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Mechanical properties and chloride permeability of normal and high strength concrete containing a mineral admixture called metakaolin are presented in this paper. The target 28 day strengths for normal and high strength concrete were 34 and 68 Mpa respectively. The major independent variables were: (i) addition of metakaolin at 5 and 9 percent as cement replacement; (ii) type of cement, ASTM Type I and III; (iii) type of curing, moist and hot water cure; and (iv) age at testing varying from 1 to 90 days. Fresh concrete was tested for slump, air content, unit weight, and concrete temperature, and the hardened concrete was tested to obtain compressive strength, modulus of elasticity, modulus of rupture, and permeability. The results indicate that metakaolin improves the compressive strength by as much as 25 percent. It is possible to obtain a one day strength of 24 MPa using metakaolin and only 305 kg/m3 of Type I cement. The one day strength can be increased to 31 MPa using Type III cement. Hot water curing can increase one day strength to as much as 54 MPa. Modulus of elasticity is slightly higher for concrete containing metakaolin. Metakaolin has very little influence on modulus of rupture. Control concretes had a low chloride ion permeability, and metakaolin decreased the permeability even further.

Autogenous shrinkage and drying shrinkage tests were carried out to determine the shrinkage characteristics of high-strength concrete. Three levels of water-cementitious materials ratios [W/(C+SF) : 20, 30 and 50%], and three levels of silica fume replacement ratios [SF/(C+SF) : 0, 7.5 and 15%] were chosen. The drying shrinkage test with specimens of 1 OxlOx4Ocm under the condition of 20+ 1°C and 6O+ 5%RH started at the age of 7 days or 28 days after the measurement of autogenous shrinkage. The autogenous shrinkage strain was also measured in other specimens until the age of about two years. The autogenous shrinkage strain increased both in its amount and its percentage in the total shrinkage strain with the decrease of W/(C+SF). Almost the same total shrinkage strain was observed after about one year in the specimens under the drying condition independent of the mixture proportions of concrete, the curing method or its period.

Corrosion of steel bars in pre-cracked prism specimens exposed in marine environment for 15-year is presented here. The size of the specimens was 100x100x600 mm. The specimens were made with ordinary Portland, slag (Type A, B and C) and fly ash (Type B) cements. A round steel bar of diameter 9 mm was embedded in each specimen. W/C were 0.45 and 0.55. Crack widths were varied from 0.1 to 5 mm. Chloride-ion concentrations in concrete and corrosion of steel bars were evaluated. Narrower cracks ( < 0.5 mm) heal irrespective of the cement types. Chloride ingress and corrosion of steel bars in concrete are highest for the specimens made with ordinary portland cement and lowest for the specimens made with slag cement of Type C. Locations of the maximum corroded area as well as the deepest corrosion pit are not necessarily at or near the cracked region Wider cracks are not healed and maximum corroded area and deepest corrosion pit are observed at the cracked region. The presence of voids at the steel-concrete interface results in corrosion pits even for chloride-ion concentration less than 0.4% of cement by weight.

Synopsis: Ecocement is a new type of hydraulic cement made from incinerator ashes. In this study, the effect of blast-furnace on the corrosive behaviour of steel bars embedded in mortars made from two types of ecocement; rapid hardening type with high chloride content, and NPC type with low chloride content, was investigated. Cement-slag mortars were prepared with both types of cement. The mortar specimens, with mild steel and stainless steel bars embedded, were placed in an environmental chamber under severe saline conditions. The corrosion of the mild steel bars was monitored by electro-chemical measurements. Chloride concentration profiles in cylindrical mortar specimens were also measured after the exposure period. The results of the various tests clearly indicate the beneficial effect of slag on the time of corrosion initiation and the degree of corrosion of the steel bars.

Two silica-manganese slags containing about 11 % MnO were ground to Blaine finenesses of 360 to 600 m*/kg. Their C/S (CaO/SiO2) modulus was very low (0.47 to 0.58) and, for this reason, these slags were considered likely to be unsuitable for use in the preparation of blended cements. They were therefore introduced in concrete instead of either fly ash or silica fume. The cement content of these concrete mixtures was in range of 2 1 0 kg/m3 t o 4 5 0 kg/m3. The quantity of each supplementary cementing material was adjusted according to the French standards and varied from 50 to 80 kg/m3. The slags behaved as well in concrete as fly ash or silica fume: no decrease in strength was observed and the water permeability was the same.