Omar Saeed Baghabra Al-Amoudi

Attack on plain and blended cements exposed to aggressive sulfate environments

The recent modifications in the cement manufacturing technology and the extensive use of mineral admixtures have introduced changes in the chemical and mineralogical composition of the present-day cements. These changes may significantly affect the durability of concrete, particularly the sulfate attack. Due to these modifications, the need for understanding the mechanisms of sulfate attack through laboratory and field exposure studies becomes all the more important. This paper reviews the studies conducted at King Fahd University of Petroleum and Minerals (KFUPM) to assess sulfate attack on plain and blended cements exposed to aggressive environments in the laboratory and the field. Based on this review, the mechanisms of sulfate attack are discussed. The effect of cation type associated with the sulfate anions on concrete deterioration due to sulfate attack and the role of chloride ions on sulfate attack in plain and blended cements are also elucidated.

Effectiveness of surface coatings in improving concrete durability

This paper reports results of a study conducted to evaluate the durability of concrete coated with concrete surface coatings representing five generic types. The durability of the uncoated and coated concrete specimens was evaluated by assessing water absorption, chloride permeability and chloride diffusion. The chemical resistance was evaluated by immersing the uncoated and coated mortar specimens in 2.5% sulfuric acid. The results indicated that epoxy and polyurethane coatings performed better than acrylic, polymer and chlorinated rubber coatings. However, noticeable variation in the performance of the same generic type procured from different manufacturers was noted. Therefore, the selection of coatings should be done after conducting trial tests rather than basing it solely on the generic type.

ROLE OF CHLORIDE IONS ON EXPANSION AND STRENGTH REDUCTION IN PLAIN AND BLENDED CEMENTS IN SULFATE ENVIRONMENTS

Abstract The deterioration of concrete due to sulfate salts in soils, groundwater and marine environments is a well-known phenomenon. While it is known that the use of low-C3A cements can provide protection against sulfate attack, the combined effect of chloride and sulfate salts on such a deterioration is highly debated and inconclusive. Moreover, the use of blended cements incorporating supplementary cementing materials, such as natural pozzolan, fly ash, blast furnace slag and silica fume, is becoming common these days. The performance of these cements in environments characterized by the conjoint presence of chlorides and sulfates, however, is not well documented. In this investigation, the effect of sulfate and sulfate-chloride environments on the expansion and reduction in strength of mortar specimens due to sulfate attack was evaluated. Results indicated that the presence of chloride ions in the sulfate environments mitigated the sulfate attack in plain and blended cements. The performance of plain cements was better than that of all blended cements. However, the performance of blended cements was observed to depend on the type of mineral admixture used, both in the sulfate and the sulfate-chloride environments.

EFFECTIVENESS OF CORROSION INHIBITORS IN CONTAMINATED CONCRETE

Abstract Four types of corrosion inhibitors (calcium nitrite at two dosages, calcium nitrate at three dosages and two organic inhibitors at their recommended dosages) were evaluated at five different levels of contamination, i.e., 0.8% chloride; 0.8% chloride plus 1.5% SO3; seawater; brackish water; and unwashed aggregates. Concrete specimens were used to assess the effect of corrosion inhibitors on the compressive strength of concrete and reinforcement corrosion. The results indicated that the corrosion inhibitors investigated in this study did not adversely affect the compressive strength of concrete. Furthermore, calcium nitrite was efficient in delaying the initiation of reinforcement corrosion in the concrete specimens contaminated with chloride, while both calcium nitrite and calcium nitrate mitigated the corrosive effects of chloride plus sulfate salts or sea water. In the concrete specimens prepared with brackish water or unwashed aggregates, all the inhibitors were effective in reducing the rate of reinforcement corrosion. The type and dosage of corrosion inhibitor were observed to be dependent on the nature and level of contamination.

Expansive characteristics of gypsiferous/anhydritic soil formations

Abstract Geology and climatic and environmental conditions have led to the formation of expansive soils in the Eastern Province of Saudi Arabia. Calcium sulphate, which commonly occurs in such soils, is well known for phase transformation and dissolution. Phase changes from gypsum to anhydrite and vice versa, and dissolution of these phases, add to the potential hazards of local expansive soils. This paper discusses the behaviour of the expansive soil formations of eastern Saudi Arabia containing gypsum and anhydrite.

