الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The national strategic plan for population re-distribution in Egypt supports the establishment of new towns and urban settlements across the coastal zones (as well as vacant desert lands) to relieve the pressure on the packed Nile Valley and Delta and to encourage internal migration to new urban coastal communities. The North – Western coast and the Eastern coast regions are expected to absorb huge ratio of the population during the coming years due to development in the touristic, residential and industrial projects as well as the oil petrochemicals natural gas and offshore industries in these areas. [Particularly after delineation of the maritime boundaries between Egypt and neighbouring countries].
Since reinforced concrete has a poor service record in these areas, great demands should be undertaken in terms of durability, safety and prevention of damage for the used reinforced concrete during its service life in these areas.
A considerable amount of research has been carried out, and is still continuing, with the intent of finding additives and techniques for modifying the concrete to reduce its vulnerability to attack. Also, variable means have been adopted to protect the steel reinforcement from the attack of penetrating aggressive elements from the surrounding hostile marine media.
An overwhelming opinion is that: the principal cause of concrete deterioration in marine environment is due to the ingress of chloride ions causing corrosion of steel reinforcement leading to cracking and spalling of concrete. In such situation, it used to be thought that , using sulfate resisting cement (SRC) (C3A " ~ " 3.5%) would provide adequate protection against sulfate attack, but, would fail to remove free chlorides. Therefore, several researchers recommended using ordinary portland cement (OPC) (having higher C3A content) as it would resist the chloride attack on concrete as well as the chloride – induced reinforcement corrosion by combining a considerable part of chloride into a calcium chlorioaluminate compound. In addition, if that cement is modified with a suitable admixture (e.g. SF), it could provide, to a certain extent, sulfate resistance.
In this respect, it is to be mentioned that, the previous overwhelming opinion did not give the needed consideration to the deleterious effect of sulfate ions:
Sulfates besides its effect on concrete yielding expansion due to ettringite formation, it could, also, provide reinforcement corrosion [of the “general” type covering the entire steel surface] that could proceed with excessive internal stresses in concrete till cracking and spalling occur.
In addition, we should remember the drawback that, using portland cement with a high C3A content results in a higher rate of heat evolution and therefore, a temperature rise. This behavior could be harmful in moderately large concrete masses often associated with structures exposed to the marine environment.
1- This situation urged us to investigate in the current study, another novel route for confronting the concomitant effect of sulfate and chloride, therefore: Type V (SRC) cement has been used for preparing concrete, That cement has been blended with a chloride – binder (chloride – scavenger) for fixing chloride into an insoluble reaction product.
As to the steel reinforcement, the current study investigated steel protection by an innovative coating in which a priming coat of portland cement slurry incorporating
a specific corrosion inhibitor has been applied over the steel surface.
Consequently, the current study presented modified concrete ingredients as well as novel steel Protective measures that, hopefully being capable of :
• Protecting concrete in (marine areas) from invading sulfates and chlorides and their inimical effects.
• Protecting the embedded steel reinforcement form corrosion.
2- The study started by an extensive literature review about the aggressive agents in marine environment and their effects on concrete. Then, the review presented previous studies on the corrosion of reinforcing steel and some relevant protective measures.
3- The behavior of sulfate resisting cement (SRC) compared to ordinary portland cement (OPC) upon exposure to sea water has been studied. This included the physico-mechanical properties of the cement pastes upon curing in tap water, then, the properties upon curing in sea water.
The results of this part of the study illucidated that the inherent physical and mechanical properties of SRC are very close to those pertaining to OPC (irrespective of the structural phases and their proportions in each of them). Consequently, SRC is the cement used in the current study.
4- Then, the study investigated admixtures capable of fixing (binding) free chlorides in concrete. Thus, SRC has been blended with a Cl--binder for fixing chloride in an insoluble product. Lead oxide (PbO) has been selected for use as a chloride – binder in concrete on the basis of applying the following equation:
PbO + CaCl2 + H2O PbCl2+ Ca(OH)2
(Poorly soluble) (Increases alkalinity)
Also, a proposed admixture has been introduced and investigated in the present study to be used as a chloride – binder that is “lead nitrate”. Such admixture has been introduced on the basis of applying the following equation:
Pb (NO3)2 + CaCl2 Pb Cl2 + Ca(NO3)2
(Anodic corrosion inhibitor)
The influence of these chloride – binders on the physical and strength properties of the hardened SRC pastes has been investigated upon curing in tap water and, then, on exposure to sea water. The effect of these chloride – binders on the alkalinity, and then carbonation occurrence, in SRC pastes has been, also, investigated.
It has been found that, these compounds [PbO and Pb (NO3)2] marginally delay the setting time, relative to control samples, yet, they improve workability, maintain alkalinity (hence carbonation resistance), yield better compressive strength. The (partially) free – chloride removal, certainly, proves the viability and robustness of these admixtures as chloride – binders. Consequently, the current study investigated the performance of these compounds upon using in concrete.
5- Concrete mixes containing the chloride – binder PbO at the concentration 0.2% (by wt. of cement) maintains compressive strength values exceeding those pertaining to the concrete Cl--binder- free samples upon exposure to sea water.
The compound proposed by the current study [i.e. Pb (NO3)2] particularly at the concentration 0.5% (by wt. of cement) proved to be an efficient chloride – binder. It causes a strength gain of concrete exceeding that obtained upon using 0.2% PbO while exposed to sea water attack.
6- In the current study, a corrosion protection scheme including“Inhibited cement – slurry coating” has been applied to the steel reinforcement. Such scheme has several advantages, among them are:
- It is compatible to the surrounding concrete.
- It is a passivating system, keeping the steel surface in a highly alkaline (high pH) environment.
- The coating protects the steel surface from the attack of invading aggressive ions from the surrounding sea water medium.
- The coating retains the bond strength between the steel and the surrounding concrete.