CONCRETE DURABILITY IN TEMPERATE MARINE EXPOSURES: 17 AND 20-YEAR FIELD TRIALS OF BINDERS

摘要

In 1982, a set of 24 reinforced concrete test beams were suspended in a temperate marine atmospheric/splash zone exposure beneath Berth 8 at the Port of Fremantle inner harbour. Three years later, in 1985, a further 68 beams were placed in a tidal marine exposure adjacent to a nearby slipway at the mouth of the Swan River. The concretes used in the exposure trials were based on local general purpose Portland (AS 1315 Type A, now typically AS 3972 Type GP) cement, along with various combinations of silica fume, iron blast furnace slag and fly ash. The effect of including a proprietary integral waterproofing admixture with the Type A and 65 percent slag blended cements was also assessed. During 2001 and 2002 the test beams beneath Berth 8 were recovered and subjected to resistivity, half-cell potential and LPR corrosion rate measurements. Samples of concrete were removed for determination of chloride penetration coefficients. The data was compared with results previously obtained at two and five years exposure. The tidal exposure beams have been left in-situ, however the beams at the upper and lower extents of the tidal range were tested and sampled in the same manner as the Berth 8 beams. Chloride ingress results were compared with data obtained at early age from duplicate specimens after one year of laboratory exposure in a wet/dry cycle salt-spray tank. From the results obtained so far, it has been concluded that: The "reference" concrete, well cured Type A cement at 400 kg/m~3 and w/cm ratio 0.4, did not provide adequate long-term corrosion protection to reinforcement under the exposure conditions. Supplementary cementitious materials (SCM's) increased protection to reinforcement. The effect was greatest for silica fume, followed by blast furnace slag and then fly ash. The hydrophobic admixture increased resistivity and reduced surface chloride concentrations. SCM's increased the surface chloride concentrations, but reduced the rate of chloride penetration. This paper presents and discusses the above data, and briefly outlines an ongoing program of further work utilising the test beams.