The selected papers represent the areas of research that I have been involved with, namely the durability of concrete and characterization and stabilization of indigenous soils, particularly the sabkha.
Since concrete durability is of major concern to the construction industry in the Arabian Gulf, research was initiated to assess the causal factors of deterioration and thereafter to improve the durability of reinforced concrete structures using blended cements, fusion-bonded epoxy-coated rebars and corrosion inhibitors. Similarly, as sabkha soils with very low strength are well scattered in eastern and western Saudi Arabia, where major industrialization and urbanization programs have been established, improvement and stabilization of these inferior soils are necessary to upgrade them to be used as a construction material in pavement layers. Furthermore, there is a need to develop a simple methodology to assess the properties of stabilized soils in the laboratory and field. One paper (#58) is included to reflect this aspect of my research activity.
1. Paper #13 in Part (i)
Al-Amoudi, O.S.B., Rasheeduzzafar, Maslehuddin, M., and Abduljauwad, S.N., “Influence of Sulfate Ions on Chloride-Induced Reinforcement Corrosion in Plain and Blended Cement Concretes,” ASTM Journal of Cement, Concrete, and Aggregates, Vol. 16, No. 1, June 1994, pp. 3-11.
Corrosion of reinforcing steel in concrete is thought to be mainly caused by chloride ions that are contributed by the mix constituents or that penetrate the hardened concrete from the service environment. However, in many situations, structures are exposed to both chloride and sulfate salts. In such situations, the mechanisms of reinforcement corrosion were not very well understood. The objective of the reported study was to assess the influence of sulfate ions on chloride-induced reinforcement corrosion in plain and blended cements. The results indicated that the sulfate ions did not influence the time to initiation of reinforcement corrosion due to their lower diffusivity (as compared with the chloride ions). However, once corrosion was initiated, the rate of reinforcement corrosion in the specimens exposed to chloride plus sulfate environments was found to be more than that in the specimens exposed to only chloride solutions. The results corroborate the field observations of accelerated corrosion noted in the marine structures and those exposed to chloride-sulfate bearing environments.
2. Paper #22 in Part (i)
Al-Amoudi, O.S.B., Maslehuddin, M., and Saadi, M.M., “Effect of Magnesium Sulfate and Sodium Sulfate on the Durability Performance of Plain and Blended Cements,” ACI Materials Journal, Vol. 92, No. 1, January-February 1995, pp. 15-24.
Deterioration of concrete due to sulfate attack is noted in many parts of the world when structures are exposed to sulfate-bearing ground waters and soils. International standards, such as ACI 318 and BS 8110, provide guidelines on the type of cement to be used for various concentrations of sulfate salts, without differentiating the role of the cations associated with the sulfate anions. The two major cations associated with sulfate anions, namely sodium and magnesium, could have varying influence on concrete durability. In the reported investigation, the performance of plain cements, Type I and Type V, and blended cements, with fly ash, silica fume and blast furnace slag, when exposed to either sodium sulfate or magnesium sulfate, was evaluated. The results indicated that the performance of blended cements was satisfactory in sodium sulfate environments. However, they did not perform very well in the magnesium sulfate environment. The need for providing additional protection, such as applying a barrier coating, to structures built with blended cements, particularly the silica fume one, and exposed to magnesium sulfate-bearing soil and ground water, was highlighted as an outcome of the results of this study.
This Paper is one of the pioneering publications, the other being by Cohen and Bentur on the effect of magnesium sulfate on concrete durability made with blended cements. This work has been cited in 15 research publications worldwide.
3. Paper #49 in Part (i)
Almusallam, A.A., Maslehuddin, M., Abdul-Waris, M., Dakhil, F.H., and Al-Amoudi, O.S.B., “Plastic Shrinkage Cracking of Blended Cement Concretes in Hot Environments,” Magazine of Concrete Research, Vol. 51, No. 4, August 1999, pp. 241-246.
The hot weather conditions prevailing in many parts of the world, particularly the Arabian Gulf, significantly influence the properties of both fresh and hardened concrete. The cracking of concrete due to plastic shrinkage adversely affects the properties of hardened concrete. Although this fact is appreciated by the concrete technologists, it was not thoroughly studied, obviously due to the non-prevalence of hot weather conditions in Europe and North America. The concrete technology research group at King Fahd University of Petroleum and Minerals initiated this study to study the cumulative effect of exposure conditions and cement type on the plastic shrinkage cracking. The results of this study indicated that the environmental parameters, such as temperature and relative humidity, influence the plastic shrinkage much more than the type of cement. Recommendations for concreting under hot-weather conditions, to avoid plastic shrinkage cracking, have been provided, based on the data developed in this study.
