In most concrete markets these days, there are several varieties of pozzolans and ground slag available for use in regular and high-performance concretes. Each one has its strong points when blended with portland cement in concrete and, properly used, will provide concrete of enhanced durability. Recently, concrete containing more than one such material has become common, even to the point of being available as ternarv or quaternarv blend. This paper reviews the data available on durability of concrete produced from‘ multiple blends and discusses some of the potential benefits to specifiers and users.

In 1997, CANMET in association with the American Concrete Institute and several other organizations in Australia sponsored the Fourth International Conference on the subject. The conference was held in Sydney, Australia. More than 120 papers from 30 countries were received and peer reviewed in accordance with the policies of the American Concrete Institute; 81 were accepted for publication. The accepted papers deal with all aspects of durability of concrete, including chloride and sulphate attack, freezing and thawing cycling, alkali-aggregate reactions, cathodic protection, and the role of supplementary cementing materials to enhance durability of fiber-reinforced concrete and performance of repaired concrete structures. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP170

The durability of cement-stabilized specimens in various aggressive media were studied by means of the Koch and Steinegger test over 56 days at 20°C. Prismatic lxlx6cm samples of normal portland cement (OPC) and normal portland cement with 80% ground granulated blast furnace slag (OPC/BFS) addition, were prepared mixing them with water containing 5,000 ppm Pb2+ (OPC samples), 15,000 ppm Pb2+ (OPC/BFS samples) or 50,000 ppm Cd 2+. Those specimens were immersed in the aggressive solutions tested: a buffered AcH/Ac- medium, a NaCl 0.45M + Na2SO4 0.03M solution (SO4= and Cl- concentrations equivalent to those of the sea water) and deionized water as reference. In addition, the concentration of toxic metals in the aggresive media. was measured I Changes into microstructure and flexural strength were evaluated by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The pore fluid solution extracted from specimens and the leachate solutions were analyzed for Pb2+, Cd2+, Ca2+, Na+,K+, SO4 and Cl-ions. Results show that normal portland cement and blast furnace slag blended cements are durable matrices in saline medium similar to sea water, but undergo an acid attack with formation of a porous degradation coating and dissolution of toxics metals in the acid medium of AcH/Ac- buffer solution.

A modified version of the Dundee rapid chloride test (1) was used to characterise the physical resistance of a range of portland cement and condensed silica fume (CSF) concrete mixtures to chloride ingress. Cubes from these mixtures were placed in submerged, tidal and spray marine exposure zones. The solution to Fick's Second Law was applied to the measured on-site chloride profiles (after 2 years) to obtain apparent diffusion coefficients, Da and surface chloride levels, Cs. The depth of the threshold chloride level, x0.4, was calculated from Da, and Cs. The rapid test results (chloride (C1-) index values) were then correlated with the on-site chloride ingress parameters, Da and x0.4. The best correlation was found between x0.4 and the C1- index values. This can be attributed to the fact that x0.4 is calculated from both Da and Cs, and therefore eliminates a large portion of the scatter arising from the process of chloride profile determinations. The differences in correlations for the different cement types were ascribed to the lower chloride binding capacities of CSF concretes. The need for a suitable chloride binding test, which could be used in conjunction with a rapid chloride test to characterize the potential durability of concrete in ternis of chloride ingress, was identified.

Polymer modified cementitious materials are used in construction for applications such as bridge deck overlays and concrete repair. When using this type of material a wet-dry curing regime is usually recommended in order to give optimum mechanical properties. However, such a curing regime is contrary to that which would be expected for a low porosity surface layer, desirable, e.g., for good resistance to chloride ingress. This paper presents the results of investigations into the influence of curing conditions on the surface porosity of polymer modified cements and its influence on chloride diffusivity. Small cement paste prisms were cast and the top faces exposed to: wet, wet-dry, and wet-dry-wet curing regimes. Pore size distributions were then determined for the top, middle and bottom layers using mercury intrusion porosimetry. Results showed that for all mixture proportions the wet-dry curing regime resulted in a surface layer which was more porous and had a coarser pore structure than the deeper layers The extent of this effect depended on: actual curing regime, W/C, and type of polymer latex used. Results were confirmed by determining the effective diffusivity of chloride ions in similar samples.