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It was found that highly reactive rice-husk ash (RHA) with more than 40 m2/g BET specific surface could be obtained by the two-step burning method. In this study, concrete specimens with different RHA blending ratios were prepared at different water-cement ratios, then cured in water, 2% HCl solution, and an accelerated carbonating chamber respectively. The results show that after the addition of RHA to the cement not only the strength of concrete is enhanced greatly but also the losses of mass and strength of the concrete cured in the HCl solution and the carbonation rate of concrete were decreased. It was also observed that the resistance of concrete to the penetration of water, air, and chloride-ion can be much improved by using RHA.

The first part of this paper provides a brief review of the critical issues met in replacing deteriorated bridge decks with precast deck systems, drawing on existing papers published by PCI and ACI. Recommended practices for typical bridge rehabilitation projects are provided. The second topic focuses on the rehabilitation of the Tappan Zee Bridge over the Hudson River near New York City. Results are presented for an experimental program conducted on a 10 m span full-scale lightweight concrete slab-steel beam composite bridge deck unit. Loading history included 10 million cycles of flexural fatigue loading, followed by a flexural load capacity test. Measured values of capacity and mid-span deflection at this ultimate load level are compared with simplified analytical predictions.

High Strength Concrete (HSC) is defined as a concrete with a 28-day characteristic compressive strength of 50 MPa or more. This paper presents the results of an experimental study on pretensioned beams made of HSC with characteristic compressive strengths at 28 days of 55, 75, 85 and 105 MPa and compares with Normal Strength Concrete (NSC) pretensioned beams (in this case 35 MPa concrete). Nine, fully prestressed concrete beams having 8mm diameter plain steel wire or 7.9 mm diameter 7-wire steel strand with stirrups at both ends (to one third of the span) were constructed and tested. The experimental results were compared with the theoretical calculations according to the current Codes of Practice, such as ACI-3 18 and AS3600. The curvature of pretensioned beams tested decreased with increasing concrete strengths from 55 to 105 MPa over the entire loading range from service to ultimate load. The final failure of the beams in all cases occurred by yielding of tendons and conventional reinforcements followed by crushing of the concrete in the constant moment region. The beam reached large curvatures prior to failure and hence appeared to be ductile enough in terms of rotation. However, a comprehensive evaluation of ductility of these beams is still required. With this in mind, the ductility indices, currently used for reinforced and prestressed concrete beams are reviewed and an index based on moment of resistance, total energy and elastic energy, suitable for pretensioned beams is presented. Pretensioned beams made of HSC up to 105 MPa are sufficiently ductile in terms of large deformations, rotations and total energy. However, the inelastic energy absorbed is less than those beams made of NSC.

A series of 16 reinforced concrete beams was tested to evaluate the flexural performance of RC beams strengthened by epoxy bonded plates after repair. The key parameters for this study were the repair materials, polymer, cementitious materials and strengthening materials, steel plates and carbon fiber sheets. The repaired specimens failed by a typical flexural mode with minor interfacial bond failure. The results show that the flexural performance of the strengthened beams is varied depending on the repaired material. Specimens with epoxy polyester resins and latex modified cementitious mortars are effective for repairing the concrete beams, compared to specimens repaired with cement mortar. The flexural capacity of specimen strengthened by epoxy bonded steel plates or carbon fiber sheets after repair are less than those of strengthened specimens without repair. The interfacial behavior between was the repair material and strengthening material observed as the major influencing factor for the composite structures.

The self-compacting concrete, which was developed in 1988 in Japan, can be filled in a formwork without using any vibrators. It is an effective means of ensuring consistent quality in concrete structures, as the human factor in consolidation can be eliminated. This type of concrete has markedly increased deformability without segregation; high deformability is achieved mainly through the use of superplasticizers, while segregation resistance is achieved mainly through viscosity of the mortar or paste components of the concrete. The focus of this study is on experimental assessment of the effects of each component of concrete mixture in self-compacting concrete on the fresh state. The main findings are as follows: (1) There are certain combinations of slump flow and funnel speed that gave optimum self-compactability, with self-compactability falling off as one moves away from these combinations. This agrees with the results of the previous studies. (2) Increasin g the coarse aggregate content above the range G/Glim = 0.50 results in loss of compaction. The decrease in compaction is in a non-linear relationship with the increase in coarse aggregate, showing a rapid falling-off in self-compactability over G/Glim = 0.50. (3) If the quantity of coarse aggregate is varied while the quantity of fine aggregate remains fixed, no clear change can be seen in the water-powder volume ratio required to achieve self-compacting concrete, but the quantity of super-plasticizer required increases.