The effect of chloride and sulfate ions on reinforcement corrosion

Abstract The effect of chloride, sulfate and chloride-sulfate solutions on corrosion of steel embedded in cement paste has been investigated. The reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density using D.C. linear polarization resistance technique. Results indicate that the corrosion activity was very minimal in specimens immersed in pure sulfate solution. The reinforcement corrosion activity was found to be higher in specimens immersed in chloride-sulfate solutions as compared to those immersed in pure chloride solution. The corrosion rate was observed to be doubled when the sulfate concentration in 15.7% Cl − solution was raised from 0.55 to 2.1%.

SULFATE ATTACK AND REINFORCEMENT CORROSION IN PLAIN AND BLENDED CEMENTS EXPOSED TO SULFATE ENVIRONMENTS

Abstract The extensive use and addition of mineral admixtures and the recent modifications in the physicochemical characteristics of portland cements have introduced a large number of variables that need to be addressed. Furthermore, the effect of cations associated with sulfate ions on these variables is inconclusive and extensively debated in the literature. On the other hand, the exposure of many reinforced concrete structures to sulfate-bearing environments has brought attention to the role of sulfate ions in the corrosion of reinforcing steel. Unfortunately, there is very little data on this aspect. The following subjects are addressed: (i) the effect of sulfate cation type on strength and expansion; (ii) the role of sulfate ions in reinforcement corrosion; (iii) the role of plain and blended cements in both sulfate attack and reinforcement corrosion; and (iv) a comparison of the performance of concrete made with the above-cited cements with that of small ( 25 mm cube) cube mortar specimens.

Compressibility and collapse characteristics of arid saline sabkha soils

Abstract Arid saline soils are well-distributed over the globe, with a variety of nomenclature. Along the seaboard of the Arabian Gulf, these soils exist widely and are known as “sabkhas”. Despite the cemented and saline characteristics of the sabkha matrix, a recent investigation indicated that flooding the saline sabkha with distilled water in the conventional oedometer apparatus was incapable of producing a sudden reduction in volume and/or a significant collapse. This study proposes a modification to the conventional oedometer on undisturbed sabkha specimens to consolidating specimens under a constant head. Tests were, therefore, conducted on undisturbed sabkha specimens to assess their compressibility and collapse potential whereby percolation of water was commenced under two pressures to evaluate the role of sustained pressure on the collapse mechanisms. Despite the low compressibility of sabkhas, results of these tests indicated that these arid, saline soils possess a high collapse potential attributable primarily to dissolution of sodium chlorides, leaching of calcium ions and soil grain adjustment. The collapse potential increases with an increase in the acting pressure at which percolation of water takes place. In contrast to other typical soils, the collapse of arid, saline soils is not instantaneous but requires sufficient volume of water to percolate in order to enhance the dissolution of the cementing agents.

Response of sabkha to laboratory tests: A case study

Abstract Sabkha is a saline, evaporative flat soil that forms under and climates. It is generally associated with saturated watertables that are very close to the ground surface. There are typically two major types of sabkhas; coastal and continental or inland. The presence of brines in the sabkha matrix and the crystallization of diagenetic minerals therein can lead to the highly variable mechanical properties of such a soil. This investigation was carried out to evaluate the engineering properties of this salt-laden and water-sensitive sabkha soil. Several laboratory tests were conducted, including compaction, permeability, unconfined compression, direct shear, triaxial, CBR, specific gravity measurements and grain-size distribution analysis. The investigation also focussed on the effect of distilled water and/or sabkha brine on the properties of this unusual type of soil.

Performance of 15 reinforced concrete mixtures in magnesium-sodium sulphate environments

Abstract A review of the literature indicates that research on the durability of reinforced concrete in sulphaterich environments has primarily been confined to studies on sulphate attack. Despite the small number of reports on the effect of sulphate ions on corrosion of reinforcing steel in concrete, the findings of these reports are controversial and inconclusive. Therefore, this investigation was conducted to assess the performance of 15 reinforced concrete mixtures in a mixed magnesium-sodium sulphate environment. These mixtures comprised a combination of three Portland cements, three mineral admixtures and two water-to-binder ratios. Deterioration of concrete due to sulphate attack and corrosion of reinforcing steel was evaluated by assessing the weight loss of concrete and measuring corrosion potentials and polarization resistance at periodic intervals. The results of this investigation indicated that plain cement concretes, irrespective of their C 3 A content, performed fairly well in terms of sulphate resistance; however, they failed to protect the rebars from corrosion. Blended cement concretes, particularly those made with fly ash and blast-furnace slag, exhibited an advanced degree of deterioration due to both sulphate attack and reinforcement corrosion. Despite its inferior performance in terms of sulphate resistance, silica fume cement concrete displayed the best performance with regard to corrosion protection. A reduction in the water-to-binder ratio was generally detrimental in terms of sulphate attack in plain and blended cement concretes.