Due to the significance of this type of research on the construction industry in the region, another investigation (MS thesis) on plastic shrinkage characteristics of blended cements made with different types of silica fume (four of densified type and one undensified) was conducted. The thesis’ report has just been submitted and at least three papers will be published on the findings of this investigation.
4. Paper #56 in Part (i)
Al-Amoudi, O.S.B., “Attack on Plain and Blended Cements Exposed to Aggressive Sulfate Environments,” Cement & Concrete Composites, Special Issue on: Sulfate Attack and Thaumasite Formation, Vol. 24, Nos. 3-4, June-August 2002, pp. 305-316.
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 its sulfate resistance. 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 invited paper reviews the recent studies conducted at King Fahd University of Petroleum and Minerals and other parts of the world to assess the sulfate resistance of plain and blended cements exposed to aggressive environments. Based on microstructural studies conducted by the author using scanning electron microscopy (SEM) and X-ray diffraction (XRD), the mechanisms of sulfate attack were elucidated. The effect of cation type associated with the sulfate anions on concrete deterioration and the role of chloride ions on sulfate attack in plain and blended cements were also explained based on laboratory and field results. This paper should be a useful reference to the researchers and engineers in understanding the mechanisms of sulfate attack, vis-à-vis the modern cements.
5. Paper #57 in Part (i)
Al-Amoudi, O.S.B., “Durability of Plain and Blended Cements in Marine Environments,” Advances in Cement Research, Vol. 14, No. 3, July 2002, pp. 89-100.
Since seas and oceans constitute about 80% of the earth surface, it is believed that the number of marine and offshore structures will increase and they will continue to be made of concrete. Concrete is the most economical and durable structural material for construction of marine structures. However, with rapid development in cement chemistry and the use of supplementary cementing materials, the performance of concrete in marine environments needs to be re-investigated. In this paper, the performance of plain and blended cements in marine environments was studied. Results of this investigation have confirmed the superior performance of silica fume cement concrete over other blended and plain cement concretes. The results of this study have shown that sulfate attack was significantly mitigated in sea water despite the high sulfate concentration which is classified as “severe”. Moreover, properly cured silica fume concrete will enhance the durability of marine structures. The author is optimistic that these findings would be useful in upgrading the specifications for marine structures.
6. Paper #59 in Part (i)
Al-Amoudi, O.S.B., Asi, I.M.K., Al-Abdul Wahhab, H.I., and Khan, Z.A., “Clegg Hammer-CBR Correlations,” ASCE Journal of Materials in Civil Engineering, Vol. 14, No. 6, December 2002, pp. 512-523.
Unbound earth materials (e.g., soils, gravels, etc.) significantly influence the design and construction of road and airfield pavements or foundations and other earth-fill structures. The assessment of the in-situ properties of these materials (i.e., when they exist as bases, subbases or subgrades) in terms of density, strength, etc., is highly desirable. However, the evaluation of compacted fills is an expensive and time consuming endeavor and, therefore, the testing of these materials is generally quite limited. In addition, the high variability encountered with most natural soil types and the number of soil types typically existing in a project necessitate the development of a test method that is inexpensive and rapid, so as to replace the CBR technique which is tedious, time consuming and expensive.
In this study, the efficacy of Clegg impact hammer in estimating the strength of compacted soils was assessed. The data developed indicated that the Clegg impact value (CIV) correlates relatively well with the CBR results for both the laboratory and field trials. As a consequence, a general and reliable best-fit model has been proposed, which can be easily applied for any soil in the world. The results of this study are a useful contribution to the pavement and geotechnical industry.
7. Paper #60 in Part (i)
Al-Amoudi, O.S.B., “Characterization and Chemical Stabilization of Al-Qurayyah Sabkha Soil,” ASCE Journal of Materials in Civil Engineering, Vol. 14, No. 6, December 2002, pp. 478-484.
The low-bearing capacity of sabkha soil, in its natural condition, is a practical obstacle to the engineers in the Arabian Gulf and elsewhere. Moreover, the collapse potential of sabkhas is a risk in normal practice. Therefore, the mechanical properties of a sabkha soil needs to be improved to enhance its bearing capacity prior to any construction. In the reported study, a “selected” sabkha soil from Al-Qurayyah, eastern Saudi Arabia, was studied to improve its properties using cement and lime at five different dosages ranging from 0 to 10%. The load-bearing capability of plain (i.e., untreated) and chemically-stabilized sabkha mixtures were evaluated using CBR, unconfined compressive strength, and Clegg impact value at different moisture contents. The results indicated that cement improved the performance of stabilized sabkha much more than lime, particularly at high moisture contents. Further, the 7% cement addition has satisfied the strength and durability requirements so that sabkha soil can be used as a base course in rigid pavements and as a subbase in flexible pavements. The findings of this study have been useful to the local construction industry whereby sabkha soil can be utilized for the first time in pavement layers.