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from Prince Edward Island, Canada’s smallest Transportation to and province, has been by ferry for the past century. The cost to operate the ferry system became an increasing burden for the Canadian government and a proposal call was solicited in 1987 to the private sector to construct and operate an alternate system to the Province of Prince Edward Island. A proposal was accepted for a private consortium to build a 12.9 km bridge from the mainland to Prince Edward Island. The bridge was completed in May, 1997. A precast concrete, post-tensioned segmental box girder structure was selected for the site. A requirement of the Government of Canada w as that the design and construction of the bridge provide a structure with a design life of 100 years. The bridge is located in a harsh marine environment, with some 100 annual cycles of freezing and thawing. Ice floes which originate in Northern waters pass through the Northumberland Strait in the winter and early spring months. Water temperatures vary from about -2 C in the winter months to +18 C in summer. The salinity of the water in the Northumberland Strait is approximately 3.5%. This paper presents some of the durability concerns which were considered during the design and construction of the bridge and describes how these concerns were addressed.

High volume waste concrete (HVWC) containing hundreds of kg of waste-derived materials in unit volume of concrete as raw materials was prepared to examine the workability, strength development, hydration of cement, composition and structure, and dissolution of harmful elements from hardened concrete to increase the amounts of waste-derived material that can be used for manufacturing concrete.The waste-derived materials tested in this experiment were incineration ash of urban refuse and sintered coal ash as the substitution for fine aggregates, and sintered sewage sludge and glass cullet as the substitution for coarse aggregates. It was determined that HVWC could keep good workability without segregation and developed higher strength than ordinary concrete even if the amounts of waste-derived aggregates in concrete exceeded 6OOkg/ms. Increase in combined water in hardened HVWC and the production of cement hydrates including C-S-H with age was normal and the influence of trace elements contained in waste-derived aggregates on the cement hydration was negligible. Decrease in the amounts of Ca(0I-Q and increase in C-S-H which was estimated from the pore volume of 3 to 6 mn in diameter was recognized in later age in the case when blastfumace slag or fly ash was used as a binder. Non-uniformity in distribution of aggregate, large pore and microgroove between aggregate and cement paste which might occur by the use of large amounts of waste-derived aggregate was not observed. There was no remarkable difference in type and quantitie of elements between HVWC and ordinary concrete dissolved from them. From the results described above, it is considered that the use of HVWC is a very promising technique to safely consume large amounts of wastes.

Magnesium-phosphate cements, which exhibit fast setting and high early strength, are already used for rapid repairs to damaged concrete. The present paper describes two new applications of them. The first application deals with the development of composites. Magnesium-phosphate cements are typically brittle in nature but their ductility can be significantly improved by addition of fibers. Composites were prepared according to the premix method, the matrix being composed of 50 % of magnesium-phosphate cement and 50 % of sand. Various fibers were used to reinforce the composites, the fiber volume fraction was in the range of 0.69 % to 1.32 %. Very ductile composites were obtained using polypropylene fibers. When subjected to accelerated aging, these composites maintained their initial performances. The second new application of magnesium-phosphate cements concerns the production of durable grouts. Composed of 50 % of magnesium-phosphate cement and 50 % class F fly ash, such grouts behaved well in severe environments like ammonium sulfate, and lactic acid.

The use of high strength normal weight and lightweight aggregate concrete (i.e. with water/binder ratios below 0.40) have shown that the concrete may be more sensitive to cracking the first hours and days after casting (due to autogenous shrinkage and thermal strains), than normal strength concretes. Two test rigs have been built in order to investigate the problem. The Shrinkage-Rig determines the free deformations (e.g. autogenous and thermal deformations), and the special Stress-Rig determines the stresses when the concrete is restrained against the deformations. The paper presents the results from testing of one high strength normal weight concrete and one high strength lightweight aggregate concrete, both with water/binder ratio 0.38, in the test rigs. Both concretes were exposed to two different temperature histories generated from heat of hydration. The normal weight concrete developed relatively high tensile strains during the cooling phase. The corresponding stresses in the Stress-Rig became very high, and in one case the concrete failed. The lightweight aggregate concrete, however, did not develop any tensile strain, due to a lack of autogenous shrinkage caused by the water supply from the LWA grains. Consequently, no severe tensile stresses were built up in the Stress-Rig.

High-strength and high-fluidity lightweight concretes have been developed using silica fume blended cement and belite-rich cement with a designed compressive strength from 40 to 60 MPa. Test conditions and parameters were water-cement ratio of 0.22,0.33 and 0.40, curing temperature of 5, 20 and 35 C, curing method of standard and sealed curing and 3 types of high-range AE water-reducing agent. Influences of above factors upon flow, flow time, compressive strength, permeability, pore size distribution and total pore volume were studied. The major findings of this study are as follows, (1) Compressive strength of silica fume blended cement concrete was higher than that of belite-rich cement concrete and the effect of water-cement ratio was small. Compressive strength at 7-day were 80 to 90% of the 28-day strength at any curing temperature. (2) Compressive strength of belite-rich cement concrete significantly increased at water-cement ratio of 0.3 to 0.4, and its evolution from 28 to 91 days became larger at lower curing temperatures. (3) Total pore volume of silica fume blended cement concrete at the age of 28 days was smaller than that of belite-rich cement concrete at all curing temperatures of 5, 20 and 35 “C, and compressive strength became larger with a decrease of total pore volume.