing steel bars had same potentials at the beginning ofimmersion (−110 to −135 mV) and after that, a differentdrop in potential was noticed. This drop was a function ofmix. Potential readings after 71 of mix no. 1 (with no Sweilehsand addition) were −350 mV with a probability of 95 % cor-rosion; after 100 days of immersion, potential of steel barsin all concrete samples dropped to more negative than −350mV except for mixes 5 and 6. Even after immersion for 216days, the potential of mix 6 was more positive than −240mV. This can be because this mix can significantly delay theingress of chlorides into the concrete/steel interface region.
Potential can be divided into three basic regions: the firstregion represents the potential of the reinforcement just afterthe immersion in chloride solution, the second represents the
Fig. 2 Potential of the reinforcements taken according to ASTM C876
drop in potential due to chloride ingress into concrete, andthe third region is the steady potential region. Potential ofreinforcements showed a slight drop just after immersion,and then a severe drop in potential, because the ingress ofchlorides into concrete to reach the concrete–steel interfaceis a function of time since it takes place by diffusion mech-anisms. Diffusion of chlorides into concrete is a function ofsome parameters regarding temperature, concentration gra-dient, diffusivity of chlorides into concrete, and this dependson permeability of concrete [15,16]. When Sweileh sand isadded to plain concrete, it fills the voids present between thecement particles and also between the cement particles andthe aggregates.
The difference in potential values of steel at the end oftest showed a drop in potential in the negative direction asSweileh sand content decreased. Mix1 represents the caseof no addition of Sweileh sand; in this case, the potentialof the reinforcement was more negative than −500 mV ver-sus CSE, but after the first addition of Sweileh sand to themix (mix 2) a noticeable change in potential was observed;the potential increased to 80 mV in the positive direction.Further addition of Sweileh sand yielded higher potentialsbetween −430 and −250 mV vs. CSE. This physical phe-nomenon is known as the filler effect. It reduces the porositywhich in turn reduces the permeability of chlorides in con-crete. There are a lot of studies concerning the effect of fineparticles addition on concrete permeability [17–22]. Perme-ability tests were not performed, but potential of steel barsgave acceptable information about its status; potential val-ues indicate the possibility of corrosion of the reinforcementwhich, in turn, is related to the amount of corrosive speciesentering to the steel concrete interface, which are chlorideions in this case.
3.2 Corrosion Rate
Figure 3 shows the corrosion rate of the reinforcements in sixdifferent concrete mixes; it is clear that corrosion rate was
Fig. 3 Corrosion rates of steel reinforcements with added Sweileh sand
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more than 0.127 mm/y for mix 1 and for mix 2 corrosionrate decreased to 0.123 mm/y. In general, as the content ofSweileh sand increased, corrosion rate decreased, this is inagreement with measured potential of the reinforcement dur-ing the test period. Since the decrease in corrosion rate canbe explained as a function of chloride ingress, then the fill-ing effect of Sweileh sand (Sweileh sand) makes retardationof chloride ingress into concrete to steel–concrete interface[23].
4 Conclusions
1. The use of fine materials (Sweileh sand) reduces theporosity of the concrete, thus increasing the electricalresistivity and reducing the water absorption due to lowerpermeability and then less diffusion of chloride ions.Thus, the corrosion rate of the reinforcement is reduced.
2. Partly, the replacement of aggregates with Sweileh sandup to about 50 % causes corrosion rate reduction of about∼50 %.
References
1. Lea, F.M.: The Chemistry of Cement and Concrete, 3rd edn.Edward Arnold, Great Britain (1970)
2. Gonzalez, J.A.; Molina, A.; Otero, E.: Lopez, W.: On the mecha-nism of steel corrosion in concrete: the role of oxygen diffusion,Mag. Concr. Res. 42–159, 23–27 (1990)
3. Wenger, F.; Galland, I.: EIS study of the protective properties ofrepair products. In: Proceedings of the Eurocorr’96; Session I: Cor-rosion in concrete. Nice: P. I OR 8-1 (1996)
4. Byfors, K.: Influence of silica fume and fly ash on chloride diffusionand pH values in cement paste. Cem. Concr. Res. 17, 115–130(1987)
5. Wheat, H.G.; Eliezer, Z.: Some electrochemical aspects on corro-sion of steel in concrete. Corros. NACE 41–11, 640–645 (1985)
7. Miyagava, T.: Durability design and repair of concrete structure:chloride corrosion of reinforcing steel and alkali-aggregate reac-tion. Mag. Concr. Res. 43–156, 155–170 (1991)
8. Seish, G.: Diffusion of ions through hardened cement pastes. Cem.Concr. Res., 11, 751 (1981)
9. Midgley, H.G.; Illston, J.M.: The penetration of chlorides into hard-ened cement. Cem. Concr. Res. 14, 546 (1984)
10. Al Asfar, J.J.; Al-Abdallat, Y.; Hamdan, M.A.: Theoretical Studyof Hydrogen Flow in Porous Medium of Local Sweileh Sand. In:Global Conference on Renewables and Energy efficiency for DesertRegions, (GCREEDER 2009), March 31st–April 2nd, 2009-01-28,Amman, Jordan
11. Kouloumbi, N.; Batis, G.; Malami, C.H.: The anticorrosive effectof fly ash, slag and a greek pozzolan in reinforced concrete. Cem.Concr. Compos. 16, 253–260 (1994)
12. Malami, C.H.; Kaloidas, V.; Batis, G.; Kouloumbi, N.: Carbonationand porosity of mortar specimens with pozzolanic and hydrauliccement admixtures. Cem. Concr. Res. 24–8, 1444–1454 (1994)
13. Ozyildirim, C.; Halstead, W.: Resistance to chloride ion penetrationof concrete containing fly ash, microsilica, or slag, permeability ofconcrete. ACI SP 100, 35–62 (1998)
15. Ganesan, N.; Sekar, T.: Permeability of steel fibre reinforced highperformance concrete composites. IE (I) J. CV 86 (2005)
16. Bernhardt, C.J.: Silica dust as cement additive. Betongen Idag 2,29–53 (1952)
17. Markestad, A.: Addition of silica fume to concrete. In: Proceedingsof the 6th Nordic Concrete Research Congress (1969)
18. Loland, K.E.; Gjorv, O.E.: Silica fume in concrete, Trondheim,Norway, 8 report June (1981)
19. Markestad, A.: An investigation of concrete in regard to perme-ability problems and factors influencing the results of permeabilitytest. Ref. 4, Report No. 65A77027, pp. 238–242 (1977)
20. Traettberg, A.: Frost action in mortar of blended cement with sil-ica dust. In: Conference on Durability of Building Materials andComponents, ASTM STP 691, pp. 536–548 (1980)
22. Whiting, D.: Rapid Determination of the Chloride Permeability ofConcrete. Report FHWA/RD-811119. FHWA, U.S. Department ofTransportation (1981)
23. Nilforousha, M.R.: The effect of micro silica on permeability andchemical durability of concrete used in the corrosive environment,Iran J. Chem. Chem. Eng. 24(2) (2005)
