International Concrete Abstracts Portal

The study is aimed at obtaining basic data for evaluating the residual strength and deformability of damaged reinforced concrete members. The behavior of membqs that suffered damage during cyclic loading such as cracking that penetrate into the cross section, plastic deformation or partial failure was compared with that of member tested under simple torsion. Reversed cyclic torsion was applied for loading because few studies have been reported in open literature although it has been estimated to cause the most bride failure. Tests and analyses identified the effect of reversed cyclic torsion with varying numbers of cycles and with varying amplitudes had on the reduction of residual strength and torsional rigidity. It was .also confirmed that a closed joint that encircles longitudinal reinforcement at the ends of transverse reinforcement was stronger and more resistant to deformatioQ than a lapped joint.

The durability and perme&i&y of concrete are of special concern in the Arabian Gulf due to the prevailing aggressive weather conditions. Very few practical examples showing the ability of the local ready-mixed industry to adapt to extreqie hot weather, characteristic of this region of the world, have and analyzed. The following paper describes extreme concrete properties in two particular projects in Saudi Arabia demonstrating how the local concrete industry has used specific measutes to produce high-performance concrete in very hot weather. In the first project concrete was hauled for 8 hours in hot weather using high dose of standard retarders and superplasticisers and following rigorous measures to control the mix temperature. In the second project high-strength high-performance concrete was hauled for 45 minutes at an ambient temperatup of 40" C and achieved 24 hours strength in excess of 50 MPa. It is concluded that controlling the temperature of fresh concrete in hot weather should be primarily based on parameters related to cost, workability retention and long-term strength. Besides, the cited examples'demonstrated how the use of admixtures in hot weather could be very beneficial even if the dosage considered did not comply with ASTM C 494 requirements and the manufacturer standard recommendations.

Norida Department of Transportation (FDOT) requires contractors to submit proposed concrete mixture proportions prior to the production of any concrete. The contractor must use mixture proportions approved by FDOT. Substitutions of ingredients, other than coarse aggregate, must be justified through trial mixtures, and authorized in writing by FDOT Engineers. The substitutions of fly ash, slag, air-entraining admixtures, and 'I).pcs A, D and G water reducing admixtures were performed on two typical FDOT hot weather mixture proportions in this study. The concrete properties considered were slump, air content, and compressive strength. Test data for substitution mixture propohons were compared with the data for the original mixture proportions on the basis of statistical criteria. Results show that the substitutions cause significant change in concrete properties for the fly ash mixture proportions. The substitution of slag and air-entraining agent in the slag mixture proportions does not cause significant change in the properties of concrete.

Numerical and experimental studies or Keactive rowaer doncrete (RPC), reinforced by short steel fibres, under biaxial tensile loading are reported. A semi-analytical model using the Eshelby’s method of inclusion to describe elastic fields perturbation is employed to predict crack nucleation under biaxial tensile strain. A criterion of crack nucleation is investigated theoretically by considering a locally oriented mass of fibres embedded in an homogeneous matrix. An original biaxial crucifonn specimen is designed and fabricated by a systematic testing program guided by the results of a numerical simulation. A prototype machine names ASTREE (developed by SCHENCWLMT) is used in the biaxial test of cruciform specimens. An adaptive control test method was designed, and digital image correlation is employed to obtain the displacement field and the microstructural stress concentration. These preliminary observations support our theoretical analysis based on Eshelby’s inclusion and aims at a better understanding of the mechanisms involved in the RPC damage process.

The behavior of liquid containing structures (LCS) subjected to seismic excitations is reviewed. The major parameters affecting the response of concrete circular tanks for LCS are discussed. Existing codes aud standards related to seismic design of LCS are reviewed. With the aid of a design example, results of the various design standards are compared. The effects of earthquake load on the behavior of reinforced concrete (RC) tanks are also investigated through a detailed example.