International Concrete Abstracts Portal

This paper describes the results of the study on the durability evaluation of Mt. Pinatubo blended cement mortar under accelerated conditions of acidic, sulphate and alkali-silica reactive regimes. Various types of ejecta materials and percentage cement replacements (i.e., 10, 20, 30, 40, 50, 60, 70, and 80%) were investigated to determine the optimum type and proportion in a cement-based mortar matrix based on the criteria of strength, dimension stability, resistance to alkali-aggregate reaction and severe environmental conditions. Test results indicated that the use of Pinatubo pozzolans are effective mineral dmixtures against acidic, sulphate, alkali-aggregate reactions. Optimum pozzolans proportions ranges from 40-60% under varying conditions. Dimension stability and shrinkage properties of mortar with Pinatubo pozzolans are basically comparable to plain portland cement mortar, indicating stability of the pozzolans as a concrete constituent material. Alkali-aggregate reactivity test of selected samples of Pinatubo aggregate also showed innocuous characteristics.

This paper presents the data on the application of the Rapid Chloride Permeability Test (RCPT) to the evaluation of chloride-ion penetration into the concretes with and without mineral admixtures. OPC concretes, fly ash 30 % concretes, blast-furnace slag 50 % concretes and silica fume 10 % concretes were prepared. The concrete blocks, 240 by 240 by 210 mm, were initially cured for 28 days, and then exposed to the three different environments : in water at 20 oC, in dry room at 20 oC and 60 % R.H. and on the roof of a building at Kanazawa University. After 5 years of exposure, five cores of 50 or 100 mm in diameter were taken from each concrete block. Physical and chemical properties of the surface and the synopsisnterior of the concretes were investigated. Changes in the chloride permeability of the concrete with the depth from the exposed surface were determined using the RCPT. Both the electrical resistivity test and the measurement of chloride-ion penetration into the concrete were also carried out. The results of the RCPT showed that both the surface and the interior of the concretes with mineral admixtures were much less permeable to chloride ions than the corresponding OPC concretes under all curing and environmental conditions. Furthermore, it was found that there was a good correlation between the charge passed in the RCPT, the initial direct current and the electrical resistivity, which also correlated well with the chloride-ion penetration depth into the specimens after the RCPT. It was concluded that the charge passed in the RCPT was an effective indicator to evaluate the chloride permeability of a large variety of concrete mixtures.

Thousands of huge pipes 7.5 m long and 4 m inner diameter are requi red in thi s project for transferring water hundreds of kilometers from the south to the north of Libya. This water from the wellfields is considered to be aggressive to the internal concrete core of the pipeline. Dissolved carbon dioxide is the most aggressive factor in the water. The acid produced by the excess carbon dioxide in the water reacts with constituents of cement paste, causing leaching of the cement binder with a consequential loss in both mechanical strength and section. Such levels of carbon dioxide decrease the design life of the PCC pipes, and many possible solutions have been studied to overcome this problem. Finally it was decided to treat the water at a central water treatment faci 1 i ty and to provide an internal Iining tc the wellfield pipes upstream of the treatment facility. It is necessary for the lining to be durable for 50 years in line with the design life of the project and the prestressed concrete cyl inder pipes. This paper describes the laboratory tests which were performed on both weathered and unweathered samples, supported with compar i sons between the two coating systems which are polyurea and polyurethane. By studying all the test results as presented in Tabl e 1-5 s the conclusion that can be drawn is that f the pol yurea coat i ng sat i sf i es the acceptance criteria for the i nternal lining application for prestressed concrete cylinder pipe (PCCP) to prevent a, i cid attack due to free carbon dioxide.

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

High Performance Concrete (HPC) has been developed primarily for its strength having a compressive strength in excess of 70 MPa, approximately double the strength of conventional concrete. The porosity of this type of concrete, especially when silica fume is added to the mix, much lower than conventional mixes. It is, therefore, assumed that high performance concrete provides significantly better protection against corrosion of reinforcing steel than conventional concrete, but this has not yet been substantiated. A field exposure program is underway with cast-in-place and pre-cast samples, containing embedded reinforcing steel probes exposed to pulp & paper industry effluent at two locations on Vancouver Island, B.C., Canada. The cast-in-place samples were loaded in three-point bending prior to exposure to initiate cracks in the location of the corrosion probes. Probes were also embedded in uncracked areas of the beams. One lower quality concrete, one industrial standard concrete, one HPC and one HPC containing silica fume were included in the test matrix. Parallel laboratory corrosion studies are being conducted on cast-in-place specimens exposed to a simulated effluent. The initial results of the field exposure showing the difference in corrosion protection of reinforcing steel in the four different types of concrete subjected to accelerated curing and conventionally cured are presented. Laboratory results investigating the effect of cracking on the corrosion protection provided by the four types of concrete are also presented. The reinforcing steel corrosion was evaluated using linear polarization resistance (LPR) and the more recently developed electrochemical noise measurement technology. The suitability of these techniques to measure and monitor the corrosion of reinforcing steel in concrete is also discussed.