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Concrete is probably the most widely used construction material in the world. In the Arabian Gulf region, deterioration of concrete due to the aggressive environment is recognized to be the main factor affecting their structural integrity. The durability of concrete structures can be preserved by various protection methods; however, using cement replacement materials is one of the most effective and economic methods of maintaining their stability as well as extending their service life. The aim of this project is to study four interrelated aspects, namely, (1) the effect of hot environment on the properties of fresh concrete incorporating mineral admixtures, (2), the influence of exposure environment on the engineering properties of hardened concrete, under various curing conditions, without and with mineral admixture, (3), the differences in porosity and pore structure of the same set of mixes, and, (4) the effect of outdoor exposure on the durability-related properties of concrete. To achieve the above aims, the experimental programme involved the study of five different mixes of combinations of silica fume/slag and silica fume. The effects of real exposure to the Arabian Gulf environment of these mixes subjected to four curing regimes, namely, continuous water curing, no water curing after demolding, and air drying after 3 and 7 days of initial water curing were investigated. The properties investigated include (1) consistency and setting times of cement pastes, workability and workability loss with time, (2) engineering properties such as compressive strength, dynamic modulus of elasticity, pulse velocity, shrinkage, expansion and thermal expansion, (3) microstructural properties such as porosity and pore size distribution, (4) durability-related properties such as permeability, water absorption and carbonation depth. The results show that exposure to hot environment results in rapid setting times, faster loss of slump, higher porosity, coarser pore structure and more permeable concretes. It was found that part cement replacement by silica fume and slag improves the quality of concrete mixtures, refined the pore structure and produced concretes with very low porosity and continuous pore diameter in both indoor and outdoor environment. The properties of concrete containing mineral admixture appear to be more sensitive to poor curing than the plain concrete, with the sensitivity increasing with increasing amount of slag in the mixture.

Increased oil exploration necessitates building of conc~ete structures for its production and storage. The effects of crude oil on concrete properties are not well known and little data is available in the published works. This investigation covers HCP, mortar and concrete. First, it studies the effects of cracking and direction of casting on the flow of water or oil of different constitutions through concrete storage tanks. Secondly, it studies the relationships between the pore structure and permeability of HCP, mortar and concrete as influenced by w/c ratio, hydration and aggregate content. OPC was used for the tests. Experimental results show that, in concrete specimens, the flow of water through cracks is generally greater than the flow of crude oil through the same type of cracks. Sorptivity can predict reasonably accurately the flow of liquids and is useful in characterizing the flow of various oil types th:r:( ,ugh HCP, mortar and concrete. No specific oil property appears to control the oil flow through cement composites. Concrete tanks should be lined when used for storing diesel and parafin. Crude oil flow through concrete tank wall was found to be 1.06 - 1.81 times flow through the tank floor. Increasing the w/c ratio, increases the total porosity, pore surface area and threshold radius but decreases the density and does not effect the hydraulic radius. Increasing the age of HCP (w/c = 0.7) from 7 days to 6 months decreases the total porosity, pore surface area, threshold radius and hydraulic radius by 12%, 19%, 71% and 9% respectively, but increases the density by 13%. Adding sand to HcP, reduces the total pore volume and the pore surface area but increases the density. Wax deposits from the crude oils blocked all pore radii <650A, which is called the "critical pore radius" (Pcr). Saturation in crude oil appears to alter the internal structure of the cement composites. Dry curing increased most pore parameters but decreased the strength of the mortars. Permeability of mortar and concrete increases with w/c ratio, applied pressure, aggregate volume concentration and drying temperature but decreases with the test period and hydration. permeability was found to relate reasonably accurately to pore structure using Kozeny's theory provided the pore parameters are for pores of radii >650A.

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