Pore structure and crude oil permeability of hardened cement paste and concrete.

Large concrete structures are being built for oil production, storage and transportation. The effects of crude oil on the properties of concrete are not well known and little data is available in the published literature. This investigation, covering hardened cement pastes (IICPs) and concrete is divided into three parts: the first studies their porosity, the second their permeability to crude oil and ways of reducing permeability, and the third, changes in their properties when oil saturated. Two types of superplasticisers were used as water reducing additives. Test results show that the porosity of D-dried pastes at 28 days were between 0.1435 and 0.4181 cc/gm of paste for OPC with W/C = 0.3 to 0.7; and 0.1925 to 0.3457 cc/gm of paste for SRPC with W/C = 0.4 to 0.6. The wide- pore volume, corresponding to Powers' capillary porosity occupy 77.5 to 901 of the. pore volume in OPC and 72 to 83% in SRPC pastes. Adding 1 and 2% superplasticiser reduced the wide-pore volume and hydraulic radius. Concrete porosity was from 16.0 to 23.4% in OPC and 16.8 to 22.3% in SRPC for effective 4J/C ratios from about 0.3 to about 0.9. The permeability of HCP and Concrete decreases with time and with low admixture concentration and increases with applied oil pressure. SRPC samples were more permeable than OPC. The permeability of concrete is influenced by workability, aggregate grading, fine aggregate concentration and cement content. Optimum values were obtained. Superplasticisers significantly reduce the permeability. The mechanical properties of HCPs and concrete studied here were adversely affected by oil saturation. Cube strength and elastic modulus were reduced by amounts depending on the porosity of the concrete, but HCP properties were nearly constant after 4 months in oil. It appears that -the oil mainly affects the paste-aggregate bond strength. Concrete deterioration with time (after initial saturation) was very small.